Hubbry Logo
Volatile organic compoundVolatile organic compoundMain
Open search
Volatile organic compound
Community hub
Volatile organic compound
logo
8 pages, 0 posts
0 subscribers
Be the first to start a discussion here.
Be the first to start a discussion here.
Volatile organic compound
Volatile organic compound
Volatile organic compound
View on Wikipedia
from Wikipedia
VOCs are found in many things, including glue, new car interiors, house mold, and upholstered furniture, sea weed, trees.

Volatile organic compounds (VOCs) are organic compounds that have a high vapor pressure at room temperature.[1] They are common and exist in a variety of settings and products, not limited to house mold, upholstered furniture, arts and crafts supplies, dry cleaned clothing, and cleaning supplies.[2] VOCs are responsible for the odor of scents and perfumes as well as pollutants. They play an important role in communication between animals and plants, such as attractants for pollinators, protection from predation, and even inter-plant interactions.[3][4][5] Some VOCs are dangerous to human health or cause harm to the environment, often despite the odor being perceived as pleasant, such as "new car smell".[6]

Anthropogenic VOCs are regulated by law, especially indoors, where concentrations are the highest. Most VOCs are not acutely toxic, but may have long-term chronic health effects. Some VOCs have been used in pharmaceutical settings, while others are the target of administrative controls because of their recreational use. The high vapor pressure of VOCs correlates with a low boiling point, which relates to the number of the sample's molecules in the surrounding air, a trait known as volatility.[7]

Definitions

[edit]

Diverse definitions of the term VOC are in use. Some examples are presented below.

Canada

[edit]

Health Canada classifies VOCs as organic compounds that have boiling points roughly in the range of 50 to 250 °C (122 to 482 °F). The emphasis is placed on commonly encountered VOCs that would have an effect on air quality.[8]

European Union

[edit]

The European Union defines a VOC as "any organic compound as well as the fraction of creosote, having at 293.15 K a vapour pressure of 0.01 kPa or more, or having a corresponding volatility under the particular conditions of use;".[9] The VOC Solvents Emissions Directive was the main policy instrument for the reduction of industrial emissions of volatile organic compounds (VOCs) in the European Union. It covers a wide range of solvent-using activities, e.g. printing, surface cleaning, vehicle coating, dry cleaning and manufacture of footwear and pharmaceutical products. The VOC Solvents Emissions Directive requires installations in which such activities are applied to comply either with the emission limit values set out in the Directive or with the requirements of the so-called reduction scheme. Article 13 of The Paints Directive, approved in 2004, amended the original VOC Solvents Emissions Directive and limits the use of organic solvents in decorative paints and varnishes and in vehicle finishing products. The Paints Directive sets out maximum VOC content limit values for paints and varnishes in certain applications.[10][11] The Solvents Emissions Directive was replaced by the Industrial Emissions Directive from 2013.

China

[edit]

The People's Republic of China defines a VOC as those compounds that have "originated from automobiles, industrial production and civilian use, burning of all types of fuels, storage and transportation of oils, fitment finish, coating for furniture and machines, cooking oil fume and fine particles (PM 2.5)", and similar sources.[12] The Three-Year Action Plan for Winning the Blue Sky Defence War released by the State Council in July 2018 creates an action plan to reduce 2015 VOC emissions 10% by 2020.[13]

India

[edit]

The Central Pollution Control Board of India released the Air (Prevention and Control of Pollution) Act in 1981, amended in 1987, to address concerns about air pollution in India.[14] While the document does not differentiate between VOCs and other air pollutants, the CPCB monitors "oxides of nitrogen (NOx), sulphur dioxide (SO2), fine particulate matter (PM10) and suspended particulate matter (SPM)".[15]

United States

[edit]
Thermal oxidizers provide an air pollution abatement option for VOCs from industrial air flows.[16] A thermal oxidizer is an EPA-approved device to treat VOCs.

The definitions of VOCs used for control of precursors of photochemical smog used by the U.S. Environmental Protection Agency (EPA) and state agencies in the US with independent outdoor air pollution regulations include exemptions for VOCs that are determined to be non-reactive, or of low-reactivity in the smog formation process. Prominent is the VOC regulation issued by the South Coast Air Quality Management District in California and by the California Air Resources Board (CARB).[17] However, this specific use of the term VOCs can be misleading, especially when applied to indoor air quality because many chemicals that are not regulated as outdoor air pollution can still be important for indoor air pollution.

Following a public hearing in September 1995, California's ARB uses the term "reactive organic gases" (ROG) to measure organic gases. The CARB revised the definition of "Volatile Organic Compounds" used in their consumer products regulations, based on the committee's findings.[18]

In addition to drinking water, VOCs are regulated in pollutant discharges to surface waters (both directly and via sewage treatment plants)[19] as hazardous waste,[20] but not in non-industrial indoor air.[21] The Occupational Safety and Health Administration (OSHA) regulates VOC exposure in the workplace. Volatile organic compounds that are classified as hazardous materials are regulated by the Pipeline and Hazardous Materials Safety Administration while being transported.

Biologically generated VOCs

[edit]

Most VOCs in Earth's atmosphere are biogenic, largely emitted by plants.[7]

Major biogenic VOCs[22]
compound relative contribution amount emitted (Tg/y)
isoprene 62.2% 594±34
terpenes 10.9% 95±3
pinene isomers 5.6% 48.7±0.8
sesquiterpenes 2.4% 20±1
methanol 6.4% 130±4

Biogenic volatile organic compounds (BVOCs) encompass VOCs emitted by plants, animals, or microorganisms, and while extremely diverse, are most commonly terpenoids, alcohols, and carbonyls (methane and carbon monoxide are generally not considered).[23] Not counting methane, biological sources emit an estimated 760 teragrams of carbon per year in the form of VOCs.[22] The majority of VOCs are produced by plants, the main compound being isoprene. Small amounts of VOCs are produced by animals and microbes.[24] Many VOCs are considered secondary metabolites, which often help organisms in defense, such as plant defense against herbivory. The strong odor emitted by many plants consists of green leaf volatiles, a subset of VOCs. Although intended for nearby organisms to detect and respond to, these volatiles can be detected and communicated through wireless electronic transmission, by embedding nanosensors and infrared transmitters into the plant materials themselves.[25]

Emissions are affected by a variety of factors, such as temperature, which determines rates of volatilization and growth, and sunlight, which determines rates of biosynthesis. Emission occurs almost exclusively from the leaves, the stomata in particular. VOCs emitted by terrestrial forests are often oxidized by hydroxyl radicals in the atmosphere; in the absence of NOx pollutants, VOC photochemistry recycles hydroxyl radicals to create a sustainable biosphere–atmosphere balance.[26] Due to recent climate change developments, such as warming and greater UV radiation, BVOC emissions from plants are generally predicted to increase, thus upsetting the biosphere–atmosphere interaction and damaging major ecosystems.[27] A major class of VOCs is the terpene class of compounds, such as myrcene.[28]

Providing a sense of scale, a forest 62,000 square kilometres (24,000 sq mi) in area, the size of the U.S. state of Pennsylvania, is estimated to emit 3.4 million kg (7.5 million lb) of terpenes on a typical August day during the growing season.[29] Maize produces the VOC (Z)-3-hexen-1-ol and other plant hormones.[30] The taste of bitterness, found in foods such as olives, coffee and dark chocolate is caused by detection of VOCs by taste receptors.[31]

Anthropogenic sources

[edit]
Paints and coatings are major anthropogenic sources of VOCs.
The handling of petroleum-based fuels is a major source of VOCs.
Part of a series on
Pollution
Air pollution from a factory
Air
Biological
Digital
Electromagnetic
Natural
Noise
Radiation
Soil
Solid waste
Space
Thermal
Visual
War
Water
Topics
Misc
Lists
Categories

Anthropogenic sources emit about 142 teragrams (1.42 × 1011 kg, or 142 billion kg) of carbon per year in the form of VOCs.[32]

The major source of man-made VOCs are:[33]

  • Fossil fuel use and production, e.g. incompletely combusted fossil fuels or unintended evaporation of fuels. The most prevalent VOC is ethane, a relatively inert compound.
  • Solvents used in coatings, paints, and inks. Approximately 12 billion litres of paint are produced annually. Typical solvents include aliphatic hydrocarbons, ethyl acetate, glycol ethers and acetone. Motivated by cost, environmental concerns, and regulation, the paint and coating industries are increasingly shifting toward aqueous solvents.[34]
  • Compressed aerosol products, mainly butane and propane, estimated to contribute 1.3 million tonnes of VOC emissions per year globally.[35]
  • Biofuel use, e.g., cooking oils in Asia and bioethanol in Brazil.
  • Biomass combustion, especially from rain forests. Although combustion principally releases carbon dioxide and water, incomplete combustion affords a variety of VOCs.

Indoor VOCs

[edit]
See also: Indoor air quality

Due to their numerous sources indoors, concentrations of VOCs indoors are consistently higher in indoor air (up to ten times higher) than outdoors due to the many sources.[36] VOCs are emitted by thousands of indoor products. Examples include: paints, varnishes, waxes and lacquers, paint strippers, cleaning and personal care products, pesticides, building materials and furnishings, office equipment such as copiers and printers, correction fluids and carbonless copy paper, graphics and craft materials including glues and adhesives, permanent markers, and photographic solutions.[37] Human activities such as cooking and cleaning can also emit VOCs.[38][39] Cooking can release long-chain aldehydes and alkanes when oil is heated and terpenes can be released when spices are prepared and/or cooked.[38] Cleaning products contain a range of VOCs, including monoterpenes, sesquiterpenes, alcohols and esters. Once released into the air, VOCs can undergo reactions with ozone and hydroxyl radicals to produce other VOCs, such as formaldehyde.[39]

Some VOCs are emitted directly indoors, and some are formed through the subsequent chemical reactions.[40][41] The total concentration of all VOCs (TVOC) indoors can be up to five times higher than that of outdoor levels.[42]

New buildings experience particularly high levels of VOC off-gassing indoors because of the abundant new materials (building materials, fittings, surface coverings and treatments such as glues, paints and sealants) exposed to the indoor air, emitting multiple VOC gases.[43] This off-gassing has a multi-exponential decay trend that is discernible over at least two years, with the most volatile compounds decaying with a time-constant of a few days, and the least volatile compounds decaying with a time-constant of a few years.[44]

New buildings may require intensive ventilation for the first few months, or a bake-out treatment. Existing buildings may be replenished with new VOC sources, such as new furniture, consumer products, and redecoration of indoor surfaces, all of which lead to a continuous background emission of TVOCs, and requiring improved ventilation.[43]

There are strong seasonal variations in indoors VOC emissions, with emission rates increasing in summer. This is largely due to the rate of diffusion of VOC species through materials to the surface, increasing with temperature. This leads to generally higher concentrations of TVOCs indoors in summer.[44]

Indoor air-quality measurements

[edit]

Measurement of VOCs from the indoor air is done with sorption tubes e. g. Tenax (for VOCs and SVOCs) or DNPH-cartridges (for carbonyl-compounds) or air detector. The VOCs adsorb on these materials and are afterwards desorbed either thermally (Tenax) or by elution (DNPH) and then analyzed by GC–MS/FID or HPLC. Reference gas mixtures are required for quality control of these VOC measurements.[45] Furthermore, VOC emitting products used indoors, e.g. building products and furniture, are investigated in emission test chambers under controlled climatic conditions.[46] For quality control of these measurements round robin tests are carried out, therefore reproducibly emitting reference materials are ideally required.[45] Other methods have used proprietary Silcosteel-coated canisters with constant flow inlets to collect samples over several days.[47] These methods are not limited by the adsorbing properties of materials like Tenax.

Regulation of indoor VOC emissions

[edit]

In most countries, a separate definition of VOCs is used with regard to indoor air quality that comprises each organic chemical compound that can be measured as follows: adsorption from air on Tenax TA, thermal desorption, gas chromatographic separation over a 100% nonpolar column (dimethylpolysiloxane). VOC (volatile organic compounds) are all compounds that appear in the gas chromatogram between and including n-hexane and n-hexadecane. Compounds appearing earlier are called VVOC (very volatile organic compounds); compounds appearing later are called SVOC (semi-volatile organic compounds).

France, Germany (AgBB/DIBt), Belgium, Norway (TEK regulation) and Italy (CAM Edilizia) have enacted regulations to limit VOC emissions from commercial products. European industry has developed numerous voluntary ecolabels and rating systems, such as EMICODE,[48] M1,[49] Blue Angel,[50] GuT (textile floor coverings),[51] Nordic Swan Ecolabel,[52] EU Ecolabel,[53] and Indoor Air Comfort.[54] In the United States, several standards exist; California Standard CDPH Section 01350[55] is the most common one. These regulations and standards changed the marketplace, leading to an increasing number of low-emitting products.

Health risks

[edit]
See also: Chronic solvent-induced encephalopathy and Substance-induced psychosis

Respiratory, allergic, or immune effects in infants or children are associated with man-made VOCs and other indoor or outdoor air pollutants.[56]

Some VOCs, such as styrene and limonene, can react with nitrogen oxides or with ozone to produce new oxidation products and secondary aerosols, which can cause sensory irritation symptoms.[57] VOCs contribute to the formation of tropospheric ozone and smog.[58][59]

Health effects include eye, nose, and throat irritation; headaches, loss of coordination, nausea, hearing disorders[60] and damage to the liver, kidney, and central nervous system.[61] Some VOCs are suspected or known to cause cancer in humans. Key signs or symptoms associated with exposure to VOCs include conjunctival irritation, nose and throat discomfort, headache, allergic skin reaction, dyspnea, declines in serum cholinesterase levels, nausea, vomiting, nose bleeding, fatigue, dizziness.[62]

The ability of organic chemicals to cause health effects varies greatly from those that are highly toxic to those with no known health effects. As with other pollutants, the extent and nature of the health effect will depend on many factors including level of exposure and length of time exposed. Eye and respiratory tract irritation, headaches, dizziness, visual disorders, and memory impairment are among the immediate symptoms that some people have experienced soon after exposure to some organics. At present, not much is known about what health effects occur from the levels of organics usually found in homes.[63]

Ingestion

[edit]

While null in comparison to the concentrations found in indoor air, benzene, toluene, and methyl tert-butyl ether (MTBE) were found in samples of human milk and increase the concentrations of VOCs that we are exposed to throughout the day.[64] A study notes the difference between VOCs in alveolar breath and inspired air suggesting that VOCs are ingested, metabolized, and excreted via the extra-pulmonary pathway.[65] VOCs are also ingested by drinking water in varying concentrations. Some VOC concentrations were over the EPA's National Primary Drinking Water Regulations and China's National Drinking Water Standards set by the Ministry of Ecology and Environment.[66]

Dermal absorption

[edit]

The presence of VOCs in the air and in groundwater has prompted more studies. Several studies have been performed to measure the effects of dermal absorption of specific VOCs. Dermal exposure to VOCs like formaldehyde and toluene downregulate antimicrobial peptides on the skin like cathelicidin LL-37, human β-defensin 2 and 3.[67] Xylene and formaldehyde worsen allergic inflammation in animal models.[68] Toluene also increases the dysregulation of filaggrin: a key protein in dermal regulation.[69] this was confirmed by immunofluorescence to confirm protein loss and western blotting to confirm mRNA loss. These experiments were done on human skin samples. Toluene exposure also decreased the water in the trans-epidermal layer allowing for vulnerability in the skin's layers.[67][70]

Limit values for VOC emissions

[edit]

Limit values for VOC emissions into indoor air are published by AgBB,[71] AFSSET, California Department of Public Health, and others. These regulations have prompted several companies in the paint and adhesive industries to adapt with VOC level reductions their products.[citation needed] VOC labels and certification programs may not properly assess all of the VOCs emitted from the product, including some chemical compounds that may be relevant for indoor air quality.[72] Each ounce of colorant added to tint paint may contain between 5 and 20 grams of VOCs. A dark color, however, could require 5–15 ounces of colorant, adding up to 300 or more grams of VOCs per gallon of paint.[73]

VOCs in healthcare settings

[edit]

VOCs are also found in hospital and health care environments. In these settings, these chemicals are widely used for cleaning, disinfection, and hygiene of the different areas.[74] Thus, health professionals such as nurses, doctors, sanitation staff, etc., may present with adverse health effects such as asthma; however, further evaluation is required to determine the exact levels and determinants that influence the exposure to these compounds.[74][75][76]

Concentration levels of individual VOCs such as halogenated and aromatic hydrocarbons vary substantially between areas of the same hospital. Generally, ethanol, isopropanol, ether, and acetone are the main compounds in the interior of the site.[77][78] Following the same line, in a study conducted in the United States, it was established that nursing assistants are the most exposed to compounds such as ethanol, while medical equipment preparers are most exposed to 2-propanol.[77][78]

In relation to exposure to VOCs by cleaning and hygiene personnel, a study conducted in 4 hospitals in the United States established that sterilization and disinfection workers are linked to exposures to d-limonene and 2-propanol, while those responsible for cleaning with chlorine-containing products are more likely to have higher levels of exposure to α-pinene and chloroform.[76] Those who perform floor and other surface cleaning tasks (e.g., floor waxing) and who use quaternary ammonium, alcohol, and chlorine-based products are associated with a higher VOC exposure than the two previous groups, that is, they are particularly linked to exposure to acetone, chloroform, α-pinene, 2-propanol or d-limonene.[76]

Other healthcare environments such as nursing and age care homes have been rarely a subject of study, even though the elderly and vulnerable populations may spend considerable time in these indoor settings where they might be exposed to VOCs, derived from the common use of cleaning agents, sprays and fresheners.[79][80] In one study, more than 200 chemicals were identified, of which 41 have adverse health effects, 37 of them being VOCs. The health effects include skin sensitization, reproductive and organ-specific toxicity, carcinogenicity, mutagenicity, and endocrine-disrupting properties.[79] Furthermore, in another study carried out in the same European country, it was found that there is a significant association between breathlessness in the elderly population and elevated exposure to VOCs such as toluene and o-xylene, unlike the remainder of the population.[81]

VOCs in hospitality and retail

[edit]

Workers in hospitality are also exposed to VOCs from a variety of sources including cleaning products (air fresheners, floor cleaners, disinfectants, etc.), building materials and furnishings, as well as fragrances.[82] One of the most common VOC found in hospitality settings are alkanes, which are a major ingredient in cleaning products (35%).[82] Other products present in hospitality that contain alkanes are laundry detergents, paints, and lubricants.[82] Housekeepers in particular may also be exposed to formaldehyde,[83] which is present in some fabrics used to make towels and bedding, however exposure decreases after several washes.[84] Some hotels still use bleach to clean, and this bleach can form chloroform and carbon tetrachloride.[85] Fragrances are often used in hotels and are composed of many different chemicals.[82]

There are many negative health outcomes associated with VOC exposure in hospitality. VOCs present in cleaning supplies can cause skin, eye, nose, and throat irritation, which can develop into dermatitis.[86] VOCs in cleaning supplies can also cause more serious conditions, such as respiratory diseases and cancer.[82] One study found that n-nonane and formaldehyde were the main drivers of eye and upper respiratory tract irritation while cancer risks were driven by chloroform and formaldehyde.[82] Some solvent-based products have also been shown to cause damage to the kidneys and reproductive organs.[86] One study showed that the star rating of the hotel may influence VOC exposure, as hotels with lower star ratings tend to have lower quality materials for the furnishings.[87] Additionally, due to a movement among higher-end hotels to be more environmentally friendly, there has been a shift to using less harsh cleaning agents.[87]

Another similar environment that exposes workers to VOCs are retail spaces. Studies have shown that retail spaces have the highest VOC concentrations compared to all other indoor spaces such as residences, offices, and vehicles.[88][89] The concentration of VOCs present as well as the types depend on the type of store, but common sources of VOCs in retail spaces include motor vehicle exhaust, building materials, cleaning products, products, and fragrances.[90] One study found that VOC concentrations were higher in retail storage spaces compared to the sales areas, particularly formaldehyde.[91] In retail spaces, formaldehyde concentrations ranged from 8.0 to 19.4 μg/m3 compared to 14.2 to 45.0 μg/m3 in storage spaces.[91] Occupational exposure to VOCs also depends on the task. One study found that workers were exposed to peak total VOC concentrations when they were removing the plastic film off of new products.[91] This peak was 7 times higher than total VOC concentration peaks of all other tasks, contributing greatly to retail workers' exposure to VOCs despite being a relatively short task.[91]

One way that VOC concentrations can be kept minimal within retail and hospitality is by ensuring there is proper air ventilation.[92] Employers can ensure proper ventilation by placing furniture in a way that enhances air circulation, as well as checking that the HVAC (heating, ventilation, and air conditioning) system is working properly to remove pollutants from the air.[92] Workers can make sure that air vents are not blocked.[92]

Analytical methods

[edit]

Sampling

[edit]

Obtaining samples for analysis is challenging. VOCs, even when at dangerous levels, are dilute, so preconcentration is typically required. Many components of the atmosphere are mutually incompatible, e.g. ozone and organic compounds, peroxyacyl nitrates and many organic compounds. Furthermore, collection of VOCs by condensation in cold traps also accumulates a large amount of water, which generally must be removed selectively, depending on the analytical techniques to be employed.[33] Solid-phase microextraction (SPME) techniques are used to collect VOCs at low concentrations for analysis.[93] As applied to breath analysis, the following modalities are employed for sampling: gas sampling bags, syringes, evacuated steel and glass containers.[94]

Principle and measurement methods

[edit]

In the U.S., standard methods have been established by the National Institute for Occupational Safety and Health (NIOSH) and another by U.S. OSHA. Each method uses a single component solvent; butanol and hexane cannot be sampled, however, on the same sample matrix using the NIOSH or OSHA method.[95]

VOCs are quantified and identified by two broad techniques. The major technique is gas chromatography (GC). GC instruments allow the separation of gaseous components. When coupled to a flame ionization detector (FID) GCs can detect hydrocarbons at the parts per trillion levels. Using electron capture detectors, GCs are also effective for organohalide such as chlorocarbons.

The second major technique associated with VOC analysis is mass spectrometry, which is usually coupled with GC, giving the hyphenated technique of GC-MS.[96]

Direct injection mass spectrometry techniques are frequently utilized for the rapid detection and accurate quantification of VOCs.[97] PTR-MS is among the methods that have been used most extensively for the on-line analysis of biogenic and anthropogenic VOCs.[98] PTR-MS instruments based on time-of-flight mass spectrometry have been reported to reach detection limits of 20 pptv after 100 ms and 750 ppqv after 1 min. measurement (signal integration) time. The mass resolution of these devices is between 7000 and 10,500 m/Δm, thus it is possible to separate most common isobaric VOCs and quantify them independently.[99]

Chemical fingerprinting and breath analysis

[edit]

The exhaled human breath contains a few thousand volatile organic compounds and is used in breath biopsy to serve as a VOC biomarker to test for diseases,[94] such as lung cancer.[100] One study has shown that "volatile organic compounds ... are mainly blood borne and therefore enable monitoring of different processes in the body."[101] And it appears that VOC compounds in the body "may be either produced by metabolic processes or inhaled/absorbed from exogenous sources" such as environmental tobacco smoke.[100][102] Chemical fingerprinting and breath analysis of volatile organic compounds has also been demonstrated with chemical sensor arrays, which utilize pattern recognition for detection of component volatile organics in complex mixtures such as breath gas.

Metrology for VOC measurements

[edit]

To achieve comparability of VOC measurements, reference standards traceable to SI units are required. For a number of VOCs gaseous reference standards are available from specialty gas suppliers or national metrology institutes, either in the form of cylinders or dynamic generation methods. However, for many VOCs, such as oxygenated VOCs, monoterpenes, or formaldehyde, no standards are available at the appropriate amount of fraction due to the chemical reactivity or adsorption of these molecules. Currently, several national metrology institutes are working on the lacking standard gas mixtures at trace level concentration, minimising adsorption processes, and improving the zero gas.[45] The final scopes are for the traceability and the long-term stability of the standard gases to be in accordance with the data quality objectives (DQO, maximum uncertainty of 20% in this case) required by the WMO/GAW program.[103]

See also

[edit]

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Volatile organic compound

View on Grokipedia
from Grokipedia
Volatile organic compounds (VOCs) are carbon-based chemicals, excluding , , and certain carbonates, that exhibit high and low water at , enabling them to readily evaporate and participate in atmospheric photochemical reactions. They encompass thousands of substances emitted from both biogenic sources, primarily vegetation such as trees releasing and monoterpenes like , and anthropogenic sources including fuel , evaporation, , and consumer products like paints and adhesives. Globally, biogenic emissions vastly outpace anthropogenic ones, comprising roughly 86% of total VOC fluxes compared to 14% from human activities, though the latter often dominate in urban and industrial settings due to localized concentrations of reactive species. In the , VOCs react with oxides under sunlight to produce tropospheric and secondary organic , driving photochemical formation and influencing through aerosol radiative effects and oxidative capacity. Certain VOCs, such as and , pose health risks including acute irritation to eyes, nose, and throat, as well as chronic effects like carcinogenicity and upon prolonged exposure, with indoor levels frequently surpassing outdoor concentrations due to off-gassing from building materials and furnishings. Regulatory definitions and exemptions vary by jurisdiction, reflecting challenges in measuring reactivity and exempting negligibly photochemically active compounds, which complicates control strategies aimed at mitigating and .

Fundamental Properties

Chemical Definition and Volatility Metrics

Volatile organic compounds (VOCs) are organic chemical substances characterized by their propensity to exist in the gaseous phase under ambient environmental conditions, primarily due to elevated saturation vapor pressures and depressed points relative to non-volatile organics. Saturation vapor pressure, typically exceeding 0.01 kPa at standard (20°C), serves as a fundamental physicochemical indicator of volatility, reflecting the equilibrium exerted by the compound in the vapor phase above its or form. provides a complementary metric, with VOCs generally exhibiting values below 250°C at 101.3 kPa, as this threshold correlates with sufficient molecular mobility to overcome intermolecular attractions at . These properties arise from first-principles considerations of molecular structure: lower molecular weights reduce the overall mass and entropic barriers to , while diminished polarity minimizes dipole-dipole interactions, and the absence of bonding weakens cohesive forces, collectively favoring to the gas state. Quantitative assessment of volatility extends to partition coefficients that describe distribution between phases. Henry's law constant (K_H), defined as the ratio of a compound's in air to its concentration in (often in units of atm·m³/mol or Pa·m³/mol), quantifies the air-water partitioning tendency; higher values indicate greater volatility from aqueous media into the atmosphere, as seen in hydrophobic organics with log K_H > -1. The octanol-air (K_OA), expressed as the ratio of concentrations in n-octanol and air phases (dimensionless, often logged), further elucidates volatility in lipophilic contexts; values below 10^8 (log K_OA < 8) signify compounds prone to aerial dispersion over sorption to organic matrices. Empirical data from chemical databases, such as those compiling vapor pressures and partition coefficients for thousands of organics, confirm these metrics' utility in distinguishing VOCs, with validation against experimental evaporation rates under controlled conditions. Intermolecular forces dominate volatility determinants at the molecular level. Nonpolar hydrocarbons, exemplified by alkanes with boiling points rising predictably by ~30°C per CH₂ increment due to increasing London dispersion forces, display higher volatility than polar analogs like alcohols, where hydrogen bonding elevates boiling points by 100–150°C (e.g., ethanol at 78°C versus propane at -42°C). Branching and reduced symmetry further enhance volatility by sterically hindering close packing and force interactions, as evidenced in isomeric comparisons where branched variants boil 10–20°C lower than linear counterparts. These principles, grounded in thermodynamic favorability of the gaseous state (ΔG_vap < 0 at ambient T), underpin VOC classification without reliance on arbitrary cutoffs, emphasizing intrinsic molecular energetics over extrinsic regulatory criteria.

Classification by Structure and Reactivity

Volatile organic compounds are structurally classified into hydrocarbons—such as alkanes, alkenes, and aromatics—and functionalized variants including oxygenated (e.g., aldehydes, ketones, alcohols), halogenated, and other heteroatom-bearing species. This taxonomy reflects organic chemistry principles where functional groups dictate bond types and electron densities, influencing atmospheric oxidation pathways. Alkanes, saturated hydrocarbons with single bonds, display low atmospheric reactivity due to high C-H bond dissociation energies, primarily undergoing slow hydrogen abstraction by hydroxyl (OH) radicals, resulting in lifetimes of days to weeks. In contrast, alkenes feature carbon-carbon double bonds enabling rapid addition reactions with OH and ozone, yielding short lifetimes on the order of hours and elevated contributions to radical chain propagation. Aromatic hydrocarbons, like benzene, exhibit intermediate reactivity through resonance-stabilized rings that favor H-abstraction over addition, leading to persistence relative to alkenes but eventual ring-opening to oxygenated products. Oxygenated VOCs vary in reactivity based on functional groups; aldehydes undergo both OH abstraction and photolysis, enhancing reactivity compared to ketones, which rely mainly on alpha-hydrogen abstraction. Halogenated VOCs, such as chlorinated hydrocarbons, persist longer in the atmosphere because halogen substituents withdraw electrons, lowering OH reaction rates and increasing lifetimes by factors up to 10 or more relative to non-halogenated analogs. For instance, unsaturated structures like isoprene (a biogenic diene alkene) react ~10 times faster with OH than benzene (an aromatic), directly linking unsaturation to accelerated degradation and secondary pollutant formation. Reactivity is quantified via scales tying structure to ozone production: the maximum incremental reactivity (MIR) measures grams of ozone formed per gram of VOC under NOx-limited conditions, with alkenes and certain aromatics scoring higher than alkanes due to efficient peroxy radical formation. Similarly, photochemical ozone creation potential (POCP) ranks VOCs against ethene, correlating positively with OH rate constants and structural features promoting tropospheric oxidant cycles. These metrics enable prediction of atmospheric fate from molecular design, emphasizing causal roles of bond multiplicity and substituents in reactivity hierarchies.

Historical Context

Early Identification and Utilization

The aromas of volatile organic compounds from plants and human emanations were noted in ancient medical practices, with Hippocratic physicians circa 460–370 BCE using olfactory analysis of breath and urine to diagnose conditions such as liver disease and diabetes, recognizing distinctive scents as indicators of physiological imbalance. Similarly, ancient Egyptians from around 3000 BCE extracted aromatic volatiles from plants like frankincense and myrrh for embalming, perfumes, and therapeutic applications, leveraging their antiseptic and preservative qualities through infusion and rudimentary pressing techniques. Distillation processes, refined by Arabic alchemists such as Jabir ibn Hayyan in the 8th century CE, marked an early systematic isolation of volatile substances, producing solvents like ethanol from fermented materials for use in extractions, elixirs, and alchemical pursuits aimed at purification and transmutation. These methods yielded essential oils and spirits, such as those derived from herbs and resins, which were applied in perfumery, medicine, and early industrial solvents, highlighting the practical exploitation of volatility for separation and concentration. By the 19th century, improved fractional distillation enabled the targeted isolation of specific VOCs, including monoterpenes like alpha-pinene from turpentine oil, which was distilled on a commercial scale for applications in varnishes, paints, and fuels as a whale oil alternative in American lamps. , long distilled in rudimentary forms, saw enhanced purity for industrial solvents and perfumery, while plant-derived terpenes were empirically valued in agriculture for their roles in resin tapping from conifers, underscoring pre-modern awareness of VOC ubiquity in natural exudates and human crafts without formalized chemical classification.

Emergence in Environmental Science

Following World War II, the expansion of petrochemical industries and increased vehicle usage led to a marked rise in emissions of synthetic volatile organic compounds (VOCs), contributing to the formation of photochemical smog in urban areas. In Los Angeles, persistent haze episodes beginning in the late 1940s prompted investigations into reactive hydrocarbons from automobile exhaust and industrial solvents, which were identified as key precursors alongside nitrogen oxides. These events, distinct from earlier sulfur-based smogs, highlighted the role of sunlight-driven reactions involving VOCs, though initial understanding focused on empirical observations of plant damage and eye irritation rather than precise chemical mechanisms. Dutch-born biochemist Arie Haagen-Smit advanced recognition of VOCs through laboratory chamber experiments in the early 1950s, demonstrating that irradiating mixtures of olefins (a class of VOCs) and nitrogen dioxide produced ozone and secondary aerosols mimicking observed smog. His 1952 publication detailed how these photochemical oxidations generated irritants like peroxyacetyl nitrate, establishing VOCs as central to tropospheric ozone formation and shifting scientific focus from particulate matter to gaseous precursors. This work, conducted at the California Institute of Technology, underscored the need for targeted measurements, as prior air quality assessments had largely overlooked VOC reactivity due to analytical limitations. Policy acknowledgment followed in the 1970 Clean Air Act, which set national ambient air quality standards for ozone and implicitly targeted VOCs—termed "hydrocarbons"—as essential precursors based on Haagen-Smit's findings. Amendments in 1977 reinforced controls by requiring states to develop plans reducing VOC emissions in non-attainment areas, marking a transition from episodic crisis response to systematic regulation informed by emerging monitoring data. By the early 1990s, global inventories quantified anthropogenic VOC emissions at approximately 110,000 gigagrams per year, primarily from solvents, fuels, and incomplete combustion, enabling more accurate modeling of their atmospheric contributions and highlighting measurement-driven progress over anecdotal evidence.

Sources

Natural Emissions: Dominance and Variability

Biogenic volatile organic compounds (BVOCs) from terrestrial vegetation constitute the predominant source of VOCs globally, with estimates ranging from 700 to 1,000 TgC yr⁻¹, primarily comprising isoprene, monoterpenes, and sesquiterpenes emitted by forests and other plant ecosystems. These emissions dwarf anthropogenic contributions, which total approximately 139–163 TgC yr⁻¹, yielding a biogenic-to-anthropogenic ratio of roughly 5–7 globally but exceeding 10-fold in vegetated regions such as temperate and tropical forests where human activity is minimal. Empirical models, such as MEGAN, underscore this dominance by integrating satellite-derived vegetation data with flux measurements, revealing that pre-industrial atmospheres relied heavily on these natural fluxes for baseline oxidative capacity, independent of human influences. Emissions exhibit high variability driven by environmental factors, particularly temperature and photosynthetically active radiation (PAR), which regulate enzymatic pathways like isoprene synthase in plant chloroplasts. For instance, isoprene release from broadleaf trees intensifies exponentially with rising leaf temperatures above 20°C and PAR levels, often doubling per 10°C increment under light saturation, while monoterpene emissions from conifers show pooled or stress-induced patterns less sensitive to light but responsive to heat. In the United States, deciduous forests dominated by oak species (Quercus spp.) account for the majority of biogenic isoprene, with oaks contributing disproportionately high emission factors—up to orders of magnitude greater than non-isoprene emitters—concentrated in the eastern broadleaf biomes. Seasonal peaks occur during summer under optimal conditions, with diurnal cycles peaking midday due to light and heat synergy, though drought or leaf age can suppress rates by altering substrate availability. Beyond vegetation, secondary natural sources include microbial activity in soils and oceans, as well as geogenic releases from geological processes, though these are minor relative to biogenic totals. Soil microbes and fungi produce VOCs like methanol and acetone through decomposition, with fluxes varying by microbial community composition and moisture, contributing negligibly to global budgets but locally influencing ecosystems. Oceanic emissions, primarily from phytoplankton and bacteria, release iodinated and sulfur-containing VOCs such as dimethyl sulfide, estimated at tens of TgC yr⁻¹ and modulated by nutrient upwelling and temperature, playing roles in marine-atmosphere exchange. Geogenic sources, including volcanic degassing and soil outgassing of alkanes and alkenes, add trace amounts, often <1% of biogenic, but can elevate locally near fault lines or hydrothermal vents. In ecosystems, natural VOCs fulfill essential functions predating industrialization, such as intra- and inter-plant signaling for defense against herbivores and pathogens via volatile cues that induce systemic resistance in neighboring plants. Terpenoids, for example, deter insects directly or attract predators, while isoprene mitigates oxidative stress from high temperatures by scavenging radicals, enhancing plant resilience in unstressed pre-industrial environments. These roles highlight causal dependencies on natural cycles, with emissions integral to atmospheric pre-human oxidant balances and biodiversity maintenance, rather than mere precursors to pollution.

Anthropogenic Emissions: Scale and Sectors

Anthropogenic emissions of volatile organic compounds (VOCs) are estimated at approximately 219 Tg per year globally as of 2021, representing a subset of total non-methane VOC (NMVOC) fluxes dominated by human activities such as industrial processes and fuel handling. These emissions have exhibited an overall upward trend, with global anthropogenic VOCs increasing by about 10-11% from the 1990s to 2017-2019, driven primarily by growth in developing economies despite reductions in some developed regions. Major sectors contributing to these emissions include solvent use, which accounts for a significant portion through evaporation in paints, coatings, adhesives, and printing processes; fuel evaporation and distribution, particularly gasoline vapors from storage, transport, and refueling; and industrial manufacturing involving chemical production and petrochemical operations. Solvent and industrial sources have increased their relative share since 2000, often comprising over 50% in urbanized areas, while transportation-related emissions from vehicles have declined in regions with stricter controls. Agriculture contributes via pesticide volatilization and solvent-based formulations, though at lower scales globally compared to urban-industrial sectors. Regional variations highlight hotspots, such as China's Beijing-Tianjin-Hebei (BTH) region, where anthropogenic VOC emissions totaled 3,278 Gg in 2015, largely from industrial solvents and petrochemical activities amid rapid manufacturing expansion. Emission inventories frequently underpredict actual releases due to unaccounted fugitive leaks in oil and gas infrastructure, which can constitute up to 39% of sectoral contributions in some assessments. These patterns underscore the dominance of evaporative and process-based releases over combustion sources in contemporary anthropogenic profiles.

Atmospheric Chemistry and Environmental Effects

Role in Ozone Formation and Photochemical Smog

Volatile organic compounds (VOCs) are essential precursors in the photochemical formation of tropospheric ozone (O₃), interacting with nitrogen oxides (NOₓ) and hydroxyl radicals (OH) under sunlight to drive catalytic cycles that amplify O₃ production. In the primary mechanism, an OH radical abstracts a hydrogen atom from a VOC molecule, forming an alkyl radical (R•) that rapidly adds O₂ to yield a peroxy radical (RO₂•). The RO₂• then reacts with NO to produce an alkoxy radical (RO•) and NO₂, regenerating OH through subsequent steps and converting NO to NO₂ without net NOₓ loss. Photolysis of NO₂ (NO₂ + hν → NO + O) followed by O + O₂ → O₃ generates ozone, with the HOₓ (OH + HO₂) and RO₂• radicals sustaining the chain propagation. This VOC-initiated cycle enables net O₃ production rates that can exceed 10 ppb per hour in sunlit conditions with sufficient precursors. The reactivity of VOCs in ozone formation varies by molecular structure, quantified by scales like Maximum Incremental Reactivity (MIR), which measures grams of O₃ formed per gram of VOC under high-NOₓ, VOC-limited conditions. Alkanes exhibit low MIR values (e.g., ethane ~0.3), while alkenes like ethene have moderate reactivity (~0.81), and aromatics such as toluene show higher values (~5.6) due to efficient radical recycling from benzyl radicals and ring-opening products. These differences arise from the ability of unsaturated and aromatic VOCs to propagate longer radical chains, contributing disproportionately to O₃ in urban settings dominated by evaporative and combustion emissions. Empirical observations from urban plumes distinguish VOC-limited regimes, prevalent in densely polluted areas with high NOₓ, from NOₓ-limited ones in cleaner or downwind environments. In the Los Angeles Basin, aircraft and ground-based studies during campaigns like RECAP-CA (2021-2022) reveal that weekday ozone peaks often align with VOC limitation, where incremental VOC reductions yield greater O₃ decreases than equivalent NOₓ cuts, which risk elevating O₃ via diminished NO scavenging of O₃. The basin's historical photochemical smog episodes, first documented in July 1943 amid wartime industrial and vehicle growth, exemplified this chemistry, with trapped emissions under inversions producing visibility-reducing haze and O₃ levels sufficient to irritate eyes and vegetation. In polluted regions, anthropogenic VOCs enable the bulk of exceedances above background O₃, with reactions accounting for over 80% of net photochemical O₃ buildup during high-pollution events, as inferred from source apportionment models tracing O₃ to precursor oxidation efficiencies. Natural VOCs, such as isoprene from vegetation, sustain baseline tropospheric O₃ at 20-50 ppb globally but contribute less to urban spikes, where human-sourced alkenes and aromatics dominate the reactive pool. Regime diagnostics, using indicators like H₂O₂/HNO₃ ratios >0.5 for VOC limitation, guide control strategies, emphasizing VOC controls in cores like to curb photochemical effectively.

Interactions with Climate and Ecosystems

Biogenic volatile organic compounds (BVOCs), such as emitted by , exert complex influences on through atmospheric processing. Oxidation of BVOCs yields secondary organic s that enhance reflectivity and scatter incoming solar radiation, contributing to a negative estimated at -0.1 to -0.5 W/m² globally. However, BVOCs also promote tropospheric formation in the presence of oxides and extend lifetimes, effects that drive positive forcings of comparable magnitude, on the order of +0.1 to +0.3 W/m². The IPCC assesses the net effect as uncertain, with regional variations hinging on NOx availability and aerosol yields, which diminish at higher temperatures due to altered chemistry. In terrestrial ecosystems, BVOCs underpin biological signaling networks essential for resilience. damage triggers emission of specific blends, termed herbivore-induced volatiles (HIPVs), which prime undamaged neighbors for defense activation, reducing subsequent herbivory by up to 30-50% in empirical trials with species like and tomatoes. These volatiles also recruit parasitoids and predators, amplifying top-down control in food webs. microbes exchange BVOCs with roots, modulating mycorrhizal associations and nutrient mobilization; for instance, fungal hyphae release sesquiterpenes that inhibit while stimulating growth hormones. Marine ecosystems feature analogous roles, with phytoplankton-derived (DMS)—a volatile sulfur analog to carbon-based VOCs—oxidizing to aerosols that seed marine stratocumulus clouds, potentially increasing planetary by 0.5-1% over regions. Projections under warming scenarios indicate biogenic VOC emissions could rise 20-50% by 2100, driven by exponential temperature sensitivity (e.g., doubles per 10°C rise) and CO₂-induced shifts toward high-emitting vegetation like broadleaf trees. Climate models frequently underpredict these dynamics by overlooking feedbacks such as drought-stressed emissions or biome migrations, leading to overattribution of forcings to anthropogenic sources; observational data from warming experiments reveal model biases exceeding 25% in simulations. This uncertainty underscores the need for empirical validation over parameterized assumptions in attributing ecosystem-climate loops.

Human Exposure and Health Effects

Pathways of Exposure

Concentrations of volatile organic compounds (VOCs) are typically higher indoors than outdoors, often by a factor of 2 to 10, with residential indoor total VOC (TVOC) levels ranging from 100 to over 2000 µg/m³ depending on ventilation and sources, compared to ambient outdoor concentrations generally below 50 µg/m³. represents the primary pathway of exposure to VOCs, as their high volatility facilitates rapid uptake through the , accounting for the majority of in most scenarios; dermal absorption occurs notably with liquid solvents or during direct contact, while contributes minimally through trace contamination in or water. Indoor exposure is dominated by off-gassing from building materials, furniture, and products, which can constitute up to 50% of ambient indoor VOCs, alongside emissions from personal care items like fragrances and cosmetics. Indoor VOC levels often spike in the evening due to reduced ventilation from cooler outdoor temperatures leading to closed windows and doors, combined with VOC-emitting activities such as cooking, showering, or laundry, while air exchange decreases. Peaks in TVOC concentrations often follow renovations or new installations, with 2023 measurements in newly constructed or refurbished homes recording levels exceeding 500 µg/m³ and reaching as high as 2634 µg/m³ shortly after occupancy. Chronic exposure arises from sustained low-level ambient sources, such as urban outdoor at 0.4–5 µg/m³ from and industrial activities, leading to prolonged but dilute uptake over months or years. In contrast, acute exposure involves short-duration, high-concentration events like chemical spills, sessions, or handling, where localized levels can surge to hundreds or thousands of µg/m³, emphasizing and dermal routes in occupational or accidental settings.

Evidence-Based Health Risks and Thresholds

Volatile organic compounds (VOCs) exhibit dose-dependent health effects, with acute exposures primarily causing sensory irritation and neurological symptoms at concentrations well above typical environmental levels, while chronic risks are more established for specific carcinogens like benzene and formaldehyde. For toluene, a common anthropogenic VOC, acute inhalation exposure to concentrations above 100 ppm has been associated with statistically significant eye and nasal irritation in controlled human studies, with headaches and dizziness reported at higher levels exceeding 500 ppm short-term exposure limits. These thresholds align with occupational standards, such as NIOSH's recommended short-term exposure limit of 150 ppm, beyond which central nervous system effects intensify, though individual variability and confounding factors like co-exposures to other solvents influence responses. Chronic exposure risks are most robustly evidenced for benzene, classified by the International Agency for Research on Cancer (IARC) as Group 1 (carcinogenic to humans) due to consistent links to leukemia, particularly acute myeloid leukemia, from occupational cohort studies with exposures averaging 1-10 ppm over decades. The inhalation unit risk factor of 7.8 × 10^{-6} per μg/m³ implies a lifetime cancer risk of 10^{-6} at approximately 0.13 μg/m³, though epidemiological data often derive from higher historical levels, with no observed safe threshold but minimal risks at ambient urban concentrations below 1-5 μg/m³ after adjusting for confounders like smoking. Formaldehyde, another IARC Group 1 carcinogen, shows the strongest causal evidence for nasopharyngeal and sinonasal cancers in occupational settings with average exposures exceeding 0.1 ppm, as supported by meta-analyses of cohort studies linking peak exposures up to 2-6 ppm to dose-response increases in tumor incidence; however, genotoxicity and irritation occur at lower levels, informing limits like NIOSH's 0.016 ppm time-weighted average. For VOC mixtures, evidence of adverse effects is weaker and often confounded by dominant individual compounds, with recent controlled studies (2020-2025) reporting no significant physiological or symptomatic changes from 2-hour exposures to diverse low-level mixtures mimicking indoor profiles, followed up to 85 minutes post-exposure. Epidemiology on total VOC (TVOC) levels indicates no consistent effects below the lowest observed level (LOAEL), such as irritation thresholds around 1,000 μg/m³, despite guideline values like 200-300 μg/m³ for sensory comfort derived from panel studies rather than . U.S. EPA and WHO do not set enforceable TVOC health-based limits, prioritizing compound-specific assessments, as aggregate metrics overlook synergistic or antagonistic interactions unverified in human data.
VOCAcute Effect ThresholdChronic Risk MetricKey Reference
>100 ppm (irritation)Minimal at <50 ppm TWA; neurotoxicity at high chronic
BenzeneN/A (low acute toxicity)~0.13 μg/m³ (10^{-6} lifetime cancer risk)
>0.1 ppm (irritation/)Increased nasal cancer at >0.1 ppm occupational average

Critiques of Alarmist Narratives

Alarmist portrayals frequently characterize volatile organic compounds (VOCs) indiscriminately as toxic threats, disregarding that ubiquitous examples like —emitted during respiration, cooking, and cleaning—persist at levels orders of magnitude below established safety thresholds. Occupational permissible exposure limits for ethanol reach 1,000 ppm as an 8-hour time-weighted average, with typical indoor concentrations from daily activities remaining under 1 ppm, posing negligible acute risks. Similarly, biogenic VOCs such as and monoterpenes, released by houseplants and natural materials indoors, often match or exceed synthetic contributions in concentration yet elicit no equivalent regulatory or media frenzy, underscoring selective emphasis on anthropogenic origins over baseline environmental ubiquity. Epidemiological evidence tying chronic low-dose VOC mixtures to respiratory ailments like exhibits substantial voids, with multiple systematic reviews classifying associations as very low certainty due to inconsistent methodologies, small effect sizes, and failure to isolate VOCs from co-exposures. For instance, 2024 guidelines from respiratory societies highlight that indoor VOC links to new-onset derive from heterogeneous studies lacking robust controls, rendering causal claims tenuous. Cancer attributions fare similarly, as low-dose extrapolations from high-exposure animal models overestimate human risks; ambient indoor , a key concern, yields lifetime cancer probabilities below 3 in 100 million at concentrations under 80 ppb, per conservative assessments. Causal inferences in VOC health narratives routinely overlook confounders, such as , which independently elevates blood levels of multiple VOCs like and , confounding attribution in observational cohorts. and particulate co-pollutants, prevalent in urban settings, further muddy mixtures' isolated effects, yet studies seldom disentangle these interactions. Projections of widespread cancer peril—such as 2024 estimates deeming 36-40% of the global exposed to "harmful" VOCs—exemplify overreach, aggregating diverse compounds against singular thresholds (e.g., 's) without compound-specific or synergies, inflating undifferentiated peril absent empirical validation at scales. Recent 2025 analyses of everyday VOC exposures to sinonasal outcomes reinforce this, documenting non-significant links for industrial and fuel-derived after acute dosing, with gaps in chronic measurement underscoring reliance on self-reports over direct quantification.

Regulatory Frameworks

Definitions and Standards Across Jurisdictions

Regulatory definitions of volatile organic compounds (VOCs) vary significantly across jurisdictions, primarily reflecting differing emphases on physicochemical properties, photochemical reactivity, and policy priorities rather than uniform scientific criteria. , the Agency (EPA) defines VOCs as any compound of carbon, excluding , , , metallic carbides or carbonates, , and compounds with negligible photochemical reactivity, such as and , to focus on precursors. This reactivity-based exclusion aims to target substances contributing to tropospheric formation, using metrics like Maximum Incremental Reactivity (MIR), where compounds with MIR values below approximately 0.5 grams of per gram of VOC are often exempted. In contrast, the defines VOCs under Directive 1999/13/EC as any with a of 0.01 kPa or more at 293.15 K (20°C) or equivalent volatility under conditions of use, without explicit exemptions for low-reactivity compounds, leading to broader inclusion of substances like , which has a of about 5.9 kPa at 20°C and is regulated in both but treated differently in limits due to U.S. reactivity adjustments. These definitional divergences—U.S. prioritizing ozone-forming potential versus EU's threshold—complicate cross-jurisdictional comparisons of emission inventories and causal assessments of air quality impacts. In , VOCs are defined as organic compounds with a greater than or equal to 0.01 kPa at 20°C or a not exceeding 260°C under standard pressure, encompassing a wide range including combustion-derived hydrocarbons, as per national standards like GB 37822-2019 for ambient air quality. lacks a centralized statutory definition equivalent to those in the U.S. or EU, with the (CPCB) operationally treating VOCs as organic compounds between 50°C and 260°C, focusing monitoring on anthropogenic sources like vehicle exhaust without formal exemptions for biogenic emissions. aligns closely with U.S. criteria under the Canadian Environmental Protection Act, excluding inorganic substances and certain low-reactivity organics listed in Schedule 1, but recent Volatile Organic Compound Concentration Limits for Certain Products Regulations (effective 2024) emphasize product-specific caps without distinct biogenic exclusions, though natural emissions are typically distinguished from regulated anthropogenic VOCs in policy implementation. Such inconsistencies, where and adopt broader -point or pressure thresholds that include more combustion products without reactivity weighting, hinder global causal modeling of VOC contributions to , as aggregated data may over- or under-represent precursors relative to jurisdiction-specific exclusions. Threshold limits for VOC content in products further illustrate policy variances over empirical uniformity. In the U.S., federal standards under 40 CFR Part 59 limit VOCs in architectural coatings, such as 250 g/L for interior flat paints and 380 g/L for non-flat, reflecting post- evolution tied to the 1990 Clean Air Act Amendments (CAAA), which mandated VOC and controls in nonattainment areas via reasonably available control technology (RACT). The EU's Directive 2004/42/EC imposes similar product limits, e.g., 30 g/L for interior wall paints by 2010, but bases compliance on total VOC mass without U.S.-style reactivity adjustments. These standards evolved from smog crises, with the 1990 CAAA expanding VOC/ trading and controls to address photochemical oxidant formation, yet jurisdictional differences—such as U.S. exemptions for ethanol blends in fuels due to lower MIR (1.7 g O3/g VOC) versus EU inclusion—prioritize domestic industry accommodation over consistent reactivity science, impeding precise international attribution of emission impacts.

Implementation Challenges and Economic Impacts

Implementation of VOC regulations imposes substantial compliance burdens on industries, particularly in sectors like refining and surface coatings, where reformulation and modifications are required to meet emission limits. In the United States, annual compliance costs for VOC controls in the oil and gas sector alone are estimated at $1.2 billion, encompassing , equipment upgrades, and operational changes, though partial offsets from product recovery may reduce net expenses to around $520 million. For automobile and light-duty truck surface coating operations, achieving proposed VOC limits of 0.028 kg per liter of applied coating solids incurs costs of approximately $6,800 per ton of VOC reduced, reflecting the expenses of advanced control technologies and reformulation efforts. These costs contribute to broader industry-wide regulatory burdens, with small manufacturers potentially facing over $50,000 in additional compliance expenditures under updated air toxics rules, exacerbating financial strain on entities with limited resources. While VOC controls have yielded ozone reductions, typically 10-15% in peak concentrations under combined strategies in non-attainment areas, the marginal benefits diminish in NOx-limited regimes prevalent in many urban settings, where VOC abatement yields lesser improvements relative to NOx controls. Abatement costs often exceed 3,000−3,000-6,000 per ton in fragmented applications like dry cleaning or coatings, surpassing the value of incremental ozone suppression when biogenic VOCs—emitted predominantly by vegetation—dominate total atmospheric loadings and render anthropogenic reductions less impactful on overall reactivity. This discrepancy highlights implementation challenges, as regulations frequently overlook regime-specific chemistry, leading to inefficient resource allocation without proportional air quality gains. Economic analyses reveal factor shifts and unintended inefficiencies from stringent VOC policies, including capital diversion from productive investments and labor reallocation away from regulated sectors. In , levying VOC environmental protection taxes has been modeled to reduce GDP, household income, total consumption, and exports, with higher tax rates amplifying pollutant cuts at the expense of macroeconomic stability and without commensurate health benefits proportional to the fiscal drag. Such measures induce compliance distortions, favoring low-emission alternatives that may increase or shift emissions to unregulated regions, underscoring overreach where natural VOC sources eclipse controllable anthropogenic fractions and regulatory costs burden industries without addressing root causal drivers of .

Analytical and Monitoring Techniques

Sampling and Detection Methods

Volatile organic compounds (VOCs) in air are sampled using methods that ensure minimal loss or contamination, such as evacuated passivated canisters (e.g., SUMMA canisters) under EPA Method TO-15, which collect whole air samples for subsequent of up to 97 target VOCs at parts-per-billion (ppb) to parts-per-trillion (ppt) concentrations. Active sampling employs pumps to draw air through adsorbent tubes packed with materials like Tenax or multisorbents, enabling controlled volume collection for targeted VOCs. Passive sampling, as in EPA Method 325A, relies on to adsorb VOCs onto tubes over extended periods (e.g., up to 14 days), providing time-integrated averages without power sources but requiring validated uptake rates for accuracy. Laboratory detection typically involves thermal desorption followed by gas chromatography-mass spectrometry (GC-MS) or flame ionization detection (FID) for VOC speciation, achieving ppb-level sensitivity and compound identification via mass spectra or retention times. GC-MS provides structural confirmation for complex mixtures, while FID offers quantitative response proportional to carbon content, both calibrated against NIST-traceable standards to ensure metrological reliability across instruments. For field measurements, detectors (PIDs) ionize VOCs using lamps (e.g., 10.6 eV), generating currents proportional to concentration for real-time monitoring down to ppb levels, though they lack and respond variably to compound ionization potentials. Breath analysis samples exhaled VOCs non-invasively via bags or tubes for detection, such as acetone at elevated levels (1-2 ppm) in conditions like , but is limited to higher-concentration species due to dilution by ambient air and physiological variability, with low-trace VOCs often below detection thresholds without preconcentration.

Innovations in VOC Analysis (2020s Developments)

In the early , advancements in (MS) integrated (AI) to enable real-time volatile organic compound (VOC) monitoring with enhanced sensitivity and data processing. For instance, AI-driven platforms combined high-resolution MS with algorithms to quantify trace VOCs in breath samples, achieving detection limits below 1 part per billion (ppb) and facilitating predictive modeling for disease biomarkers. Similarly, -enhanced direct MS analysis improved accuracy in identifying non-volatile breath metabolites associated with conditions like , reducing analysis time from hours to minutes. Portable VOC sensors with wireless connectivity proliferated, supporting on-site real-time monitoring in complex environments. Devices such as the ppbRAE 3000+ achieved ppb-level sensitivity (1 ppb to 10,000 ppm) with response times under 3 seconds and integrated connectivity for remote data transmission, aiding causal inference in industrial and urban settings. The portable VOC monitor market expanded rapidly, valued at USD 500 million in 2024 and projected to reach USD 1.2 billion by 2033 at a 10.2% CAGR, driven by demand for compact, networked sensors in environmental compliance. Methods for distinguishing biogenic from anthropogenic VOC sources advanced through refined emission modeling and . A 2024 study in urban areas used receptor modeling to apportion contributions of , monoterpenes, and , revealing biogenic dominance in summer (up to 70% for certain ) via correlations with meteorological data and source profiles. These techniques improved causal attribution by integrating high-resolution with ambient arrays for monitoring. Atmospheric modeling refinements addressed systematic underpredictions of VOC concentrations. Evaluations across European sites in 2024 showed chemical transport models underestimated observed levels by 20-50% due to incomplete emission inventories and reaction schemes, prompting updates to biogenic emission algorithms for better alignment with measurements. Breath biopsy techniques cataloged human-derived VOCs for non-invasive health profiling. Owlstone Medical's Breath Biopsy VOC Atlas, updated through 2025, identified and quantified 148 on-breath VOCs using standardized GC-MS with orthogonal confirmation, enabling holistic linked to and disease states like sinonasal disorders via wearable-compatible sampling. This catalog supports differentiation of endogenous VOCs from environmental exposures, enhancing causal realism in epidemiological studies.

Mitigation and Applications

Control Strategies and Technologies

Substitution of high-VOC solvents with low-VOC alternatives, such as water-based coatings, has demonstrated emission reductions where solvent-based formulations release up to 65% of VOC content during application, compared to only 5% for water-based equivalents. Implementing low-VOC coating substitutions in industrial processes can achieve approximately 8.7% overall emission cuts, based on predictive modeling of scenario analyses. Process enclosures and programs enable targeted containment and repair, with empirical data from refineries showing 42-57% VOC emission reductions after repairing 42-81% of identified leaking components, primarily from high-leak sources like valves and open-ended lines accounting for over 88.5% of total leaks. Adsorption combined with , often using TiO2-based catalysts on supports like zeolites, achieves removal efficiencies of 80-95% for low-concentration VOCs in integrated systems, leveraging adsorption for capture followed by UV-driven degradation. Specific applications, such as photocatalytic oxidation under visible , have reached 99.3% efficiency for indoor VOCs after 300 minutes of low-energy irradiation (40 Wh with an 8 W source). Thermal incineration and provide high-destruction rates for industrial streams, with catalytic incinerators consistently exceeding 95% VOC removal efficiency across diverse gaseous organics when properly engineered for heat recovery and low inlet concentrations. These methods operate effectively at lower temperatures (313-343 K) than non-catalytic incineration, reducing energy demands while oxidizing VOCs to CO2 and . Despite these efficacies, anthropogenic VOC controls face rebound effects from natural biogenic emissions, which exhibit variability influenced by environmental factors and plant species, potentially offsetting reductions as biogenic sources like from forests contribute substantially to total atmospheric burdens. In developing regions, cost-effectiveness diminishes due to high capital and operational expenses for advanced technologies, with broader economic analyses indicating negative macroeconomic impacts from scaled VOC abatement efforts.

Industrial and Biological Benefits

Volatile organic compounds (VOCs) serve as essential solvents in , particularly in the formulation of paints, coatings, adhesives, and pharmaceuticals, where they facilitate the dissolution of resins and polymers, enabling uniform application and rapid for efficient and curing. In automotive and , VOC-based solvents support metal cleaning and surface preparation, contributing to high-throughput production by improving and reducing processing times. These properties enhance product durability and manufacturing scalability across sectors valued in billions annually, as organic solvents constitute the primary components of VOC utilization in such applications. In fuel systems, certain VOCs act as additives in and diesel formulations, boosting and combustion efficiency to optimize performance and fuel economy. Biogenic VOCs (BVOCs), emitted by such as and isoprenes, play critical roles in ecological signaling and defense mechanisms, repelling herbivores through or deterrence while attracting pollinators and natural enemies of pests to uninfested tissues. These compounds mediate inter-plant communication, priming neighboring for enhanced resistance to pathogens and herbivores via volatile cues that trigger systemic defenses. BVOCs also support by guiding pollinators to flowers and contribute to stress , including against oxidative damage from environmental stressors. In human physiology, VOCs detectable in exhaled breath serve as non-invasive biomarkers for disease diagnostics; for instance, specific VOC profiles correlate with metabolic disruptions in , enabling early detection through breath analysis. Similarly, elevated VOCs such as alkanes and aldehydes in breath have been identified as indicators for and other cancers, with studies validating their discriminatory potential against healthy controls via gas chromatography-mass spectrometry. At low concentrations, VOCs in essential oils and fragrances provide therapeutic benefits, including stress reduction, analgesia, and mood enhancement through , as demonstrated by randomized trials showing decreased levels and improved relaxation with oils like lavender. These applications, rooted in the bioactive properties of plant-derived VOCs such as monoterpenes, support immune modulation and sleep quality without evidence of widespread harm at diluted exposures.

References

  1. https://www.epa.gov/indoor-air-quality-iaq/technical-overview-volatile-organic-compounds
  2. https://www.epa.gov/air-emissions-inventories/what-definition-voc
  3. https://acp.copernicus.org/articles/23/2963/2023/
  4. https://pmc.ncbi.nlm.nih.gov/articles/PMC8700805/
  5. https://pubs.acs.org/doi/10.1021/acs.est.1c01481
  6. https://www.epa.gov/ground-level-ozone-pollution/volatile-organic-compound-exemptions
  7. https://acp.copernicus.org/articles/24/7063/2024/
  8. https://www.epa.gov/indoor-air-quality-iaq/volatile-organic-compounds-impact-indoor-air-quality
  9. https://www.epa.gov/ground-level-ozone-pollution/revision-regulatory-definition-volatile-organic-compounds
  10. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/volatile-organic-compound
  11. https://downloads.regulations.gov/EPA-HQ-OLEM-2021-0397-0364/attachment_6.pdf
  12. https://acp.copernicus.org/preprints/14/29615/2014/acpd-14-29615-2014.pdf
  13. https://pmc.ncbi.nlm.nih.gov/articles/PMC9292506/
  14. https://pubs.acs.org/doi/10.1021/ie061156w
  15. https://www.siyavula.com/read/za/physical-sciences/grade-12/organic-molecules/04-organic-molecules-04
  16. https://pmc.ncbi.nlm.nih.gov/articles/PMC4012514/
  17. https://www.thermofisher.com/us/en/home/industrial/environmental/environmental-learning-center/contaminant-analysis-information/volatile-organic-compounds-analysis.html
  18. https://www.sciencedirect.com/science/article/abs/pii/S1352231099004604
  19. https://acp.copernicus.org/articles/22/10937/2022/
  20. https://www.sciencedirect.com/science/article/abs/pii/S0048969722029989
  21. https://pmc.ncbi.nlm.nih.gov/articles/PMC5745158/
  22. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019JD032243
  23. https://ww2.arb.ca.gov/sites/default/files/barcu/regact/2009/mir2009/mir10.pdf
  24. https://www.sciencedirect.com/topics/engineering/photochemical-ozone-creation-potential
  25. https://www.fluorocarbons.org/environment-climate/environmental-impact/photochemical-ozone-creation-potential/
  26. https://pmc.ncbi.nlm.nih.gov/articles/PMC9893210/
  27. https://napiers.net/blogs/news/essential-oils-the-benefits-and-uses-of-natures-most-powerful-remedies
  28. https://www.sciencehistory.org/stories/magazine/al-kimiya-notes-on-arabic-alchemy/
  29. https://condorchem.com/en/blog/brief-history-distillation-technologies/
  30. https://www.researchgate.net/publication/385384279_Some_Instances_in_the_History_of_Distilled_Oil_of_Turpentine_The_Disappearing_Painters%27_Material_2015_updated_2024
  31. https://www.mdpi.com/2223-7747/11/6/789
  32. https://thisis.caltech.edu/news/fifty-years-clearing-skies-39248
  33. https://www.mdpi.com/2073-4433/12/10/1354
  34. https://www.aqmd.gov/home/research/publications/50-years-of-progress
  35. https://earthobservatory.nasa.gov/features/AirQuality/page2.php
  36. https://www.rsc.org/images/history-of-smog_tcm18-210190.pdf
  37. https://ww2.arb.ca.gov/about/history
  38. https://www.epa.gov/clean-air-act-overview/clean-air-act-requirements-and-history
  39. https://www.congress.gov/crs-product/RL30853
  40. https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/92JD00682
  41. https://pmc.ncbi.nlm.nih.gov/articles/PMC4370762/
  42. https://www.sciencedirect.com/science/article/pii/S0013935122017133
  43. https://www.sciencedirect.com/science/article/abs/pii/S1309104222000836
  44. https://www.pnas.org/doi/10.1073/pnas.2008901117
  45. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2007JD008950
  46. https://bg.copernicus.org/articles/20/4391/2023/
  47. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2012JD017642
  48. https://www.sciencedirect.com/science/article/abs/pii/S0141113623003057
  49. https://www.researchgate.net/publication/366238856_Volatile_organic_compounds_as_mediators_of_plant_communication_and_adaptation_to_climate_change
  50. https://www.researchgate.net/publication/359022654_Role_of_Volatile_Organic_Compounds_in_Plant_Growth_Communication_and_Defense
  51. https://egusphere.copernicus.org/preprints/2025/egusphere-2025-4036/egusphere-2025-4036.pdf
  52. https://ui.adsabs.harvard.edu/abs/2022AGUFMGH45A..07X/abstract
  53. https://archive.ipcc.ch/ipccreports/tar/wg1/140.htm
  54. https://www.sciencedirect.com/science/article/pii/S0160412021003354
  55. https://pmc.ncbi.nlm.nih.gov/articles/PMC9685044/
  56. https://acp.copernicus.org/articles/19/5905/2019/
  57. https://nap.nationalacademies.org/read/1889/chapter/8
  58. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2001JD000932
  59. https://csl.noaa.gov/assessments/ozone/1994/chapters/chapter5.pdf
  60. https://ww2.arb.ca.gov/sites/default/files/2020-12/cp_reg_mir-tables.pdf
  61. https://pubs.acs.org/doi/10.1021/es060296u
  62. https://pubs.acs.org/doi/10.1021/acsestair.4c00026
  63. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2021JD035606
  64. https://acp.copernicus.org/articles/22/11675/2022/
  65. https://www.epa.gov/ground-level-ozone-pollution/ground-level-ozone-basics
  66. https://pmc.ncbi.nlm.nih.gov/articles/PMC6834528/
  67. https://nph.onlinelibrary.wiley.com/doi/10.1111/j.1469-8137.2009.02859.x
  68. https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-6/
  69. https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter06.pdf
  70. https://pmc.ncbi.nlm.nih.gov/articles/PMC6899487/
  71. https://www.sciencedirect.com/science/article/pii/S0960982223004736
  72. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2021GB006969
  73. https://www.sciencedirect.com/science/article/pii/S2590162120300216
  74. https://www.nature.com/articles/s41467-025-63437-8
  75. https://www.ipcc.ch/site/assets/uploads/2018/02/ar4-wg1-chapter7-1.pdf
  76. https://pmc.ncbi.nlm.nih.gov/articles/PMC10218183/
  77. https://www.researchgate.net/publication/335702100_How_are_Humans_Exposed_to_Organic_Chemicals_Released_to_Indoor_Air
  78. https://www.ncbi.nlm.nih.gov/books/NBK215288/
  79. https://www.health.state.mn.us/communities/environment/air/toxins/voc.htm
  80. https://pmc.ncbi.nlm.nih.gov/articles/PMC11080066/
  81. https://www.frontiersin.org/journals/built-environment/articles/10.3389/fbuil.2023.1292531/full
  82. https://www.canada.ca/content/dam/hc-sc/documents/services/publications/healthy-living/benzene-releases-gasoline-stations-implications-human-health/benzene-releases-gasoline-stations-implications-human-health.pdf
  83. https://www.healtheffects.org/system/files/SR16-Benzene.pdf
  84. https://nap.nationalacademies.org/read/18796/chapter/10
  85. https://www.cdc.gov/niosh/idlh/108883.html
  86. https://publications.iarc.who.int/_publications/media/download/6037/4d6f5591b8276f4e8582d5f6af59c9c060f689ff.pdf
  87. https://www.eaht.org/m/journal/view.php?number=965
  88. https://www.cancer.gov/about-cancer/causes-prevention/risk/substances/formaldehyde/formaldehyde-fact-sheet
  89. https://publications.iarc.who.int/_publications/media/download/3805/c24b0ad4f82efe0d57ddf335f2c12e9badb9507b.pdf
  90. https://www.cdc.gov/niosh/idlh/50000.html
  91. https://pmc.ncbi.nlm.nih.gov/articles/PMC12222567/
  92. https://www.sciencedirect.com/science/article/pii/S0160412022003671
  93. https://www.ncbi.nlm.nih.gov/books/NBK592498/
  94. https://foobot.io/guides/threshold-limit-values-volatile-organic-compounds.php
  95. https://www.osha.gov/annotated-pels/table-z-1
  96. https://pubmed.ncbi.nlm.nih.gov/38366695/
  97. https://pmc.ncbi.nlm.nih.gov/articles/PMC9487771/
  98. https://eaaci.org/wp-content/uploads/2024/11/for-public-comment-EAACI-Guideline-on-indoor-pollution-1.pdf
  99. https://iaqscience.lbl.gov/vocs-and-cancer
  100. https://archpublichealth.biomedcentral.com/articles/10.1186/s13690-023-01070-x
  101. https://www.nature.com/articles/s41612-024-00598-1
  102. https://www.nature.com/articles/s41598-024-81873-2
  103. https://www.ecfr.gov/current/title-40/chapter-I/subchapter-C/part-59
  104. https://www.bswllp.com/uh-oooo-more-regulation-for-oil-and-gas-production
  105. https://www.federalregister.gov/documents/2023/05/09/2023-09587/review-of-standards-of-performance-for-automobile-and-light-duty-truck-surface-coating-operations
  106. https://trdsf.com/blogs/news/epa-regulations-impact-on-small-firms
  107. https://nap.nationalacademies.org/read/1889/chapter/13
  108. https://www.chicagofed.org/publications/chicago-fed-letter/1993/july-71
  109. https://www.researchgate.net/publication/383372901_Environmental_and_Economic_Impact_Analysis_of_Levying_VOCs_Environmental_Protection_Tax_in_China
  110. http://www.hjkxyj.org.cn/en/article/doi/10.13198/j.issn.1001-6929.2023.09.10
  111. https://www.epa.gov/quality/analysis-volatile-organic-compounds-air-contained-canisters-method-15-sop-no-hw-31-revision
  112. https://lcslaboratory.com/air-testing/industrial-hygiene/air-sampling-of-volatile-organic-compounds/
  113. https://www.epa.gov/sites/default/files/2017-08/documents/method_325a.pdf
  114. https://www.alsglobal.com/sv/News-and-publications/2025/01/Passive-Air-Sampling-for-VOCs---Selecting-the-Best-Technique
  115. https://www.sciencedirect.com/science/article/abs/pii/S0048969711010096
  116. https://www.nist.gov/programs-projects/development-standards-world-meteorological-organization-global-atmosphere-watch
  117. https://www.nist.gov/calibrations/traceability
  118. https://www.indsci.com/en/blog/qa-a-deeper-look-at-pid-technology
  119. https://www.ametekmocon.com/pressreleases/news/2020/october/the-photoionization-technique-for-gas-detection
  120. https://pmc.ncbi.nlm.nih.gov/articles/PMC10339195/
  121. https://www.sciencedirect.com/science/article/abs/pii/S0956566324010686
  122. https://ui.adsabs.harvard.edu/abs/2025GAnCh..1400284L/abstract
  123. https://pubs.rsc.org/en/content/articlelanding/2025/ay/d5ay01304f
  124. https://farrwest.com/product/ppbrae/
  125. https://www.verifiedmarketreports.com/product/portable-voc-monitor-market/
  126. https://www.sciencedirect.com/science/article/pii/S0048969724017583
  127. https://acp.copernicus.org/articles/24/219/2024/
  128. https://pmc.ncbi.nlm.nih.gov/articles/PMC11379754/
  129. https://www.owlstonemedical.com/science-technology/breath-biopsy-voc-atlas/
  130. https://www.thefabricator.com/tubepipejournal/article/tubepipeproduction/eliminating-solvents-reducing-vocs
  131. https://www.mdpi.com/2073-4433/14/4/662
  132. https://pubmed.ncbi.nlm.nih.gov/32663111/
  133. https://papers.ssrn.com/sol3/Delivery.cfm/00e97c49-c1e3-4d1a-bfcc-cc0e5bc586d1-MECA.pdf?abstractid=4245544&mirid=1&type=2
  134. https://pmc.ncbi.nlm.nih.gov/articles/PMC7599939/
  135. https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=2000THXT.TXT
  136. https://ect-journal.kz/index.php/ectj/article/view/265
  137. https://www.mdpi.com/2305-6304/13/5/364
  138. https://pmc.ncbi.nlm.nih.gov/articles/PMC11419898/
  139. https://blog.chesterton.com/wear-protection/low-volatile-organic-compound-voc-coatings/
  140. https://ww2.arb.ca.gov/sites/default/files/2023-12/voc_epa-453_r-94-066-a.pdf
  141. https://pmc.ncbi.nlm.nih.gov/articles/PMC11436172/
  142. https://www.epa.gov/indoor-air-quality-iaq/what-are-volatile-organic-compounds-vocs
  143. https://www.owlstonemedical.com/about/blog/2022/feb/22/voc-biomarkers-diabetes/
  144. https://jnanobiotechnology.biomedcentral.com/articles/10.1186/s12951-025-03526-4
  145. https://www.sciencedirect.com/science/article/pii/S0378874124004793
  146. https://pmc.ncbi.nlm.nih.gov/articles/PMC12378133/
  147. https://www.frontiersin.org/journals/pharmacology/articles/10.3389/fphar.2021.740302/full
Add your contribution
Related Hubs
User Avatar
No comments yet.