Volatile Organic Compounds (VOCs)

Volatile Organic Compounds are defined as a hydrocarbon. They contain at least one carbon and hydrogen atom in its structure, defined as in aliphatic and aromatic structure solvents or directly involved in chemical reactions in chemical, pharmaceutical and hydrocarbon industries. According to USEPA, a total of 188 air pollutants as dangerous air pollutants and 149 were VOCs. They are separated into three parts; volatile, semi-volatile, VOCs and very persistent with chlorinated and brominated compounds, which have pressure higher than 10-1 torr at 25 °C and 760 mmHg.

According to The European Union (EU), Volatile Organic Compounds are organic compounds which are observed as boiling point less than or equal to 260 °C at a standard pressure of 101.3 kPa. The countries that are members of the EU has been checked based on Directive 2004/42/EC of the European Parliament and of the Council of 21 April 2004 on the limitation of emissions of VOCs due to the use of organic solvents in different products Directive 1999/13/EC. These countries make a decision to reduce the hydrocarbon emissions about 30% also for lower the ozone formation potential need to stop nitrogen oxides emission.

Many international protocols have been made to control carbon dioxide (CO2) and nitrogen oxides (NOx). They found a solution with the Montreal Protocol on Protection of Ozone Layer in 1987, London Revisions to do Protocol in 1990 and Copenhagen’s Protocol in 1992. Also, the Kyoto Protocol’s reduction of methane carbon dioxide and nitrous oxide aimed in 1997.

The Physical and Chemical Properties of Volatile Organic Compounds

The VOCs have been included in hazardous air pollutant (HAP) due to chemical properties and various health problems. They release into the atmosphere, also cause their elimination from the atmosphere because oxygenated with a photochemical process. Generally, numerous reactions begin with the hydroxyl radical (.OH) and O3, NO3, Cl, Br, which has different atmospheric lifetime depending on their severity of solar radiation, chemical structure and radical concentration. NO is changing to NO2 while photolysis and contributes to tropospheric ozone formation due to VOCs diminished in contaminated air masses at night time.

Nontrivial .OH radicals are the most crucial interacting substance and there are approximately 1.1×106 radicals/cm3 in the degradation of VOCs. Another radical is Cl, which has not been certainly checked as a global scale. Even though its reactions have been identified in some cities. The situation for alkanes that can seriously pollute when it reacts with O3 and NO3.

The physical and chemical behavior of the troposphere affects to VOCs in many ways. For example, the most significant contribution to air pollution is the photochemical ozone formation. The VOCs are based on the temporal and spatial type of emission, molecular-dependent potential to produce ozone and the photochemical reaction rates. The use of VOCs’ scale, which are their ozone production skill under atmospheric conditions, are the photochemical ozone creation potential (POCP) and maximum incremental reactivity (MIR). POCP tells the quantity of O3 while calculating of its contour models under real-world conditions in Eq. (1). When comparing VOCs’ ozone potential, it is calibrated by rating its values with these other VOCs (i.e., benzene) as follows.


Carter et al. evaluated ozone formation along with the range of up to a day with optimum VOC/NOx situations in urban areas in the United States by the other scale that MIR specified from irradiation of a more simple model of photochemical systems.

Most of the VOCs given in Table 1 are emitted from motor vehicle emissions in various solvent production, dry cleaning and usually reach higher concentration values in winter. These VOCs vary depending on different situations. They are like the limit values determined by NHMRC. Concentrations computed at specific temperature and 101.3 kP compared with the NHMRC indoor air (1-h) target, set at 500 μg/m3 for TVOC and 250 μg/m3 for any Volatile Organic Compounds.

The properties of some Volatile Organic Compounds

Sources of Volatile Organic Compounds

People have basic needs, such as eating and drinking, shelter and transportation, which release invisible dangerous gases. These activities humankind do in our daily life cause some pollutants like VOCs. According to the National Air Quality and Emissions Trends Report; the estimate of fuel combustion emissions, industrial processes, transportation and miscellaneous. Almost 100 TgC/year is surmised to be exuded from technology brought by technology besides the 150 TgC/year from all human-made sources, including biomass burning.

Coal production, which is the energy source of industry and residences, causes significant methane causes emission and minor emissions of ethane and propane. Also, liquid fossil fuel production, storage and distribution result a wider variety of organic gas emissions to the outside.

The production platforms of crude oil are healthy point sources of hydrocarbons, for instance, methane, ethane, propane, butanes, pentanes, hexanes, heptanes, octanes and cycloparaffins. The primary sources from processing liquid fossil fuels are catalytic cracking (0.25–0.63 kg/m3 of feed), coking (about 0.4 kg/m3 of meal) and asphalt blowing (about 27 kg of VOC/m3 of asphalt). Moreover, supposedly leakage emissions can come true from leaks and evaporation from all equipment and installations.

However, not many volatile emissions are estimated to be 2.9 kg/t of fuel at petrol and service stations where have filled a car with gasoline or gasoline. Substantially petrochemical products involve in a limited number of compound classes such as acyclic alkanes, cyclic alkanes, monoaromatics and diaromatics. Each of many (tens of thousands) individual homologs and isomers consist of them. This report reflects that on-road vehicles, solvent utilization, non-road engines and cars are the highest sources of Volatile Organic Compounds in the United States in Table 2.4. This Table also reveals a wide variety of other manufacturing processes. The total emissions have shown almost 0.32% of the US’s unlimited electric utilization usage.

National emissions estimate of VOCs for 1999

There are many sources available for direct and indirect release Volatile Organic Compounds. At the beginning of indirect sources are photolysis and oxidation. The natural sources are biomass burning, anthropogenic activities and vegetation. The largest Volatile Organic Compounds’ direct source is vegetation and total emissions estimated at 770-1400 Tg/yr, although isoprene (C5H8) has been attributed to as 500-750 Tg/yr ratio.

This release is also known as biogenic Volatile Organic Compounds (BVOCs). Table 2 shows that isoprene, terpenes, terpenoids, alcohols, aldehydes, organic acids and esters emitted with potentially many compounds. BVOCs have profoundly temporarily and geographically variables such as plant species, solar volume, warming and phenological events and other parameters excluding CO2 that is not certain whether increases or not.

VOCs’ second size of emission is biomass burning and fires, which emissions are more significant than 400 Tg/yr. Alkanes, alkenes, alcohols, aldehydes, ketones and organic acids, as well as nitrogen and sulfur-containing species such as nitric oxide (NO), nitrogen dioxide (NO2), nitrous oxide (N2O), ammonia (NH3), hydrogen cyanide (HCN), acetonitrile (CH3CN), sulfur dioxide (SO2) and carbonyl sulfide (OCS) are release from sources.

The other considerable factors are anthropogenic sources, which emissions were approximately 160 Tg for the year 2008 by the Emission Database for Global Atmospheric Research. This rate depends on population, transportation, agriculture, cooking, painting, smog, etc.

Effects of Volatile Organic Compounds

People spend most of their time in houses, works, hospitals, universities, sports halls, restaurants, cafes and entertainment places such as indoor environments and the remaining time is spent outside that both of them cause released Volatile Organic Compounds from used materials by there. This situation is getting worse because recent epidemiologic studies indicate that lung problems can be linked to health problems and even death. Another serious problem is growing asthma and allergic cases.

The tropospheric ozone problem is another issue, which can irritate airways. It can allow us to predict and to evaluate the efficiency of emissions between Volatile Organic Compoundsand NOx. The reaction of O3 to changes in Volatile Organic Compounds and NOx emissions, although gases, reveal a complex dependence on the levels and ratio of Volatile Organic Compounds to NOx emissions. To the constant level of Volatile Organic Compounds emissions peak, O3 increases as NOx emissions increase until the critical ratio of VOC to NOx is reached and then as a reverse proportion, O3 decreases and NOx emissions.


HCHO+hv →2HO2rxn11
Alkene+O3→ radicalsrxn12
OH+VOCi → a HO2+b RO2+CO3rxn13
HO2+NO→ NO2+OHrxn14
RO2+NO→ d (NO→NO2 + conversions) + HC oxidation productsrxn15
RCO3 + NO→ e( NO→NO2 conversions) + HC oxidation productsrxn16
NO2 +hv→ NO+Orxn17

Starting with rxn10 and rxn11, which reaction chain results consist of photochemical O3 (rxn17) by free radicals. This chain continues with .OH oxidizes VOCs (rxn13), forming peroxy radicals as photolyzed (rxn17) O3 that turn into NO to NO2 (rxn14- rxn16) and rxn15- rxn16 sections are the conversions of NO2. Then loop of reactions is being completed for another cycle by remodeling both OH in rxn14 and NO in rxn17. In rxn13 part, it could be CO, hydrocarbon, or HCHO instead of VOCs that enters the reaction.

The VOCs that contain gases such as chlorine, fluorine, bromine, or iodine break down ozone in the stratosphere. Contrary to the troposphere’s ozone, Volatile Organic Compounds’ adverse effects on the ozone layer protect people against harmful ultraviolet (UV) rays in the stratosphere.

Chlorine, fluorine, bromine or iodine reaching the stratosphere with solar, then they are separated from this structure by the effect of light and become free. In this case, these substances are very reactive in their free form, attacking the O3, which tends to react and disintegrate it. Until these substances disappeared in the stratosphere, they repeatedly turn into other states and break down hundreds and thousands of molecules of ozone.

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