Precursor Volatile Organic Compounds

The ability of a given volatile organic compound (VOC) to produce during its atmospheric oxidation secondary organic aerosol depends on three factors  

Oxidation of VOCs leads to the formation of more highly substituted and therefore lower volatility reaction products. The reduction in volatility is due mainly to the fact that adding oxygen and/or nitrogen to organic molecules reduces volatility (Seinfeld and Pankow 2003). Addition of carboxylic acid, alcohol, aldehyde, ketone, alkyl nitrate, and nitro groups to the precursor VOC can reduce its volatility by several orders of magnitude (see Section 14.5.1). The reactions of VOCs with 03, OH, and N03 can all lead to SOA formation in the atmosphere. 

The ability of almost all such oxidation products to dissolve in the organic particulate phase suggests that, in theory at least, every VOC contributes to SOA formation [see, e.g., (14.24), where, for any AROG 0, some nonzero SOA is formed]. However, the 

As a result of the above constraints, VOCs that for all practical purposes do not produce organic aerosol in the atmosphere include all alkanes with up to six carbon atoms (from methane to hexane isomers), all alkenes with up to six carbon atoms (from ethene to hexene isomers), and most other low-molecular-weight compounds. An important exception is isoprene, a five-carbon atom molecule with two double bonds (see Section 6.11) isoprene photooxidation produces SOA in laboratory chambers (Kroll et al. 2005, 2006) and its oxidation products have been detected in ambient aerosols (Claeys et al., 2004a Edney et al. 2005). In general, large VOCs containing one or more double bonds are expected to be good SOA precursors. A set of structure-SOA formation potential relationships have been proposed by Keywood et al. (2004) for cycloalkenes  

FIGURE 14.17 SOA yield data as a function of the produced organic aerosol mass for four cycloalkenes (Keywood et al. 2004). 

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Instruments and methods that can in near real time characterize more fully the speciated organic composition of secondary and combustion aerosols and that of the gas phase. In conjunction with laboratory studies, one may hope to use these techniques to elucidate the pathways and connect precursor volatile organic compounds to the nature of particulate matter. 

In 1966, the Los Angeles Air Pollution Control Board designated trichloroethylene as a photochemically reactive solvent that decomposes in the lower atmosphere, contributing to air pollution. In 1970 all states were requited to submit pollution control plans to EPA to meet national air quaUty standards. These plans, known as State Implementation Plans (SIPS), controlled trichloroethylene as a volatile organic compound (VOC). They were designed to have each state achieve the National Ambient Air QuaUty Standard (NAAQS) for ozone. The regulations were estabUshed to control the emission of precursors for ozone, of which trichloroethylene is one. 

Volatile organic compounds and other ozone precursors (CO... 

VOC (VOCs) volatile organic com-pound(s) volatile organic compounds are regulated because they are precursors to ozone carbon-containing gases and vapors from... 

If handled responsibly, PFCs can be excellent choices to replace ozone-depleting compounds in many demanding, high-performance applications. Perfluorinated liquids are colorless, odorless, essentially nontoxic, and nonflammable. In addition, since they are not precursors to photochemical smog, PFCs are exempt from the U.S. EPAs volatile organic compounds (VOC) definition. Most importantly, these materials do not contain the carbon-bound chlorine or bromine, which can cause ozone depletion. 

Volatile organic compounds (VOCs), especially trihalomethanes, are frequently found in drinking water due to the chlorination of humic acids. When UV irradiation is applied to the pre-ozonation of humic acids, the decomposition of VOC precursors increases (Hayashi et al., 1993). The ozonation rates of compounds such as trichloroethylene, tetrachloroethylene, 1,1,1-trichloroethane, 1,2-dichloroethane, and 1,2-dichloropropane were found to be dependent on UV intensity and ozone concentration in the aqueous phase by Kusakabe et al. (1991), who reported a linear relationship between the logarithmic value of [C]/[C0] and [03]f for 1,1,1-trichloroethane, trichloroethylene, and tetrachloroethylene. The other two organochlorines followed the same first-order kinetics with and without UV irradiation (Kusakabe et al., 1991). Thus, the decomposition rate can be expressed as ... 

So what are nitrogen oxides Where does they come from And why is there a concern about the amount that enters the atmosphere Nitrogen dioxide (NO2) is a brownish, highly reactive gas that is present in all urban atmospheres. N02 can irritate the lungs, cause bronchitis and pneumonia, and lower resistance to respiratory infections. Nitrogen oxides are an important precursor both to ozone (Oj) and acid rain, and may affect both terrestrial and aquatic ecosystems. The major mechanism for the formation of NO2 in the atmosphere is the oxidation of the primary air pollutant, nitric oxide (NO). NOx plays a major role, together with VOCs (Volatile Organic Compounds), in the atmospheric... 

Volatile Organic Compounds (VOC) are widely found as solvents in industrial processes and domestic use. Considered as major air contaminants for inducing directly health troubles, or for being precursors of tropospheric ozone, polluted air streams are mainly treated by adsorption on a porous solid [6]. 

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