Urban atmosphere alkanes

More than 130 different types of alkanes have been identified in the atmosphere [27] and they comprise a major fraction of the organic pollutants found in urban atmospheres (see Table 3). They are released in large amounts in activities connected with the extraction, refining, distribution, and combustion of fossil fuels. Alkanes are also released during the combustion of organic matter and by microbiological processes associated with the decay... 

Bi X, Sheng G, Peng P, Chen Y, Zhang Z, Fu J (2003) Distribution of particulate- and vapor-phase n-alkanes and polycyclic aromatic hydrocarbons in urban atmosphere of Guangzhou. China Atmos Environ 37 289-298... 

Assume an accidental release of a mixture of gaseous alkanes and alkenes into an urban atmosphere early in the morning. If the atmosphere at the release site is monitored for these compounds, what can be said about their total and relative concentrations at the end of the day Explain. 

Cyclic alkanes present in the troposphere are oxidized in part to cyclic ketones. The cyclic ketones are also emitted into the urban atmosphere from a variety of anthropogenic sources see table I-C-4. The mechanisms of photodecomposition of these ketones are reviewed briefly in this section. 

Photolysis of atmospheric pollutants by solar radiation results in an increase of ozone concentration in certain urban areas and is the cause of a sequence of oxidation reactions with polymers. Ozone reacts with practically all organic materials especially with alkenes. The rate of its reaction with alkene is several orders of magnitude higher than that with alkane. The ratio of the rate constants of ozone with ethene/ethane is 1.5 x 105, with propene/propane 1.6 x 106, and with butene- 1/butane 1.1 x 106, at room temperature [5],... 

The number of hydrocarbons in the atmosphere is potentially very large, since vapor pressures are favorable and the heavier species admit many isomers. In urban areas several hundred different hydrocarbons have been identified by gas chromatography (Appel et al, 1979 Louw el al, 1977). They include saturated compounds (alkanes) unsaturated species with one carbon-carbon double bond (alkenes) or two double bonds (alkadienes), acetylene type compounds (alkynes), and benzene derivatives or aromatic compounds (arenes). To separate that many different compounds requires... 

Alkenes and aromatic compounds have atmospheric lifetimes shorter than those of the low-weight alkanes. After 2 days of transport, propene and the butenes are reduced to a few percent of their original abundances relative to acetylene. If propene and the butenes are found at rural measurement sites, they must have local sources. Ethene, toluene, and ethylbenzene are less reactive. Their abundances relative to acetylene are reduced by a factor of about two after 2 days of transport. Toluene and ethylbenzene are primarily anthropogenic compounds. Both may serve as tracers for urban hydrocarbons in the same way as acetylene. In the cities the abundance... 

Organic aerosols formed by gas-phase photochemical reactions of hydrocarbons, ozone, and nitrogen oxides have been identified in both urban and rural atmospheres (Grosjean, 1977). Most of these species are di- or poly-functionally substituted alkane derivatives. These compounds include aliphatic organic nitrates (Grosjean and Friendlander, 1975), di-carboxylic acids (adipic and glutaric acids) (O Brien et al., 1975), carboxylic acids derived from aromatic hydrocarbons (benzoic and phenylacetic acids), polysubstituted phenols, and nitroaromatics from aromatic hydrocarbons (Kawamuraet al., 1985 Satsumakayashi et al., 1989, 1990). Some species that have been identified in ambient aerosol and are be-... 

Volatile organic compounds include many products such as volatile hydrocarbons (alkanes, alkenes, aromatic compounds), carbonyl compounds (ketones, aldehydes), etc. In urban areas, they originate from motor vehicle exhaust gases, the evaporation of gasoline at filling stations, liquid fuels and industrial activities using solvents. Then-concentration may reach 50 ag-m in the atmosphere of large urban areas. 

The photodecomposition of the various oxidation products of the alkanes, alkenes, and the aromatic hydrocarbons play important roles in the chemistry of the urban, mral, and remote atmospheres. These processes provide radical and other reachve products that help drive the chemistry that leads to ozone generation and other important chemistty in the troposphere. In this chapter, we have reviewed the evidence for the nature of the primary processes that occur in the aldehydes, ketones, alkyl nitrites, nittoalkanes, alkyl nitrates, peroxyacyl nitrates, alkyl peroxides, and some representative, ttopospheric, sunlight-absorbing aromatic compounds. Where sufficient data exist, estimates have been made of the rate of the photolytic processes that occur in these molecules by calculation of the photolysis frequencies ory-values. These rate coefficients allow estimation of the photochemical lifetimes of the various compounds in the atmosphere as well as the rates at which various reactive products are formed through photolysis. 

---