Formaldehyde atmospheric chemistry

Grosjean et al. (1996) investigated the atmospheric chemistry of cyclohexene with ozone and an ozone-nitrogen oxide mixture under ambient conditions. The reaction of cyclohexene and ozone in the dark yielded pentanal and cyclohexanone. The sunlight irradiation of cyclohexene with ozone-nitrogen oxide yielded the following carbonyls formaldehyde, acetaldehyde, acetone, propanal, butanal, pentanal, and a C4 carbonyl. 

In addition to the role of atmospheric reactions in the fate of airborne FLAPs, atmospheric chemistry also plays a role in the formation of some of them, most notably formaldehyde and acetaldehyde. Thus, the potential formation of such compounds from the oxidation of precursors in the atmosphere must also be taken into account in their risk assessments. 

Photodissociation of atmospheric molecules by solar radiation plays a fundamental role in the chemistry of the atmosphere. The photodissociation of trace species such as ozone and formaldehyde contributes to their removal from the atmosphere, but probably the most important role played by these photoprocesses is the generation of highly reactive atoms and radicals. Photodissociation of trace species and the subsequent reaction of the photoproducts with other molecules is the prime initiator and driver for the bulk of atmospheric chemistry. 

N03 is known to react with aldehydes, alkenes, terpenes, and substituted benzenes at moderate rates (Morris and Niki, 1974 Japar and Niki, 1975 Bandow et al. 1980 Atkinson et al, 1984, b, 1985 Cantrell et al., 1985). The significance of these reactions to atmospheric chemistry remains to be clarified, however. The laboratory studies show that aldehydes undergo hydrogen abstraction, whereas alkenes react with N03 by addition. Formaldehyde is one of the more abundant constituents of air, and its reaction with N03 is entered in Fig. 9-6 for illustrations. The gas-phase reaction of N03 with water is endothermic and slow. Even the reaction of N03 with S02, which is exothermic, is negligibly slow (Calvert and Stockwell, 1984). The reaction N03+ NO — 2N02 is rapid and important in polluted air. Under pristine conditions, daytime NO is quickly converted to N02 after the sun sets, so that the reaction of N03 with NO should become negligible, too, at night. 

Aldehydes are important constituents of atmospheric chemistry. We have already seen the role played by formaldehyde in the chemistry of the background troposphere. Aldehydes are formed in the atmosphere from the photochemical degradation of other organic compounds. Aldehydes undergo photolysis, reaction with OH radicals, and reaction with NO3 radicals. Reaction with N03 radicals is of relatively minor importance as a consumption process for aldehydes, thus the major loss processes involve photolysis and reaction with OH radicals. 

Aldehydes are important constituents of atmospheric chemistry. We have already seen the role played by formaldehyde in the chemistry of the background troposphere. Aldehydes are formed in the atmosphere from the photochemical degradation of other organic com-... 

Of the atmospheric chemistry of the biogenic hydrocarbons, by far the most is known about isoprene. Whereas rate constants of many other biogenic hydrocarbons with OH, O3, and NO, have been measured, comparatively little is known about the distribution of products. Hatakeyama et al. (1989, 1991) and Arey et al. (1990) have measured some of the products of the a-pinene-O, reaction, including pinonaldehyde, norpinonaldehyde, formaldehyde, CO, and COj. Considerable work remains to be done in elucidating the atmospheric oxidation mechanisms of biogenic hydrocarbons. 

Wardman, P. (1989) Reduction potentials of one-electron couples involving free radicals in aqueous solution. Journal of Physical Chemical Reference Data 18, 1637-1755 Warneck, P. and C. Wurzinger (1988) Product yields for the 305-nm photodecomposition of NO3 in aqueous solution. Journal of Physical Chemistry 92, 6278-6283 Warneck, P. (1988) Chemistry of the natural atmosphere. Academic Press, San Diego, 753 pp. Warneck, P. (1989) Sulfur dioxide in rain clouds gas-liquid scavenging efficiences and wet deposition rates in the presence of formaldehyde. Journal of Atmospheric Chemistry 8, 99-117... 

Inomata, S.,Tanimoto, H., Kameyama, S., Tsunogai, U., Irie, H., Kanaya, Y., Wang, Z. (2008) Technical note determination of formaldehyde mixing ratios in air with PTR-MS laboratory experiments and field measurements. Atmospheric Chemistry and Physics, 8,273-284. 

Sumner AL, Shepson PB, Grannas AM, Bottenheim JW, Anlauf KG, Worthy D, SchroederWH, Steffen A, Domine F, Perrier S, Houdier S (2002) Atmospheric chemistry of formaldehyde in the Arctic troposphere at Polar Sunrise, and the influence of the snowpack. Atmos Environ 36 2553... 

Methane is oxidized primarily in the troposphere by reactions involving the hydroxyl radical (OH). Methane is the most abundant hydrocarbon species in the atmosphere, and its oxidation affects atmospheric levels of other important reactive species, including formaldehyde (CH2O), carbon monoxide (CO), and ozone (O3) (Wuebbles and Hayhoe, 2002). The chemistry of these reactions is well known, and the rate of atmospheric CH4 oxidation can be calculated from the temperature and concentrations of the reactants, primarily CH4 and OH (Prinn et al., 1987). Tropospheric OH concentrations are difficult to measure directly, but they are reasonably well constrained by observations of other reactive trace gases (Thompson, 1992 Martinerie et al., 1995 Prinn et al., 1995 Prinn et al., 2001). Thus, rates of tropospheric CH4 oxidation can be estimated from knowledge of atmospheric CH4 concentrations. And because tropospheric oxidation is the primary process by which CH4 is removed from the atmosphere, the estimated rate of CH4 oxidation provides a basis for approximating the total rate of supply of CH4 to the atmosphere from aU sources at steady state (see Section 8.09.2.2) (Cicerone and Oremland, 1988). 

Calvert, J. G. (1980). The homogeneous chemistry of formaldehyde generation and destruction within the atmosphere. NATO Advanced Study Institute on Atmospheric Ozone Its Variation and Human Influences (M. Nicolet and A. C. Aikin, FAA-EE-80-20, pp. 153-190. U.S. Dept. Transportation, Federal Aviation Administration, Washington, D.C. 

Formaldehyde is a first-generation oxidation product of CH4 and, it turns out, of many other hydrocarbons. Indeed, the chemistry of formaldehyde is common to virtually all mechanisms of tropospheric chemistry. Formaldehyde undergoes two main reactions in the atmosphere, photolysis... 

Dassau TM, Sumner AL, Koeniger SL, Shepson PB, Yang J, Honrath RE, Cullen NJ, Steffen K, Jacobi HW, Frey M, Bales RC (2002) Investigation of the role of the snowpack on atmospheric formaldehyde chemistry at summit, Greenland. J Geophys Res Atmos 107 9-14... 

---