Atmospheric chemistry, “normal polluted atmospheres

Singlet molecular oxygen is of interest in connection with atmospheric chemistry with respect both to its mode of excitation and to the consequences of its presence in the upper or lower atmosphere. The first part of this section deals with processes of importance in normal, unpolluted atmospheres, while the second part examines the possibility, only recently appreciated, that singlet molecular oxygen may play a part in the chemistry of polluted urban atmospheres. 

The tropospheric sulfur chemistry is different. Unlike the nitrogen and carbon chemistry, where combustion is an insignificant source, the combustion source of SO2 appears to be very important. While OH reactions can be shown to convert sulfides to SO2, it is not clear that normal atmospheric chemistry is important in the next step—the conversion of S02 to H2SO, which is then removed from the atmosphere by rainout. It has also been suggested that a large amount of SO2 is removed directly by rainout. Unfortunately we have the fewest data, both kinetic and atmospheric, on sulfur compounds. Most of the kinetic data we do have are at high temperatures, and most of the atmospheric data are for polluted environments. 

The consequences of local peculiarities for global atmospheric chemistry are still uncertain but if the levels of hydroxyl radical would be decreased, many pollutants that are normally oxidized by OH radical could build up, leading to significant relevant... 

The order of the compounds determined by the magnitude of the mass emissions is not intended to reflect the relative influence of these compounds on atmospheric chemistry, greenhouse effect, or other atmospheric phenomena. To illustrate this point, compare in table I-C-5 the orders of importance of the top 31 species in mass emissions in table I-C-2 as estimated from a consideration of criteria other than mass emissions. We list the normalized relative values for molecular emissions (proportional to mass emissions/molecular weight), relative rate of attack by OH radicals (proportional to molecular emissions x oh), the relative rate of ozone generation as estimated for a polluted urban atmosphere (proportional to mass emissions x MIR, the maximum incremental reactivity factor Carter, 1998), and the relative number of CO2 molecules that atmospheric oxidation of this species will ultimately generate (proportional to molecular emissions x number of C-atoms molecule" ). The latter comparison... 

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