B LIFETIMES OF TYPICAL ORGANICS IN THE TROPOSPHERE

Such reactions may also be important in other situations in the troposphere. For example, Shaw (1991) has observed salt particles as far as 900 km inland in Alaska, and chloride salts are used on many roads in cold climates in the wintertime. In addition, in the plumes from oil well burning in Kuwait, salt particles were observed, due to the brine that was mixed with the oil in the wells (e.g., see Cahill et al., 1992). 

In short, while there is evidence that atomic chlorine is generated from sea salt reactions and contributes to organic oxidations in the marine boundary layer, the nature and strength of the sources remain to be elucidated. 

To pare the list of VOC oxidations down to the most important processes, we can calculate the effective lifetimes of organics with respect to reactions with each of the oxidants listed in the previous section. Since these natural lifetimes are defined as r = 1 / [X], we also need to assume an average concentration for the oxidant, [X]. We can therefore take a typical organic from each of the major classes (alkane, alkene, aromatic, etc.) and compare the individual lifetimes for reaction with OH, 03, N03, etc. Those reactions having very long lifetimes are insignificant with respect to their contribution to tropospheric chemistry and hence can be ignored for the purposes of this discussion. 

Alkanes OH, to a lesser extent N03, and in the marine boundary layer (MBL) Cl Alkenes OH, 03, N03, and to a lesser extent Cl (MBL) 

TABLE 6.1 Estimated Lifetimes of Representative Organics in the Troposphere11 

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