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0.49''

" Except where noted, from Betterton and Hoffmann (1988) and Olson and Hoffmann (f989). hH = [RCHO]aq/[RCHO]g.

1 H* = {[RCHO]aq + [RCH(OH)2]aq}/[RCHO]g = H( 1 + Khydr). rfA:hvdr = [RCH(OH)2]aq/[RCHO]aq. ' Xu et al. (1993). ' Sham and Joens (1995).

" Except where noted, from Betterton and Hoffmann (1988) and Olson and Hoffmann (f989). hH = [RCHO]aq/[RCHO]g.

1 H* = {[RCHO]aq + [RCH(OH)2]aq}/[RCHO]g = H( 1 + Khydr). rfA:hvdr = [RCH(OH)2]aq/[RCHO]aq. ' Xu et al. (1993). ' Sham and Joens (1995).

Formation of the diols causes a significant change in the absorption spectra compared to the gas phase, with the shift to shorter wavelengths decreasing their photolysis in solution (Xu et al., 1993; Sham and Joens, 1995).

Because of this hydration, the total solubility, i.e., effective Henry's law constant, is larger than expected based on physical solubility alone. The data in Table 8.3 show that most aldehydes have quite large effective Henry's law constants (//*), the exceptions being ac-etaldehyde and benzaldehyde. As a result of these high solubilities, significant concentrations can occur in fogs and clouds and hence be available to complex with S(IV).

For complex formation between aldehydes and S(IV) to be important in the troposphere, the aldehydes not only must have high solubility but also be present in air at significant concentrations and form stable adducts with S(IV) at a sufficiently fast rate that it can occur during the lifetime of a typical cloud or fog event. Table 8.4 gives the rate constants k ยก4 and k^ for formation of the S(IV) complexes as well as the stability constants Ku and apparent stability constant defined as

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