Nonraining Cloud Effects on Aerosol Concentrations

Significant production of sulfate has been detected and/or predicted in clouds and fogs in different environments (Hegg and Hobbs 1987, 1988 Pandis and Seinfeld 1989 Husain et al. 1991 Pandis et al. 1992 Swozdiak and Swozdiak 1992 Develk 1994 Liu et al. 1994). Detection of sulfate-producing reactions is often hindered by variability of cloud 

FIGURE 17.19 Measured composition of the small and large cloud droplets collected in coastal stratus clouds at La Jolla Peak, California, in July 1993 (Collett et al. 1994). 

FIGURE 17.20 Measured pH of small and large droplets in a series of clouds and fogs in typical environments (Collett et al. 1994). 

FIGURE 17.21 Schematic of the cloud processing of an aerosol particle. 

FIGURE 17.22 Measurements of the gas-phase partial pressures of H202 versus the S02 partial pressure for interstitial cloud air (Daum et al. 1984). Arrows signify that the mixing ratio was below the detection limit. 

Available evidence suggests that the single most important reaction during aerosol processing by clouds is the oxidation of HSO3 by H2O2. This reaction, as we saw in Chapter 

Cloud processing is a major source of sulfate and aerosol mass in general on regional and global scales. Walcek et al. (1990) calculated that, during passage of a midlatitude storm system, over 65% of tropospheric sulfate over the northeastern United States was formed in cloud droplets via aqueous-phase reactions. The same authors estimated that. 

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