X. Rao et Jl. Collett, THE DROP SIZE-DEPENDENCE OF IRON AND MANGANESE CONCENTRATIONS IN CLOUDS AND FOGS - IMPLICATIONS FOR SULFATE PRODUCTION, Journal of atmospheric chemistry, 30(2), 1998, pp. 273-289
Differences in total iron and manganese concentrations between large (
d > 23 mu m) and small (4 < d < 23 mu m) cloud and fog drops were inve
stigated at four locations in the United States. The study examined co
astal stratus and stratocumulus clouds in southern California and nort
hern Oregon, frontal and orographic clouds at Mt. Mitchell, North Caro
lina, and radiation fogs in California's San Joaquin Valley. The speci
ation of iron as a function of drop size was also examined in some fog
samples from the San Joaquin Valley. Total iron and manganese concent
rations were generally higher in large drops than in small drops in cl
ouds sampled at Mt. Mitchell and along the southern California coast.
These species were typically enriched in small drops at the Oregon coa
st and San Joaquin Valley sites. Ratios of dissolved Fe(III) to total
dissolved Fe ranged from 0.88 to 0.93 in small fog drops. Non-uniform,
distributions of iron and manganese across the drop size spectrum can
influence rates of metal catalyzed S(IV) autooxidation. Approximately
50% of the sampled clouds were calculated to experience autooxidation
rate enhancements greater than 30% due to variations in drop acidity
and catalyst concentrations with drop size.