Abstract
The time variation of chemical composition of individual aerosol particles (including residues of fog droplets) was examined before, during and after fog events, simultaneously with chemical analysis of fog water, near the top of Mt. Norikura in Japan. In this experiment, particle morphology and the presence of S02-4, N0-3 and NH+4 in individual particles were determined with an electron microscope using thin-film chemical methods.
Acidity (pH) measurements showed that the values of bulk fog water were strongly influenced by fog water content, while those of small size fog droplets (γ≤4.0μm) were not. It was found that change in pH is a function of the droplet size. The pH of the smallest droplets (γ≤2.0μm) sometimes reached as low as 1.6 justYbefore fog dissipation. Particle analysis using a thin film chemical method showed that the nitrate ion was detected in fog droplet residues together with the sulfate ion, even if no nitrate-containing particles were found before fog formation. Direct evidence for sulfate production within fog droplets is also presented. Possible processes which lead to the formation of acidic fog droplets are discussed, based on chemical changes of individual aerosol particles during and outside fog events.
