HUMIDITY SORPTION DUE TO DEPOSITED AEROSOL-PARTICLES STUDIED IN-SITU OUTDOORS ON GOLD SURFACES

Accumulation rates of deposited aerosol particles on an inert gold sur face and the resulting humidity interactions were investigated in situ outdoors using an atmospheric corrosivity probe based on the quartz c rystal microbalance technique. In six exposures in one rural and two u rban sites the common behavior is that the gold surfaces undergo both irreversible mass increase and reversible mass changes. Irreversible m ass increase is interpreted as a deposit mainly consisting of aerosol particles from the accumulation mode. The irreversible mass increase c ould be correlated to aerosol particle concentrations measured at the exposure sites. The reversible mass changes are mainly due to water so rption, which is influenced by deposited aerosol particles and varies with relative humidity. Upon closer analysis of the reversible mass ch anges, typical episodic cases are identified. An analogy between the h umidity interaction of wetted metal surfaces and of aerosol particles explains the wetting characteristics of the surface. Time of wetness, defined by predetermined levels of temperature and relative humidity i s shown to severely underestimate the actual time period when a surfac e with aerosol particle deposits is wetted.