Initial uptake of ozone on Saharan dust at atmospheric relative humidities

To better evaluate heterogeneous loss mechanisms for ozone in the atmosphere, the initial uptake kinetics of ozone on mineral dust surfaces was studied at room temperature under dry conditions and at elevated relative humidity. Ozone was added to a static absorption cell containing a glass tube coated with a thin film of Saharan dust collected from silt deposits on the Cape Verde Islands. Ozone concentrations were monitored by UV absorption at 254 nm, from which the reactive uptake coefficient in the first 10 s was calculated. An increase in initial ozone concentration from 2x10(12) to 1x10(14) cm(-3) results in a decrease in the initial reactive uptake coefficient from 6x10(-6) to 2x10(-7), respectively, revealing a negative dependence of initial reactive uptake on initial ozone concentration. Simultaneously exposing the Saharan dust to ozone and water vapor at 50% and 75% relative humidity does not significantly change the initial reactive uptake coefficient.