Chamber measurements of Cl depletion in cloud-processed sea-salt aerosol

Cl(-) depletion in sea-salt CCN was measured in chamber experiments after cloud formation in the presence of SO2 and O3. In each experiment, two successive clouds were formed on a sea-salt aerosol generated from the nebulization of filtered seawater, while chamber SO2 (g) and O3 (g) concentrations ranged from 4.8-8.3 ppb and 69-75 ppb. Particle growth from cloud processing reactions was measured with a differential mobility analyzer (DMA) immediately after cloud dissipation, and particles activated from dry radii of 0.02-0.03 micron showed growth to 0.08 and 0.12 micron, with total aerosol mass increases of 7.0 and 2.4 micro-g/cu m (assuming a particle density of 2.4 g/cu cm). Particle growth was greater than that predicted by standard SO2-O3 oxidation kinetics and cannot be accounted for by the buffering capacity of the sea-salt CCN. Micro-orifice impactor (MOI) measurements of inorganic ions in the postcloud aerosol size distributions show, within analytical error, a 1:1 displacement of Cl(-) with nss - SO4(2-), until the SO4(2-) is in excess and the Cl(-) is completely depleted at the smaller CCN sizes. Calculations of Cl(-) depletion, based upon the input size distribution and assuming particle growth via sulfate addition, show greater Cl(-) depletion on smaller size particles than the measured values. However, there is agreement within the uncertainty of the measured values. (Author)