Chamber measurements of CI 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 μm showed growth to 0.08 and 0.12 μm, with total aerosol mass increases of 7.0 and 2.4 μg m−3 (assuming a particle density of 2.4 g cm−3). 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 ‐ SO42−, until the SO42− 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.