With support from DOE's Atmospheric Sciences Program, the Cumulus Humilis Aerosol Processing Study (CHAPS) was conducted in the vicinity of Oklahoma City, Oklahoma during the summer of 2007 to investigate changes to aerosol chemical and optical properties during passage through shallow convective clouds. During the CHAPS, the Department of Energy's Gulfstream-1 aircraft was equipped to measure the chemical composition of aerosols, as well as the concentration of a number of atmospheric trace gases including ozone, carbon monoxide, and various hydrocarbons. In addition to these measurements, observations of the aerosol scattering and absorption were made below, within, and above the cloud layer. In order to investigate the chemical composition of the aerosols that nucleated to form cloud drops, an Aerodyne Aerosol Mass Spectrometer (AMS) was operated downstream from a Counter-flow Virtual Impactor (CVI) inlet. The CVI is able to exclude interstitial aerosols and small cloud droplets so, that by evaporating the cloud droplets that get past the counter-flow, we were able to examine the composition of the residual kernel of the larger cloud drops.

This work will report initial results from the AMS on the DOE Gulfstream-1 for below cloud, within cloud, and above cloud conditions. Preliminary examination of the data suggests that the composition of aerosols in the subcloud layer is dominated by organics and sulfates. Aerosols that were nucleated to form cloud droplets where observed to have a higher concentration of nitrate compared to the unactivated aerosols, which is likely indicative of the uptake of nitric acid by the cloud droplets. Changes to aerosol scattering and absorption as a function of composition and position relative to the clouds, and the potential consequences, will also be presented