ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-11-11511-2011 Fast sulfur dioxide measurements correlated with cloud condensation nuclei spectra in the marine boundary layer Thornton D. C. 1 Bandy A. R. 1 Hudson J. G. 2 Department of Chemistry, Drexel University, Philadelphia, PA, USA Desert Research Institute, Nevada System of Higher Education, Reno, NV, USA 21 11 2011 11 22 11511 11519 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/11/11511/2011/acp-11-11511-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/11/11511/2011/acp-11-11511-2011.pdf

During the Rain in (shallow) Cumulus over the Ocean (RICO) project simultaneous high rate sulfur dioxide (SO<sub>2</sub>) measurements and cloud condensation nuclei (CCN) spectra were made for the first time. For research flight 14 (14 January 2005) the convective boundary layer was impacted by precipitation and ship plumes for much of the midday period but not in the late afternoon. Number densities of accumulation mode aerosols (0.14 to 0.2 μm diameter) were a factor of two greater in the later period while CCN were 35% to 80% greater for aerosols that activate at supersaturations >0.1%. Linear correlations of SO<sub>2</sub> and CCN were found for SO<sub>2</sub> concentrations ranging from 20 to 600 parts-per-trillion (pptv). The greatest sensitivities were for SO<sub>2</sub> and CCN that activate at supersaturations >0.1% for both clean and polluted air. In a region unaffected by pollution SO<sub>2</sub> was linearly correlated only with CCN at >0.2% supersaturation. These correlations imply that the smallest CCN may be activated by SO<sub>2</sub> through heterogeneous conversion. Evidence for entrainment of CCN from the cloud layer into the CBL was found.

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