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Published April 16, 2009 | Published
Journal Article Open

Cloud condensation nuclei activity, closure, and droplet growth kinetics of Houston aerosol during the Gulf of Mexico Atmospheric Composition and Climate Study (GoMACCS)


In situ cloud condensation nuclei (CCN) measurements were obtained in the boundary layer over Houston, Texas, during the 2006 Gulf of Mexico Atmospheric Composition and Climate Study (GoMACCS) campaign onboard the CIRPAS Twin Otter. Polluted air masses in and out of cloudy regions were sampled for a total of 22 flights, with CCN measurements obtained for 17 of these flights. In this paper, we focus on CCN closure during two flights, within and downwind of the Houston regional plume and over the Houston Ship Channel. During both flights, air was sampled with particle concentrations exceeding 25,000 cm^(−3) and CCN concentrations exceeding 10,000 cm^(−3). CCN closure is evaluated by comparing measured concentrations with those predicted on the basis of measured aerosol size distributions and aerosol mass spectrometer particle composition. Different assumptions concerning the internally mixed chemical composition result in average CCN overprediction ranging from 3% to 36% (based on a linear fit). It is hypothesized that the externally mixed fraction of the aerosol contributes much of the CCN closure scatter, while the internally mixed fraction largely controls the overprediction bias. On the basis of the droplet sizes of activated CCN, organics do not seem to impact, on average, the CCN activation kinetics.

Additional Information

©2009. American Geophysical Union. Received 31 December 2008; accepted 13 May 2009; published 30 July 2009. We acknowledge support from the National Oceanic and Atmospheric Administration (NOAA) under contracts NA05OAR4310101 and NA06OAR4310082, the support of an NSF CAREER grant, and the Office of Naval Research. S.L. would like to acknowledge the support of a Georgia Institute of Technology (Georgia Tech) Presidential Fellowship, a National Center for Atmospheric Research (NCAR) Advanced Study Program (ASP) Graduate Fellowship, and a National Research Council Research Associateships Program Fellowship (awarded January 2008). We also thank C. Brock and three anonymous reviewers for helpful comments, as well as A. Stohl and S. Ekhardt for providing the Flexpart back trajectory results. M.K.D. and C.M. thank LANL-LDRD and DOE-Office of Science-OBER-ASP for support of the photoacoustic deployment.

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