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Published September 2002 | Published
Journal Article Open

Can chemical effects on cloud droplet number rival the first indirect effect?


An increase in cloud droplet number concentration resulting from an increase in ambient aerosol (and subsequent albedo increase) is typically identified as the first indirect (or "Twomey") climatic effect of aerosols [Twomey, 1974]. A key question is whether chemical effects (dissolution of soluble gases and slightly soluble substances, surface tension depression by organic substances and accommodation coefficient changes) could potentially rival changes in droplet number from changes in aerosol number concentration. We assess the sensitivity of cloud droplet number concentration to such chemical factors, using a cloud parcel model. We find that numerous conditions exist, for which chemical influences on cloud droplet activation can indeed rival the Twomey effect.

Additional Information

Copyright 2002 by the American Geophysical Union. Received 9 April 2002; revised 2 July 2002; accepted 9 July 2002; published 13 September 2002. A. Nenes and J. H. Seinfeld were supported by U.S. Office of Naval Research grant N00014-96-1-0119. We would also like to thank P. Y.Chuang and J.Snider for their important comments during the review process. Finally, we would like to acknowledge M. Mircea for helpful suggestions during the preparation of the manuscript.

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