1. R. J. Charlson is in the Department of Atmospheric Sciences and Department of Chemistry, University of Washington, Seattle, WA 98195, USA.
2. F. P. J. Valero is in the Center for Atmospheric Sciences, Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA 92093, USA.
3. J. H. Seinfeld is in the Department of Chemical Engineering and the Department of Environmental Science and Engineering, California Institute of Technology, Pasadena, CA 91125, USA.