My principal research interest is in the multi-phase chemistry of the troposphere. Specific interests include (i) the role of atmospheric aerosols in the biogeochemical cycles of nitrogen, sulfur and other elements, (ii) how aerosols--sea salt aerosols in particular--affect boundary layer photochemical processes, and (iii) aerosol radiative forcing of climate.

My continuing work on these topics began the mid-1980s when it was hypothesized that aerosols created photochemically in the atmosphere from reduced sulfur gases of marine biogenic origin may be part of a natural climate regulation mechanism. I was among the first to investigate the size distribution of aerosol sulfur in the Antarctic and equatorial Pacific marine boundary layers. I co-organized a major experiment in the North Atlantic in 1988 among whose results were (i) a first assessment based on measurements of the roles of dimethylsulfoxide and dimethylsulfone in the atmospheric sulfur cycle, (ii) evidence that a significant fraction of sulfur dioxide is converted to sulfate in sea salt aerosols, and (iii) evidence of "unexplained" chloride loss from sea salt aerosols. Since then, with colleagues from the University of Virginia and elsewhere I have sought to test the hypothesis that these chloride deficits result from release of chlorine species much more reactive than hydrogen chloride from sea salt aerosols. This work included development of an improved experimental technique for estimating aerosol pH.

From January 1993 through October 2001 I also served as executive officer for the International Global Atmospheric Chemistry (IGAC) Core Project of the International Geosphere-Biosphere Programme (IGBP). In this role I helped to frame discussions of the future course of global atmospheric-biospheric chemistry research, how this research will be coordinated internationally and interfaced with that of other elements of the IGBP, and how its findings will improve understanding of key biogeochemical cycles and reduce the scientific uncertainties that hinder prediction of climate change.