ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-11-4679-2011 Decreases in elemental carbon and fine particle mass in the United States Murphy D. M. 1 Chow J. C. 2 Leibensperger E. M. 3 Malm W. C. 4 Pitchford M. 5 Schichtel B. A. 6 Watson J. G. 2 White W. H. 7 Chemical Sciences Division, Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO 80305, USA Division of Atmospheric Sciences, Desert Research Institute, Reno Nevada, 89512, USA School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, 02138, USA Cooperative Institute for Research in the Atmosphere, Colorado State University, Fort Collins, CO 80523, USA Air Resources Laboratory, National Oceanic and Atmospheric Administration, Las Vegas, NV 89119, USA National Park Service, Colorado State University, Foothills Campus, Fort Collins, Colorado 80523, USA Crocker Nuclear Laboratory, University of California Davis, Davis, CA 95616, USA 19 05 2011 11 10 4679 4686 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/11/4679/2011/acp-11-4679-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/11/4679/2011/acp-11-4679-2011.pdf

Observations at national parks and other remote sites show that average elemental carbon and fine particle mass concentrations in the United States both decreased by over 25 % between 1990 and 2004. Percentage decreases in elemental carbon were much larger in winter than in summer. These data suggest that emissions controls have been effective in reducing particulate concentrations not only in polluted areas but also across the United States. Despite the reduction in elemental carbon, the simultaneous decrease in non-absorbing particles implies that the overall radiative forcing from these changes was toward warming. The use of a 2005 instead of 1990 as a baseline for climate-relevant emissions from the United States would imply a significantly lower baseline for aerosol emissions. The use of older data will overestimate the possibility for future reductions in warming due to black carbon controls.

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