ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-8-15031-2008 Inverse modeling and mapping US air quality influences of inorganic PM<sub>2.5</sub> precursor emissions using the adjoint of GEOS-Chem Henze D. K. 1 3 Seinfeld J. H. 2 Shindell D. T. 3 Earth Institute, Columbia University, New York, NY, USA Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, USA NASA Goddard Institute for Space Studies, New York, NY, USA 08 08 2008 8 4 15031 15099 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-discuss.net/8/15031/2008/acpd-8-15031-2008.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/8/15031/2008/acpd-8-15031-2008.pdf

Influences of specific sources of inorganic PM<sub>2.5</sub> on peak and ambient aerosol concentrations in the US are evaluated using a combination of inverse modeling and sensitivity analysis. First, sulfate and nitrate aerosol measurements from the IMPROVE network are assimilated using the four-dimensional variational (4D-Var) method into the GEOS-Chem chemical transport model in order to constrain emissions estimates in four separate month-long inversions (one per season). Of the precursor emissions, these observations primarily constrain ammonia (NH<sub>3</sub>). While the net result is a decrease in estimated US NH<sub>3</sub> emissions relative to the original inventory, there is considerable variability in adjustments made to NH<sub>3</sub> emissions in different locations, seasons and source sectors, such as focused decreases in the midwest during July, broad decreases throughout the US~in January, increases in eastern coastal areas in April, and an effective redistribution of emissions from natural to anthropogenic sources. Implementing these constrained emissions, the adjoint model is applied to quantify the influences of emissions on representative PM<sub>2.5</sub> air quality metrics within the US. The resulting sensitivity maps display a wide range of spatial, sectoral and seasonal variability in the susceptibility of the air quality metrics to absolute emissions changes and the effectiveness of incremental emissions controls of specific source sectors. NH<sub>3</sub> emissions near sources of sulfur oxides (SO<sub>x</sub>) are estimated to most influence peak inorganic PM<sub>2.5</sub> levels in the East; thus, the most effective controls of NH<sub>3</sub> emissions are often disjoint from locations of peak NH<sub>3</sub> emissions. Controls of emissions from industrial sectors of SO<sub>x</sub> and NO<sub>x</sub> are estimated to be more effective than surface emissions, and changes to NH<sub>3</sub> emissions in regions dominated by natural sources are disproportionately more effective than regions dominated by anthropogenic sources. NO<sub>x</sub> controls are most effective in northern states in October; in January, SO<sub>x</sub> controls may be counterproductive. When considering ambient inorganic PM<sub>2.5</sub> concentrations, intercontinental influences are small, though transboundary influences within North America are significant, with SO<sub>x</sub> emissions from surface sources in Mexico contributing almost a fourth of the total influence from this sector.

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