1Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, CA 90095, USA
2Joint Institute for Regional Earth System Science and Engineering, University of California, Los Angeles, CA 90095, USA
3Department of Earth System Science, University of California, Irvine, CA 92697, USA
4Fire Sciences Laboratory, U.S. Forest Service, Missoula, MT, 59808, USA
*now at: National Center for Atmospheric Research, Boulder, CO 80307, USA
**now at: Department of Mechanical Engineering, University of Colorado Boulder, Boulder, CO 80302, USA
Abstract. We estimate biomass burning emissions of black carbon (BC) in the western United States (WUS) for May–October 2006 by inverting surface BC concentrations from the Interagency Monitoring of PROtected Visual Environment (IMPROVE) network using a global chemical transport model. We first improve the spatiotemporal distributions of the BC emissions from the Global Fire Emissions Database (GFEDv2) using 8-day active fire counts from the Moderate Resolution Imaging Spectroradiometer (MODIS) from a 3 yr period (2005–2007). The resulting emissions are then used as the a priori for the inversion analyses. The adjustment primarily shifts emissions from late to early and middle summer (33% decrease in September-October and 56% increase in June–August). The adjusted emissions lead to non-negligible increases in the simulated surface BC concentrations in early and middle summer at sites below 2 km. We conduct analytical inversions at both 2° × 2.5° and 0.5° × 0.667° (nested over North America) horizontal resolutions. Simulated surface BC concentrations with the a posteriori emissions capture the observed major fire episodes at many sites and substantial enhancements at the 1–2 and 2–3 km altitude ranges. The a posteriori emissions lead to substantial bias reductions in the simulated surface BC concentrations (~ 50% on average) at both resolutions and significant increases in the Taylor skill scores (86% at 2° × 2.5° and 132% at 0.5° × 0.667°). We find that the inversion is rather sensitive to the model resolution. The a posteriori biomass burning emissions increase by factors of 4.7 from the inversion at 2° × 2.5° and 2.8 at 0.5° × 0.667°, while as the a posteriori anthropogenic emissions decrease by 48% and 36%, respectively, relative to their corresponding a priori emissions. The two a posteriori estimates differ largest in biomass burning emissions in California and the Southwest (a factor of 5.9) and in the Pacific Northwest (a factor of 2).