Abstract
Abstract. We estimate biomass burning and anthropogenic emissions of black carbon (BC) in the western US 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 use active fire counts from the Moderate Resolution Imaging Spectroradiometer (MODIS) to improve the spatiotemporal distributions of the biomass burning BC emissions from the Global Fire Emissions Database (GFEDv2). The adjustment primarily shifts emissions from late to middle and early summer (a 33% decrease in September–October and a 56% increase in June–August) and leads to appreciable increases in modeled surface BC concentrations in early and middle summer, especially at the 1–2 and 2–3 km altitude ranges. We then conduct analytical inversions at both 2° × 2.5° and 0.5° × 0.667° (nested over North America) horizontal resolutions. The a posteriori biomass burning BC emissions for July–September are 31.7 Gg at 2° × 2.5° (an increase by a factor of 4.7) and 19.2 Gg at 0.5° × 0.667° (an increase by a factor of 2.8). The inversion results are rather sensitive to model resolution. The a posteriori biomass burning emissions at the two model resolutions differ by a factor of ~6 in California and the Southwest and by a factor of 2 in the Pacific Northwest. The corresponding a posteriori anthropogenic BC emissions are 9.1 Gg at 2° × 2.5° (a decrease of 48%) and 11.2 Gg at 0.5° × 0.667° (a decrease of 36%). Simulated surface BC concentrations with the a posteriori emissions capture the observed major fire episodes at most sites and the substantial enhancements at the 1–2 and 2–3 km altitude ranges. The a posteriori emissions also lead to large bias reductions (by ~30% on average at both model resolutions) in modeled surface BC concentrations and significantly better agreement with observations (increases in Taylor skill scores of 95% at 2° × 2.5° and 42 % at 0.5° × 0.667°).
Highlights
Black carbon (BC), as a component of fine particulate matter, has deleterious effects on human health (e.g., Anenberg et al, 2011, 2012; Smith et al, 2009)
Upon examining the averaging kernel and degrees of freedom for signal (DOFs), we find that the inversion system is unable to distinguish the biomass burning from the northern vs. the southern Rockies
The anthropogenic emissions are divided by 3 in the figures, for the sake of clarity, because the anthropogenic emissions are considerably larger than biomass burning emissions
Summary
Black carbon (BC), as a component of fine particulate matter, has deleterious effects on human health (e.g., Anenberg et al, 2011, 2012; Smith et al, 2009). BC is known as the agent to cause both degraded air quality (e.g., Anenberg et al, 2011, 2012) and warming due to its strong absorption of solar radiation (e.g., Ramanathan and Carmichael, 2008; Horvath, 1993). BC has considerable impacts on global climate (Fuglestvedt et al, 2010; Shindell et al, 2008; Levy II et al, 2008; Reddy et al, 2007; IPCC, 2007; Jacobson, 2001, 2004). Because of its shorter lifetime relative to long lived greenhouse gases such as carbon dioxide, BC shows a much stronger regional
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