AEROSOL OBSERVATIONS FROM SPACE, AIRCRAFT AND SURFACE ANALYZED WITH A GLOBAL MODEL

Abstract

We interpret satellite, aircraft, and ground-based measurements using the GEOS-Chem Chemical Transport Model (CTM) to better understand the global transport and distribution of fine aerosol (PM2.5). Using satellite retrievals of Aerosol Optical Depth (AOD) from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Multiangle Imaging Spectroradiometer (MISR), we estimate an annual growth in Chinese sulfur emissions of 6.2-9.6% between 2000-2006, in agreement with bottom-up inventories. Using aircraft measurements from the Intercontinental Chemical Transport Experiment (INTEX-B) with a CTM, we calculate that 56% of measured sulfate between 500-900 hPa over British Columbia is due to East Asian sources. We find evidence of a 72-85% increase in the relative contribution of East Asian sulfate to the total burden in spring off the northwest coast of the United States since 1985. We interpret retrievals AOD from MODIS and MISR using GEOS-Chem to estimate global long-term (2001-2006) mean PM2.5 concentrations at a resolution of 0.1° x 0.1°. Evaluation of the satellite-derived estimate with ground-based in-situ measurements indicates significant spatial agreement with North American measurements (r = 0.77, slope = 1.07, n = 1057) and with non-coincident measurements elsewhere (r = 0.83, slope = 0.86, n = 244). The one standard deviation uncertainty in the satellite-derived PM2.5 is 25%, inferred from the AOD retrieval and aerosol vertical profiles errors and sampling. The global population-weighted mean uncertainty is 6.7 µg/m3. We find a global population-weighted geometric mean PM2.5 concentration of 20 ?g/m3. The World Health Organization Air Quality PM2.5 Interim Target-1 (35 µg/m3 annual average) is exceeded over central and eastern Asia for 38% and 50% of the population, respectively. Annual mean PM2.5 concentrations exceed 80 µg/m3 over Eastern China. We test the capability of remotely-sensed PM2.5 to capture extreme short-term events by examining the major biomass burning event around Moscow in summer 2010. We find good agreement (r2=0.85, slope=1.06) between daily estimates of PM2.5 from in-situ and satellite-derived sources in the Moscow region during the fires. Both satellite-derived and in-situ values have peak daily mean concentrations of approximately 600 ?g/m3 on August 7, 2010 in the Moscow region.