APRIL 2003: Sources of carbonaceous aerosols over the US

This figure shows annual mean concentrations of elemental carbon (EC, left) and organic carbon (OC, right) aerosols in surface air over the United States, as simulated in 1998 by the GEOS-CHEM model. Sources of EC and OC were optimized with an inverse model analysis to fit aerosol observations from the IMPROVE netork of sites in the United States. Our best estimates of EC and OC sources in the United States are 0.60 Tg yr^-1 EC and 0.52 Tg yr^-1 OC from fossil fuel; 0.07 Tg yr^-1 EC and 0.89 Tg yr^-1 OC from biofuel; 0.08 Tg yr^-1 EC and 0.60 Tg yr^-1 OC from wildfires; and 1.10 Tg yr^-1 OC from vegetation. We find that fires in Mexico and Canada contributed 40-70% of annual mean natural EC in the United States in 1998, and 20-30% of annual mean natural OC, with important implications for reducing natural visibility. Transpacific transport from Asian pollution sources amounted to less than 10% of the natural EC and less than 2% of the natural OC; in contrast to ozone, we find that intercontinental transport of anthropogenic carbonaceous aerosols does not enhance significantly the natural background. More information about this work can be found in Park et al. [2003] (pdf).