Atmospheric Carbon Particles in the Detroit Urban Area: Wintertime Sources and Sinks

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Abstract
The sources and sinks of organic carbon (OC) and elemental carbon (EC) were studied in the Detroit area during the 1983–1984 and 1984–1985 winters. Based on fuel usage and emission estimates, the largest carbon source was residential wood burning, which contributed 60% of OC emissions and 49% of EC emissions. Diesel vehicles contributed another 6% of OC emissions and 2% of EC emissions. Commercial and residential coal burning also contributed 27% of OC and 13% of EC. The sinks of atmospheric carbon were determined by measuring the carbon content of atmospheric particles, wet deposition and dry deposition. Carbon levels in air particles averaged 5.6 μg/m3 OC and 2.2 μg/m3 EC. Precipitation concentrations averaged 760 μg/L OC and 160 μg/L EC. The OC/EC ratio was higher in precipitation (4.7) than in ambient particles (2.5), indicating that a high OC/EC ratio increases the hygroscopicity of the particles, and hence, their removal by precipitation. Based on the known oxidation rate, insufficient EC is available in the atmosphere to significantly catalyze the oxidation of SO2 to sulfuric acid.