NASA - National Aeronautics and Space Administration

The impact of aerosols on regional air quality and climate necessitates improved understanding of their emission and microphysical properties. The size distributions of black carbon (BC) and light scattering particles (LSP) were measured with a single particle soot photometer on board the NASA DC-8 aircraft during the ARCTAS mission 2008. Air sampling was made in the air plumes of both urban and forest fire emissions over California during the CARB (California Air Resources Board) phase of the mission. A total of eleven plumes were identified using SO2 and CH3CN tracers for fossil fuel (FF) combustion and biomass burning (BB), respectively. The enhancements of BC and LSP in BB plumes were significantly higher compared to those in FF plumes. The average mass concentration of BC in BB plumes was more than twice that in FF plumes. Except for the BC/CO ratio, distinct emission ratios of BC/CO2, BC/CH3CN, CH3CN/CO, and CO/CO2 were observed in the plumes from the two sources. Similarly, the microphysical properties of BC and LSP also showed distinct behaviors. The BC count median diameter (CMD) of 115 Æ 5 nm in FF plumes was smaller compared to 141 Æ 9 nm in the BB plumes. BC aerosols were thickly coated in BB plumes, the average shell/core ratios were 1.47 and 1.24 in BB and FF plumes, respectively. In the total mass of submicron aerosols, organic aerosols constituted about 67% in the FF plumes and 84% in BB plumes. The contribution of sulfate was also significant in the FF plumes.