Airborne Aerosol Mass Spectrometer Measurements of the Submicron Aerosol Chemical Composition Downwind of Sources

The Aerodyne Aerosol Mass Spectrometer (AMS) provides mass spectra as well as organic, sulfate, ammonium, and nitrate mass distributions of non-refractory aerosol particles. Results will be shown from the International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) field study during July-August 2004, where an AMS was deployed aboard the NOAA WP-3D aircraft above the Northeastern United States, and 30-second averaged data were collected for particles with vacuum aerodynamic diameters between roughly 65 and 500 nm due to the use of a pressure controlled inlet upstream of the AMS. A wide variety of air masses were sampled during the intensive period, including clean continental, fresh and aged urban, biomass burning, and power plant plumes. In general, the non-refractory submicron aerosol mass was predominantly composed of sulfate and organic material, with a lower mass fraction of ammonium and minor amounts of nitrate. However, there was a wide variety of aerosol compositions at low altitudes, and a trend of increasing organic mass fraction as a function of altitude was observed. The dominant organic source at altitudes above 3 km was biomass burning from the Alaskan forest fires. The organic material in biomass burning particles was oxidized and did not change much with time after fours days since emission. The next most common contributor to submicron aerosol mass was sulfate from power plant sources. In power plant plumes that were transected during the day, fresh particle formation was observed in both the sulfate mass and particle volume distributions. Urban sources tended to play a less important role in submicron aerosol mass during this field study compared to biomass burning and power plant plumes.