Understanding sources and processes of submicron particles at an urban downwind location: results from DOE ALC-IOP at BNL

Description

The Department of Energy (DOE) sponsored the Aerosol Life Cycle Intensive Operational Period (ALC-IOP) field campaign, which took place at the Brookhaven National Laboratory (BNL) on Long Island, New York, from July 1 to August 15, 2011. An Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) was deployed after a temperature-stepping thermodenuder during this study to acquire highly time-resolved, quantitative data on the mass-based size distribution, chemical composition, and volatility profile of the non-refractory fraction of submicron particles (NR-PM1). The average mass concentration of NR-PM1 was high (13.3 ±7.7) μg/m3, with organics (64.4%) and ammonium sulfate (31.6%) dominating the composition. Our results indicate that particles at Long Island were originated from different air masses, influenced by urban plumes from New York City, regional pollution enriched of ammonium sulfate, forest fire plumes transported from Canada, and oceanic emissions with elevated methanesulfonic acid concentrations. In addition, relatively high concentrations of metal species such as Na, Mg, K, Fe, Mn, Cu, Zn, Sb, Sn, and their adduct ions were observed from the night of July 4 to the early morning of July 5, indicating the detection of firework smoke arising from the Independence Day celebration. Due to the influences of different sources, organic aerosol composition and oxidation degree varied substantially during the campaign. Positive matrix factorization of the high-resolution mass spectra of organics identified three distinct OA factors: a low volatility, highly oxidized oxygenated OA (LV-OOA; O/C = 0.79); a semi-volatile OOA (SV-OOA; O/C = 0.41); and a nitrogen-enriched OOA (NOA; O/C = 0.15 and N/C = 0.185). The volatility of the LV-OOA is higher than that of ammonium sulfate but lower than that of ammonium nitrate. The volatility profiles of NOA and ammonium nitrate are similar, while SV-OOA is clearly more volatile than ammonium nitrate. The mass spectrum of NOA also indicates that it is likely composed mainly of amine salts. Based on these result, the sources and life cycle processes of OA at this urban downwind location will be discussed.