AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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Characteristics and Processing of Black Carbon Particles in an Urban Environment: Insights from a Soot Particle – Aerosol Mass Spectrometer (SP-AMS)
Sonya Collier, Leah Williams, Timothy Onasch, Christopher Cappa, Xiaolu Zhang, Lynn Russell, QI ZHANG, University of California, Davis
Abstract Number: 589 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract The coating of black carbon (BC) particles, i.e., inorganic and organic matter internally mixed with BC, can enhance light absorption and affect atmospheric lifetimes of BC particles thus having significant implications on regional and global climate. In order to study the physical and chemical characteristics of atmospheric BC and its associated coating, a soot-particle aerosol mass spectrometer (SP-AMS) was deployed during the winter of 2014-2015 for 4 weeks alongside a single particle soot photometer (SP2) in Fresno, a polluted city located in the San Joaquin Valley of California. The SP-AMS uses an infrared laser to volatilize absorbing particles and provides real-time size resolved chemical information on particles containing BC. During this campaign the SP-AMS was operated using only the laser without the thermal vaporizer in order to selectively analyze BC particles. We found that most BC-containing particles appeared to be associated with residential wood burning and vehicular traffic. However, a substantial fraction of the coating was found to be secondary in nature and this fraction was significantly enhanced via aqueous-phase processing during periods of persistent fog. Specifically, compared to periods with no visible fogs, the BC coating contained a higher concentration and larger fraction of secondary species including nitrate and oxidized organic matter and the size distribution of BC-containing particles displayed a prominent droplet accumulation mode during foggy periods.