American Association for Aerosol Research - Abstract Submission

AAAR 36th Annual Conference
October 16 - October 20, 2017
Raleigh Convention Center
Raleigh, North Carolina, USA

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Chemical Characterization of Secondary Organic Aerosol under High NH3 in a Transitional Season of Biogenic VOC Emission using HR-ToF-AMS

YUNLE CHEN, Theodora Nah, David Tanner, Masayuki Takeuchi, Hongyu Guo, Amy P. Sullivan, Rodney J. Weber, Greg Huey, Lu Xu, Nga Lee Ng, Georgia Institute of Technology

     Abstract Number: 400
     Working Group: Carbonaceous Aerosols in the Atmosphere

Abstract
The effects of human activities on secondary organic aerosol (SOA) have long been an intriguing topic. With high emissions from both anthropogenic and biogenic sources, the southeastern U.S. is an ideal area to study the interactions between the two. Here, the formation and evolution of SOA was investigated at Yorkville, a rural site 55km NW of Atlanta, in late summer (mid-August ~ mid-October, 2016), a period when the NH3 concentration was high (average 8.1 ppb) and BVOC emissions were gradually decreasing. A High-Resolution Time-of-Flight Mass Spectrometer (HR-ToF-AMS) was deployed to characterize non-refractory submicron particles. Co-located instruments (CIMS, FIGAERO-CIMS, GC-MS, PILS-IC, etc.) were used to comprehensively characterize both gas- and particle-phase composition.

Positive Matrix Factorization (PMF) analysis of HR-ToF-AMS measurements resolved five factors, including isoprene-derived organic aerosol (Isop-OA), less-oxidized oxygenated OA (LO-OOA), two more-oxidized oxygenated OA (MO-OOA1, MO-OOA2), and an unknown OA (unknown-OA). The PMF results are different from previous measurements at the same site in early summer and in winter, implying different aerosol chemistry and composition during this specific transitional period. It is found that Isop-OA is decreasing throughout the campaign, as temperature and isoprene emission decrease. The LO-OOA factor and unknown-OA factor show correlation with particulate C10 and C15 organic nitrates, indicating possible aerosol sources from nitrate radical chemistry and/or photooxidation in the presence of NOx. One of the MO-OOA factors correlates with organic acids in the particles, suggesting that it could be from aging of organic aerosols.