AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Formation of Secondary Organic Coating on BC Particles and Its Impact on Mixing State of Carbonaceous Aerosol in the Urban Atmosphere
ALEX K. Y. LEE, Raghu Betha, Chia-Li Chen, Jun Liu, Derek Price, Xiaolu Zhang, Jonathan Abbatt, Christopher Cappa, Lynn Russell, University of Toronto
Abstract Number: 257 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Black carbon (BC) particles emitted from fossil fuel combustion and biomass burning can result in a significant warming effect on climate. Organic coatings can be formed on BC surfaces by condensation of co-emitted primary organic aerosol (POA) material near emission sources and secondary organic aerosol (SOA) during transport, modifying light absorption and cloud condensation nuclei activity of BC. Understanding the mixing state of ambient BC and the characteristics of its associated coatings are therefore particularly important to evaluate the fate and environmental impacts of ambient BC. In this study, we examine the mixing state of BC, POA and SOA in an urban environment (Fontana, California) in summer 2015 using both single particle and ensemble measurements from an Aerodyne Soot-Particle Aerosol Mass Spectrometer (SP-AMS). The SP-AMS was operated in a configuration that can detect BC-containing particles exclusively. Using NOx/NOy ratio as a proxy for photochemical age of air masses, we observed substantial formation of SOA coatings on BC particles during the daytime. Positive matrix factorization and elemental analysis of ensemble data illustrate that most of the observed SOA coatings are freshly formed (O:C ratios ranged from 0.30 to 0.44), providing a opportunity for investigating SOA coating formation on BC particles near emissions. Preliminary results of cluster analysis of single particle measurements further indicate the presence of various types of POA and SOA coatings on BC particles based on their mass spectral characteristics and size distributions. Our observations can be used for further developing our understanding of BC mixing state and its evolution in the urban atmosphere.