AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
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Influences of Primary Emission and Secondary Coating Formation on the Particle Diversity and Mixing State of Black Carbon Particles
ALEX LEE, Laura-Helena Rivellini, Chia-Li Chen, Jun Liu, Derek Price, Raghu Betha, Lynn Russell, Xiaolu Zhang, Christopher Cappa, National University of Singapore
Abstract Number: 234 Working Group: Carbonaceous Aerosol
Abstract The mixing state of black carbon (BC) affects its environmental fate and impacts. This work investigates particle diversity and mixing state for refractory BC (rBC) containing particles in an urban environment (Fontana, California). The chemical compositions of individual rBC-containing particles were measured by a soot-particle aerosol mass spectrometer (SP-AMS) with the single particle detection capability, from which a mixing state index and particle diversity were determined. The mixing state index varied between 26 % and 69% with the average of 48% in this study, and was slightly enhanced with the photochemical age of air masses, indicating that most of the rBC-containing particles cannot be simply explained by fully externally (0%) and internally (100%) mixed model. The average particle species diversity and the bulk population species diversity both increased with primary traffic emissions and elevated nitrate concentrations in the morning but gradually decreased with secondary organic aerosol (SOA) formation in the afternoon. Based on the single particle clustering results with the support of source apportionment of ensemble measurements, primary traffic emissions and entrainment of nitrate-containing rBC particles from the residual layer to the surface could lead to more heterogeneous aerosol compositions, whereas substantial fresh SOA formation near vehicular emissions made the rBC-containing particles more homogeneous. This work highlights the importance of considering particle diversity and mixing state for investigating the chemical evolution of rBC-containing particles. We also demonstrates that the single particle mass spectrometry technique used in this study has a great potential to improve our understanding of rBC absorption enhancement due to the presence of coating as the influences of emissions and atmospheric processes on the coating thickness and particle diversity on specific particles types and size can be better described in model simulations.