AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Measurements to Determine Mixing State of Black Carbon Emitted from the 2017/2018 California Wildfires and Urban Los Angeles
JOSEPH KO, Trevor Krasowsky, George Ban-Weiss, University of Southern California
Abstract Number: 747 Working Group: Biomass Combustion: Emissions, Chemistry, Air Quality, Climate, and Human Health
Abstract The importance of atmospheric black carbon (BC) and its effects on climate have been established, but uncertainties remain regarding its impacts at different spatiotemporal scales. Here, we seek to understand the mixing state evolution of BC emitted from various sources and aged over different timescales, using measurements in the Los Angeles (LA) region. We measured refractory black carbon (rBC) with a single-particle soot photometer (SP2) on Catalina Island, California. During the first campaign (September 2017), the sampling location was upwind of the dominant regional sources of BC (i.e., urban emissions from the LA basin). In the second and third campaigns (December 2017, November 2018), atypical winds advected rBC to our sampling location from California wildfires and urban emission. We observed the largest number fraction of thickly coated particles (fBC) and coating thickness (CTBC) during the first campaign (~0.27 and ~36 nm, respectively), and during a period of the third campaign when we suspect that measured rBC was dominated by long-range transport from the Camp Fire in Northern California (~0.35 and ~52nm, respectively). In contrast, during periods when measured rBC was dominated by particles from Southern California fires or urban emissions, we found lower fBC and CTBC values (~0.03 and ~0-10 nm, respectively). We conclude that an aging timescale on the order of ~hours is not long enough for rBC to become coated thickly in the LA region. We found that measured rBC acquired substantial coatings when aging timescales were greater than ~24 hours. Results presented here suggest that rBC mixing state is highly dependent on emissions source-type and atmospheric context since the CTBC (per hour of atmospheric aging) was found to be smaller than what has been previously reported in literature in other locations around the world.