AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Investigating the Evolution of Coatings on Black Carbon at Rapid Time Scales
TREVOR KRASOWSKY, Scott Fruin, Constantinos Sioutas, George Ban-Weiss, University of Southern California
Abstract Number: 401 Working Group: Single Aerosol Particle Studies - Techniques and Instrumentation
Abstract As black carbon (BC) particles are transported into the atmosphere, they acquire soluble coatings. However, there is still vast uncertainty associated with “how” and “when” coatings accumulate on BC particles, including at rapid time-scales (<1 hour). This study uses real-world measurements to investigate spatiotemporal changes in coatings on black carbon at rapid time scales after being emitted. The hypothesis is that as BC is emitted, coatings develop when supersaturated semi-volatile organics condense massively on freshly emitted BC near the roadway, and through subsequent atmospheric dilution following immediately, these semi-volatile coatings preferentially partition back into the gas phase down wind of the emissions source where exposed black carbon particles begin acquiring coatings thought to develop on longer time-scales (>1 hour).
Individual BC particle measurements were made using a Single-Particle Soot Photometer (SP2) at varying distances downwind of the 405 freeway at the Los Angeles National Cemetery. The location is ideal for measuring freshly emitted BC heavily dominated by roadway traffic with little influence from surrounding sources. Coating thickness was analyzed using two common methods, the “Lag-Time” and “Leading Edge Only” methods, to provide a comparison of the techniques and characterize the BC coatings at different aging times. Continuous measurements of BC mass concentration, CO2 mixing ratio, and particle number concentration were also made at the roadway using a MicroAeth, Licor-840A CO2 analyzer, and DiSCmini, respectively, to correct for background variation in source emissions during the measurement periods.