AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Aging Diesel Black Carbon with SOA Coatings and Coagulation to Probe Morphology-dependent Aerosol Absorption Enhancements (Eabs)
ALLISON AIKEN, Manvendra Dubey, Shang Liu, Rahul Zaveri, John Shilling, Claudio Mazzoleni, Swarup China, Noopur Sharma, Alla Zelenyuk, Jacqueline Wilson, Gourihar Kulkarni, Mikhail Pekour, Duli Chand, R. Subramanian, Los Alamos National Lab
Abstract Number: 724 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Climate warming due to BC has large uncertainties, specifically due to morphology and mixing state, e.g. Cappa et al., 2012. Classic core-shell coated BC is expected to enhance light absorption (Eabs) by up to a factor of 2, while non-core shell BC morphologies, observed in wildfire emissions (Sedlacek et al., 2012), are predicted to have little to no Eabs. The Soot Aerosol Aging Study (SAAS at PNNL’s Environmental Chamber) was designed to investigate the relationship between internally-mixed BC with different morphologies (coated vs. coagulated) and the measured BC Eabs for visible light. 3 different types of experiments were conducted using size-selected diesel BC (120 nm diameter) and secondary organic aerosol (SOA): (1) BC coated with SOA, (2) BC coagulated with SOA, (3) BC coagulated then coated with SOA. Direct on-line BC measurements with the single particle soot photometer (SP2) are coupled with photoactoustic measurements across multiple wavelengths spanning the visible range to probe Eabs in BC when mixed with SOA. Eabs at 781 nm are tracked throughout SOA growth on BC and quantified with SP2 coating thickness. BC coagulated with SOA produces minimal absorption enhancement (<1.1), whereas coatings have significant enhancement at 300 degrees C, up to 1.7 +/- 0.4 for thickly coated BC. Thermal denuder (TD) experiments are conducted and Eabs are calculated from 2 different methods that agree well with each other, confirming observed results. BC measurements are also compared with co-located measurements from SPLAT-II and filter analysis using SEM and TEM. Since we did not observe appreciable Eabs for coagulated BC, we expect ambient emissions dominated by this particle type to have enhancements due co-emission and or mixing with other sources, e.g. brown carbon (BrC; Saleh et al., 2014, Liu et al., submitted 2015).