AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Absorption Enhancement and Optical Properties of Black Carbon – Aging Diesel Emissions with Alpha-Pinene SOA Coatings
ALLISON AIKEN, Manvendra Dubey, Alla Zelenyuk, Rahul Zaveri, Claudio Mazzoleni, John Shilling, Los Alamos National Lab
Abstract Number: 635 Working Group: Aerosols, Clouds, and Climate
Abstract Black carbon (BC) absorption enhancements (Eabs) assumed in climate models remain un-validated and depend strongly on BC morphology and composition. Core-shell Mie Theory predicts Eabs up to a factor of 2 for non-absorbing coatings. Ambient measurements indicate that BC Eabs may depend on different sources (Cappa et al., 2012, Liu et al., 2015). To further understand CARES 2010 results, the Soot Aerosol Aging Study (SAAS) at PNNL’s Environmental Chamber investigates the relationship between internally-mixed BC with different morphologies and BC absorption enhancements. With the same BC core (120 nm mobility diameter) from a diesel engine and different coating thicknesses of α–pinene secondary organic aerosol (SOA) we isolate the effect of morphology on diesel BC Eabs.
Direct on-line measurements with the single particle soot photometer (SP2) of fresh and aged BC are coupled with photoactoustic spectroscopy to probe changes in BC light absorption when coated with different thicknesses of SOA. We focus on enhancements at 781nm for the SOA coating experiments that are tracked through SOA growth and quantified with SP2 coating thickness. Thermal denuder (TD) experiments determine Eabs, and are calculated using 2 different methods that agree well. TD loss rates are quantified at 14%-30% for 100-300 degC and Eabs are reported from 1.08–1.48 from 100-300 degC for coatings of 50+ nm. BC mass absorption coefficients (MAC’s), single scatter albedo (SSA) and absorption enhancements (Eabs) are measured directly for SOA coating experiments and are compared with Mie theory. BC measurements from SPLAT-II confirm the presence of collapsed BC cores with SOA coatings. Our observations of Eabs, BC core size, coating thickness and morphology are used to perform closure studies by comparing measurements with calculated Mie Theory to evaluate Mie radiative modules that are currently used in climate models.