Optical Properties and Mixing State of Aerosols from Residential Wood Burning and Vehicle Emissions in Central and Southern California
Abstract:Light-absorbing materials such as black carbon (BC) and brown carbon (BrC) in atmospheric aerosols play important roles in regulating the earth’s radiative budget and climate. However, the representations of BC and BrC in state-of-the-art climate models remain highly uncertain, in part due to the poor understanding of their microphysical and optical properties. Direct observations and characterizations of the mixing state and absorption enhancement of ambient aerosols could provide invaluable constraints for current model representations of aerosol radiative effects.
Here, we will discuss results from measurements of aerosol light absorption and absorption enhancement (Eabs), using a thermodenuder-absorption method, made during two recent field studies in central and southern California. The winter study took place in Dec/Jan of 2014/2015 in Fresno, CA. This region is severely impacted by particulate matter from local and regional residential biomass burning. The summer study took place in July 2015 in Fontana, CA, a region ~80 km downwind of Los Angeles and strongly impacted by vehicular emissions, and thus provides a sharp contrast to the Fresno study. Eabs of BC particles due to the “lensing” effect from coatings to BC core and/or the presence of BrC will be quantified and compared between the two studies. Additionally, the chemical composition of bulk and the BC-containing particles are determined via a HR-ToF-AMS and a SP-AMS, respectively. Variations in the composition and mixing state of the ambient particles and how these affect the observed Eabs will be examined. The overall measurements suggest a relatively small role for lensing-induced absorption enhancements for ambient particles in these regions.