Estimation of Brown Carbon in PM_(2.5) Samples from IMPROVE and CSN Networks

摘要

The addition of seven-wavelength attenuation measurement on the DRI Model 2015 thermal/optical carbon analyzer allows estimating BC and BrC abundances on every filter sample without additional carbon analysis effort while maintaining continuity of long-term OC and EC database. Analysis of the 2016 samples show that on average, non-urban IMPROVE samples had higher BrC fraction absorption than urban CSN samples, owing to greater influence from biomass burning and aged aerosols, as well as to higher primary BC contributions from engine exhaust at urban sites. Pairing of urban with nearby nonurban samples holds the possibility of separating local from regional events related to carbon concentrations, especially for biomass burning and secondary aerosol formation. Sequential samples taken during an Everglades National Park wildfire demonstrate the evolution from flaming to smoldering, with the BrC fraction increasing as smoldering begins to dominate the fire event. The optical information, along with OC and EC, can help attribution to PM sources, such as biomass burning, SOA, and engine exhaust. It is useful for evaluating control strategy effectiveness, identifying exceptional events, and determining natural visibility conditions.