AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
The Impact of Emissions from Mobile Sources and Biomass Burning on Ambient PM2.5 EC and OC in the SEARCH Network, 1999 - 2013
CHARLES BLANCHARD, George Hidy, Envair
Abstract Number: 118 Working Group: Air Quality and Climate in the Southeast US: Insights from Recent Measurement Campaigns
Abstract Haze in the southeastern US is widely identified with anthropogenic pollution aerosol superimposed on a background of secondary organic aerosol (SOA) from oxidation of isoprene and other biogenic volatile organic compounds. Long-term measurements obtained from the Southeastern Aerosol Research and Characterization (SEARCH) network of urban and rural sites between 1999 and 2013 offer additional information on the contributions of anthropogenic emissions to observed organic aerosol concentrations and trends. The SEARCH measurements of trace gases and aerosols document important changes in air chemistry resulting from reductions of air pollutant emissions in the region. Anthropogenic emissions of sulfur dioxide (SO2), nitrogen oxides (NOx = NO + NO2), volatile organic compounds (VOC), carbon monoxide (CO), and motor-vehicle PM2.5 each decreased by approximately a factor of two in the southeastern U.S. between 1999 and 2013. During the same period, all eight sites (four urban, four non-urban) of the SEARCH network exhibited declining ambient concentrations of primary and secondary air pollutants. SEARCH ambient trends in SO2, NOy, CO, NMOC, EC, OC, SO4, and particulate NO3 tracked same-pollutant or precursor emission trends. The SEARCH data show that OC and EC emissions from biomass burning and mobile-source exhaust are major (>50% combined) contributors to particle carbon both locally and regionally in the Southeast. This result derives from different analyses that include (a) chemical mass balance receptor modeling, accounting for transportation emissions and open burning, (b) statistical investigation of combined EC-OC trends and emissions, (c) integration of thermal-desorption measurements of non-polar OC compounds with EC and OC observations, (d) application of non-soil potassium as a tracer of biomass burning, and (e) evaluation of modern vs. fossil carbon concentrations and source emissions. The findings provide an important perspective on the role of primary particle emissions compared with SOA production processes.