Secondary Organic Aerosol Formation from the Photo-oxidation of Biomass Burning Emissions

CHRISTOPHER J. HENNIGAN (1), Marissa A. Miracolo (1), Gabriella J. Engelhart Farnham (1), Amy P. Sullivan (2), Jeffrey L. Collett Jr. (2), Sonia M. Kreidenweis (2), Cyle E. Wold (3), Allen L. Robinson (1)

(1) Carnegie Mellon University, (2) Colorado State University, (3) Missoula Fire Sciences Laboratory

     Abstract Number: 581
     Last modified: May 13, 2010

Abstract
Biomass burning emissions represent a significant source of aerosol and gas-phase compounds into the atmosphere, and thus have important implications for tropospheric chemistry, global climate, and human health. Global estimates of secondary organic aerosol (SOA) formation from biomass burning are extremely uncertain, though recent studies and the magnitude of emissions suggest that it could be substantial. As part of the Fire Lab at Missoula Experiments study (FLAME-III), smog chamber experiments were conducted to investigate the photo-oxidation of biomass burning emissions. Specific objectives were to characterize SOA formation from different biomass fuels and to investigate the oxidation and chemical evolution of primary organic aerosol (POA). Experiments were performed at atmospherically-relevant aerosol and oxidant concentrations using 12 fuels burned under conditions simulating common North American wildfires.

The dynamic nature of biomass burning emissions was evident in the variability observed in SOA production from different biofuel sources. After 3-5 hours of photo-oxidation, wall loss-corrected SOA:POA ratios ranged from -0.2 to 1.9. A negative SOA:POA ratio, observed in several experiments, indicates a net loss of organic aerosol mass from photochemical processing. In every experiment, even those with little aerosol mass enhancement, the organic aerosol became significantly more oxidized (as indicated by the ratio of m/z 44 to total organics measured by the AMS). Oxidation without significant new mass production indicates extensive transformation of the POA. The production of new OA mass was not correlated with and often greatly exceeded the amount of isoprene, toluene, and terpenes reacted, suggesting that SOA production from traditional precursors was not important. There was, however, evidence suggesting a potentially important contribution from oxidation of semi-volatile vapors to SOA. Overall, the results provide new insight into the range of SOA formation and the chemical transformation of emissions from different biomass fuel sources.