AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Comparison of Biomass Burning Organic Aerosol Mixing Ratios and Their Evolution With Aging
MATTHEW JOLLEYS, Hugh Coe, Gordon McFiggans, Gerard Capes, James Allan, Jonathan Crosier, Paul Williams, Grant Allen, Keith Bower, Jose-Luis Jimenez, University of Manchester
Abstract Number: 131 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract No evidence for a regional net source of secondary organic aerosol (SOA) has been identified in measurements of biomass burning-influenced ambient air masses. Measurements included in this study were obtained from the deployment of an Aerodyne Quadrupole Aerosol Mass Spectrometer during four field campaigns, involving both research aircraft flights and ground-based measurements. OA concentrations, normalized to excess CO (OA/dCO), show strong regional and local scale variability, with a difference of more than a factor of five across fresh OA emissions between campaigns. Average OA/dCO is typically higher in the near-field than at a greater distance from source, indicating an absence of significant SOA formation, despite evidence to suggest OA becomes increasingly oxidized with age. This trend is in contrast with observations of anthropogenic OA in urban environments, where OA/dCO is consistently shown to increase with distance from source. There is no such agreement in the case of biomass burning OA (BBOA) amongst the literature base, with conflicting examples relating to the influence of SOA on aerosol loadings. A wide range of average initial emission ratios close to source are observed both within the datasets analysed here and within the literature, together with considerable variability in OA/dCO values throughout individual fresh biomass burning plumes. The extent of this variability far outweighs any change in average OA/dCO, suggesting that source conditions are of greater importance for the propagation of BBOA loadings within the ambient atmosphere. However, the exact effects of the fire conditions influencing emissions from biomass burning events remain poorly constrained, with results from chamber experiments showing inconsistencies in relationships with factors such as fuel type and combustion phase. These uncertainties regarding the evolution of biomass burning emissions emphasise the need for improved characterisation of BBOA to ensure accurate representation in global climate models.