Oxygenated compounds in aged biomass burning plumes over the Eastern Mediterranean: evidence for strong secondary production of methanol and acetone

[摘要] Airborne measurements of acetone, methanol, PAN, acetonitrile (by ProtonTransfer Reaction Mass Spectrometry), and CO (by Tunable Diode LaserAbsorption Spectroscopy) have been performed during the MediterraneanIntensive Oxidants Study (MINOS August 2001). We have identified ten biomassburning plumes from strongly elevated acetonitrile mixing ratios. Thecharacteristic biomass burning signatures obtained from these plumes revealsecondary production of acetone and methanol, while CO photochemicallydeclines in the plumes. Mean excess mixing ratios - normalized to CO - of1.8%, 0.20%, 3.8%, and 0.65% for acetone, acetonitrile,methanol, and PAN, respectively, were found. By scaling to an assumed globalannual source of 663-807Tg CO, biomass burning emissions of 25-31 and 29-35Tg/yr for acetone and methanol are estimated, respectively. Our measurementssuggest that the present biomass burning contributions of acetone andmethanol are significantly underestimated due to the neglect of secondaryformation within the plume. Median acetonitrile mixing ratios throughout thetroposphere were around 150pmol/mol, in accord with current biomass burninginventories and an atmospheric lifetime of ~6 months.

[学科分类] 大气科学