AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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Light Absorption Properties of Polar and Non-polar Aerosols in Fresh and Aged Biomass-Burning Emissions
DEEP SENGUPTA, Vera Samburova, Chiranjivi Bhattarai, Michealene Iaukea-Lum, Adam Watts, Hans Moosmuller, Andrey Khlystov, Desert Research Institute
Abstract Number: 647 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Fresh and atmospherically aged biomass-burning (BB) aerosols are mostly comprised of Black Carbon(BC) and Brown Carbon (BrC), which significantly contribute to light absorption properties of combustion emissions. There is a lack of data on physical and chemical properties of atmospheric BB aerosols, leading to high uncertainties in estimates of BB impact on air quality and global climate, especially in the case of BrC. Polarity of chemical compounds determines their fate in the atmosphere. Most attention so far has been given to the water-soluble (polar) fraction of BrC, while non-polar fraction of BrC was largely ignored. In the present study, abundance and light absorption properties of polar and non-polar fractions of fresh and aged BB emissions were studied to estimate the contribution of different polarity organic compounds to the light absorption of BB BrC aerosols.
In our experiments, representative fuels were burned under open flame and smoldering conditions using the DRI’s chamber facility. To mimic the atmospheric oxidation process (5-7 days), BB emissions were aged using an Oxidative Flow Reactor (OFR). Fresh and OFR-aged BB aerosols were collected on filters and extracted with water and hexane. The high molecular weight organic fraction was separated from inorganics and low molecular weight organics by the Solid-Phase Extraction (SPE) technique. All extracts were analyzed with UV-Vis spectrophotometer in the range of wavelengths between 190 and 900 nm. The measured spectra were used to calculate Mass Absorption Coefficients (MAC) and Absorption Ångström Exponents (AAE). The MAC and AAE values were compared among different fuel extracts and then plotted against OM/OC ratios to characterize the evolution of light absorption properties of BB emissions with OFR-aging. Comparison of light absorption properties of different polarity extracts (water, hexane, SPE) provides insights into the chemical nature of BB BrC and its transformation during atmospheric oxidation.