AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Toward Development of a Metric to Relate Molecular Characteristics with Optical Properties for Biomass Burning Aerosol
NISHIT SHETTY, Apoorva Pandey, Simeon Schum, Maryam Khaksari, Lynn Mazzoleni, Rajan K. Chakrabarty, Washington University in St. Louis
Abstract Number: 495 Working Group: Aerosol Chemistry
Abstract Emissions from biomass burning are a significant source of light-absorbing organic aerosol, also called brown carbon (BrC), in the atmosphere. The complex composition of these aerosols along with source dependent diversity of BrC impedes quantitative predictions of the contribution of BrC light absorption to overall atmospheric radiative forcing. In addition to this, most models have computational limitations while incorporating a large amount of chemical detail in simulations underscoring the need for concise metrics which can capture the complexity of such aerosols to a good degree. Past studies have tried to capture the vast chemical information of organic aerosols using concise metrics such as the overall carbon oxidation state as a representation of the oxidative age of the aerosol. However, no attempts have been made to develop a concise metric to relate chemical composition to the optical properties of organic aerosols.
Here, we generated BrC aerosol from smoldering combustion of peat, cattle dung, and acacia wood. Optical properties of the emitted aerosol were characterized using multi-wavelength photoacoustic spectroscopy and ultraviolet-visible (UV-Vis) spectrophotometry on particle-laden filter samples. Molecular characterization of the aerosol extracts was performed using ultrahigh resolution mass spectrometry with both atmospheric pressure photoionization (APPI) and electrospray ionization (ESI). APPI provided chemical information for the nonpolar compounds which are otherwise not observed in the commonly-used ESI ionization technique. We explored several different chemical metrics such as the average oxidation state and mean molecular mass and compared their evolution with varying optical parameters such as the Absorption Ångström Exponent and complex refractive index of aerosols. We will present our findings on the correlation of these parameters.