10th International Aerosol Conference
September 2 - September 7, 2018
America's Center Convention Complex
St. Louis, Missouri, USA

Abstract View


Measuring Light Absorption by Organic Aerosols: Correction Factors for Solvent Extraction Based Photometry Techniques

NISHIT SHETTY, Apoorva Pandey, Wei Min Hao, Rajan K. Chakrabarty, Washington University in St. Louis

     Abstract Number: 594
     Working Group: Carbonaceous Aerosol

Abstract
Recent studies have shown that organic carbon (OC) aerosol could have a non-trivial role in atmospheric light absorption at shorter visible wavelengths. Good estimates of OC absorption are therefore necessary to accurately calculate radiative forcing due to these aerosols in climate models. One of the common techniques used to measure OC light absorption is the solvent extraction technique from filter samples which involves the use of a spectrophotometer to measure the bulk absorbance of the solvent-soluble organic fraction of particulate matter. The bulk absorbance is subsequently converted to particulate absorption using correction factors. The appropriate correction factors to use for performing this conversion under varying scenarios of EC/OC ratios has been an unexplored area of research. The conventional view is to apply a correction factor of 2 for water-extracted OC based on Mie calculations.

We performed a comprehensive laboratory study involving four solvents (water, methanol, acetone, hexane) to investigate the corrections factors for primary OC aerosol emitted from biomass burning as a function of EC-to-OC ratio and single scattering albedo (SSA). The aerosol emissions were collected on quartz fiber filters for calculating their bulk OC absorption coefficients using UV-Vis spectrophotometry. In parallel to the filter sampling set up, the aerosols were simultaneously measured for their particle-phase optical properties using multi-wavelength integrated photoacoustic nephelometers. Conversion factors for bulk-to-particulate OC absorption were calculated. Additionally, from the spectroscopic data, we analyzed and compared the Absorption Ångstrom Exponents derived from both analytical techniques. This presentation will conclude with recommendations for future research needed in this direction.