Evaporation of Volatile Components Transforms Optical Properties and Composition of Aged BrC Aerosol

DIEGO CALDERON-ARRIETA, Ana Morales, Anusha P.S. Hettiyadura, Chunlin Li, Taylor Estock, Yinon Rudich, Alexander Laskin, Purdue University

     Abstract Number: 300
     Working Group: Aerosol Chemistry

Abstract
Atmospheric brown carbon (BrC) summarizes a matrix of atmospheric organic aerosol components with varying light absorbing properties that influence air quality and climate forcing. BrC can be secondarily generated from transformations of anthropogenic emissions and directly emitted from biomass burning (BB). Once released, BB-BrC transforms rapidly via interactions with other air pollutants and solar irradiation. Current climate models cannot adequately assess warming effects of BrC because of large uncertainty in the light absorption properties inherent to the highly variable composition of BrC and its dynamic atmospheric aging. Our previous study has found that the atmospheric pressure (0.5-1.0 atm) determined gas-particle partitioning (evaporation) of volatile chromophores can shift light absorption of BB-BrC from very-weakly to moderately absorbing. To better understand the relationship between light absorption and volatility of BB-BrC species, and also to probe fractions of BB-BrC chromophores of varying volatility, we investigated effects of thermal-evaporation processes on the BB-BrC optical properties. Lab generated BrC materials from wood pyrolysis were conditioned at ~350 ^oC for different time periods with protection of inert gas. Based on comprehensive analysis via high performance liquid chromatography, optical spectroscopy, and high-resolution mass spectrometry, it was found that evaporation of volatile components of BrC is an important factor in enhancing BB-BrC light absorption. For the first time, this study distinguishes fractions of BB-BrC with different volatility and light absorption characteristics, which inform predictive understanding of BrC transformations and associated climate-health effects in the atmosphere.