Multi-Day Evolution of Organic Aerosol Mass and Composition from Biomass Burning Emissions

ABRAHAM DEARDEN, Ali Akherati, Charles He, Christopher Lim, David Hagan, Christopher Cappa, Jesse Kroll, Jeffrey R. Pierce, Shantanu Jathar, Colorado State University

     Abstract Number: 352
     Working Group: Biomass Combustion: Outdoor/Indoor Transport and Indoor Air Quality

Abstract
Biomass burning is an extremely important source of primary organic aerosol (POA) and volatile organic compounds (VOCs) to the atmosphere. Yet there are large uncertainties surrounding the oxidation chemistry of POA and VOCs leading to SOA formation, especially over long photochemical ages. Recently, Lim et al. (ACP, 2019) performed photooxidation experiments on biomass burning emissions using a small environmental chamber (~150 L) at the Fire Sciences Laboratory in Missoula MT. A total of 20 experiments were performed on emissions from ~15 different fuels found in the western United States. In this work, we use a state-of-the-science model, SOM-TOMAS (Statistical Oxidation Model-TwO Moment Aerosol Sectional), to simulate the physicochemical evolution of organic aerosol (OA) in these chamber experiments. Here, SOM-TOMAS simulates the oxidation chemistry, thermodynamic properties, and microphysics of OA, in addition to accounting for rapid dilution and wall losses. The model was able to simulate the time-dependent evolution of the OA mass concentration and its oxygen-to-carbon ratio when initially applied to several select fires. These preliminary results also indicated that the same VOC classes that have previously been found to be important for SOA formation in smoke (oxygenated aromatic, heterocyclic, and semi-volatile compounds) at shorter photochemical ages (<12 hours) are also relevant at longer photochemical ages (~1 day to ~1 week). However, the relative contribution of the different VOC classes to the total SOA formation varied significantly with time. Ongoing work is focused on model application to the complete dataset as well as an investigation of the complex role of semi-volatile organic compounds and heterogeneous chemistry on the evolution of OA mass and composition.