Three-Dimensional Modeling of the Explicit Chemistry of Organic Aerosols: Formation, Removal, and Comparison with Observations

Principal Investigator(s):
Sasha Madronich, University Corporation for Atmospheric Research

Organic aerosols (OA) remain one of the most uncertain components of the atmosphere, despite their enormous importance to public health, visibility, and climate forcing.  Recent studies confirm that most OA are formed by atmospheric reactions of a myriad of gaseous hydrocarbon precursors, each leading to its own myriad of products that can condense to form OA particles.  We have developed the world’s most detailed model of atmospheric organic chemistry (the Generator of Chemistry and Kinetics of Organics in the Atmosphere, GECKO-A), representing the chemistry of several million organic compounds and predicting their chemical, thermodynamic, and optical properties.  The model has already been shown to predict accurately the OA yields measured in laboratories and in realistic urban environments (Mexico City), and is the only explicit chemical model known to do so.

The proposed work will use GECKO-A model to interpret measurements made during three DOE-led field campaigns: GoAmazon, BBOP, and HI-SCALE.  Each campaign offers specific challenges and opportunities to evaluate and improve GECKO-A:  GoAmazon sampled at the interface of regions dominated by biogenic or anthropogenic hydrocarbons, providing a contrast between chemical regimes that should be within the current predictive capability of GECKO-A.  BBOP provides an opportunity to test and improve the chemistry of light-absorbing compounds, important to radiative forcing (brown carbon) and OA lifetimes (photolysis), with updates based on our Tropospheric Ultraviolet Visible model.  HI-SCALE is expected to provide simultaneous measurements of organic molecules in air, aerosols, and cloud droplet residuals, and will be used to test our extension of GECKO-A to cloud chemistry.  We anticipate that this will elucidate the formation of carboxylic acids, which observations show to be ubiquitous but are not fully explained; and the formation of OA particles when cloud droplets evaporate, which some (but not all) previous studies have suggested as major contributors to the global burden of organic aerosols.  Successful improvements will be parameterized for implementation a three-dimensional regional chemistry-transport model WRF-Chem and will be made available to the community.