A Model Study of the Chemistry of Biomass Burning Smoke Plumes Constrained by Aircraft Data

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Biomass burning is a major source of trace gases and particles to the atmosphere, but current models have not yet captured the processes that lead to the significant formation of ozone and secondary organic aerosol (SOA) that is often observed in the first few hours after emission. This project will develop a new state-of-the-art modeling framework that incorporates recent advances in modeling gas- and aerosol-phase photochemistry into a high resolution Lagrangian dispersion model. The new modeling framework will be evaluated against detailed measurements of the chemical evolution of two North American smoke plumes. This will allow the following science questions to be addressed: * What causes the high ozone and hydroxyl radical (OH) concentrations observed in fresh biomass smoke plumes? * What are the sources of SOA within the smoke plumes? * What is the impact of smoke aerosols on photolysis rates, and hence photochemistry, within the smoke plumes?The aircraft measurements of young biomass burning smoke plumes from the 2006 MILAGRO (Megacity Initiative Local and Global Research Observations) campaign in Mexico and the 2009 San Luis Obispo Biomass Burning (SLOBB) experiment in California provide comprehensive trace gas and aerosol evolution data, including the first in situ observations of OH in biomass burning plumes, and are thus ideal to evaluate the model development. The chemical evolution of these plumes will be modeled using a new version of the Aerosol Simulation Program (ASP) that will incorporate the semi-empirical two-dimensional Volatility Basis Set (2D-VBS) scheme that has been used successfully to model SOA formation in Mexico City. This updated version of ASP will be incorporated into an enhanced version of the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) dispersion model driven by high-resolution output from the Weather Research and Forecasting (WRF) model. The combined models, constrained by aircraft and GOES satellite observations, will then be used to study the formation of O3 and SOA within the smoke plumes.This research will lead to a better fundamental understanding of the climate, air quality, and human health impacts of biomass burning. Use of the WRF-HYSPLIT framework for modeling atmospheric dispersion in this work will facilitate the future inclusion of the model into the existing forecasting system models. This project will establish collaboration between an academic scientist specializing in the measurement of trace gases in biomass burning smoke plumes and two private sector scientists, one specializing in the modeling of atmospheric chemistry within smoke plumes and one specializing in modeling the dispersion of atmospheric plumes. The work will also stimulate and support the continued development of the WRF and ASP models, which were developed with previous NSF support. Two graduate students will be trained to use the developed models, which will give them the opportunity to work with scientists in a non-academic environment.