Impact of Biomass Burning on Regional Air Quality and Weather Patterns in Texas

Fires are one of the most important sources of aerosol and pollutant gases. The influence of fires on the atmosphere concerns not only air quality but also weather patterns. Large uncertainties still exist in our quantitative understanding of how fires will both affect and respond to changes in weather and climate. Motivated by this knowledge gap, the present thesis aims to provide a better understanding of the effects of fire-emitted pollutants on air quality and weather patterns over Texas. This thesis examined the influence of fire pollutants, from both long-range transport and local wildfires, on Texas air quality and weather patterns. Using the GEOS-Chem passive tracer simulation, we quantified that the long-range transport of Central American fire emissions contributes an enhancement of 9-12 ppbv in maximum daily average 8-hr (MDA8) ozone and of 3-4 g/m3 in daily PM2.5 in Texas cities along the Gulf Coast. With respect to local wildfires, we first developed a quantile regression model to predict monthly wildfire burned area in Eastern Texas for two peak fire seasons during 2003-2015. Key predictors of wildfires for this region were identified and ranked by the model; they include drought, climatic anomaly of minimum relative humidity and maximum temperature, and climatology of precipitation. Applying the projected meteorological fields from the Coupled Models Inter-comparison Project (CMIP5), the fire prediction model projects that future median and 95th percentile burned area will decrease by 25% and increase by 24%, respectively. The reduction of the burned area at the median level is mainly driven by increasing relative humidity anomaly, while the enhancement of the 95th percentile burned area is mostly caused by rising temperature anomaly in the midcentury. Lastly, increasing fire emissions were implemented in the single column model (SCM) of version 6 of the Community Atmosphere Model (CAM6) to investigate the influences of fires on weather patterns over the Houston area. Increased fire emissions would cause larger influences on shortwave radiative fluxes and planetary boundary layer height under dry conditions, which are further extended to meteorological factors such as temperatures and relative humidity in the lower atmosphere and to precipitation under dry conditions.