Estimating the contribution of forest fire emissions to ozone peaks during a 14-20 July 2005 prescribed fire escape in central California using CMAQ modeling system

The southern Sierra Nevada and the San Joaquin Valley (SJV) of Central California faces major air quality challenges because they can easily exceed the federal standards for ozone and particulate matter (PM) by a large margin. In addition to impacts from other many emission sources, the southern Sierra Nevada and SJV are the most susceptible to air pollution contribution from wildland, agricultural and prescribed fires. Smoke from fire contains chemical compounds such as carbon monoxide, volatile organic compounds (VOC) and nitrogen oxides (NOx) (Cheng 1998), which are the main precursors for formation of ozone and PM.

Utilization of a photochemical modeling system to estimate the contributions of different emission sources is necessary for understanding of the separate influence of the meteorology and emission sources to the regional air quality of central California (e.g., SJV and southern Sierra Nevada). In addition to exploring how to accurately predict air quality by different treatments of meteorological model physics options and air quality model gas-phase chemical mechanisms, in this study we examine and estimate the contribution of air pollution, primarily ozone, to central California from wildfire and prescribed burns by use of the CMAQ photochemical air quality modeling system. CMAQ requires emission data from point, area, on-road and non-road mobile, and biogenic sources using emission inventory model to perform the chemical transport processes. CMAQ is being run for three different emission data inputs: (1) emission data without the contribution of wild fires; (2) including emission from forest fires; and (3) only emissions from forest fires. The outputs of these three different scenario runs are compared to each other for model performance evaluation, to check fire contributions to ozone increase and for observation comparisons from ground monitoring stations. Preliminary ozone analysis of model results from anthropogenic emissions show a general underestimation of ozone from observations over most of central California during the 14-20 July 2005 prescribed fire escape ozone peaks, which may be attributed to absence of contribution of forest fire emissions into the model and the inaccuracy of simulated mesoscale meteorological results.