Effects of changing climate on fires and the consequences for U.S. regional air quality, using global and regional chemistry and climate/meteorology models

This study provides an integrated assessment of the effects of forest fires in a future climate on ozone and particulate matter air quality in the United States. Utilizing the results of the Goddard Institute for Space Studies – Global Climate Model (GISS-GCM) and the Goddard Earth Observing System – Chemistry model (GEOS-Chem), we applied dynamic downscale modeling with the PSU/NCAR mesoscale model (MM5) and the Community Multiscale Air Quality (CMAQ) to provide regional meteorology and chemistry for the present and future years. For downscaling and projection of future fire activities subject to climate change, we developed a novel method to develop synthetic forest fires utilizing the probability of wildfire occurrence on different land cover types, Haines index estimated with regional meteorological model output, and the satellite fire observation from Hazard Mapping System (HMS) data. Fire emission inputs were estimated using the wildfire emission algorithm with satellite derived land use data and fine resolution fuel loading data. Due to the increased temperature in the future climate simulation, the ozone levels in the North America increase mostly. With fixed anthropogenic emissions, the change of climate leads to increased ozone production in the Midwest and Eastern US, and another small increase in the Pacific region. The increase of PM2.5 in the upper Middle Western states and decrease in the Ohio valley area are mostly led by the change of sulfate concentrations, which in turn was results of change in the precipitation pattern. Wildfire emissions affect both ozone and PM chemistry further. Ozone increases 2-3 ppb by adding wildfire emissions in the present day, and results in up to 5 ppb increase by the future wildfires. For the 2000 base run, the mean PM2.5 concentration over the U.S. is 5.6 µg /m3. By adding 2000 fire emissions, the PM2.5 mean changes to 6.16 µg /m3, showing around 10% increase. By the change of climate, the mean PM2.5 increases to 6.6 µg/m3 (18% increase from 2000 base), and increases to 8.1 µg/m3 with additional wildfire emission. With additional wildfire emissions, the mean PM2.5 increases 18.9% and 22.7% in 2000 and 2050, respectively.