Influence of fires on O3 concentrations in the western US

Jaffe, D.; Chand, D.; Hafner, W.; Westerling, A.; Spracklen, D.

Because forest fires emit substantial NOx and hydrocarbons-known contributors to O-3 production-we hypothesize that interannual variation in western U.S. O-3 is related to the burned area. To evaluate this hypothesis we used a gridded database of western U.S. summer burned area (BA) and biomass consumed (BC) by fires between 101-125 degrees W. The fire data were compared with daytime summer O-3 mixing ratios from nine rural Clean Air Status and Trends Network (CASTNET) and National Park Service (NPS) sites. Large fire years exhibited widespread enhanced O-3. The summer BA was significantly correlated with O-3 at all sites. For each 1 million acres burned in the western U.S. during summer, we estimate that the daytime mean O-3 was enhanced across the region by 2.0 ppbv. For mean and maximum fire years, O-3 was enhanced by an average of 3.5 and 8.8 ppbv, respectively. At most Sites O-3 was significantly correlated with fires in the surrounding 5 x 5 degrees and 10 x 10 degrees regions, but not with fires in the nearest 1 x 1 degrees region, reflecting the balance between O-3 production and destruction in a high NOx environment. BC was a slightly better predictor of O-3, compared with BA. The relationship between O-3 and temperature was examined at two sites (Yellowstone and Rocky Mountain National Parks). At these two sites, high fire years were significantly warmer than low fire years; however, daytime seasonal mean temperature and O-3 were not significantly correlated. This indicates that the presence of fire is a more important predictor for O-3 than is temperature.

Influence of fires on O3 concentrations in the western US

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