Estimating contributions of wildland and prescribed fires to air quality in the Southern Sierra Nevada, California

A comprehensive network for monitoring air pollution (ozone, nitrogen dioxide, ammonia, gaseous nitric acid and particulate matter) in the southern Sierra Nevada was established in order to better understand the contribution of wild-land fires to air quality form the perspective of exceedance of federal and state standards. We used the network of passive and active monitors deployed over a three year span to estimate background spatial and temporal distributions of air pollutants resulting from urban and agricultural activities. Between years differences in the spatial patterns were compared with differences in the levels of fire activity, precipitation, and temperature as possible sources of variation.

Additionally, we developed a statistical model to assess and forecast the contribution of fire smoke on ambient ozone and PM at sensitive sites in the Sierra Nevada. Hourly PM2.5 concentrations predicted by a dynamic smoke transport model (BlueSky) were used as a surrogate for the amount of ozone precursors coming from nearby fires. We found the model useful for forecasting next-day ozone levels and for assessing the utility of the BlueSky model in predicting the contributions of fires. The statistical analysis detected a small but significant effect of fires on ozone variation. Ozone levels appear to increase on average when fire activity in the region increases. The overall effect, however, seemed to be small compared with variation due to meteorological factors and sources other than fires.

It is anticipated that the forecasts from the statistical model can be used to support decision making by land and air resource managers regarding air quality and prescribed burns in the Class-I areas of the Sierra Nevada and other sensitive areas.