Implications of North American Boreal Fires on Air Quality and Composition in Nearby and Remote Regions

During the summer of 2004, Alaska and Canada experienced intense wildfire episodes that emitted large amounts of pollutants and aerosols into the atmosphere. We are using simulations with the global chemistry transport model MOZART to study the impact of these emissions on air quality and composition over North America, the Northern Atlantic region, and Europe. The emission inventory we apply for the Alaskan and Canadian wildfires in these simulations is based on a top-down approach using MODIS fire counts, MOPITT CO observations, and the MOZART model. The model has been evaluated by comparison with a large suite of observations such as data from ozone sondes, surface measurements of CO, ozone and nitrogen species, and aircraft observations. The impact of the fires on the concentrations and distributions of the aforementioned trace species will be discussed, including aspects related to air quality. The mid- and lower tropospheric ozone load over North America for summer 2004 is about 7% higher in a simulation including the Alaskan/Canadian wildfires compared to a reference simulation without fires in this region. During July 2004 we estimate that, for about half the time, at least 30% of the ozone load in the lower and middle troposphere over Eastern Canada can be attributed to chemical production from precursors emitted by the fires. Over Western Europe, we find contributions of 10% and higher about one-third of the time. We are investigating the importance of the injection height of fire emissions on atmospheric transport and chemistry, e.g. on the production of tropospheric ozone, and examine the effects of the non-linearity in ozone chemistry. We further compare the radiative forcing of the fire induced increase in ozone concentrations to the radiative forcing of greenhouse gases released by the fires such as CO2 and methane.