Transport of boreal forest fire emissions from Canada to Europe

In August 1998, severe forest fires occurred in many parts of Canada, espec ially in the Northwest Territories. In the week from August 5 to 11, more t han 1000 different fires burned >1 x 10(6) ha of boreal forest, the highest 1-week sum ever reported throughout the 1990s. In this study we can unambi gously show for the first time that these fires caused pronounced large-sca le haze layers above Europe and that they influenced concentrations of carb on monoxide and other trace gases at the surface station Mace Head in Irela nd over a period of weeks. Transport took place across several thousands of kilometers. An example of such an event, in which a pronounced aerosol lay er was observed at an altitude of 3-6 km over Germany during August 1998, i s investigated in detail. Backward trajectories ending at the measured aero sol layer are calculated and shown to have their origin in the forest fire region. Simulations with a particle dispersion model reveal how a substanti al amount of forest fire emissions was transported across the Atlantic. The resulting aerosol lamina over Europe is captured well by the model. In add ition, the model demonstrates that the forest fire emissions polluted large regions over Europe during the second half of August 1998. Surface measure ments at Mace Head are compared to the model results for an anthropogenic a nd a forest fire carbon monoxide tracer, respectively. While wet deposition removed considerable amounts of aerosol during its transport, forest fire carbon monoxide reached Europe in copious amounts. It is estimated that dur ing August 1998, 32%, 10%, and 58% of the carbon monoxide enhancement over the background level at Mace Head were caused by European and North America n anthropogenic emissions and forest fire emissions, respectively.