A modeling study of the export pathways of pollution from Europe: Seasonal and interannual variations (1987-1997)

[1] We present a study of the export pathways of pollution from Europe from 1987 to 1997, using a three-dimensional model of chemistry and transport. The dominant export pathways in winter are advection to the (1) middle/high latitudes of the North Atlantic Ocean, (2) Russia and the Russian Arctic, and (3) middle/low latitudes of the North Atlantic Ocean from western Europe and from northern Africa via the Mediterranean Basin. In summer, export occurs by both advection and convection; advective transport occurs predominantly to Russia and the Mediterranean Basin/northern Africa. There are two major regions of convection in summer that loft European pollution into the free troposphere, one centered over Germany and the other over the Ural Mountains in Russia. Another region of lofting, not associated with moist convection, occurs in northwestern Africa by the Western Saharan Low. Summertime ozone in our model is enhanced by European pollution (similar to5 ppbv on average) in the middle troposphere near these three regions of lofting. European pollution causes summertime surface ozone levels in northern Africa and the Near East to exceed regularly the European Council's human health standard. The two dominant causes of interannual variation in European pollution export are variations in transport, especially associated with the North Atlantic Oscillation (NAO), and changes in anthropogenic emissions. The tropospheric burden of carbon monoxide (CO) from European sources varies by as much as +/-20% over both western Europe and the North Atlantic and +/-15% over the Arctic in winter because of interannual variations in transport. When the NAO is in the positive (negative) phase, the CO burden from European sources tends to be lower (higher) over the North Atlantic and higher (lower) over the Arctic. European emissions of CO and nitrogen oxides decrease by 36% and 20% over the study period, respectively, with a nearly linear concomitant decrease in the CO burden associated with European emissions. We find that it is necessary to consider both of these factors when interpreting trends in observed trace gas concentrations over Europe.