A Modeling Study of the Export Pathways of Pollution from Europe: Seasonal and Interannual Variations (1987-1997)

We present a study of the seasonal and interannual variations of the export pathways of pollution from Europe for eleven years, 1987-1997, using the GEOS-CHEM model of 3-d trace gas/aerosol chemistry and transport. The dominant export pathways in winter are advection to i. the middle and high latitudes of the North Atlantic Ocean, including the European Arctic; ii. Russia and the Russian Arctic; and iii. the middle and 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. Transport by advection 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 quasi-permanent Western Saharan Low. Summertime ozone in our model is enhanced by European pollution (~5 ppbv on average) in the middle troposphere near these three regions of lofting. In addition, European pollution causes summertime, surface ozone levels in northern Africa and the Near East, regions with a total population of about 200 million people, to exceed regularly the European Council’s human health standard. European pollution does not contribute as significantly to ozone levels in other populated regions outside of Europe. The two dominant causes of interannual variation in the export of European pollution over our study period are variations in transport, especially associated with the North Atlantic Oscillation (NAO), and changes in anthropogenic emissions. The tropospheric burden of carbon monoxide from European sources varies by as much as ±20% over both western Europe and the North Atlantic Ocean and ±15% over the Arctic during the 11year study period in winter because of interannual variations in transport. When the NAO is in the positive (negative) phase, the carbon monoxide burden from European sources tends to be lower (higher) over the North Atlantic Ocean and higher (lower) over the Arctic. Emissions of carbon monoxide and nitrogen oxides decrease by 36% and 20%, respectively, in Europe during