TROPOSPHERIC MIXING RATIOS OF NO OBTAINED DURING TROPOZ-II IN THE LATITUDE REGION 67-DEGREES-N-56-DEGREES-S

Vertical profiles of NO were measured during the TROPOZ II aircraft ca mpaign in January 1991. Altogether, 30 flights were made along the coa stlines of western Europe, eastern North America, South America, and w estern Africa, covering latitudes between 67 degrees N and 56 degrees S and altitudes between 0 and 11 km. As a result of the general wind p attern, westerly winds at all northern and southern midlatitudes, the NO data show large-scale outflow of NO-polluted air along the east coa sts of the North and South American continents and inflow of clean mar itime air over the west coasts of South America, North Africa, and Eur ope. The NO concentrations in the free tropospheric air flowing out fr om the (winter) North American continent lie between 100 and 300 parts per trillion by volume (pptv) with a weakly C-shaped vertical profile . The air coming off the (summer) South American continent has a facto r of 3 lower NO concentrations, between 40 and 100 pptv, but a more pr onounced C-shaped vertical profile with NO mixing ratios of up to 200 pptv in the upper troposphere of the tropics. The salient features in the NO distribution are discussed with the help of 3 day back trajecto ries.