The VOTALP Mesolcina Valley campaign 1996 - concept, background and some highlights

The Mesolcina Valley campaign was an important part of the VOTALP project. Its main goals were the study of the effects of thermal wind systems on hor izontal and vertical ozone transport over various distances, and on local p roduction of ozone in an Alpine valley. The field measurements took place i n the Mesolcina Valley in southern Switzerland in July and August 1996. The Mesolcina Valley is typical for the Alps for its size and its rural charac ter, and contains an important traffic route. Ground-based and airborne ins truments were deployed to obtain a four-dimensional chemical and physical p icture of the valley atmosphere and the surroundings. Field measurements we re complemented by numerical modeling studies. An overview of the campaign, its geographic background, and the measurement plan is given together with selected highlights of the results obtained so far. A synoptic-climatologi cal approach tries to evaluate the representativeness of the observation da ys. It was found that during the campaign representative data for typical o zone days were collected, while extreme events did not occur. The main resu lts of the campaign are that very high pollutant concentrations at the Alpi ne crests are the effect of advective, larger-scale transport, mainly from the Alpine forelands. The valley is very effective in pumping air into elev ated layers during the day, with the slope winds probably carrying the bulk of the air volume to higher levels. Up to five times the valley volume may be exported during one upwind phase. Net local production is estimated to be approximately 3-8 ppb h(-1) of ozone, but seems to be compensated by dry deposition. This indicates that the Alpine valleys may be important net si nks of air pollutants, which may lead to negative impacts on the Alpine eco systems. (C) 2000 Elsevier Science Ltd. All rights reserved.