The VOTALP Mesolcina Valley Campaign 1996 – concept, background and some highlights

Abstract

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 horizontal and vertical ozone transport over various distances, and on local production of ozone in an Alpine valley. The field measurements took place in 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 character, and contains an important traffic route. Ground-based and airborne instruments were deployed to obtain a four-dimensional chemical and physical picture of the valley atmosphere and the surroundings. Field measurements were 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-climatological approach tries to evaluate the representativeness of the observation days. It was found that during the campaign representative data for typical ozone days were collected, while extreme events did not occur.The main results of the campaign are that very high pollutant concentrations at the Alpine crests are the effect of advective, larger-scale transport, mainly from the Alpine forelands. The valley is very effective in pumping air into elevated 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 sinks of air pollutants, which may lead to negative impacts on the Alpine ecosystems.

Quantification of topographic venting of boundary layer air to the free troposphere

“…The measurement setup of the VOTALP Mesolcina experiment is described in detail by Furger et al (2000). During the CHAPOP Leventina experiment multiple aircraft were used to investigate the structure and chemical composition of the valley's atmosphere.…”

Introduction to the European Monitoring and Evaluation Programme (EMEP) and observed atmospheric composition change during 1972–2009

“…Furthermore, the dominant westerly wind flow causes a gradual build-up of continental emissions and ozone as air moves across the continent. The topography of the Alps has a strong influence in that sites at different altitudes are exposed to very different ozone levels (Loibl et al, 1994), and sometimes the mixing between the boundary layer and the free troposphere act as an effective means of transporting manmade ozone and precursors from populated valleys into the free troposphere (Furger et al, 2000;Ordóñez et al, 2005). Already the EUROTRAC project TOR showed that there is a spatial gradient across Europe with ozone increasing from northwest to southeast in summer and an opposite gradient in winter (Scheel et al, 1997).…”

Measurement and simulation of the 16/17 April 2010 Eyjafjallajökull volcanic ash layer dispersion in the northern Alpine region

“…between 06:00 and 10:00 UTC (see also Schreiter, 2010). It can be speculated that the strongly increased vertical exchange over the Alps (see, e.g., Furger et al, 2000 leads to a rapid dilution of the ash cloud so that the ash concentration decreases and the sharp contours of the cloud decay. Synoptic weather analysis reveals that this development is also associated to a meso-scale low pressure system to the south of the Alps inducing a change from northeasterly to southerly wind directions and associated topographic subsidence at the northern fringes of the Alps.…”