The influence of meteorological phenomena on trace gas concentrations at the cerro tololo global watch station (chile)

The human, industrial, and agrarian activities alter the chemical composition of the atmosphere relatively quickly, both at a regional and at a global scale. This is producing perturbations of the basic functions of the atmosphere. Taking this into account, the WMO has established the Global Atmospheric Watch (GAW) Net, which is composed of several regional sub nets which deal with several regional aspects (e. g. rain chemistry, tropospheric ozone) and global ones (e. g. stratospheric ozone, greenhouse gases). As a part of the "Southern Cone Net", a monitoring station of radiation and superficial ozone was installed on the premises of the Cerro Tololo Interamerical Observatory (AURA, INC.). The station is operated and maintained by the Direccion Meteorologica de Chile. This Cerro Tololo Global watch station is planned to be enlarged to an air chemistry monitoring station. The Cerro Tololo is located about 50 km east of the bay of La Serena. Its height is 2200 m. The orography can be described as very complex. The valleys around these mountains are deep, down to 550 m. The next mountains with heights of more then 6000 m are only 30 km east of the Cerro Tololo. Regions with such a complex terrain are frequently characterized by diurnal cyclic wind systems, such as mountain, valley, and slope winds. These wind systems are very important in connection with airborne pollutant transport processes between the flat areas and the mountain tops. As the concept of the global watch stations requires that the observations are performed in "undisturbed" conditions of the free atmosphere, so that the data represent the state of the free atmosphere, it is important to know, if and when the measurements are influenced by transport of air pollutants from the surface. Here the results from an ongoing project will be presented which aims to analyse the development, as a function of time and space, of the valley wind system and the boundary layer in the area of Elqui valley, and to describe the transport and dispersion of air masses from the Elqui valley to the global watch station at the Cerro Tololo. Additionally it should be studied under which conditions the measurements of the global watch station at the Cerro Tololo are influenced by polluted air from La Serena/Coquimbo and the agricultural areas of the river Elqui. The results include calculations with the Karlsruher mesoscale model KAMM as well as obser-vations performed at different sites in the Elqui valley.