Quasi-continuous measurements of non-methane hydrocarbons (NMHC) in the Greater Athens area during medcaphot-trace

During the comprehensive field campaign MECAPHOT-TRACE (20 August to 20 September 1994) quasi-continuous measurements of NMHC in the range of C4–C12 were carried out for the first time in the Greater Athens area simultaneously at two sites, by means of on-line gas-chromatographic methods. The results show a heavy load of hydrocarbons in ambient air, especially during stagnant weather conditions that favour the development of land–sea-breeze circulations. Overall the urban hydrocarbon mix reflects the emission of traffic. This influence is confirmed through correlation analyses of hydrocarbon ratios, especially aromatic compound ratios, and their dependence on both wind direction and wind velocity at a suburban receptor site. The ethylbenzene/m-xylene-ratio turned out to be a good indicator for the impact of anthropogenically related hydrocarbon chemistry leading to the formation of secondary pollutants. Episodes will be discussed that elucidate the importance of hydrocarbons in the course of ozone formation.