Photochemical air pollution characteristics at the station of the NCSR-Demokritos, during the MEDCAPHOT-TRACE campaign in Athens, Greece (20 August–20 September 1994)

Abstract

In this paper the continuous meteorological and air pollution measurements collected at the station of the NCSR-Demokritos during the MEDCAPHOT-TRACE campaign (20 August–20 September 1994) are presented and discussed. The station site is located about 10 km east from the center of Athens at 280 m altitude. The air pollution species measured were O 3, NO, NO 2 and SO 2 while the meteorological parameters were recorded on a 84 m high meteorological mast. Ozone values up to 180 ppb have been measured during pollution episodes. The maximum hourly average ozone mixing ratio from the western sector (urban) is about 50 ppb higher than the corresponding value of the NE sector (rural). At the same time the average ozone rate of increase during the morning hours was about 20 ppb h -1 and the typical wind speeds from 3 to 4 m s -1. The creation of this excess ozone amount is mainly attributed to the daily photochemistry. In the air masses coming from all wind directions comparable nighttime levels of O x (NO 2+O 3) around 65 ppb are observed while the ozone and nitrogen dioxide values are clearly anticorrelated. The observed mixing ratios coming from the NE rural sector vary between 50 and 80 ppb and they are almost indifferent of the wind speed. For wind speeds higher than 7 m s -1 the average ozone value was 68±7 ppb (1.8 ppb for nitrogen dioxide). Such ozone levels despite the altitude of our station (280 m above sea level) are considered as high rural concentrations, if they are compared with similar values in Central Europe.