OZONE FORMATION IN THE GREATER CAIRO AREA

Ozone formation in the greater Cairo area was studied in 1990 in a 3-w eek measurement period performed at three sites (Shoubra El-Kheima, Mo kattam Hill, Helwan), covering a north-south direction of 27 km, and i n 1991, from the beginning of April until the end of October, by measu rement of the seasonal variation of ozone at one site at El-Kobba. The sinusoidal shape in the diurnal volume fraction plots with peak value s of 120 ppb and daily mean value of 50 ppb throughout the year indica te a substantial contribution of photochemistry to the ozone content o f the atmosphere. Ozone is produced predominantly over the industrial area in the north and in the centre of Cairo and transported southward by the prevailing northerly winds. Contrary to many urban areas in Eu rope and in North America, fairly high average ozone levels of 40 ppb are observed during the night throughout the spring and the summer. Th is may imply that health hazards and crop damage are higher in the gre ater Cairo area than in Central Europe.