Ten years trends of the urban air pollution in Thessaloniki. Part II. The secondary pollutants

The temporal trends of the secondary air pollutants NO2 (nitrogen dioxide) and O-3 (ozone) in the urban area of Thessaloniki (Greece) and their spatia l distribution are examined statistically. The decreasing trend of primary air pollutants during the decade 1988-97 is not observed in the case of pho tochemical pollutants (NO2 and O-3) The improvement of fuel quality, the te chnological innovations in industry and the recent considerable renewal of the vehicle fleet did not Influence similarly the trend of secondary pollut ants. The photochemical pollutant temporal evolution in the areas with high traffic shows that the increasing vehicle fleet (mainly the fleet of the n ew technology passenger cars) is a determinant factor for their levels.