Benzene and toluene levels measured with a commercial DOAS system in Thessaloniki, Greece

Benzene, toluene and p-xylene were measured above the buildings level in Thessaloniki, Greece for around eight months during the period December 1993-August 1994 by means of a commercial differential optical absorption spectrometer (OPSIS DOAS). Daily mean mixing ratios for benzene and toluene varied between 1-6 and 1-32 ppb, respectively. The data indicate that the annual mean benzene concentrations most probably lie in the range 2-3 ppb, which is below the guide values but above the target values of European countries that have set limits for benzene. Mean diurnal variations of benzene and toluene during summer and winter months reflect the effects of emission, photochemical degradation and mixing. Benzene and toluene hourly values correlated well with each other and with NO2. Toluene and benzene hourly values were negatively correlated with ozone during summertime. During wintertime, considerable enhancements of benzene and toluene mixing ratios might be associated with the passage of synoptic weather systems of fair weather. Although the measurement of p-xylene is, in principle, efficiently performed with the DOAS technique, the OPSIS instrument p-xylene measurements contradict current understanding of its sources and sinks and are thus attributed to errors of the instrument in the evaluation of this substance. (C) 2000 Elsevier Science Ltd. All rights reserved.