Monoaromatic hydrocarbon emissions in Paris

Abstract

For over three years, daily measurements of concentrations of monoaromatic hydrocarbons (MAH) in the Paris air have been taken by the Laboratoire Central de la Prefecture de Police. Seven MAH were measured benzene, toluene, ethylbenzene, meta- and para-xylenes, ortho-xylene and l,2,4-trimethylbenzene. MAH were trapped through active charcoal tubes, desorbed with carbon disulfide and analysed using gas chromatography. Measurements were carried out on two sites exposed to road traffic a narrow street under average traffic conditions and a busy junction. A measurement campaign was also conducted in a road tunnel. Annual average concentrations of benzene amounted to 11.1 µg m³ in 1994 and 10.6 µg m³ in 1995 for the street site. These values reached 31 µg m³ in 1994 and 29.8 µg m³ in 1995 for the junction site. Toluene, which is the most significant compound, showed annual average values of 39.9 µg m³ in 1994 and 40.6 µg m³ in 1995 for the Street site, and 103 µg m³ in 1994 and 103.4 µg m³ in 1995 for the junction site. In a road tunnel, an underground car park or a filling station, daily average values recorded range from 88 mg m 3 to 121 µg m³ for benzene and 306 µg m³ to 534 µg m³ for toluene. MAH concentration changes in the ambient air were calculated for both sites from tendency curves over the whole measurement period. These changes seem to differ as a function of the compounds studied. Correlation factors between MAH concentrations and those of other pollutants were calculated, and traffic impact was studied for the Street site. The influence of weather factors seems to be dominant for these pollutants, and traffic changes are not solely responsible for MAH concentration variations in the ambient air.