Benzene and Toluene in the surface air of North Eurasia fromTROICA-12 campaign along the Trans-Siberian railway

Abstract. Volatile organic compounds (VOCs) were measured by proton transfer reaction – mass spectrometry (PTR-MS) on a mobile laboratory in a transcontinental TROICA-12 (21.07.2008–04.08.2008) campaign along the Trans-Siberian railway from Moscow to Vladivostok. Surface concentrations of benzene (C6H6) and toluene (C7H8) along with non-methane hydrocarbons (NMHCs), CO, O3, SO2, NO, NO2 and meteorology are analyzed in this study to identify the main sources of benzene and toluene along the Trans-Siberian railway. The most measurements in the TROICA-12 campaign were conducted under low-wind/stagnant conditions in moderately (~ 78 % of measurements) to weakly polluted (~ 20 % of measurements) air directly affected by regional anthropogenic sources adjacent to the railroad. Only 2 % of measurements were identified as characteristic of highly polluted urban atmosphere. Maximum values of benzene and toluene during the campaign reached 36.5 ppb and 45.6 ppb, correspondingly, which is significantly less than their one-time maximum permissible concentrations (94 and 159 ppb for benzene and toluene, correspondingly). About 90 % of benzene and 65 % of toluene content is attributed to motor vehicle transport and 10 % and 20 %, correspondingly, provided by the other local and regional-scale sources. The highest average concentrations of benzene and toluene are measured in the industrial regions of the European Russia (up to 0.3 and 0.4 ppb for benzene and toluene, correspondingly) and south Siberia (up to 0.2 and 0.4 ppb for benzene and toluene, correspondingly). Total contribution of benzene and toluene to photochemical ozone production along the Trans-Siberian railway is about 16 % compared to the most abundant biogenic VOC – isoprene. This contribution, however, is found to be substantially higher (up to 60–70 %) in urbanized areas along the railroad suggesting important role of anthropogenic pollutant sources in regional ozone photochemistry and air quality.