Abstract. The isotopic composition of carbon monoxide (•3C,
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 July-4 August 2008) campaign along the TransSiberian Railway from Moscow to Vladivostok. Surface concentrations of benzene (C 6 H 6 ) and toluene (C 7 H 8 ) along with non-methane hydrocarbons (NMHCs), CO, O 3 , SO 2 , NO, NO 2 and meteorology are analyzed in this study to identify the main sources of benzene and toluene along the TransSiberian 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 railway. 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 and 45.6 ppb, respectively, which is significantly less than their short-term exposure limits (94 and 159 ppb for benzene and toluene, respectively). About 90 % of benzene and 65 % of toluene content is attributed to motor vehicle transport and 10 and 20 %, respectively, 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, respectively) and south Siberia (up to 0.2 and 0.4 ppb for benzene and toluene, respectively). Total contribution of benzene and toluene to photochemical ozone production along the Trans-Siberian Railway is about 16 % compared to the most abundant organic VOC -isoprene. This contribution, however, is found to be substantially higher (up to 60-70 %) in urbanized areas along the railway, suggesting an important role of anthropogenic pollutant sources in regional ozone photochemistry and air quality.
[1] The chemical composition of the surface boundary layer over the Eurasian continent is still an area of high uncertainty. In the framework of the Trans-Siberian Observations Into the Chemistry of the Atmosphere (TROICA) project, measurements of O 3 , NO, NO 2 , CO, CO 2 , CH 4 , 222 Rn, J(NO 2 ), and black carbon aerosol were carried out on the TransSiberian railroad during June-July 1999. Boundary layer data over more than 16,000 km, from Kirov ($58°N, 49°E; 972 km east of Moscow) to Khabarovsk ($48°N, 135°E) and back to Moscow, were obtained without significant contamination, emphasizing the potential of using the Trans-Siberian railroad system for atmospheric measurements. The 222 Rn and CO 2 concentrations were determined for the first time using our laboratory wagon. The diurnal variations of these gases and of CH 4 due to micrometeorological conditions, as well as their dependence on various soil sources and vegetation types, were used to estimate ecosystem fluxes of CO 2 and CH 4 . The highest soil flux of CH 4 was 70 ± 35 m mol m À2 h À1 for the wet habitats of the West Siberian lowlands, and the lowest CH 4 flux was 3.2 ± 1.6 m mol m À2 h À1 for drier habitats of eastern Siberia. Although the wet tundra emissions found between 67°and 77°N are higher than in comparable environments at much lower latitudes [Christensen et al., 1995], boreal wetlands in Siberia at 50°-60°N represent a very important player in the global methane budget. The CO 2 density fluxes exhibited the opposite to CH 4 fluxes tendency. Ozone mixing ratios varied from a few nmol/mol during nighttime inversions to more than 60 nmol/mol during the day. These values were generally higher than during the 1996 summer campaign (TROICA 2). CH 4 and CO levels followed the pattern observed during TROICA 2; elevated levels of CH 4 with a mean mixing ratio of 1.97 ± 0.009 mmol/mol were found over the West Siberian lowlands, decreasing to 1.88 ± 0.13 mmol/mol toward East Siberia. Conversely, while background CO levels of the West Siberian wetlands were generally below 140 nmol/mol, high CO concentrations, once even exceeding 2 mmol/mol, were registered east of Chita ($52°N, 113°E), as a consequence of forest and other vegetation fires, which significantly affect the chemical composition of the air over parts of Russia.
Volatile organic compounds (VOCs), ozone (O3), nitrogen oxides (NOx), carbon monoxide (CO), meteorological parameters, and total non-methane hydrocarbons (NMHC) were analyzed from simultaneous measurements at the MSU-IAP (Moscow State University—Institute of Atmospheric Physics) observational site in Moscow from 2011–2013. Seasonal and diurnal variability of the compounds was studied. The highest O3 concentration in Moscow was observed in the summer daytime periods in anticyclonic meteorological conditions under poor ventilation of the atmospheric boundary layer and high temperatures (up to 105 ppbv or 210 μg/m3). In contrast, NOx, CO, and benzene decreased from 8 a.m. to 5–6 p.m. local time (LT). The high positive correlation of daytime O3 with secondary VOCs affirmed an important role of photochemical O3 production in Moscow during the summers of 2011–2013. The summertime average concentrations of the biogenic VOCs isoprene and monoterpenes were observed to be 0.73 ppbv and 0.53 ppbv, respectively. The principal source of anthropogenic VOCs in Moscow was established to be local vehicle emissions. Yet, only about 5% of the observed isoprene was safely attributed to anthropogenic sources, suggesting significant contribution of biogenic sources into the total levels of ozone precursors. The non-linear O3–NOx dependence shows a decrease in ground-level O3 with an increase in NOx during the summers of 2011–2013, which is typical for the VOC-sensitive photochemical regime of O3 formation. Nevertheless, during the elevated ozone episodes in July 2011, the photochemical regime of ozone production was either transitional or NOx-sensitive. Contribution of various anthropogenic and biogenic VOCs into the measured ozone values was evaluated. The ozone-forming potential (OFP) of total VOCs was 31–67 μg/m3 on average and exceeded 100 μg/m3 in the top 10% of high ozone events, reaching 136 μg/m3. Acetaldehyde, 1.3-butadiene, and isoprene have the highest ozone production potential in Moscow compared to that of other measured VOCs.
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