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.

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.

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Ground-based levels of important biogenic volatile organic compounds (BVOCs), isoprene and monoterpenes, as well as NO x and O 3 measured simultaneously along the Trans-Siberian railway on a mobile railway laboratory in TROICA-12 campaign in summer 2008 are analyzed. It was shown that the highest isoprene (≥2.5 ppb) concentration was observed in the daytime in the Far East region where several favorable factors for its emissions occurred: a large amount of deciduous forests, high temperatures (>28°C) and light conditions. Maximum levels of monoterpenes (up to 3-9 ppb) along the Trans-Siberian railway were observed during the nighttime in the Ural region and in Central Siberia where coniferous vegetation is located. To evaluate the relative importance of isoprene and monoterpenes in ground-level ozone formation in Russian cities along the Trans-Siberian railway, where high NO x concentration leads to tropospheric ozone generation, daytime ozone-forming potential (OFP) was calculated. The chemical losses of the studied BVOCs during their transport from sources to the measurement point were taken into account. Calculated OFPs due to isoprene (OFP iso) and monoterpenes (OFP mono) along the Trans-Siberian railway are in average 15±13 and 18±25 ppbv of ozone, respectively. The highest OFP iso (up to 40 ppbv) were estimated in Central Siberia and in the Far East. OFPmono was the highest in the regions of coniferous vegetation, Ural and Central Siberia, and reached 80 ppbv. In the most cities along the Trans-Siberian railway, where high NO x concentration (10-20 ppbv) along with high daytime temperatures (>25°C) were observed, monoterpenes made a main contribution to tropospheric ozone formation. Only in the Far East cities, where the largest deciduous vegetation area of the Trans-Siberian railway is located, isoprene played the main role in tropospheric ozone generation. It was also noted that OFP iso increases with the population-size of the cities. It can be either due to the greater proportion of deciduous vegetation in the large cities along the Trans-Siberian railway or due to the impact of anthropogenic isoprene source. OFP mono was the lowest in the medium cities and the highest in the small ones.

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