[1] The impact of wildfires on surface air composition over central Siberia is investigated based on near-surface carbon monoxide (CO) measurements conducted at Zotino Tall Tower Observatory (ZOTTO), a remote station in the center of Siberia, during 2007 and 2008 warm seasons. Seasonal variations of intensity and spatial distribution of wildfires in south of western and eastern Siberia are found to be important factors contributing a substantial part of synoptic and year-to-year variability of background CO levels in the region. Based on the MODIS area burned product, the estimate of the total yearly CO emitted from wildfires in the regions potentially affecting the measurement site (

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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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. Boreal forest fires are currently recognized as a significant factor in climate change and air quality problems. Although emissions of biomass burning products are widely measured in many regions, there is still lack of information on the composition of wildfire emissions in Siberia, a region known for its severe wildfire activity. Emission ratios (ERs) are important characteristics of wildfire emissions as they may be used to calculate the mass of species emitted into the atmosphere due to combustion of a known mass of biomass fuel. We analyze observations of carbon dioxide (CO 2 ), carbon monoxide (CO), methane (CH 4 ), total nonmethane hydrocarbons (NMHCs), nitrogen oxides NO x (= NO + NO 2 ), particulate matter (PM 3 ), and black carbon (BC) within two forest fire plume transects made by the moving railway observatory during TRanscontinental Observations Into the Chemistry of the Atmosphere (TROICA) expeditions. Slopes in linear regressions of excess levels of the pollutants are used to obtain ER CO / CO 2 = 10-15 %, ER CH 4 / CO = 8-10 %, ER NMHC / CO = 0.11-0.21 % ppmC ppmC −1 , ER NO x / CO = 1.5-3.0 ppb ppm −1 , ER PM 3 / CO = 320-385 ng m −3 µg m −3 −1 , and ER BC / CO = 6.1-6.3 µg m −3 ppm −1 , which fall within the range of uncertainty of the previous estimates, being at the higher edge for ER CH 4 / CO , ER NMHC / CO , and ER PM 3 / CO and at the lower edge for ER NO x / CO . The relative uncertainties comprise 5-15 % of the estimated ER CH 4 / CO , ER NMHC / CO , and ER PM / CO and 10-20 % of ER NO x / CO , ER CO / CO 2 , and ER BC / CO . The uncertainties are lower than in many other similar studies and associated mainly with natural variability of wildfire emissions.