I. B. Belikov

Gaseous admixtures in the atmosphere over Moscow during the 2010 summer

In the summer of 2010, the Moscow megacity during two months was within the zone of action of a blocking anticyclone. The accumulation of pollutants in a closed air mass sharply changed the surface air quality. At the end of July-the first half of August, the extreme situation became even more complicated, because the air from regions of turf and grass fires came into Moscow. According to measurement data of the Moscow IAP RAS station, the maximal hourly mean concentrations of chemically active gases NO, NO2, CO, O3, and SO2 were 175.9, 217.4, 15.8, 134.2, and 15.2 ppb, respectively. For NO2 and CO, these values are largest over the entire decadal period of observations at the station and many times exceed the MPC level (see table). The concentrations of greenhouse gases CO2, CH4, and nonmethane hydrocarbons also sharply increased. Analysis of the variability of gas contents in the surface air and in the atmospheric boundary layer showed a close relation between extreme changes in the atmospheric composition and its vertical stratification.

Variability of Trace Gases in the Atmospheric Surface Layer from Observations in the City of Moscow

The results of continuous minute measurements of the surface concentrations of ozone, nitric oxide, nitrogen dioxide, carbon monoxide, and sulfur dioxide during the 2002–2004 period at the environmental station of the Oboukhov Institute of Atmospheric Physics, Russian Academy of Sciences (IAP), and the Faculty of Geography, Moscow State University (MSU), are discussed. It is shown that the conditions of Moscow’s southwestern region remote from large local pollution sources reflect the general regularities of the variability of trace gases in an urban atmosphere. This is manifested in the mean annual value of the ratio NO/NO2 (a little less than 1), decreased daylight values of O3, increased values of the rest of the trace gases as compared to the background region, and the presence of a secondary nocturnal maximum in the diurnal cycle of O3. The features of the annual and diurnal cycles of the concentrations of the substances under analysis are discussed. In the diurnal cycle of the primary products of combustion (NO and CO), an excess of the morning maximum (over the evening one) is observed during both warm and transition periods and higher values of the night maximum (as compared to the daylight one) are noted for summer. The temperature stratification properties determined from the MSU long-term acoustic sounding data serve as a possible cause for both of the effects revealed. The annual cycle of the concentration of surface ozone is characterized by the highest values for spring and summer. The annual cycles of NO, NO2, CO, and SO2 do not demonstrate any obvious seasonal regularities. A significant seasonal variation of the ratio NO/NO2, which is associated with the oxidizing properties of the urban atmosphere, is revealed. The record high concentrations of trace gases in the atmosphere over Moscow are given, and the meteorological conditions for their accumulation are discussed.

Gas composition of the surface air in Moscow during the extreme summer of 2010

In summer 2010, anomalously hot weather occurred in the European part of Russia. It was caused by a blocking anticyclone of an unusually high intensity. West winds were stopped in the whole column of the troposphere, from the Earths surface up to the lower stratosphere, for two months. During this entire period, the concentration of gaseous and aerosol pol� lutants grew in the nearsurface air. In the end of July and the first half of August, this extreme situation become even more complicated due to the arrival of air masses from the areas of forest, peat, and grass fires to Moscow. By the measurements data from the station of the Institute of Physics of the Atmosphere, Russian Academy of Sciences (IPA RAS), the concentrations of reactive gases NO, NO 2 , CO, and O 3 exceeded both the average daily and the general maximum permissi� ble concentration (MPC). The concentrations of greenhouse gases CO2, CH4, and other hydrocarbons were also excessive. Analysis of variation in gas content in the nearsurface air and in the atmospheric bound� ary layer has shown a close dependence on vertical stratification of the atmosphere. The blocking anticyclone above the European part of Russia recorded in summer 2010 significantly exceeded all the previously recorded ones in its dura� tion. According to (1), the duration of summer block� ing anticyclones in the Northern and Southern Hemi� spheres has not exceeded three weeks for the last forty years, while the longest periods of anticyclonic weather in winter have not lasted more than a month. Anomalies in the frequency and intensity of atmo� spheric blockings were recorded most often in the years of El Nino/La Nina phenomenon, including 2010 (see, for instance, (2)). The formed hot weather lead to the outbreak of numerous forest and peat wildfires. In total, 29 000 wild� fires were recorded in summer 2010 with a total burned area of 1.2 million ha (3). And though the wildfire intensity in 2010 was weaker than in some other years (e.g., 40 000 wildfires with a total burned area of about 1.5 million ha were recorded in 1972; 28 000 wildfires of 4.2 million ha, in 1998; 29 000 wildfires of 2.4 mil� lion ha, in 2009), the economic, ecological, and social consequences were more significant. The most important consequence of the emer� gency situation that appeared in summer 2010 was change in the chemical composition of the atmo� sphere above the European territory of Russia and West Siberia. Cities and settlements were covered with a dense haze when they happened to be in smoke trails of forest and peat wildfires. The presence of obviously extreme quantities of aerosols in the nearsurface air caused extreme concern and a demand for introduc� tion of required protective activities (3). No less nega� tive an effect on peoples health and ecosystems was made by a significant change in gas composition of the atmosphere.

Temporal variations in carbon dioxide and methane concentrations under urban conditions

Temporal variations in the surface concentrations of two greenhouse gases (carbon dioxide and methane) in the atmosphere over a large city are studied on the basis of the data obtained during the 2003–2005 observations at a Moscow station for environmental monitoring. This station is based on the TROICA mobile observatory and located at the meteorological station of the Faculty of Geography, Moscow State University, on Vorob’evy gory. The methods of isolating the background concentrations of greenhouse gases under urban conditions are proposed, and the excess concentrations of CO2 and CH4 over their background values are estimated for different seasons and times of day. The CO2 and CH4 concentrations are shown to have more pronounced diurnal cycles in summer than in winter. The main causes of temporal variations in the surface concentrations of CO2 and CH4 under urban conditions and the differences between the mean concentrations of these greenhouse gases in Moscow and other areas of Russia are analyzed. It is shown that variations in the surface concentrations of carbon dioxide and methane on different time scales are caused by different atmospheric processes (global circulation, mesoscale gravity waves, surface temperature inversions, etc.)

Ozone and nitric oxides in the surface air over northern Eurasia according to observational data obtained in TROICA experiments

The results of the 1995–2008 observations of the concentrations of ozone and nitric oxides in the surface air over the Trans-Siberian Railway using a mobile laboratory (the TROICA experiments) are analyzed. The features of the spatial distribution and time variability of these gases over the continent within the latitudinal belt 48°–58° N are revealed individually for polluted and background conditions. The characteristic features of their distribution are a decrease in the concentration of nitric oxides and an increase in the concentration of ozone in an eastward direction. On the whole, the process of photochemical ozone formation over the territory of Siberia is slow. Noticeable increases in the concentration of ozone are associated with both forest and steppe fires and with the transboundary transport of pollution from the countries of eastern Asia. The dry precipitation of trace gases plays a significantly larger role in Siberia than in coastal and high-altitude unpolluted regions due to powerful and long temperature inversions.

On contents of trace gases in the atmospheric surface layer over Moscow

The results of the 2002–2012 continuous once-a-minute measurements of the composition of the surface air over Moscow, which were taken at the joint ecological station of the Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences, and the Geographic Faculty of Moscow State University, are discussed. It is shown that the annual increase (on the order of 1%) in the content of surface ozone is stable and the decrease in the content of nitric oxide is statistically significant, while the content of nitric dioxide remains almost unchanged. Reliable regularities in both diurnal and annual variations in the contents of the five trace gases O3, NO, NO2, CO, and SO2 have been studied in detail. Statistical relations of the content of sulfur dioxide with the amount of reserve fuel (black oil) used in city heating (this relation is the strongest one), wind velocity in an atmospheric layer up to a height of 200 m, and air temperature have been analyzed. The influence that wind velocity has on the surface contents of trace gases and carbon dioxide has been studied for the first time on the basis of long-term ‘MODOS’ sodar data. It is shown that, with an increase in wind velocity, the contents of nitric and carbon oxides generally decrease, the content of ozone increases, and the content of sulfur dioxide decreases starting from an intermediate value of 1–2 m/s due to the prevalence of high sources of this gas. An additional maximum found in the content of carbon dioxide at high wind velocities may be associated with the long-range transport of CO2.

Estimation of biogenic CH4 and CO2 emissions and dry deposition of O3 using 222Rn measurements in TROICA expeditions

On the basis of simultaneous measurements of surface concentrations of CH4, CO2, O3, and 222Rn during 6 TROICA (TRanscontinental Observations Into the Chemistry of the Atmosphere) expeditions along the Trans-Siberian Railway from Moscow to Vladivostok in 1999–2008, we have estimated the biogenic emissions of CH4 and CO2 from terrestrial ecosystems and the nighttime sink of O3 on the underlying surface from data on the accumulation rate of 222Rn under conditions of near-surface temperature inversion. The regional emissions of CH4 were the highest in summer in the Far East (0.87 ± 0.52 μg m−2 s−1) and in West Siberia (0.77 ± 0.41 μg m−2 s−1), which is associated with significant methane flows from wetlands and moist soils that are typical for these regions. The biogenic emissions of CO2 vary on average from 0.18 ± 0.04 μg m−2 s−1 in West Siberia to 0.89 ± 0.07 μg m−2 s−1 in East Siberia. The nighttime sink of O3 has a seasonal maximum in summer and varies from 0.05 ± 0.01 μg m−2 s−1 in West Siberia to 0.07 ± 0.01 μg m−2 s−1 in Central Siberia; the dry deposition rate of O3 varies from 0.10 ± 0.08 cm s−1 in West Siberia to 0.33 ± 0.21 cm s−1 in East Siberia and the Far East.

EVIDENCE OF ATMOSPHERIC RESPONSE TO METHANE EMISSIONS FROM THE EAST SIBERIAN ARCTIC SHELF

Average atmospheric methane concentration (CH 4 ) in the Arctic is generally higher than in other regions of the globe. Due to the lack of observations in the Arctic there is a deficiency of robust information about sources of the methane emissions. Measured concentrations of methane and its isotopic composition in ambient air can be used to discriminate sources of CH 4 . Here we present the results of measurements of the atmospheric methane concentration and its isotope composition (δ 13 C CH4 ) in the East Siberian Arctic Seas during the cruise in the autumn 2016. Local sections where the concentration of methane in the near-water layer of the atmosphere reaches 3.6 ppm are identified. The measurements indicated possibility of formation of high methane peaks in atmospheric surface air above the East Siberian Arctic Shelf (ESAS) where methane release from the bottom sediments has been assumed.

Variations in PM2.5 Surface Concentration in Moscow according to Observations at MSU Meteorological Observatory

We considered Moscow-specific features of time variations in PM2.5 mass concentration in the surface air layer as a function of a number of atmospheric parameters such as the concentrations of certain atmospheric trace gases, aerosol optical depth, surface air temperature, humidity, and wind speed. The time series of concentrations of PM2.5 and gaseous pollutants SO2, NH3, NOx, CO, and O3, obtained during continuous observations in 2011–2013, were analyzed. We studied the diurnal and seasonal variations in concentrations of PM2.5 and the trace gases, revealed correlations between them, analyzed variations in PM2.5 concentration as a function of concentration of certain gases participating in the formation of atmospheric aerosols, and as a function of meteorological parameters. Data on PM2.5 surface concentrations are compared with measurements of aerosol optical depth.

Aromatic volatile organic compounds and their role in ground-level ozone formation in Russia

This paper reports proton mass spectrometry data on aromatic volatile organic compounds (VOCs) (benzene, toluene, phenol, styrene, xylene, and propylbenzene) obtained in different Russian regions along the Trans-Siberian Railway from Moscow to Vladivostok, based on expedition data retrieved using the TRO-ICA-12 mobile laboratory in the summer of 2008. The contribution of aromatic VOCs to ozone formation in the cities and regions along the measurement route has been estimated quantitatively. The greatest contribution of aromatic VOCs to ozone formation is characteristic of large cities along the Trans-Siberian Railway (up to 7.5 ppbv O3) specified by the highest concentrations of aromatic VOCs (1–1.7 ppbv) and nitrogen oxides (>20 ppbv). The results obtained are indicative of a considerable contribution (30–50%) of anthropogenic emissions of VOCs to photochemical ozone generation in the large cities along the Trans-Siberian Railway in hot and dry weather against the background of a powerful natural factor such as isoprene emissions controlling the regional balance of ground-level ozone in warm seasons.