ISSN 00014338, Izvestiya, Atmospheric and Oceanic Physics, 2011, Vol. 47, No. 6, pp. 672–681. © Pleiades Publishing, Ltd., 2011. Original Russian Text © N.F. Elansky, I.I. Mokhov, I.B. Belikov, E.V. Berezina, A.S. Elokhov, V.A. Ivanov, N.V. Pankratova, O.V. Postylyakov, A.N. Safronov, A.I. Skorokhod, R.A. Shumskii, 2011, published in Izvestiya AN. Fizika Atmosfery i Okeana, 2011, Vol. 47, No. 6, pp. 729–738.
Gaseous Admixtures in the Atmosphere over Moscow during the 2010 Summer N. F. Elansky, I. I. Mokhov, I. B. Belikov, E. V. Berezina, A. S. Elokhov, V. A. Ivanov, N. V. Pankratova, O. V. Postylyakov, A. N. Safronov, A. I. Skorokhod, and R. A. Shumskii Oboukhov Institute of Atmospheric Physics, Russian Academy of Sciences, Pyzhevskii per. 3, Moscow, 119017 Russia email:
[email protected] Received May 24, 2011; in final form, May 31, 2011
Abstract—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 stratifica tion. Keywords: atmospheric ozone, atmospheric composition, gaseous admixtures, air quality, chemistry of the atmosphere, urban ecology. DOI: 10.1134/S000143381106003X
INTRODUCTION During the summer of 2010, there was anoma lously hot weather in European Russia (ER). This heat was caused by a blocking anticyclone of an unusually high intensity. For two months the anticyclone blocked the way for westerly winds in the tropospheric layer from the earth’s surface to the lower stratosphere. In its duration, the blocking anticyclone, which was formed over ER, far exceeded those observed previ ously. According to [1], the duration of summer block ing anticyclones during the past four decades in the Northern and Southern hemispheres did not exceed three weeks, and the most prolonged winter periods of anticyclonic weather lasted for no more than one month. Anomalies in the frequency and intensity of atmospheric blockings were most frequently noted in the years of for mation of the El Niño/La Niña phenomena, one of which was 2010 (see, for example, [2]). The settled hot weather led to multiple forest and turf fires. Altogether, 33 000 fires were recorded during the summer of 2010, and the area encompassed by them was 108 000 km2 [3, 4]. Although the number of fires in 2010 was smaller than in some other years due to their small number to the east of the Urals, the area of fires was maximal over the entire period of observa tions. For example, in 1972, when Moscow was in a similar situation with 2month heat, 40000 fires were
noted and the area encompassed by them was only about 15 000 km2. Economical, ecological, and social consequences were also very perceptible. The fires encompassed the most densely populated parts of ER. Here they began in the first decade of July and ended mainly at the end of August. The number of fires in ER reached 13600 and their area was 22000 km2 [3]. The maximal spreading of fires in ER took place on July 28–29, 2010. According to our calculations with the use of the MODIS data and the methods described in [6, 7], in these days the fire encompassed 1500 km2 of coniferous forests, 630 km2 of mixed forests, 550 km2 of meadows with rarefied bush, 100 km2 of agricultural lands, and about 30 km2 of peatbogs. In these days the total area of fires in ER was 3000 km2. Forest and steppe fires also occurred in the Urals and western Siberia, and smoky trails from them extended to ER in the system of anticyclonic circulations (Fig. 1). Changes in the atmospheric composition were the most important consequence of the extraordinary ecological situation settled during the summer of 2010. Cities, towns, and populated areas were encom passed by dense haze or mist when smoky trails of for est and turf fires reached them. The presence of an obviously extreme amount of aerosols in the surface air caused great anxiety and favored the introduction of necessary measures for protection [3]. Changes in
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the gaseous composition of the atmosphere that were substantial but invisible to the naked eye had a less conspicuous but no less adverse impact on human health and the ecosystem. The unique situation of the summer of 2010 heavily affected the surface air composition in the Moscow megacity. Under conditions of a recordbreaking air temperature for Moscow, the evaporation of fuels, lubricants, paints, lacquers, and other substances increased. Products from burning grass, wood, turf, and multiple dumping grounds were supplied into the urban atmosphere for a long time with southerly and easterly winds. The blocking anticyclone produced favorable conditions for the accumulation of admix tures in the surface air and the intensification of their chemical transformation. The sharp deterioration of the air quality had multiple consequences, the most adverse of them being the worsening of the health of the inhabitants of Moscow and an increase in mortal ity in July 2010 by more than 50% when compared with the same month in other years [3]. Such an IZVESTIYA, ATMOSPHERIC AND OCEANIC PHYSICS
anomalous ecological situation calls for extensive investigations. This work presents the results of observations of concentrations of chemically active gaseous constitu ents of the urban air which were conducted in the sum mer of 2010 at the ecological stations of the Institute of Atmospheric Physics, Russian Academy of Sciences (IAP RAS), located southwest of Moscow at Vorob’evy gory on the territory of Moscow State Uni versity (MSU) (55.707° N, 37.523° E) and in the city center at the open site of the IAP RAS building. CONDITIONS OF OBSERVATIONS The Moscow megacity was in the zone of action of the blocking anticyclone from June 18 through August 18, 2010. Dry hot weather continued in all these days (Fig. 2). The city was in the zone of influence of cold fronts of Atlantic cyclones (which caused insignificant shortterm temperature decreases) only three times over this period. July 2010 was the hottest month in the Vol. 47
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history of Moscow. The monthly mean temperature was 26.4°С, which exceeds the monthly mean temper ature over the entire period of meteorological observa tions by 7.8°. The recordbreaking temperature of 38.2°С was determined in Moscow on July 29. The amount of precipitation in this month in Moscow was 12 mm (13% of the norm). Rains took place on July 8, 9, and 25. Smoke from forest and turf fires near the earth’s surface began to be felt in the third decade of July (Fig. 2). Judging from backward trajectories, bio mass burning products appeared at heights of 1.0– 1.5 km as early as July 16–19. In the first half of August, the maximal daytime temperature was at the level 30°–36°. The only rain took place on August 1. Aerosol haze was observed most of the time. Smog came in from August 6 to August 10. The range of visibility in the city dropped to 200 m and, in the north of the Moscow, to 100 m (on August 7–8). During daytime hours, the wind was weak and had southward and southeastward direc tions. At night, the wind velocity dropped to zero. Powerful and prolonged nearsurface temperature inversions, which are noncharacteristic of Moscow, were noted within the city. In the middle of August, the blocking anticyclone began to weaken and retreat to the southeast. August 18 was the last hot day when the air temperature exceeded 33°C. On August 19, the atmospheric front passed over Moscow, and the dry continental air mass changed to a moist air mass from the Atlantic. The maximal temperature dropped by 7°C. The synoptic situation radically changed on August 20, when the secondary active atmospheric front, accompanied by rains and a further decrease in temperature, passed through Moscow.
If, under anticyclonic conditions, nighttime tem perature inversions are usually destroyed within 2–3 h after sunrise in the summer in Moscow, under condi tions of smoke the atmosphere was highly stable throughout nearly the entire first half of the day, when the traffic intensity was at a maximum. Low wind velocities and the displacement of convective mixing to the second half of the day sharply enhanced the accumulation of pollutants in the air basin of the city. At the IAP RAS station, the concentrations of minor admixtures O3, CO, CO2, CH4, NO, NO2, SO2, NH3, and 222Rn and volatile organic compounds (15– 20 substances), as well as the integral contents of non methane hydrocarbons and aerosols, in the surface air layer have been measured since February 2002. All of the measurement instruments are included into the system of Global Atmosphere Watch of the World Meteorological Organization (GAW WMO). The instruments possess a high sensitivity sufficient for measuring small background concentrations, as well as high stability. All of the instruments are regularly calibrated: the gas analyzer of ozone is calibrated against the mobile standard ENV 0341M no. 1298 and the national standard SRP no. 38; the other instruments are calibrated against the standard mix tures of the Mendeleev VNII of Metrology and the NOAA of the United States. The automatic measure ment complex, as well as individual instruments and methods of observations, is described in [11]. Remote measurements of the NO2 integral content (further, NO2 IC) in the atmospheric boundary layer were conducted occasionally in the same years (and since 2010, regularly). In the summer of 2010, the NO2 IC was also observed from the site of the IAP RAS building in the center of the city. An original method was elaborated for measuring the NO2 IC in the vertical column within the atmo spheric boundary layer. The NO2 content on the inclined path of the ray is calculated in the visible region from solar radiation spectra scattered in the zenith [8]. The contribution of the stratosphere is esti mated from the measurements conducted at sunrise and sunset of the same day. Then the NO2 IC in the vertical column within the atmospheric boundary layer is reconstructed from the obtained inclined NO2 content in the troposphere [9, 10]. The NO2 IC is cal culated within the framework of the scenario, accord ing to which the main NO2 mass is concentrated in the troposphere within the atmospheric boundary layer (ABL) [10]. Such a scenario is supported by the absence of significantly increased values of the tropo spheric NO2 content in the summer of 2010 over the Moscow region in the data of the satellite OMI instru ment (see Fig. 6b), although the tropospheric OMI measurements are more sensitive precisely to the pol lution of the free troposphere and underestimate the NO2 content in the surface layer [25]. The total error of the method (the sum of the systematic and random components for a single measurement), including the
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10 0 1 6 11 16 21 26 1 6 11 16 21 26 31 5 10 15 20 25 30 June July August Fig. 3. Hourly mean surface concentrations of gases from observations at the IAP RAS station (Vorob’evy gory) in the summer of 2010. Dotted lines indicate diurnal mean MPC values.
measurement accuracy of the inclined NO2 content, the determination accuracy of the stratospheric NO2 component, and the accuracy of the inverse problem solution, was 15% for the conditions of the summer of 2010. The time of one measurement is 5 min. The NO2 IC was measured at two observational points under both cloudy and cloudless conditions. The error of calculating the NO2 IC difference between the two points is virtually completely controlled by a random component of about 5%. The distance between the observational points is 7.1 km, and the height differ ence is 70 m. The surface concentrations of the gaseous constit uents controlling the air quality (ozone (O3), methane (СН4), oxides of nitrogen (NO and NO2), carbon (CO and СО2), and sulfur (SO2), as well as the integral con tents of nonmethane hydrocarbons (NMHC), were measured continuously with a frequency of 1 min, whereas the NO2 content in the vertical column of the ABL was measured every five minutes during the light of day from 07:00 to 20:00 Moscow Time. IZVESTIYA, ATMOSPHERIC AND OCEANIC PHYSICS
Fig. 4. Weekly cycles of gas concentrations in the surface air from observations at the IAP RAS station (Vorob’evy gory).
GAS CONCENTRATIONS IN THE SURFACE LAYER The hourly mean concentrations of gaseous admixtures obtained from observations in the summer period of 2010 are presented in Fig. 3. As was shown many times previously (see, for example, [12, 13]), under anticyclonic conditions (weak or no wind, pow erful nighttime temperature inversion, and high day time temperature and illuminance), an increased air pollution encompasses the entire air basin of the city. The data of the IAP RAS station obtained under these conditions characterize the state of the urban air medium as a whole. The increase in the concentrations of all measured gaseous admixtures in the period of action of the atmospheric blocking is a characteristic feature of the summer of 2010 in Moscow (Fig. 3). In this case, the main role belonged to the meteorological conditions favoring the accumulation of pollutants in the surface air; increased emissions of substances of anthropo genic origin; and, on the contrary, decreasing biogenic emissions as the drought intensifies (as well as the weakening of the sink on the earth’s surface). The action of forest, steppe, and turf fires was superposed on these processes caused by the influence of the blocking, which sharply changed the surface air com position. Vol. 47
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Inversion duration, h
16:00 12:00 08:00 04:00 00:00 20:00 16:00 28 3 8 13 18 23 28 2 7 12 17 22 27 July August Fig. 5. Times of the formation and destruction of the near surface temperature inversion from remote observations at the IAP RAS station (MTP5 profilometer). Days with dense aerosol haze are marked by hatching.
The estimates of the growth rates of gaseous con centrations in the urban air under the conditions of the blocking anticyclone prior to the arrival of biomass burning products are presented in the table. The larg est values are characteristic of NO2, CO, and SO2 gases, which have predominantly anthropogenic ori gins and lifetimes comparable with the synoptic period (see below). In Moscow, like in other cities, automo bile transport is the main source of these gases. In the summer period, its contribution amounts to about 85% [12, 14]. The industry and communal services give up to 15%. On the other hand, the concentration of anthropogenic NO2 gas virtually did not change. This fact is explained by its high reaction ability and by the high ozone content, whose deficit under usual conditions restricts the oxidation rate of NO and its removal from the atmosphere. The concentration of methane, which is partially of biogenic origin, did not change either. In the hot summer period (a time of holidays), the consumption of natural gas by the city sharply decreased and biological sources became less active due to the drying of soil and bodies of water.
Intermediate values are obtained for CO2 and NMHC. The prolonged drought led to the soil dehy dration and weakened the photosynthesis of plants, which reduced the CO2 consumption by them and the CO2 accumulation in the surface air. On the other hand, due to the disturbance of the respiration of plants, nighttime CO2 emissions became weaker. The action of natural and anthropogenic factors on NMHC takes place in the opposite way. On the one hand, emissions of these admixtures increase due to the increasing evaporation of different substances; however, on the other hand, their soil and vegetation sources become weaker. The increase in the CO and NMHC concentra tions under conditions of a high air temperature and a high solar illuminance sharply intensified the ozone generation. In June–July 2010, in the absence of smoke, the ozone concentration increased by 0.48 ppb per day. The weakening of the wet and dry deposition of ozone made a certain contribution to this process. In particular, the ozone consumption by vegetation noticeably decreased. At the same time, no О3 con centration increase was observed during the working week, which was due to an increase in the concentra tions of NO and NO2 (favoring the ozone destruction) in the air by the end of the week [11, 14]. That is why the О3 accumulation in the period of blocking is asso ciated with its concentration increase in the surface atmospheric layer over ER as a whole. The influence of advection of a cleaner air into Moscow on Sundays distinctly manifests itself in an ozone concentration increase and, on the contrary, in a decrease of pollut ant concentrations (Fig. 4). A sharp drop of air pollu tion on Sundays indicates that the city is well venti lated. Beginning from July 28, 2010, the concentration of pollutants in the surface air of Moscow significantly increased due to the arrival of biomassburning prod ucts. This concentration was largest on August 6–9, when the air was polluted simultaneously by close and remote fires, whereas the city ventilation was weak ened (on August 7 and 8, a calm settled in Moscow).
Maximal hourly and diurnal concentrations of gases in the surface air and their growth rates under the conditions of block ing in the absence of the influence of fires (June 18–July 21, 2010) and during the weekly cycle from Monday to Saturday Admixture O3, ppb NO, ppb NO2, ppb CO, ppm CO2, ppm CH4, ppm NMHC, ppm SO2, ppb
Maximal diurnal values 50.8 84.7 90.4 9.8 492.9 3.1 2.3 4.2
Maximal hourly values 134.2 175.9 214.7 15.8 548.4 3.9 3.2 15.2
MPCdm 16 50 21.7 2.6 – – – 19.2
Growth rates (day–1) over the peri Growth rates during od from June 18 to July 21 the weekly cycle (day–1) 0.48 ± 0.09 0.04 ± 0.12 0.63 ± 0.09 0.010 ± 0.002 0.57 ± 0.20 –0.001 ± 0.002 0.005 ± 0.002 0.04 ± 0.01
–0.08 ± 0.36 3.25 ± 0.93 2.61 ± 0.47 0.043 ± 0.012 2.51 ± 0.52 0.016 ± 0.006 0.021 ± 0.009 0.01 ± 0.05
Note: MPCdm is the diurnal mean gas concentration at T = 30°C. IZVESTIYA, ATMOSPHERIC AND OCEANIC PHYSICS
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Fig. 6. (a) NO2 integral content in the atmospheric boundary layer from observations at the MSU and IAP RAS stations; (b) mean NO2 IC from observations at two points (IAP RAS and MSU) and satellite OMI data; and (c) mixing layer height over Moscow averaged over the period of NO2 observations. The dashed lines in (b) and (c) indicate the values of the NO2 IC and the mixing layer height averaged over 7 days.
The hourly and diurnal mean concentrations of all measured admixtures, which were recordbreaking over the entire time of observations in Moscow, were fixed during these days (table). In particular, the diur nal mean values of О3, CO, and CO2 reached 50.8 ppb, 9.8 ppm, and 492.9 ppm, respectively. Shortterm increases in the concentrations of toxic compounds IZVESTIYA, ATMOSPHERIC AND OCEANIC PHYSICS
О3, СО, and NO2 substantially exceeded not only diurnal mean but also onetime values of their maxi mum permissible concentrations (MPC), which obvi ously affected the health of Moscow inhabitants. A comparison of the data on pollutant concentra tions in the surface air with data on the vertical strati fication of the ABL (the height of its upper boundary Vol. 47
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over Moscow varied during daytime hours from 1.5 to 3.5 km), where an intense daytime mixing takes place, makes it possible to refine the mechanisms of accumu lation of pollutants and their removal from the air basin of the city. Under specific conditions of the blocking anticyclone existence, the nighttime temper ature inversion is formed early (at 21:00–22:00 Mos cow Time) and is destroyed late (at about 09:00–10:00 Moscow Time) (Fig. 5). Therefore, the intense activity of motor transport at the morning peak hours and par tially at the evening time increases the concentrations of nearly all main pollutants in the surface air and leads to their maximal concentrations being reached in the first half of the day. In the presence of dense aerosol haze produced by fires (July 28–29; August 2– 4 and 6–10), the inversion is settled somewhat earlier (at 19:00–20:00) and was destroyed later (at 10:00– 11:00). In other words, the inversion encompasses not only the morning peak hours, but also the evening ones, which additionally increases the surface air pol lution. In addition, the aerosol haze, which absorbs the thermal radiation of the earth’s surface, increases the stability of the nighttime boundary layer (Fig. 5). The inversion intensity (the maximal temperature dif ference between the upper boundary of the ABL and the earth’s surface) increased from 1.5°–2.0° in the absence of smoke (typical of Moscow [15]) to 3°–7° in the presence of haze and mist. The maximal value of 10.5° was observed on July 3. Such prolonged and intense inversions, which are unusual for Moscow, considerably increased the accumulation of admix tures in the air basin of the city. The superposition of urban pollutions and biomassburning products resulted in recordbreaking concentrations of admix tures at the beginning of August 2010. NO2 INTEGRAL CONTENT IN THE BOUNDARY LAYER The integral content of gases in the vertical column within the ABL depends on temperature inversions to a lesser degree than surface concentrations. After the inversion destruction, convective and turbulent mix ing in the unstable atmosphere mainly redistributes the admixtures accumulated in the surface layer dur ing the nighttime along the vertical. Emissions and the advective transport from near and remote sources affect their content in the ABL under anticyclonic conditions; therefore, the NO2 IC is distributed more or less uniformly over the city territory. The NO2 IC observations conducted at two points (at the IAP and MSU sites) yield close values during the entire lifetime of the blocking anticyclone. The small systematic excess of the NO2 IC values at the IAP site over those at the MSU site (equal, on average, to 0.4 × 1016 mol/cm2) is caused by the higher (by 70 m) position of the second observational point. In the conditions of daytime mix ing, the value 0.4 × 1016 mol/cm2 in the 70mhigh column corresponds to the NO2 surface concentration
of 35 ppb, which approximately coincides with its mean value (38 ppb) for the daytime conditions in the period of blocking action. The fact that the upper boundary of the mixing layer over the center of the city and its elevated part (Vorob’evy gory) is at the same height over the level of the Moskva River is also con firmed by the data of sodar observations [16]. The NO2 IC values in the ABL averaged daily and over two observational points are presented in Fig. 6. As is seen from a comparison of Figs. 3 and 6, the extremes of NO2 IC and surface NO2 concentration often do not coincide. Even the maximal mean day time value of the NO2 IC (7.5 × 1016 mol/cm2) was observed on August 3, whereas the surface NO2 con centration attained its largest values on August 6 and 7. The action of different factors on the NO2 IC and sur face concentration is responsible for their weak corre lation throughout most of the day, with the exception of the afternoon, when the surface atmosphere is well mixed (for the period 12:00–15:00, the correlation coefficient is 0.72). The coinciding features of the variability of these concentrations can be identified. In the period of blocking, prior to the appearance of a dense aerosol haze, the NO2 IC increased at a high rate (approximately 0.05 × 1016 mol/cm2 per day). In the entire lifetime of the blocking anticyclone, the weekly cycle with the NO2 IC increase during working days and its abrupt drop on Sunday clearly manifested itself (Fig. 7). In the conditions of blocking, the influ ence of synoptic processes with the period 5–7 days is virtually absent, and the formation of the weekly NO2 IC cycle is evidently controlled by the action of anthropogenic factors, which also affect the ABL stratification. The average over the 2month period weekly variations of the upper boundary of the stable ABL during morning hours (06:00–09:00), when the NO2 IC measurements began, are presented in Fig. 7 [17]. Similar variations, but less distinctly pro nounced, in the position of the upper daytime ABL boundary and in the values of the turbulent mixing coefficient were observed. Such an impact of anthro pogenic activity on the state of the atmosphere is noted by different authors (see, for example, [18]); however, this impact most clearly manifests itself in a stable anticyclonic air mass. The disturbances caused either by the increased NO2 accumulation during a prolonged absence of wind or by the arrival of polluted air from fires were superposed onto the regular weekly cycle. The extreme values of the NO2 IC on July 21 and 31 and on August 3, 6, 7, and 11 were formed due to the superposition of these factors. According to satellite photographs and backward trajectories, the air mass saturated with combustion products from nearMoscow peatbogs was noted in the surface the atmospheric layer (to a height of about 300 m) (the twoday trajectory in Fig. 1), and the air mass containing combustion products from remote forest fires was noted higher (in the ABL (the 12day trajectories in Fig. 1)). The influence of trains from
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(а) Deviation Deviation of mixing layer of NO2 integral content , height, m 1016 mol/cm2
turf fires was also manifested as sharp jumps of the O3, NO, CO, and NMHC concentrations far exceeding their jumps, which can be produced in the city under the influence of local sources. In addition, O3 concen trations higher than 100 ppb indicate that the main ozone precursors (NOx, CO, and MNHC) were con tained in the atmosphere at least several hours prior to the moment of measurements, which corresponds to the time of the air mass motion from the places of turf fires to Moscow. Specific features of the location of transport and industrial sources within Moscow and its immediate vicinity also have a certain influence on the NO2 IC. As the railway laboratory (TROIKA experiments [11, 19]) circuits around Moscow showed, such sources are mainly concentrated in the eastern parts of Moscow and Moscow oblast. That is why winds from the east ern sector must increase the NO2 IC. Indeed, most extremely high values obtained at the MSU and IAP sites coincided in time with the easterly transport, even before the smoke from turf fires began to come into Moscow (also from the east). The influence of the vertical ABL stratification on the NO2 IC manifests itself in the largest NO2 IC decrease when the mixing layer height increases (on average, by 0.2 × 1016 mol/cm2, if the height of the upper ABL boundary increases from 1000 to 2500 m). There is no dependence of the NO2 IC on the coeffi cient of vertical turbulent diffusion Kz in the period prior to the influence of fires. Evidently, in the condi tions of hot sunny weather, when exchange processes were very active and the coefficient Kz attained 400 m2/s [17], mixing in the ABL was fast and Kz vari ations did not affect the NO2 IC. However, from July 27 to August 18, when smoking took place and Kz did not exceed 150 m2/s, the NO2 IC decreased with the Kz increase. In this case, the regression relation can be presented as the NO2 IC = 3.1–0.005 × Kz and the cor relation coefficient between the NO2 IC and Kz is 0.72. Measurements of the NO2 IC in the period of blocking did not reveal significant regular changes in it during the light of day, although the daily cycle is dis tinctly recognizable in emissions and the ABL stratifi cation [12, 14]. This fact points to a strong influence of irregular actions, especially the arrival of air masses with combustion products at different levels. The observed admixtures have different lifetimes in the atmosphere: NO, several hours; О3, NO2, and NMHC, from one to several days; CO, SO2, and NMHC, from one week to one month; and СН4, about ten years. Therefore, their accumulations strongly differ. The shortlived admixtures (NO, NO2, and O3) are removed from the atmosphere mainly as a result of photochemical processes and deposition on the earth’s surface. Their concentrations vary sharply during the day, as well as with increasing distances from their sources. Even at a distance of 40 km from Moscow, at the Zvenigorod scientific station (ZSS) of the IAP RAS, the NO and NO2 concentrations, on
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Fig. 7. (a) Weekly cycle of the NO2 IC in the atmospheric boundary layer over Moscow and (b) height variations of the stable boundary layer during morning hours (06:00– 09:00 Moscow Time).
average, are 2–3 times lower than in Moscow, not only in the surface air but also in the boundary layer [20]. The longer lived admixtures (CO, SO2, NMHC, and СН4) have smaller daily variations. They are removed from the air basin of the city mainly due to the hori zontal advection and the exportation from the bound ary layer into the free troposphere, which is demon strated by satellite observations showing a more or less uniform CO accumulation in the troposphere over the entire central part of ER encompassed by the blocking anticyclone. According to satellite data (although they are insufficiently sensitive to variations in the surface layer), the total CO contents in the atmosphere over Moscow and over the ZSS are virtually the same dur ing the entire summer period [21–23]. The gas concentration changes in 2002, when the blocking anticyclone (the air temperature is presented in Fig. 2), although less stable and prolonged, was also observed in the summer over Moscow, displayed the same specific features [20]. Under similar conditions, the О3, NO, and NO2 concentrations attained approx imately the same high values as in 2010, because their sources and sinks changed little. However, in 2002, longlived admixtures had much lower concentrations than in 2010. CONCLUSIONS The anomalously persistent blocking anticyclone over the central part of ER in the summer of 2010 con siderably changed the gaseous composition of the urban air due to the accumulation of admixtures in a closed anticyclonic air mass. An increased probability of the repetition of such extreme situations in the future [26] calls for updating the existing system of airquality monitoring. National calibration and coordination centers must be orga nized, and unified standards for estimating the quality Vol. 47
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of operation of the monitoring system must be devel oped. Insufficiently exact information about ecologi cally important atmospheric admixtures prevents the elaboration of means for improving the ecological sit uation. In addition, this can lead to an erroneous esti mation of the ecological situation in Moscow and in the country as a whole. For example, in work [24] devoted to a comparison of the air quality in the largest megacities, Moscow is mentioned among the six cities of the world most unfortunate in their integral index of pollution. Much weight was given to the NO2 concen tration in Moscow, whose annual mean value was assumed by experts to be 170 ppb. Moscow is the world leader according to this index [24]. For comparison, according to the same data [24], the annual mean NO2 concentrations in the most polluted megacities of the world, i.e., in Beijing and Mexico City, are 122 and 56 ppb, respectively. Such high NO2 concentrations for Moscow do not correspond to their actual values. Concentrations exceeding 100 ppb are recorded in Moscow only as shortterm outbursts near NO2 sources, in particular, near turnpikes or under such extreme conditions as in the summer of 2010. Accord ing to data of longterm observations in Moscow, real annual mean NO2 concentrations do not exceed 30 ppb [12–14, 18]. On the whole, the anomalous situation of the sum mer of 2010 further supports the development of a national system for monitoring the air quality and pre dicting its sharp variations. ACKNOWLEDGMENTS This work was supported by scientific programs of the RAS and the Ministry of Education and Science (project “Megapolis”), as well as by the Russian Foun dation for Basic Research (project nos. 100500272, 100590014Bel_a, 090592505IK_a, 1105 01139a). REFERENCES 1. J. M. Wiedenmann, A. R. Lupo, I. I. Mokhov, et al., “The Climatology of Blocking Anticyclones for the Northern and Southern Hemispheres: Block Intensity as a Diagnostic,” J. Clim. 15 (23), 3459–3473 (2002). 2. I. I. Mokhov, “Interrelation between Variations in the Global Surface Air Temperature and Solar Activity Based on Observations and Reconstructions,” Dokl. Earth Sci. 409 (5), 805–809 (2006). 3. Global Fire Monitoring Center, Freiburg, Germany. http://www/fire/unifreiburg/de/current/globalfire/ htm 4. V. G. Bondur, “The Urgency and the Need for Space Monitoring of Natural Fires in Russia,” Vestnik ONZ RAN 2 (NZ11001) (2010). doi: 10.2205/2010 NZ000062 5. Information Materials of the State Duma, Parla mentskaya gazeta, September 14, 2010. www.pnp.ru/ newspaper/20100914/4372.html.
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GASEOUS ADMIXTURES IN THE ATMOSPHERE OVER MOSCOW 20. N. F. Elansky, I. I. Mokhov, I. B. Belikov, et al., “Gas Composition of the Surface Air in Moscow during the Extreme Summer of 2010,” Dokl. Earth Sci. 437 (1), 357–363 (2011). 21. MOPITT (Measurements of Pollution in the Tropo sphere). http://eosweb.larc.nasa.gov/PRODOCS/ mopitt/table_mopitt.html. 22. AIRS (Atmospheric Infrared Sounder). http://www airs.jpl.nasa.gov/. 23. E. V. Fokeeva, A. N. Safronov, V. S. Rakitin, et al., “Study of the Effect of Fires in July–August 2010 on the Pollution of the Atmosphere with Carbon Monox ide in Moscow and in the Surrounding Area and the Assessment of Emissions,” Izv. Atmos. Ocean. Phys. 47 (2011) (in press).
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