— Carbon monoxide (CO) total column (TC) measurements of the TROPOMI high-resolution orbital spectrometer have been validated by ground-based spectroscopic measurements at sites of the A.M. Obukhov Institute of Atmospheric Physics (OIAP), Russian Academy of Sciences, in Moscow and Zvenigorod for the period from June 28, 2018, to December 31, 2021. Correlation coefficients ( R ) between TROPOMI orbital data and ground-based stationary data are determined and analyzed. The high values of the correlation coefficient are obtained ( R ~ 0.81–0.97) depending on the observation point, spatial averaging, and filtration applied. For different averaging of satellite data, the dependences of correlation parameters on the orbital angles, underlying surface albedo, and the height of atmospheric boundary layer are being investigated. No influence of albedo on the correlation parameters of orbital and ground-based measurements is found for both observation sites. No significant dependence of correlation parameters on the viewing zenith angle is detected either. However, the correlation coefficients depend on the viewing azimuth angles and the height of the atmospheric boundary layer. An increase in the correlation is obtained during observations at viewing azimuth angles of less than 40° (up to R ~ 0.97), as well as under an increase in the height of the atmospheric boundary layer (up to R ~ 0.90).

A comparative study was carried out to explore carbon monoxide total columnar amount (CO TC) in background and polluted atmosphere, including the stations of ZSS (Zvenigorod), ZOTTO (Central Siberia), Peterhof, Beijing, and Moscow, during 1998–2014, on the basis of ground- and satellite-based spectroscopic measurements. Interannual variations of CO TC in different regions of Eurasia were obtained from ground-based spectroscopic observations, combined with satellite data from the sensors MOPITT (2001–14), AIRS (2003–14), and IASI MetOp-A (2010–13). A decreasing trend in CO TC (1998–2014) was found at the urban site of Beijing, where CO TC decreased by 1.14%±0.87% yr −1 . Meanwhile, at the Moscow site, CO TC decreased remarkably by 3.73%±0.39% yr −1 . In the background regions (ZSS, ZOTTO, Peterhof), the reduction was 0.9%–1.7% yr −1 during the same period. Based on the AIRSv6 satellite data for the period 2003–14, a slight decrease (0.4%–0.6% yr −1 ) of CO TC was detected over the midlatitudes of Eurasia, while a reduction of 0.9%–1.2% yr −1 was found in Southeast Asia. The degree of correlation between the CO TC derived from satellite products (MOPITTv6 Joint, AIRSv6 and IASI MetOp-A) and ground-based measurements was calculated, revealing significant correlation in unpolluted regions. While in polluted areas, IASI MetOp-A and AIRSv6 data underestimated CO TC by a factor of 1.5–2.8. On average, the correlation coefficient between ground- and satellite-based data increased significantly for cases with PBL heights greater than 500 m.

A. M. Obukhov IAP of RAS performs regular measurements of the integral content of tropospheric nitrogen dioxide (NO2) by the MAX-DOAS method at the Zvenigorod Scientific Station (ZSS) since 2009. ZSS is located to the West from Moscow and is in background air mass of Central Russian about 80% of time, while polluted air of Moscow megacity cover it in about 20% of time. We calculate the fields of the average contribution of potential sources on the integral content of NO2 on ZSS using the concentration weighted trajectory (CWT) method. The NO2 measurements performed in cloudless sky were used for the analysis. Five-day backward trajectories of air particles arriving into the convective boundary layer of the atmosphere above ZSS were calculated using the NOAA HYSPLIT_4 trajectory model and the NCEP GDAS1.0 meteorological variables data fields. The differences of the fields of contribution of potential sources in warm (April-September) and cold (October-March) seasons of the year are analyzed.

A.M. Obukhov Institute of Atmospheric Physics (OIAP) of Russian Academy of Sciences (RAS) performs regular measurements of the integral tropospheric content of such reactive gases as nitrogen dioxide (NO2) and formaldehyde (HCHO) by the MAX-DOAS method at the Zvenigorod Scientific Station (ZSS) since 2009. For each average hourly gas contents in the troposphere at ZSS in 2009-2017 the backward trajectories of the air particles were calculated using the trajectory model NOAA HYSPLIT_4 and the grid meteorological data NOAA NCEP GDAS0p5. Using the backward trajectories, the PSCF (potential source contribution function) method was used to calculate detailed (resolution 0.1 degrees x0.1 degrees) fields of probability of the transport to ZSS of air masses which are extremely polluted with formaldehyde and nitrogen dioxide from a potential source. Similarly, using the CWT (concentration weighted trajectory) method, detailed fields of the average contribution of the potential source to the tropospheric NO2 and HCHO contents at ZSS were reconstructed. The relative influence of the Moscow megacity and the industrialized region in the east of the Moscow Oblast on the contamination of the lower troposphere of the Western Moscow Oblast with nitrogen dioxide and formaldehyde is specified.

Trends of total CO and CH4 contents are estimated from satellite AIRS spectrometer data for the Eurasian domain (0–180° E, 0–85° N) for different time periods and seasons. The results are compared with similar estimates, obtained from ground-based spectroscopic measurements at seven stations of the European Network for the Detection of Atmospheric Composition Change (NDACC) and at measurement sites of the Institute of Atmospheric Physics, Russian Academy of Sciences (Zvenigorod Scientific Station (ZSS), Zotto, and Beijing) and St. Petersburg University (Peterhof), located in the study domain. Overall, the total CO decreased over northern Eurasia during the period of 2003–2015 at a rate of 0.05–1.5%/yr, depending on the region; while the total CH4 increased at a rate of 0.16–0.65%/yr. Since 2007, the total CO has been increased during summer and autumn months in most mid- and high-latitude Eurasian background regions, and the total CH4 growth has been accelerated. Changes in the global photochemical system, proceeding against the background of global climate change and, in particular, changes in the “sources/sinks” ratio for minor atmospheric admixtures are suggested as possible causes of this dynamic of trends of the atmospheric CO and CH4 contents.

Formaldehyde (HCHO) in the atmosphere is directly emitted by anthropogenic and biogenic sources and, more significantly, produced during oxidation of methane and other volatile organic compounds (VOCs), and so its content is one of observable indicators of air pollution by VOCs. HCHO has a sufficiently large absorption cross-section in the UV spectral region to be detected by the technique of the differential optical absorption spectroscopy (DOAS). Spectral measurements of scattered solar radiation are performed at Zvenigorod Scientific Station (ZSS, 55°41'49'"N, 36°46'29'"E) located in 38 km west from Moscow Ring Road by MAXDOAS instrument since 2008. This location of the observational station allows evaluating the background levels of formaldehyde in the troposphere and the levels that are associated with pollution from Moscow. For analysis of the HCHO variability we selected spectra taken in cloud free conditions from October 2009 to April 2016. Version 1.3 of the retrieval algorithm is used. It uses information on the surface albedo and the height of the atmospheric boundary layer inferred from a model. It has optimized interpolation parameter of DOAS processing. Cloud screening algorithm using UV color index (the ratio of 370-nm radiance to 340-nm one) was implemented. The obtained data quantify the Moscow megapolis influence on air quality at Zvenigorod by comparison of HCHO VCD for east and west wind directions. HCHO VCD at East winds in average more than one at West winds for 0.4 ± 0.1×1016mol×cm-2 at air temperatures from +5 to +35°C, and for 0.8 ± 0.2×1016 mol×cm-2 at temperatures from -20 to +5°C. It may be caused by Moscow emissions of HCHO precursors. Strong dependence of HCHO VCD on air temperature is noticeable in our data for air temperatures from +5 to +35°C. In different wind conditions the gradient of the temperature effect is about 0.86 ± 0.07 ×1015 mol×cm-2×°C-1 in average. The increase of the formaldehyde content with the increase of the air temperature can be caused by the HCHO formation from non-methane biogenic volatile organic compounds for which more emission is expected at higher temperatures.

A significant amount of satellite and ground-based data on the CO, CO2, and CH4 total contents for 2010–2013 was collected, classified, and analyzed. Transition relations between satellite and groundbased data on the content of impurities under study at different measuring sites (NDACC/ GAW and OIAP RAS stations) with different spatial and temporal resolutions have been found. A high correlation between daily average satellite-measured CO contents (AIRS v6 (R 2 = 0.48–0.96), IASI MetOp-A (R 2 = 0.25–0.86), and MOPITT v6 Joint (R 2 = 0.30–0.83) products, averaging over 1° × 1°) and the ground-based solar spectrometers’ data was ascertained for background conditions. In the case of high pollution of the mixing layer, a significant underestimation of the CO total content (by 1.7–4.7 times, depending on the sensor and observation point) by satellite sensors has been noted. Representative transition relations and correlation coefficients (R 2 ≥ 0.5) between satellite data on daily average CH4 contents and the data from ground-based diffraction spectrometers of A.M. Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences (IAP RAS) and Fourier spectrometers of GAW stations have been found only for the AIRS sensor. The best correlation with ground-based measurement data on CO2 (R 2 = 0.25 for daily average values, averaging over 1° × 1°) was found for the IASI sensor. The daily average CH4 total contents from the IASI MetOp-A sensor weakly correlate with the ground-based data and with AIRS data.

Formaldehyde (HCHO) in the atmosphere is a product of oxidation of methane and other volatile organic compounds (VOCs), and so its content is an important index of air pollution by VOCs. HCHO has strong absorption cross-section in the UV spectral region and, hence, HCHO vertical column density (VCD) can be measured by remote optical methods including differential optical absorption spectroscopy (DOAS). Spectral measurements of scattered solar radiation are performed at Zvenigorod Scientific Station (ZSS, 55 degrees 41'49 '' N, 36 degrees 46'29 '' E) located in 38 km west from Moscow Ring Road by MAX-DOAS instrument since 2008.For analysis of the HCHO variability we selected spectra taken in cloud free conditions. Version 1.2 of retrieval algorithm is used. It uses information on the surface albedo and the height of the atmospheric boundary layer inferred from a model. Data screening using color index was implemented. The obtained data quantify the Moscow megapolis influence on air quality at Zvenigorod by comparison of HCHO VCD for east and west wind directions. HCHO VCD for east winds is grater one for west winds for 0.5x10(16) molxcm(-2) in average. Strong dependence of HCHO VCD on air temperature is noticeable in our data for air temperatures from +5 to +35 degrees C. In different conditions of the atmosphere gradient of the temperature effect is about 1.1-1.2x10(15) molxcm(-2)x degrees C-1. The increase of the formaldehyde content with the increase of the air temperature can be caused by the HCHO formation from non-methane biogenic volatile organic compounds for which more emission is expected at higher temperatures.

The measurements of submicron aerosol and black carbon (BC) surface concentrations, and carbon monoxide (CO) total column in 1992–2012 in Beijing and Moscow are illustrated. The specific features in the long-term variations in the studied impurities in these megacities are discussed. The level of pollution with all three impurities in Beijing is substantially higher than in Moscow. From 1992 to 1999, the monthly means of black carbon and aerosol increased in Beijing. These concentrations substantially decreased beginning from 2000. From 2007 to 2011, black carbon decreased and submicron aerosol increased. In 1996–2003 the urban part of CO total column (TC) in Beijing was on average higher than in 2006–2012 by a factor of 1.4. The anthropogenic part of CO in Moscow decreased in 2006–2012. High aerosol and CO concentrations, comparable with concentrations rather typical of Beijing, were observed in Moscow only during wildfires in 2010. Using the cluster analysis statistical methods, it has been indicated that the main sources of the air pollution in Beijing are located 100–500 km southward.

Measurements of the formaldehyde (HCHO) atmospheric column are performed at Zvenigorod Scientific Station, Moscow Region, Russia since 2008 by the MAX-DOAS instrument. A previously developed algorithm for the formaldehyde retrieval was updated by adding an availability to use information on the surface albedo and the height of the atmospheric boundary layer provided by other measurements and/or modeling. We present preliminary results of the analysis of observations performed in 2010-2012.The obtained data allow quantifying the Moscow megapolis influence on air quality at Zvenigorod. The average HCHO vertical column density observed at the east winds is larger than one at the west winds. The Moscow influence causes the difference of about 0.85x10(16) mol cm(-2) between these values. This difference slightly depends on the air temperature and the season.A temperature effect is noticeable in the formaldehyde atmospheric column. Our data show statistically significant positive temperature effect in formaldehyde for the background and polluted conditions for temperatures from -5 degrees C to +35 degrees C. The temperature trend in formaldehyde data at Zvenigorod varies between 7.5x10(14) and 9.3x10(14) mol cm(-2 degrees)C(-1) for all wind directions. The increase of the formaldehyde atmospheric column with the increase of the air temperature can be caused by the HCHO formation from non-methane biogenic volatile organic compounds (mainly -isoprene) for which more emission is expected at higher temperatures, and by growth of areas of forest and turf fires.

The anthropogenic CO column content in the atmosphere is derived from measurements with infrared grating spectrometers in Beijing,China,and Moscow,Russia,during 1992–2012.Some specific variation characteristics and long-term variation trends of the CO column content in the atmosphere in these regions are discussed.An evident variation trend of anthropogenic CO in the atmosphere for the Beijing region is not observed during 1992–2012,while for the Moscow region,it decreases yearly by about 1.4% for the same period.High CO concentrations appear quite frequently in Beijing,but much less frequently in Moscow,except during the natural fire events in summer 2010.From back trajectory analysis,the high CO concentration observed in Beijing can be attributed to the intensive CO emission sources in its surrounding areas.