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.

Measurements of CO and 15 volatile organic compounds (VOCs) at the IAP-RAS (A.M. Obukhov Institute of Atmospheric Physics) site located in the center of Moscow were analyzed. Acetaldehyde, ethanol, 1.3-butadiene, isoprene, toluene and C-8 aromatics were established to be the main ozone precursors in the observed area, providing up to 82% of the total ozone formation potential of the VOCs measured. Diurnal and seasonal variations of the compounds are discussed. The concentrations of anthropogenic VOCs (acetaldehyde, benzene, 1.3-butadiene, toluene, and C-8 aromatics) did not exceed their maximum permissible levels, reaching their maxima in summer and autumn in the morning and evening hours. Biogenic ethanol and isoprene were the highest in summer midday but their concentrations were low enough (up to 4 and 0.4 ppbv, respectively) due to small vegetation area around the site. Emission ratios (ERs) for the main ozone precursors—acetaldehyde, ethanol, 1.3-butadiene, isoprene, toluene, and C-8 aromatics—were estimated from two-sided linear regression fits using benzene and CO as tracers for anthropogenic emissions, with spatial and temporal filters being applied to account for the influence of chemistry and local emission sources. The best estimates of ERs were obtained using benzene as a reference species. Anthropogenic fractions of VOCs (AFs) were then estimated. As expected, acetaldehyde, toluene, 1.3-butadiene, and C8aromatics were entirely anthropogenic and emitted mainly from urban vehicle exhausts throughout the day, both in summer and in winter. AFs of isoprene and ethanol did not exceed 30% and 50% in summer, respectively, during both daytime and nighttime hours. In winter, the anthropogenic fractions of isoprene and ethanol were slightly higher (up to 35% and 60%, respectively).

Measurements of near-surface methane (CH₄) mixing ratio and its stable isotope ¹³C were carried out from January 2018 to December 2020 at the A.M. Obukhov Institute of Atmospheric Physics (IAP) research site in the center of Moscow city. The data show moderate interannual variations in monthly mean CH₄ with maximum values being observed predominantly in winter (2.05–2.10 ppmv on average). The most δ¹³C depleted CH₄ (up to −56‰) is observed in summer and autumn following seasonal decrease in traffic load in the city. The highest CH₄ concentrations (>2.2 ppmv) were likely to be caused by air transport from the E–SE sector where potentially large microbial CH₄ sources are located (landfills and water treatment plants, Moscow River). Keeling plots of these episodes in different seasons of 2018–2020 showed δ¹³C isotopic signatures of about −58–−59‰ for the spring–autumn period and −67‰ for winter. A good correlation was observed between CH₄ and other pollutants: CO₂, CO, and benzene in daytime (10:00–19:00) hours (R > 0.7). Contribution of urban methane emissions due to vehicle exhausts (∆[CH₄]_auto) and microbial activity (∆[CH₄]_micro+) along with regional baseline mixing ratios of CH₄ ([CH₄]_base) and CO ([CO]_base) were estimated from the linear orthogonal regression analyses of the measured daytime mixing ratios. A significant role of microbial methane in the formation of CH₄ maximums in Moscow was revealed. Contributions of the upwind continental CH₄ and CO sources to the measured species levels were estimated through comparison with the Mace Head site data representative for the Northern Hemisphere baseline air. The study provides, for the first time, important insights into the long- and short-term variations of CH₄ levels in Moscow in connection to the local (urban) emissions and long-range transport from upwind continental sources. The results will contribute to elaboration of a default emission inventory in air quality modeling and help to identify the areas for targeted mitigation efforts.