During the AeroRadCity-2018 spring aerosol experiment at the Moscow State University Meteorological Observatory the aerosol properties of the atmosphere and radiative aerosol effects were analyzed using a wide complex of measurements and model COSMO-ART simulations over Moscow domain. The program of measurements consisted of columnar aerosol AERONET retrievals, surface PM10, black carbon (BC) and aerosol gas precursors mass concentrations, as well as radiative measurements under various meteorological conditions. We obtained a positive statistically significant dependence of total and fine aerosol optical depth (AOD) mode (R2 ~0.4) with PM concentrations. This dependence has revealed a pronounced bifurcation point around PM10=0.04 mgm-3. The modelled BC concentration is in agreement with the observations and has a pronounced correlation with PM, but not with the AODs. The analysis of radiative effects of aerosol has revealed up to 30% loss for UV irradiance and 15% - for shortwave irradiance at high AOD in Moscow. Much intensive radiation attenuation is observed in the afternoon when remote pollution sources may affect solar fluxes at elevated boundary layer conditions. Negative (cooling) radiative forcing effect at the top of the atmosphere from -18 Wm-2 to -4 Wm-2 has been evaluated. Mean difference in visible AOD between urban and background conditions in Moscow and Zvenigorod was about 0.01 according to measurements and model simulations, while in some days the difference may increase up to 0.05. The generation of urban aerosol was shown to be more favorable in conditions with low intensity of pollutant dispersion, when mean deltaAOD550 was doubled from 0.01 to 0.02.

Abstract. Urban aerosol pollution was analyzed over the Moscow megacity region using the COSMO-ART (COSMO – COnsortium for Small-scale MOdelling, ART – Aerosols and Reactive Trace gases) online coupled mesoscale model system and intensive measurement campaigns at the Moscow State University Meteorological Observatory (MSU MO, 55.707∘ N, 37.522∘ E) during the April–May period in 2018 and 2019. We analyzed mass concentrations of particulate matter with diameters smaller than 10 µm (PM10), black carbon (BC) and aerosol gas precursors (NOx, SO2, CHx) as well as columnar aerosol parameters for fine and coarse modes together with different meteorological parameters, including an index characterizing the intensity of particle dispersion (IPD). Both model and experimental datasets have shown a statistically significant linear correlation of BC with NO2 and PM10 mass concentrations, which indicates mostly common sources of emissions of these substances. There was a pronounced increase in the BC/PM10 ratio from 0.7 % to 5.9 %, with the decrease in the IPD index related to the amplification of the atmospheric stratification. We also found an inverse dependence between the BC/PM10 ratio and columnar single-scattering albedo (SSA) for the intense air mixing conditions. This dependence together with the obtained negative correlation between wind speed and BC/PM10 may serve as an indicator of changes in the absorbing properties of the atmosphere due to meteorological factors. On average, the relatively low BC / PM10 ratio (for urban regions) of 4.7 % is the cause of the observed relatively high SSA = 0.94 in Moscow. Using long-term parallel aerosol optical depth (AOD) measurements over the 2006–2020 period at the MSU MO and under upwind clean background conditions at Zvenigorod Scientific Station (ZSS) of the IAP RAS (55.7∘ N, 36.8∘ E), we estimated the urban component of AOD (AODurb) and some other parameters as the differences at these sites. The annual mean AODurb at 550 nm was about 0.021 with more than 85 % of the fine aerosol mode. The comparisons between AODurb obtained from the model and measurements during this experiment have revealed a similar level of aerosol pollution of about AODurb=0.015–0.019, which comprised 15 %–19 % of the total AOD at 550 nm. The urban component of PM10 (PM10urb) was about 16 µg m−3 according to the measurements and 6 µg m−3 according to the COSMO-ART simulations. We obtained a pronounced diurnal cycle of PM10urb and urban BC (BCurb) as well as their strong correlation with the IPDs. With the IPD index change from 3 to 1 at night, there was about a 4 times increase in PM10urb (up to 30–40 µg m−3) and a 3 times increase in BCurb (up to 3–3.5 µg m−3). At the same time, no pronounced daily cycle was found for the columnar urban aerosol component (AODurb), although there was a slight increase in model AODurb at night.

<p>Atmospheric aerosol has a noticeable effect on the microphysical and optical properties of the atmosphere, solar radiation, temperature and humidity conditions, thereby determining the quality of the forecast of important meteorological elements and affecting the regional climate and the dynamics of geochemical processes. Using the results of the spring AeroRadCity experiment at the MSU Meteorological Observatory in 2018-2019, and numerical calculations on the base of modern COSMO and COSMO-ART mesoscale models using Russian (-Ru) configurations we determined the level and main features of urban air/aerosol pollution, and assessed its magnitude and its impact on the radiative and meteorological characteristics of the atmosphere in typical conditions (Chubarova et al., 2020). In the context of the coronavirus pandemic in 2020, especially during the period of lockdown in the spring, there was a significant decrease in emissions of pollutants in many countries, including Russia. The aim of this study is to show the consequences of decrease in emissions of pollutants on the air quality and on urban aerosol pollution. A special attention is paid to the division between the effects of meteorological factors and the influence of pollution emission on aerosol and gas concentration. The effects of the air pollution decrease on solar radiation and air temperature during this period have been analyzed using COSMO-Ru-ART model.  For a more detailed study of the observed spatial aerosol distribution on solar radiation and air temperature, we have developed a methodology of the implementation of the satellite aerosol optical thickness (AOT) data in the COSMO-Ru model. Using this approach we evaluated the radiative and temperature effects observed due to aerosol in typical conditions during the spring of 2018-2019 and during the period of lockdown in the spring of 2020 under various meteorological conditions. To do this, the satellite AOT data from the MAIAC/MODIS algorithm and aerosol measurements from Cimel sun photometers data were used for characterising the urban aerosol in typical and lockdown conditions. We also discuss the aerosol indirect effects on cloud properties using an experimental scheme of COSMO-Ru model and their influence on solar radiation and surface temperature during this period. The aerosol study has been partially supported by the RSF grant number 18-17-00149; the analysis of gas species has been partially funded by the megagrant number 2020-220-08-5835.</p><p>Reference:</p><p>Chubarova N.Ye., Ye.Yu. Zhdanova., Ye.Ye. Androsova, A.A. Kirsanov, M.V. Shatunova, Yu.O. Khlestova, Ye.V. Volpert, A.A. Poliukhov, I.D. Eremina, D.V. Vlasov, O.B. Popovicheva, A.S. Ivanov, Ye.V. Gorbarenko, Ye.I. Nezval, D.V. Blinov, G.S. Rivin. The aerosol urban pollution and its effects on weather, regional climate and geochemical processes: Monograph / Edited by N.Ye. Chubarova – Moscow, MAKS Press, 2020. 339 pp.  ISBN 978-5-317-06464-8</p>

<p>The AeroRadCity urban aerosol experiment over Moscow megacity have been carried out during spring 2018 and 2019. The experiment included measurement campaign at the Moscow MSU MO and numerical experiments using COSMO-ART model (Vogel et al., 2010, Vilfand et al., 2017). We examined the dynamic of aerosol properties and their radiative effects under various meteorological conditions using both columnar and surface aerosol measurements (AERONET dataset, mass concentration of PM10, black carbon (BC), different aerosol gas-precursors, etc.). For qualifying urban pollution special attention was given to the analysis of columnar and surface Angstrom absorption coefficients, low values of which indicated the BC dominance as a result of high-temperature combustion of natural fuel in transport engines. We obtained a positive statistically significant dependence of AOD on PM and BC concentrations with a pronounced bifurcation point around PM10=0.04 mgm<sup>-3</sup>. Model and experimental data demonstrated positive BC relationships with PM10, NO<sub>2</sub> and SO<sub>2</sub> at Moscow megacity (Chubarova et al., 2019). The analysis of radiative effects of aerosol in clear sky conditions has revealed up to 30% loss for UV irradiance and 15% - for shortwave irradiance at high AOD. Much intensive radiation attenuation is observed in the afternoon, when remote pollution sources affected solar fluxes at elevated boundary layer conditions. Negative (cooling) RF effect at TOA varied from -20 Wm<sup>-2</sup> to -1 Wm<sup>-2</sup> with average of -8 Wm<sup>-</sup>2. The minimum (absolute) RF effect corresponded to the lowest AOT and single scattering albedo. A statistically significant regression dependence of the single scattering albedo on BC/PM10 fraction was obtained at high level of particle dispersion intensity.</p> <p>The urban AOT550 calculations in COSMO-ART model were compared with the results of measurements in Moscow and Zvenigorod at the A. M. Oboukhov IFA RAS institute. They showed a satisfactory agreement between model and measured values of city aerosol pollution (respectively, dAOT= 0.017  and dAOT= 0.013). In some days the difference increased up to 0.05 in conditions with low intensity of pollutant dispersion.</p> <p>During the experiment a high correlation (R<sup>2</sup>=0.95) was revealed between the insoluble component and the total mineralization of rain precipitation, which indicates that 70% of aerosol deposition occurs as the insoluble fraction. We show that at the initial concentration of C<sub>0</sub>(PM)>10 μgm<sup>-3</sup> exponential washout coefficients are significant for PM (alfa (PM)=0.17+-0.09 hour<sup>-1</sup>) and insignificant for BC (alfa (BC) =0.07+-0.10 hour<sup>-1</sup>). At C<sub>0</sub>(PM) <10 μgm<sup>-3</sup>, the alfa values both for PM and BC are close to zero. According to the numerical experiments with and without account of wet deposition the alfa value was estimated to be 0.08 hour<sup>-1</sup>, which fits the confidence interval obtained from the measurements. The work was supported by the Russian Science Foundation, grant # 18-17-00149.</p> <p>References:</p> <p>Chubarova N.E. et al. (2019). <em>GEOGRAPHY, ENVIRONMENT, SUSTAINABILITY</em>. 2019;12(4):114-131. <a href="https://doi.org/10.24057/2071-9388-2019-72" target="_blank" rel="noopener">https://doi.org/10.24057/2071-9388-2019-72</a></p> <p>Vogel et al., (2010). In Integrated Systems of Meso-meteorological and Chemical Transport Models, Springer, pp. 75-80.</p> <p>Vilfand et al. (2017). Russian Meteorology and Hydrology, vol. 42, № 5, pp. 292–298. DOI:10.3103/S106837391705003X.</p>