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Urban aerosol pollution was analyzed over the Moscow megacity region using COSMO-ART chemical transport model and intensive measurement campaigns at the Moscow State University Meteorological Observatory (MSU MO, 55.707° N, 37.522° E) during April-May period in 2018 and 2019. We analyzed mass concentrations of Particulate Matter with diameter smaller 10 micron (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 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 an indicator of changes in the absorbing properties of the atmosphere due to meteorological factors. On average, relatively low for urban regions BC / PM10 ratio 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 in 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 average AODurb at 550 nm was about 0.021 with more than 85 % of fine aerosol mode. The comparisons between AODurb obtained from model and measurements during the 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 0.016 mg m-3 according to the measurements and 0.006 mg 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 4 times increase in PM10urb (up to 0.030-0.040 mg m-3) and 3 times increase in BCurb (up to 0.003-0.0035 mg m-3). At the same time, no pronounced daily cycle was found for the columnar urban aerosol component (AODurb), although there is a slight tendency to the increase in model AODurb at night. We also obtained a close relationship between the calculated and measured PM10urb values, their dependence on IPD index, and the pronounced growth of PM10urb with the PM10 increase. [ABSTRACT FROM AUTHOR]

The increase in built surfaces constitutes the main reason for the formation of the Urban Heat Island (UHI), that is a metropolitan area significantly warmer than its surrounding rural areas. The urban heat islands and other urban-induced climate feedbacks may amplify heat stress and urban flooding under climate change and therefore to predict them correctly has become essential. Currently in the COSMO model, cities are represented by natural land surfaces with an increased surface roughness length and a reduced vegetation cover, but this approach is unable to correctly reproduce the UHI effect. By increasing the model resolution, a representation of the main physical processes that characterize the urban local meteorology should be addressed, in order to better forecast temperature, moisture and precipitation in urban environments. Within the COSMO Consortium a bulk parameterization scheme (TERRA_URB or TU) has been developed. It parametrizes the effects of buildings, streets and other man-made impervious surfaces on energy, moist and momentum exchanges between the surface and atmosphere, and additionally accounts for the anthropogenic heat flux as a heat source from the surface to the atmosphere. TU implements an impervious water-storage parameterization, and the Semi-empirical Urban canopy parametrization (SURY) that translates 3D urban canopy into bulk parameters. This paper presents evaluation results of the TU scheme in high-resolution simulations with a recent COSMO model version for selected European cities, namely Turin, Naples and Moscow. The key conclusion of the work is that the TU scheme in the COSMO model reasonably reproduces UHI effect and improves air temperature forecasts for all the investigated urban areas, despite each city has very different morphological characteristics. Our results highlight potential benefits of a new turbulence scheme and the representation of skin-layer temperature (for vegetation) in the model performance. Our model framework provides perspectives for enhancing urban climate modelling, although further investigations in improving model parametrizations, calibration and the use of more realistic urban canopy parameters are needed. [ABSTRACT FROM AUTHOR]