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Abstract. We estimated the distribution of aerosol optical thickness (AOT) with a spatial resolution of 1 km over the Moscow megacity using the MAIAC aerosol product based on MODIS satellite data (Lyapustin et al., 2018) for the warm period of the year (May–September, 2001–2017). AERONET (Aerosol Robotic Network)-based validation of satellite estimates near the city centre at Moscow_MSU_MO and over the Moscow suburbs at Zvenigorod revealed that MAIAC AOT at 0.47 µm is in agreement with AERONET AOT though underestimated by 0.05–0.1 for AOT<1 and overestimated for smoke conditions with AOT>1. The MAIAC AOT biases were almost the same for the Moscow_MSU_MO and Zvenigorod AERONET sites, which indicated that the MAIAC algorithm effectively removed the effect of the bright urban surface in the city centre. For the ground-based measurements, the difference between annual median AOT at Moscow_MO_MSU and Zvenigorod (ΔAOT) varied within −0.002 to +0.03, with statistically significant positive bias for most years, and an average ΔAOT was about 0.02. According to the MAIAC dataset, the ΔAOT varied within ±0.01 and was not statistically significant. The ΔAOT started decreasing recently due to intensive urban development of the territory around Zvenigorod and the decrease in pollutant emissions in Moscow, which is mainly caused by the environmental regulations. According to the MAIAC dataset, the most pronounced spatial AOT differences over the territory of Moscow were observed at the 5 % quantile level, where they reached 0.05–0.06 over several locations and could be attributed to the stationary sources of aerosol pollution, for example, large areas of construction sites, aerosol pollution from roads and highways, or agriculture activities. The differences between the maximum and the mean AOT for different quantiles, except the 95 % quantile, within the Moscow region, were about 0.02–0.04, which could be attributed to the local aerosol sources. The application of the MAIAC algorithm over the whole Moscow region has revealed a decreasing AOT trend over the centre of Moscow and an increasing trend over the “New” Moscow territory which experienced an intensive build-up and agricultural development.

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Stereoisomers of 2,4-diaminoglutaric and 2,5-diaminoadipic acids were synthesized from glutamic and 2-aminoadipic acids, respectively. The stereo, chemistry of the products was established by IH NMR spectroscopy and X-ray analysis.Key words: 2,4-diaminoglutaric acid, 2,5-diaminoadipic acid. nucleophilic substitution; stereoisomers; racemization.2,4-Diaminoglutaric acid (In) has been previously isolated as a natural product t,z and synthesized by different methods. 1"4 The (2S,4S)-enantiomer of la has been synthesized 4 and its complexing properties have been studied. 5 Methods for the synthesis of 2,5-diaminoadipic acid (lb) ~,~ and its stereoisomers s are also known. It is interesting to note that derivatives of acids la,b exhibit antitumor activity. 9,t~We have developed simple methods for the synthesis of diastereomers of compounds la,b from the corresponding monoaminodicarboxylic acids, viz., glutamic (2a) and 2-aminoadipic (2b) acids.Compound 2a is readily transformed into methyl 4-bromo-N-phthalylglutamate (3a). !1 Its reaction with potassium phthalimide (PP) in DMF followed by separation of the mixture of diastereomers afforded methyl 2,4-diphthalimidoglutarates (threo-4a and meso-4a), whose acid hydrolysis resulted in threo-and meso-la diastereomers (Scheme 1).An attempt to obtain the threo-forrn of 4a from erythro-3a was unsuccessful, since the reaction of the latter with PP in DMF ,,vas accompanied by racemization. Stirring of an equimolar mixture of meso-4aand PP in DMF for 3 h at ~ 20 ~ resulted in a mixture of diastereomers of 4a (meso/threo = 5 according to HPLC data). Evidently, PP is a very strong base, since the inversion of the carbanion follows the abstraction of the a-proton. The alternative mechanism of racemization of the phthalimide group involving nucleophilic substitution by the phthalimide ion is impossible, since heating of an equimolar mixture of meso-4aand potassium 4-nitrophthalimide in DMF for 6 h at 68 ~ did not afford (HPLC) diastereomers of methyl 2-phthalimido-4-(4-nitrophthalimido)glutarate (5),

Moscow megacity has a big gap in assessment of air quality, resulting in severe aerosol pollution. Black carbon (BC) concentrations over different timescales, including weekly and diurnal, are studied during four seasons of 2019–2020 at urban background site. Seasonal BC varies from 0.9 to 25.5 μg/m3 with a mean of 1.7 ± 1.4 μg/m3. Maximum mean BC equal to 2.2 ± 1.8 μg/m3 was observed in spring. Diurnal trends of black carbon concentrations differ in spring/summer and autumn/winter periods, they exhibit morning and evening peaks corresponding to traffic combined with the boundary layer height effect. The weekly cycle of BC characterizes the highest amount of combustion-related pollution on working days and the characteristics of population migration from a city for weekend. Seasonal pollution roses show the direction of the highest BC contamination. For identification of BC sources relating to traffic, heat and power plants, and industry around the site, polar plots are used. The spectral dependence of the aerosol light attenuation provides the estimate for Absorption Angstrom Exponent (AAE). We use the AAE above 1.3 and high frequency of AAE observation above 1 in order to support the assessment for a contribution of biomass burning in the region around Moscow in autumn and winter as well as of agriculture fires and wildfires in warm seasons. Air masses arriving to a city from fire-affected regions in spring and summer impact urban air pollution.

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Temporal variability in erythemal radiation over Northern Eurasia (40°–80° N, 10° W–180° E) due to total ozone column (X) and cloudiness was assessed by using retrievals from ERA-Interim reanalysis, TOMS/OMI satellite measurements, and INM-RSHU chemistry–climate model (CCM) for the 1979–2015 period. For clear-sky conditions during spring and summer, consistent trends in erythemal daily doses (Eery) up to +3%/decade, attributed to decreases in X, were calculated from the three datasets. Model experiments suggest that anthropogenic emissions of ozone-depleting substances were the largest contributor to Eery trends, while volcanic aerosol and changes in sea surface temperature also played an important role. For all-sky conditions, Eery trends, calculated from the ERA-Interim and TOMS/OMI data over the territory of Eastern Europe, Siberia and Northeastern Asia, were significantly larger (up to +5–8%/decade) due to a combination of decrease in ozone and cloudiness. In contrast, all-sky maximum trends in Eery, calculated from the CCM results, were only +3–4%/decade. While Eery trends for Northern Eurasia were generally positive, negative trends were observed in July over central Arctic regions due to an increase in cloudiness. Finally, changes in the ultraviolet (UV) resources (characteristics of UV radiation for beneficial (vitamin D production) or adverse (sunburn) effects on human health) were assessed. When defining a “UV optimum” condition with the best balance in Eery for human health, the observed increases in Eery led to a noticeable reduction of the area with UV optimum for skin types 1 and 2, especially in April. In contrast, in central Arctic regions, decreases in Eery in July resulted in a change from “UV excess” to “UV optimum” conditions for skin types 2 and 3.