The article analyzes the chemical composition (ions, elements, and polycyclic aromatic hydrocarbons) of the atmospheric aerosol in the near-water layer of the atmosphere above Lake Baikal during wildfires in Siberia. Aerosol deposition affects the aquatic environment of the watershed basin and the lake itself. The current law on Lake Baikal limits the activity of the permanent stationary anthropogenic sources of the aerosol in the central ecological zone, and they do not have a significant negative impact. Wildfires can have a much greater impact on the environment. Smoke emissions entering the area of Lake Baikal due to wildfires change the chemical properties of the atmospheric aerosol and increase its mass and number concentration. The concentrations of NH₄⁺, K⁺, NO₃⁻, and SO₄²⁻, which enter with submicron aerosol fraction, increase in the ionic composition of the aerosol. The composition of polyaromatic compounds changes, and their concentrations increase. Elevated concentrations of B, Mn, Zn, As, Sr, Cd, and Pb in the composition of aerosol indicate the influx of air masses from the areas prone to wildfires. Despite the sporadic effects of these natural factors, they affect the pollution of various Baikal ecosystems, especially small tributaries of the lake, whose main supply is atmospheric.

Eutrophication is a major ecological problem and affects and endangers freshwater bodies, making assessment of the trophic status of water bodies crucial for their restoration and sustainable use. Lake Baikal is affected by a number of environmental stressors, including coastal eutrophication. Daily measurements of concentrations of nutrients, dissolved oxygen (DO), chlorophyll-a (Chl-a), weekly measurements of algae abundance and biomass in the open water season in June-December 2020, and measurements of concentrations of nutrients at 2–7-day intervals in June-October 2021 were made in the littoral of the South Baikal for the first time. It was shown that nitrate and phosphate concentrations decreased by July-August, their minimum content was maintained until September, concentrations began to increase in October and reached a maximum in December. The maximum abundance and biomass of algae and chlorophyll concentrations were only observed in early July. Storm situations increased the content of nitrogen, phosphorus and DO in water, the duration of their influence was not more than 2 days. A correlation matrix revealed significant positive correlations of NO₃⁻-DO, phosphate (SPR)-NO₃⁻, SRP-DO and biomass-Chl-a and strong negative correlations between water temperature (Tw)-DO, Tw-NO₃⁻, Tw-total nitrogen (TN) and Tw-SRP. Based on SRP and NO₃⁻ concentrations and TN:TP ratios, it was concluded that algal development was limited to nitrogen and phosphorus in summer. The trophic status of the Southern Baikal littoral zone was assessed using classifications based on TN, TP, NO₃⁻, SRP, Chl-a content and algal biomass, as well as the Carlson index (TSI) and probabilistic assessment. The results of assessments using different methods of trophic status determination showed that the Baikal littoral zone in the study area belongs to the oligotrophic type with minor elements of mesotrophy. According to the saprobity index, water purity of littoral waters varies within the oligosaprobic and β-mesosaprobic zones and corresponded to quality classes II and III (clean and moderate purity); the system demonstrates a high capacity for self-purification.

The measured concentrations of inorganic pollutants, such as ozone (2015–2018), sulfur, and nitrogen oxides (2012–2018) at air monitoring sites in the south of Eastern Siberia were sampled, following the passive sampling method, and analyzed. The spatial inhomogeneity of atmospheric gas concentrations is presented. The ozone concentration is lower in urban areas than those in rural areas and the background level. However, the nitrogen and sulfur oxide concentrations are higher in the atmosphere over the city site. The seasonal dependence of the ozone concentration was determined using its maximum (March–April) and minimum (September–October) levels. The dynamics of the nitrogen and sulfur oxide concentrations indicate that they are at their highest in December–June and their lowest in July–August. To verify the validity of the pollutant concentration measurements sampled by passive sampling, we compared our results with those obtained following the automatic and filter pack methods. A linear regression analysis and a pairwise modification of Student’s t test evaluated the concentrations of the air pollutant, sampled and measured using different methods, and they correlate well (r = 0.7–0.9). Full validation of the passive sampling method is not possible for some sites; therefore it is necessary to remove the remaining systematic errors in future work.

We examine the acid deposition monitoring results (2000–2010) for the southern territory of East Siberia (the Irkutsk-Angarsk industrial center). It is established that acid deposition events are most frequently recorded in the area of South Baikal (70–100 km south-east of the Irkutsk-Angarsk industrial center), with the acidity of precipitation continuing to increase. Atmospheric precipitation acidity data are compared with long-term monitoring results for Europe.

Since 2004, we have carried out yearly measurements of physicochemical aerosol characteristics onboard research vessels at Southern Hemisphere high latitudes (34–72° S; 45° W–110° E). In this work, we statistically generalize the results from multiyear (2004–2021) measurements in this area of the aerosol optical depth (AOD) of the atmosphere, concentrations of aerosol and equivalent black carbon (EBC), as well as the ionic composition of aerosol. A common regularity was that the aerosol characteristics decreased with increasing latitude up to the Antarctic coast, where the aerosol content corresponded to the global background level. Between Africa and Antarctica, AOD decreased from 0.07 to 0.024, the particle volume decreased from 5.5 to 0.55 µm³/cm³, EBC decreased from 68.1 to 17.4 ng/m³, and the summed ion concentration decreased from 24.5 to 2.5 µg/m³. Against the background of the common tendency of the latitude decrease in aerosol characteristics, we discerned a secondary maximum (AOD and ion concentrations) or a plateau (aerosol and EBC concentrations). The obtained spatial distribution of aerosol characteristics qualitatively agreed with the model-based MERRA-2 reanalysis data, but showed quantitative differences: the model AOD values were overestimated (by 0.015, on average); while the EBC concentrations were underestimated (by 21.7 ng/m³). An interesting feature was found in the aerosol spatial distribution in the region of Antarctic islands: at a distance of 300 km from the islands, the concentrations of EBC decreased on average by 29%, while the aerosol content increased by a factor of 2.5.