## 5 Conclusions  
This study analyzes the behaviour of gaseous pollutants, such as nitrogen and sulfur oxides, in the ground-level atmosphere in the urban (Irkutsk station) and background (Listvyanka station) areas of the Southern Baikal region and determines their sources and relationship with the meteorological conditions in the region. Analysis of continuous monitoring of 4-year measurements of nitrogen and sulfur dioxide concentrations in the air at two stations, located 70 km apart in the Southern Baikal region, revealed similarity in their annual variability with maximum values in the winter months and minimum values in the summer. Both stations showed the highest concentrations of gaseous pollutants in February. Thermal power plants and motor vehicles are the main sources of air pollution with nitrogen and sulfur oxides in the Southern Baikal region. Meteorological parameters of the atmosphere, such as air temperature, precipitation, boundary layer thickness, and wind speed and direction, have a direct impact on the concentrations of gaseous pollutants. An increase in precipitation in the warm season decreases the concentrations of sulfur and nitrogen oxides in the air, whereas a high number of calms and temperature inversions in the winter dramatically increases these concentrations. We determined the daily variations in gaseous pollutants at the monitoring stations, which differed in time scale. There was a clear dependence of the increase in the nitrogen oxide concentrations at the urban station with the increase in road traffic during rush hours. In the morning and evening hours, the nitrogen dioxide concentrations were 3 times higher than at night. The highest sulfur dioxide concentrations in the air above the city were observed in the evening. In the rural area, the highest concentrations were recorded at night,  
Figure 10: Air mass transport trajectories from large anthropogenic sources in Irkutsk, Angarsk, and Shelekhov calculated using the HYSPLIT model: (**a**) 13 December 2023 (6 a.m.) and (**b**) 14 December 2023 (10 p.m.). which was likely due to the increase in the frequency of the transport of the pollutants from their sources through the system of low-level jet streams. Using the nonparametric wind regression (NWR) model, we classified the meteorological conditions, under which acid gases enter the atmosphere of the southern basin of Lake Baikal. The highest concentrations of nitrogen and sulfur oxides were recorded on the west coast of the southern basin of Lake Baikal, with westerly and northwesterly winds and wind speed ranging from 6 to 12 m per second. This corresponds to the locations of the large industrial centers in the Irkutsk region. The distribution of nitrogen monoxide measured at the station differed from the above gases. In spring, summer, and autumn, nitrogen monoxide concentrations had an additional maximum with southerly winds, which is likely due to the emissions from numerous ships in Listvenichny Bay. The transport pathways of the anthropogenic air masses can be predicted from synoptic maps and confirmed using the HYSPLIT modelling of air mass back trajectories. This study revealed that westerly and northwesterly winds prevailing in the lower boundary layer above the southeast of Siberia transported plumes directly to the water area of Lake Baikal. Therefore, this study provided information on the characteristics and transport of trace gases and allowed us to understand their potential impact on air quality near the southern basin of Lake Baikal. Conceptualization, methodology, data analysis, writing, review and editing: M.Y.S. and Y.V.M. ; data collection and analysis, software, and visualization: V.A.O., V.L.P. and E.S.L. ; project administration, review and editing: T.V.K. All authors have read and agreed to the published version of the manuscript. This study was supported by the state project No.