## 3 Results and Discussion
### Weekly and Daily Variations of SO\({}_{2}\), NO, and NO\({}_{2}\)  
Figure 7 shows the data on the daily and weekly variability of the concentrations of sulfur and nitrogen oxides in the air. As known from the literature, the intensity and nature of the emission sources, as well as the spatiotemporal dynamics of ABL, affect these indicators [65; 66]. Because ABL is closely related to the heating of the surface by solar irradiance, it has a typical daily variability. If we compare the data from the two stations, we can notice significant differences in the daily and weekly variations (Figure 7).  
At the Irkutsk station, there are two typical increases in the nitrogen oxide concentrations, which occur from Monday to Friday in the morning (8 to 10 a.m.) and in the evening (6 to 7 p.m). The morning peak in nitrogen oxide concentrations in Irkutsk is associated with an increase in automobile traffic and the minimum depth of ABL. After 11 a.m. to 12 p.m., when the ABL depth increases, the air pollutants dissipate faster, and the nitrogen oxide concentrations decrease at the station (see Figure 7). The second daily peak (6 to 7 p.m.) is also associated with the evening rush hour in the city. From 9 p.m. to 6 a.m., the nitrogen oxide concentrations decrease to background urban values.  
Analysis of the weekly dynamics of gaseous pollutants in the air at the Irkutsk station demonstrates a so-called \"weekend effect.\" The assessment of fluctuations in air pollutants, depending on the day of the week, revealed that the road traffic affects the concentration of nitrogen oxides in the air of urban areas. On Saturday and Sunday, the nitrogen oxide concentrations decrease by 20-30% compared with weekdays [67; 68; 69]. The difference between the pollution on weekdays and weekends varies, depending on the season. It is the most obvious in the cold season of the year due to the increase in the volume of fuel burnt to warm up the engine and the interior of the cars.  
Daily cycles of nitrogen dioxide in the air above Irkutsk have one broad peak between 12 and 6 p.m. Unlike nitrogen oxides, morning and evening peaks are not typical of nitrogen dioxide in the daily and weekly cycles of concentrations, indicating that the main source of this gas entering the urban air is the combustion of coal by thermal power plants.  
Analysis of the data on the concentration of gaseous pollutants in the air at the Listvyanka station revealed that the daily variations in the sulfur dioxide concentrations are generally similar to the variations in the nitrogen dioxide concentrations and have a unimodal distribution, with a peak in the morning from 6 to 11 a.m. However, during the heating season, a second peak appears in the distribution of nitrogen dioxide, in the evening or at night, which begins at about 6 p.m. In the weekly variations, there is a slight increase in the NO concentrations on weekends. Daily variations of the sulfur dioxide concentrations are generally similar and have a unimodal distribution, with a peak in the morning from 6 to 11 a.m. However, during the heating season, a second peak appearsin the distribution of nitrogen dioxide, in the evening or at night, which begins at about 6 p.m. This may be due to the increase in the number of cars in the settlement on weekends. There are no large industrial enterprises in the settlement; the heating sources are the boiler facility and house stoves. The number of residents in the settlement is small (less than 2000 people in 2021). The regional transport of the polluted air from the cities of the Baikal region and the motor vehicles that contribute to air pollution all year around are likely the main sources of air pollution by nitrogen oxides near the Listvyanka settlement.