## 3 Results and Discussion  
### Concentration of the Main Ions in the Snow Waters of the Baikal Basin  
Based on the data on the concentrations of the main ions in snow water, boxplots were constructed. Figure 3 shows the results of the chemical analysis of meltwater samples taken in 2017-2022 at fourteen sites (Figure 1). In Figure 3, the ordinate shows the values of concentrations (in mg/dm\({}^{3}\)), and the abscissa manifests the number of the region. The diagram shows the median (thick line), the first quartile (Q1, the lower limit of the \"box\"), and the third quartile (Q3, the upper limit of the \"box\"), as well as one-time outliers, which are atypical values that fall out of the general series of observations and exceed the limits of one and a half product differences between Q3 and Q1 (circles). Despite the diversity of industrial facilities in the region (Table 1), their influence is local and concentration maxima are obtained near the source (Figure 3). As can be seen from Table 1, the main anthropogenic sources in the region are heat power facilities and motor transport [67]. Therefore, the concentrations of sulfates, the tracer of coal combustion, in years. Irkutsk, Angarsk, and Ulan-Ude have on average similar values: (median from 5.7 to 6.2 mg/L). Concentrations are similar to the results, as in the cities of the European part of Russia: 2.2-7.7 mg/L in Moscow [68] and 3.4-5.6 in Izhevsk [69] and the Far East: 4.9 mg/L, (Vladivostok) [70]. In areas remote from sources (plots No. 9, 10, 11, 13 14) median concentrations of sulfates vary from 0.01 to 0.95 mg/L. This is less or comparable to the concentrations of sulfates (0.86 mg/L) in the snow cover in the north of the country (Komi Republic) [71]. Nitrogen oxides (Figure 3) are distributed over the territory, although more evenly, and an increase in concentrations was also noted near industrial sources (No. 2, 4) in the cities of Ulan-Ude (median = 3.8 mg/L; maximum = 11.5 mg/L) and Angarsk (median = 1.2 mg/L; maximum = 6.9 mg/L). A comparison of our results with the results obtained in [68; 69; 70] showed that the concentrations of nitrates in the snow cover of Ulan-Ude are 1.5 times higher than in Moscow (1.5 mg/L) and Izhevsk (2.4 mg/L) and close to the concentration in Vladivostok (3.4 mg/L). By analogy with sulfates, elevated concentrations of ni  
Figure 3: Concentrations of the main ions in the snow water of the Baikal Basin; Data analysis and discussion; Sampling area number: (1) Irkutsk; (2) Angarsk; (3) Shelekhov; (4) Ulan-Ude; (5) Selenginsk and Kamensk; (6) Irkutsk—Listvyanka; (7) Irkutsk—B. Goloustnoe; (8) Selenga delt; (9) Ulan-Ude—Kurumkan; (10) Southeast cost; (11) Baikal Nature Reserve; (12) Ice of South Baikal; (13) Ice of Middle Baikal; (14) Ice of Nothern Baikal. The diagram shows the median (thick line), the first quartile (Q1, the lower limit of the “box”) and the third quartile (Q3, the upper limit of the “box”), as well as one-time outliers being atypical values that fall out of the general series of observations and exceeding the limits of one and a half product differences between Q3 and Q1 (circles). trates are recorded along the direction of the main transport (No. 8) up to 23 mg/L (median = 2.4 mg/L), and on the ice of the Southern Basin of Lake Baikal (No. 12), up to 9.1 mg/L (median = 2.5 mg/L). If we consider the marker substances of other industrial enterprises, we can see a similar picture (Figure 3). For example, sodium and fluorine, markers of aluminum smelting [72,73], are concentrated near the aluminum plant of the city of Shelekhov. The maximum concentrations are 29.3 mg/L (Na) and 50.7 mg/L (F). The median fluoride content in Shelekhov's snow cover (3.8 mg/L) is close to the values in Bratsk (from 3 to 6 mg/L) [74] and Krasnoyarsk [75], where large aluminum plants are also located. When moving away from cities, there is a sharp decrease in fluorine concentrations to 0.03-0.2 mg/L, and sodium to 0.1-0.2 mg/L. The maximum of chlorine ions is localized near the Angarsk Polymer Plant (Figure 3).