# Black Carbon in the Air of the Baikal Region, (Russia): Sources and Spatiotemporal Variations
## 3 Results and Discussion
### Black Carbon in the Air Basin of Lake Baikal
In the summer months, the variability of eBC concentrations was low; arithmetic means and medians were \(\sim\) 0.1 \(\upmu\)g m\({}^{-3}\), and the maximum values were \(>\) 0.8 \(\upmu\)g m\({}^{-3}\). With the onset of the winter season, arithmetic means of eBC concentrations and their medians increased twofold to threefold, and the maximum values by up to sevenfold. At the same time, the medians appeared to be lower than the arithmetic means, indicating the periodic influence of strong eBC sources. Sulfur dioxide also demonstrated a similar seasonal variation, indicating a common source of this gas and eBC in the air of the study area. This also allows us to assume that the winter maximum was primarily due to the increased operation of thermal power plants, which depends on temperature [43]. Therefore, there is a strong inverse linear relationship between the mean monthly air temperature and the concentration of sulfur dioxide, particulate matter, and black carbon during the winter months in the atmosphere at the Listvyanka station (Table 3 and Figure 8). Figure 7: Diurnal variation of the eBC mass concentration under background conditions (**a**) and near populated areas. (**b**) RMSD areas are highlighted in color. Large coal-fired thermal power plants of the Baikal region are the main common source of eBC and SO\({}_{2}\). Figure 9 shows mean hourly concentrations of these components at the Listvyanka station in January 2024, the coldest period of the year, clearly indicating the direct connection between these pollutants in the air. The concentration dynamics of eBC and sulfur dioxide at the monitoring station strongly depended on the variability of wind direction given in Table 4 for the summer and winter seasons. The maximum concentrations of these pollutants in the air were associated with northwesterly (\(310=340^{\circ}\)) air mass transport from the Irkutsk-Angarsk industrial complex located 70 to 100 km from the Listvyanka station. The lowest eBC concentrations were recorded with northeasterly (0-90\({}^{\circ}\)) winds blowing from the sparsely populated taiga areas in the northern part of the lake, and the highest from the northwestern (270-360\({}^{\circ}\)) land areas allocating large cities of the Baikal region. Of special interest was the northwesterly direction (330-350\({}^{\circ}\)), with winds blowing along the Angara River valley (Table 4), where the concentrations were also the highest. In addition to the directions of air mass transport, the precipitation intensity also influenced the eBC concentration. For instance, its relatively high concentrations were determined during a long absence of rains, from 14 to 21 September 2023, with a short-term decrease in the eBC \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & **N BC** & **eBC Mean** & \begin{tabular}{c} **eBC** \\ **Mediane** \\ \end{tabular} & **Max eBC** & \begin{tabular}{c} **Min** \\ **eBC** \\ \end{tabular} & \begin{tabular}{c} **PM \(\leq\) 2.5 um** \\ **Mean** \\ \end{tabular} & \begin{tabular}{c} **PM \(\leq\) 2.5 μm** \\ **Mediane** \\ \end{tabular} & \begin{tabular}{c} **BC/PM \(\leq\) 2.5 μm** \\ **BC/PM \(\leq\) 2.5 μm** \\ \end{tabular} & \
\begin{tabular}{c} **SO\({}_{2}\)** \\ **SO\({}_{2}\)** \\ \end{tabular} \\ \hline \multirow{3}{*}{
\begin{tabular}{c} May \\ June \\ July \\ August \\ September \\ November \\ December \\ \end{tabular} } & 116 & 0.07 & 0.06 & 0.19 & 0.01 & - & - & - & 10 \\  & 157 & 0.10 & 0.09 & 0.31 & 0.01 & 7 & 5 & 14 & 10 \\  & 363 & 0.13 & 0.12 & 0.50 & 0.03 & 9 & 6 & 14 & 8 \\  & 709 & 0.10 & 0.07 & 0.72 & 0.01 & 12 & 8 & 12 & 7 \\  & 629 & 0.13 & 0.10 & 0.64 & 0.01 & 10 & 6 & 13 & 10 \\  & 661 & 0.14 & 0.10 & 1.21 & 0.01 & 12 & 9 & 11 & 12 \\  & 682 & 0.24 & 0.21 & 1.09 & 0.02 & 27 & 21 & 10 & 18 \\  & 700 & 0.34 & 0.22 & 2.44 & 0.01 & 41 & 27 & 8 & 34 \\ \hline \multirow{2}{*}{2024} & January & 743 & 0.36 & 0.38 & 2.04 & 0.04 & 41 & 31 & 13 & 36 \\  & 458 & 0.36 & 0.33 & 1.20 & 0.05 & 46 & 39 & 8 & 33 \\ \hline \hline \end{tabular}
\end{table}