# 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

Table 3: Mean monthly characteristics of hourly concentrations of eBC, particulate matter (PM \(\leq\) 2.5 μm), and SO\({}_{2}\) based on the automatic measurements at the Listvyanka station from May 2023 to February 2024, \(\mu\)g m\({}^{-3}\). Figure 8: Dynamics of mean monthly temperature and humidity at the Listvyanka station in 2023–2024. concentrations on 19-10 September 2023 due to the change in the wind direction from NW to SE (from the lake). At the same time, during heavy precipitation on 25-26 September 2023, despite the predominance of the NW transport on these days, the eBC concentrations decreased significantly (Figure 10). Relative Black Carbon Concentration in Submicron Aerosol Based on the Results of the Shipborne and Listvyanka Station Measurements  
We analyzed the results of joint measurements of the concentrations eBC and submicron aerosol particles (PM \(\leq\) 2.5 \(\upmu\)m, PM\({}_{2,5}\)) at the Listvyanka station and above the water area of Lake Baikal during the summer expeditions onboard the RV (Tables 1-3). To study the total concentration and distribution of particles, we used DUSTTRAK 8533 spectrometer (TSI Incorporated, Shoreview, MN, USA) dust analyzer (PM\({}_{10}\), PM\({}_{2,5}\), and PM\({}_{1.0}\)) display cumulative and differential data on the number of particles [40]. Analysis of the Tables 1-3 revealed that the relative concentration of eBC in the submicron aerosol recorded in the air above the water area of Lake Baikal in the summer of 2019 changed from 2-4% in the northern background areas of the lake to 9-13% in the areas with the local air pollution sources near the large coastal settlements. In 2023, this ratio was higher both in background areas (8-9%) and near the local air pollution sources (14-18%). That year, we recorded a particularly high relative concentration (eBC/PM\({}_{2.5}\)) in the water area of the lake, near the Slyudyanka town (29%) during a local fire on the lake's coast and at the Angara River source (28%) where air pollution from local coastal sources was observed and intense navigation in Listvennichny Bay strongly affected. \begin{table}
\begin{tabular}{l l l l l l l} \hline \hline  & **Wind Direction** & **NE (0–90°)** & \begin{tabular}{l} **SE (90°-180°)** \\ **(Northern Part of the Lake)** \\ **the Lake)** \\ \end{tabular} & \begin{tabular}{l} **SW (180°-270°)** \\ **(Southern Part of the Lake)** \\ **the Lake)** \\ \end{tabular} & \begin{tabular}{l} **NW (270°-360°)** \\ **(from the Land to** \\ **the Lake)** \\ \end{tabular} & \begin{tabular}{l} **NW (330°-350°, \(<\)3 m/s)** \\ **(along the Angara** \\ **River Valley)** \\ \end{tabular} \\ \hline \multirow{3}{*}{\
\begin{tabular}{l} August \\ 2023 \\ \end{tabular} } & Number of cases & 10 & 21 & 160 & 350 & 218 \\  & Mean eBC, \(\upmu\)g m\({}^{-3}\) & 0.07 & 0.08 & 0.11 & 0.17 & 0.21 \\  & Max eBC, \(\upmu\)g m\({}^{-3}\) & 0.16 & 0.21 & 0.32 & 0.61 & 0.61 \\ \hline \multirow{3}{*}{
\begin{tabular}{l} January \\ 2024 \\ \end{tabular} } & Number of cases & 23 & 343 & 231 & 310 & 18 \\  & Mean eBC, \(\upmu\)g m\({}^{-3}\) & 0.23 & 0.28 & 0.29 & 0.49 & 0.70 \\ \cline{1-1}  & Max eBC, \(\upmu\)g m\({}^{-3}\) & 0.43 & 0.97 & 1.31 & 2.04 & 1.34 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Mean eBC concentrations (\(\upmu\)g m\({}^{-3}\)) for different wind directions at the Listvyanka station in August 2023 and January 2024. Figure 9: Mean hourly concentrations of eBC and SO\({}_{2}\) at the Listvyanka station, January 2024. At the <<Listvyank>> monitoring station during the cold season (from November to January 2024), with a change in mesoscale atmospheric circulation, an increase in the emissions from anthropogenic sources, and a decrease in the height of the atmospheric boundary layer, the eBC relative concentration ranged from 8 to 13%, and from 11 to 14% in the warm season.