# 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
\begin{table}
\begin{tabular}{c l c c c c} \hline \hline
**Emission Type** & **Area** & **Mean MeBC \(\pm\) SD,** & **Min** & **Max** & **\(N\)** \\ \hline Background level & Water area near the southwest coast, & 0.28 \(\pm\) 0.09 & 0.12 & 0.53 & 54 \\  & 25 to 27 July 2019 & Water area near northeast coast, & 0.17 \(\pm\) 0.08 & 0.06 & 0.38 & 40 \\  & 28 to 29 July 2019 & & & & \\ \hline  & Listvennichny Bay, & & & & \\  & 24 to 25 July 2019, & 0.59 \(\pm\) 0.25 & 0.18 & 1.06 & 19 \\ Anthropogenic & 03 August 2019 & Water area near the Baikalsk town, & & & \\ impact & 25 July 2019, 03 August 2019 & 0.93 \(\pm\) 0.26 & 0.59 & 1.54 & 18 \\  & Water area near the Slyudyanka town, & 1.08 \(\pm\) 0.43 & 0.55 & 1.61 & 5 \\  & 25 July 2019 & & & & \\ \hline  & Water area near the towns of & & & & \\  & Severobaiakalsk town and & 1.09 \(\pm\) 0.38 & 0.47 & 2.16 & 41 \\ Wildfires & 28 July 2019 & & & & \\  & Chivyrkuy Bay–Barguzin Bay & & & & \\  & –water area along the Turka & 4.17 \(\pm\) 0.83 & 2.46 & 6.33 & 104 \\  & settlement-the Selenga delta route, & & & & \\  & 29 July to 01 August 2019 & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Statistical analysis of different types of eBC emissions into the water area of Lake Baikal in the summer of 2019.  
than 100 times higher. By the evening of 1 August 2019, the air began to clear, reaching 0.2 \(\div\) 0.4 ug m\({}^{-3}\) on 3 and 4 August 2019 in the southern part of the lake (Figure 3). Analysis of air mass transport backward trajectories (HYSPLIT) for this period indicated that local wildfire near Sosnovka Bay on the northeast coast of Lake Baikal made an additional contribution to the increase in the concentrations of BC and sulfur dioxide, as well as to the amount of submicron fraction of particles. Satellite monitoring data on 26 July 2019 confirmed the hypothesis of the appearance of smoke plumes from nearby sources. It recorded a wildfire on the east coast of Lake Baikal near Sosnovka Bay (Figure 5a). Analysis of backward trajectories calculated using the HYSPLIT model (Figure 5b) revealed that smoke from the wildfire on the east coast was spreading above the lake to the northwest. Figure 4: Satellite image of the territory near Lake Baikal: (**a**) with wildfire sites in the north (28–29 July 2019); (**b,c**) backward trajectories calculated using the HYSPLIT models for 29 July 2019 (GMT) ([[http://fires-dv.kosmosmimki.ru](http://fires-dv.kosmosmimki.ru)]([http://fires-dv.kosmosmimki.ru](http://fires-dv.kosmosmimki.ru)), accessed on 1 June 2024). Figure 5: Satellite image of the central basin of Lake Baikal: (**a**) with smoke plume from a wildfire near Sosnovka Bay (red circle); (**b**) backward trajectories calculated using the HYSPLIT model for 26 July 2019 (GMT). In the summer of 2023, from 5 to 15 August, we continued our studies of the air composition above Lake Baikal onboard the RV G.Yu. Vereshchagin. A cyclone northwest of Lake Baikal, with its center over the Krasnoyarsk Territory, determined the general synoptic situation during the expedition. The weather was mostly cloudy and rainy, with low clouds and occasional clearing. The principal difference between the 2023 expedition and the 2019 was the absence of wildfires in the Baikal region, allowing us to more clearly identify the contribution of local regional sources to air pollution above the lake and trace the transport of regional and long-distance transboundary pollutants. During the expedition, we recorded 849 series of eBC measurements, excluding measurements associated with pollution from the RV during moorings (emissions from exhaust pipe). We determined mean daily eBC mass concentration under background conditions and near settlements (Figure 6, Table 2). Like in 2019, in 2023, there were episodes with high eBC concentrations during works near large settlements, especially in the south of the lake, both at the beginning of the expedition, on 5-7 August 2023, and at the end, on 14-15 August 2023.