# 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
Figure 3 and Table 1 demonstrate four episodes with different degrees of increase in the eBC concentrations and two episodes with background values of eBC mass concentration in the air above the water area of the lake in 2019. The first growth of the eBC concentration was recorded in the southern basin near the large settlements, such as Listvyanka, Baikalsk, and Slyudyanka. The Listvyanka settlement is the large tourist center on the west coast of the southern basin where tourist camps, private houses, and a high-traffic highway are located in the limited area along the coast. Furthermore, ships operating on diesel fuel moor in Listvenichny Bay bordering the settlement, also increasing the eBC concentration in the air above the lake. On the east coast of the southern basin, the towns of Slyudyanka and Baikalsk allocate large coal-fired heat sources, highways and railways. In these areas, the eBC concentration increased on average from 0.59 \(\mu\)g m\({}^{-3}\) in Listvenichny Bay to 0.93 \(\mu\)g m\({}^{-3}\) in Baikalsk and 1.08 \(\mu\)g m\({}^{-3}\) in Slyudyanka. Figure 3: Spatiotemporal variability of the eBC mass concentration in the coastal zone of Lake Baikal during the 2019. The first lidar responses from wildfire smoke above the water area of the lake occurred on the night of 27 July 2019 in the area of the northern basin. On 28 July 2019, measurements near the Severobaiakalsk and Nizhneangarsk towns were carried out under the influence of smoke plumes from wildfires, which came to the water area of the lake from the north of the Irkutsk Region. Then, the smoke aerosol began to descend, filling the atmosphere down to the lake's surface. From 28 to 29 July 2019, satellite monitoring ([[http://fires-dv.kosmosnimki.ru](http://fires-dv.kosmosnimki.ru)]([http://fires-dv.kosmosnimki.ru](http://fires-dv.kosmosnimki.ru)), accessed on 1 June 2024) recorded many wildfire sites north of Lake Baikal (Figure 4a). A backward trajectory analysis (Figure 4b) revealed that smoke aerosol was transported to the lake from the north. At the same time, based on the data on the general synoptic situation above the Northern Hemisphere on 29 July 2019, the anticyclone shifted to the southeast. The elevated eBC concentrations in the northern part of Lake Baikal on 28 and 29 July near the Severobaiakalsk and Nizhneangarsk towns were associated both with the activities of these large settlements and with an increase in the smog from wildfires in the northern areas of the Irkutsk Region. In these areas, the mean BC concentrations increased to 1.09 \(\upmu\)g m\({}^{-3}\), with the maximum eBC concentration of 2.16 \(\upmu\)g m\({}^{-3}\) (Figure 3, Table 1). On 29 and 30 July 2019, smoke aerosol descended to the lake's surface, which remote sensing and local monitoring devices recorded. From the evening of 29 July to 1 August 2019, along the northern basin-Chivyrkuy Bay-Selenga delta route, the RV moved through a vast area of thick smoke plumes. From 30 July to 1 August 2019, relative aerosol concentration in the atmospheric layer up to 1000 m above the water area of the lake was approximately three times higher than the background values. At the same time, in addition to distant wildfire sites, when the RV navigated in the central basin, local measuring instruments (gas analyzers) recorded a dramatic increase in eBC in the near-water atmospheric layer, up to 5.0-6.0 \(\upmu\)g m\({}^{-3}\) with background values of 0.1 \(\div\) 0.2 \(\upmu\)g m\({}^{-3}\). The concentration of sulfur dioxide increased to 47 \(\upmu\)g m\({}^{-3}\), with background values of 5-8 \(\upmu\)g m\({}^{-3}\). The mean particle size (110 \(\div\) 160 nm) was higher than the background values above the lake (30 \(\div\) 70 nm). There is also a sharp increase in the concentration of submicron aerosol (SMA) from 60 cm\({}^{-3}\) to 300 cm\({}^{-3}\). The eBC mass concentrations in smoke plumes from wildfires above the water area of Lake Baikal were on average 25 times higher than the background level and, for single measurements, they were more