# 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  
Nowadays, freshwater ecosystems are experiencing stresses associated with both climate changes and anthropogenic impact [38]. Lake Baikal, a unique ecosystem of a global scale, is of great interest in terms of its comprehensive study. The atmosphere above the lake occupies a vast area (31,500 km\({}^{2}\)) and significantly differs in the composition and variability of gaseous and aerosol components in the air compared to continental regions. It still remains a poorly studied object. Large industrial centers and settlements in the Baikal and Transbaikal regions are distributed unevenly across different areas of this territory. The physical and geographical position of some Lake Baikal areas, the heterogenous orography of the coastal zone, the distribution of pollution sources in the lake's basin, and the prevailing circulation of air masses in a certain area largely determine the spatiotemporal variability of gas and aerosol air pollutants above Lake Baikal. Atmospheric circulation plays an important role in the turbulence and concentration of pollutants in the air [39]. Previous assessments of atmospheric circulation characteristics in the Baikal region indicated the highest frequency of the air mass transport from large stationary air pollution sources in the Irkutsk Region to the southern and central basins of the lake. The air mass transport to the water area from the industrial centers of the Republic of Buryatia mainly occurs in the Selenga River delta (20%) [40]. Despite the general pattern, the air mass transport frequency can vary significantly throughout the year, from 42% in summer to 85% in winter [41]. This, together with other meteorological conditions, also influences the number of pollutants  
Figure 2: Location and equipment of the atmospheric monitoring station “Listvyanka”: (1) layout of the Listvyanka reference station with the largest air pollution sources at Lake Baikal; (2) station location on the hilltop; (3) the main module of the reference station; (4) MTP-5 temperature profiler; (5) Sokol-M1 meteorological complex; (6) RA-915 AM spectrometer; gas analyzer; (7) Hg; gas analyzer; (8) K-100 (CO); (9) R-310A gas analyzer (NO\({}_{2}\) and NO); (10) CV-320 gas analyzer (SO\({}_{2}\)); (11) BAC-10 aethalometer analyzer eBC; (12) DUSTTRAK 8533 dust analyzer (PM\({}_{10}\), PM\({}_{2,5}\), and PM\({}_{1,0}\)). released in the air above the lake during regional transport. In recent years, impact on the ecosystem of Lake Baikal has been increasing due to the infrastructure expansion of tourist and recreational areas in the lake's coastal zone, and the higher frequency of wildfires. In 2015-2016, wildfires on the coast of Lake Baikal completely destroyed the forests on the mountain slopes in some areas, which could affect the restructuring of the biota in the littoral zone of the lake [42]. The influence of eBC on the aerosol composition and ecology of the Lake Baikal air basin, especially during wildfires, determines the importance of studying the temporal and spatial variability of BC mass concentration and fluxes onto the water surface in the fire-hazardous summer seasons. In the summer of 2019, Siberia experienced extreme fire-hazardous weather conditions, with the largest wildfires over the past 20 years, which lasted from June to September. The area of fires at that time was \(\sim\)5 mln ha. The prevailing easterly wind caused air smoke in Western and Eastern Siberia, Kazakhstan, and the Arctic. During the 2019 expedition, there were smoke plumes from extensive wildfires in the Irkutsk Region, Krasnoyarsk Territory, and Yakutia. From 22 to 27 July 2019, when the RV moved along the west coast northwards, the concentrations of eBC and gas impurities, as well as the mass concentration of particles with different size aerosol fractions in the air, showed background values. According to the AARI data, the cyclone came to the region from the northwest, with low clouds and intermittent rains that cleared the atmosphere.