# Black Carbon in the Air of the Baikal Region, (Russia): Sources and Spatiotemporal Variations
## 4 Conclusions  
The investigations conducted in 2019 and 2023 to study the mass concentration of eBC and submicron aerosol above the water area of Lake Baikal and the west coast of its southern basin (Listvyanka station) revealed their main sources and spatiotemporal variability. The background level of the eBC mass concentration in the air above the water area of Lake Baikal ranged from 0.2 to 0.3 \(\mu\)g m\({}^{-3}\), with minimum values of 0.7-0.15 \(\mu\)g m\({}^{-3}\) recorded in the northern basin of Lake Baikal (Ayaya Bay). During the air mass transport along the valleys of the lake's large tributaries, the Selenga and Barguzin rivers, as well as at the Angara River source and near the towns of Slyudyanka, Baikals, and Severobaikalsk located on the coast, the eBC concentrations were elevated in the water area of the lake. Here, the eBC concentrations rose to an average of 0.9-1.8 \(\mu\)g m\({}^{-3}\). Thick smoke plumes  
Figure 10: Mean hourly concentrations of BC, nitrogen oxide, and sulfur dioxide (**a**) and meteorological parameters at the Listvyanka station (**b**), September 2023.  
from intense wildfires in 2019 covering the Irkutsk Region, Krasnoyarsk Territory, and Yakutia, as well as the local fire on the east coast of the lake, led to an increase in the eBC concentration to 5-6 \(\upmu\)g m\({}^{-3}\) in the near-water layer of the atmosphere in the central basin. We determined the diurnal dynamics of eBC in different areas of the lake. The diurnal variability was poorly manifested under background conditions. We recorded the highest values during the evening and night hours during breeze circulation from the coastal zone near the large settlements in the southern basin and with the air mass transport along the valleys of the lake's tributaries (the Selenga, the Barguzin and in the source of the Angara River). The evening maximum was up to 10 times higher than the daytime maximum. During the summer of 2019, the proportion of eBC in the total mass of submicron aerosol in the air above the water are of Lake Baikal ranged, depending on the direction of air mass flows, weather conditions, and smoke emission transport, from 2-4% at the background sites of the lake to 9-13% near the large settlements on the coast. In 2023, this proportion was higher both at the background sites (8-9%) and near the local air pollution sources (14-18%). At the air monitoring station near the Listvyanka settlement (west coast of the southern basin), we analyzed the seasonal dynamics of the eBC concentrations, mass particle (\(\leq\)2.5 \(\upmu\)m) and gas impurity (sulfur and nitrogen dioxides) concentrations. Long-range transport of emission plumes from regional coal-fired thermal power plants situated in the large cities of the Baikal region mostly contributed to the eBC concentration in the air of this area in winter. In summer, the air near the Listvynka station was relatively clean when the pollutants were removed by precipitation. The proportion of eBC in the total mass of submicron aerosol in this area ranged from 8 to 13% in the cold season and increased to 11-14% in the warm season. The study of eBC in the air of the Baikal region continues. We take samples and analyze the chemical composition of organic compounds (soot and PAHs) of aerosol particles with such size fractions as 10, 5, 2.5, and 1.0 \(\upmu\)m. Under the electron scanning microscope, we examine morphology and elemental composition of carbon-bearing and other aerosol particles at the Listvyanka station in different seasons of the year, and above the water area of Lake Baikal in the summer. Conceptualization, original design and methodology, T.V.K. ; data collection and analysis, software and visualization, E.P.Y., M.Y.S., G.S.Z., A.S.Z. and L.P.G. ; writing and editing the manuscript T.V.K., M.Y.S. and L.P.G. All authors have read and agreed to the published version of the manuscript. This research was supported by the project of the Russian Science Foundation (RSF) No. 19-77-20058 P.  
Not applicable.