# Black Carbon in the Air of the Baikal Region, (Russia): Sources and Spatiotemporal Variations
## 1 Introduction  
Intensive economic growth in Eastern Siberia requires constant environmental monitoring and protection. There are both high-capacity industrial centers and unique natural objects, such as Lake Baikal, large rivers, and extensive forests. The Baikal region is located in the central part of Eastern Siberia and has direct access to the Mongolian borders. Its area of 315 thou km\({}^{2}\) covers the watershed basin of Lake Baikal and includes three subjects of the Russian Federation (Irkutsk Region, Trans-Baikal Territory, and Republic of Buryatia). The total amount of pollutants entering the atmosphere of the Baikal region consists of about 100 items. According to [PERSON], the main release of pollutants into the atmosphere of the Baikal region comes from thermal power plants burning solid organic fuels (coal). Sulfur dioxide, nitrogen oxides, carbon monoxide, solid particles, and black carbon predominate in the emissions of these facilities [1]. Enterprises of the fuel and energy industry, chemistry and petrochemistry, metallurgy, woodworking, and pulp and paper manufacturing play animportant role in the industrial structure of the Irkutsk Region, which is the most developed in the Baikal region [2]. Lake Baikal is the most important strategical resource of the Baikal region. It is the world's deepest (1642 m) and oldest (\(\sim\)25 million years) lake and the largest repository of the world freshwater reserves (20%), the ecosystem of which concentrates about 70% of endemics. In 1996, Lake Baikal was included on the UNESCO World Heritage List. Currently, the economic activities of the Baikal region, which are carried out within the watershed of Lake Baikal, have a significant impact on its ecological state. Research concerning the physical characteristics of the chemical composition of air in the Baikal region and above the water area of Lake Baikal, which began at the end of the 20 th century, mainly confirmed the background parameters of the continental atmospheric aerosol over this area. Forests, the largest source of natural aerosols responsible for the stable composition of air, cover 70% of the area in the Baikal region [3]. In recent decades, the composition of air, precipitation, and ice, as well as surface water temperature in Lake Baikal, have been changing in the Baikal region due to climate change. In this area, the climate warming trend, with the annual air temperature trend of +1.3 \({}^{\circ}\)C, is twice the global temperature trend of +0.6 \({}^{\circ}\)C over 100 years. Over 20 years, the surface water in the lake has warmed by 2 \({}^{\circ}\)C. The lake also showed physical and biological changes associated with warming and eutrophication [4; 5; 6; 7; 8]. Man-made emissions from industrial centers of the Baikal region also influence the composition of aerosol, precipitation, and other natural environments in some areas of the lake's watershed basin. For example, the transport of sulfur and nitrogen oxides over distances of <70-100 km from large coal-fired power plants in the Irkutsk Region has a significant impact on the composition of precipitation and, hence, acidification of river waters in the coastal areas of the southern basin of Lake Baikal [9]. Wildfires are one of the major sources of climate-sensitive substances released into the atmosphere [10; 11; 12]. In Russia, Siberia particularly suffers from wildfires where the climate warming trend is more widespread. From 2017 to 2022, the total area of wildfires amounted to 45.2 mln ha. Large-scale wildfires between 2017 and 2022 covered from 70 to 90% of Siberia and the Far East [13; 14]. Overall, the total carbon emissions resulted from wildfires are estimated for the past decades at 180-200 TgC yr [15] In recent years, the environmental impact of wildfires in the Baikal region has also increased [16; 17].