Spatial-Temporal Variability of Small Gas Impurities Over Lake Baikal During the Forest Fires in the Summer of 2019

atmosphere

Article Spatial-Temporal Variability of Small Gas Impurities over Lake Baikal during the Forest Fires in the Summer of 2019

Galina Zhamsueva *, Alexander Zayakhanov, Vadim Tcydypov, Ayuna Dementeva and Tumen Balzhanov

Institute of Physical Materials Science Siberian Branch, Russian Academy of Sciences, 670047 Ulan-Ude, Russia; [email protected] (A.Z.); [email protected] (V.T.); [email protected] (A.D.); [email protected] (T.B.) * Correspondence: [email protected]; Tel.: +7-30-1243-4664

Abstract: Lake Baikal—a unique ecosystem on a global scale—is undoubtedly of great interest for a comprehensive study of its ecosystem. In recent years, one of the most significant sources of atmospheric pollution in the Baikal region was the emission of smoke aerosol and trace gases from forest fires, the number of which is increasing in the region. The transport and accumulation of aerosol and small gas impurities over water area of Lake Baikal is observed every summer due to forest fires occurring in the boreal forests of Siberia. The atmosphere above the lake covers a huge area (31,500 km2) and is still a little-studied object. This article presents the results of experimental studies of ground-level ozone, sulfur dioxide, and nitrogen oxides in the atmosphere over Lake Baikal, carried out on a research vessel during the boreal forest fires in Siberia in the summer of 2019.

Keywords: Lake Baikal; ground-level ozone; nitrogen oxides; sulfur dioxide; forest ﬁres; research vessel “Academik V.A. Koptyug”

Citation: Zhamsueva, G.; 1. Introduction Zayakhanov, A.; Tcydypov, V.; All fresh-water ecosystems are exposed to the stress inherent in a complicated sys- Dementeva, A.; Balzhanov, T. tem of changes in the climate of the planet [1]. Lake Baikal—a unique ecosystem on a Spatial-Temporal Variability of Small global scale—is undoubtedly of great interest for a comprehensive study of its ecosystem. Gas Impurities over Lake Baikal The principal reasons for choosing Baikal as a natural laboratory to study global climate during the Forest Fires in the Summer of 2019. Atmosphere 2021, 12, 20. change are determined by the unique properties of the Baikal ecosystem. 2 https://dx.doi.org/10.3390/atmos12 The atmosphere over Lake Baikal covers a vast area (31,500 km ) and has more signifi- 010020 cant differences in the composition and variability of gaseous and aerosol components in atmospheric air than in coastal continental areas and is still a poorly studied object. In the Received: 20 October 2020 zone of atmospheric influence of Lake Baikal are large industrial centers and settlements of Accepted: 23 December 2020 the Baikal and Trans-Baikal, which are distributed very unevenly along the coastal zone. Published: 25 December 2020 The spatial and temporal variability of anthropogenic impurities over the Baikal is largely formed under the influence of outflows from these territories, i.e., it is determined by the Publisher’s Note: MDPI stays neu- geographical distribution of continental sources and the prevailing circulation of air masses tral with regard to jurisdictional claims in a particular area [2–5]. in published maps and institutional With increasing anthropogenic and natural impact on the atmosphere of the lake the affiliations. study of the background characteristics of atmospheric pollutants is becoming relevant and becomes important. In the atmosphere of the Baikal basin, there are many factors that affect natural complexes, but the most significant in recent years have been forest fires,

Copyright: © 2020 by the authors. Li- which cause damage not only to nature, but also to the economy of the region. Assessment censee MDPI, Basel, Switzerland. This of environmental damage to the ecosystem of Lake Baikal is still an unsolved problem article is an open access article distributed due to the increasing anthropogenic load and extreme natural events, such as forest ﬁres, under the terms and conditions of the because of insufﬁcient data on the composition of chemically active gas components, Creative Commons Attribution (CC BY) aerosols, considering various factors that affect the composition and quality of atmospheric license (https://creativecommons.org/ air. In this regard, the study of spatial and temporal variability of the composition and licenses/by/4.0/). properties of the atmosphere, assessment of the transboundary contribution of pollutants,

Atmosphere 2021, 12, 20. https://dx.doi.org/10.3390/atmos12010020 https://www.mdpi.com/journal/atmosphere Atmosphere 2021, 12, 20 2 of 14

their forecast, as well as a clear definition of their possible consequences for the environment of Lake Baikal, is currently an urgent scientific problem. In contrast to the Baikal region, there is a lot of research that has been done to study the quantitative and qualitative composition of atmospheric air in North America and Europe, including the European part of Russia [6–13]. In the Baikal region, there are few such studies, and they are different because there is no integral program for monitoring air pollution that meets modern requirements. At present, the experimental research of quantitative and qualitative composition of atmospheric impurities are mostly episodic. Basically, research is carried out in an expedition in the summer with the participation of scientific teams of the Siberian Branch, Russian Academy of Sciences (Institute of Physical Materials, V.E. Zuev Institute of Atmospheric Optics, Limnological Institute). The most complete studies have been conducted on the chemical composition of atmospheric precipitation in the Baikal region in the seventies of the last century [14,15]. It is established that in the last decade, the chemical composition of atmospheric precipitation in the Baikal region has undergone qualitative changes: the total salt content has decreased, and the acidity of precipitation has increased. Currently, the physical and chemical properties of atmospheric aerosol are being studied [16–18]. Since 1999, the program of long-term continuous monitoring of atmospheric precipitation under the EANET international program has been operating at three stations in the Baikal region [19]. The results of experimental studies of the distribution of small gas impurities and aerosols in the lake area show that the southern part of Lake Baikal is most susceptible to pollution [20–24]. The important role of breeze circulations in daily variations of ozone and other small gas impurities near the coastal zone of Lake Baikal is revealed. Breeze circulations significantly affect the transport and dispersion of atmospheric impurities in the region [25]. According to experts, about 20% of annual emissions from biomass burning in the world are accounted for by forest fires occurring in the boreal regions of Russia, Canada, and Alaska [26]. According to satellite observations, fires occur annually on an area of 10–14 million hectares and in the forest and forest-steppe zones of Siberia [27]. Air quality impacts from forest fires are not only due to emissions of primary pollutants such as greenhouse gases, photochemically active compounds, and small and large particulate matter, but also due to secondary pollutants (e.g., ground-level ozone O3, secondary organic aerosol (SOA)). These emissions significantly affect the chemical composition of the atmosphere and the Earth’s climate system. Fires are a major source of ozone precursors, such as nitrogen oxides and non-methane organic compounds [28]. The transfer and accumulation of aerosol-gas impurities in the water area of Lake Baikal is observed every summer due to forest fires occurring in the boreal forests of Siberia. In the summer of 2019 in Eastern Siberia, there were extreme fire-weather conditions with the most large-scale forest fires in the last 20 years, which lasted from June to Septem- ber [29]. So, in July 2019, the scale of the catastrophe from forest fires in Siberia amounted to about 3 million hectares, the main centers were located in the Krasnoyarsk region, Irkutsk region and the Republic of Sakha (Yakutia). According to the FBU Avialesohrana, as of 31 July 2019, there were 140 forest fires in the Irkutsk region on an area of about 709 thousand hectares, in the Krasnoyarsk territory—110 seats of fire on an area of about 1.06 million hectares, in Yakutia—139 forest fires on about 1.14 million hectares of land [30]. By mid-August, the area of forest fires reached a record 5 million hectares. With the prevailing east wind direction, air smoke was observed in Western Siberia, Kazakhstan, and the Arctic. Despite the significant number and scale of annual forest fires in Siberia, scientific publications on studies of their emissions and estimates are extremely limited [31]. Atmosphere 2021, 12, 20 3 of 14

Nature conservation of Lake Baikal, as a World Heritage Site, has received more and more attention in recent years. One of the important channels for the entry of pollution into the lake basin is the atmosphere. The real-time observation monitoring can provide the most complete information for assessing the current state of the air basin [32]. However, observations of individual components of the aerosol and gas composition of the atmosphere are currently conducted only at coastal “continental” stations and only occasionally from a ship [2,23,24]. In the summer of 2018, for the first time, we carried out targeted studies of gaseous impurities in the drive layer of Lake Baikal on the science research vessel (SRV) “Academik V.A. Koptyug” during the forest fires in Siberia. The highest concentrations of gaseous impurities were found in the near-water atmosphere of the river Selenga River delta, Barguzinsky Bay, Peschanaya Bay. A sharp increase of sulfur dioxide concentration (SO2) −3 −3 up to 40 µg m and concentration of nitrogen dioxide (NO2) up to 30 µg m was noted when approaching Peschanaya Bay, to places of rest for tourists, and the maximum values −3 of SO2 (60 µg m ) were observed during anchorage in the bay [33,34]. During the period of the ship expedition (15–26 July 2018), continuous synchronous observations of the concentration of ground-level ozone (O3), sulfur dioxide, meteorological parameters of the atmosphere were carried out at the Boyarsky scientific station located on the southeastern coast of Lake Baikal. When comparing the concentrations of ground-level ozone as a secondary pollutant, measured simultaneously under similar meteorological and weather conditions at the Boyarsky station and in the water area of Lake Baikal, good agreement was noted in the behavior of ozone in the time interval as a whole, including its short-term variations, despite the fact that ground-based and route measurements of the temporal variability of ozone are separated in space. We can also note a good coincidence of daily maxima in the ozone distribution, both in concentration levels and in the observation time. In general, judging by the O3 distribution in Boyarsk and in the water area of Lake Baikal, it can be concluded that the air flows on Lake Baikal are well mixed. In 2019, our investigations were continued on the lake’s water area with the help of a research vessel, aimed at analyzing and assessing atmospheric pollution over Lake Baikal during a fire hazardous summer period.

2. Methods and Materials The route of the science research vessel “Academik V.A. Koptyug” took place along the entire perimeter of Lake Baikal from 24 July to 4 August, 2019 (Figure1a). The Circum- Baikal map of the expedition route 2019 on the science research vessel is shown in Figure1b. The beginning and end of the route was the port of Listvyanka. Initially, the vessel headed north along the perimeter of Lake Baikal. The vessel moved along the coast at a distance from 30 m to 5 km. The total length of the route was ~1700 km. In the Figure1b, arrows indicate the vessel’s route. The coordinates of the measurement points were determined by the ship’s GPS system. Atmosphere 2021, 12, x FOR PEER REVIEW 4 of 13 Atmosphere 2021, 12, 20 4 of 14

(а) (b)

Figure 1.Figure The 1.scientificThe scientiﬁc research research vessel vessel “Akademik “Akademik V.A. V.A. Koptyug”Koptyug” (a );(a schematic); schematic map map of the of vessel’s the vessel’s route (b route). (b).

GeneralThe set synoptic of equipment processes for measuring over the the gasregion composition were analyzed of the Baikal on drive the layerbasis was of surface installed in the lower deck of the vessel to exclude the influence of the ship’s emissions, weatherthe acoustic maps meteorologicalfrom Arctic and complex Antarctic “AMK-03” Research [35] was Institute installed [36]. on the To upper analyze deck the of the transport of smokevessel. aerosol Air samples and for its gas-aerosol spatial distribution instrumentation on a wereregional taken scale, using Teflonthe data pipes obtained at an from the altitudeMODIS of (Moderate 6 m above theResolution water surface. Imaging The 3.02 Sp P-A,ectroradiometer) P-310A, C-310A [37] chemiluminescent and CALIPSO (The Cloud-Aerosolgas analyzers Lidar (OPTEK and Inc., Infrared St. Petersburg, Pathfinder Russia) Satellite were used Observation) to measure the[38] small satellites gas were used,impurities and the such paths as thefor concentrationsthe transfer of ozone,air masses nitrogen trajectory oxides, and were sulfur calculated dioxide. Theat three P- alti- µ tude310A levels: and C-310A100, 500, gas and analyzers 1000 measured m using the the concentrations HYSPLIT in(The the rangeHybrid from Single-Particle 0 to 1000 g La- m−3 with an error of ±25%, and the 3.02 P-A gas analyzers in the range from 0 to 500 µg grangianm−3 with Integrated an error of Trajectory±20%. Calibration model) and trajectory zeroing were reanalysis performed model automatically and archival with the meteor- ologicalhelp ofdata built-in of the microflux National sources Oceanic according and Atmospheric to commands fromAdministration gas analyzers’ (USA) processor. [39]. The gas analyzer measurement accuracy is controlled using Mod. 8500 Monitor Labs 3. Resultscalibrator and (Monitor Discussion Labs. Inc., United States). General synoptic processes over the region were analyzed on the basis of surface In the summer of 2019, large-scale forest fires were observed in the Irkutsk Region, weather maps from Arctic and Antarctic Research Institute [36]. To analyze the transport Krasnoyarskof smoke aerosol Region and and its spatialYakutia. distribution According on a regionalto MODIS scale, satellite the data observations, obtained from the the smog fromMODIS forest (Moderate fires since Resolution the end Imagingof July has Spectroradiometer) spread throughout [37] and the CALIPSO water area (The Cloud-and the coast of LakeAerosol Baikal. Lidar Figure and Infrared 2 shows Pathfinder images Satelliteof atmospheric Observation) smoke [38] satellitesin the Baikal were used,region from forestand fires the on paths 13 forJuly the and transfer 7 August of air 2019. masses Th trajectorye vertical were movements calculated arising at three from altitude fires raise significantlevels: 100, masses 500, andof warm 1000 m air using in convective the HYSPLIT st (Theructures Hybrid to Single-Particlehigh altitudes. Lagrangian It makes it pos- Integrated Trajectory model) trajectory reanalysis model and archival meteorological data sibleof for the them National to spread Oceanic in and the Atmospheric upper layers Administration over large (USA)areas. [39].

3. Results and Discussion In the summer of 2019, large-scale forest fires were observed in the Irkutsk Region, Krasnoyarsk Region and Yakutia. According to MODIS satellite observations, the smog from forest fires since the end of July has spread throughout the water area and the coast of Lake Baikal. Figure2 shows images of atmospheric smoke in the Baikal region from forest fires on 13 July and 7 August 2019. The vertical movements arising from fires raise significant masses of warm air in convective structures to high altitudes. It makes it possible for them to spread in the upper layers over large areas.

(а) (b) Figure 2. Satellite images of atmospheric smoke over Lake Baikal, July–August 2019 (MODIS): (a) 13 July 2019; (b) 7 August 2019.

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(а) (b) Figure 1. The scientific research vessel “Akademik V.A. Koptyug” (a); schematic map of the vessel’s route (b).

General synoptic processes over the region were analyzed on the basis of surface weather maps from Arctic and Antarctic Research Institute [36]. To analyze the transport of smoke aerosol and its spatial distribution on a regional scale, the data obtained from the MODIS (Moderate Resolution Imaging Spectroradiometer) [37] and CALIPSO (The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) [38] satellites were used, and the paths for the transfer of air masses trajectory were calculated at three altitude levels: 100, 500, and 1000 m using the HYSPLIT (The Hybrid Single-Particle La- grangian Integrated Trajectory model) trajectory reanalysis model and archival meteorological data of the National Oceanic and Atmospheric Administration (USA) [39].

3. Results and Discussion In the summer of 2019, large-scale forest fires were observed in the Irkutsk Region, Krasnoyarsk Region and Yakutia. According to MODIS satellite observations, the smog from forest fires since the end of July has spread throughout the water area and the coast of Lake Baikal. Figure 2 shows images of atmospheric smoke in the Baikal region from forest fires on 13 July and 7 August 2019. The vertical movements arising from fires raise Atmosphere 2021, 12, 20 significant masses of warm air in convective structures to high altitudes. It makes5 of 14 it possible for them to spread in the upper layers over large areas.

Atmosphere 2021, 12, x FOR PEER REVIEW 5 of 13 (а) (b)

FigureFigure 2. Satellite 2. Satellite images images of atmosphe of atmosphericric smoke smoke over over Lake Lake Baikal,Baikal, July–AugustJuly–August 2019 2019 (MODIS): (MODIS): (a) 13(a) July 13 July 2019; 2019; (b) 7 (b) 7 AugustAugust 2019. 2019. In order to study the distribution of the dominant aerosol components over the Baikal regionIn order in to the study summer the distribution of 2019, of the the resu dominantlts of aerosolmeasurements components of oververtical the Baikalprofiles of theregion parameters in the summerof suspended of 2019, particles the results by the of measurementsspace-based CALIOP of vertical lidar proﬁles on the of theCALIP- SOparameters satellite were of suspended analyzed. particlesA spatial by section the space-based of the vertical CALIOP atmospheric lidar on the depth CALIPSO in units of weakenedsatellite wereaerosol analyzed. backscattering A spatial showed section ofthat the in vertical July–August atmospheric 2019 depthover Lake in units Baikal, of on someweakened days, a aerosolhomogeneous backscattering filling showedof the atmospheric that in July–August layer with 2019 smoke over aerosol Lake Baikal, up to 3–4 kmon was some observed days, a homogeneous(Figure 3). ﬁlling of the atmospheric layer with smoke aerosol up to 3–4 km was observed (Figure3).

(a) (b)

FigureFigure 3. The 3. plotThe plotof CALIPSO of CALIPSO aerosol aerosol vertical vertical profile. proﬁle. The The X axis—latitudeaxis – latitude and and longitude, longitude, the the Y axis—altitude, Y axis - altitude, the colors the colors scale –scale—type type of aerosol. of aerosol. (a) aerosol (a) aerosol subtype, subtype, UTC: UTC: 2019-07-13; 2019-07-13; ((bb)) aerosolaerosol subtype, subtype, UTC: UTC: 2019-08-08. 2019-08-08.

FigureFigure 44 showsshows the experimentalexperimental data data on on the the spatial–temporal spatial–temporal distribution distribution of the of the concentrationconcentration of of ozone, sulfur sulfur dioxide, dioxide, nitrogen nitrogen oxides, oxides, meteorological meteorological parameters parameters (tem- (temperature,perature, pressure) pressure) along along the route the ofroute the vesselof the over vessel water over area water of Lake area Baikal of Lake in a 10-min Baikal in a measurement interval. The spatial–temporal variability of O3 and small gas impurities 10-min measurement interval. The spatial–temporal variability of O3 and small gas im- (NO2, SO2) is extremely heterogeneous over the lake’s water area. Both extended areas purities (NO2, SO2) is extremely heterogeneous over the lake’s water area. Both extended with an increased content of O3, SO2, NO2, and separate local outbreaks are distinguished. areas with an increased content of O3, SO2, NO2, and separate local outbreaks are distinguished.

(а)

(b)

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In order to study the distribution of the dominant aerosol components over the Baikal region in the summer of 2019, the results of measurements of vertical profiles of the parameters of suspended particles by the space-based CALIOP lidar on the CALIP- SO satellite were analyzed. A spatial section of the vertical atmospheric depth in units of weakened aerosol backscattering showed that in July–August 2019 over Lake Baikal, on some days, a homogeneous filling of the atmospheric layer with smoke aerosol up to 3–4 km was observed (Figure 3).

(a) (b) Figure 3. The plot of CALIPSO aerosol vertical profile. The X axis – latitude and longitude, the Y axis - altitude, the colors scale – type of aerosol. (a) aerosol subtype, UTC: 2019-07-13; (b) aerosol subtype, UTC: 2019-08-08.

Figure 4 shows the experimental data on the spatial–temporal distribution of the concentration of ozone, sulfur dioxide, nitrogen oxides, meteorological parameters (temperature, pressure) along the route of the vessel over water area of Lake Baikal in a 10-min measurement interval. The spatial–temporal variability of O3 and small gas impurities (NO2, SO2) is extremely heterogeneous over the lake’s water area. Both extended

Atmosphere 2021, 12, 20 areas with an increased content of O3, SO2, NO2, and separate local outbreaks 6are of 14 distinguished.

(а)

(b)

Figure 4. The spatial—temporal variability along route of the research vessel “Akademik V.A. Koptyug”: (a) round-level of ozone, nitrogen dioxide and sulfur dioxide concentrations; (b) temperature, pressure.

At the beginning of the route measurements on 24 July, the region of South Baikal was under the influence of a low-gradient low-pressure baric field. The direction of air flows was predominantly southeast according to the data of the State Scientific Center of the Rus- sian Federation the Arctic and Antarctic Research Institute [36]. From the next day, 25 July, a displacement of the formed cyclone center to the southeast was observed, which continued in the following days until 28 July due to its displacement by the southwestern branch of the anticyclone. Under the conditions of the formation of a stable air mass in the warm sector of the cyclone, high daytime air temperatures were observed up to 25 ◦C and higher. At the same time, high concentrations of ground-level ozone were noted up to 120 µg m−3. During this period, increased concentrations of sulfur dioxide were also observed with maximum daily concentrations up to 30 µg m−3, but the concentrations of nitrogen oxides (NO, NO2) did not exceed the background values. During the measurement period from 24 July to 29 July, when high levels of sulfur dioxide were noted, the direction of air flows to the lake’s water area was east, south-east, and north-east. An analysis of the backwards trajectories of air masses according to the HYSPLIT model shows that the drift of air masses into the area of the ship passage occurred from the territories where large settlements and industrial centers of the Republic of Buryatia are located, such as Ulan-Ude, Gusinoozersk, Kamensk, Selenginsk, Timlyui, Kabansk. In Figure5 shows the backwards trajectories of air mass transfer for the periods corresponding to the passage of the vessel near the settlements Bolshaya Goloustnaya (Figure5a) and Buguldeika (Figure5b), located on the southwestern coast of Lake Baikal. Atmosphere 2021, 12, x FOR PEER REVIEW 6 of 13

Figure 4. The spatial–temporal variability along route of the research vessel “Akademik V.А. Koptyug”: (a) round-level of ozone, nitrogen dioxide and sulfur dioxide concentrations; (b) temperature, pressure.

At the beginning of the route measurements on 24 July, the region of South Baikal was under the influence of a low-gradient low-pressure baric field. The direction of air flows was predominantly southeast according to the data of the State Scientific Center of the Russian Federation the Arctic and Antarctic Research Institute [36]. From the next day, 25 July, a displacement of the formed cyclone center to the southeast was observed, which continued in the following days until 28 July due to its displacement by the southwestern branch of the anticyclone. Under the conditions of the formation of a stable air mass in the warm sector of the cyclone, high daytime air temperatures were observed up to 25 °C and higher. At the same time, high concentrations of ground-level ozone were noted up to 120 μg m−3. During this period, increased concentrations of sulfur dioxide were also observed with maximum daily concentrations up to 30 μg m−3, but the concentrations of nitrogen oxides (NO, NO2) did not exceed the background values. During the measurement period from 24 July to 29 July, when high levels of sulfur dioxide were noted, the direction of air flows to the lake’s water area was east, south-east, and north-east. An analysis of the backwards trajectories of air masses according to the HYSPLIT model shows that the drift of air masses into the area of the ship passage occurred from the territories where large settlements and industrial centers of the Republic of Buryatia are located, such as Ulan-Ude, Gusinoozersk, Kamensk, Selenginsk, Timlyui, Kabansk. In Figure 5 shows the backwards trajectories of air mass transfer for the periods corresponding to the passage of the vessel near the settlements Bolshaya Goloustnaya (Figure 5a) and Buguldeika (Figure 5b), located on the southwestern coast of Lake Atmosphere 2021, 12, 20 Baikal. 7 of 14

(a) (b)

Figure 5. BackwardsFigure 5. Backwards trajectories trajectories of air ofmasses air masses tran transfersfer according according to to the the HYSPLIT model: model: (a )( Bolshayaa) Bolshaya Goloustnaya; Goloustnaya; (b) Buguldeika.(b) The Buguldeika. paths for The the paths transfer for the transferof air masses of air masses trajectory trajectory at three at three altitude altitude levels: levels: 100100 m m (red (red color), color), 500 m500 (blue m (blue col- or) and 1000color) m and(green 1000 color). m (green color).

In the Lake Baikal region, one of the major sources of sulfur dioxide emissions is Inthe the Selenginsky Lake Baikal pulp region, and cardboard one of mill, the where major the sources production of sulfur of sulphate dioxide unbleached emissions is the Selenginskycellulose pulp is accompanied and cardboard by emissions mill, of where both basic the and production specific pollutants of sulphate containing unbleached sulfur (dimethyl sulfide, methyl mercaptan, sodium sulfate, carbon disulfide). Although the main inputs of sulfur compounds into the troposphere are associated with anthropogenic sources, there are also natural sources of sulfur dioxide input into the atmosphere. So, in the area of the Selenga delta there are vast swamps, which are a source of hydrogen sulfide. With the participation of free radicals, hydrogen sulfide in the atmosphere, as well as dimethyl sulfide, is oxidized sequentially in several stages to sulfur dioxide:

− H2S + OH → HS + H2O (1)

− HS + O2 → OH + SO (2) − SO + HO2 → SO2 + OH (3) As is known, in the zone of pine forest contamination with industrial emissions containing sulfur dioxide, in two-year-old pine needles, an increased sulfur content is accumulated due to the absorption of SO2 from the atmospheric air in comparison with the control samples, namely, up to 0.137% based on dry matter weight [40]. Sulfur-containing compounds accumulated in forest and soil vegetation enter the atmospheric air during ﬁres in the form of sulfur dioxide, the lifetime of which is 2–5 days [41]. The distance of its transfer from the source can be more than 500 km, with an average wind speed of 3–4 m/s and the lifetime by SO2 in the atmosphere for 2 days [42]. Most of the sulfur dioxide is concentrated in the lower near-surface layer of the atmosphere, since it is about twice as heavy as air. Consequently, in the water area of Baikal, the accumulation of sulfur Atmosphere 2021, 12, 20 8 of 14

dioxide is possible due to temperature inversions when the lower temperature of the water surface in comparison with the surrounding air and the poor solubility of sulfur dioxide in water are observed. Usually the concentration of SO2 changes much more slowly than the concentration of water vapor [43]. Despite the observed high concentrations of SO2 along the Listvyanka-Khuzhir route (Olkhon Island), the concentrations of nitrogen oxides (NO, NO2) remained at the background level (3–7 µg m−3) (Figure4a), although their concentrations usually increase synchronously with SO2 concentrations. It is known that the rate of NO2 oxidation is five times higher than that of SO2, that is gaseous nitrogen oxides are transformed into nitrates faster than sulfur dioxide into sulfates [44]. Therefore, the absence of nitrogen dioxide at high concentrations of SO2 may mean that, possibly, the detected plume of SO2 pollution near the southwestern coast accumulated for a rather long time (up to several hours), and gaseous nitrogen oxides had time to oxidize to nitrates. Due to the higher oxidation rate of NO2 as compared to SO2, lower concentrations of nitrogen oxides or their complete absence are recorded (Figure4a). Similar results were noted in [ 45] during the period of experiments on Lake Baikal. −3 An increase in the concentration of sulfur dioxide SO2 up to 28 µg m was noted as the research vessel approached the settlement of Khuzhir in the Maloe More on 26 July, which significantly exceeded the background concentrations (Figure6a). On average, the concentration remained high, right up to the exit from the Maloe More. In the behavior of sulfur dioxide there was noted no noticeable changes during the passage of the ship in the immediate vicinity. Figure6b shows the results of calculating the backwards trajectories of air mass transfer (HYSPLIT), maps of the pyrogenic situation [31] in this area (Figure6c), which indicate the drift of smoke gases from the nearest forest fires center Atmosphere 2021, 12, x FOR PEER REVIEW 8 of 13 in the Barguzinsky Nature Reserve on the northeastern coast of Baikal and in the north of the Irkutsk region. After the research vessel left the Maloe More for the open Baikal, the concentration decreased by 12 µg m−3 (Figure6a).

(а) (b) (c)

Figure 6.Figure Temporal 6. Temporal variation variation of the of concentration the concentration of ofsulfur sulfur dioxide dioxide inin thethe water water layer layer of Lakeof Lake Baikal Baikal during during of 26 Julyof 26 July 2019 (a); 2019backwards (a); backwards trajectories trajectories of air of masses air masses according according to to the the HYSPLITHYSPLIT model model (b); (b the); the paths paths for the for transfer the transfer of air masses of air masses trajectorytrajectory at three at three altitude altitude levels: levels: 100 mm (red (red color), color), 500 m500 (blue m (blue color) andcolor) 1000 and m (green 1000 color);m (green map ofcolor); ﬁres in map the northern of fires in the northernpart part of of Lake Lake Baikal Baikal for thisfor periodthis period (c). The (c number). The number of ﬁres is of indicated fires is inindica the centerted in of the the center circle. of the circle.

Furthermore, during the passage and anchorage of the research vessel near Cape Muzhinay, when the wind direction changed to the south, from the southeast, a sharp increase in the content of sulfur dioxide was observed up to 32 μg m−3 (Figure 7a). Anal- ysis of backwards trajectories of air mass transfer trajectories (HYSPLIT) during this period indicates that the main contribution to the increase in SO2 content was made by the forest fires in the area of Sosnovka on the northeastern coast of Lake Baikal (Figure 7c). In the north of Baikal, the main contribution to the increase in the SO2 content in the atmosphere was also made by closely located forest fires center in the Sosnovka area. The presence of smoke aerosol over Lake Baikal during this period was also observed visually, a high content of sulfur dioxide and ozone in the water layer persisted throughout the day along the vessel’s route in the north of lake (Figure 4a).

(а) (b) (c) Figure 7. Temporal variation of concentration of sulfur dioxide in the Lake Baikal water layer: Cape Muzhinai (27 July 2019) (a); Severobaikalsk (28 July 2019) (b); backwards trajectories of air masses transfer (28 July 2019) the paths for the transfer of air masses trajectory at three altitude levels: 100 m (red color), 500 m (blue color) and 1000 m(green color) (c).

Atmosphere 2021, 12, x FOR PEER REVIEW 8 of 13

(а) (b) (c) Figure 6. Temporal variation of the concentration of sulfur dioxide in the water layer of Lake Baikal during of 26 July 2019 (a); backwards trajectories of air masses according to the HYSPLIT model (b); the paths for the transfer of air masses trajectory at three altitude levels: 100 m (red color), 500 m (blue color) and 1000 m (green color); map of fires in the northern part of Lake Baikal for this period (c). The number of fires is indicated in the center of the circle.

Atmosphere 2021, 12, 20 9 of 14 Furthermore, during the passage and anchorage of the research vessel near Cape Muzhinay, when the wind direction changed to the south, from the southeast, a sharp −3 increase inFurthermore, the content during of sulfur the passage dioxide and was anchorage observed of theup researchto 32 μg vessel m (Figure near Cape 7a). Anal- ysis ofMuzhinay, backwards when trajectories the wind direction of air mass changed transfer to the trajectories south, from the(HYSPLIT) southeast, during a sharp this pe- −3 riod indicatesincrease in thethat content the main of sulfur contribution dioxide was to observed the increase up to 32 µing mSO2 (Figurecontent7a). was Analysis made by the forestof fires backwards in thetrajectories area of Sosnovka of air mass on transfer the no trajectoriesrtheastern (HYSPLIT) coast of duringLake Baikal this period (Figure 7c). indicates that the main contribution to the increase in SO content was made by the forest In the north of Baikal, the main contribution to the increase2 in the SO2 content in the at- ﬁres in the area of Sosnovka on the northeastern coast of Lake Baikal (Figure7c). In the mosphere was also made by closely located forest fires center in the Sosnovka area. The north of Baikal, the main contribution to the increase in the SO2 content in the atmosphere presencewas alsoof smoke made by aerosol closely locatedover Lake forest Baikal ﬁres center during in thethis Sosnovka period area.was Thealso presence observed visually, ofa high smoke content aerosol overof sulfur Lake Baikaldioxide during and this ozone period in wasthe alsowater observed layer visually,persisted a highthroughout the daycontent along of sulfurthe vessel’s dioxide route and ozone in the in thenorth water of layer lakepersisted (Figure throughout4a). the day along the vessel’s route in the north of lake (Figure4a).

(а) (b) (c)

Figure 7. FigureTemporal 7. Temporal variation variation of concentration of concentration of of sulfur dioxide dioxide in thein Lakethe Lake Baikal Baikal water layer: water Cape layer: Muzhinai Cape (27 Muzhinai July 2019) (27 July 2019) (a);( aSeverobaikalsk); Severobaikalsk (28(28 July July 2019) 2019) (b); ( backwardsb); backwards trajectories trajectories of air masses of air transfer masses (28 Julytransfer 2019) the(28 pathsJuly for2019) the transferthe paths of for the transfer ofair air masses masses trajectory trajectory at three at altitudethree altitude levels: 100 levels: m (red 100 color), m (red 500 mcolor), (blue color)500 m and (blue 1000 color) m(green and color) 1000 (c). m(green color) (c).

When the research vessel passed near the Sosnovka Bay on 29 July, the highest concen- −3 trations of SO2 along the entire route were observed up to 47 µg m due to the proximity of forest fires (Figure8). Under the conditions of smoke outflow, the ozone concentration significantly decreased to 20 µg m−3, nitrogen oxides are below the detection limit due to the fact that smoke can completely absorb NOx [46], ozone sink in such conditions mainly occurs on aerosol particles [47]. We also selected aerosol samples along the route using a high-volume sampler for filters, and then carried out a chemical analysis for the ionic composition. It was found that under the influence of nearby fires, the concentration of sulfate ions increases to 4.7 µg m−3 against 0.14 µg m−3, the concentration of potassium ions up to 0.32 µg m−3 against 0.069 µg m−3. Atmosphere 2021, 12, x FOR PEER REVIEW 9 of 13

When the research vessel passed near the Sosnovka Bay on 29 July, the highest concentrations of SO2 along the entire route were observed up to 47 μg m−3 due to the proximity of forest fires (Figure 8). Under the conditions of smoke outflow, the ozone concentration significantly decreased to 20 μg m−3, nitrogen oxides are below the detection limit due to the fact that smoke can completely absorb NOx [46], ozone sink in such conditions mainly occurs on aerosol particles [47]. We also selected aerosol samples along the route using a high-volume sampler for filters, and then carried out a chemical Atmosphere 2021, 12, 20 analysis for the ionic composition. It was found that under the influence of nearby fires, 10 of 14 the concentration of sulfate ions increases to 4.7 μg m−3 against 0.14 μg m−3, the concentration of potassium ions up to 0.32 μg m−3against 0.069 μg m−3.

Figure 8. Temporal variation of SO2 near Sosnovka Bay (29 July 2019). Figure 8. Temporal variation of SO2 near Sosnovka Bay (29 July 2019). Under the conditions of smoke exposure during the passage of the vessel along the Under the conditions of smoke exposure during the passage of the vessel along the eastern coast of Middle Baikal, an additional anthropogenic influence of enterprises and eastern coast of Middle Baikal, an additional anthropogenic influence of enterprises and the residential sector of the settlement of Ust-Barguzin on the general pollution of the theBaikal residential atmosphere sector was observed. of the settlement So, when oftheUst-Barguzin ship approached on the the Svyatoi general Nos pollution Penin- of the Baikalsula, a atmospheresignificant increase was observed. in ozone So,concentration when the shipwas observed approached up to the 73 Svyatoi μg m−3, Nossulfur Peninsula, −3 adioxide significant concentration increase up in ozoneto 15 μ concentrationg m−3, nitrogen was dioxide observed up to up5–7 toμg 73 mµ−3g with m a, sulfursharp dioxide − − concentrationchange in the wind up to direction 15 µg m to3 the, nitrogen south from dioxide a large up settlement to 5–7 µg mUst-Barguzin3 with a sharp due to change in thethe screening wind direction effect of to the the mountain south from range a large of the settlement Svyatoi Nos Ust-Barguzin Peninsula. Anthropogenic due to the screening effectemissions of the from mountain the territories range where of the large Svyatoi settlements Nos Peninsula. and industrial Anthropogenic facilities are emissionslocated from thehave territories a significant where impact large on settlementsthe formation and of the industrial spatial and facilities temporal are distribution located have of agas significant impactimpurities on over the formationthe lake’s water of the area. spatial and temporal distribution of gas impurities over the lake’sWhen water the area. research vessel enters the bay of Bezymyanka in the Middle Baikal, the influenceWhen of thethe researchcoastal settlements vessel enters of Goryac the bayhinsk of Bezymyanka and Turka begins in the to Middle manifest Baikal, itself the influ- noticeably. Upon arrival at the parking lot in Turka, an increase in sulfur dioxide con- ence of the coastal settlements of Goryachinsk and Turka begins to manifest itself noticeably. centration is observed from background values of 4–5 μg m−3 to 30 μg m−3 (Figure 9a). Upon arrival at the parking lot in Turka, an increase in sulfur dioxide concentration is An increase in SO2 concentration was found at the mouths of the river Selenga near the −3 −3 observedvillage Kharauz, from background where a stable values high oflevel 4–5 ofµ gsulfur m dioxideto 30 µ gis mobserved(Figure even9a). atAn night, increase in Atmosphere 2021, 12, x FOR PEER REVIEWSOright2 concentration up to the ship’s was exit foundfrom this at area the mouths(Figure 9b). of the river Selenga near the village10 of Kharauz,13 where a stable high level of sulfur dioxide is observed even at night, right up to the ship’s exit from this area (Figure9b).

(а) (b)

FigureFigure 9. Temporal 9. Temporal variation variation of sulfur of sulfur dioxide dioxide concentration concentration over over the the water water area area of of Lake Lake Baikal Baikal nearnear settlements:settlements: ( (aa)) Turka Turka (31 July 2019); (b) Kharauz (1–2 August 2019). (31 July 2019); (b) Kharauz (1–2 August 2019). When the vessel moves near the coastal zone of the southeastern coast of Lake Baikal, the influence of settlements is clearly visible (Figure 10). This figure shows the largest settlements on the southeastern coast of Lake Baikal. The lowest concentrations are observed, as a rule, far from settlements, but nevertheless, under the conditions of the night breeze, the influence of anthropogenic outflows is noticeably manifested in the water area of Lake Baikal at a distance of 7–8 km from the coastal settlements of Tank- hoy and Vidrino. This confirms that anthropogenic emissions from the territories where large settlements are located. Industrial facilities have a significant impact on the formation of the spatial and temporal distribution of gas impurities in the Lake’s water area.

Figure 10. Temporal variation of sulfur dioxide concentration over the water area of Lake Baikal along the southeastern coast in the period 2–3 August 2019.

4. Conclusions Complex experimental studies of spatial–temporal variability of small gas impurities (in the near-surface layer over the lake, using research vessel “Academik V.A. Kop- tyug”, were performed from 24 July to 4 August 2019, in order to analyze and estimate the pollution of the atmosphere over Baikal in the firehazardous summer period with the purpose of creating the physical models of formation and transport of trace gas admixtures and aerosol fields of the atmosphere, taking into account the specific physical-geographic features of the Baikal region.

Atmosphere 2021, 12, x FOR PEER REVIEW 10 of 13

(а) (b) Figure 9. Temporal variation of sulfur dioxide concentration over the water area of Lake Baikal near settlements: (a) Turka (31 July 2019); (b) Kharauz (1–2 August 2019).

Atmosphere 2021, 12, 20 11 of 14 When the vessel moves near the coastal zone of the southeastern coast of Lake Baikal, the influence of settlements is clearly visible (Figure 10). This figure shows the largest settlements on the southeastern coast of Lake Baikal. The lowest concentrations When the vessel moves near the coastal zone of the southeastern coast of Lake Baikal, are observed, as a rule,the influence far from of settlementssettlements is, clearlybut nevertheless, visible (Figure under10). This the figure conditions shows the of largest the night breeze, thesettlements influence on of the anthropogeni southeasternc coast outflows of Lake is Baikal. noticeably The lowest manifested concentrations in the are ob- water area of Lake Baikalserved, asat aa rule, distance far from of settlements, 7–8 km from but nevertheless, the coastal under settlements the conditions of Tank- of the night hoy and Vidrino. Thisbreeze, confirms the influence that anthropogenic of anthropogenic outflowsemissions is noticeably from the manifested territories in thewhere water area large settlements areof Lakelocated. Baikal Industrial at a distance facilities of 7–8 km have from the a coastalsignificant settlements impact of Tankhoy on the and for- Vidrino. This confirms that anthropogenic emissions from the territories where large settlements are mation of the spatiallocated. and tempor Industrialal facilitiesdistribution have aof significant gas impuri impactties on in the the formation Lake’s ofwater the spatial ar- and ea. temporal distribution of gas impurities in the Lake’s water area.

FigureFigure 10. 10.Temporal Temporal variation variation of sulfur of dioxide sulfur concentrationdioxide concentr over theation water over area the of Lakewater Baikal area along of Lake the southeastern Baikal coastalong in thethe period southeastern 2–3 August coast 2019. in the period 2–3 August 2019.

4. Conclusions 4. Conclusions Complex experimentalComplex studies experimental of spatial–temporal studies of spatial–temporal variability variability of small of smallgas impuri- gas impurities ties (in the near-surface(in the layer near-surface over the layer lake over, using the lake, research using research vessel vessel “Academik “Academik V.A. V.A. Kop- Koptyug”, tyug”, were performedwere from performed 24 July from to 24 4 JulyAugust to 4 August2019, in 2019, order in orderto analyze to analyze and and estimate estimate the pollution of the atmosphere over Baikal in the firehazardous summer period with the the pollution of the atmospherepurpose of creating over the Baikal physical in modelsthe firehazardous of formation and summer transport period of trace with gas admixtures the purpose of creating andthe aerosol physical fields models of the atmosphere, of formation taking and into transport account the of specific trace physical-geographicgas admixtures and aerosol fieldsfeatures of of thethe Baikal atmosphere, region. taking into account the specific physical-geographic features Fromof the the Baikal results region. of on-ship observations of air pollutants, we found significant differences in the composition and nature of the variability of gas and aerosol components in the atmospheric air than in the continental regions near Lake Baikal. Anthropogenic emission from the territories where large settlements and industrial facilities are located have a more significant impact on the formation of the spatial and temporal distribution of gas impurities over the Lake Baikal. One of the major sources of sulfur dioxide emissions is the Selenginsky pulp and cardboard mill. We suggest that the absence of nitrogen dioxide and high concentrations of SO2 may mean that, possibly, the detected plume of SO2 pollution near the southwestern coast accumulated for a rather long time (up to several hours), and gaseous nitrogen oxides had time to oxidize to nitrates. Over the water area of Lake Baikal, the content of nitrogen dioxide is significantly lower than that of sulfur dioxide. A comparative analysis of the results of measurements of trace gases SO2, NO2 over the Lake’s water area and at the coastal station showed that during long-distance transport of anthropogenic impurities, gaseous nitrogen oxides are usually transformed into nitrates due to a higher oxidation rate of NO2 than SO2. At coastal stations (Boyarsk station, Listvyanka station) NO2 concentrations, as a rule, increase synchronously with SO2 concentrations. Atmosphere 2021, 12, 20 12 of 14

High concentrations of ground-level ozone were noted up to 120 µg m−3 under the conditions of the formation of a stable air mass in the warm sector of the cyclone. With the MODIS satellite observations, the HYSPLIT model and on-ship observations, we established that the spatial–temporal variability of gas impurities over the water area of Lake Baikal is largely formed under the influence of transport from anthropogenic sources, including flue gases from forest fires, that is, it depends on the geographical distribution of their sources and the prevailing circulation of air masses in a particular area. Despite the spatial heterogeneity of the SO2 field distribution over the water area of Lake Baikal, in general, a stable daily variation of SO2 is observed with a maximum in the daytime and a minimum in the morning hours.

Author Contributions: Conceptualization, G.Z. and A.Z.; methodology, A.Z. and G.Z.; data curation, A.Z., G.Z., V.T., A.D. and T.B.; software, V.T., T.B. and A.D.; investigation, A.Z., G.Z., T.B., A.D. and V.T.; resources, A.Z.; writing—review and editing, A.Z., G.Z., V.T., A.D. and T.B.; formal analysis, V.T., T.B. and A.D.; visualization, V.T., T.B. and A.D.; writing-original draft, A.Z. and G.Z.; supervision, G.Z., A.Z.; project administration, G.Z. and A.Z.; funding acquisition, G.Z. and A.Z. All authors have read and agreed to the published version of the manuscript. Funding: This research was supported by the project of the Russian Science Foundation (RSF) No. 19- 77-20058. The investigations were carried out using the gas analyzers under the financial support of the Ministry of Science and Higher Education of the Russian Federation (budget funds for IPMS SB RAS). The measurements of meteorological parameters of the atmosphere were conducted by the meteorological complex of the Center for Collective Use of Scientific Equipment, “Atmosphere”, of the V.E. Zuev Institute of Atmospheric Optics of the Siberian Branch of the Russian Academy of Science (IAO SB RAS). Institutional Review Board Statement: “Not applicable” for studies not involving humans or animals. Informed Consent Statement: “Not applicable” for studies not involving humans. Data Availability Statement: Data Availability Statements in section “MDPI Research Data Policies” at https://www.mdpi.com/ethics. Conflicts of Interest: The authors declare no conflict of interest.

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