Results of expedition measurements of PM 10 , PAHs and mercury above the water area of Lake Baikal in August 2023

I. I. Marinaite; Маринайте И. И.; T. V. Khodzher; Ходжер Т. В.; M. Y. Shikhovtsev; Шиховцев М. Ю.; E. S. Lutskin; Луцкин Е. С.; V. L. Potemkin; Потёмкин В. Л.

doi:10.31951/2658-3518-2024-A-3-171

Results of expedition measurements of PM₁₀, PAHs and mercury above the water area of Lake Baikal in August 2023

Authors: Marinaite I.I.¹, Khodzher T.V.¹, Shikhovtsev M.Y.¹, Lutskin E.S.¹, Potemkin V.L.¹
Affiliations:
1. Limnological Institute Siberian Branch of the Russian Academy of Sciences
Issue: No 3 (2024)
Pages: 171-180
Section: Articles
URL: https://bakhtiniada.ru/2658-3518/article/view/282624
DOI: https://doi.org/10.31951/2658-3518-2024-A-3-171
ID: 282624

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Abstract

As a continuation of regular research to obtain information about mechanisms and sources of air pollution above the water area of Lake Baikal, we present the results of the expeditionary studies on the concentrations of РМ₁₀, polycyclic aromatic hydrocarbons and gaseous elemental mercury in the near-water layer of the atmosphere above Lake Baikal in August 2023. On the route of the vessel along the perimeter of the lake, the concentrations of pollutants in the near-water atmosphere increased near the local sources of air pollution located on the coast of the southern basin (Listvyanka, Slyudyanka and Baikalsk) as well as at the source of the Angara River with the northwesterly transport from the industrial cities of the Baikal region. Over the study period, the РМ₁₀ concentrations averaged 6.0 µg/m³, PAHs–1.1 ng/m³, and gaseous elemental mercury–0.75 ng/m³, which was lower than the values recorded during wildfires between 2016 and 2020 in some areas of Siberia. The resulting concentrations of the investigated air components did not exceed air quality standards. Pairwise correlations during the study period were high between РМ₁₀ and PAHs (0.71) and low between PAHs and mercury (0.21).

Keywords

air pollution, PМ10 particles, PAHs, mercury, Lake Baikal

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1. Introduction

Monitoring of such air pollutants as polycyclic aromatic hydrocarbons (PAHs) and gaseous elemental mercury (GEM) is mandatory due to their carcinogenic and toxic hazards for the environment and human health (Kaleta and Kozielska, 2023). The combustion of coal, oil and wood are the primary anthropogenic sources of their release into the atmosphere (Marinaite et al., 2023; Tripathee et al., 2019). From the atmosphere, pollutants enter the underlying surface through wet (precipitation and fog) and dry (gases and particles) deposition. Over the past decade, researchers have been intensively studying climate change and air pollution from industrial enterprises in the Baikal region and local sources of air pollution on the coast of Lake Baikal. Observations of the atmosphere above Lake Baikal during large wildfires in the Baikal region, Krasnoyarsk Territory and Yakutia between 2016 and 2020 revealed the increase in the content of aerosol particles and gaseous impurities (Khodzher et al., 2019; Zhamsueva et al., 2022), total PAH concentration (Marinaite et al., 2018) and gaseous mercury (Mashyanov et al., 2021) in the air above the water area and the coast of the lake. These toxic substances are deposited onto the water area of the lake, polluting its water (Gorchkov et al., 2021). Control of air pollutants above Lake Baikal is among the priorities in its water quality monitoring.

2. Materials and methods

To assess the contribution of anthropogenic sources of air pollution in the Baikal region and hazardous natural phenomena (wildfires) to air pollution above Lake Baikal, continuous measurements of number and mass concentrations of aerosol particles and GEM were carried out from the board on the research vessel (RV) “G.Yu. Vereshchagin” from 5 to 15 August 2023. 25 aerosol samples were taken and analysed for PAHs. The expedition route ran along the entire perimeter of Lake Baikal with stops in areas having large local sources of air pollution on the lake’s coast and in estuarine areas of large tributaries and bays (Fig. 1).

Fig.1. Schematic map of the RV “G.Yu. Vereshchagin” route throughout the water area of Lake Baikal (5–15 August 2023).

To study number concentration and particle size distribution, a Handheld 3016 IAQ particle counter (Lighthouse, USA) was used, allowing continuous measurements of particle sizes in six channels (0.3, 0.5, 1.0, 2.5, 5.0, and 10.0 µm) with averaging over 5 minutes. GEM was measured with a Lumex РA-915М portable automatic mercury analyzer (Russia). The aerosol composition for 21 PAH components was analysed via gas chromatography with mass spectrometric detection on a GC/MS Triple Quad 7000C instrument with GC System 7890B (Agilent Technologies, USA).

3. Results and discussion

Unlike expeditions during wildfires (2018–2020), in 2023, we observed no smoke aerosol in the air above the lake despite fires in Yakutia at the end of summer. The total particulate matter (TPM) ranged from 1 to 12 µg/m³, with the maximum of 10-12 µg/m³, which was up to 10 times higher than the background values. In the central basin of Lake Baikal, the concentration ranged from 3 to 4 µg/m³, and in the northern basin–1 to 2 µg/m³. Overall, the concentrations obtained throughout the water area of the lake did not exceed the average daily MPC (60 µg/m³) for the environmental air and were comparable with the 2022 data.

The dynamics of the number concentration of aerosol particles showed the changes both in the medium aerosol fraction with a size of up to 1.0 µm and in a coarse fraction of up to 10 µm. During the expedition, there were several episodes of an increase in the concentration of medium fraction particles (PM₁< 1 µm). On the route, the medium fraction (PM₁< 1 µm) was 62% (Fig. 3, sample 14) at the background site along the east coast (the middle of the route from Ayaya Bay to Lokhmaty Island). At the estuary of the Kharauz River, during the transition from the east coast of the west coast (the Kharauz estuary–Bolshoye Goloustnoye), the concentration of the medium fraction reached 65% (samples 21-23) due to the cyclone above Lake Baikal during that period. As we approached local sources of air pollution in the southern basin, the number of the medium aerosol fraction decreased dramatically from 43% to 27% (samples 2-3) and down to 24% in the central basin near the Ust-Barguzin settlement (Fig. 3, sample 15).

Fig.3. Mass concentration variability (µg/m³) of the medium (PM₁< 1µm) and coarse (PM₁₀from 1 µm to 10 µm) aerosol fractions and the share (%) of the medium fraction in the total aerosol of the near-water atmosphere above Lake Baikal (5-15 August 2023).

The resulting dynamics of the concentration distribution of the total PAHs corresponded to the dynamics of the aerosol particle concentration above the water area of Lake Baikal (Fig. 2), which the close correlations between them confirmed (Table 1) and indicated similar sources of their origin. There was practically no correlation between the concentration of gaseous mercury and the concentrations of PAHs and РМ₁₀ (Table 1).

Fig.2. ТРМ (µg/m³) averaged for each sample and the total amount of 21 PAHs (ng/m³) in the air above the water area of Lake Baikal (5–15 August 2023).

Table 1. Pair correlation coefficients between the total PAH concentration, mass concentration of aerosol particles with different size fractions and mercury above the surface of Lake Baikal

	PAHs	TPM	PM₁<1 µm	PM₁₀>1 µm	Mercury
PAHs	1.00
TPM	0.49	1.00
PM₁<1 µm	0.71	0.79	1.00
PM₁₀>1 µm	0.32	0.96	0.58	1.00
Mercury	0.21	0.23	0.48	0.09	1.00

Note: TPM–total particulate matter; PM₁< 1 µm–medium aerosol fraction with particle size less than 1 µm; PM₁₀> 1 µm–coarse aerosol fraction with particle size of up to 10 µm (Ivlev and Dovgolyuk, 1999).

During the study period, the total PAH concentration in the near-water atmosphere varied from 0.008 to 8.4 µg/m³ (mean value 1.1± 2.0 µg/m³), with the highest values in the southern basin (6.3-8.4 µg/m³). In the central basin, it varied from 0.050 to 1.5 µg/m³, and in the northern basin–from 0.045 to 0.46 µg/m³. The data obtained during the 2023 expedition appeared to be lower than the concentrations during wildfires on the lake’s coast in 2016 (0.22–133 µg/m³, mean 5.9± 22.6 µg/m³), close to the values above the water area of the lake recorded in 2019 (0.11–4.6 µg/m³, mean 0.96±1.0 µg/m³) but higher than the PAH concentrations in 2020 (0.07–2.5 µg/m³, mean 0.4±0.5 µg/m³).

In the southern basin, the elevated PAH concentrations, up to 180 times higher than the background values, were observed along the west coast towards Kadilny–Listvyanka–the Angara River source (up to 3.7 µg/m³, samples 1–2, Fig. 2) as well as during moorings near the towns of Slyudyanka (up to 8.4 µg/m³, sample 4) and Baikalsk (up to 1.1 µg/m³, sample 5) under calm weather and aerosol transport from local sources of air pollution on the coast. Along the east coast and then along the west coast from the southern basin to the central basin and further to the northern basin (Boyarsk settlement–Kharauz estuary–Olkhon Island–Elokhin Cape–Severobaikalsk town), the total PAH concentration in the aerosol was low (0.05 µg/m³) with a gradual increase (up to 0.12 µg/m³, Fig. 2) near the town of Severobaikalsk. Almost all that time, there was low cloudiness in the atmosphere accompanied by periodical precipitation, leading to a clearing of the air. In the northern basin, we recorded high total PAH concentrations near Severobaikalsk (0.46 µg/m³, sample 11) presumably due to emissions of combustion products from the local thermal power plant. When the RV moved along the east coast from the background areas of the northern basin (Ayaya Bay–Khakusy–Chivyrkuy Bay), the total PAH concentration was low (0.045–0.16 µg/m³, samples 12-19). The meteorological conditions at that time were characterised by the presence of small inversions, low cloudiness and periodical precipitation, leading to a clearing of the air. The concentrations of pollutants decreased in the central basin during the transition from Baklaniy Cape to the Kharauz estuary (0.07–0.09 µg/m³, samples 20–21). During the transition from the east coast to the west coast along the Kharauz estuary–Bolshoye Goloustnoye route and further along the west coast to the southern basin (Cadilny Cape–Bolshiye Koty–Listvyanka), the PAH concentration increased from 1.5 to 6.4 µg/m³ (samples 21–23, Fig. 2). We also recorded its growth in the Angara River source (0.97 µg/m³, samples 24–25). The concentration of benzo[a]pyrene standardised in Russia ranged from 0.001 to 0.84 µg/m³(mean 0.09±0.2 µg/m³) above the entire water area of Lake Baikal and did not exceed MPC (1 µg/m³).

The composition of individual PAHs sampled from various areas above the lake surface was different (Fig. 4). Among 21 detected PAHs, the proportion of the major compounds decreased in the following sequence: pyrene (11.8%) > benzo[k]fluoranthene (11.7%) > indeno[1,2,3-c,d]pyrene (8.3%) > benzo[e]pyrene (7%), benzo[a]pyrene (7%). A group of PAHs with four, five or six benzene rings predominated in the aerosol samples near local sources of air pollution in the southern basin (samples 4, 11 and 23), with their proportion of up to 84% from the total mass. This indicates the pyrogenic nature of the air pollution sources during combustion of coal, wood and liquid fuels (Othman et al., 2022). In sample 12, along the Severobaikalsk town–Ayaya Bay route, the amount of retene (biomass combustion component) reached 18% of the total mass of detected compounds.

Fig.4. Proportion (%) of individual compounds from the total PAH concentration in aerosol samples 4, 11,12, and 23 above the surface of Lake Baikal (5–15 August 2023).

We estimated PAH fluxes from the atmosphere to the surface of the lake. To determine them, we used a particle sedimentation rate of 0.02 m/s adopted in (Duce and Neil, 1991). Like in case of the concentrations, we identified the maximum PAH fluxes near the local air pollution sources along the west (Listvyanka settlement and the Angara source) and east (Slyudyanka town) coasts of the southern basin (1.7–102 µg/ m²/week). In the central basin, PAH fluxes amounted to 0.6–1.7 µg/ m²/week, and in the northern basin–0.5–5.6 µg/ m²/week with an elevated value near Severobaikalsk. The results turned out to be 15 times lower than the fluxes calculated for the Buguldeika area during wildfires in the summer of 2016 (490-1600 µg/ m²/week) (Marinaite et al., 2018).

The GEM concentration above the lake varied from 0.18 to 1.29 µg/m³. The highest values were in the southern basin (0.4–1.29 µg/m³, mean 0.76±0.19 µg/m³). In the central basin, it ranged from 0.18 to 1.07 µg/m³ (mean 0.73±0.13 µg/m³), and in the northern basin–from 0.19 to 1.02 µg/m³(mean 0.72±0.12 µg/m³). Therefore, during the 2023 expedition, average GEM concentrations above the lake varied insignificantly and appeared to be lower than the average value of 1.1 µg/m³(Mashyanov et al., 2021) analysed above the lake in July 2018 during smog from wildfires. No significant anomalies in the mercury concentrations in the air above the lake were observed during the expedition. Some increase in its concentration in the southern basins can be explained by the transport from the local air pollution sources, such as boiler houses and thermal power plants located in the settlements on the coast, as well as by the transport of pollutants from large thermal power plants located in the cities of the Baikal region along the valley of the Angara River (Fig. 5). Mercury degassing through deep fault zones may be a potential natural source of mercury emissions into the air because Lake Baikal is situated within the seismically active Baikal Rift Zone. The literature provides the data on a slight increase in the mercury concentration up to 1.6 µg/m³ above gas hydrate deposits and oil seepages onto the lake surface (Mashyanov et al., 2021), although unambiguous evidence of a connection between airborne mercury anomalies and tectonic structures has not been found. The mean mercury concentration of 0.74±0.17 µg/m³ recorded above Lake Baikal during the expedition was two times lower than the mean value of 1.6±0.15 µg/m³ recorded at the coastal monitoring station on the west coast of the southern basin in the Listvyanka settlement on the same days of observations (Lutskin et al., 2023) and can be explained by its deposition from the atmosphere during moisture condensation above the water surface.

Fig.5. Variability of the GEM concentrations (ng/m³) in the air above the water surface in the southern, central and northern basins of Lake Baikal (5–15 August 2023).

4. Conclusion

During the expedition onboard the RV “G.Yu. Vereshchagin” from 5 to 15 August 2023, we revealed a spatiotemporal pattern of pollutant distribution (PM₁₀, PAHs and GEM) in the air above the water area of Lake Baikal and estimated fluxes of pollutants onto the water surface of the lake. A 180-fold increase in the concentrations in comparison with the background values for PAHs and a 10-fold increase of PM₁₀ determined in clean areas of the lake were observed in the southern basin near the settlements (Listvyanka, Slyudyanka and Baikalsk) under calm weather conditions and at the source of the Angara River with northwesterly wind. At the same time, the concentrations of benzo[a]pyrene and aerosol particles did not exceed air quality standards. The concentration of the total PAHs and the medium (PM₁< 1 µm) and coarse (PM₁₀from 1 to 10 µm) aerosol fractions showed a positive correlation, indicating a similar location of their sources. PAH fluxes onto the water surface of the lake were 15 times lower than the values obtained during the fire danger period of 2016. The mean mercury concentration in the air above the lake (0.74±0.17 µg/m³) was lower than the coastal values obtained at the monitoring station in the Listvyanka settlement (1.6±0.15 µg/m³).

5. Acknowledgments

This study was supported by the Russian Science Foundation (19–77–20058 P). Chemical analysis of PAHs was carried out using the equipment of the Collective Instrumental Center “Ultromicroanalysis” at Limnological Institute SB RAS.