Physical and chemical parameters
Snow meltwaters in the background area were acidic. The mean pH was 4.3 units (ranging from 4.0 to 5.1). Snow acidification is typical of all northern regions of Western Siberia. Long-term observations in the polar and subpolar regions of Western Siberia have shown that the pH value of snow meltwaters varies from 4.6 to 5.5 (Moskovchenko and Babushkin 2012; Shevchenko et al. 2017; Kobelev et al. 2019). The acidification of atmospheric precipitation in Western Siberia is associated with a lack of acid neutralizers, primarily Ca and Mg (Vasilenko et al. 2007). Another reason is the flaring of associated gas at oil production facilities, resulting in the formation of nitrogen and sulfur oxides (Moiseenko et al. 2017).
The average pH value increases to 6.0 units in the city. There is a significant variation in the parameter, there are samples with a neutral and alkaline reaction (Fig. 2). The reason for the increase in pH is the deposition of carbonate dust particles originating from construction work and transport.
The EC and TDS in snow meltwater in the city increase by an average of 6 times compared to the background area (Fig. 2). The mean TDS was 4.4 mg l-1, which is typical of background conditions. The mineralization of precipitation at the level of < 15 mg l-1 is considered a background value in Russia (Svistov and Polishchuk 2014). In the city, the average TDS increased to 19 mg l-1, and the maximum values were 60–74 mg l-1. The increase in TDS and electrical conductivity is associated with the use of NaCl-based deicers.
The amount of aerial deposition of dust particles is an important indicator of the ecological state of atmospheric air (Sarangi et al., 2020; Heindel et al., 2020). In the snowpack of the background polar regions, the concentration of dust particles is reported to be 0.2–3 mg l-1 (Shevchenko et al. 2007). In the north of Western Siberia, the concentration of total suspended solids varies within the same range. The concentration of insoluble particles in the snow cover of the Ob River Basin in 2020 varied from 0.48 to 3.42 mg l-1 (Shevchenko et al. 2020). At the background sites in the vicinity of Nizhnevartovsk, the dust concentration in snow meltwaters averaged 0.8 mg l-1 varying from 0.4 to 1.3 mg l-1, which fits into the above range, typical of background areas.
In the city, the concentration of dust particles increases by many times. The average concentration of TSS in the city is 17.2 mg l-1, which is 23 times more than the average background value. In the most polluted areas located in the city center, the content of insoluble particles reaches 48 mg l-1.
The deposition rate of dust in the background area averages 74 mg m-2. In the city, it varies from 77 to 5075 mg m-2 (averaging 1492 mg m-2). The daily value of the dust load (mg m-2 per day) is often used in Russia to assess the aerial deposition of dust. Taking into account the snow cover duration of 144 days, the average dust load in Nizhnevartovsk was 10.4 mg m-2 per day (varying from 1 to 35 mg m-2 per day). This is a relatively low load, given that in the Norilsk Industrial Area (northern Siberia) the dust load exceeds 1000 mg m-2 per day in some places (Onuchin et al. 2014). In other Russian cities, the dust load is slightly higher than in Nizhnevartovsk. In Moscow, an average of 27 mg m-2 per day deposits from the atmosphere during the winter period (Kasimov et al. 2012). In the cities of Western Siberia, the following values were obtained: Tomsk, 25–28 mg m-2 per day (Talovskaya et al. 2014); Tobolsk, 15 mg m-2 per day (Moskovchenko et al. 2021a); Tyumen, 20 mg m-2 per day (Moskovchenko et al. 2021b).
The distribution of dust load can be seen in Fig. 3. The maximum aerial deposition of dust accounts for the central part of the city, where traffic is most intense.
TMMs in the particulate fraction of snow
The mean concentration and parameters of deposition of TMMs in the snow in Nizhnevartovsk and background areas are presented in Table 1.
Table 1
Mean concentration (M), deposition (D), and deposition factor (DF) of TMM in the particulate fraction of snow from Nizhnevartovsk City and surrounding background area
Elements
|
M urb± SD,
µg l-1 (n = 25)
|
M b ± SD,
µg l-1 (n = 6)
|
Durb±SD,
µg m-2 (n = 25)
|
Db
µg m-2 (n = 6)
|
Mean DF
|
V
|
2.0 ± 2.4
|
0.024 ± 0.012
|
165 ± 205
|
2.8 ± 0.25
|
58.2
|
Cr
|
3.1 ± 2.5
|
0.35 ± 0.12
|
261 ± 238
|
41.1 ± 15.6
|
6.4
|
Mn
|
12.8 ± 11.9
|
0.098 ± 0.10
|
1072 ± 1169
|
11.5 ± 12.0
|
93.2
|
Fe
|
627 ± 555
|
9.9 ± 6.2
|
52424 ± 54198
|
1153 ± 739
|
45.5
|
Co
|
0.41 ± 0.40
|
0.006 ± 0.003
|
34.5 ± 39.0
|
0.68 ± 0.22
|
50.9
|
Ni
|
2.7 ± 2.8
|
0.085 ± 0.07
|
226 ± 260.7
|
9.9 ± 8.7
|
22.8
|
Cu
|
3.2 ± 1.9
|
0.19 ± 0.06
|
269 ± 186.1
|
21.4 ± 6.4
|
12.6
|
Zn
|
14.5 ± 12.8
|
0.32 ± 0.20
|
1214 ± 1131
|
37.4 ± 25.1
|
32.4
|
As
|
0.13 ± 0.15
|
0.0016 ± 0.0008
|
10.6 ± 14.9
|
0.2 ± 0.02
|
57.1
|
Sr
|
2.3 ± 2.6
|
0.049 ± 0.029
|
196 ± 263
|
5.8 ± 3.5
|
33.7
|
Mo
|
0.88 ± 0.075
|
0.0015 ± 0.0005
|
7.4 ± 7.3
|
0.17 ± 0.02
|
43.6
|
Cd
|
0.016 ± 0.009
|
0.001 ± 0.0005
|
1.3 ± 0.9
|
0.11 ± 0.06
|
11.9
|
Sb
|
0.16 ± 0.11
|
0.0080 ± 0.0054
|
13.5 ± 11.0
|
0.9 ± 0.67
|
14.4
|
Ba
|
6.2 ± 5.8
|
0.17 ± 0.15
|
516 ± 578
|
20.6 ± 17.8
|
25.1
|
W
|
0.84 ± 0.78
|
0.0035 ± 0.0018
|
70.2 ± 75.8
|
0.41 ± 0.21
|
171.3
|
Hg
|
0.0016 ± 0.0008
|
0.00071 ± 0.0057
|
0.14 ± 0.10
|
0.08 ± 0.07
|
1.7
|
Pb
|
1.7 ± 1.3
|
0.10 ± 0.06
|
145 ± 113
|
11.6 ± 7.1
|
12.4
|
Bi
|
0.020 ± 0.028
|
0.0005 ± 0.43
|
1.7 ± 2.6
|
0.06 ± 0.04
|
26.6
|
SD – standard deviation |
The composition of dust particles contained in the atmosphere originate from both natural (soil, rocks) and anthropogenic sources (emissions from industrial enterprises, transport, etc.). As, Pb, Zn, Hg, Cd, Sb and Se are typical representatives of long-range transported air masses (Steinnes and Friedland 2006). Pb, Cu, Zn, Sn, Cr, Cd, Sb, and Bi are concentrated in snow dust in the background areas near Nizhnevartovsk; the concentration of Fe, Mn, Ba, Sr, V, and As is reduced (Fig. 4). If compared with the results of other studies of the solid phase of snow in various regions of Western Siberia (Shevchenko et al. 2017; Moskovchenko et al. 2021a,b), the composition of snow dust near Nizhnevartovsk turns out to be typical of the region, except for the low content of As. For instance, the particulate fraction of snow in the south of Western Siberia is enriched in such elements as Pb, Cu, Zn, Cd, Sb, Bi, and As, in contrast to the upper part of the continental crust (Moskovchenko et al. 2021 a, b). In the northern regions of Western Siberia, snow dust is enriched in Sb, Zn, and Cd to the fullest extent (Shevchenko et al. 2017). Therefore, the entire region is characterized by snow dust enriched in chalcophile metals, especially Sb, Zn, Pb, and Cd, in background areas.
The tendency for the concentration of chalcophile elements in the solid phase of snow is observed in different background regions of the Earth. A pool of pollutants similar to our results has been observed in the mountainous regions of Asia, where snow contains high concentrations of Cd, Zn, Pb, As, Mo, and Cu (Li et al. 2015). In Canada, the solid phase of snow is enriched in Cd, As, Sb, Ag, Pb, Cu, Zn, Mo, Ni, and Cr (Telmer et al. 2004). It has been noted that Pb, Zn, Hg, Cd, and Sb are transported in the atmosphere over long distances (102-103 km) in the form of ultrafine aerosols (Steinnes and Friedland 2006). In European Russia, aerosols are usually enriched in Cd, Pb, Sn, Zn, Cu, Ni, and Cr (Kasimov et al. 2012). Therefore, the elemental composition of dust particles that accumulate in the snow of the background area in Nizhnevartovsk District is typical of the background areas of the Earth and depends mainly on the processes of long-range atmospheric transport.
Dust particles in the background area are weakly enriched in Ni and V, which are considered indicators of oil burning (Nriagu and Pacyna 1988). The concentration of Ni in the background area averages 116 ng g-1 and does not exceed the mean value of 145 ng g-1 for the north of Western Siberia (Shevchenko et al. 2017). The content of V was below the detection limit in the majority of the samples. The content of Ni modestly surpasses its content in local soils (see Fig. 4). Therefore, the effect of oil combustion on the composition of dust aerosols in the background area is not visible.
In contrast to the background areas, the deposition of W, Mn, As, V, Co (DF > 50) increases many times in the city, which indicates the presence of local anthropogenic sources of these elements. The deposition of W increases most (DF = 171) (see Table 1). Tungsten is released into the environment through its use in studded winter tires that contain tungsten carbide (Kabata-Pendias 2011; Furberg et al. 2019). Winter tires are widely used in Russia due to climatic conditions. They account for approximately 50% of all car tire sales (Filippov and Noev 2018). Studies carried out in various cities of Russia have shown that the content of W in the snow is, as a rule, very high. In the transport area of eastern Moscow, the deposition of W during snowfall is 45 times higher than the background values; in terms of the DF index, W ranks second after Mo (Kasimov et al. 2016). In Tyumen (south of Western Siberia), the concentration of W in the solid phase of snow in urban land surpasses the background values more than 100 times (Moskovchenko et al. 2021b). Snow dust contamination with W has been observed in the transport area of the Siberian city of Tobolsk, where the deposition of W surpluses the background values more than 570 times (Moskovchenko et al. 2021a).
The deposition of Mn, As, V, Co, and Fe in the city is 45–93 times higher than the background level. V is associated with motor fuel combustion (Nriagu and Pacyna, 1988). In Tyumen, accumulation of Mn and V in the snowpack is associated with the operation of thermal power plants (Guseinov et al. 1997). Enrichment of dust with Co and Fe is caused by the abrasion of metal parts of vehicles (Moskovchenko et al. 2021b). The maximum deposition of Co, Mn, and V is observed on the central streets and at the exit from the city, where the intensity of the traffic flow is the highest.
The deposition of Ni, Sr, Zn increases by 23–32 times (Table 2). It is slightly higher than the growth of the dust load, which indicates a weak enrichment of dust with these elements. However, it should be noted that there is a significant variation in the intensity of deposition. In some sampling sites, Zn surpasses the average background values by 120 times; Ni, by 74 times; and Bi, by 200 times. The variation in the concentration of trace elements originating from natural sources is less than the variation of those of anthropogenic origin (Yuan et al. 2014, Cao et al. 2018). Therefore, a significant variation in the city is indicative of the presence of local sources of pollution. The spatial analysis also showed the highest concentration in the central part of the city, near busy highways. It is evidence of transport as a source of pollution. Indeed, Zn and Ni have a close relationship with fossil fuel combustion (Cong et al. 2010).
Deposition of Hg, Cr, Cu, Cd, Pb, and Sb in the snow cover showed the weak excess above the background values (DF ≤ 15). Taking into account that the amount of dust deposition in the city increases by an average of 23 times, the increase in the emission of these elements is less than the increase in dust load, which indicates a low concentration of these elements in snow dust and the absence of sources of these elements in the city.
The calculations of the enrichment factors (EF) confirmed that dust particles in the background areas are enriched in these elements more than in the city (Fig. 5). In our opinion, this counter-intuitive fact is associated with differences in the accumulation of elements in particles of different sizes. In the background areas, TMMs are predominantly contained in ultrafine aerosols brought there via the long-range atmospheric transport (Shevchenko et al.2017; Zdanowicz et al. 2017). In the city, the share of coarse particles increases, and the concentration of TMMs in them is, as a rule, lower than in ultrafine aerosols. It has been repeatedly shown that fine particles are more enriched in trace elements than coarse ones (Vlasov et al. 2015; Lanzerstorfer 2018; Zhang et al. 2020; Cowan et al. 2021). A weak enrichment of snow dust in some trace elements has been observed in Moscow, where the concentration of Pb, Cu, Zn, and Mn is close to the background level (Kasimov et al. 2016).
We compared the obtained results with the data from other Russian cities and neighboring countries in order to assess the level of snow pollution with TMMs in Nizhnevartovsk (Table 2). The amount of deposited TMMs in different cities varies significantly depending on local and regional sources of anthropogenic emissions. In Nizhnevartovsk, in comparison with other cities, there is an average concentration of V, Pb, Cu, Ni, and Co in the snow and a low content of As, Cd, Mn, and Zn. The content of Pb is higher than in Vladivostok (Kondrat'ev et al. 2017), Svirsk (Grebenshchikova et al. 2017), and Tianjin (China) (Wu et al. 2016), but significantly less than in the transport area of Moscow. The concentration of Cd in the snow of Nizhnevartovsk is low. One of the main sources of Cd is non-ferrous metals smelters (Nriagu and Pacyna1988). In Siberia, the release of Cd into the atmosphere has been associated with coal combustion at boiler stations (Talovskaya et al. 2016). The thermal power plant and heating boiler stations of Nizhnevartovsk use natural gas as fuel, there is no metallurgical industry in the city.
Table 2
A comparison of TMM concentrations in snow from different locations (µg∙ l− 1).
City, country
|
As
|
Cd
|
Co
|
Cu
|
Mn
|
Ni
|
Pb
|
V
|
Zn
|
Source
|
Nizhnevartovsk, Russia
|
0.13
|
0.016
|
0.41
|
3.2
|
12.8
|
2.7
|
1.7
|
2.0
|
14.5
|
This study
|
Tyumen, Russia
|
0.47
|
0.038
|
1.58
|
8.0
|
31.5
|
27.8
|
4.6
|
2.16
|
25.0
|
Moskovchenko et al. 2021 b
|
Moscow, Russia, traffic zones
|
0.27
|
0.053
|
1.6
|
17
|
55
|
6.1
|
5.0
|
12
|
33.0
|
Vlasov et al. 2020
|
Vladivostok, Russia (total)
|
-
|
0.11
|
-
|
2.8
|
36.4
|
0.64
|
0.91
|
0.69
|
32
|
Kondrat’ev et al. 2017
|
Svirsk, Russia
(total)
|
3.7
|
0.07
|
0.41
|
2.3
|
-
|
2.3
|
0.48
|
3.3
|
18
|
Grebenshchikova et al. 2017
|
Poznan, Poland (total)
|
0.71
|
0.08
|
-
|
2.03
|
-
|
3.77
|
4.93
|
-
|
13.2
|
Siudek et al. 2015
|
Tianjin, China
(total)
|
1.37
|
0.66
|
0.17
|
1.96
|
13.6
|
1.25
|
0.17
|
0.34
|
22.1
|
Wu et al. 2016
|
Levels and compositional profiles of PAHs in the particulate fraction of snow
PAHs concentrations in the particulate fraction of snow and deposition are presented in Table 3. The total content of PAHs in the background area averaged 33.5 ng l-1 (varying from 13 to 70 ng l-1). The content of high molecular weight (HMW) 4–6 ring PAHs is 11.8 ng l-1 ( 33.5%); low molecular weight (LMW) 2–3 ring PAHs account for 21.8 ng l-1 ( 66.5%). It is known that LMW PAHs are predominant in petrogenic PAH mixture, while HMW PAHs are mainly produced by pyrogenic sources (Zakaria et al. 2002). Therefore, the predominance of LMW PAHs in the background area is indicative of the dominant influence of petrogenic sources. The concentration of some PAHs decreases in the following sequence: Phe > Flt > Pyr > Ant > Flu > BghiP > BbF > BaA > Nap > BaP > BkF > DahA. Such 3–4 ring PAHs as Phe, Flt, and Pyr predominate. Similarly, in southern Siberia, the share of 3–4 ring PAHs reaches 80% of the total amount of PAHs in the snow (Zhuravleva et al. 2014). The highest concentrations is observed of phenanthrene, which is formed under natural conditions during the biochemical and microbiological transformation of soil organic matter (Vasilevich et al. 2014; Haustov 2017). Therefore, the predominance of phenanthrene indicates the geogenic source of the formation of the solid phase of snow. The dominance of Phe in the composition of PAHs has been also observed in the snow of Tver oblast, European Russia (Zhidkin et al. 2017). In Northeast China, three-ring PAHs accounted for 25–74% of the total PAHs in fresh snow, while five- to six-ring PAHs only accounted for 2–18% (Wei et al. 2017). Therefore, the predominance of Phe found in the background areas in the vicinity of Nizhnevartovsk is typical of the background conditions.
Table 3
Mean concentration (M) and deposition (D) of 12 EPA PAHs in the particulate fraction of snow from Nizhnevartovsk City and the surrounding background area
PAHs
|
M urb ± SD,
(n = 25)
|
M b ± SD,
(n = 6)
|
D urb ± SD, µg/m2 (n = 25)
|
Db
µg/m2 (n = 6)
|
Mean DF
|
|
ng l-1
|
ng g-1
|
ng l-1
|
ng g-1
|
|
|
|
NaP
|
2.2 ± 2.7
|
186 ± 239
|
0.47 ± 0.12
|
316 ± 224
|
0.19 ± 0.31
|
0.054 ± 0.030
|
3.5
|
Flu
|
5.7 ± 3.4
|
648 ± 1226
|
1.5 ± 0.12
|
1058 ± 846
|
0.47 ± 0.39
|
0.17 ± 0.10
|
2.7
|
Phe
|
53 ± 28
|
6378 ± 13033
|
18.2 ± 0.10
|
13580 ± 14565
|
4.43 ± 3.18
|
2.1 ± 1.67
|
2.1
|
Ant
|
6.7 ± 7.7
|
1044 ± 3174
|
1.6 ± 6.2
|
1280 ± 1692
|
0.56 ± 0.89
|
0.19 ± 0.19
|
2.9
|
Flt
|
16.1 ± 6.8
|
1561 ± 2344
|
5.1 ± 0.003
|
3766 ± 3729
|
1.34 ± 0.78
|
0.60 ± 0.46
|
2.2
|
Pyr
|
12.7 ± 6.9
|
1234 ± 2079
|
3.1 ± 0.07
|
2277 ± 2078
|
1.06 ± 0.79
|
0.37 ± 0.24
|
2.9
|
BaA
|
4.3 ± 3.5
|
284 ± 247
|
0.48 ± 0.06
|
331 ± 354
|
0.36 ± 0.40
|
0.057 ± 0.06
|
6.3
|
BbF
|
11.3 ± 8.8
|
732 ± 583
|
1.0 ± 0.20
|
658 ± 316
|
0.95 ± 1.00
|
0.12 ± 0.06
|
7.9
|
BkF
|
2.7 ± 2.3
|
195 ± 176
|
0.3 ± 0.8
|
192 ± 109
|
0.23 ± 0.26
|
0.04 ± 0.02
|
6.5
|
BaP
|
4.7 ± 4.4
|
340 ± 339
|
0.43 ± 0.029
|
276 ± 140
|
0.39 ± 0.50
|
0.05 ± 0.03
|
7.8
|
DahA
|
3.7 ± 3.7
|
201 ± 160
|
0.044 ± 0.5
|
30 ± 9
|
0.31 ± 0.43
|
0.005 ± 0.001
|
61.8
|
BghiP
|
25.1 ± 19.9
|
1463 ± 908
|
1.3 ± 0.5
|
879 ± 638
|
2.10 ± 2.28
|
0.15 ± 0.11
|
13.7
|
∑LMW PAHs (2–3)
|
67.5
|
8256
|
21.8
|
16236
|
7.7
|
2.5
|
3.8
|
∑HMW PAHs (4–6)
|
80.7
|
6011
|
11.8
|
8408
|
9.2
|
1.4
|
18.7
|
∑12PAHs
|
148.2
|
14267
|
33.5
|
24644
|
17.0
|
3.9
|
13.7
|
M urb - mean concentration in the city; M b – background mean concentration; D urb – mean deposition in the city; Db - background mean deposition; DF - deposition factor |
In the city, the total content of 12 PAHs in insoluble particles varies significantly, from 43 to 333 ng l-1. The average value is 148.2 ng l-1, which is 4.4 times more than the background level. The total deposition of 12 PAHs during the winter varies from 4.3 to 38.1 µg/m2 (17 µg/m2 on average). The maximum content of PAHs was observed in the central part of the city, where traffic is most intensive, and in the southern low-rise residential area of the city (Fig. 6).
The background area is dominated by petrogenic LMW PAHs, whereas in the city, HMW PAHs contributed on average 54.4% to the total PAHs in snow dust (Fig. 7). The concentration of 6-ring DahA and BghiP increases especially strongly compared to the background area (by 86 and 19 times, respectively). DahA is a typical compound for diesel emissions (Simcik et al. 1999). BghiP are reported as tracers of vehicle sources (Larsen and Baker 2003; Zuo et al. 2007). The ratio of LMW / HMW PAHs varied in areas with different land use patterns. The total content of PAHs decreases in the following order: industrial area > business area > low-rise residential area > high-rise residential area (Fig. 8a). In the industrial area, the total content of 12 EPA PAHs averages 173 ng l-1, which is 5 times higher than the background values. Pollution with HMW PAHs is at most in the low-rise residential area, where their share is approximately 1.8 times higher than the share of LMW PAHs.
An analysis of the distribution of the dust load and the genesis of PAHs allows us to assume that PAHs depend both on emission sources and the dustiness of the atmosphere. Dust load in different land-use areas decreases in the following order: industrial area (24 mg m-2 day-1) > high-rise residential area (22 mg m-2 day-1) > business area (20 mg m-2 day-1) > low-rise residential area (13 mg m-2 day-1). The maximum amount of 12 PAHs in the industrial area and the dominance of petrogenic LMW PAHs correspond to the maximum dust load. In the low-rise residential area, the concentration of PAHs is disproportionate to the level of the dustiness of the atmosphere, and the increase in the content of PAHs is associated with an increase in the content of pyrogenic HMW PAHs.
Ratios between individual PAHs are usually used to assess their genesis. The Ant/(Phe + Ant) ratio below 0.1 was usually taken as an indication of petroleum, while the ratio over 0.1 indicated a dominance of combustion (Yunker et al. 2002; Li et al. 2011). Yunker et al. (2002) reported that the Flt/(Pyr + Flt) ratio was below 0.4 for most crude petroleum pollution and above 0.5 for the combustion of wood and coal, and the ratio was between 0.4 and 0.5 for the combustion of petroleum and its refining products. The choice of LMW/HMW ratio was founded on the fact that the petrogenic contamination was characterized by the predominance of the lower molecular weight PAHs (Berner et al. 1990; Soclo et al. 2000), while the higher molecular weight PAHs dominated in the pyrolytic PAH contamination (Muel andSaguem 1985; Zakaria et al. 2002).
Gas flares are an important source of PAHs in the north of Western Siberia. The burning of associated petroleum gas leads to an increase in the share of pyrene, benzo(ghi)perylene, and benzo(a)pyrene at a relatively low content of phenanthrene and fluoranthene in snow dust (Zavgorodnyaya et al. 2021). That's why an increase in the ratio ∑ (Pyr + BaP + BghiP)/ ∑ (Phe + Flt) is indicative of the pyrogenic origin of PAHs from associated gas flares among other sources.
We used the above diagnostic ratios of Ant/(Phe + Ant), LMW/HMW, Flt/(Pyr + Flt), and ∑ (Pyr + BaP + BghiP)/ ∑ (Phe + Flt) in the analysis of sources of PAHs in Nizhnevartovsk. The results of our calculations for each land-use area can be seen in Table 4.
Table 4
Diagnostic ratios of PAHs in Nizhnevartovsk and the background areas.
|
Ant/(Phe + Ant)
|
∑LMW/∑HMW
|
Flt/(Pyr + Flt)
|
(Pyr + BghiP + BaP)/
(Phe + Flt)
|
Background area
|
0,072
|
1,85
|
0.61
|
0.30
|
Urban area
|
0,097
|
0,84
|
0.57
|
0.64
|
Including
Industrial
|
0.092
|
0,94
|
0.58
|
0.58
|
Business
|
0.086
|
0,78
|
0.56
|
0.63
|
High-rise residential
|
0.103
|
1,06
|
0.57
|
0.54
|
Low-rise residential
|
0.119
|
0,55
|
0.59
|
0.93
|
Our calculations demonstrate that both petrogenic and pyrogenic sources of PAHs are common in Nizhnevartovsk. The Ant/(Phe + Ant) ratio in low-rise and high-rise residential areas is > 0.1, which is indicative of the predominant influence of pyrogenic sources (Yunker et al. 2002; Li et al. 2011). This confirms the predominance of pyrogenic sources in the low-rise residential area, and the LMW/HMW ratio is minimal there.
The Flt/(Pyr + Flt) ratio is usually in the range of 0.5–0.6, which is indicative of the input of PAHs from wood and coal combustion (Yunker et al. 2002). An increase in the average values of the Flt/(Pyr + Flt) ratio was observed in the series as follows: business area - industrial area - high-rise residential area - low-rise residential area - background area (Fig. 8b).
Values of 0.4 < Flt/(Pyr + Flt) < 0.5 were twice observed in the business area, which is the effect of burning oil and oil products. These sites are located in the city center, where traffic is the most intensive. Values < 0.4, which would indicate the impact of oil spills (Yunker et al. 2002), were not observed.
The ratio ∑ (Pyr + BaP + BghiP)/ ∑ (Phe + Flt) showed the best results as the indication of PAH sources. The differences between the background areas, the low-rise residential area, and the rest of the city are very clear. An increase in the ratio is indicative of either the influence of associated gas flares (Zavgorodnyaya et al., 2021) or household pyrogenic emissions (Stogiannidis and Laane 2015; Vasilevich et al. 2014). Since the low-rise residential area is located in the southeast of Nizhnevartovsk and is the most remote from the Samotlor oil field, it can be assumed that the sources of PAHs are the combustion of coal, wood, and gas in the dwellings, as well as the burning of household waste.
The analysis of indicative ratios shows that the nearby oil fields do not have a marked effect on the deposition of PAHs in the city because: 1) the ratio Flt / (Pyr + Flt) < 0.4 indicating oil spills has not been recorded; 2) high values of the ratio (Pyr + BaP + BghiP)/(Phe + Flt), indicating the effect of gas flares, have not been observed at the sampling sites close to the Samotlor oil field. However, the lack of impact of oil fields likely has a seasonal pattern. It is obvious that in winter the spilled oil does not evaporate from snow-covered areas and the wind does not blow particles of polluted soil. In summer, these processes can have a strong influence on the composition of the atmosphere, which has been demonstrated by studies on the chemical composition of the aerosol in Nizhnevartovsk, where the input of pollution from adjacent fields has been identified (Antonovich et al. 2000). For more details on this issue, a study on the composition of air and atmospheric dust during warm months is necessary.
To validate the results obtained, we compared them with the results of the study of PAHs in snow from other parts of the Earth. The comparison is presented in Table 5. The works cited use different assemblages of priority-controlled PAHs and differ in the study subject (insoluble dust or the total content in the liquid and solid phases). Nevertheless, the data can be used for comparison because the main share of PAHs is concentrated in the insoluble phase (Sharma and McBean 2001; Vijayan et al.,2019; Moskovchenko et al. 2021b).
Table 5
A comparison of PAHs concentrations in snow from different locations
City, country
|
Concentration
|
Deposition, µg m-2
|
Source
|
ng l-1
|
µg g-1
|
Nizhnevartovsk City, Russia,
∑ 12 PAHs (particulate)
|
33.5 (background)
148.2 (urban)
|
18.4 (background)
14.3 (urban)
|
3,9 (background)
17,0 (urban)
|
This study
|
Moscow, Russia
∑ 16 PAHs (particulate)
|
ND
|
ND
|
45–57 (residental area)
140–264 (traffic zone)
|
Zavgorodnyaya et al. 2019
|
Yamalo-Nenets Autonomous Region, Russia ∑10 ПАУ (particulate)
|
ND
|
0.3 (undisturbed Arctic)
5–20 (gas fields), 15 (urban)
|
ND
|
Zavgorodnyaya et al. 2021
|
Syktyvkar City, Russia ∑13 PAHs (total)
|
ND
|
ND
|
3.5–4.1 background
20.1–76.3 industrial
|
Vasilevich et al.2009
|
Khabarovsk City, Russia ∑16PAHs (total)
|
34.8–79.8 (background)
43-695.7(urban)
|
ND
|
ND
|
Levshina 2019
|
Tyrolean Alps (Austria) (total)
|
0.5–8.4
|
ND
|
ND
|
Arellano et al. 2014
|
Erzurum, Turkey ∑18PAHs (particulate)
|
23820
|
ND
|
ND
|
Bayraktar et al. 2016
|
Changchun City, Northeast China, ∑16PAHs (total)
|
26600–36900
|
ND
|
ND
|
Wei et al. 2017
|
ND – no data |
The comparison shows that in the background area situated in the vicinity of Nizhnevartovsk, the total content of 12 EPA PAHs, averaging 33.5 ng l-1, is slightly less than in the Russian Far East, where a variation from 34.8 to 79.8 ng l-1 has been observed (Levshina 2019). In the glaciers of Tibet, the total content of 16 EPA PAHs varied within similar limits, from 20.45 to 60.57 ng l-1 (Li et al. 2011). In the Tyrolean Alps, the content of PAHs in snow varied from 0.5 to 8.4 ng l-1 (Arellano et al. 2014), which is a lot lower than in the vicinity of Nizhnevartovsk.
The concentration of the total PAHs in the background area is 24.6 µg g-1 on average. A similar value has been observed in the north of Western Siberia, where the concentration of PAHs in snow dust amounted up to 20 μg g-1 in the area of influence of the large Zapolyarnoye gas field (Zavgorodnyaya et al., 2021). In summary, it can be concluded that the PAH concentration results obtained in this study are in a comparable range with those reported in the literature.
In Nizhnevartovsk, deposition of PAHs (from 4.3 to 38.1 μg m-2, averaging 17 μg m-2) was low in comparison to cities where similar studies were carried out. In the industrial zone of Syktyvkar (Russia), with a geographical location and population similar to Nizhnevartovsk, the input of PAHs was 20.1 - 76.3 μg m-2/m2 (Vasilevich et al., 2009). In Moscow, the deposition of PAHs with snow dust is also more intense, in particular, 45–57 μg m-2 in the residential area, and 140–264 μg m-2 in the transport impact area (Zavgorodnyaya et al., 2019). In Erzurum (Turkey) and Changchun (Northeast China), the concentration of PAHs is higher than in Nizhnevartovsk by a factor of 100.
Benzo(a)pyrene is a strong carcinogen (Xiong et al. 2021), which is why the assessment of its concentration is of particular interest). In Nizhnevartovsk, 0.39 μg m−2 BaP drops out with solid precipitation in winter (see Table 3), or 2.7 ng m−2 per day. In the recreational area of Moscow, 2.4 ng m−2 of 3,4-benzo(a) pyrene drops out with the solid phase of snow per day. As to the residential area, this parameter varies from 7 to 43 ng m−2 per day (Kosheleva et al. 2017; Kasimov et al. al. 2017). Therefore, the input of BaP in Nizhnevartovsk is approximately the same as in the recreational areas of Moscow and somewhat less than in the Moscow’s residential areas.
The total level of pollution
The TDF index in Nizhnevartovsk varies from 90 to 3196. 18 sampling sites (72%) are classified as lowly polluted (TDF<1000), 6 sites (24%), as moderately polluted, and 1 (4%), as highly polluted. DF values in different land-use areas are shown in Fig. 9. The mean values of DF indices were shown to decrease in the following order: W(184)>Mn(93) > DahA(85) > As(61) > V(59) > Co(51) > Fe(46 ) > Sr(36) >Zn(33) > Bi(28) >Ni(23). The maximum TDF values are observed in the industrial area, where the main pollutant is W (Fig. 9). This is probably due to heavy traffic, including trucks. In the low-rise residential area, the deposition of V, DahA, and BaP increases, which is due to the combustion of solid and liquid fuels used for heating. However, despite the significant deposition of PAHs, low TDF values are observed here, because the input of W is weak due to the low traffic intensity.
An analysis of the spatial distribution of TDF values shows the highest values in the central part of the city. In the high-rise residential area, where the main part of the population lives, the intensity of deposition is low.