3.1. Meteorology and Aerosol Concentration
In Raipur, the wind generally blows from southwest to northeast from April to September, whereas from October to March, it blows from southeast to northeast. The winds from the southwest direction, occurring from June to August, featured the highest speeds (approximately 8 m/s), while the lowest wind speeds corresponded to winds from the southeast, observed from October to January (Figure S1).
The meteorological parameters such as temperature, relative humidity, vapor pressure, evaporation, wind speed, and rainfall over the study period (refer to Table 1) were in the following ranges: 17–38.1 °C, 30–91%, 7.4–24.4 mm, 2.3–13.9 mm day−1, 1.5–9.6 km h−1, and 0–16.8 mm, respectively. The lowest values of ambient temperature, vapor pressure, and wind speed were observed in the December–January period. The annual PM10 concentration over the entire year ranged from 70 to 475 μg m−3, with a mean value of 240±63 μg m−3, 12 times higher than the recommended limit of 20 μg m−3 (WHO 2005). The ambient temperature, vapor pressure, evaporation, and wind speed meteorological parameters showed moderate to strong negative correlations (r values in the −0.43 to −0.88 range) with PM10 concentration.
Table 1. PM10 sampling details and meteorology.
Sample number
|
Sampling date
|
PM10 (µg m−3)
|
T (°C)
|
RH (%)
|
VP (mm)
|
WS (km h−1)
|
EP (mm day−1)
|
RF (mm)
|
1
|
12 January
|
336
|
21.6
|
62
|
11.1
|
4.2
|
2.5
|
0.0
|
2
|
19 January
|
425
|
21.4
|
78
|
14.1
|
3.0
|
2.8
|
0.0
|
3
|
09 February
|
375
|
22.4
|
73
|
14.1
|
4.0
|
5.0
|
2.8
|
4
|
18 February
|
345
|
24.0
|
62
|
12.4
|
2.0
|
4.0
|
0.0
|
5
|
23 March
|
266
|
17.0
|
58
|
7.4
|
6.0
|
8.1
|
0.4
|
6
|
13 April
|
261
|
27.3
|
46
|
10.7
|
5.2
|
8.5
|
0.7
|
7
|
4 May
|
100
|
31.1
|
39
|
13.1
|
9.6
|
12.7
|
1.1
|
8
|
1 June
|
83
|
33.8
|
30
|
11.5
|
7.2
|
13.9
|
2.4
|
9
|
6 July
|
70
|
38.1
|
36
|
16.1
|
8.2
|
5.2
|
0.0
|
10
|
27 July
|
87
|
29.9
|
71
|
22.3
|
7.0
|
3.0
|
16.9
|
11
|
24 August
|
115
|
27.0
|
91
|
24.0
|
3.0
|
2.8
|
6.9
|
12
|
12 September
|
88
|
28.0
|
85
|
24.4
|
7.4
|
4.3
|
7.8
|
13
|
12 October
|
228
|
27.8
|
84
|
23.7
|
5.4
|
4.4
|
1.9
|
14
|
9 November
|
187
|
27.6
|
80
|
20.2
|
3.6
|
3.4
|
0.0
|
15
|
30 November
|
475
|
23.0
|
68
|
14.7
|
1.5
|
2.3
|
0.0
|
16
|
7 December
|
337
|
22.2
|
57
|
9.5
|
2.1
|
3.0
|
0.0
|
17
|
28 December
|
308
|
19.8
|
62
|
9.0
|
2.2
|
3.4
|
0.0
|
RH, VP, WS, EP, and RF stand for relative humidity, vapor pressure, wind speed, evaporation, and rainfall, respectively.
3.2. Organic Compounds
The total concentration of identified organic compounds ranged from 5106 to 29099 ng m−3 (mean: 16701±3355 ng m−3). Dominant constituents (Table 2, Table S1) were fatty acids, phthalate esters, sugars, fatty alcohols, sterols, n-alkanes, PAHs, and lignin and resin products (annual mean concentration values of 4794±1550, 4710±1507, 3185±1224, 1988±618, 1174±384, 906±422, 243±112, and 221±93 ng m−3, respectively).
Table 2. Concentration of organics in ambient associated with PM10. All values are expressed in ng m−3.
Compound
|
Formula
|
MW
|
Min.
|
Max.
|
Mean
|
Std
|
n-alkanes
|
|
|
|
|
|
|
n-nonadecane
|
C19H40
|
254
|
0
|
24
|
6.9
|
7.3
|
n-eicosane
|
C20H42
|
268
|
0
|
42
|
8.4
|
13.2
|
n-heneicosane
|
C21H44
|
282
|
0
|
74
|
33.8
|
24.7
|
n-docosane
|
C22H46
|
296
|
0
|
88
|
25.4
|
31.6
|
n-tricosane
|
C23H48
|
310
|
0
|
127
|
32.2
|
40.1
|
n-tetracosane
|
C24H50
|
324
|
0
|
155
|
49.6
|
51.4
|
n-pentacosane
|
C25H52
|
338
|
0
|
251
|
68.2
|
78.1
|
n-hexacosane
|
C26H54
|
352
|
0
|
186
|
69.1
|
59.9
|
n-heptacosane
|
C27H56
|
366
|
0
|
194
|
69.1
|
65.3
|
n-octacosane
|
C28H58
|
380
|
0
|
245
|
62.0
|
60.9
|
n-nonacosane
|
C29H60
|
394
|
0
|
296
|
103.2
|
87.6
|
n-triacontane
|
C30H62
|
408
|
1
|
278
|
63.6
|
65.0
|
n-hentriacontane
|
C31H64
|
422
|
1
|
339
|
108.9
|
89.5
|
n-dotriacontane
|
C32H66
|
436
|
0
|
452
|
62.5
|
102.5
|
n-tritriacontane
|
C33H68
|
450
|
2
|
261
|
73.2
|
66.4
|
n-tetratriacontane
|
C34H70
|
464
|
0
|
110
|
22.6
|
27.7
|
n-pentatriacontane
|
C35H74
|
478
|
0
|
360
|
28.6
|
83.7
|
n-hexatriacontane
|
C36H76
|
506
|
0
|
89
|
18.9
|
24.8
|
Total
|
|
|
14
|
3355
|
906.1
|
861.7
|
PAHs
|
|
|
|
|
|
|
1,3,4-triphenylbenzene
|
C24H18
|
306
|
0
|
1
|
0.2
|
0.4
|
1,2,4-triphenylbenzene
|
C24H18
|
306
|
0
|
37
|
8.8
|
10.1
|
Phenanthrene
|
C14H10
|
178
|
0
|
1
|
0.2
|
0.4
|
Anthracene
|
C14H10
|
178
|
2
|
175
|
56.5
|
42.9
|
Fluoranthene
|
C16H10
|
202
|
1
|
37
|
16.2
|
11.7
|
Pyrene
|
C16H10
|
202
|
0
|
29
|
8.5
|
9.1
|
Benzo(b)fluorene
|
C17H12
|
216
|
0
|
4
|
0.8
|
1.3
|
Benzo(a)anthracene
|
C18H12
|
228
|
0
|
35
|
7.2
|
10.5
|
Chrysene/triphenylene
|
C18H12
|
228
|
0
|
38
|
8.2
|
11.6
|
Benzo(b)fluoranthene
|
C20H12
|
252
|
0
|
242
|
61.8
|
67.2
|
Benzo(e)pyrene
|
C20H12
|
252
|
0
|
28
|
5.9
|
7.6
|
Benzo(a)pyrene
|
C20H12
|
252
|
0
|
97
|
24.5
|
26.2
|
Perylene
|
C20H12
|
252
|
0
|
43
|
4.9
|
11.7
|
Benzo(k)fluoranthene
|
C20H12
|
252
|
0
|
10
|
0.9
|
2.4
|
Indeno(1,2,3-cd)pyrene
|
C22H12
|
276
|
0
|
76
|
14.3
|
19.1
|
dibenz(a,h)anthracene
|
C22H14
|
278
|
0
|
13
|
2.1
|
3.8
|
Benzo(ghi)perylene
|
C22H12
|
276
|
0
|
86
|
18.0
|
22.8
|
Anthanthrene
|
C22H12
|
276
|
0
|
5
|
0.3
|
1.2
|
Coronene
|
C24H12
|
300
|
0
|
21
|
2.3
|
5.9
|
Retene
|
C18H18
|
234
|
0
|
1
|
0.2
|
0.4
|
Total
|
|
|
13
|
851
|
242.5
|
228.4
|
Lignin and Resin
|
|
|
|
|
|
|
3-hydroxybenzoic acid
|
C7H6O3
|
138
|
0
|
67
|
17.1
|
15.1
|
4-hydroxybenzoic acid
|
C7H6O3
|
138
|
2
|
374
|
92.3
|
85.8
|
Vanillic acid
|
C8H8O3
|
168
|
1
|
129
|
37.0
|
31.1
|
Syringic acid
|
C9H10O5
|
198
|
1
|
150
|
34.4
|
36.5
|
Dehydroabietic acid
|
C20H28O2
|
300
|
3
|
115
|
40.0
|
33.0
|
Total
|
|
|
7
|
834
|
220.8
|
190.4
|
Sugars
|
|
|
|
|
|
|
Galactosan
|
C6H10O5
|
180
|
10
|
203
|
59.4
|
50.7
|
Mannosan
|
C6H10O5
|
162
|
14
|
494
|
148.1
|
130.9
|
Levoglucosan
|
C6H10O5
|
162
|
0
|
8434
|
2210.5
|
2381.7
|
Arabitol
|
C5H10O5
|
152
|
3
|
61
|
29.8
|
18.9
|
Fructose
|
C6H12O6
|
180
|
0
|
37
|
10.8
|
11.2
|
Glucose
|
C6H12O6
|
180
|
10
|
106
|
47.4
|
22.6
|
Glucose
|
C6H12O6
|
180
|
5
|
108
|
48.6
|
23.1
|
Mannitol
|
C6H14O6
|
182
|
0
|
114
|
26.5
|
33.6
|
Inositol
|
C6H12O6
|
182
|
0
|
65
|
9.3
|
14.4
|
Sucrose
|
C12H22O11
|
342
|
0
|
174
|
38.6
|
46.1
|
Trehalose
|
C12H22O11
|
342
|
1
|
73
|
36.9
|
23.8
|
Xylose
|
C5H10O5
|
150
|
4
|
196
|
36.7
|
42.7
|
Maltose
|
C12H22O11
|
342
|
1
|
58
|
22.9
|
15.2
|
Total
|
|
|
327
|
9103
|
2725.6
|
2505.2
|
Sterols
|
|
|
|
|
|
|
Cholesterol
|
C27H46O
|
386
|
5
|
190
|
81.1
|
53.5
|
β-cholesterol
|
C27H46O
|
386
|
0
|
987
|
296.2
|
232.0
|
Ergosterol
|
C28H44O
|
396
|
15
|
1787
|
608.2
|
457.9
|
Stigmasterol
|
C29H44O
|
412
|
0
|
38
|
12.3
|
12.1
|
β–sitosterol
|
C29H50O
|
536
|
0
|
474
|
175.8
|
139.5
|
Total
|
|
|
22
|
2988
|
1173.6
|
784.2
|
Fatty acids
|
|
|
|
|
|
|
Dodecanoic acid
|
C12H24O2
|
200
|
27
|
847
|
252.9
|
208.5
|
Tridecanoic acid
|
C13H26O2
|
214
|
0
|
53
|
10.0
|
13.0
|
Tetradecanoic acid
|
C14H28O2
|
228
|
67
|
904
|
248.1
|
200.5
|
Pentadecanoic acid
|
C15H30O2
|
242
|
19
|
146
|
57.2
|
32.6
|
Hexadecanoic acid
|
C16H32O2
|
256
|
22
|
8327
|
1880.3
|
1812.3
|
Heptadecanoic acid
|
C17H34O2
|
270
|
2
|
63
|
15.5
|
15.2
|
Octadecanoic acid
|
C18H36O2
|
284
|
10
|
2418
|
866.6
|
608.4
|
Nonadecanoic acid
|
C19H38O2
|
298
|
0
|
30
|
8.9
|
9.1
|
Eicosanoic acid
|
C20H40O2
|
312
|
2
|
222
|
74.8
|
68.3
|
Heneicosanoic acid
|
C21H42O2
|
326
|
0
|
53
|
20.0
|
17.3
|
Docosanoic acid
|
C22H44O2
|
340
|
2
|
358
|
115.6
|
98.7
|
Tricosanoic acid
|
C23H46O2
|
354
|
1
|
192
|
50.9
|
54.3
|
Tetracosanoic acid
|
C24H48O2
|
368
|
5
|
715
|
285.0
|
225.3
|
Pentacosanoic acid
|
C25H50O2
|
382
|
1
|
147
|
46.6
|
46.7
|
Hexacosanoic acid
|
C26H52O2
|
396
|
3
|
2093
|
460.2
|
579.7
|
Heptacosanoic acid
|
C17H34O2
|
270
|
0
|
81
|
25.2
|
25.3
|
Octacosanoic acid
|
C28H56O2
|
424
|
0
|
806
|
233.6
|
222.9
|
Nonacosanoic acid
|
C29H58O2
|
438
|
0
|
74
|
12.7
|
17.9
|
Triacontanoic acid
|
C14H28O2
|
228
|
0
|
362
|
82.8
|
107.5
|
Henatriacontanoic acid
|
C31H62O2
|
466
|
0
|
42
|
7.2
|
10.7
|
Dotriacontanoic acid
|
C32H64O2
|
480
|
0
|
144
|
27.1
|
39.0
|
Tetratriacontanoic acid
|
C34H68O2
|
508
|
0
|
10
|
1.8
|
2.8
|
Octadecenoic acid
|
C18H34O2
|
282
|
0
|
13
|
5.2
|
3.7
|
Octadecadienoic acid
|
C18H32O2
|
280
|
0
|
23
|
6.1
|
6.8
|
Total
|
|
|
751
|
12962
|
4794.3
|
3162.9
|
Fatty Alcohols
|
|
|
|
|
|
|
Myristyl alcohol
|
C14H30O
|
214
|
0
|
306
|
55.4
|
95.5
|
Cetyl alcohol
|
C16H34O
|
242
|
0
|
72
|
18.5
|
19.6
|
Heptadecyl alcohol
|
C17H36O
|
256
|
0
|
97
|
27.4
|
25.7
|
Stearyl alcohol
|
C18H38O
|
270
|
0
|
14
|
1.4
|
3.8
|
Nonadecan-1-ol
|
C19H40O
|
284
|
0
|
1731
|
419.6
|
565.0
|
Arachidyl alcohol
|
C20H42O
|
298
|
0
|
43
|
14.1
|
10.7
|
Heneicosyl alcohol
|
C21H44O
|
312
|
0
|
42
|
12.6
|
14.9
|
Docosanol
|
C22H46O
|
326
|
0
|
68
|
23.3
|
21.7
|
Tricosan-1-ol
|
C23H48O
|
340
|
0
|
192
|
33.9
|
46.4
|
Lignoceryl alcohol
|
C24H50O
|
354
|
6
|
111
|
52.5
|
32.9
|
Pentacosan-1-ol
|
C25H52O
|
368
|
0
|
352
|
50.6
|
87.2
|
Ceryl alcohol
|
C26H54O
|
382
|
0
|
897
|
216.4
|
258.2
|
1-Heptacosanol
|
C27H56O
|
396
|
0
|
1820
|
281.0
|
525.1
|
Montanyl alcohol
|
C28H58O
|
410
|
9
|
767
|
310.1
|
208.5
|
1-Nonacosanol
|
C29H60O
|
424
|
0
|
349
|
58.6
|
90.0
|
Myricyl alcohol
|
C30H62O
|
438
|
12
|
867
|
256.2
|
207.1
|
1-hentriacontanol
|
C31H64O
|
452
|
0
|
333
|
48.6
|
83.9
|
1-Dotriacontanol
|
C32H66O
|
466
|
0
|
391
|
108.2
|
110.9
|
Total
|
|
|
41
|
4270
|
1988.1
|
1261.2
|
Phthalate Esters
|
|
|
|
|
|
|
Dimethyl phthalate
|
C10 H10O4
|
194
|
0
|
8
|
1.8
|
2.1
|
Diethyl phthalate
|
C12H14O4
|
222
|
0
|
1513
|
154.3
|
428.2
|
Diisobutyl phthalate
|
C16H22O4
|
278
|
0
|
4770
|
1393.1
|
1442.6
|
di-n-butyl phthalate
|
C16H22O4
|
278
|
0
|
1086
|
348.5
|
288.9
|
Bis 2-ethylhexyl phthalate
|
C24H38O4
|
390
|
24
|
10488
|
2800.8
|
2772.5
|
Bisphenol A
|
C15H16O2
|
228
|
0
|
59
|
11.5
|
15.9
|
Total
|
|
|
25
|
10882
|
4710.1
|
3074.6
|
3.3. Alkanes
n-alkanes in the atmosphere originate from diverse sources, including fossil fuel combustion, biomass burning, and resuspended plant debris (Zhu et al., 2005; Rushdi et al., 2017). In this study, n-alkanes ranging from C19 to C36 were detected in ambient aerosols (Table 2, Table S1). While n-alkanes in the C23 to C25 range are typically linked to vehicular emissions, higher molecular weight n-alkanes, especially those with odd carbon numbers (C27, C29, and C31), are indicative of plant sources, as they are abundant in the waxy outer layer of plants.
The total annual concentration (ΣC19–C36) ranged from 14 to 3355 ng m−3, with a mean value of 906±422 ng m−3, similar to the concentration of n-alkanes in the ambient PM of Delhi reported by (Li et al. 2014) (874±438 ng m−3). The concentrations of the lightest n-alkanes, C19–C20, were low (7–8 ng m−3), while those of higher n-alkanes, C24–C33, were present at moderate concentration levels, ranging from 19 to 109 ng m−3, with the highest value for C31. The sum of total concentrations of odd (C19+C21+C23+C25+C27+C29+C31+C33) and even (C20+C22+C24+C26+C28+C30+C32+C34) n-alkanes were 524 and 382 ng m−3, respectively, with a mass ratio of 1.4.
The carbon preference index (CPI) values of n-alkanes (sum of the odd alkanes to sum of the even alkanes ratio; CPI = (C23+C25+C27+C29+C31+C33)/(C24+C26+C28+C30+C32+C34)) (Choi et al. 2015; Mancilla et al., 2021) were examined for source identification. In the literature, the CPI values of 1 (Cai et al., 2017), 1.1 (Cai et al., 2017), 1.5 (Schauer et al., 2001), 1.7 (Mancilla et al., 2021), and 1.08–3.02 (Zhao et al., 2019) were associated with wood, diesel, and gasoline combustion, and cooking activities. On the other hand, higher CPI values indicate a contribution of plant waxes [Kawamura et al., 2003]. In this study, the CPI values ranged from 0.62 to 13.09, with a mean value of 2.0±1.1, indicating that biogenic emission sources (CPI > 1) prevail over the year, except from July to September, when anthropogenic sources (CPI < 1) predominate.
The proxy ratio (Paq = (C23+C25)/(C23+C25+C29+C31)) (Ficken et al. 2000) ranged from 0 to 0.45, with a mean value of 0.23±0.07, indicating emissions from terrestrial plants (<0.1) as well as from emergent macrophytes (0.1–0.4) (Oyo-ita et al. 2010).
3.4. Alkanoic acids
The abundance of even-numbered n-alkanoic acids, with a peak at C16 (Table 2, Table S1), suggests primary origins from microbial sources rather than vascular plants [Simoneit 1989]. The fatty acids identified in the aerosol samples from the studied area ranged from C12:0 to C34:0 and included C18:1 and C18:2 (Table 2, Table S1).
The total annual concentration of 24 fatty acids (Σ(C12:0–C34:0)+(C18:1+C18:2)) ranged from 751 to 12962 ng m−3, with a mean value of 4794±1550 ng m−3. Among them, a remarkably high concentration (1880 ng m−3) of C16:0 was noticed. The sum of the concentrations of even acids was found to be several times higher (>17.7) than that of odd acids, due to higher thermal stability and enhanced emissions.
The concentration of fatty acids in the ambient air of Raipur City was significantly higher than those reported in other urban areas around the world (Fu et al. 2008; Abas and Simoneit, 1996; Didyk et al. 2000; Kang et al. 2016).
3.5. Alkanols
Analysis of n-alkanol distribution in aerosol samples reveals evidence of vascular plant wax input originating from semi-tropical to tropical regions (Rushdi et al. 2006). The fatty alcohols were identified in the C14 to C32 range (Table 2, Table S1). The total annual concentration of 10 fatty alcohols, ΣC14–C32, ranged from 41 to 4270 ng m−3, with a mean value of 1988±618 ng m−3. Six alcohols (C19, C26–C28, C30, and C32) were present at moderate concentrations (108–420 ng m−3), while other alcohols were detected at low concentrations, in the 1–58 ng m−3 range.
The concentration of the alcohols detected in the present study was significantly higher than those reported in Delhi (Kang et al. 2016).
3.6. Sugars
Levoglucosan, a sugar compound formed during carbohydrate pyrolysis, serves as a specific marker for biomass burning in atmospheric PM samples (Simoneit, 1999). Its exceptional thermal stability allows it to function as a tracer for the long-range transport of biomass-derived aerosols (Fraser and Lakshmanan, 2000). The total annual concentrations of the 13 detected sugars (namely arabitol, fructose, galactosan, glucose, inositol, levoglucosan, maltose, mannitol, mannosan, sucrose, trehalose, and xylose; (Table 2, Table S1) varied from 481 to 9103 ng m−3, with a mean value of 3185±1224 ng m−3. Among them, levoglucosan was the most abundant compound (2210±1167 ng m−3), while the others were present at low concentrations (9–148 ng m−3).
For comparison purposes, the total sugar concentration in the ambient aerosols of São Paulo ranged from 280 to 12500 ng m−3 (Scaramboni et al. 2014); the average levoglucosan winter concentrations reported in Delhi, Kolkata, and Mumbai were 5300±1100, 5500±1100, and 910±180 ng m−3, respectively (Wan et al. 2017); and the annual average concentration of levoglucosan reported in the Indo-Gangetic Plain was 734 ng m−3 (Wan et al. 2017).
3.7. Phthalates esters
Chemicals like phthalates are linked to endocrine system disruption and the development of asthma and allergies. Phthalates, widely used as plasticizers in various products, enhance flexibility and stability and act as fragrance solvents. Diisodecyl phthalate (DiDP), di-2-ethylhexyl phthalate (DEHP), and diisononyl phthalate (DiNP) are among the most commonly produced phthalates. Studies have shown that phthalates can interfere with human hormonal development, potentially leading to estrogen-mimicking effects (Howdeshell et al., 2008). Therefore, chronic exposure to these chemicals in the environment may pose significant health risks to the local population.
The annual concentration of phthalates (Table 2, Table S1) varied from 25 to 10882 ng m−3, with a mean value of 4710±1507 ng m−3. Two phthalates, diisobutyl phthalate (DiBP) and di-n-butyl phthalate (DnBP), were detected at significant concentrations (1316 and 2645 ng m−3, respectively), while others (DEHP and BPA) were detected at much lower concentrations (2 and 11 ng m−3).
The concentration of phthalates in Raipur was higher than those reported in Delhi and several Chinese cities (Fu et al. 2010; Fu et al. 2008).
3.8. Lignin and resin products
In the samples from Raipur, the total annual concentration of five lignin and resin products (namely 3- and 4-hydroxybenzoic acid, dehydroabietic acid, syringic acid, and vanillic acid; (Table 2, Table S1) ranged from 7 to 834 ng m−3, with a mean value of 221±93 ng m−3, higher than those reported for Chinese cities (Fu et al. 2008; Li et al. 2014).
3.9. Sterols
Sterols, found throughout various ecosystems, derive from biogenic sources and offer valuable insights into the origin and dynamics of organic matter in the environment (Volkman et al., 1981; Rushdi et al., 2006). This diverse class of compounds typically contains between C26 and C30 carbon atoms (Moreau et al., 2002). Cholesterol (C27) is a prominent sterol abundant in animal fats, plankton, and certain terrestrial plants. Phytosterols, found in higher plants, are characterized by one or two carbon-carbon double bonds within the sterol ring or side chain and range from C28 to C30 (Brassell et al., 1983).
The annual concentration of the five detected sterols ranged from 22 to 2988 ng m−3, with a mean value of 1174±384 ng m−3 (Table 2, Table S1). Tree of them, β-cholesterol, ergosterol, and β-sitosterol, were found at high levels (176–608 ng m−3), while the other two (cholesterol and stigmasterol) were detected at low levels, in the 12 to 81 ng m−3 range.
The ambient aerosol concentrations observed in Raipur city surpassed those recorded in Chinese cities, as reported by Wang et al. (2006) and Fu et al. (2008).
3.10. Polycyclic aromatic hydrocarbons
Polycyclic aromatic hydrocarbons result from the pyrolysis of organic matter during incomplete combustion and are primarily linked to fine particles. Their mutagenic and carcinogenic properties have been extensively studied, as noted by Wogan et al. (2004). The annual concentration of the 20 detected PAHs ranged from 13 to 851 ng m−3, with a mean value of 243±112 ng m−3, exceeding those reported for megacities like Kolkata (63.5 ng m−3) or Beijing (142.8 ng m−3), as documented by Chowdhury et al. (2007).
Among the PAHs, six (anthracene (Ant), benzo[b]fluoranthene (BbF), benzo[e]pyrene (BeP), benzo[ghi]perylene (BghiP), indeno[1,2,3-cd]pyrene (IndP), and fluoranthene (Fla)) were detected at moderate levels, in the 14 to 62 ng m−3 interval. Nine others were present at lower concentration levels (1.0–8.7 ng m−3), and the remaining PAHs were detected at trace levels (<1.0 ng m−3). Benzo(a)pyrene (BaP), the most toxic PAH, exceeded the 1 ng m−3 tolerance limit several-fold during January and February (NAAQS 2009).
To assess PAH sources in the air, two diagnostic ratios were employed: the low molecular weight (LMW)/high molecular weight (HMW) ratio, and the [Fla]/[Fla+Pyr] ratio, where Pyr stands for pyrene (Wang et al. 2006; Li et al. 2006). The LMW/HMW ratio distinguishes between pyrogenic and petrogenic sources by representing the abundance of lower (3-ring) to higher (4- to 6-ring) hydrocarbons. Values <1.0 indicate pyrogenic sources, while values >1.0 suggest petrogenic origins (Wang et al. 2006). The [Fla]/[Fla+Pyr] ratio differentiates between petroleum and combustion sources; ratios > 0.5, 0.5 > – > 0.4, and < 0.4 indicate emissions from grass/wood combustion, coal combustion, and petroleum sources, respectively (Li et al. 2006).
In Raipur aerosols, [LMW]/[HMW] and [Fla]/[Fla+Pyr] ratios ranged from 0.1 to 3.9 and 0.5 to 1.0, with mean values of 0.7±0.5 and 0.7±0.1, respectively (Table S2). These findings point towards pyrogenic sources, likely biomass burning (Yunker et al. 2002; Tsapakis and Stephanou 2003; Tang et al. 2005; Ravindra et al. 2006; Pope and Dockery 2006). However, the IndP/(IndP + BghiP) ratio suggests petroleum combustion remains a significant PAH source, with ratios of 0.25 in summer, 0.37 in autumn, and 0.47 in winter (Table S2).
Among the 20 detected PAHs, five compounds (benzo(a)anthracene (Baa), Bbf, benzo(k)fluoranthene (Bkf), dibenz(a,h)anthracene (Dba), and IndP) exhibit notable toxicity. Their carcinogenic potential is often expressed relative to benzo[a]pyrene using the benzo[a]pyrene equivalent (BapE = 0.06×Baa + 0.07×Bbf + 0.07×Bkf + 1.00×Bap + 0.6×Dba + 0.08×IndP) value. In this study, BapE values ranged from 0 to 78 ng m−3 (Table S3), with a mean value of 13±10 ng m−3, with the highest carcinogenic toxicity values observed in the winter season (37±32 ng m−3).
3.11. Seasonal Variations
Meteorological factors, including temperature, humidity, precipitation, and wind speed and direction, significantly influence the formation, transport, and transformation of aerosols and related compounds in the atmosphere. The resulting monthly variations of PM10 and associated organic compounds are depicted in Figure 2. Notably high concentrations of PM10, n-alkanes, PAHs, and lignin products were detected in December–February. Alcohols, fatty acids, sterols, and sugars peaked between August and December. Phthalate levels showed no distinct seasonal trend (Guha et al. 2015).
The highest concentrations of PM10 and PAHs were recorded in the winter season, while high concentrations of n-alkanes, alcohols, lignin products, sterols, and sugars were observed during both the autumn and winter seasons. A high concentration of fatty acids was detected throughout the year except in the summer. Regarding phthalates, high concentrations were observed during the summer and autumn seasons.
3.12. Segregation
The organic compounds were studied for size-segregated particulate matter (PM10.0–9.0, PM9.0–5.8, PM5.8–4.7, PM4.7–3.3, PM3.3–2.1, PM2.1–1.1, PM1.1–0.7, PM0.7–0.1, and PM0.1 modes) to gain insight into their accumulation trends and potential health hazards. All classes of compounds (except phthalates and PAHs) exhibited a trend toward higher accumulation in the fine and ultrafine modes (Figure 3). PAHs showed higher accumulating only in the ultrafine mode. However, phthalates largely accumulated in the coarse modes. Similar size-segregated accumulation patterns of organic compounds have been reported by Sevimoglu and Rogge (2015).
3.13. Composition of Aerosols
The organic fraction of the aerosols of the studied area ranged from 3.9 to 33.1%, with a mean value of 10.0±3.9%. Alcohols, fatty acids, phthalates, and sugars were present at significant levels (>1%), while other organic species (n-alkanes, resin products, sterols, and PAHs) were present at trace levels, <1%. The highest organic fractions were observed during the rainy and autumn seasons, with the highest value detected in September. Similar organic fractions in aerosols from other locations have been reported in the literature, such as in Xi'an and New Delhi (Li et al. 2014).
3.14. Correlation and Source Apportionment
The organic aerosols generally showed a moderate negative correlation with the ambient temperature and wind speed, and positive correlations with humidity and vapor pressure (Table S4). The organic aerosols showed a poor correlation with PM10, indicating that they originate from other sources, such as evaporation, atmospheric transformations, etc. Among themselves, they generally showed moderate to strong correlations, suggesting origins from multiple sources.
Based on the FA, five source profiles that explain that 85.01% of the total variance of measured compounds in aerosol samples were obtained (Table S5).
PAHs, n-alkanes ranging from C19 to C35, and PM10 were found to be major compounds for the first factor. Pyrene, benzo(b)fluoranthene, Bkf, IndP, and BghiP are usually associated with vehicular emissions and oil combustion (Motelay-Massei, 2005; Sadiktsis et al., 2012; Cai et al., 2017). Accordingly, the first factor —explaining 25.71% of the total variance— was attributed to vehicular emissions.
Factor 2 explains that 25.33% of the total variance was mostly associated with PM10, levoglucosan, 3-hydroxybenzoic acid, 4-hydroxybenzoic acid, vanillic acid, syringic acid, dehydroabietic acid, fatty acids (C17-C25), anthracene, BPA, alkanes ranging from C22 to C29 and C36. Levoglucosan is an atmospheric tracer of wood smoke (Jordan et al., 2006). Furthermore, it is also emitted from charbroiled cooking activities (Mancilla et al., 2021). Dehydroabietic, p-hydroxybenzoic, syringic, and vanillic acids are also key tracers of biomass-burning emissions in the atmosphere (Wan et al., 2019). In addition to cooking, biomass burning, crop emissions, and traffic are the sources of fatty acids in the atmosphere (Li et al., 2012; Yu et al., 2021). Anthracene is one of the tracers of wood combustion (Saraga et al., 2010). The levoglucosan to mannosan ratio (Lev/Man) and levoglucosan to the sum of mannosan and galactosan (Lev/(Man+Gal)) are used to determine the emissions from different fuels (Janoszka and Czaplicka, 2022). In the study, the average (Lev/Man) and (Lev/(Man+Gal)) ratios were 16.77 ±11.05 and 11.46±8.18. High values indicate the contribution of emissions from the combustion of hardwood and crop residues (Mkoma et al., 2013). Moreover, the average ratio of vanillic acid to syringic acid was calculated as 1.47±0.70, implying the combustion of crop and hardwood residues (Wan et al., 2017). BPA also indicates open burning of plastics (Fu et al., 2009). Therefore, the second factor was attributed to mixed emissions from biomass burning, charbroiled cooking, and open burning of municipal wastes. The seasonal variation of factor scores of the FA analysis also implies a source related to combustion due to higher contributions of F2 during the cold months.
The third factor —accounting for 15.89% of the total variance— was significantly loaded with galactosan, mannosan, maltose, β-cholesterol, ergosterol, C14, and C26-C28 fatty alcohols. Ergosterol is the biomarker for fungal spores in the atmosphere [Burshtein et al., 2011]. Anhydrosaccharides and disaccharides can be attributed to airborne/soil-borne microbes and other biogenic materials. Furthermore, higher contributions from sugar compounds also indicate crustal emissions (Li et al., 2012). Hence, this factor was identified as a natural background.
Fatty acids ranging from C27 to C30, cholesterol, stigmasterol, β-sitosterol, and C32-C34 fatty alcohols were major compounds of the fourth factor. Cholesterol is accepted as a meat cooking tracer [Cass, 1998]. On the other hand, sterols have been linked to waxes of plants (Gal et al., 2022). High molecular fatty acids are also linked to plant emissions (Fu et al., 2010). Accordingly, this factor explaining 9.62% of the total variance was found to be plant emissions and cooking.
The last factor was highly loaded with C12-C18 fatty acids and mannitol. In the study, the average ratio of stearic acid (C18) to palmitic acid (C16) was 0.64±0.64, which indicates road dust (Cachon et al., 2023). On the other hand, mannitol can be ascribed to biogenic sources (i.e., plant emissions) (Xu et al., 2020). Consequently, the last factor was a mixed factor related to urban dust and biogenic sources.