Comparison of Air Pollution in Metropolises in China (Beijing) and Japan (Osaka and Nagoya) on the Basis of the Levels of Contaminants and Mutagenicity

Abstract

Public concern regarding the transport of air pollutants from mainland East Asia to the leeward area by the prevailing westerlies in spring and winter monsoon has been growing in recent years. We collected total suspended particle (TSP) in Beijing, a metropolis of China located windward of Japan, in spring (late February 2011–May 2011) and in winter (November 2012–early February 2013), then analyzed metals, ions, and organic compounds and mutagenicity, and compared the pollution levels with samples collected at two Japanese metropolises (Osaka and Nagoya) during the same periods. The medians of concentration of TSP and other factors in Beijing were much larger than those in the Japanese metropolises. Especially, the concentrations of polycyclic aromatic hydrocarbons (PAHs) were remarkably high in Beijing in winter, and the median of total PAHs concentration in Beijing was 62–63 times larger than that in the Japanese sites. The mutagenicity of TSP from Beijing toward Salmonella typhimurium YG1024, with and without a mammalian metabolic system (S9 mix), was 13–25 times higher than that from the Japanese sites in winter. These results suggest that air pollution levels in Beijing are very high compared with those at the two Japanese metropolises we evaluated. The diagnostic ratios of PAHs and nitrated polycyclic aromatic hydrocarbons (NPAHs) suggest that the major sources of PAHs and NPAHs in Beijing are different from those at the two Japanese sites in winter, and that the major source in Beijing is coal/biomass combustion.

The International Agency for Research on Cancer (IARC) has classified outdoor air pollution and particulate matter, which is a major component of outdoor air pollution, as carcinogenic to humans (group 1).¹⁾ In recent decades, primary energy consumption has rapidly increased in northeast Asia, especially in China,²⁾ and as the consequence of unprecedented economic development and industrial growth in China, the emissions of anthropogenic air pollutants have drastically increased. Coal is the primary energy source in China,²⁾ and the vast majority of coal has been consumed in northern, central, and eastern China.³⁾ The Beijing–Tianjin–Hebei region is located in northern China and is of special concern because of severe haze.⁴⁾ Haze is an atmospheric phenomenon where visibility is decreased by dry particulate matters, such as dust and smoke. Zhao et al.⁵⁾ collected PM_2.5 (airborne particles with an aerodynamic diameter of less than or equal to 2.5 µm) at four urban sites in the Beijing–Tianjin–Hebei region over four seasons from 2009 to 2010, and revealed that the PM_2.5 concentrations at Shijiazhuang and Chengde were highest in winter and that the PM_2.5 pollution was dominated by coal combustion. Various mutagenic/carcinogenic substances, such as polycyclic aromatic hydrocarbons (PAHs) and nitrated PAHs (NPAHs), are generated by the incomplete combustion of fossil fuels, such as coal and petroleum, by anthropogenic activities, and emitted into the atmosphere.^6–9)

Several studies have reported that dust particles and anthropogenic air pollutants have been transported by the prevailing westerlies and winter monsoon from mainland East Asia to leeward areas, including Taiwan, Korea, and Japan.^10–12) We examined air pollutants containing mutagens and other chemicals in western Japan, namely, Dazaifu in Fukuoka Prefecture and Yurihama in Tottori Prefecture, for one year. Highly mutagenic airborne particles were collected at both sites in January and February 2013.^13,14) At Yurihama, high mutagenicity was also detected in many samples collected in March 2013.¹⁴⁾ Because atmospheric concentrations of lead (Pb) and sulfate ion (SO₄²⁻), which are indicators of transboundary air pollution from mainland East Asia,^15,16) were increased in those particles, the mutagens in those particles were presumed to be transported from mainland East Asia. However, information on the air pollution containing mutagens and the mutagenicity of airborne particles in the windward side, China, is limited.

The purpose of this study was to clarify the air pollution levels at Beijing, which is a metropolis in China and is located windward of Japan, in winter and spring, and to compare the pollution levels with those at metropolises in Japan, namely, Osaka and Nagoya. Beijing has a population density of about 5500/km² (population, 21009000; area, 3820 km²) in 2014. Osaka and Nagoya are the central cities of Keihanshin metropolitan area and Chukyo metropolitan area, respectively. The population density of Osaka was 11960/km² (population, 2694000; area, 225 km²) and that of Nagoya was 6990/km² (population, 2280000; area, 326 km²) in 2015. We collected airborne particles at those three sites in spring and winter, quantified the constituents, and examined their bacterial mutagenicity. As constituents, we analyzed iron (Fe), Pb, SO₄²⁻, nitrate ion (NO₃⁻), PAHs, and NPAHs. Fe is a major element in the earth’s crust and is an indicator of the amount of sand in total suspended particle (TSP).¹⁵⁾ Pb is a minor element in the crust and is emitted into the atmosphere by combustion of coal and refuse incineration.¹⁷⁾ SO₄²⁻ and NO₃⁻ are formed from sulfur oxides and nitrogen oxides, which are produced by combustion of fossil fuels, such as coal and petroleum. PAHs and NPAHs are formed by incomplete combustion of organic substances and are representative environmental mutagens/carcinogens.^6–9) Mutagenicity was examined using Salmonella typhimurium YG1024, which is sensitive to atmospheric mutagens without and with a mammalian metabolic activation system (S9 mix).¹⁸⁾ Moreover, we calculate diagnostic ratios of chemical constituents, namely, PAHs and NPAHs, to estimate the sources of air pollutants.

MATERIALS AND METHODS

Chemicals

Pyrene (PY, CAS 129-00-0) and fluoranthene (FR, CAS 206-44-0) were purchased from Nacalai Tesque Inc. (Kyoto, Japan). 2-Acetylaminofluorene (CAS 53-96-3), benz[a]anthracene (BaA, CAS 56-55-3), 1-nitropyrene (1-NPY, CAS 5522-43-0), 2-nitropyrene (2-NPY, CAS 789-07-1), 4-nitropyrene (4-NPY, CAS 57835-92-4), and dibenz[a,h]anthracene (DahA, CAS 53-70-3) were obtained from Tokyo Chemical Industry Co., Ltd. (Tokyo, Japan). 2-Nitrofluoranthene (2-NFR, CAS 13177-29-2) was obtained from Chiron AS (Trondheim, Norway). Benzo[k]fluoranthene (BkF, CAS 207-08-9), indeno[1,2,3-cd]pyrene (IcdP, CAS 193-39-5), benzo[b]fluoranthene (BbF, CAS 205-99-2), benzo[a]pyrene (BaP, CAS 50-32-8), nitric acid (HNO₃, CAS 7697-37-2), perchloric acid (HClO₄, CAS 7601-90-3), and hydrochloric acid (HCl, CAS 7647-01-0) were obtained from Wako Pure Chemical Industries, Ltd. (Osaka, Japan). Phenobarbital (CAS 50-06-6), chrysene (CH, CAS 218-01-9), β-naphthoflavone (CAS 6051-87-2), benzo[ghi]perylene (BghiP, CAS 191-24-2), 3-nitrofluoranthene (3-NFR, CAS 892-21-7), and 6-nitrochrysene (6-NCH, CAS 7496-02-8) were obtained from Sigma-Aldrich Co., LLC (St. Louis, MO, U.S.A.).

Sampling

TSP were collected at three sites (Fig. 1), namely, Beijing (116.34°E, 40.01°N), Osaka (135.53°E, 34.99°N), and Nagoya (136.92°E, 35.10°N). Sampling was performed by the method described previously.¹⁸⁾ TSP were collected on quartz filters (Pall Life Sciences, Port Washington, NY, U.S.A.) at a flow rate of 400–1000 L/min for about 24 h using a high volume air sampler (HV1000R, Shibata Scientific Technology, Soka, Japan). Sampling was performed in spring (late February 2011–May 2011) and winter (November 2012–early February 2013) as shown in Table 1. The sampling periods were each 20 d at Beijing and 16 d at Osaka and Nagoya. The amount of TSP was calculated from the difference of weights of the filter before and after sample collection, and the atmospheric concentration of TSP was calculated by dividing the weight of TSP by the volume of the air that had passed through the filter.

Fig. 1. Locations of Beijing, Osaka, and Nagoya

Table 1. Sampling Days

Sampling site	Spring				Winter
	2011				2012		2013
	February	March	April	May	November	December	January	February
Beijing	11–16	7–11	11–15	24–28	5–9	10–14	7–11	4–8
Osaka	16, 21, 22	10, 14, 22–24	11–14	23–26	5–8	10–13	7–10	4–7
Nagoya	14, 15, 17	7–10	11–15	23–26	5–8	10–13	7–10	4–8

Sampling periods were as follows: spring (late February 2011–May 2011) and winter (November 2012–early February 2013). Sampling periods were each 20 d at Beijing and 16 d at Osaka and Nagoya.

Quantification of Metals

Fe and Pb were measured by the method described previously.¹³⁾ Sample solutions were prepared from 10% of each sample filter by digestion using mixtures of HNO₃/HCl and HNO₃/HF/HClO₄ and adjustment using 0.2 M HNO₃. Fe and Pb were analyzed by inductively coupled plasma-atomic emission spectrometry (IRIS 1000, Thermo Fisher Scientific, Waltham, MA, U.S.A.) and Zeeman electro-thermal atomic absorption spectrometry (Analyst 600, PerkinElmer, Inc., Waltham, MA, U.S.A.), respectively.

Quantification of Water Soluble Ionic Species

SO₄²⁻, and NO₃⁻ were quantitated by the method described previously.¹³⁾ Sample solutions were prepared from 5% of each sample filter by ultra-sonication with distilled water and filtration using a DISMIC-25CS syringe filter (Advantec Co., Ltd., Tokyo, Japan). SO₄²⁻ and NO₃⁻ were analyzed using an ion chromatograph (600E/700, Waters Co., Ltd., Milford, MA, U.S.A.) with an anion suppressor (ASRS 300, Thermo Fisher Scientific) and an AS4A-SC column (Thermo Fisher Scientific).

Quantification of PAHs and NPAHs

Ten PAHs, namely, BghiP, DahA, BaP, PY, FR, IcdP, BbF, BaA, BkF, and CH, which are classified as priority pollutants by the United States Environmental Protection Agency, and six NPAHs, namely, 1-NP, 2-NP, 4-NP, 6-NC, 2-NFR, and 3-NFR, were analyzed. Sample solutions were prepared from 40% of each sample filter by ultra-sonication using methanol as described previously.¹³⁾ The extract was evaporated to dryness, and the residue was dissolved in ethanol. PAHs were analyzed by HPLC using a Wakosil-PAHs column (4.6 mm i.d. × 250 mm, Wako Pure Chemical Industries, Ltd.) and a fluorescence detector (RF-20AXs, Shimadzu Co., Kyoto, Japan). The wavelengths of excitation (Ex)/emission (Em) were as follows: BghiP, DahA, and BaP, 296 nm/410 nm; PY and FR, 250 nm/420 nm; IcdP, 300 nm/500 nm; and BbF, BaA, BkF, and CH, 270 nm/400 nm.¹³⁾

A portion of the ethanol sample solution was evaporated to dryness, and the residue was dissolved in 50% tetrahydrofuran. The sample solution was injected into a COSMOSILπNAP column (4.6 mm i.d. × 250 mm, Nacalai Tesque) to clean up NPAHs.¹⁹⁾ NPAHs were analyzed as corresponding amino compounds with a two-dimensional HPLC system using the first separation column (Inertsil ODS-EP column (4.6 mm i.d. × 250 mm, GL Science, Tokyo, Japan)), a concentration column (COSMOSIL 5C18-AR-II column (4.6 mm i.d. × 10 mm, Nacalai Tesque)), the second separation column (COSMOSIL 5C18-AR-II column (4.6 mm i.d. × 250 mm, Nacalai Tesque)), a reducer column (Np pak RL column (4.6 mm i.d. × 30 mm, Jasco, Tokyo, Japan)), and the fluorescence detector as described previously.²⁰⁾ The wavelengths of Ex/Em were as follows: 1-, 2-, and 4-aminopyrene isomers, 244 nm/438 nm; 2- and 3-aminofluoranthene, 244 nm/528 nm; and 6-aminochrysene, 270 nm/430 nm.²¹⁾

Mutagenicity Assay

The mutagenicity of organic extracts of TSP was assayed by the Ames test using Salmonella typhimurium YG1024 with and without S9 mix.¹³⁾ Forty percent of each sample filter was extracted with methanol by ultra-sonication. The extract was evaporated to dryness, and the residue was dissolved in dimethyl sulfoxide. S. typhimurium YG1024, which was kindly provided by Dr. Nohmi of the National Institute of Health, is an O-acetyltransferase-overproducing derivative of S. typhimurium TA98²²⁾ and is sensitive to the mutagenicity of the organic extracts of TSP.¹⁸⁾ A mammalian metabolic system (S9 mix), was prepared with livers of male Sprague-Dawley rats (SLC Inc., Shizuoka, Japan) treated with phenobarbital and β-naphthoflavone as described previously.²³⁾ 1-NPY and 2-acetylaminofluorene were used as positive controls without and with S9 mix, respectively. The slope of the dose–response curve obtained with three doses and duplicate plates at each dose was adopted as the mutagenic potency. Samples were judged as positive when they induced twofold increases over the average of spontaneous revertants and showed well-behaved concentration–response patterns.

Statistical Analysis

Statistical analysis (calculation of correlation coefficients, Dunnett’s test, and others) was carried out with Microsoft Office Excel 2013. The differences in the diagnostic ratios of PAHs and NPAHs in TSP collected at Beijing from those at two Japanese sites were analyzed by non-repeated one-way ANOVA followed by Dunnett’s test.

RESULTS

Atmospheric Concentrations of TSP and the Chemical Constituents

Table 2 shows the medians, minimums, and maximums of the atmospheric concentrations of TSP and the chemical constituents, namely, Fe, Pb, SO₄²⁻, NO₃⁻, PAHs, and NPAHs, in the TSP collected at Beijing, Osaka, and Nagoya in spring (late February–May 2011) and winter (November 2012–early February 2013). For PAHs and NPAHs, we analyzed 10 PAHs and 6 NPAHs to estimate the levels of PAHs and NPAHs in TSP, and total PAHs and total NPAHs present the sum of the concentrations of these 10 PAHs and 6 NPAHs, respectively. In spring, the medians of the concentrations of TSP and most chemical constituents from Osaka were similar to those from Nagoya. In addition, the maximums of the concentrations of TSP and the chemical constituents from Osaka and Nagoya showed similar levels. The medians of the concentrations of TSP and the constituents from Beijing were 3–12 times larger than those from the two Japanese sites. The maximums of the concentrations of TSP and the chemical constituents from Beijing were 5–57 times larger than those from Japanese sites. Large differences were found for total PAHs, and the maximum from Beijing (405.0 ng/m³) was 41 times and 57 times larger than those from Osaka (9.8 ng/m³) and Nagoya (7.1 ng/m³), respectively.

Table 2. Medians, Minimums and Maximums of the Concentrations of TSP and Their Chemical Constituents

	Spring						Winter
	(a) Beijing	(b) Osaka	(c) Nagoya	Ratio			(d) Beijing	(e) Osaka	(f) Nagoya	Ratio
				a/b	a/c	b/c				d/e	d/f	e/f
TSP (µg/m3)
Median	308.7	53.9	41.6	6	7	1.3	286.9	37.7	32.7	8	9	1.2
Minimum	82.8	17.0	19.6	5	4	0.9	48.6	21.6	16.8	2	3	1.3
Maximum	1372.9	121.2	102.6	11	13	1.2	829.9	66.0	54.4	13	15	1.2
Fe (ng/m3)
Median	4713	1329	896	4	5	1.5	4855	1069	746	5	7	1.4
Minimum	810	431	238	2	3	1.8	1792	410	223	4	8	1.8
Maximum	15065	2511	2235	6	7	1.1	10618	1871	1397	6	8	1.3
Pb (ng/m3)
Median	142.4	23.7	12.4	6	12	1.9	150.9	14.3	11.0	11	14	1.3
Minimum	16.6	4.5	5.6	4	3	0.8	8.5	3.9	3.9	2	2	1.0
Maximum	680.5	53.6	64.1	13	11	0.8	683.3	88.1	21.0	8	33	4.2
SO42− (µg/m3)
Median	11.9	4.5	3.0	3	4	1.5	17.5	3.7	3.5	5	5	1.1
Minimum	2.6	0.9	1.4	3	2	0.6	2.4	1.5	1.4	2	2	1.0
Maximum	78.9	10.8	8.3	7	10	1.3	96.3	6.7	6.0	14	16	1.1
NO3− (µg/m3)
Median	13.6	5.1	3.1	3	4	1.6	18.9	3.1	2.4	6	8	1.3
Minimum	1.0	0.7	1.1	1	1	0.7	1.0	1.2	1.0	1	1	1.2
Maximum	51.2	10.8	7.5	5	7	1.4	66.2	6.1	5.2	11	13	1.2
Total PAHs (ng/m3)
Median	18.9	2.1	1.8	9	10	1.1	146.9	2.3	2.4	63	62	1.0
Minimum	5.2	0.3	0.7	19	7	0.4	25.0	0.9	1.3	29	19	0.7
Maximum	405.0	9.8	7.1	41	57	1.4	1407.3	16.0	5.1	88	278	3.2
Total NPAHs (pg/m3)
Median	117.6	27.9	45.0	4	3	0.6	719.6	33.3	28.1	22	26	1.2
Minimum	32.0	4.4	14.5	7	2	0.3	44.0	5.5	8.1	8	5	0.7
Maximum	1025.6	188.9	141.6	5	7	1.3	1657.3	90.3	73.2	18	23	1.2

Sampling periods were as follows: spring (late February 2011–May 2011) and winter (November 2012–early February 2013). Sampling periods were each 20 d at Beijing and 16 d at Osaka and Nagoya. Total PAHs means the sum of the concentrations of 10 PAHs (BghiP, DahA, BaP, PY, FR, IcdP, BbF, BaA, BkF, and CH). Total NPAHs means the sum of the concentrations of 6 NPAHs (1-NPY, 2-NPY, 4-NPY, 6-NCH, 2-NFR, and 3-NFR).

For samples collected in winter, the medians of the concentrations of TSP and most chemical constituents from Osaka were similar to those from Nagoya. The medians of the concentrations of TSP and the constituents from Beijing were 5–63 times larger than those from the two Japanese sites. Large differences were found for total PAHs and total NPAHs. For total PAHs, the medians from Beijing (146.9 ng/m³) were 63 times and 62 times larger than those from Osaka and Nagoya, respectively. The median of total NPAHs concentration from Beijing (719.6 pg/m³) was 22 times and 26 times larger than those from Osaka and Nagoya, respectively. The maximums of the concentrations of TSP and the constituents from Beijing were 6–278 times larger than those from the Japanese sites. Large differences were found for total PAHs, and the maximum concentration from Beijing (1407.3 ng/m³) was 88 times and 278 times larger than those from Osaka and Nagoya, respectively. The maximum concentration of total NPAHs from Beijing (1657.3 pg/m³) was about 20 times larger than those from the two Japanese sites.

For Osaka and Nagoya, there was no large difference in the median for the concentrations of TSP and all chemical constituents between spring and winter. For Beijing, the medians for TSP and most chemical constituents showed similar levels in the two sampling periods. However, the medians for total PAHs and total NPAHs in winter were 8 times and 6 times larger than those in spring, respectively.

Mutagenic Activity of TSP

Table 3 shows the medians, minimums, and maximums of the mutagenicities of organic extracts of TSP collected at Beijing, Osaka, and Nagoya in spring and winter. In spring, the medians of the mutagenicities of TSP from Osaka and Nagoya were similar under each metabolic condition, namely, the absence or the presence of S9 mix. The medians of the mutagenicities of TSP from Beijing without and with S9 mix (198.5 revertants (rev.)/m³ and 423.5 rev./m³, respectively) were 6–9 times larger than those from Osaka and Nagoya. The maximums of the mutagenicities of TSP from Beijing without and with S9 mix (2176.8 and 5214.9 rev./m³, respectively) were 15–30 times larger than those from the two Japanese sites. In winter, there were no large differences between the mutagenicities of TSP from Osaka and Nagoya without or with S9 mix. The medians of the mutagenicities of TSP from Beijing without and with S9 mix (789.4 and 987.3 rev./m³, respectively) were 13–25 times larger than those from the two Japanese sites. The maximums of the mutagenicities without and with S9 mix at Beijing (2158.4 and 3057.9 rev./m³) were 17–29 times larger than those at the two Japanese sites. Furthermore, the medians of the mutagenicities without and with S9 mix at Beijing in winter were 2–4 times larger than those in spring. Similarly, the medians of the mutagenicities without and with S9 mix at Osaka and Nagoya in winter were slightly larger than those in spring.

Table 3. Medians, Minimums and Maximums of the Mutagenicities of Organic Extracts from TSP

	Spring						Winter
	(a) Beijing	(b) Osaka	(c) Nagoya	Ratio			(d) Beijing	(e) Osaka	(f) Nagoya	Ratio
				a/b	a/c	b/c				d/e	d/f	e/f
Mutagenicity (revertant/m3)
Without S9 mix
Median	198.5	33.9	28.8	6	7	1.2	789.4	41.6	31.6	19	25	1.3
Minimum	43.4	10.8	10.6	4	4	1.0	56.8	24.6	21.3	2	3	1.2
Maximum	2176.8	140.6	76.6	15	28	1.8	2158.4	125.1	73.5	17	29	1.7
With S9 mix
Median	423.5	48.2	47.0	9	9	1.0	987.3	64.3	76.7	15	13	0.8
Minimum	130.7	9.4	27.0	14	5	0.3	58.5	15.0	33.8	4	2	0.4
Maximum	5214.9	171.1	191.3	30	27	0.9	3057.9	141.0	160.3	22	19	0.9

Sampling periods were as follows: spring (late February 2011–May 2011) and winter (November 2012–early February 2013). Sampling periods were each 20 d at Beijing and 16 d at Osaka and Nagoya.

Correlations between Mutagenicity and Atmospheric Concentrations of TSP and the Constituents

To clarify the association between the mutagenicity and the levels of contaminants, we calculated their coefficients of correlation. Table 4 summarizes the correlation coefficients (r) between the mutagenicity and the atmospheric concentrations of TSP and the constituents in TSP collected at Beijing, Osaka, and Nagoya for the two periods. At Beijing, strong (r≥0.7) or moderate (0.7>r≥0.4) positive correlations were obtained for TSP and most constituents without and with S9 mix in spring and winter. The correlations between the mutagenicity with and without S9 mix and the concentrations of Pb, SO₄²⁻, and total PAHs were very strong (r≥0.9) in spring. At Osaka and Nagoya, strong or moderate positive correlations were found between the mutagenicity and the concentrations of total PAHs and total NPAHs in spring and winter both without and with S9 mix.

Table 4. Correlation Coefficients between the Mutagenicity and the Atmospheric Concentrations of TSP and the Constituents

	Spring			Winter
	Beijing	Osaka	Nagoya	Beijing	Osaka	Nagoya
Without S9 mix
TSP	0.694	0.002	0.499	0.895	0.276	0.222
Fe	0.079	0.312	0.625	0.589	0.498	0.214
Pb	0.930	0.507	0.213	0.601	0.231	0.095
SO42−	0.914	0.127	0.080	0.836	0.137	0.375
NO3−	0.762	0.220	0.520	0.878	0.417	0.378
Total PAHs	0.981	0.545	0.408	0.736	0.845	0.551
Total NPAHs	0.789	0.882	0.843	0.450	0.480	0.478
With S9 mix
TSP	0.585	0.185	0.556	0.898	0.241	0.508
Fe	0.088	0.610	0.716	0.636	0.315	0.372
Pb	0.906	0.618	0.498	0.627	0.164	0.316
SO42−	0.879	0.370	0.368	0.816	−0.035	0.383
NO3−	0.692	0.538	0.580	0.857	0.316	0.735
Total PAHs	0.923	0.656	0.848	0.745	0.839	0.510
Total NPAHs	0.723	0.802	0.599	0.481	0.550	0.501

Sampling periods were as follows: spring (late February 2011–May 2011) and winter (November 2012–early February 2013). Sampling periods were each 20 d at Beijing and 16 d at Osaka and Nagoya. Total PAHs means the sum of the concentrations of 10 PAHs (BghiP, DahA, BaP, PY, FR, IcdP, BbF, BaA, BkF, and CH). Total NPAHs means the sum of the concentrations of 6 NPAHs (1-NPY, 2-NPY, 4-NPY, 6-NCH, 2-NFR, and 3-NFR).

Diagnostic Ratios of PAHs and NPAHs

To characterize the emission sources of PAHs and NPAHs, we calculated diagnostic ratios of PAHs and NPAHs in TSP collected at Beijing, Osaka, and Nagoya in spring and winter. Figure 2 shows the ratio of the concentration of IcdP to that of IcdP and BghiP ([IcdP]/([IcdP]+[BghiP])) for TSP collected at each site in the two seasons. In spring, the [IcdP]/([IcdP]+[BghiP]) ratio for TSP from Beijing were not significantly different from those for TSP from Osaka and Nagoya, and the medians of the ratios for TSP from these three sites were 0.373–0.407. In contrast, the ratio for TSP collected at Beijing in winter was significantly (<0.01) larger than those from the two Japanese sites. The medians of the ratio for TSP from Beijing, Osaka, and Nagoya were 0.810, 0.370, and 0.388, respectively. No large differences were found for the medians of the ratios for TSP from the two Japanese sites in the two periods. Figure 3 shows the ratio of the concentration of 1-NPY to that of PY ([1-NPY]/[PY]) for TSP collected at Beijing, Osaka, and Nagoya in the two periods. In spring, there were no significant differences between the ratio for TSP from Beijing and those from two Japanese sites. The medians of the ratios for the three sites in spring were as follows: Beijing, 0.007; Osaka, 0.011; Nagoya, 0.015. In contrast, the ratio for Beijing was significantly (<0.01) smaller than those for Osaka and Nagoya in winter. The medians of the ratios for TSP from Beijing, Osaka, and Nagoya were 0.004, 0.013, and 0.014, respectively.

Fig. 2. Ratio of the Atmospheric Concentration of IcdP to That of IcdP and BghiP ([IcdP]/[IcdP]+[BghiP])

The ratios were analyzed by Dunnett’s test. The intervals for collecting TSP were as follows: spring (late February 2011–May 2011) and winter (November 2012–early February 2013).

Fig. 3. Ratio of the Atmospheric Concentration of 1-NPY to That of PY ([1-NPY]/[PY])

The ratios were analyzed by Dunnett’s test. The intervals for collecting TSP were as follows: spring (late February 2011–May 2011) and winter (November 2012–early February 2013).

These two diagnostic ratios suggest that the major sources of PAHs and NPAHs in TSP collected at Beijing were different from those at Osaka and Nagoya in winter.

DISCUSSION

To reveal and compare the air pollution levels at metropolises in China (Beijing) and Japan (Osaka and Nagoya), we collected TSP at these three sites in spring (late February 2011–May 2011) and winter (November 2012–early February 2013), quantified the constituents, and examined mutagenicity. Moreover, we calculated the diagnostic ratios of PAHs and NPAHs to estimate the sources of PAHs and NPAHs. Several ratios have been used to estimate the sources of PAHs and NPAHs in literatures.^24–26) For instance, the [IcdP]/([IcdP]+[BghiP]) ratio is larger than 0.50 for PAHs emitted from coal or biomass combustion and lower than 0.50 for PAHs emitted from petroleum combustion.^24,25) Zhou et al.²⁷⁾ investigated 17 PAHs in aerosol particles in urban and suburban sites of Beijing in 2003, and concluded that coal combustion for domestic heating was probably the major contributor to the higher PAHs loading in winter on the basis of the ratio of [IcdP]/([IcdP]+[BghiP]). Although the [IcdP]/([IcdP]+[BghiP]) ratio is one of the most commonly used ratios to estimate the source of PAHs in airborne particles, the differences of the ratios among PAHs sources are not large enough to identify the source in some cases. Therefore, we adopted another diagnostic ratio, namely, [1-NPY]/[PY], to estimate the source of PAHs and NPAHs. The [1-NPY]/[PY] ratio for coal-smoke particulates (0.001) was much smaller than the ratio of diesel-engine exhaust particles (0.36).²⁶⁾ At Osaka and Nagoya, the medians of the concentrations of TSP and the chemical constituents were similar in the two periods. At Beijing, the medians of the concentrations of TSP, Fe, Pb, SO₄²⁻, and NO₃⁻ were also similar in the two periods, but they were 3–14 times larger than those for the two Japanese sites (Table 2). On the other hand, the medians for total PAHs and total NPAHs in TSP collected at Beijing in winter were 6–8 times larger than those in spring, and the medians for PAHs and NPAHs from Beijing in winter were 62–63 and 22–26 times larger than those from the two Japanese sites. These pollution levels were similar to those reported in the previous study.²⁸⁾ These results indicate that air pollution with PAHs and NPAHs was very severe at Beijing in winter as compared with the two Japanese metropolises. The high values of the [IcdP]/([IcdP]+[BghiP]) ratio for TSP from Beijing in winter (median, 0.810, Fig. 2) suggest the dominance of coal combustion emissions such as domestic heating. The small ratio of [1-NPY]/[PY] for Beijing in winter (median, 0.004, Fig. 3) also implies a large effect of coal combustion on the atmospheric PAHs. The medians for total PAHs and total NPAHs from the two Japanese sites were similar in the two periods and the [IcdP]/([IcdP]+[BghiP]) and [1-NPY]/[PY] ratios for the two Japanese sites were significantly different from those for Beijing in winter. These results suggest that the effects of long-range transport of air pollution from Beijing were not large in Osaka and Nagoya in winter.

At each sampling site, the medians of the mutagenicities of TSP with and without S9 mix were larger in winter than in spring (Table 3). The medians of the mutagenicities of TSP from Beijing were 6–9 times larger than those from Osaka and Nagoya in spring, and the medians of the mutagenicities for Beijing were 13–25 times larger than those from the two Japanese sites in winter. At Beijing, strong or moderate positive correlations with the mutagenicity were observed for TSP and most constituents without and with S9 mix in spring and winter (Table 4). At Osaka and Nagoya, strong or moderate positive correlations were found between the mutagenicity and the concentrations of total PAHs and total NPAHs without and with S9 mix in the two periods. Pb, SO₄²⁻, NO₃⁻, PAHs, and NPAHs are emitted into the atmosphere by combustion of fossil fuels. These results suggest that the atmosphere was more polluted with mutagens at Beijing as compared with the two Japanese sites, especially in winter, and the dominant mutagens at these three sites were formed by combustion. Because many kinds of PAHs and NPAHs are mutagenic toward S. typhimurium YG1024 with and without S9 mix, respectively, these chemicals may have contributed to the mutagenicity of the extract from TSP examined in the present study. Dong et al.²⁹⁾ detected six mutagenic/carcinogenic heterocyclic aromatic amines, such as 2-amino-1-methyl-6-phenyl-imidazo[4,5-b]pyridine (PhIP), in airborne particles collected at urban sites in Beijing from March 2005 to January 2006, and speculated that combustion aerosols emitted from cooking, coal, and petroleum were the source of these chemicals in the atmosphere. Because these heterocyclic aromatic amines are formed by combustion of organic matter and show potent mutagenicity toward S. typhimurium YG1024 with S9 mix, these chemicals may have been present in the samples collected in the present study and have affected the mutagenicity in some extent.

The results of the present study indicate that air pollution levels were very high in Beijing, a windward area of Japan, in winter and spring as compared with those at metropolises in Japan (Osaka and Nagoya), and contamination with PAHs was quite severe in Beijing in winter. These results suggest that transboundary air pollution can occur in East Asia by winter monsoon and the prevailing westerlies. However, the diagnostic ratios of PAHs and NPAHs suggest that the effect of the long-range transport of PAHs and NPAHs from Beijing was not large at Osaka and Nagoya in winter. In our previous study of air pollution at Dazaifu and Yurihama, increases of air pollutants and mutagenicity, which were expected to occur by transboundary air pollution, were found in winter and spring.^13,14) These results suggest that air pollution from domestic sources was dominant at Osaka and Nagoya, while effects of long-range transport of air pollutants were relatively small. Information on the long-range transport of air pollutants and their health effects are still limited. Further studies in this field are ongoing in our laboratory.

Acknowledgments

This study was supported by the Environment Research and Technology Development Fund (C-1154) of the Japanese Ministry of the Environment and Health and Labour Sciences Research Grants for Research on Global Health Issues from the Ministry of Health, Labour, and Welfare of Japan. SC was granted scholarship assistance by Otsuka Toshimi Scholarship Foundation.

Conflict of Interest

The authors declare no conflict of interest.

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