Long-term exposure to air pollution and the risk of developing sudden sensorineural hearing loss

Table 3 Distributions of air pollutants among urbanization zones

Pollutants	Levels	Highly Urbanized (n = 22,054)		Moderately Urbanized (n = 22,975)		Boomtown (n = 10,896)		Others (n = 10,396)		p	Total (n = 64,321)
PM_2.5 (μg/m³)	Mean (SD)	32.71 (7.85)		35.68 (9.16)		37.24 (8.44)		34.86 (9.04)		< 0.001	34.79 (8.75)
	Low	9906	44.9	6335	30.2	2651	24.3	2593	24.9	< 0.001	21,485	33.4
	Moderate	7680	34.8	6067	28.9	3538	32.5	3050	29.3		20,335	31.6
	High	4468	20.3	8573	40.9	4707	43.2	4753	45.7		22,501	35.0
SO₂ (ppb)	Mean (SD)	4.88 (2.09)		5.23 (2.53)		5.76 (2.74)		3.86 (1.97)		< 0.001	4.98 (2.41)
	Low	7275	33.0	6100	29.1	2700	24.8	5693	54.8	< 0.001	21,768	33.8
	Moderate	6833	31.0	6737	32.1	3233	29.7	2999	28.8		19,802	30.8
	High	7946	36.0	8138	38.8	4963	45.5	1704	16.4		22,751	35.4
CO (ppm)	Mean (SD)	0.81 (0.30)		0.69 (0.24)		0.70 (0.22)		0.59 (0.21)		< 0.001	0.72 (0.27)
	Low	5516	25.0	7839	37.4	3492	32.0	5859	56.4	< 0.001	22,706	35.3
	Moderate	4810	21.8	6904	32.9	4534	41.6	3087	29.7		19,335	30.1
	High	11,728	53.2	6232	29.7	2870	26.3	1450	13.9		22,280	34.6
NO (ppb)	Mean (SD)	14.14 (12.66)		9.94 (8.21)		10.73 (8.43)		6.80 (6.75)		< 0.001	11.01 (10.15)
	Low	4156	18.8	7342	35.0	3177	29.2	7198	69.2	< 0.001	21,873	34.0
	Moderate	6556	29.7	7551	36.0	4205	38.6	1937	18.6		20,249	31.5
	High	11,342	51.4	6082	29.0	3514	32.3	1261	12.1		22,199	34.5
NO₂ (ppb)	Mean (SD)	24.58 (6.51)		22.06 (6.30)		23.39 (5.19)		18.43 (6.41)		< 0.001	22.56 (6.56)
	Low	4245	19.2	7283	34.7	2547	23.4	6041	58.1	< 0.001	20,116	31.3
	Moderate	6127	27.8	7354	35.1	4930	45.2	2974	28.6		21,385	33.2
	High	11,682	53.0	6338	30.2	3419	31.4	1381	13.3		22,820	35.5

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