Table 1. Characteristics of ambient air pollutants based in Wuhan 2011–2013, and findings from published studies investigating ambient air pollution of O₃, SO₂, NO₂ and CO and the occurrence of CHDs.

Study	Study location	Period	Design	Exposure assessment methods	Results	Air Pollutants	Mean	Minimum	25th percentile	Median	75th percentile	Maximum	IQR
The current study	China	2011–2013	Cohort	Average of daily concentration of pollutants measured at nearest monitoring station	O3 exposure and CHDs overall, and VSD and TF individually	O3	72.4 μg/m3	1 μg/m3	31.9 μg/m3	63.6 μg/m3	106 μg/m3	334.3 μg/m3	74.1 μg/m3
							(36.9 ppb)	(0.5 ppb)	(16.3 ppb)	(32.4 ppb)	(54 ppb)	(170 ppb)	(37.7 ppb)
						SO2	38.5 μg/m3	2 μg/m3	18 μg/m3	32.6 μg/m3	53.9 μg/m3	261 μg/m3	35.9 μg/m3
							(14.7 ppb)	(0.8 ppb)	(6.9 ppb)	(12.5 ppb)	(20.6 ppb)	(99.6 ppb)	(13.7 ppb)
						NO2	59.6 μg/m3	7.1 μg/m3	38 μg/m3	55.8 μg/m3	77 μg/m3	174 μg/m3	39 μg/m3
							(31.7 ppb)	(3.8 ppb)	(20.2 ppb)	(29.6 ppb)	(40.9 ppb)	(92.5 ppb)	(20.7 ppb)
						CO	1.0 mg/m3	0.02 mg/m3	0.71 mg/m3	1 mg/m3	1.3 mg/m3	4.3 mg/m3	0.59 mg/m3
							(0.91 ppm)	(0.01 ppm)	(0.62 ppm)	(0.85 ppm)	(1.1 ppm)	(3.8 ppm)	(0.48 ppm)
Gianicolo et al.34	Southern Italy	2001–2010	Case-control	Daily average exposure measured by 3 monitoring stations over week 3-8 of pregnancy	Exposure to the 90th percentile of SO2 to be associated with CHDs	SO2	2.8μg/m3	—	—	—	—	—	—
Schembari et al.6	Barcelona	1994–2006	Case-control	Daily spatio-temperal air pollutants estimates over week 3–8 of pregnancy	A significant association between NO2 and coarctation of the aorta	NO2	—	—	—	55.7 μg/m3	—	—	12.2 μg/m3
Stingone et al.15	Nine U.S.states	1997–2006	Case-control	Daily maximum concentrations using the closest air monitor within 50 km to their residence	NO2 was associated with coarctation of the aorta and pulmonary valve stenosis.	O3	—	—	32.2ppb	42.9ppb	51.8ppb	—	—
						SO2	—	—	—	9.7ppb	—	—
						NO2	—	—	—	33.3ppb	—	—	—
						CO	—	—	—	1.16ppm	—	—	—
Agay-Shay et al.11	Israel	2000–2006	Cohort	Geographic Information System-based spatiotemporal approach with weekly inverse distance weighting modeling	No significant association had been revealed	O3	—	0.45ppb	7.8ppb	26.5ppb	39.1ppb	128ppb	—
						SO2	—	0.33ppb	1.5ppb	2.1ppb	3.3ppb	51.4ppb	—
						NO2	—	0.2ppb	15.6ppb	23.1ppb	32.3ppb	104.5ppb	—
						CO	—	0.15ppm	0.7ppm	0.9ppm	1.3ppm	13.5ppm
Padula et al.26	San Joaquin Valley of California	1997–2006	Case-control	Daily average concentration during the first two months from from more than 20 locations with a maximum interpolation radius of 50 km.	No significant association had been revealed	O3(8-h maximum)	—	10.49ppb	29.05ppb	46.94ppb	62.64ppb	91.92ppb	—
						NO2	—	2.4 ppb	13.36 ppb	16.81 ppb	20.53 ppb	38.93 ppb	—
						CO	—	0.13 ppm	0.39 ppm	0.52 ppm	0.71 ppm	1.37 ppm	—
Vinikoor-Imler et al.16	North Carolina	2003–2005	Cohort	Estimated averaged concentration across weeks 3 through 8 for 12 km x 12 km grid.	No significant association had been revealed	O3	40.7 ppb	—	—	42.15 ppb	—	—	30.19 ppb
Dadvand et al.19	Northeast England	1993–2003	Case-control	Weekly average of pollutants at nearest of 6 monitors to maternal residence	No significant association between SO2 and CHDs	SO2	—	—	17.6 μg/m3	—	31.2 μg/m3	—	—
Dadvand et al.22	Northeast England	1985–1996	Case-control	Two-stage spaiotemporal modeling of weekly exposure levels at maternal residence	Exposure to CO to be associated with VS,DCSM and CPVS. NO was associated with TF.	O3	—	—	33.2 μg/m3	—	42.4 μg/m3	—	—
						NO2	—	—	29.2 μg/m3	—	38.4 μg/m3	—	—
						CO	—	—	0.39 mg/m3	—	0.64 mg/m3	—	—
Dolk et al.3	England	1991–1999	Cohort	Estimated annual mean of air pollution for 1 km x 1 km grid	A significant association between SO2 and TF	SO2	—	—	—	7.86 μg/m3	—	—	—
						NO2	—	—	—	35.11μg/m3	—	—	—
Hansen et al.35	Brisbane, Australia	1997–2004	Case-control	Daily averaged measurements of air pollution at 18 nearest monitoring stations.	O3 was associated with an increased risk of pulmonary artery and valve defects, SO2 was associated with an increased risk of aortic artery and valve defects	O3	25.8 ppb	4.3 ppb	—	—	—	54.4 ppb	—
					SO2	1.5 ppb	0 ppb	—	—	—	7.1 ppb	—
					NO2	8.2 ppb	1.4 ppb	—	—	—	22.7 ppb	—
CO	1.1 ppm	0.02 ppm	—	—	—	7 ppm	—
Rankin et al.36	Northern region, UK	1985–1990	Case-control	Daily average concentration during the first trimester from 62 monitors within 10 km of the mother’s residence.	No significant association between SO2 exposure and CHDs	SO2			2.7 μg/m3		4.4 μg/m3
Strickland et al.35	Atlanta, USA	1986–2003	Cohort	Average of daily measuremtns of pollutants from one central monitoring station	No significant association between SO2, O3, NO2, and CO exposure and CHDs	O3	—	—	—	—	—	—	29.9 ppb
						SO2	—	—	—	—	—	—	4.0 ppb
						NO2	—	—	—	—	—	—	5.7 ppb
						CO	—	—	—	—	—	—	0.3 ppm
Ritz et al.9	California, USA	1987–1993	Case-control	Average of 24-hr measurements of pollutants at nearest monitoring station	Second-month CO exposure was associated with an increased risk of VSD	O3	—	—	1.06 pphm	1.94 pphm	2.84 pphm	—	—
						CO	—	—	1.14 ppm	1.6 ppm	2.47 ppm	—	—