Table 1.

Descriptive statistics of change in NO₂ and PM_2.5, urban expansion and urban characteristic variables from 2000–2010 stratified by urban population

	Urban Size
	100,000–250,000 (n=235)		250,000–1,000,000 (n=340)		> 1,000,000 (n=255)
	Mean	Std dev	Mean	Std dev	Mean	Std dev
Change in Air Pollution
NO2 (ppb)	1.21	1.75***	2.07	2.15***	2.25	3.03***
PM2.5 (μg/m3)	10.54	10.19***	12.53	10.91***	11.02	12.42***
Urban Expansion
Area (sq km)	6.93	7.67***	49.27	63.86***	3.79×102	8.72×102***
Population (1,000s)	23.47	32.29	3.42×102	2.25×102***	2.18×103	1.96×104***
Change in Urban Characteristics
Compactness Index (0–1)	−1.72×10−2	4.65×10−2***	−2.87×10−2	8.43×10−2***	−2.35×10−2	9.09×10−2***
Population Density (pop/km2)	7.72×102	1.12×103***	2.76×103	2.94×103***	4.56×104	2.93×105
NDVI (-1-1)	0.35	0.10***	0.33	0.11***	0.31	0.12***
Impervious Surface Area (%)	−0.10	10.96***	−0.13	11.10***	10.16	11.15***
Lights at Night (%)	12.09	7.83***	10.62	6.26***	8.79	7.11***
Change in Urban Characteristic Heterogeneity
Population Density	5.21×102	1.03×103***	3.31×103	2.76×103***	6.33×103	5.13×103***
NDVI (-1-1)	8.24×10−2	2.83×102***	8.32×102	3.57×10−2***	9.05×10−2	3.77×10−2***
Impervious Surface Area (%)	−15.96	8.92***	−16.82	7.92***	−13.43	7.13***
Lights at Night (%)	0.69	2.84**	−1.47	3.34	−3.20	3.81***
Baseline (2000) Urban Characteristics
NO2 (ppb)	1.58	1.27	1.77	1.28	2.51	1.27
PM2.5 (μg/m3)	28.05	19.15	31.42	21.07	23.86	17.81
Area (sq km)	53.54	43.90	1.14×102	93.51	5.50×102	43.90
Population (1000s)	52.18	73.05	1.41×102	2.17×102	1.68×103	7.31
NDVI (-1-1)	1.41×10−2	3.06×10−3	1.33×10−2	2.88×10−3	1.28×10−2	3.06×10−3
Impervious Surface Area (%)	24.46	9.35	28.27	11.21	33.14	9.35
Lights at Night (%)	35.49	11.00	37.75	11.31	11.16	11.00

^*p-value < 0.05,

^**p-value < 0.01,

^***p-value < 0.001.

Differences between 2000 and 2010 levels were tested for significance using multiple paired t-tests with Bonferroni-adjusted confidence intervals.