The impact of three recent coal-fired power plant closings on Pittsburgh air quality: A natural experiment

Figures & data

Figure 1. Topographical map of study domain with EPA ground stations.

Table 1. PM_2.5 means by closing period from EPA ground station locations.

	PM2.5 at all 12 EPA ground stations				PM2.5 excluding data from stations likely to be affected by unconventional natural gas extraction
	Mean (μg/m^3)	95% CI	N	Missing	Mean (μg/m^3)	95% CI	N	Missing
Period 1^a	10.93	(10.48, 11.38)	263	1	10.37	(9.86, 10.89)	198	0
Period 2^b	10.52	(10.16, 10.88)	144	0	10.27	(9.87, 10.67)	108	0
Period 3^c	9.99	(9.57, 10.42)	168	0	9.37	(8.94, 9.80)	126	0
Total			575	1			432	0

^aPeriod 1 spans from January 2011 through October 2012, when all three plants were open.

^bPeriod 2 spans from November 2012 through October 2013, when Elrama was closed, but Hatfield’s Ferry and Mitchell were still open.

^cPeriod 3 spans from November 2013 through December 2014, when all three plants were closed.

Table 2. AOD means by closing period from EPA ground station locations.

	Combined Terra & Aqua AOD
	Mean	95% CI	N	Missing
Period 1^a	0.159	(0.148, 0.171)	262	2
Period 2^b	0.113	(0.102, 0.124)	144	0
Period 3^c	0.099	(0.087, 0.112)	155	13
Total			561	15

^aPeriod 1 spans from January 2011 through October 2012, when all three plants were open.

^bPeriod 2 spans from November 2012 through October 2013, when Elrama was closed, but Hatfield’s Ferry and Mitchell were still open.

^cPeriod 3 spans from November 2013 through December 2014, when all three plants were closed.

Table 3. GAM results for two different dependent EPA ground station data sets.

	PM2.5 at all 12 EPA ground stations (N = 575)			PM2.5 excluding data from stations likely to be affected by unconventional natural gas extraction (N = 432)
	Y-intercept = 10.82			Y-intercept = 10.27
Predictors	edf^a	p Value	Adjusted R^2	edf^a	p Value	Adjusted R^2
f(Time)	1.0	0.909	0.61	1.7	0.105	0.68
f(Elrama_Fuel)	11.1	1.51e-9		11.2	1.00e-9
f(Mitchell&Hatfield_Fuel)	17.0	2.71e-7		15.5	7.35e-6
f(Temperature)	2.1	0.00571		36.9	2.30e-5
f(Humidity)	18.9	1.04e-13		15.6	2.71e-13
f(Elrama_Advection)	11.0	0.0440		1.0	0.00269
f(Mitchell_Advection)	2.0	1.26e-5		1.0	1.54e-5
f(Hatfield_Advection)	18.3	7.75e-5		5.9	0.00239
f(Elrama_Dispersion)	11.3	0.00297		7.4	0.00535
f(Mitchell_Dispersion)	1.0	0.0243		1.0	0.0545
f(Hatfield_Dispersion)	10.4	0.000607		2.2	0.00844

^aedf = effective degrees of freedom.

Table 4. GAM results testing AOD as a predictor of ground station PM_2.5 concentration.

PM2.5 at all ground stations predicted by temperature and humidity (N = 575)				PM2.5 at all ground stations predicted by temperature, humidity, and AOD (N = 561)
Y-intercept = 10.6				Y-intercept = 10.6
Predictors	edf^a	p Value	Adjusted R^2	Predictors	edf^a	p Value	Adjusted R^2
f(Time)	1.0	2.81e-8	0.40	f(Time)	1.2	0.000377	0.46
f(Temperature)	3.3	2.50e-6		f(Temperature)	2.4	2.30e-5
f(Humidity)	16.4	<2e-16		f(Humidity)	15.5	<2e-16
				f(AOD)	20.1	1.55e-6

^aedf = effective degrees of freedom.

Table 5. GAM results for dependent AOD data corresponding to the locations of 12 EPA ground stations (N = 562).

	Y-intercept = 0.131
Predictors	edf^a	p Value	Adjusted R^2
f(Time)	1.0	0.0222	0.76
f(Elrama_Fuel)	12.6	3.23e-16
f(Mitchell&Hatfield_Fuel)	18.6	<2e-16
f(Temperature)	1.0	0.0115
f(Humidity)	6.0	0.246
f(Elrama_Advection)	4.4	2.96e-6
f(Mitchell_Advection)	1.8	0.0002
f(Hatfield_Advection)	5.5	1.14e-8
f(Elrama_Dispersion)	4.2	0.0029
f(Mitchell_Dispersion)	1.8	0.0231
f(Hatfield_Dispersion)	5.9	0.0163

^aedf = effective degrees of freedom.

Figure 2. Combined Aqua and Terra AOD by closing period. Period 1 is January 2011 to October 2012, when all three plants were operating. Period 2 is November 2012 to October 2013, when Elrama was closed, but Hatfield’s Ferry and Mitchell were still open. Period 3 is November 2013 to December 2014, when all three plants were closed. Monthly AOD values were aggregated by season (winter = December, January, February; spring = March, April, May; summer = June, July, August; fall = September, October, November). The values displayed are averages by closing period and CMAQ grid cell, with each season equally weighted.