Low level air pollution and exacerbation of existing copd: a case crossover analysis

Table 3 Correlation between air pollutant and meteorological variables

	SO₂ ^a	NO₂ ^a	PM_2.5 ^a	Temperature^b
NO₂ ^a	Spring: 0.14	--	--	--
	Summer: −0.03
	Fall: 0.52**
	Winter: 0.80**
PM_2.5 ^a	Spring: 0.30**	Spring: 0.41**	--	--
	Summer: 0.20*	Summer: 0.45**
	Fall: 0.39**	Fall: 0.73**
	Winter: 0.79**	Winter: 0.83**
Temperature^b	Spring: 0.34**	Spring: 0.02	Spring: 0.52**	--
	Summer: 0.24**	Summer: 0.15*	Summer: 0.62**
	Fall: 0.02	Fall: −0.04	Fall: −0.15*
	Winter: −0.13	Winter: 0.09	Winter: 0.11
Relative Humidity^b	Spring: 0.09	Spring: 0.07	Spring: −0.01	Spring: −0.25**
	Summer: −0.13	Summer: 0.02	Summer: −0.07	Summer: 0.22**
	Fall: −0.14*	Fall: −0.24**	Fall: −0.28**	Fall: 0.38**
	Winter: −0.02	Winter: 0.03	Winter: 0.08	Winter: 0.22**

Values shown are Pearson Correlation Coefficients; * indicates p < 0.05 and ** indicates p <0.0001
^a24-h average concentrations; Worcester, Ware and Springfield monitors from 2011 to 2012
^b24-h average measurements; Worcester Regional Airport meteorological site from 2011–2012

ISSN: 1476-069X