Spatiotemporal trends of PM and its major chemical components at urban sites in Canada.

To evaluate the effectiveness of emission control regulations designed for reducing air pollution, chemically resolved PM data have been collected across Canada through the National Air Pollution Surveillance network in the past decade. 24-hr time integrated PM collected at seven urban and two rural sites during 2010-2016 were analyzed to characterize geographical and seasonal patterns and associated potential causes. Site-specific seven-year mean gravimetric PM mass concentrations ranged from 5.7 to 9.6 µg/m. Seven-year mean concentrations of SO, NO, NH, organic carbon (OC), and elemental carbon (EC) were in the range of 0.68 to 1.6, 0.21 to 1.5, 0.27 to 0.71, 1.1 to 1.9, and 0.37 to 0.71 µg /m, accounting for 10.8%-18.1%, 3.7%-16.7%, 4.7%-7.4%, 18.4%-21.0%, and 6.4%-10.6%, respectively, of gravimetric PM mass. PM and its five major chemical components showed higher concentrations in southeastern Canada and lower values in Atlantic Canada, with the seven-year mean ratios between the two regions being on the order of 1.7 for PM and 1.8-7.1 for its chemical components. When comparing the concentrations between urban and rural sites within the same region, those of SO and NH were comparable, while those of NO, OC, and EC were around 20%, 40%-50%, and 70%-80%, respectively, higher at urban than rural sites, indicating the regional scale impacts of SO and NH and effects of local sources on OC and EC. Monthly variations generally showed summertime peaks for SO and wintertime peaks for NO, but those of NH, OC, and EC exhibited different seasonality at different locations.