"Regional average peak sulphur dioxide concentrations, Canada, 2009 to 2023",,,,,,,,,,,,,,, ,,,,,,,,,,,,,,, ,Atlantic Canada,Atlantic Canada,Atlantic Canada,Southern Quebec,Southern Quebec,Southern Quebec,Southern Ontario,Southern Ontario,Southern Ontario,Prairies and northern Ontario,Prairies and northern Ontario,Prairies and northern Ontario,British Columbia,British Columbia,British Columbia Year,Average peak (99th percentile) 1-hour concentration (parts per billion),10th percentile (parts per billion),90th percentile (parts per billion),Average peak (99th percentile) 1-hour concentration (parts per billion),10th percentile (parts per billion),90th percentile (parts per billion),Average peak (99th percentile) 1-hour concentration (parts per billion),10th percentile (parts per billion),90th percentile (parts per billion),Average peak (99th percentile) 1-hour concentration (parts per billion),10th percentile (parts per billion),90th percentile (parts per billion),Average peak (99th percentile) 1-hour concentration (parts per billion),10th percentile (parts per billion),90th percentile (parts per billion) 2009,56.2,11,160,49.3,5,133,48.9,12,120,23.8,5,61,40.2,6,86 2010,39,3.4,119.1,70.5,4,218,49.7,4,103,23.5,4,53,36,3.8,78.9 2011,30.2,6.7,59.6,38.8,7,118,50.6,4,87,17,5,28,30.7,3.8,69.6 2012,30.2,4.4,61,46.6,6,121,50.2,5,105,19.2,2.2,56,32,5,71.1 2013,31.8,4,60.9,40.2,3.1,95.6,53.4,5.1,149.6,20.6,3,48,31.2,4.1,80.2 2014,34.5,2.2,70.3,36.5,4.4,111.8,54.5,6.2,168.1,17.2,2,36,22,4.4,77.3 2015,27.9,1.6,59.1,33.4,5.2,100.6,46.9,6.1,133,16.6,1.3,36,23.5,3.6,72.8 2016,28.1,1.6,66.6,35.5,5.2,102,40.5,5.4,165.6,21.5,1.2,55,21.4,3.1,43.3 2017,21.9,1.7,49.2,27.7,4,87.8,35.7,2.6,90.6,22,2,59,25.4,3.6,73.5 2018,33.2,5.8,67,30.3,2.4,93,36.8,2.3,106.3,19,3,38,21.3,3,59.9 2019,27.7,4.7,62.5,30.3,5.7,88.8,34.5,1.5,82.4,17.4,3.7,27,17.8,3,57.8 2020,26.9,2.3,63,29.9,4.9,100.1,29.5,2.2,72.6,20.3,3.1,64,18.5,1.9,32.6 2021,27.9,2,98.2,29.8,1.2,98.4,36.1,2.8,90.8,19,2.6,34,17.2,0.9,37.5 2022,29.3,1,72.7,34.7,4,94.9,33,1.5,79.1,19.7,2,54,15,1,39.5 2023,26.2,0.7,48,37.6,4.5,96.8,38.5,8,84.4,21.5,1.1,39.6,14.1,1.1,45.3 2020 standard ,70,n/a,n/a,70,n/a,n/a,70,n/a,n/a,70,n/a,n/a,70,n/a,n/a Annual trend ,-0.64,n/a,n/a,-1.18,n/a,n/a,-1.54,n/a,n/a,No trend ,n/a,n/a,-1.69,n/a,n/a ,,,,,,,,,,,,,,, "Note: n/a = not applicable. The regional average peak SO2 concentration indicator is based on the annual 99th percentile of the daily maximum 1-hour average concentrations recorded at 10 monitoring stations in the Atlantic Canada region, 9 in the southern Quebec region, 10 in the southern Ontario region, 31 in the Prairies and northern Ontario region and 26 in British Columbia. There were not enough stations to report results for the northern territories region. The comparison to the Canadian Ambient Air Quality Standard is provided for illustrative purposes only and should not be used for evaluating overall air quality in Canada. A statistically significant trend is reported when the Mann-Kendall test indicates the presence of a trend at the 95% confidence level. For more information, consult the Methods section (www.canada.ca/en/environment-climate-change/services/environmental-indicators/air-quality.html#Methods).",,,,,,,,,,,,,,, Source: Environment and Climate Change Canada (2025) National Air Pollution Surveillance (NAPS) Program - Open Government Portal (https://open.canada.ca/data/en/dataset/1b36a356-defd-4813-acea-47bc3abd859b).,,,,,,,,,,,,,,, Available on the Environmental indicators website (www.canada.ca/environmental-indicators).,,,,,,,,,,,,,,,