"National average peak sulphur dioxide concentrations, Canada, 2009 to 2023",,, ,,, Year,Average peak (99th percentile) 1-hour concentration (parts per billion),10th percentile (parts per billion),90th percentile (parts per billion) 2009,36.5,5,86 2010,36.6,4,81 2011,28.7,5,69.6 2012,30.7,4.8,67 2013,30,4,71 2014,26.4,2.7,70.3 2015,24.7,2.9,65.7 2016,25.3,2,55 2017,24.7,2.3,64 2018,24,2.9,59.9 2019,21.6,3,62.3 2020,22.1,2,65.1 2021,22.2,1.5,69.5 2022,21.8,1.3,61.1 2023,22.5,1.2,51.4 2020 standard ,70,n/a,n/a Annual trend ,-0.84,n/a,n/a ,,, "Note: n/a = not applicable. The national average peak SO2 concentration indicator is based on the annual 99th percentile of the daily maximum 1-hour average concentrations recorded at 88 monitoring stations across Canada. The comparison to the Canadian Ambient Air Quality Standard is provided for illustrative purposes only. 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).,,,