"National average ozone concentrations, Canada, 2009 to 2023",,, ,,, Year,Average concentration (parts per billion),10th percentile (parts per billion),90th percentile (parts per billion) 2009,31.9,26,37 2010,33.2,27,39 2011,33.2,28,39 2012,33.7,28,39 2013,33,26,38 2014,33,28,38 2015,33.2,27,38 2016,32.5,27,39 2017,33.7,29,38 2018,34,29,38 2019,32.9,27,37 2020,32.7,28,37 2021,34,30,39 2022,33.4,28,39 2023,34.2,28,39 Annual trend,No trend ,n/a,n/a ,,, "Note: n/a = not applicable. The national average O3 concentration indicator is based on the annual average of the daily maximum 8-hour average concentrations recorded at 169 monitoring stations across Canada. No comparison with CAAQS is shown as there is no comparable O3 standard. 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) and the Canadian Air and Precipitation Monitoring Network (www.canada.ca/en/environment-climate-change/services/air-pollution/monitoring-networks-data/canadian-air-precipitation.html).,,, Available on the Environmental indicators website (www.canada.ca/environmental-indicators).,,,