Ambient levels of ozone

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Ozone (O3) in the upper atmosphere (10 to 50 kilometres above the earth's surface) protects the earth from the sun's harmful ultraviolet radiation. In the lower atmosphere and at ground level, O3 is harmful to human health. It can cause breathing problems, reduce lung function and aggravate asthma and other lung diseases.Footnote 1 Ozone is not directly emitted, but is formed in the lower atmosphere when precursor gases such as nitrogen oxides (NOX) and volatile organic compounds (VOCs) react in sunlight. Ground-level O3 is one of two major components of summertime smog, the other being fine particulate matter. Ground-level O3 can damage vegetation, and materials such as rubber.

There are two national O3 indicators:

  1. An annual average concentration indicator that is based on the annual average concentrations (of the daily maximum 8-hour averages) is used to capture prolonged or repeated exposures over longer periods or chronic exposure.
  2. An annual peak (4th-highest) 8-hour indicator that is based on the annual 4th-highest daily maximum 8-hour average concentrations is used to capture immediate or acute short-term exposure. The peak O3 indicator is calculated using an approach that is aligned with the 2015 Canadian Ambient Air Quality Standards (the Standards).Footnote 2

National ambient levels of ozone

In 2014, the national annual average concentration of ground-level O3 was 32.9 parts per billion (ppb), or 0.1% higher than in 2013. The annual peak (4th-highest) 8-hour O3 concentration in 2014 was 53.4 ppb, or 3.5% lower than in 2013. Although the annual peak concentration of O3 was frequently above the 2015 Standard before 2008, it has consistently been below for the last seven years.

Since 2000, a decreasing trend of 0.82 ppb per year was detected in the peak O3 concentration. No trend was detected in the annual average O3 concentration. The reduction in emissions of ground-level O3 precursor gases (NOX and VOCs) from Canada and the United States is an important factor in this downward trend.

Ozone concentrations, Canada, 2000 to 2014

Line chart of the national annual average and peak 8-hour concentrations of ozone - Long description below
Long description

The line chart shows the national annual average and peak (4th-highest) 8-hour concentrations of ozone from 2000 to 2014. It also shows the 2015 Canadian Air Ambient Quality Standards for the 8-hour standard (peak) of 63 parts per billion. Although the annual peak concentration of ozone was frequently above the 2015 Standard before 2008, it has consistently been below the standard for the last seven years. A decreasing trend was detected in the peak concentration for ozone since 2000, but was not detected in the annual average concentration.

Data for this chart
Ozone concentrations, Canada, 2000 to 2014
Year Annual average concentration (parts per billion) Annual peak (4th-highest) 8-hour concentration (parts per billion)
2000 30.3 58.9
2001 32.8 67.6
2002 32.7 67.9
2003 33.4 67.8
2004 31.4 59.8
2005 32.7 63.3
2006 32.5 61.6
2007 32.9 64.5
2008 32.3 59.9
2009 31.7 57.2
2010 33.0 59.6
2011 32.8 56.7
2012 33.6 60.5
2013 32.8 56.3
2014 32.9 54.3
2015 standard Not applicable 63
Annual trend No trend -0.82

Download data file (Excel/CSV; 1.42 KB

How this indicator was calculated

Note: The national annual average ozone concentration indicator is based on the annual average of the daily maximum 8-hour average concentrations recorded at 142 monitoring stations across Canada. The national annual peak (4th-highest) 8-hour ozone indicator is based on the average of the 4th-highest daily maximum 8-hour average concentrations recorded at 146 monitoring stations across Canada. The horizontal dashed line represents the value of the 8-hour standard of the 2015 Canadian Ambient Air Quality Standards. The Canadian Ambient Air Quality Standard is shown for indicative purposes only and not for evaluation of the achievement status of the standard.
Source: Environment and Climate Change Canada (2016) National Air Pollution Surveillance Program and the Canadian Air and Precipitation Monitoring Network.

Regional ambient levels of ozone

Annual average concentration

In 2014, the annual average concentrations of O3 in the air varied by region from 27.7 ppb in British Columbia to 36.6 ppb in southern Ontario. Annual average concentrations were lower in 2014 than in 2013 for all regions except British Columbia, where it was 6% higher.

Since 2000, an increasing trend of 0.21 ppb per year was detected in the annual average concentration of O3 in the region of British Columbia. No trends were detected in the other regions.

Regional average ozone concentrations, Canada, 2000 to 2014

Line chart of the annual regional average concentrations of ozone - Long description below
Long description

The line chart shows the annual average concentrations of ozone from 2000 to 2014 for five regions in Canada: Atlantic Canada, southern Quebec, southern Ontario, Prairies and northern Ontario, and British Columbia. Since 2000, an increasing trend was detected for British Columbia. No trends were detected in all the other regions.

Data for this chart
Regional average ozone concentrations, Canada, 2000 to 2014
Year Atlantic Canada annual average concentration (parts per billion) Southern Quebec annual average concentration (parts per billion) Southern Ontario annual average concentration (parts per billion) Prairies and northern Ontario annual average concentration (parts per billion) British Columbia annual average concentration (parts per billion)
2000 30.2 30.9 34.2 31.7 24.0
2001 33.6 34.4 37.4 32.6 25.4
2002 33.6 33.6 37.8 31.9 25.5
2003 34.8 33.9 37.1 34.0 26.8
2004 32.8 31.9 34.8 31.6 25.8
2005 33.0 33.5 38.9 31.3 24.9
2006 34.4 30.9 36.2 33.4 28.4
2007 34.5 32.4 38.8 32.4 25.5
2008 32.2 31.5 37.4 32.9 26.6
2009 32.6 30.4 35.5 33.0 27.6
2010 32.8 33.1 37.8 32.7 27.4
2011 32.3 32.3 36.7 34.8 27.6
2012 32.6 33.6 38.2 33.2 28.7
2013 33.1 34.1 36.7 33.8 26.0
2014 32.5 33.2 36.6 32.7 27.7
Annual trend No trend No trend No trend No trend 0.21

Download data file (Excel/CSV; 1.62 KB)

How this indicator was calculated

Note: The annual average ozone concentration indicator is based on the annual average of the daily maximum 8-hour average concentrations recorded at 17 monitoring stations in Atlantic Canada, 37 in southern Quebec, 34 in southern Ontario, 24 in the Prairies and northern Ontario and 29 in British Columbia.
Source: Environment and Climate Change Canada (2016) National Air Pollution Surveillance Program and the Canadian Air and Precipitation Monitoring Network.

Annual peak (4th-highest) 8-hour concentration

In 2014, the highest annual peak (4th-highest) 8-hour concentration of O3 was recorded in southern Ontario at 62.7 ppb. British Columbia recorded the lowest concentration level at 48.2 ppb, or 3% higher than in 2013. Annual peak concentrations of O3 were 3% to 7% lower in the four other regions compared to 2013.

Since 2000, the annual peak concentrations of O3 were below the 2015 Standard for the Prairies and northern Ontario region, British Columbia and Atlantic Canada, with the exception of Atlantic Canada in 2001. From 2008 to 2014, the annual peak concentrations of O3 were also below the 2015 Standard in southern Quebec. The annual peak concentrations for southern Ontario were above the standard for all years, except 2014. From 2000 to 2014, decreasing trends of 1.0 ppb, 1.2 ppb and 1.4 ppb per year were detected for Atlantic Canada, southern Quebec and southern Ontario, respectively. No trends were detected for British Columbia and the Prairies and northern Ontario region.

Regional peak ozone concentrations, Canada, 2000 to 2014

Line chart of the regional peak concentrations of ozone - Long description below
Long description

The line chart shows the peak (4th-highest) 8-hour concentrations of ozone from 2000 to 2014 for five regions in Canada: Atlantic Canada, southern Quebec, southern Ontario, Prairies and northern Ontario, and British Columbia. It also shows the 2015 Canadian Air Ambient Quality Standards 8-hour standard (peak) of 63 parts per billion. Since 2000, all the annual peak concentrations of ozone were below the 2015 standard for the Prairies and Northern Ontario region, British Columbia and Atlantic Canada, with the exception of Atlantic Canada in 2001. From 2008 to 2014, the annual peak concentrations of ozone were below the 2015 Standard in southern Quebec, while for southern Ontario, the annual peak concentrations were above for all years, except for 2014. Since 2000, decreasing trends were detected in Atlantic Canada, southern Quebec and southern Ontario. No trends were detected for British Columbia and the Prairies and northern Ontario region.

Data for this chart
Regional peak ozone concentrations, Canada, 2000 to 2014
Year Atlantic Canada annual peak (4th-highest) 8-hour concentration (parts per billion) Southern Quebec annual peak (4th-highest) 8-hour concentration (parts per billion) Southern Ontario annual peak (4th-highest) 8-hour concentration (parts per billion) Prairies and northern Ontario annual peak (4th-highest) 8-hour concentration (parts per billion) British Columbia annual peak (4th-highest) 8-hour concentration (parts per billion)
2000 54.8 58.0 73.6 55.8 47.3
2001 64.5 75.1 85.7 55.7 48.9
2002 60.5 72.8 88.0 58.5 49.1
2003 60.9 71.7 84.7 60.4 50.9
2004 55.4 60.9 69.1 53.2 55.6
2005 54.2 67.5 81.4 54.0 49.1
2006 58.4 61.6 73.9 57.0 52.4
2007 58.5 67.4 80.9 56.6 49.4
2008 53.5 59.6 71.9 57.4 51.6
2009 54.5 55.4 66.7 55.9 50.5
2010 53.4 60.8 71.1 58.2 49.4
2011 50.9 55.7 67.3 58.3 46.9
2012 50.3 61.3 76.2 55.7 49.8
2013 50.3 57.5 64.9 57.5 46.7
2014 48.6 53.8 62.7 53.3 48.2
2015 standard 63 63 63 63 63
Annual trend -1.0 -1.2 -1.4 No trend No trend

Download data file (Excel/CSV; 1.91 KB)

How this indicator was calculated

Note: The annual peak (4th-highest) 8-hour ozone indicator is based on the average of the 4th-highest daily maximum 8-hour average concentrations recorded at 19 monitoring stations in Atlantic Canada, 37 in southern Quebec, 36 in southern Ontario, 24 in the Prairies and northern Ontario and 29 in British Columbia. The horizontal dashed line represents the value of the 8-hour standard of the 2015 Canadian Ambient Air Quality Standards. The Canadian Ambient Air Quality Standard is shown for indicative purposes only and not for evaluation of the achievement status of the standard.
Source: Environment and Climate Change Canada (2016) National Air Pollution Surveillance Program and the Canadian Air and Precipitation Monitoring Network.

Ambient levels of ozone at monitoring stations

The National Air Pollution Surveillance and the Canadian Air and Precipitation Monitoring Network programs measure air pollutant concentrations at monitoring stations across Canada. The Canadian Environmental Sustainability Indicators provide this information through an interactive indicator map. With the interactive map, you can drill down to the average O3 concentrations and peak O3 concentrations at specific monitoring stations.

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