Map of Simcoe Muskoka


Ozone and Fine Particulate Matter

Key Messages
Fine Particulate Matter (PM2.5)

Key Messages

  • The key contributors to smog and poor air quality in Simcoe Muskoka are ozone (O3) and fine particulate matter (PM2.5).
  • Air quality in Simcoe Muskoka has improved since 2003, with the number of days where ozone or PM2.5 levels exceeded provincial air quality criteria dropping to nearly 0 since 2012.


  • Mean ozone levels in Barrie in the winter increased by about 1% per year from 2003 to 2018.
  • During the summer in Dorset, mean ozone levels dropped by about 2% per year from 2003 to 2018.
  • Ozone levels in Simcoe Muskoka have not exceeded the provincial air quality criteria since 2012.



According to the 2016 Air Quality Report in Ontario, the average ozone level increased by one per cent each year from 2007 to 2016. However, while ozone is increasing overall, it has been decreasing by 3% each year during the summer.

Average ozone levels during the summer stayed around the same in Barrie from 2003 to 2018, but decreased by 2% (0.9%, 2.3%) per year in Dorset.

During the winter, average ozone levels in Barrie increased by 1% (0.5%, 1.4%) per year but did not change in Dorset.


The number of days each year where ozone levels exceeded Ontario’s air quality criteria for ozone has decreased from more than 10 per year in 2003 to 2007 in Barrie and Dorset, to zero days since 2012.

Ozone irritates the respiratory tract and eyes. Exposure to ozone in sensitive people can result in chest tightness, coughing and wheezing. Children who are active outdoors during the summer when ozone levels are highest are particularly at risk. Individuals with pre‐ existing respiratory disorders such as chronic obstructive pulmonary disease (COPD) are also at risk.

Fine Particulate Matter (PM2.5)

  • Since 2007, there have been four days in Barrie with fine particulate matter (PM2.5) levels exceeding Ontario’s air quality criteria.
  • There have been no reported days since 2007 in Dorset with fine particulate matter (PM2.5) levels exceeding Ontario’s air quality criteria.


PM2.5 exceedances have been rare at both the Barrie and Dorset air monitoring stations over the past ten years. Since 2007, four days have been reported with PM2.5 levels exceeding the provincial criteria in Barrie, in 2009, 2015, 2017, and most recently in January of 2018. No exceedances have been reported in Dorset since 2007. Between 2003 and 2007, there were an average of 6 PM2.5 exceedances in Barrie and 3 in Dorset each year.

The health effects of inhaling fine particulate matter (PM2.5) can include acute illness from short-term exposure (e.g. asthma-related emergency department visits) and chronic illnesses and death from longer-term exposure (e.g. cardiovascular disease and lung cancer).

Further Reading

For more information about air quality in Simcoe Muskoka, see:

Page Last Modified: August 18, 2020.