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% (0.4%, 1.1%) per year from 2003 to 2021, but did not change in Dorset.
  • During the summer in Dorset, mean ozone levels dropped by about 1.4% (0.9%, 1.9%) per year from 2003 to 2021, and by 0.6% (0%, 1.1%) in Barrie.
  • Ozone levels in Barrie exceeded the provincial air quality criteria on one day in May, 2021. This is the first since 2012.
  • According to the 2020 Air Quality Report in Ontario, there have been no significant trends in annual or seasonal ozone levels across Ontario over the past 10 years (2011-2020). However, ozone maximums have been decreasing over time.
  • The number of days each year where the 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 from 2013 to 2020, and only one in 2021.




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)

  •  PM2.5 exceedances have been rare at both the Barrie and Dorset air monitoring stations over the past ten years.
  • Since 2007, there have been seven days in Barrie with fine particulate matter (PM2.5) levels exceeding Ontario’s air quality criteria: one each in 2009, 2015, 2017, 2018 and 2021 and 2 days in 2019.
  • In 2021, there was one day in Dorset with fine particulate matter (PM2.5) levels exceeding Ontario’s air quality criteria. This was the first exceedance reported 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 February 8, 2023