Map of Simcoe Muskoka


Ozone and Fine Particulate Matter

The key contributors to smog and poor air quality in Simcoe Muskoka are ozone (O3) and fine particulate matter (PM2.5).

Ground-level ozone is formed when pollutants from vehicle exhaust emissions react in sunlight. Ozone can accumulate in suburban and rural areas (like Simcoe Muskoka) because the pollutants originating from urban areas react in the sunlight during the time taken to travel out of the cities. 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 preexisting respiratory disorders, such as asthma and chronic obstructive pulmonary disease (COPD), are also at risk.

According to the 2014 Air Quality Report in Ontario, overall provincial ozone annual means have increased by three per cent from 2005 to 2014; however, ozone summer means have remained decreased by eight per cent over the same period. In Barrie, between 2003 and 2014, the ozone summer mean concentrations have remained relatively stable; whereas, the winter mean ozone concentrations have increased by an average of one per cent per year which was statistically significant. In Dorset during the same time period, summer ozone concentrations have decreased by two per cent per year, which was statistically significant; however, winter ozone concentrations in Dorset have remained flat over this twelve-year time period.


Throughout the year, levels of ozone in Simcoe Muskoka occasionally exceed Ontario’s air quality criteria. These exceedances vary from year to year. There have not been any ozone exceedances observed at either the Barrie or Dorset stations since 2013. In 2012, though, the ozone levels recorded at the Barrie air monitoring station exceeded the Ontario criteria of 80 parts-per-billion (ppb) on six separate days for a total of 16 hours. While in Dorset in 2012, only two hours (both on separate days) exceeded the Ontario criteria for ozone.


Fine particulate matter (PM2.5) refers to inhalable particles that are less than 2.5 microns in diameter. Due to their small size (30 times smaller than a human hair), they can penetrate deep into the respiratory system. The health effects of inhalable particles can include acute illness from short-term exposure (e.g. asthma related hospital visits) as well as chronic illnesses and death from longer-term exposure (e.g. cardiovascular disease and lung cancer).

Fine particulate matter (PM2.5) exceedances occur when the daily average readings are greater than the Ontario criteria (30 μg/m3). PM2.5 exceedances have been rare at both the Barrie and Dorset air monitoring stations over the past eight years, with just two occurrences in Barrie since 2007 (one in 2009 and one in 2015). Between 2003 and 2007, there was an average of 6 PM2.5 exceedances in Barrie and 3 in Dorset.