Air Quality: Ground-Level Ozone

There are two types of ozone (O3), each affecting our quality of life. Naturally occurring as a gas in the stratosphere surrounding the earth, O3 protects everything living on the surface from the harmful ultraviolet rays of the sun. However, ground-level O3, which is monitored by the SLEA, is formed through reactions of precursor compounds, like nitrogen oxides and volatile organic compounds, in sunlight and impairs the quality of our air.

 At normal background levels, O3 is a colourless and odourless gas, forming a major component of smog. In addition to the amount of bright sunlight, temperature, as well as wind speed and direction, influence its formation. Elevated concentrations of O3 are often detected on hot, sunny days during the months of May through September. Health effects of O3 include irritation of the respiratory tract and eyes, with children and people with respiratory disorders being the most vulnerable. Plants can also be adversely affected by O3, stunting the growth rates and yields of such species as white beans, potatoes and tomatoes.

SLEA consultants continuously measure Ozone present in the air. Hourly averages are recorded at monitoring stations in Corunna and Sarnia.

In 2008, 7 hours in Sarnia and 4 hours in Corunna were recorded during which Ontario's Criteria of 80 parts per billion was exceeded.  Note in the chart below very few exceedances occurred during the summer of 2008 due to the abnormally high level of rainfall received; production of ozone is powered by the sun; it is a photochemical process.

The chart below displays the monitoring results for each month in 2008 as well as the Annual Totals of Exceedances from 2003 to 2008.

Front St. and Corunna Monitoring Results

 

*Trigger - when the concentration of ozone is less than 50 ppb, the Ontario Ministry of Environment's rating of the air is good; above 50 ppb, the rating is poor.

The graph below displays annual totals of hours during which ozone concentrations exceeded the Ontario Ozone Criteria of 80 parts per billion.