Air Quality Index (AQI) ratings:  The Air Quality Index (AQI) monitors concentrations of five major pollutants (carbon monoxide, fine particulate matter, nitrogen dioxide, ozone and sulphur dioxide) to determine whether the quality of air is Good, Fair, Poor, or Very Poor. Good is the best possible rating and means there are no known harmful effects to human or environmental health. Example: January 1, 2007 to December 31, 2007, Niagara’s air quality measured Good 77.3% of the time. In 2007,Ontario recorded 59 poor air quality days overall; Niagara recorded 5 poor air quality days;Windsor (17 days),London (3 days) andKitchener (6 days) over the same time period.

Several state-of-the-art air monitoring stations, operated by the Ministry across the province, form the Air Quality Index (AQI) network.  In Niagara Region, readings are taken in St. Catharines. The Ministry takes real-time air quality data from its AQI monitoring sites to produce AQI readings for each location. AQI readings are reported to the public and news media hourly at Here is a sample of the data on air quality available on July, 2011 related to hourly ozone concentrations and fine particulate matter concentrations.

Figure 3.7
St. Catharines: Hourly Ozone O3 Concentrations from July 26, 2011 to July 28, 2011.
Note: Ontario 1-hour Ambient Air Quality Criterion (AAQC) for O3 = 80 ppb.

Ozone Concentrations

Figure 3.8

Particulate Matter


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