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How can I tell if it's smoggy?

What is the AQI?

The Air Quality Index, or AQI, is a rating of how clean the air is. It is issued by the Ministry of the Environment, which monitors our air quality every day. The AQI evaluates the following air pollutants:

  • carbon monoxide
  • nitrogen dioxide
  • ozone
  • fine particulate matter (particles that can be inhaled, which are less than 2.5 micrometres in diameter)
  • sulphur dioxide
  • total reduced sulphur compounds
  • total suspended particles

The AQI scale ranges from 0 to 120. Higher numbers mean higher health risks. A reading of 0-15 is considered as very good, 16-31 as good, 32-49 as moderate, 50-99 as poor, and 100 or over as very poor. Two kinds of Smog Alerts are issued. A Smog Watch is issued when there is a 50% chance of a smog day within the next 3 days. When the AQI is expected to get higher than 50 in the next 24 hours, a Smog Advisory is issued. To learn about AQI levels in your community, contact your provincial ministry of health or go to Environment Canada's website.

Environment Canada has introduced another index of air quality called the Air Quality Health Index (AQHI). Although not available for all cities across Canada, the AQHI is a tool that was created to help people understand what the air quality means to their health. It is calculated based on the health risk level from the pollutants ozone, particulate matter, and nitrogen oxide. It is reported on a scale of 1 to 10+. An AQHI of 1-3 indicates low health risk, of 4-6 indicates moderate health risk, of 7-10 indicates high health risk, and of 10+ indicates very high health risk. The AQHI also provides information on how you can modify your activity level when air quality is poor and on how you can improve air quality. For more information about AQHI, go to Environment Canada's website.

Can I tell if it is smoggy by looking outside?

Even without access to a weather report, you can easily get an idea of the air quality. Generally, the hotter the weather is, the worse the ozone smog is likely to be. Similarly, the hazier it is, the higher the concentrations of smog particles. Smog alerts often occur on sunny days without wind or rain (water washes some of the pollution out of the atmosphere). Although smog alerts occur mostly from early May to late September, they can occur at any time of the year, including the winter season.

Since air pollution can cause harm at concentrations well below smog warning levels, it is important to take action if you experience any warning signs of smog-induced health effects.

Look out for these signs:

  • breathing difficulties (especially during exercise), including shortness of breath
  • increased mucus production in the nose and throat
  • chest tightness
  • cough or throat irritation
  • eye irritation
  • light-headedness
  • low energy
  • wheezing

All material copyright MediResource Inc. 1996 – 2022. Terms and conditions of use. The contents herein are for informational purposes only. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Source:

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