Ozone: Good up high, bad nearby!
Ozone (O3) is a gas that exists in both the upper atmosphere and at ground level. It can be good or bad for your health, depending on its location. Ozone is one of the naturally occurring trace gases that make up the upper atmosphere and the ozone layer which keep the planet warm, and protects us from the sun's UV rays. Ozone is indispensable for life on Earth.
But ozone can also be formed at ground level when sunlight interacts with pollution, and this is a key ingredient to urban smog. This ozone can enter your indoor air from the outside.
Ground-level ozone can cause a variety of symptoms in healthy people and people with respiratory problems, including the following:
Most of the ozone in homes comes in from outside. The level of ozone indoors is generally lower than the level outside the home.
To find out more about outdoor air quality conditions in your local area, and what steps you should take to protect your health from outdoor ozone and other pollutants, please consult the Air Quality Health Index (AQHI)
Health Canada has developed an indoor air quality guideline for ozone in residences. The guideline sets a recommended maximum ozone level for long-term exposure (over days) of 20 parts per billion (ppb) (40 µg/m³), based on a 8-hour average
The long-term exposure limit is meant to protect against respiratory problems, such as shortness of breath, which may be caused by extended exposure to ozone.
Levels of ozone in most Canadian homes are below those recommended by Health Canada, and do not pose a major health concern for most homeowners.
Air cleaners are designed to help remove impurities from the air. They can be useful, but they can't remove all sources of pollutants and are therefore not appropriate as the only means of improving indoor air quality.
There are several types of air cleaners on the market. When selecting an air cleaner for your home, Health Canada advises against using those types that are designed to intentionally generate ozone - because of concerns about possible health effects from exposure to higher levels of ozone. At lower concentrations, which are known to be safe for human health, ozone offers little value in terms of removing indoor air pollutants.
Devices that intentionally generate ozone include portable "bread box" size units that plug into the wall, along with smaller battery-powered units. These devices have one or more control buttons and most are sold door to door, rather than through retail outlets.
See "Tips for Healthy Indoor Air" for more information.