Typically, warm air sits near the ground, and air rises easily, carrying away polluting substances. During a temperature inversion, cold air is trapped near the ground by warm air several hundred meters above it. The warm air acts like a lid, and polluting substances can’t rise and disperse as readily. As a result, a higher AQHI rating is realized.
The AQHI is a tool that helps people understand what the local outside air quality means to their health. Moderate to high AQHI ratings may lead to health problems for at-risk populations, such as children, the elderly and those with pre-existing respiratory conditions.
Some sources of polluting substances, like industrial emissions and wetlands, stay fairly constant throughout the year, no matter the season. But in the winter, fireplaces, wood stoves, home heating and idling vehicles contribute to higher concentrations. A temperature inversion traps a build-up of these substances near the ground until wind, a snowstorm, or some other weather change sweeps them away.
Fortunately, temperature inversions that cause high or very high AQHI ratings don’t happen very often. Fort Air Partnership (FAP), the organization that monitors the air people breathe in and around Alberta’s Industrial Heartland, reported only 133 hours of high or very high AQHI ratings throughout 2022. Although it is challenging to determine precisely how many of these hours were due to wintertime temperature inversion, FAP estimates it is about 5%. The majority of exceedances are due to wildfire smoke.
What you can do
People can reduce their impact on air quality by not idling vehicles when parked, avoiding excessive fireplace or wood stove use, and using energy-efficient products. People can also keep track of current and forecast local AQHI levels on the FAP website, and if levels are high, adjust their outdoor activities accordingly. You can also follow FAP on Facebook, Instagram, and Twitter.