Air Quality Health Index classroom kit, grades 5 and 6, environment: chapter 8

C. Ground-Level Ozone

You could say that there are two kinds of ozone: good and bad.

The good ozone is in the stratosphere, floating 25 kilometres above our head. This “ozone layer” protects life on Earth. It is the planet’s natural sunscreen, shielding it from the sun’s harmful ultraviolet (UV) rays.

The bad kind of ozone is ground-level ozone. This ozone is produced in the air closest to the earth’s surface (the troposphere). Ground-level ozone is one of the two main unhealthy parts of smog. Smog also contains PM.

Ground-level ozone is formed in the air.

It takes two things to make ground-level ozone: VOCs and NO_x. VOC are fumes that get into the air when liquid chemicals evaporate. You can sometimes smell them in the air. NO_x is a gas that forms in the air when fossil fuels are burned.

Ground-level ozone is formed in the air when VOC react with NO_x. This often happens when it is sunny and warm.  

Ground-level ozone is found in the city and in the countryside.

Ground-level ozone collects over cities and builds up when the air is still. If there is wind, it carries the ground-level ozone a few hundred kilometres into the countryside.

Ground-level ozone hurts plants.

Ground-level ozone can damage leaves and prevent plants from growing well. It can make it hard for plants to survive insects and disease. When ozone levels are fairly high for a long time, food crops and other agriculture can suffer.

The solution is in our hands.

Every person can help bring the fresh air back. That’s because we each create pollution in the first place: the exhaust from our automobiles is the number-one cause. Even if each of us leaves the car at home just once a week, we will reduce air pollution. Also, think about switching to cleaner fuels and cleaner ways of generating electricity. 

Zap It!

Most clouds are formed in the troposphere, where weather takes place. Is good ozone above or below the clouds? What about bad ozone?