When we think of “ozone”, many of us think about the hole in the ozone layer, located high up in the stratosphere—about 12 kilometers, or 7 miles above the earth’s surface. It’s much higher than Mount Everest and most types of clouds.
The ozone layer is important because it blocks harmful ultraviolet rays from the sun; without it, we wouldn’t be able to survive on Earth! The ozone layer is formed naturally by chemical reactions involving ultraviolet radiation from the Sun and oxygen molecules. They continually break apart and combine to form ozone molecules. The radiation that the ozone layer blocks would cause intense sunburn, widespread skin cancer, blindness, and even damage to our DNA if it were to reach the earth’s surface.
From this perspective, ozone is not only beneficial, but necessary for the survival of humans and most other living things. However, ozone is not always a good thing for us. When ozone is in the troposphere, where you and I live, it can cause a lot of problems. But how does ozone end up in the troposphere? Naturally, some ozone will transfer between the stratosphere and the troposphere. But this small amount does not account for the damaging levels of ozone we often observe in cities. Instead, ozone is generated as a “secondary pollutant” by different human activities. This means that humans generally do not directly release ozone into the air, but the ozone is formed chemically from man-made precursors. Power plants, cars, and fires release hydrocarbons and nitrogen oxides into the troposphere, where they react to generate ozone.
Ozone can also be formed indoors, through the use of consumer products. Products that use high voltages can form what is called a “corona discharge” that generates a small amount of ionized oxygen, which react to form ozone. Some examples include laser printers and ion generators that are used as air cleaners.
Ozone loves to destroy molecules with double bonds, and nature happens to contain a lot of double bonds. This powerful chemistry can drive chemical reactions both indoors and outdoors. So, the same compound that is so beneficial in the stratosphere can be really damaging to life in the troposphere. It causes cell damage, respiratory irritation, coughing, headaches, and congestion for humans. It can also worsen health conditions like asthma, emphysema, and heart disease. Plants may slow down their rate of photosynthesis and can suffer damage to their cells. Leaves may turn yellow, brown, and brittle. For living things in the troposphere, high levels of ozone can be devastating.
So what can you do? To limit the production of ozone, you can avoid products that emit it indoors and you can limit your use of fossil fuels outdoors.