No, the troposphere does not contain the ozone layer. The ozone layer sits in the stratosphere, the next layer up, approximately 15 to 40 kilometers (10 to 25 miles) above Earth’s surface. About 90% of all atmospheric ozone is concentrated there, forming the protective shield commonly called “the ozone layer.”
Where the Ozone Layer Actually Sits
Earth’s atmosphere is divided into layers. The troposphere is the lowest, stretching from ground level up to roughly 10 kilometers (6 miles) at the poles and about 17 kilometers at the equator. This is where weather happens, where clouds form, and where you live. Above it lies the stratosphere, extending from about 10 to 50 kilometers altitude. The ozone layer occupies the lower and middle portion of that stratosphere, with the densest concentration between 15 and 30 kilometers up.
Stratospheric ozone absorbs most of the sun’s ultraviolet radiation before it reaches the surface, protecting living organisms from DNA damage, skin cancer, cataracts, and ecosystem harm. This is sometimes called “good ozone” because of its protective role.
Ozone in the Troposphere Is a Different Story
The troposphere does contain some ozone, but not the ozone layer. The natural concentration of ozone near Earth’s surface is only about 10 parts per billion, a tiny fraction of what exists in the stratosphere. And rather than being protective, ozone at ground level is a pollutant.
Ground-level ozone forms when pollutants from cars, power plants, refineries, and industrial facilities react chemically in sunlight. Specifically, oxides of nitrogen and volatile organic compounds combine to produce ozone as a byproduct. This is the main ingredient in smog. Breathing it irritates the lungs, worsens asthma, and can cause chest pain and coughing, particularly on hot, sunny days when ozone production peaks.
So the same molecule plays two very different roles depending on altitude: protective in the stratosphere, harmful in the troposphere.
Tropospheric Ozone and Climate Change
Ground-level ozone also acts as a greenhouse gas. It absorbs heat radiated from Earth’s surface and traps it in the lower atmosphere, contributing a warming effect. According to NOAA, increases in tropospheric ozone since preindustrial times have created a net positive warming force. This warming effect is separate from, and in some ways opposite to, what happens in the stratosphere, where ozone depletion has produced a slight cooling influence. When you add the two together, the warming from tropospheric ozone increases outweighs the cooling from stratospheric ozone loss.
The Ozone Layer Is Recovering
After decades of damage from industrial chemicals (mainly chlorofluorocarbons), the stratospheric ozone layer is slowly healing. The 1987 Montreal Protocol banned the worst offenders, and that intervention is working. The most recent scientific assessment, published in 2022 by the World Meteorological Organization, projects that the ozone layer will return to its pre-1980 levels by around 2040 for most of the world, by 2045 over the Arctic, and by 2066 over the Antarctic, where the famous “ozone hole” forms each spring.
This recovery is expected to significantly reduce risks of skin cancer, cataracts, and UV-related ecosystem damage over the coming decades.