DISCUSSION: When you hear someone say, “There is ozone in the atmosphere,” should you be worried? Well, that depends. Ozone, a chemical molecule formed by three oxygen atoms, has different effects on the earth, depending on where in the atmosphere it exists. Here, we quickly compare two types of ozone: tropospheric ozone (near the surface) and stratospheric ozone (up in the stratosphere). Let’s take a closer look.
There is very little natural tropospheric ozone, so most ozone that forms in the troposphere is purely anthropogenic. Most of the tropospheric ozone is also a secondary pollutant, meaning that it is not directly emitted into the atmosphere, but instead forms when the right conditions occur. Emissions from automobiles and other industrial processes cause higher ozone concentrations during the day. Through some slightly complicated chemistry, when these emissions react with sunlight (known as a photochemical reaction), ozone is formed. High ozone levels at the surface pose a threat to human health, such as respiratory infections. Exposure to ozone can increase the risk of bacteria, such as pneumonia or bronchitis. So, the short answer – ozone at the tropospheric level is bad.
Stratospheric ozone, on the other hand, occurs much higher in the atmosphere, and in a much higher concentration – but this is actually a good thing. This layer of ozone in the stratosphere, aptly named “the ozone layer,” is vital to life on earth. It filters out harmful ultraviolet (UV) radiation that would otherwise make earth uninhabitable. This layer, however, has been depleted in the past by the release of aerosol chlorofluorocarbons (CFCs), a chemical that contains carbon, chlorine, and fluorine. Through some more complex chemistry, these CFCs destroy stratospheric ozone, therefore resulting in their ban in 1978.
It is worth mentioning that there can be an exchange between stratospheric ozone and tropospheric ozone. Although a stable layer of air exists between the troposphere and stratosphere, trace measurements have shown that there is in fact gas exchange between these two layers of the atmosphere, but it takes place very slowly – on the order of years.
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© 2018 Meteorologist Joseph Fogarty