How does ozone form at ground level?

Ground-level ozone forms when sunlight reacts with nitrogen oxides and volatile organic compounds.

Ozone at ground level is not emitted directly into the air, but is created by chemical reactions between nitrogen oxides (NOx) and volatile organic compounds (VOCs). This happens when pollutants emitted by cars, power plants, industrial boilers, refineries, chemical plants, and other sources chemically react in the presence of sunlight.

Nitrogen oxides are a group of gases that are formed during high-temperature combustion processes, such as those occurring in power plants and motor vehicles. Volatile organic compounds, on the other hand, are released from a variety of sources, including petrol, paints, solvents, and even some trees and other vegetation.

When these two groups of pollutants come into contact with each other in the atmosphere and are exposed to sunlight, they undergo a series of chemical reactions. These reactions result in the formation of ozone. It's important to note that these reactions are facilitated by heat, which is why ground-level ozone is a particular problem during the summer months when temperatures are high.

This process is a significant concern because, unlike the beneficial ozone that occurs naturally in the upper atmosphere and protects us from the sun's harmful ultraviolet rays, ground-level ozone can have detrimental effects on human health and the environment. It can cause respiratory problems, trigger asthma, reduce lung function and cause lung diseases.

In summary, ground-level ozone is formed by a series of sunlight-driven chemical reactions involving nitrogen oxides and volatile organic compounds, which are primarily emitted by human activities such as burning fossil fuels.