My Research

Tropospheric and Surface Ozone : Drivers and Impacts

Ozone in the Atmospere

Ozone is a gas made up of three oxygen atoms (O3). It occurs naturally in small (trace) amounts in the upper atmosphere (the stratosphere). Ozone protects life on Earth from the Sun’s ultraviolet (UV) radiation. In the lower atmosphere (the troposphere) near the Earth’s surface, ozone is created by chemical reactions between air pollutants from vehicle exhaust, gasoline vapors, and other emissions. At ground level, high concentrations of ozone are toxic to people and plants.

Tropospheric “bad” ozone

Although ozone in the stratosphere is beneficial as it shields life on Earth from harmful radiation, direct exposure to ozone at ground level can be detrimental to both plants and animals, including humans. Ground-level ozone, also known as "bad" ozone, is formed when nitrogen oxide gases, typically emitted by vehicles and industries, react with volatile organic compounds like paint thinners, which easily evaporate into the air. In the troposphere, which is close to the Earth's surface, the natural concentration of ozone is approximately 10 parts per billion (0.000001 percent).

According to the Environmental Protection Agency (EPA), exposure to ozone levels exceeding 70 parts per billion for more than 8 hours is considered unhealthy. Such concentrations are often found in or near urban areas during periods when the atmosphere is warm and stable. The harmful effects of high ozone levels can include irritation of the throat and lungs, as well as the exacerbation of respiratory conditions like asthma or emphysema.