Although ozone in the stratosphere protects us from harmful UV rays from the sun, ozone at ground level causes serious health effects such as asthma and damages crops and ecosystems.
Ground-level ozone is formed in the atmosphere in the interaction of sunlight with volatile organic compounds (VOCs) and oxides of nitrogen (NOx) emitted by automobiles and industrial processes. Because of its toxicity, ozone is regulated by the Environmental Protection Agency as one of six Criteria Air Pollutants.