Science, Tech, Math › Science Atmospheric Science: What Is an Ozone Warning? Upper Atmospheric Ozone Vs. Ground-Level Ozone Share Flipboard Email Print tatisol/Getty Images Science Weather & Climate Understanding Your Forecast Storms & Other Phenomena Chemistry Biology Physics Geology Astronomy By Rachelle Oblack Rachelle Oblack is a K-12 science educator and Holt McDougal science textbook writer. She specializes in climate and weather. our editorial process Rachelle Oblack Updated July 03, 2019 Ozone is a pale blue gas with a distinctively pungent smell. Ozone is present in low concentrations throughout the Earth's atmosphere (stratosphere). In total, ozone makes up only 0.6 ppm (parts per million) of the atmosphere. Ozone smells similar to chlorine and is detectable by many people at concentrations of as little as 10 ppb (parts per billion) in the air. Ozone is a powerful oxidant and has many industrial and consumer applications related to oxidation. This same high oxidizing potential, however, causes ozone to damage mucus and respiratory tissues in animals, and also tissues in plants, above concentrations of about 100 ppb. This makes ozone a potent respiratory hazard and pollutant near ground level. However, the ozone layer (a portion of the stratosphere with a higher concentration of ozone, from 2 to 8 ppm) is beneficial, preventing damaging ultraviolet light from reaching the Earth's surface to the benefit of both plants and animals. Unhealthy Ozone Ozone depletion may be a common news story, but many forget about the dangerous formation of ozone at ground level. The Air Quality Index (AQI) in your local weather forecast may often issue an "unhealthy warning" based on ground level ozone measurements if ground-level ozone is going to affect people in a particular area. All persons in an area are advised to be on the lookout for health effects related to ozone pollutants when a warning or watch is issued. The Environmental Protection Agency (EPA) warns that although ozone in the stratosphere protects us from harmful UV radiation, low-level ozone is dangerous. Infants, children, and those with respiratory problems may be in particular danger. What Causes Ground-Level Ozone Ground-level ozone is caused when the sun reacts with pollutants from cars and industrial plants to form ozone at or near the surface of the earth. The sunny weather you enjoy in many parts of the world may, unfortunately, be increasing the chances of the formation of ground-level ozone. Summertime is especially dangerous in many traditionally sunny areas, especially those areas with large populations. The EPA issues warnings and advisories for five major air pollutants. ground-level ozoneparticle pollutioncarbon monoxidesulfur dioxidenitrogen dioxide Ozone Alert Days According to associate writer Fred Cabral, “Ozone ignorance is a problem. Many people do not listen to the warnings given by local forecasters on the dangers of ozone.” While interviewing locals in the area, Cabral discovered 8 reasons why people choose to ignore “Ozone Alert Days”. "Avoiding complacency is key to being safe from the dangers of ozone", Fred indicates, "and people should not become complacent about the issue." After multiple street interviews, Cabral has investigated the ways to remain safe. In fact, ozone alert days (sometimes called ozone action days depending on where you live) are days when high heat and humidity cause unhealthy and unsafe levels of air pollution in the ozone layer. Pollution levels are monitored via the Air Quality Index, which was designed by the Environmental Protection Agency (EPA) so that cities and states can measure and report levels of pollutants in our air.