The Effects of Temperature on Ground Level Ozone

Sunlight and heat create ozone near the ground when they interact with natural and man-made emissions of nitrogen oxides and volatile organic compounds. Ozone is a gas composed of three oxygen atoms that also occurs in the stratosphere many miles above the Earth's surface. Motor vehicles and fossil fuel-burning power plants generate large quantities of emissions that cause ground level ozone, which is the main component of the air pollution known as smog.

Weather Influence

• Strong sunlight and high air temperatures increase ozone levels when nitrogen oxides and volatile organics are in the air. In areas with heavy motor vehicle traffic and factories, ozone begins to form after the sun comes up. Levels peak during the hottest part of the day and drop sharply after sunset. Less ozone is generated on cool, overcast days. Ozone levels are highest during hot summer months and lowest during cold winter months with little sunshine.

Temperature Inversion

• Air is normally warmer near the ground than at higher altitudes. Warm air tends to rise so ground level air pollution is usually pulled away from the surface and mixed into colder air higher up. A temperature inversion reverses the situation. A higher altitude layer of warm air keeps colder air near the ground from mixing. The ground level ozone is trapped and builds up over time, causing strong concentrations of polluted air.

Good and Bad

• Ozone can be good or bad depending on where it is. High in the stratosphere, it blocks ultraviolet radiation that can cause deadly skin cancer in people. At ground level, it harms people, crops and ecosystems. Breathing ozone can damage lungs, worsen asthma and hurt your immune system's ability to fight respiratory infections. Ozone causes about $500 million a year in reduced farming yields in the United States, according to a U.S. Environmental Protection Agency estimate.