Ozone Action Day
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An Ozone Action Day, which can be declared by a local municipality, county or state, is observed at certain times during the summer months, when weather conditions (such as heat, humidity, and air stagnation) run the risk of causing health problems.
Ozone Action Days, alternately called an "Ozone Alert" or a "Clean Air Alert", primarily center in the midwestern portion of the United States; particularly in well-urbanized areas such as Chicago, Cleveland, Detroit, and Indianapolis.
Surface ozone vs. the ozone layer
Although the ozone found at the Earth's surface is the same chemical species as that found in the ozone layer, they have very different sources, atmospheric chemistry, and affect human health differently as well. The ozone layer protects people from the sun's most damaging ultraviolet rays. Because the ozone layer is located high in the atmosphere, people are not directly exposed to it.
Ground-level ozone, however, is a health hazard because people breathe it. It is formed through a complex set of chemical reactions involving hydrocarbons, nitrogen oxides and sunlight on calm summer days where the weather may also be warm and humid. High levels of ground ozone affects the breathing process and aggravates asthma in chronic sufferers. The young, elderly, and those with lung diseases are especially susceptible.
Ozone is most likely to exceed safety limits from May through October when seasonal heat and sunlight are at their highest  However, similar conditions can occur at other times of the year in specific urbanized areas; namely the Los Angeles area, which is well known for smog formation.
Sources of ground ozone
A major cause of the conditions is due to pollutants in the air released by heavy industry (manufacturing plants, refineries, coal-fired power plants). Therefore, Ozone Action Days occur most frequently in the Midwestern United States. In recent years, many sites have taken steps to help reduce the amount of pollutants they discharge.
Secondary sources include automotive emissions (leaky auto exhaust systems, excessive engine idling) and liberal use of household chemicals or sprays. It is believed that nearly fifty percent of pollutant ozone molecules are attributed to the presence of these 
State, county, and even local governments can announce Ozone Action Days as much as a day in advance through the monitoring of approaching weather conditions and the Air Quality Index (AQI). The AQI is divided into six levels: the higher the number (on a 0-300 scale), the more severe the ozone threat Air quality index.
What can be done
Heavy industries make up a high percentage of pollutants causing ground ozone. Without drastically altering or eliminating industrial production in an area altogether, air quality improvements are very slight, though noticeable. Non-industrial pollutants, while not thought of to be a major pollutant group, can be more controlled with more positive change occurring.
Basic steps in limiting ground ozone during Ozone Action Days are:
- Controlling of auto emissions
- Eliminate excessive engine idling
- Ensure automotive exhaust system functions properly
- Avoid unnecessary driving whenever possible
- Don't refuel until after 6:00 pm
- Take public transportation (Cities such as Toledo provide free bus service on Ozone Action Days).
- Limit the use of lawn mowers and outdoor grills to after 6:00 pm
- Conserve energy
- Smart Communities Network website listing strategies, state ordinances, additional articles and resources
- Vast link page to various worldwide sites on general air pollution, pollution monitoring, and the environment - courtesy Louisville (KY) Metro Air Pollution Control District
- Tulsa's Ozone Alert Oklahoma pollution gallery, alerts, and information
- Ozone Prevention success stories - Georgia-based website