Ozone Facts

What is Ozone?

Ozone is a colorless gas that can be found in the air we breathe. Each molecule of ozone is composed of three atoms of oxygen, one more than the oxygen molecule we need to breathe to sustain life. The additional oxygen atom makes ozone extremely reactive. Ozone exists naturally in the Earth's upper atmosphere, known as the stratosphere, where it shields the Earth from the sun's ultraviolet rays. However, ozone is also found close to the Earth's surface. This ground-level ozone is a harmful air pollutant. Ozone is primarily a summertime air pollution problem in Phoenix (May through September).

Where does ground-level ozone come from?

Ground-level ozone is formed by a chemical reaction between volatile organic compounds (VOCs) and oxides of nitrogen in the presence of sunlight. Sources of VOCs and oxides of nitrogen include:

• automobiles, trucks, and buses

• large industry and combustion sources such as utilities

• small industry such as gasoline dispensing facilities and print shops

• consumer products such as paints and cleaners

• off-road engines such as aircraft, locomotives, construction equipment, and lawn and garden equipment.

• Ozone concentrations can reach unhealthy levels when the weather is hot and sunny with relatively light winds.

Why is Ozone Harmful?

Ozone is to your lungs what the sun is to your skin. Repeated exposure to unhealthful levels of ground-level ozone will stiffen lung tissue much like repeated sunburn will lead to leathery, wrinkled skin.

• Ozone is a severe irritant that can cause choking, coughing and stinging eyes.

• Ozone damages lung tissue, aggravates respiratory disease and makes people more susceptible to respiratory infections.

• While anyone who is active or works outdoors is affected by unhealthful ozone levels, children and the elderly are especially vulnerable to its harmful effects.

What is a High Pollution Advisory Day?

A High Pollution Advisory Day may be called by the Arizona Department of Environmental Quality when ozone levels are forecast to reach unhealthy levels. These programs, often in partnership with local businesses, encourage Valley residents to reduce emissions of pollutants that contribute to ground-level ozone formation. The Ozone standard set by the Environmental Protection Agency is for a one-hour exposure. A violation occurs when any one monitor records four or more exceedances in three consecutive years. Monitors operated by Maricopa County and ADEQ have not measured any exceedances of the one-hour ozone standard since 1996.

What can you do to help?

• Sign up to receive the Ozone E-Alerts. You can sign-up to receive HPA's via email by registering at www.ValleyMetro.org.

• Reduce driving - consolidate or combine trips.

• Carpool, ride the bus, telecommute, and don't drive during lunch - brown bag it instead

• Refuel after 4:00 p.m.

• Limit engine idling

• Don't use gas powered garden equipment when an HPA is in effect or buy electric gardening equipment.

• Schedule painting projects during the cooler months, and when painting, use water-based products.

• Call 602.262.RIDE or logon to ShareTheRide.com to find a car/vanpool partner.

• Call 602.253.5000 for bus route information. 

What strategies are in place to reduce Ozone?

To help combat ground-level ozone, there are a number of air quality improvement programs in place in Arizona.

• Cleaner burning gasoline is sold in the Phoenix-metro area during the summer months.

• Vapor Recovery Systems control emissions of gasoline vapors when you fill your gas tank.

• Enhanced Vehicle Emissions Testing Program - I/M147

• Voluntary Vehicle Repair and Retrofit Program provides for the installation of an emission upgrade kit designed to reduce exhaust emissions.

• The Clean Air Campaign is a public education and marketing campaign that encourages the use of alternative forms of transportation and other pollution reducing strategies.

• Maricopa County's Trip Reduction Program requires Valley employers with 50 or more employees to encourage their employees not to drive to work alone.

The Clean Air Campaign is sponsored by the Arizona Departments of Environmental Quality and Transportation, Greater Phoenix Chamber of Commerce, Maricopa Association of CLEAN AIR Governments, Maricopa County, and Valley Metro.