United States
                     Environmental Protection
                     Agency
                   Air and Radiation
                   Washington, DC 20460
                 EPA-456/F-99-002
                 July 1999
                 http://www.epa.gov/airnow
&EPA          Air  Quality  Guide for Ozone
    Air Quality
Air Quality Index
Protect Your Health
       Good
       0-50
No health impacts are expected
when air quality is in this range.
     Moderate
      51-100
Unusually sensitive people should
consider limiting prolonged outdoor
exertion.
   Unhealthy for
  Sensitive Groups
     101-150
Active children and adults, and
people with respiratory disease,
such as asthma, should limit
prolonged outdoor exertion.
     Unhealthy
     151-200
Active children and adults, and
people with respiratory disease,
such as asthma, should avoid pro-
longed outdoor exertion; everyone
else, especially children, should
limit prolonged outdoor exertion.
        Very
     Unhealthy
      (Alert)
     201-300
Active children and adults, and
people with respiratory disease,
such as asthma, should avoid all
outdoor exertion; everyone else,
especially children, should limit
outdoor exertion.
   For more information visit EPA's web site at: www.epa.gov/airnow

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                       What  You  Should  Know About  Ozone

 Ozone is a major element of urban smog. Ozone can limit the ability to take a deep breath, and it can cause coughing,
 throat irritation, and breathing discomfort. There is also evidence that ozone can lower resistance to respiratory disease
 (such as pneumonia), damage lung tissue, and aggravate chronic lung disease (such as asthma or bronchitis).
 Children and those with pre-existing lung problems (such as asthma) are sensitive to the health effects of ozone. Even
 healthy adults involved in moderate or strenuous outdoor activities can experience the unhealthy effects of ozone.
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 which 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.

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 fuel combustion sources such as utilities
• small industry such as gasoline dispensing stations and print
  shops
• consumer products such as some paints and cleaners
• emissions from 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.
 How does ozone  affect  human health?
 Even at relatively low levels,  ozone may cause inflammation and
 irritation of the respiratory tract, particularly during physical
 activity. The resulting symptoms can include breathing difficulty,
 coughing, and throat irritation. Breathing ozone can affect lung
 function and worsen asthma attacks. Ozone can increase the
 susceptibility of the  lungs to  infections,  allergens, and other air
 pollutants. Medical studies have shown  that ozone damages lung
 tissue and complete recovery may take several days after expo-
 sure has ended.
 Who is sensitive to ozone?
 Groups that are sensitive to  ozone include children and adults
 who are active outdoors, and people with  respiratory disease,
 such as asthma. Sensitive people who experience effects at lower
 ozone  concentrations are likely to experience more serious
 effects at higher concentrations.
 What is  an  Ozone Action Day?
 An Ozone Action Day may be called by your State or local air
 quality agency when ozone levels are forecast to reach unhealthy
 levels. These programs, often in partnership with local businesses,
 encourage voluntary actions  to reduce  emissions of pollutants
 that contribute to ground-level ozone formation.
                             How You Can  Keep the Air Cleaner
  Every day tips:
  • Conserve energy—at home, at work, everywhere.
  • Follow gasoline refueling instructions for efficient vapor
    recovery. Be careful not to spill fuel and always tighten
   your gas cap securely.
  • Keep car, boat, and other engines tuned up according to
    manufacturers' specifications.
  • Be sure your tires are properly inflated.
  • Car pool, use public transportation, bike, or walk
   whenever possible.
  • Use environmentally safe paints and cleaning products
   whenever possible.
  • Some products that you use at your home or office are
    made with smog-forming chemicals that can evaporate into
   the air when you use them. Follow manufacturers'
    recommendations for use and properly seal cleaners, paints,
   and other chemicals to prevent evaporation into the air.
Ozone Action Day tips:
• Conserve electricity and set your air conditioner at a
  higher temperature.
• Choose a cleaner commute—share a ride to work or use
  public transportation. Bicycle or walk to errands when
  possible.
• Defer use of gasoline-powered lawn and garden
  equipment.
• Refuel cars and trucks after dusk.
• Combine errands and reduce trips.
• Limit engine idling.
• Use household, workshop, and garden chemicals in ways
  that keep evaporation to a minimum, or try to delay using
  them when poor air quality is forecast.

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