What is ozone?
Ozone is a gas found in the air we breathe.
Ozone can be good or bad, depending where it occurs:
• Good ozone is present naturally in the Earth’s upper
atmosphere—approximately 6 to 30 miles above the Earth’s surface.
This natural ozone shields us from the sun’s harmful ultraviolet rays.
• Bad ozone forms near the ground when pollutants
(emitted by sources such as cars, power plants, industrial boilers, refineries, and chemical plants) react chemically
in sunlight.
Ozone pollution is more likely to form during warmer months.
This is when the weather conditions normally needed to form ground-level ozone—lots of sun—occur.
Who is most at risk?
Several groups of people are particularly sensitive to ozone, especially when they are active outdoors.
This is because ozone levels are higher outdoors, and physical activity causes faster and deeper breathing, drawing more ozone into the body.
What is particle pollution?
Particle pollution (also known as “particulate matter”) consists of a mixture of solids and liquid droplets.
- emitted directly; others form when pollutants emitted by various sources react in the atmosphere.
- can be very unhealthy and even hazardous during events such as forest fires.
- can be elevated indoors, especially when outdoor particle levels are high.
Particles come in a wide range of sizes.
Ø < 10 µm (smaller than the width of a single human hair) are so small that they can get into the lungs, where they can cause serious health problems.
• Coarse particles (between 2.5 - 10 µm in diameter) are referred to as “coarse.”
Sources of coarse particles include crushing or grinding operations, and dust stirred up by vehicles traveling on roads.
• Fine particles. The smallest particles (Ø < 2.5 µm) are called “fine” particles.
These particles are so small they can be detected only with an electron microscope.
Major sources of fine particles include motor vehicles, power plants, residential wood burning, forest fires, agricultural burning, some industrial processes, and other combustion processes.
For particles Ø >2.5 µm:
EPA intends to update the AQI rule to reflect the Agency’s September 2006 standards for fine particle pollution (PM2.5).
AQI forecasts and reports on the AIRNow Web site use the new 24-hour fine particle standard—35 µg/m3—as the 100 level of the AQI.
For particles Ø > 10 µm : An AQI of 100 corresponds to 150 µg/m3(averaged over 24 hours).
What is ozone?
Ozone is a gas found in the air we breathe.
Ozone can be good or bad, depending where it occurs:
• Good ozone is present naturally in the Earth’s upper
atmosphere—approximately 6 to 30 miles above the Earth’s surface.
This natural ozone shields us from the sun’s harmful ultraviolet rays.
• Bad ozone forms near the ground when pollutants
(emitted by sources such as cars, power plants, industrial boilers, refineries, and chemical plants) react chemically
in sunlight.
Ozone pollution is more likely to form during warmer months.
This is when the weather conditions normally needed to form ground-level ozone—lots of sun—occur.
Who is most at risk?
Several groups of people are particularly sensitive to ozone, especially when they are active outdoors.
This is because ozone levels are higher outdoors, and physical activity causes faster and deeper breathing, drawing more ozone into the body.
What is particle pollution?
Particle pollution (also known as “particulate matter”) consists of a mixture of solids and liquid droplets.
- emitted directly; others form when pollutants emitted by various sources react in the atmosphere.
- can be very unhealthy and even hazardous during events such as forest fires.
- can be elevated indoors, especially when outdoor particle levels are high.
Particles come in a wide range of sizes.
Ø < 10 µm (smaller than the width of a single human hair) are so small that they can get into the lungs, where they can cause serious health problems.
• Coarse particles (between 2.5 - 10 µm in diameter) are referred to as “coarse.”
Sources of coarse particles include crushing or grinding operations, and dust stirred up by vehicles traveling on roads.
• Fine particles. The smallest particles (Ø < 2.5 µm) are called “fine” particles.
These particles are so small they can be detected only with an electron microscope.
Major sources of fine particles include motor vehicles, power plants, residential wood burning, forest fires, agricultural burning, some industrial processes, and other combustion processes.
For particles Ø >2.5 µm:
EPA intends to update the AQI rule to reflect the Agency’s September 2006 standards for fine particle pollution (PM2.5).
AQI forecasts and reports on the AIRNow Web site use the new 24-hour fine particle standard—35 µg/m3—as the 100 level of the AQI.
For particles Ø > 10 µm : An AQI of 100 corresponds to 150 µg/m3(averaged over 24 hours).
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