Ozone Facts

Updated September 2014

What is Ozone Anyway? How Does "Bad" Ozone Affect Me?
The "Good" Ozone Layer: Earth’s Sunscreen How Are We Dealing With  Ozone Pollution?
The Ozone Hole is not a Hole What Can I Do?
Is Anyone Doing Anything About the Ozone Hole ? --Reduce Ground-Level "Bad" Ozone
Why Can't We Just Make More Ozone? --Protect High-Altitude "Good" Ozone
What Causes "Bad" Ozone? --Protect Myself from UV

What is Ozone Anyway?

Ozone (03) is made naturally in the atmosphere when three oxygen atoms join together to form a colorless gas.  Ozone can have good or bad effects, depending on where it's located in the atmosphere. One way to remember this is, "good up high, bad nearby."

  • For more about how ozone forms, watch the video O3 - Good Up High, Bad Nearby
    (Video includes audio and requires the Adobe Flash player)
Flash Ozone- Good Up High Bad Nearby
02:34 min/sec


The "Good" Ozone Layer: Earth’s Sunscreen

The earth is wrapped in layers of air called the atmosphere. “Good” ozone is in the earth’s upper atmosphere, 10 to 30 miles above the surface. Life couldn't exist without this protective ozone, which is also called the "ozone layer."

Ozone in the atmosphere.

The sun gives off light, heat, and other types of radiation.  Too much UV (ultraviolet) radiation can cause skin cancer, cataracts, and harm plants and animals.  Ozone high in the atmosphere absorbs, or takes in, some of the sun's harmful UV rays before they reach the ground.  Just as sunscreen helps protect your skin from getting burned, ozone up high works like Earth’s sunscreen.   

The Ozone Hole is Not a Hole  

Although we say "hole in the ozone layer" or "ozone hole," there's no actual hole.  Instead, the protective layer contains less good ozone than it used to.  This thinning is found all over the earth, but the biggest losses are over the North and South Poles. That’s because ozone destruction is worse when it’s very cold.

To see current levels of ozone over the South Pole, go to: ozonewatch.gsfc.nasa.gov/.

The trouble with ozone destruction starts when certain chemicals used in air conditioners, fire extinguishers, insulating foams, and solvents are let out during use. These chemicals eventually reach the upper atmosphere and are broken down by the sun's radiation, releasing chlorine and bromine atoms.  These atoms take away one of the oxygen atoms from ozone and use them to make other substances.  Chlorine and bromine atoms are catalysts, meaning they can speed up a chemical reaction without changing, and can repeat the destructive cycle again with another ozone molecule. So one chlorine or bromine atom can destroy thousands and thousands of ozone molecules, causing ozone to disappear much faster than nature can replace it.

People often confuse the ozone hole with global warming, but they are two different problems

Is Anyone Doing Anything About the Ozone Hole (That’s Not a Hole)?

The Montreal Protocol is an international treaty that protects the ozone layer by phasing out the manufacture and use of ozone-depleting chemicals. It was enacted in 1989, and all of the countries in the world have signed it. Many ozone-depleting chemicals are now illegal to use, or are only used in small quantities. If all countries meet the terms of the Montreal Protocol, scientists expect the ozone layer to heal by around 2050.

Ozone - Too  Much Here Too Little There

Because of the Montreal Protocol, levels of most ozone-depleting chemicals in the atmosphere have slowly gone down. As a result, the size of the ozone “hole” has remained pretty much the same in recent years.

Today, any products in the U.S. containing CFCs and other ozone-depleting chemicals must have warning labels.  The U.S. also prohibits the release of refrigerants used in car and home air conditioners into the air, because they still use ozone-depleting chemicals.

Why Can't We Just Make More Ozone?

Ozone molecules are constantly being made and destroyed by the sun’s ultraviolet light in natural processes. Normally, the amount made and the amount destroyed is about the same, so nothing changes. Think of the amount of ozone as the water level in a bathtub with the faucet running and the drain open. If you turn on the water just right, you can make the amount of water leaving the bathtub equal to the amount coming in, so that the water level never changes. But right now, the drain has gotten faster, and the amount of ozone destroyed is more than the ozone being made.

A big reason we can’t make more ozone to send into the upper atmosphere is because it would take a LOT of energy.  In fact, to make the amount of ozone normally found in the upper atmosphere, you'd need about double the electricity that we use in the U.S. every year. In the atmosphere, this huge amount of energy comes from the sun.  We also don’t have a way to transport the ozone to the right places in the atmosphere. Since we can't make more ozone, the solution is to slow the flow down the drain back to its normal rate. And the only way to do that is to stop using ozone-depleting chemicals.


What Causes "Bad" Ozone?

“Bad” ozone is found at ground level. In cities, it’s made when emissions from vehicles, power plants, chemical plants, and other sources react with heat and sunlight.  The hotter the day and the stronger the sun, the more ozone is formed.  That's why ozone is usually worst on windless, hot summer afternoons. High levels of ozone are mainly a concern for people from April 1–September 30.

You’re most likely to find high levels of "bad" ozone in urban areas.  You might hear it called “smog.” However, other areas can also have high ozone levels when winds blow pollution hundreds of miles from their original sources.

  • For more on bad ozone, watch the video, How Ozone is Formed
    (Video includes audio and requires the Adobe Flash player)
Flash - How Ozone is Formed
00:35 sec

How Does "Bad" Ozone Affect Me?

Even at low levels, breathing ozone can cause chest pains, coughing, and throat irritation. It can also aggravate lung diseases like emphysema, bronchitis, and asthma. The more ozone pollution a person breathes, the more permanent damage it can do to her lungs.

Because it usually forms in hot weather, anyone who spends time outdoors in the summer may be affected - children, older people, outdoor workers, and people exercising may be particularly susceptible. The higher the ozone level, the more people who will experience health symptoms. Millions of Americans live in areas where ozone levels are higher than the national health standards, and should pay attention to ozone levels when the weather is hot and sunny.

Ways to Protect Your Health on Bad Ozone Days:

How Are We Dealing With Ozone Pollution?

The Clean Air Act Amendments of 1990 require the US Environmental Protection Agency, the States, and cities to carry out programs that reduce emissions of ozone-forming chemicals from sources like cars, industry, power plants, and consumer products. Power plants and industry are reducing emissions and companies are developing cleaner cars and fuels. We’re making progress, but we still have work to do.


We can control some things, and some things we can’t.  Here are some things you can do.  And remember, lots of small steps add up to big differences!

To Limit "Bad," Nearby Ozone

  • Keep your car tuned-up and running well.
  • Carpool, use mass transit, walk, bicycle, and plan trips efficiently to reduce driving, especially on hot summer days.
  • Be careful not to spill gas when filling up your car or gas-powered lawn equipment. During the summer, fill your gas tank during cooler evening hours.
  • Make sure your car's tires are properly inflated and your wheels are aligned.
  • Participate in your local utility's energy conservation programs.
  • Seal containers of household cleaners, workshop solvents, and garden chemicals to prevent chemicals from evaporating into the air. Dispose of them properly.

To Protect "Good" Ozone Up High

  • Have your car, home air conditioning, and refrigerator checked for leaks.
  • Make sure that the technicians working on your air conditioners and refrigerator are certified to recover the refrigerant, as required by law.
  • Find out from your local government the best way to get rid of old refrigerators and air conditioners.

How Can I Protect Myself from UV Rays?

Use the UV (ultraviolet) Index: The UV Index tells you how strong the sun’s rays will be for the day.

Protect yourself from UV rays
Basic steps for protection against UV rays.
SLIP! SLOP! SLAP! WRAP!™ is a trademark of the American Cancer
Society, Inc.

Don’t Get Burned: Sunburns, especially for children, significantly increase the risk of getting skin cancer over your lifetime.

Avoid Sun Tanning and Tanning Beds: The UV radiation causes skin cancer and wrinkling.

Use Enough Sunscreen: At least 15 minutes before going outside, put on about one ounce of sunscreen over all exposed skin. Sunscreen should have a Sun Protection Factor (SPF) of at least 30 and provide protection from both ultraviolet A (UVA) and ultraviolet B (UVB) rays. Reapply every two hours, even on cloudy days, and after swimming or sweating.

Wear Protective Clothing, such as a long-sleeved shirt, pants, a wide-brimmed hat, and sunglasses, when possible.

Seek Shade when you can. Remember, the sun’s rays are strongest from 10 am to 4 pm.

Use Extra Caution Near Water and Sand: They reflect the sun’s rays, which can increase your chance of sunburn.

Get Vitamin D Safely: Choose foods fortified with Vitamin D or take vitamin supplements. Don't seek the sun.

The Shadow Rule

Look for your shadow to estimate your UV exposure:

  • If your shadow is taller than you are (in the early morning and late afternoon), you’re probably getting less UV exposure.
  • If your shadow is shorter than you are (around midday), you are getting higher levels of UV radiation. Seek shade and protect your skin and eyes.
Top of page