Frequently Asked Questions

1. What is the Spare the Air program and who’s involved?
2. What is a Spare the Air Day?
3. When do Spare the Air days usually occur?
4. How will I know when a Spare the Air day is forecast?
5. Can I receive an AirAlert?
6. What causes air pollution?
7. What’s the difference between “good” and “bad” ozone?
8. Can you see ozone?
9. When the air looks murky, is it always from pollution?
10. What are the health effects of ozone and who is affected?
11. Is it safe to do vigorous exercise on a Spare the Air day?
12. Are there any other environmental consequences of ground-level ozone?
13. What are the Bay Area’s major sources of summer air pollution?
14. What can I do to help reduce summer air pollution?
15. Do I have to worry about Spare the Air Day if the forecast for my city is “good?”
16. How can I monitor air quality in my area?
17. What is an ozone movie?

1. What is the Spare the Air program and who’s involved?

Spare the Air was established by the Bay Area Air Quality Management District, in 1991, to reduce air pollution and provide advance notice when a "bad air day" -a day when air quality is forecast to exceed federal standards- is likely to occur.

Because most air pollution is preventable, Spare the Air is focused on educating the public and promoting changes in behavior that will help prevent poor air quality. The program reaches out to several audiences:

• AirAlert is an email service that informs the public the day before a Spare the Air day is predicted to occur. It encourages Bay Area residents to modify their behavior to prevent, or at least reduce, the anticipated bad air and gives advance notice to people with respiratory sensitivities, such as asthma or emphysema. Click here for more information, or to sign up to receive your own AirAlerts.

• The Employer Program provides more than 2,100 businesses with free tools to help them educate employees about pollution prevention and advises them when an AirAlert is issued. For more information on the Employer program, Click here.

• Over 100 Cities and Counties have adopted legislation and developed programs to support Spare the Air and encourage their residents to follow suit. Click here to find out who they are, what they're doing, and how to join them.

• Community Resource Teams provide an opportunity for all interested people to work together and plan educational activities and programs to reduce air pollution in their communities. Click here to learn about some of their projects, or to join your area's team.

2.  What is a Spare the Air day?

A Spare the Air day is a day forecast to have ozone levels high enough to exceed federal health-based standards. A Spare the Air advisory is issued the day before this is expected to occur. Area residents are asked to modify their behavior to help minimize pollution, and people who are sensitive to unhealthy air are advised to limit their time outdoors, particularly in the afternoon hours.

Because ozone is a preventable pollutant, doing things like cutting back on driving and the use of other gasoline powered equipment can make a substantial difference in the amount of pollution that occurs. For a complete list of ways you can help prevent air pollution, click here.

3.  When do Spare the Air days usually occur?

In the Bay Area, the summer Spare the Air season runs from June through mid-October when clear skies, hot temperatures, lighter than usual winds and a strong temperature inversion combine and trap air pollutants near the ground.

4.  How will I know when a Spare the Air day is forecast?

For those who sign up for e-mail notification, an AirAlert will be issued the day before the Spare the Air day is predicted to occur. It will warn Bay Area residents that unhealthy air is forecast and encourage them to modify their behavior the next day to help prevent or minimize air pollution.

Many television and radio stations also carry Spare the Air advisories. Several Bay Area newspapers carry the air quality forecast, usually on the weather page of the papers.

Residents can also check the daily forecasts on the home page of this Spare the Air website, or call the Air District's toll-free line at 1-800-HELP AIR.

5.  Can I receive an AirAlert?

Yes.  AirAlert is automatically emailed to the media; participating employers, cities and counties; and any individual who requests it.  To sign up, all you have to do is click here.  In addition to receiving AirAlert by email, there are two optional features to consider.

• Get your AirAlert where ever you are by signing up to receive it as a text message in your cell phone or pager, and

• If you want to know what air quality is like EVERY day, you can sign up to receive a daily Air Quality Forecast via email, as well.

6.  What causes air pollution? 

Air pollution can be both natural- such as fires or volcanic eruptions- and man-made. Most of the air pollution in the Bay Area is man-made, and results from industrial processes and everyday activities like driving, boating, using household products or lawn and garden equipment, burning wood, painting, barbecuing, etc.

In the summertime, ground-level ozone causes the most serious air quality problems. Commonly referred to as "smog", ozone is a gas formed when sunlight reacts with oxides of nitrogen and volatile organic compounds emitted by cars, buses, trucks, construction equipment, gas stations, refineries, and many other sources.

While some ozone is produced every day, cooler temperatures and steady winds normally keep it from accumulating to unhealthy concentrations. However, on long, hot, stagnant days, ozone can build up to levels that violate federal and state health-based standards.

In the wintertime, especially between the months of November and February, particulate matter is the chief air quality concern. Small particles, either solid or liquid, can be produced by a variety of natural and man-made sources. Particles less than 10 micrometers in diameter can cause significant health problems, with those under 2.5 micrometers, known as "fine" particles, considered to be the most dangerous. These latter are produced by any kind of combustion (motor vehicles, wood burning, power plants, etc.) and some industrial processes.

7.  What’s the difference between “good” and “bad” ozone?

Ozone can be good or bad, depending on where it is.

Ozone is a molecule that is similar to oxygen (O2), except that it consists of three oxygen atoms (O3) and tends to be unstable. It is found in both the upper and lower atmosphere.

Stratospheric or "good" ozone occurs naturally, high in the atmosphere from about 15 to 35 miles above the earth's surface. Here, it protects us by absorbing the sun's damaging rays and is essential for human, plant and animal life on earth.

Ground level or "bad" ozone is a pollutant that damages human health, crops, and the environment. Ground-level ozone develops from chemical reactions that occur between sunlight and the emissions from some human activities. For example, exhaust from cars, lawn mowers, leaf blowers and other gas-powered engines, as well as emissions from power plants, dry cleaners, paints, and even some common household products all react with the sun and create bad ozone.

8.  Can you see ozone?

No, ozone is a colorless gas.  However, on days with high levels of ground-level zone, there is usually poor visibility.  This is caused by two factors:

• The reddish-brown haze is from oxides of nitrogen, better known as NOx. NOx is converted into ozone air pollution when it "cooks" in the direct ultraviolet rays of the sun.
• Fine particles (often referred to as “particulate matter”) suspended in the air also contribute to reduced visibility. Fine particles consist mainly of soot and other by-products of combustion, particularly from automobile combustion.

9.  When the air looks murky, is it always from pollution?

Not always. Small particles of water vapor can cause light to be scattered so thoroughly that the blue of the sky does not come through. This phenomenon is common in the South Bay during warm weather.

10.  What are the health effects of air pollution and who is affected?

Many residents experience some kind of air pollution-related symptoms such as watery eyes, coughing or wheezing. Even for healthy people, polluted air can cause respiratory irritation or breathing difficulties during exercise or outdoor activities. Your actual risk depends on your current health status, the pollutant type and concentration, and the length of exposure to polluted air.

The people most susceptible to severe health problems from air pollution are:

• Individuals with heart or lung disease
• Individuals with respiratory problems such as asthma or emphysema
• Pregnant women
• Outdoor workers
• Children under age 14 whose lungs are still developing
• Elderly residents whose immune systems are weaker
• Athletes who exercise vigorously outdoors

High air pollution levels can cause immediate health problems, such as:

• Aggravated cardiovascular and respiratory illness
• Added stress to heart and lungs causing them to work harder to supply the body with oxygen
• Damaged cells in the respiratory system
• Damage to deep portions of the lungs, even after symptoms such as coughing or a sore throat disappear
• Wheezing, chest pain, dry throat, headache or nausea
• Increased reactivity to allergens and particles
• Eye irritation
• Reduced resistance to infection, increased fatigue, or weakened athletic performance

Long-term exposure to polluted air can have permanent health effects, including:

• Accelerated aging of the lungs and loss of lung capacity
• Decreased lung function
• Development of diseases such as asthma, bronchitis, emphysema, and possibly cancer

11.  Is it safe to do vigorous exercise on a Spare the Air day?

On Spare the Air days, it is usually safest to exercise in the morning because ground-level ozone doesn't build up to unhealthy levels until the afternoon.

12.  Are there any other environmental consequences of ground-level ozone?

Ground-level ozone also causes damage to plants and crops.

• Ozone interferes with the ability of plants to produce and store food so that growth, reproduction, and overall plant health are compromised. Plants and trees weakened in this way become more susceptible to disease, pests, and environmental stresses.

• Ozone can kill or damage leaves so that they fall off the plants too soon or become spotted or brown. These effects can significantly decrease the natural beauty of an area, such as in national parks and recreation areas.

• Ozone has also been shown to reduce agricultural yields for many economically important crops, such as soybeans, kidney beans, wheat, and cotton.

Scientists believe the effects of ground-level ozone on long-lived species, such as trees, add up over many years, so that whole forests or ecosystems can be affected.

13.  What are the Bay Area’s major sources of summer air pollution?

Overall, mobile sources - particularly cars and light duty trucks - are the biggest source of Bay Area air pollution, contributing 75 percent of the emission inventory. However, as the table below indicates, both consumer products and industrial/commercial coatings and solvents are major contributors of volatile organic compounds, as well.

San Francisco Bay Area
Summer Emission Inventory – 2006

14.  What can I do to help reduce summer air pollution? 

There's a lot you can do, probably much more than you realize. Taking any of the actions listed below will help, and the more you do, the more air pollution you will help prevent.

The biggest action you can take is to drive less. Here are a few ideas to consider:

• Burn calories not fuel – use your legs and walk or bike
• Take public transit and read a book during your commute
• Call 511 to find rideshare opportunities
• Put off all nonessential trips and activities that require engines until the air is better
• Telecommute if your employer will allow it
• Take your lunch to work and avoid mid-day driving

If you must drive:

• Offer a ride to a friend or coworker
• Combine trips – your car emits more pollution right after a cold start
• Run your errands at night, after dark
• If you must refuel, do it after dark and don’t top off the tank
• Drive your most fuel-efficient car
• Keep your car well tuned and your tires inflated
• Drive smoothly, this saves fuel and lowers emissions
• Drive the speed limit, higher speeds mean more pollutants
• Consider purchasing a reduced-emission vehicle, such as a hybrid.

Things to do at home:

• Use an electric or old fashioned push lawn mower
• If you can’t put off mowing with a gas mower, do it late in the day
• Use a broom instead of a leaf blower
• Use an electric starter or charcoal chimney to start your barbecue (there’s no need to ever use lighter fluid)
• Turn off the lights and any other appliances you can do without
• Use water-based paints
• Go “natural” for the day and keep your hairspray in the cabinet
• Keep all aerosol spray cans in the cabinet until the air improves

15.  Do I have to worry about Spare the Air Day if the forecast for my city is “good”?

Yes, if there is a Spare the Air day warning in effect. 

Air is almost always on the move, and pollution created in one area can drift to another where it can "cook" into smog later in the day. If the forecast for your area is good, you don't have to worry about your health, but what you do that day can make a big difference in the lives of others. This is particularly true in the Bay Area where winds tend to blow pollution from San Francisco and other urban areas into neighboring valleys in the East and South Bay.

16.  How can I monitor air quality in my area?

Daily air quality forecasts are available on the Spare the Air home page, and you can find more information about air quality by clicking on the drop down Air Quality button. Daily air quality forecasts are also available on the Air District's toll-free phone line at 1-800 HELP AIR. Many newspapers in the Bay Area also carry daily air quality forecasts.

17.  What is an ozone movie?

Ozone Movies use real-time air monitoring data to show ozone air pollution levels throughout the region, by animating ozone concentrations as they build up on a map of the Bay Area.

What are the harmful health effects of ozone?

Ground-level ozone can cause several types of short-term health effects:

• Ozone can irritate the respiratory system. Ozone can cause coughing, irritate your throat, eyes, or nose, and/or cause headaches. These symptoms can last for a few hours after ozone exposure and may even become painful.

• Ozone can reduce lung function. "Lung function" refers to the amount of air that you draw in when you take a full breath and the speed at which you are able to blow it out. Ozone can make it more difficult for you to breathe as deeply and quickly as you normally would.

• Ozone can aggravate asthma. When ozone levels are high, more asthmatics have asthma attacks that require a doctor's attention or the use of additional medication. Ozone makes people more sensitive to allergens (such as dust mites, pets, and pollen) which are the most common triggers for asthma attacks.

• Ozone can inflame and damage the lining of the lung. Ozone's effect on the lining of the lung is comparable to the effect of sunburn on the skin. Ozone damages the cells that line the air spaces in the lung. Within a few days, the damaged cells are repaired, just as our skin recovers from a sunburn naturally.

Scientists suspect that ozone may have other effects on people's health, as well. Ozone may aggravate chronic lung diseases, such as emphysema and bronchitis. Also, studies in animals suggest that ozone may reduce the immune system's ability to fight off bacterial infections in the respiratory system.

Most of these effects are considered short-term because they eventually cease once ozone levels subside. However, there is concern that repeated short-term damage from ozone exposure may permanently injure the lung. For example, repeated ozone impacts on the developing lungs of children may lead to reduced lung function as adults.

Who is most at risk for experiencing the health effects of ozone?

• Children. Children are more sensitive to pollution than adults. Children typically spend more time and are more active outdoors. Pound for pound, they breathe more than adults. They breathe, drink, and eat to grow, not just to maintain themselves. Their air passages are also narrower than adults, so it takes less inflammation or irritation to obstruct a child's airways. Children are also more likely to have asthma or other respiratory illnesses.

• Adults who are active outdoors. Healthy adults of all ages who exercise or work vigorously outdoors are considered a "sensitive group" because they have a higher level of exposure to ozone than people who are less active outdoors. Ozone is typically a problem in the afternoon due to pollution generated in the morning.

• People with respiratory diseases, such as asthma. There is no evidence that ozone causes asthma or other chronic respiratory disease, but these diseases do make the lungs more vulnerable to the effects of ozone.

• People with unusual susceptibility to ozone. Scientists don't yet know why, but some healthy people are simply more sensitive to ozone than others.