Frequently Asked Questions

What is ground-level ozone and what causes it?

Ground-level ozone pollution is formed when emissions from everyday items combine with other pollutants and “cook” in the heat and sunlight. Sources of such emissions include local industry, gasoline-powered vehicles and lawn equipment, and household paints, stains and solvents.

Weather plays a key role in ozone formation. The highest ozone levels are usually recorded in summer months when temperatures approach the high 80s and 90s and when the wind is stagnant or light.

Why should we worry about ground-level ozone?

At ground level, ozone pollution is harmful to all of us, especially the young and elderly. Ozone can also trigger attacks and symptoms in individuals with pre-existing health conditions, such as asthma or other respiratory infections.

High levels of ozone pollution often affect healthy people who work or exercise outdoors and can cause breathing difficulties, eye irritation and reduced resistance to lung infections and colds with exposure for prolonged periods.

What is an ozone action alert?

Denver’s ozone season runs from June through August. During this time, the RAQC works with meteorologists at the Colorado Department of Public Health and Environment (CDPHE) to issue “Ozone Action Alerts,” notifying the public when ozone levels could potentially reach unhealthy levels.
Between June 1 and August 31, the Regional Air Quality Council (RAQC) will issue daily ozone advisories at 4:00 p.m. The RAQC issues the alerts to the media, individuals, local governments and businesses.
An Ozone Action Alert is issued on days when meteorologists from the CDPHE expect weather conditions to lead to increased ground-level ozone concentrations in the metropolitan Denver and Front Range region.

An alert indicates the potential for elevated eight-hour ozone levels. The alert will remain in effect for 24 hours.

How do I know when an alert is in effect?

To find out about current air quality conditions, visit this site often, sign up to receive Ozone Action Alerts via e-mail on the homepage or call the 24-hour hotline number at 303-758-4848.

What should I do when an alert is in effect?

During an Ozone Action Alert, you can help out by making an effort to:

  • Stop at the click – do not overfill gas tanks when refueling.
  • Keep vehicles regularly maintained.
  • Tighten gas caps after refueling.
  • Mow in the evening.
  • Refuel in the evening.
  • Use new earth-friendly lawn equipment.

By taking these actions, you can help keep the metropolitan Denver region a healthy, clean city in which to live, work and play.

How are the alerts determined?

Meteorologists at the CDPHE analyze weather forecasts and ozone-monitoring data from around the region to predict expected ozone levels. In general, hot, sunny and windless conditions increase the likelihood of high ozone concentrations, while clouds, wind and more moderate temperatures can help prevent ozone formation.

What can residents do to help take care of our summer air?

When an Ozone Action Alert is in effect, it means during hot, still weather you need to take special precautions. Just chill. Keep the car in the garage if you can. And avoid unnecessary idling when you’re waiting in the parking lot. Roll down the window and turn off that engine.

And why mow your lawn or paint your house in the hot, hot sun? Kick back and watch the grass grow – it can wait until evening. Avoid painting and staining decks in the heat of the day. Chill. Relax in the shade instead.

Reduce your emissions. Let’s take care of our summer air

What can I do to help in the yard:

  • Delay mowing until evening – don’t mow, let it grow.
  • Use a new earth-friendly lawn mower – an electric- or battery-powered mower, a non-motorized push mower, or a new gasoline-powered mower.
  • Maintain your mower to help it run cleaner – change the air filter, oil and spark plugs at least once each season. Keep the underside of the mower free of grass build-up.
  • Avoid using two-stroke gasoline-powered yard equipment, such as weed trimmers, since they emit a disproportionate share of air pollution.
  • Use a funnel to refuel equipment – avoid even small spills and drips.
  • Reduce lawn watering and fertilizing to discourage excessive lawn growth.
  • Xeriscape to reduce lawn area, or change to native western grasses to reduce the need for irrigation and mowing.Choose an alternative to charcoal grilling.
  • Don’t use petroleum distillate charcoal lighter fluids, which emit a lot of harmful vapors. Use an electric starter or charcoal chimney instead.

What can I do to help around the house:

  • Avoid solvent-based products, which have pollution-causing vapors (VOCs). Use water-based paint, stain and sealants.
  • If you must use a solvent-based product, avoid using it on Ozone Action Alert days, or use it in the evening.
  • Avoid spray paints, most of which are solvent based. Very fine spray also can become airborne. Use paint brushes and rollers instead.
  • Tightly cap all solvents (gasoline, paint thinners, strippers, degreasers) and store in a cool place to avoid evaporation.
  • Plan major painting, stripping and refinishing projects for spring and fall to avoid summer heat and sun, which react with vapors to create ozone pollution.
  • Avoid use of flammable household products, such as some floor wax, furniture polish, fabric cleaners and insect foggers – all of which tend to have solvents.

What can I do to help on the road:

Keep your car tuned up and tires well inflated to increase mileage and reduce the need for refueling. Refuel in the evening, so fuel vapors will not have a chance to “cook” into ozone. When refueling your car, stop at the click – when the nozzle clicks off. Don’t overfill or drip fuel. Fuel creates ozone-causing vapors as it evaporates. Avoid idling your car unnecessarily while waiting in parking lots or service lines. Turn off the engine. Reduce your driving by delaying trips, combining errands into one trip, car pooling, walking or biking, or using public transportation. By taking these actions, you can help keep the metropolitan Denver region a healthy, clean city in which to live, work and play. To find out about current air quality conditions, visit this site often, sign up for Ozone Action Alerts on the homepage or call the 24-hour hotline number at 303-758-4848.


I have more questions. Who should I ask?

Media Contact:
Meg Alderton
Communications Manager
Regional Air Quality Council (RAQC)
O: 303-629-5450, ext. 220