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Current 8-Hour Ozone Summary

Ozone Summary through September 25, 20238- hour Ozone Summary is based on 8-hour averages of raw 1-hour ozone data from the Colorado Department of Public Health and Environment (CDPHE) through EPA AirNow and consistent with Data Reporting and Handling Conventions...

End of 2023 ozone season shows meaningful progress for air quality, with more work to be done

Ground-level ozone remains the Front Range’s most pressing air quality problem. The human-caused emissions that combine to form this invisible, odorless pollutant in the heat and sunshine of beautiful Colorado days come mainly from diesel and gas-powered vehicles, gas-powered lawn and garden equipment, and oil and gas production.  

“Ozone season” in Colorado therefore runs from each June through August, the three months of the year with the highest ground-level ozone levels. While May or September can include a few days with higher levels of ozone, it’s unlikely the Front Range will have additional high ozone days this year.  

2023 has shown meaningful progress towards improving the state’s air quality and reaching attainment for both national ozone standards set by the Environmental Protection Agency (EPA). In 2023, the Front Range experienced: *  

  • – The fewest “Ozone Action Alert Days” since 2019. These days are called as a preventative measure by the Colorado Department of Public Health and Environment (CDPHE) when high ozone levels are forecasted on a given day after 4 p.m. or for the next day before 4 p.m. The CDPHE called 38 Ozone Action Alert Days in 2023, compared to 43 in 2020, 73 in 2021, and 46 in 2022.  
    • – From June 1 through August 31—the official ozone summer season—CDPHE called 37 Ozone Action Alert Days in 2023, compared to 43 in 2020, 65 in 2021, and 40 in 2022.  
    • – One Action Day was called in early September 2023. 
  • – The fewest violations of the less stringent, 2008 EPA 75 ppb standard since 2019: 9 exceedances. Only one monitoring location registered four exceedances (the threshold to be out of attainment). All others had three or fewer this calendar year. 
  • – The fewest violations of the stronger, 2015 EPA 70 ppb standard since 2019: 26 exceedances. 6 of 15 monitoring locations showed 3 or fewer exceedances, an improvement from only 3 of 15 in 2022, and zero monitors in 2021.

*These numbers are based on raw data and have not yet been finalized by the Colorado Air Pollution Control Division (APCD).  

The improvements can be attributed to an array of combined factors: increased public awareness and individual actions (such as combining car trips, reducing vehicle idling, and working from home), large scale public transit efforts during the peak ozone months of July and August by multiple agencies (such as “Zero Fare for Better Air”), voluntary vehicle and equipment electrification, regulatory efforts to require lower emission rates, and more.  

Weather with cooler days and more rain also created atmospheric conditions less likely to form higher ozone levels. Wildfire smoke that travels longer distances, such as from the widespread Canadian wildfires this year, can have more of an impact on ground-level ozone creation than local fires, which mostly produce particulate matter and is less likely to create higher ozone along the Front Range.  

While ozone levels are improving, there is still more work that needs to be done. The RAQC is rolling out new and larger projects ahead of the 2024 ozone season.  

The summer ozone seasons from 2024 through 2026 in the Denver Metro / North Front Range region are also an important timeframe to measure ozone levels. The National Ambient Air Quality Standards (NAAQS) include this three-year monitoring data window to analyze whether our region is in attainment. To reach attainment, each of the monitoring sites in our region must record a 4th highest daily ozone value—averaged over those 3 years—of less than or equal to the standard.  

Regulatory Proposals 

  • – The RAQC has forwarded a proposal to the Air Quality Control Commission (AQCC) to limit the use of gas-powered lawn and garden / parks equipment by public entities and commercial companies, as well as banning the sale of residential gas-powered small equipment within the nonattainment area, which will phase out the use of high polluting equipment. 
  • – The RAQC is forming additional regulatory proposals for the Oil and Gas industry, which will also be forwarded to the AQCC by the end of the year.

Public Awareness and Collective Action

  • – Simple Steps. Better Air., the RAQC’s signature public engagement campaign, partnered with over 50 media outlets in 2023, expanded in-person tabling at area events, supported and promoted partner efforts like “Zero Fare for Better Air,” increased the number of recipients who receive email and/or text ozone alerts, and improved engagement and awareness of ground-level ozone in-person and online.  
  • – The residential Mow Down Pollution program—which provides individuals who recycle old gas-powered lawn equipment with $75 or $150 vouchers (based on the item recycled) and $75 vouchers for residents who don’t own gas equipment, to purchase new electric or manual lawn equipment—issued over 2,300 vouchers to individuals in 2023, with more than double the funding in the program than was spent in 2022.

“Collective action can and will continue to make a meaningful difference in reducing ground-level ozone. Roughly half of ozone precursors come from industry, but the other half come from all of us: driving gas vehicles, using gas lawn equipment, and burning other fossil fuels,” said Kelsey Simpkins, Communications and Programs Coordinator for the RAQC. “Individuals are not only half the solution to reducing this invisible air pollutant, but it’s also their health and that of their communities here in the Front Range which will benefit.”

Large Scale Programs 

  • – Mow Down Pollution (Local Government), is awarding over $1.2 million in grants to local governments to electrify parks equipment, with over half of those funds already awarded. 
  • – Charge Ahead Colorado has distributed over $400,000 for EV infrastructure in 2023, expanding charging options across the Front Range.*  
  • – Alt Fuels has distributed over $4.5 Million towards electric vehicles, replacing diesel vehicles that are being scrapped.*

*These programs are phasing out as the state is doing additional work in this area. The RAQC is proud to have run these programs successfully and for the state to take on that work at a larger scale.

2024 Programs 

In 2024, the RAQC will be rolling out a slew of new and larger programs aimed at direct ozone reduction efforts, including:  

  • – Applying $600,000 to the Mow Down Pollution programs, as part of a September 2023 Supplemental Environmental Program (SEP) settlement related to Suncor air quality violations. 
  • – Residential lawn and garden equipment exchanges in communities close to the Commerce City Suncor facility.  
  • – Additional funding to local governments electrifying parks and other equipment at scale. 
  • – Anti-idling campaigns, targeting reductions in both commercial vehicle idling across the region and passenger vehicle idling near schools. 
  • – Employer micro-grants to support businesses who encourage employees to take alternative transportation or increased work from home. 
  • – Auto Maintenance and Repair programs that provide no-cost repairs for older vehicles that have or likely will fail emissions tests. 
  • – Increased community marketing and engagement, including new hyper-localized efforts.

The RAQC will also continue reporting progress on reaching the ozone standards with monitoring data collected by the APCD, conduct studies to update and improve emissions estimates for control strategy evaluation, improved ozone modeling, emissions source tracking, analytical support for other organizations, and the like.

Media contact: Kelsey Simpkins, Communications and Programs Coordinator.

Headed inside due to bad outdoor air? Here’s how to improve your indoor air quality.

To avoid breathing in unhealthy levels of ground-level ozone or wildfire smoke in Colorado, sometimes the best choice is to stay indoors. However, allergens, smoke, and airborne viruses—like those which cause influenza and COVID-19—can all find their way inside and build up indoors, degrading the quality of your indoor air. To make the most of your time inside as we head into the fall, be sure to freshen up your indoor air with some ventilation and filtration. 

Why stay indoors for ozone?  

Ozone is an invisible, highly reactive gas that forms naturally in the Earth’s upper atmosphere, where it protects us by reducing the amount of harmful UV radiation that reaches the Earth’s surface. But when it forms closer to where we breathe, known as ground-level ozone, it can be harmful.  

Notably, it’s not emitted directly by any air pollution source: It forms in a chemical reaction between volatile organic compounds (VOCs), nitrogen oxides (NOx) and sunlight, and can be amplified by hot temperatures. Colorado’s abundance of sunlight and heat, combined with VOCs and NOx emitted by chemical plants, power plants, gasoline pumps, motor vehicles, lawn and garden equipment, and oil and gas production, makes it a particular hot spot for ozone.

The easiest way to avoid breathing in higher levels of ozone on bad air days is to stay inside and close the windows and doors, as the molecule is likely to react with the building exterior before it gets inside. While VOCs can make their way indoors (no building is completely airtight), ozone has a much harder time forming indoors because windows filter out the UV light needed to catalyze the chemical reaction.  

To get alerts for ground-level ozone in the Front Range from the Regional Air Quality Council (RAQC), sign up here. When a high ozone day is anticipated the next day or happening now, the RAQC will send you a text or email to let you know. You can also take advantage of how ozone levels vary throughout the day. For example, ozone levels are higher in the afternoons and evenings. So if you can’t resist exercising outdoors, do it early.  

Can’t smell it? Don’t ignore it.  

Besides being colorless, ground-level ozone is also odorless. And sometimes, so is smoke from far away fires or that which has drifted for a long time in the atmosphere before settling down to ground level where we breathe. This can lead people to underestimate just how bad the air quality is. If you wait until your eyes feel itchy, you start coughing, you smell it or see ash falling, you’re not paying enough attention, according to Marina Vance, an assistant professor in the Paul M. Rady Department of Mechanical Engineering at the University of Colorado Boulder.  

“Relying on smell to detect air pollution can be really deceiving,” said Vance. 

To check if smoke is at unhealthy levels, she recommends using The overall Air Quality Index incorporates five major pollutants that are regulated by the Clean Air Act into its rating, including PM2.5: The term used for tiny bits of particulate matter in smoke which can be harmful if breathed in. You can also check the Colorado Smoke Outlook from the Colorado Department to Public Health and Environment (CDPHE) and sign up to receive email updates about wildfire smoke in the state.  

Cleaning indoor air 

To catch and filter out wildfire smoke, allergens, and other particulate matter indoors, Vance recommends first sealing up your house: Close windows and doors. If you live in a house, replace your furnace filter with a high quality one (MERV13 is a popular and inexpensive filter). And if you have air conditioning, recirculate the indoor air within the house to further reduce particulate matter.  

If living in an apartment or condo, she recommends purchasing a portable air cleaner that uses a high-quality HEPA (high efficiency particulate air) filter, a type of pleated mechanical air filter. Keep the portable filter in the room you’re in. You can also add portable air cleaners to a house to further improve its indoor air quality.  

If you don’t have air conditioning and need to leave the windows open, you can still run an air cleaner using HEPA filters—it just won’t be as effective as with windows and doors closed, and you’ll need to run in on a higher setting, which uses more energy. Consider placing a box fan with a HEPA filter attached (on the intake side of the fan) in your window, and blowing outdoor air in, so that the air entering your home is filtered.  

Build your own DIY air filter 

Need a portable, affordable air filter that will do the trick in a pinch? Go the DIY route. You can create a Corsi-Rosenthal Box, which is an efficient and long-lasting DIY filter for removing airborne virus particles and particulate matter (like smoke) from large indoor spaces like homes, offices, and other shared indoor spaces—all for less than $100. Find more information and a how-to video here. A Spanish video tutorial is available here.  

A smaller Corsi-Rosenthal Box may be appropriate for smaller spaces, such as dorm rooms, bedrooms, and private offices. Find more information and a how-to video here.  

These DIY portable air purifiers do not filter out ozone.  

Avoid getting sick  

Due to the airborne transmission of the SARS-CoV-2 virus, which causes COVID-19, spending time indoors with other people is an activity that also comes with the risk of infection. Fortunately, the same MERV13 or HEPA air purification systems which filter out smoke and allergens can also help catch and keep viruses out of the air.  

When changing your filter, you don’t need to worry that it’s COVID-laden, because the virus is simply not going to survive on it, said Vance. But avoid ionizing bipolar, ionizers and UV light air purifiers at home—there’s no need for them, and some types of UV light can be harmful.  

This piece was adapted from an article originally published by Kelsey Simpkins for CU Boulder Today on Sept. 7, 2021: “Amid wildfires and a pandemic, here’s how to keep your indoor air clean.” Additional relevant reading: Indoor pollution can make you sick. Here’s how to keep your home’s air clean, from National Public Radio (NPR), published August 18, 2023. 

Regional Quality Air Council receiving $600,000 through Supplemental Environmental Program from Suncor Settlement

Funding will be used to directly reduce ozone precursors and other air pollutants on Front Range

In response to a recent violation at the Commerce City Suncor facility, the Environmental Protection Agency has fined the oil and gas producer $760,660 for noncompliant fuel produced by Suncor that resulted in excess amounts of hazardous air pollution, such as carcinogenic benzene and volatile organic compounds released into the air and neighboring communities. For details on that violation or fine, please refer to the release from EPA.

Supplemental Environmental Programs (SEPs) are state or federal programs that utilize a portion of fine money from industries to organizations doing work in impacted communities. The Regional Air Quality Council (RAQC) periodically receives SEP funds. This is the 10th time RAQC has conducted a SEP related to a Suncor violation. RAQC is receiving $600,000 of the overall $760,660 fine.

RAQC will be using the funds to electrify small engine equipment in the area through its Mow Down Pollution programs. Funding will be used in both the residential program, which offers residents $75 to $150 vouchers toward the purchase of electric or manual lawn and garden equipment, as well as the RAQC’s local government grant program, which offers up to $50,000 to electrify parks and other lawn and garden equipment. The residential program spending is specifically in communities closer to the Suncor facility and the grant program will support emissions reductions throughout the greater Front Range.

“No program can undo the damage from violations like Suncor’s, but initiatives like the RAQC’s Mow Down Pollution program directly reduce ozone precursors, greenhouse gas emissions, and other air pollutants in impacted areas,” said David Sabados, Communications and Programs Director for the RAQC.

The RAQC also applauds the EPA’s recent objection to Suncor’s plant 2 clean air permit, which directs CDPHE to evaluate whether additional operational requirements are needed.

Unlike some energy companies that are transitioning to cleaner energy products, Suncor’s CEO recently stated they are deemphasizing cleaner options and instead refocusing on oil production. The Suncor corporation, which operates multiple facilities in Canada and the U.S., including the Commerce City facilities, reported $1.88 billion in earnings in Q2. Based on Q2 earnings, the fines would represent less than one hour’s earnings to the corporation.

The RAQC is available to answer questions about SEP implementation and programs, while questions regarding details of the violation should be directed to the EPA or Suncor.

RAQC media contact: David Sabados, RAQC Communications and Programs Director

The Regional Quality Air Council Celebrates RTD for Zero Fare for Youth pilot program

Beginning September 1, 2023, riders age 19 and younger will ride for free and breathe easier.

Regional Transportation District (RTD) fares are currently free for all riders through the end of August 2023 as part of the Zero Fare for Better Air initiative to help reduce ground-level ozone in the Front Range. But when September begins, youth will continue to be able to ride anywhere in the district’s 9-county region at no cost.  

Approved on July 25, 2023, the pilot program Zero Fare for Youth will allow riders ages 19 and under to use RTD’s services for free, from September 1, 2023 through August 31, 2024. All trains, buses, and FlexRide services are included in the program.  

“The idea that a car is the symbol of freedom for teenagers is a farce. Cars often end up being a financial burden just as teens are starting to earn money and plan for life after high school,” said David Sabados, Communications and Programs Director for the RAQC. “Free transit service for Front Range teens means they can spend their money elsewhere, and there’s fewer cars on the road creating pollution. It’s a win-win for everyone and helps create good lifelong habits.” 

Zero Fare for Youth promotes equity by ensuring transportation is not a barrier to accessing education or employment. The program also promotes equity and affordability by reducing costs and increasing cost competitiveness of public transit for families traveling together. Finally, riding transit for free reduces the number of vehicles on the road and resulting air pollution; improving air quality in our communities and increasing health benefits for the people who live in them. 

To participate, riders must present a valid student or government-issued ID. RTD hopes to continue the program after the pilot. For more information, including a full list of acceptable ID options, visit:  

Where to find the RAQC in summer 2023

The RAQC is pleased to join and support several free public events this summer in the Denver metro area. Come by our table to say hi and grab new swag, information, and resources about what we call can do to help reduce ground-level ozone in the Front Range. We look forward to seeing you!

Bike to Work Day

On June 28, put some joy back into your commute! Join thousands of Denver-region residents for Bike to Work Day this summer. Register to swap a ride in your car for a ride on two wheels on Wednesday, June 28, and help improve air quality.

Join the RAQC at the Bannock Street station at Civic Center Park from 6 a.m. to 9:30 a.m. for free coffee, burritos, swag and more!

¡Viva! Streets Denver

¡Viva! Streets Denver is a free community event series that celebrates Denver’s vibrant neighborhoods and supports local business with temporary car-free streets. Over four Sundays from May through August, approximately 3.5 miles of downtown streets will close to cars and open to people. All ages are invited to walk, bike, roll, jog, scoot, or dance down activated streets in the heart of our city and connect with community through exercise, entertainment, and food.

Come find the RAQC on July 9 and August 6 at Broadway and W 9th Ave in Denver! We’ll have information and fun new swag to give away.

Civic Center EATS

Civic Center EATS is the annual food truck event that brings a variety of Denver’s best mobile restaurants together for lunch throughout the summer. Come down to Civic Center Park on Wednesdays and Thursdays from 11 a.m. to 2 p.m. The RAQC will be present on six of these dates, which are currently scheduled as follows.

Wednesday, July 12
Thursday, July 20
Thursday, July 27
Wednesday, August 2
Thursday, August 10
Thursday, August 17

Regional Air Quality Council joins RTD for Zero Fare for Better Air in July and August

Community members encouraged to swap car trips for public transit to reduce ground-level ozone

The Regional Transportation District (RTD) will launch Zero Fare for Better Air: a collaborative, statewide initiative designed to reduce ground-level ozone by increasing use of transit starting July 1. The Regional Air Quality Council is proudly partnering with RTD to encourage community members to increase RTD ridership for cleaner air.

Through a partnership with the Colorado Energy Office, made possible by Colorado Senate Bill 22-180, RTD will offer zero fares for the second consecutive year, expanding to cover fares for both July and August.

The RAQC encourages residents of the RTD service area to take advantage of this free service and #JustSkip2 car trips each week in July and August to help achieve significant air quality, health, environmental, and economic benefits.

Improved air quality

While we cannot see or smell it, ground-level ozone is the Front Range’s most pressing air quality problem. Emissions from gas-powered vehicles, lawn equipment, and oil and gas production combine on sunny, summer Colorado days to form this invisible pollutant that irritates our throats and lungs, increases our susceptibility to respiratory infections, and exacerbates ailments such as asthma.

Taking public transit keeps cars off the road, limiting traffic congestion, air pollution, and ground-level ozone. If just 10% of the population within the RTD service area (about 308,000 people) just skipped two car trips per week for both July and August this summer, the Denver metro area would see an emissions reduction of more than 17 tons of volatile organic compounds (VOCs) and 16 tons of Nitrous Oxides (NOx) — the two chemicals that react to form ground-level ozone when combined with sunlight and heat. That means fewer ozone action alert days, and healthier air in which to enjoy the great outdoors here in Colorado.

Sign up for ozone alerts from the Regional Air Quality Council (RAQC) to be in the know about ground-level ozone. Visit to sign up for emails and/or text “BetterAirCO” to 21000 to receive air quality alerts on your phone. When a high ozone day is occurring or anticipated for the next day, the RAQC will send you a text or email to let you know, so you can make a plan to reduce your emissions.

Reduced carbon emissions

Transportation is a major source of greenhouse gas emissions causing climate change. Approximately 85% of the greenhouse gas emissions in the U.S. that come from transportation are due to day-to-day commutes. By leaving the car at home and hopping on a bus or train, a person can save up to 20 pounds of carbon dioxide emissions every day.

In fact, if just 10% of the RTD area population swapped two car trips per week for public transit in both July and August, the Front Range would save 84,000,000 pounds (42,000 tons) of greenhouse gas emissions from being released into the atmosphere. That’s the equivalent of 1.75 million mature trees pulling carbon dioxide out of the air for an entire year, or taking almost 10,000 cars off the road for the year.

Cost savings

With gas hovering around $4 per gallon, switching to public transit frees up additional funds in Front Range residents’ everyday budgets. If 10% of residents serviced by RTD replaced two car trips a week with public transit, they would together save a combined more than 4 million gallons of gas and $16 million dollars in July and August alone.

To learn how to hop on board to participate in Zero Fare for Better Air, visit

Visit for more information about how to reduce your ozone impact this summer and help your Colorado community breathe easier.

APCD Ozone Public Listening Sessions / Recordatorio: Sesiones de escucha pública sobre el ozono

Join the Air Pollution Control Division for an Ozone Public Listening Session

Wednesday, May 31st, 5:30 – 7 p.m.:

  • Register to attend in person at the Irving Street Library, Westminster OR
  • Register to attend over Zoom

Saturday, August 19th, 10 a.m. – 12 p.m.

  • Register to attend over Zoom


Colorado is actively planning next steps in addressing ground-level ozone in the North Front Range.

The Air Pollution Control Division will use these meetings to discuss updated emissions inventories and provide updates on the work to reduce ozone. These sessions will also share Air Pollution Control Division efforts to assess technical analyses that support air quality planning efforts and advance potential reduction strategies. Join us to learn about ozone planning, ask questions, learn how to stay involved, and share comments!

For more information about this meeting or future ozone meetings hosted by the APCD, please sign up to receive notifications or find more information on our webpage.


Acompáñenos en una sesión de escucha para el público sobre el ozono

Miércoles, 31 de mayo, 5:30 a 7:00 p.m.:

  • Regístrese para unirse en personaen Irving Street Library, Westminster o
  • Regístrese en Zoom


Sábado, 19 de agosto, 10 a.m. a 12 p.m.:

  • Regístrese en Zoom


Colorado está planificando activamente los próximos pasos que se darán para hacer frente al ozono a nivel del suelo en la zona del Front Range.

Durante estas reuniónes hablaremos de los inventarios de emisiones actualizados y proporcionaremos actualizaciones acerca del trabajo para reducir el ozono. Estas sesiónes incluye la evaluación de los análisis técnicos que respaldan la labor de planificación de la calidad del aire y la promoción de las posibles estrategias de reducción. ¡Acompáñenos para obtener más información sobre los planes del ozono, hacer preguntas, aprender cómo puede mantenerse involucrado o involucrada y compartir sus comentarios!

Para obtener más información sobre esta reunión u otras reuniones que la División de Control de la Contaminación del Aire organice en el futuro sobre el ozono, regístrese para recibir notificaciones o busque más información en nuestra página web.

RAQC Welcomes New Communications & Programs Coordinator

The Regional Air Quality Council welcomes Kelsey Simpkins to the RAQC staff.  Prior to joining the RAQC, Kelsey worked at the University of Colorado Boulder in media relations and as a science writer, specializing in climate and environmental science. She previously worked for sustainability science NGO Future Earth as a digital engagement and communications specialist, and for the Twin Cities-based ecological restoration nonprofit Great River Greening in development and communications.

As Communications and Programs Coordinator, Kelsey will manage media, public relations, and community outreach and events for the Simple Steps Better Air program.

RAQC Welcomes New Planning Director

The Regional Air Quality Council welcomes a new Planning Director, Tom Moore.  He came to the RAQC after serving as the Technical Services Program manager at the State’s Air Pollution Control Division as well as working for many years for the Western Regional Air Partnership, coordinating air quality analysis and planning for the 15-state WRAP region. He has served as the Vice Chair for the Air Quality Enterprise Board and chaired the Fort Collins Air Quality Advisory Board. Tom has a B.S. degree in Physical Geography from Arizona State University.

As the Planning Director, he will be working on air quality control strategies, coordinating development of the State Implementation Plan components, and leading emission inventory and photochemical modeling analyses.