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If you live in Denver, Boulder, or anywhere along Colorado’s northern front range, you’ve likely had to deal with some pretty terrible air quality this summer. Many of us habitually check our phones each morning for the air quality report, and often, the number indicates it’s time to change activities plans and schedules, or worse, stay inside.

In 2024, . The city violated multiple ground-level ozone standards set by the U.S. Environmental Protection Agency (EPA). The American Lung Association recently .

“Between ozone pollution and wildfire smoke, summertime air quality in the Colorado Front Range tends to be pretty bad,” said , a fourth-year doctoral candidate in the Department of Chemistry. Anderson studies wildfire smoke and urban air quality using remote sensing, modeling and air quality measurements. 

As ozone pollution in the front range continues to get worse, Anderson gives her take on what ozone pollution is and what might be the solutions.

Where does ground-level ozone come from?

Ground-level ozone is a toxic air pollutant that is produced when oxides of nitrogen (NOx) react with volatile organic compounds (VOCs) in the presence of sunlight. In the Colorado Front Range, we have sources of NOx, VOCs and background ozone that travels from other states.

Front Range NOx emissions come from oil and gas operations, traffic emissions and lawn equipment. Essentially, anything that uses diesel or gasoline. VOCs come from natural sources, like plants and trees, along with oil and gas operations, cleaning supplies, and even personal care products like shampoos and deodorants.

Why do levels spike in the summer?

High temperatures, lots of sunshine, dry air and our geography all cause Front Range ozone to spike in the summer. Sunshine and dry conditions drive the chemical reaction between VOCs and NOx emissions, leading to ozone production.

What makes the Front Range one of the worst areas for ozone pollution in the US?

In addition to our high temperatures and sunshine, which drive ozone production, wildfire smoke also contributes to our summertime ozone levels.  Another reason for high ozone is related to mountain and valley geography. Sometimes we can get a layer of warm air that traps cooler air underneath, allowing ozone concentrations to climb without being able to diffuse away.

Why is ozone pollution bad for the environment?

Exposure to ozone pollution damages plant cells and tissues, which lowers the plant’s ability to make its own food through photosynthesis. Plants react to this by making more leaves, which drain the roots and stem of resources, weakening the plant and making it more at risk of disease and drought. Ozone pollution also lowers agricultural yields, which can cause significant economic loss.

We’ve heard ozone has negative impacts on human health. Can you give some examples?

Ozone is an irritant that damages tissues in the respiratory tract, which includes the nose, throat and lungs. This irritation can make it difficult to breathe. It can also cause a cough and a sore and itchy throat. Ozone pollution can also aggravate lung diseases such as asthma, which can lead to increased hospital visits. Children, older adults, people with lung diseases, people who work outdoors and people who exercise during the day outside are most at risk of experiencing the effects of high ozone.

This August, Colorado failed the federal air quality benchmark for ozone. What does that mean?

So far this summer, we have had almost where the ozone was at a level that is beyond what is accepted by the EPA. Additionally, Denver and much of the Front Range are now considered to be in “severe nonattainment” of a threshold for ozone pollution that was set by the EPA in 2015. This means that the government needs to come up with an actionable plan to make the air quality better with a new deadline of Aug. 3, 2027.

What can we do to improve our air quality?

The most important thing to do on a high ozone day would be to protect yourself, especially if you are a person with a lung condition. This would look like limiting your time outside when possible and exercising during the morning instead of the afternoon when ozone concentrations usually peak. This also looks like checking the Air Quality Index (AQI) on my phone to decide whether it is safe for me to exercise outdoors at that time.

We can personally work to help lower ozone pollution in the Front Range by limiting the use of personal vehicles on high ozone days, not running gas-powered lawn equipment or waiting until the evening time. We can also help by sealing household cleaning supplies, paint and household solvents.

More importantly, we can help improve air quality by becoming involved in community organizations like , signing air quality , donating to local air quality advocate groups like , and voting for people who will make legislation and improvements in air quality a priority. Individual actions can make an impact on air quality, but big changes come from community organizing and legislation.

K-12 students will return to school in the next couple of weeks. Will high concentrations of ground-level ozone affect learning?

Children's lungs are still in development, and they tend to spend a lot of time playing outside, making them particularly vulnerable to the harmful effects of ozone pollution. When playing outside during a high ozone day, young students are at a higher risk of inflammation, irritation and asthma attacks.

While students of all ages who have asthma or other lung diseases are at an increased risk for breathing difficulties on high ozone days, all students who participate in outdoor exercise or strenuous work outdoors can experience negative health effects from ozone pollution. It is important for schools, parents and sports coaches to help protect students on days with poor air quality.