The first time Danica Lombardozzi noticed tiny brown and black spots covering the leaves of her garden plants, she was thrilled. Her garden was serving its purpose.

Each summer, Lombardozzi, a climate scientist at the National Center for Atmospheric Research, watches excitedly as cutleaf coneflowers, milkweed, snap beans and potatoes sprout in a small garden bed nestled at the entrance of NCAR in Boulder.

Then she waits.

By late August, her plants are blighted with yellow, brown and black spots — symptoms of long-term exposure to the pollutant ground-level ozone.

The plants, part of a national network of ozone gardens managed by researchers across the country, help Lombardozzi understand how ground-level ozone damages plants, and the cascading impact the pollutant has on human health, crop productivity and the climate as a whole. The plants are also a handy educational tool.

“People can see that the plants are being damaged and I think that’s an important connection for people to make. Plants can show us things about our environment that are not readily visible to us,” Lombardozzi said.

Danica Lombardozzi started her ozone garden as a personal project and in the last seven years the project has proved to be crucial in understanding the effects of the powerful greenhouse gas on different plant species along the Front Range. (Nina Riggio, Special to The Colorado Sun)

Ground-level ozone, commonly called smog, forms near the Earth’s surface (not to be confused with the ozone found high in the stratosphere, which shields the planet from the sun’s harmful ultraviolet rays.)

The invisible gas is one of six main air pollutants monitored by the Environmental Protection Agency and forms when nitrogen oxides (NOx) and volatile organic compounds (VOCs) –– emitted from things like cars, lawn mowers, paints, cleaning solutions, factories and wildfires –– chemically react with sunlight and high temperatures.

“Trees also naturally release VOCs, which is one of the reasons ozone is such a big problem here in the Front Range,” Lombardozzi said. “We have high levels of natural VOCs, we have lots of sunlight and then we are adding all of these human emissions.”

Because the chemical reaction needs high-energy sunlight and temperature, ozone levels fluctuate daily as well as seasonally. In Colorado, ground-level ozone typically peaks in the summer months, by mid-afternoon when the weather is hot, calm and sunny. Last summer, there were 55 ozone action days from June to September, meaning the air quality was not safe for sensitive groups, which includes children, the elderly and sick individuals.

Denver County has been out of compliance with ground-level ozone standards since 2012. Currently, the Denver-Aurora area ranks 12th among most ozone-polluted cities in the country. Fort Collins ranks 24th.

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Though air quality has improved significantly since the passage of the 1970 Clean Air Act, a 2018 data analysis, which used satellite and ground-level observations, shows that the improvements slowed significantly in the United States from 2011 to 2015.

“Ozone can be a tricky pollution to address because it’s not directly emitted by one particular source. It’s formed from a bunch of different chemicals found in the atmosphere that react with sunlight,” said Owen Cooper, a research scientist with the National Oceanic and Atmospheric Administration.

“That’s why you have to think of air quality not only as a local issue, but as a global one. We need to be looking at emissions from around the world. Clean air is a valuable natural resource for the United States and benefits human health as well as crop and ecosystem productivity.”

In 2015, the EPA changed the ozone standard to a maximum of 70 parts per billion from 75 ppb.

Last year, Denver and the Northern Front Range region missed an extended deadline to meet federal air-quality health standards. In March, Gov. Jared Polis withdrew a waiver with the EPA which would have given Colorado more time to comply with the standards from 2008. Instead, Polis said he’s focused on developing zero-emissions vehicle standards, reforming oil and gas regulations and advancing his 100% renewable energy goals.

MORE: Front Range air quality is terrible, but Colorado’s efforts are showing some improvement in ozone pollution

“We are moving forward to make our air cleaner now,” the governor said in a public statement.

But on Thursday, the EPA said it plans to downgrade the region’s status to serious non-attainment from moderate and will direct the state to develop a plan to meet the 75 ppb ozone standard by July 20, 2021.

Though a handful of regulatory changes in Colorado have been preliminarily successful at cleaning up the Front Range’s polluted air, including stricter oil and gas emissions standards and improvements in the automobile industry, Lombardozzi says there is still plenty to do.

“From a plant perspective and an ecosystem perspective, concentrations above 40 ppb cause damage to plants,” Lombardozzi said. “Even a regulation of 70 ppb is allowing plants to be harmed. Those things are really contributing to climate change, and it’s a really big thing we need to think about.”

“She knew a lot about the atmospheric chemistry side, and I knew a lot about the plants”

While pursuing her Ph.D. at Cornell University, Lombardozzi studied how plants respond to ozone and how this affects their ability to perform photosynthesis and transpiration. She had heard of ozone gardens while in graduate school, but it wasn’t until she moved to Boulder in 2012 that her ozone garden came to fruition. She was approached by Kateryna Lapina, a then- post-doctoral researcher at CU, who was working on a project about how air quality impacts crops.

“It was a really amazing pairing. She knew a lot about the atmospheric chemistry side, and I knew a lot about the plants and the impacts from ozone,” Lombardozzi said.

The pair approached Cathy Regan at CU’s Museum of Natural History and proposed an ozone garden outside the museum that could be used as both a monitoring site as well as an educational tool to teach the general public about the effects of ozone pollution. The garden is now in its sixth year. Other Colorado-based ozone gardens can be found at the Beaver Meadows Visitor Center in Rocky Mountain National Park, the University of Denver and at the CU Mountain Research Center on Niwot Ridge above Nederland.

“The strength of the ozone gardens is that they make the invisible, visible,” said Regan, who designed an ozone exhibit at CU’s Museum of Natural History (inspired by Lombardozzi’s research) in 2018.

Red-tailed bumblebees probe a cutleaf coneflower planted in the ozone garden at NCAR in Boulder. (Nina Riggio, Special to The Colorado Sun)

“Information about the role of ground-level ozone has been shared with the public for close to 50 years, yet very few people understand the term ‘ground-level ozone,’ know that it’s a major contributor to health and environmental damage or are aware of their role in creating this pollutant.”

Since 2014, Lombardozzi has helped facilitate the creation of 20 more ozone gardens sprinkled across the country, as well as a handful in the United Kingdom and one in Norway. Volunteers and citizen scientists collect data from the gardens, which Lombardozzi is working to compile into a data-set for other researchers to use.

Lombardozzi says the ozone gardens aren’t going to solve the world’s ground-level ozone problem, but she hopes they will get more citizens interested and involved in the quality of air they breathe every day.

MORE: Read more environmental coverage from The Colorado Sun.

Plants use evolutionary trick to deal with ozone

Unlike humans who can retreat to the safety of their homes when ozone is too high, plants remain rooted and rely on some evolutionary tricks tucked away in their DNA to help battle the effects of ozone.

The plants employ common defenses such as dropping damaged leaves or killing off the part of the plant that is the most damaged. They also “shut out” ozone and other pollutants by closing their leaves’ pores, called stomata. Though this protects the plant from acute damage, it also has serious implications for humans.

When a plant is healthy, the stomata take in carbon dioxide and release oxygen and water, storing the carbon inside the leaf. When a plant is damaged by ozone, the cells that make sugars become compromised, reducing the plant’s ability to perform photosynthesis — the process in which plants utilize sunlight to produce energy. With reduced ability to photosynthesize, the plants can’t pull carbon out of the atmosphere. It also decreases plant productivity and crop yields.

A leaf from cutleaf coneflowers growing in Lombardozzi’s garden at NCAR shows dark pinpoints called stippling, a signal that the plant has has taken in too much ozone. (Nina Riggio, Special to The Colorado Sun)

In addition to the ozone gardens, Lombardozzi uses global modeling tools to predict how ozone damage impacts crop yields, food availability, plant productivity and carbon storage. She specifically researches trends in global photosynthesis (plant carbon gain) and transpiration (plant water loss), both of which drastically decrease in response to ozone.

When Lombardozzi holds a single leaf damaged by ground-level ozone in the palm of her hand, she knows that the damage has rippling effects throughout the entire ecosystem. One leaf may seem inconsequential, she says, but collect all the leaves that cover the Earth’s land surface, and the ecological impact of a single leaf becomes resounding.

“If we don’t have enough food to feed society, and if that is in part due to poor air quality, that’s on us. That’s why this research is important,” Lombardozzi said.

Change on the horizon

Parts of California, Arizona, Colorado, Texas, the Midwest and the Middle Atlantic region experience more than 15 days a year with ozone pollution at dangerous levels for human health, according to a paper published last year in the journal Elementa: Science of the Anthropocene.

Increases in oil and gas development, housing development, the number of cars and the severity and frequency of forest fires all have contributed to high levels of ozone along the Front Range. The increase in wildfires also decreases the amount of carbon stored in the environment, further exacerbating climate change and increasing the global temperature.

According to the statewide meteorological records, Colorado’s climate has warmed by 2 degrees Fahrenheit over the past three decades, and predictions show that the state could see an increase of between 2.5 and 6.5 degrees by 2050. Because high temperatures are a precursor for ozone formation, a warming planet will have serious impacts for air quality around the world.

Milkweed plants near the entry to the iconic NCAR building in Boulder. (Nina Riggio, Special to The Colorado Sun)

“Poor air quality isn’t a new issue on the Front Range,” said Michael Silverstein, executive director of Colorado’s Regional Air Quality Council. “We’ve been regulating industrial emissions for many, many years now. And we’ve made progress.

“Vehicles and cars are cleaner, the oil and gas industry is cleaner,” he added. “But there is still lots to do. On the Front Range, the oil and gas sector is the biggest emission contributor, because of the leaks and the general operation from drilling and pumping the gas to the plant. Then transportation is next.”

Silverstein, who has been tackling air quality issues in the Denver area since 1986, says individuals, in tandem with regulations, can have a positive impact on addressing ground-level ozone. He says simple actions like carpooling, not filling your gas tank in the afternoons (when ozone is high), and exchanging your gas-guzzling lawn mower for a more fuel efficient one can significantly reduce emissions and the formation of ground-level ozone.

He says education is a big piece of the solution as well.

“Air pollution might not be in front of people’s minds. But air quality is an important issue for Colorado. The environment is a big reason a lot of people move to the Front Range, and air quality is something we’ve really struggled with,” Silverstein said. “The legislation and Gov. Polis have said this is an important issue we have to solve.”

“This [damage] is happening to our plants, and the same thing is happening to the tissues in your respiratory system. The plants, and the spots and the wilted leaves, help illustrate what ground-ozone can do.”

The Hunt family, visiting from Orlando, Florida, learns about the effects of ozone gas on certain species of plants in the garden from Danica Lombardozzi, project scientist at the Climate and Global Dynamics Lab at NCAR in Boulder. She introduces her project to visitors three times a week. The tours include information about how to plant an ozone garden, identify damage and record data. (Nina Riggio, Special to The Colorado Sun)

Joining the citizen science project



NCAR climate scientist Danica Lombardozzi says the best way for citizens to get involved in monitoring ground-level ozone is to attend one of NCAR’s Public Tours, which take place noon to 1 p.m. every Monday, Wednesday and Friday.



Participants can learn how to plant their own potatoes, snap beans, milkweed and cutleaf coneflowers and collect data from the gardens. A website is in the works, too, which she hopes to launch by next summer, though basic information about the project is available here.

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