The air knows no boundaries

By Ashley Miller

Prevailing winds carry ozone to Utah from upwind states as well as across the Pacific

This time of year there is a lot of buzz about ozone air pollution. Ozone plagues areas of Utah every summer when the temperatures rise and the sun shines bright. Ozone also troubles areas of the Uinta Basin in the wintertime—a phenomenon that is not so well understood, since ozone pollution is typically associated with summertime temperatures and sunlight.

What is ozone and what does it do?

Ozone is a powerful oxidant that can irritate the airways. Even relatively low levels of ozone can lead to health problems. Ozone exposure damages the lining of our lungs, similar to a sunburn on your skin. Exposure over time can lead to numerous health conditions like asthma, emphysema, chronic bronchitis, and COPD. Ozone affects children especially, because their lungs are still developing.

In addition to human health, ozone can also negatively impact environmental health. Ozone pollution affects vegetation and ecosystems, including forests, parks, wildlife refuges and wilderness areas.

When enough ozone enters the leaves of sensitive vegetation, it can reduce photosynthesis, interfering with the ability of sensitive plants to produce and store food. This can ultimately slow growth and increase the risk of disease, insect damage, harm from severe weather and effects of other pollutants. Plant species that are particularly sensitive to the effects of ozone on their growth include trees found in numerous areas of the United States—black cherry, quaking aspen, tulip poplar, white pine, ponderosa pine and red alder, to name a few.

Ozone’s impacts on food production

Agriculture is one of the largest contributors of ozone precursor emissions like ammonia and other nitrogen compounds, which contribute both to PM2.5 and ozone pollution. There is increasing evidence that food production is greatly threatened by air pollution. Ozone precursor emissions are particularly concerning because ozone penetrates into the plant structure and can impair the plant’s ability to develop.

Ozone can vastly impact crops during the growing season. Wheat and soybean crops have been found to be more sensitive than others. Rice, potato and corn are also susceptible to problems from ozone pollution. These sensitive crops are all staple foods for the population.

Entire ecosystems can also suffer from exposure to elevated ozone—loss of species diversity among not only plants but animals, insects and fish as well. It can also lead to changes to habitat quality and water and nutrient cycles.

Ozone is, unfortunately, a particularly challenging problem in Utah. There are many man-made sources of precursor emissions that lead to ozone formation locally—vehicles, consumer products like solvents and paints, and industrial sources. States are required to put controls and implement emissions-reducing strategies on manmade sources of ozone precursor emissions, and many of the controls in place to combat PM2.5 pollution should reduce ozone pollution as well. But due to several factors—many out of our control—local emissions are decreasing but ozone pollution is on an upward trend.

Wildfires: a wild card

Wildfires are no doubt problematic for Utah’s air quality, and wildfires are abundant in the West. Wildfire contribution to ozone formation is, however, difficult to quantify. A 2016 study from Colorado State University explains that predicting the relationship of ozone and wildfire smoke is tricky due to the fact that some individual smoke plumes have been linked to a dramatic spike in ozone, but others have seen ozone production actually suppressed within wildfire smoke.

For ozone to form you need a recipe of volatile organic compounds (VOCs), nitrogen oxide (NOx) and sunlight reacting together. When you add a wildfire, it’s the what and how that matters: what is burning, how hot it is burning, and how much sunlight is penetrating through the smoke. These factors combined determine how much a wildfire contributes to ozone levels. In other words, each wildfire contributes to ozone formation differently.

The CSU study hints that wildfire smoke interacting with pollutants in urban areas helps form ozone. There is no perfect equation to determine how much wildfire smoke in general contributes to ozone formation.

But there is a general understanding that wildfires can, and likely will continue to add to the increasing summertime air pollution problem particularly in Western states.

Wildfires are especially troublesome for Utah because wildfire season has been growing increasingly worse each year within and surrounding the state, and smoke wafting into the valleys leads to elevated PM2.5 pollution. When ozone is high and PM2.5 is elevated, we are hit with a double-punch of bad air.

What about ozone that comes from other countries?

The troubling information gathered in several studies on international transport shows that although the United States is emitting less, ozone pollution is still rising in the West because of the pollutants released in Asian countries that then drift over the Pacific.

One particular 2017 study of ozone levels from 1980 to 2014 showed that Asian pollution contributed as much as 65% of an increase in Western ozone in recent years. The study points to China and India as the worst offenders.

Scientists say NOx emissions in Asian countries have tripled since 1990. When NOx blows into North America, its impact offsets the measures within the United States to reduce NOx emissions locally. This study, published in the journal Atmospheric Chemistry and Physics, was led by NOAA and EPA scientists and concluded that manmade emissions in Asia are the “major driver” of rising ozone levels in the Western United States.

According to a study by the University of British Columbia’s Faculty of Medicine, coal is the leading culprit of air pollution in Asia, Earth’s largest continent. In China, 75% of the premature deaths are caused by the 152 coal-fired power plants in Hebei Province alone.

How do outside sources of ozone pollution affect Utah?

Several areas in Utah exceeded the 2015 ozone standard and were designated as “marginal non-attainment” by the EPA last year (see CATALYST, June 2018). According to an EPA white paper on background ozone, only 9-20% of ozone in the Wasatch Front is caused by manmade sources within Utah. This includes cars, trucks, business and industrial sources. Roughly 50-69% of the local ozone comes from manmade sources within the U.S., which means approximately 22-30% comes from international transport: manmade sources outside of the U.S.

Considering how difficult the ozone problem is to address, we all must remember to do our part to reduce the emissions that we personally contribute into the atmosphere. Little things add up. Use electric or hand-powered yard equipment. Drive less and carpool or take transit. Protect your family’s health by checking the UtahAir app or DAQ website to find the current air quality conditions before recreating.

On a broader scale, consider supporting organizations and individuals who can be catalysts for change on the national and international scene. In situations involving air quality, it becomes poignantly clear that planet Earth ultimately has no walls or borders.


Ashley Miller, J.D., is the vice-chair of Breathe Utah. She is also the vice-chair of Utah’s Air Quality Policy Advisory Board and a member of the Salt Lake County Environmental Quality Advisory Commission. She recently became the Senior Government Affairs representative for Marathon Petroleum Corporation.

This article was originally published on July 31, 2019.