Ozone pollution in Maricopa County has declined over the past two decades, but not enough to escape an "F" rating from the American Lung Association, which tracks air quality across the nation.

The health organization released its 20th annual "State of the Air" report Wednesday and ranked Phoenix as the 7th most ozone-polluted metropolitan area in the country. That's one spot worse than last year's 8th place ranking.

"A lot has to do with climate change," said JoAnna Strother, the Lung Association's director of advocacy for the Southwest region. "That and Phoenix has 1.6 million people and a big chunk of them live in the metro area where a lot of people are driving and sitting in standstill traffic. All of that contributes to ozone."

Ozone is a colorless, odorless gas that, in high levels, can be extremely hazardous for lungs, Strother said.

The toxic gas forms when nitrogen oxides (NOx) and volatile organic compounds (VOCs) react in the sunlight. Combine a high volume of vehicle emissions — cars make up the biggest source of NOx and VOCs in Phoenix — with the Arizona desert's plentiful sunshine and the result is a recipe for ozone.

Climate change adds to the problem with an uptick of warmer temperatures across the country, Strother said. Since ozone production speeds up in higher temperatures, those car emissions are cooking up in the heat, she explained.

Blue skies don't mean clean air

Although Phoenix's ozone pollution is among the highest in the U.S., data provided by the Maricopa County Air Quality Department shows the Phoenix area's ozone reading actually fell 11.2 percent on average from 1990 to 2018.

Air quality experts point to two reasons for the decrease: The national Clean Air Act and more fuel-efficient cars.

A set of amendments introduced in 1990 to the Clean Air Act expanded regulations for toxic pollutants and strengthened enforcement.

The changes show how rules, such as controlling power plants, affect the industrial sector, said Ron Pope, an atmospheric scientist at the Maricopa County Air Quality Department.

Cars are also a lot cleaner today and get a lot better fuel mileage, Pope said, explaining how cars have tougher emissions standards today than in the past. That means less fuel burning, and less emissions coming out.

"Put two together and there's less of those precursor pollutants that go up in air and react to create pollution, despite more people and more cars," Pope said. That results in a reduction over time.

After cars, solvents from small industrial businesses are the next largest contributor to ozone in Phoenix, Pope said. That includes paint at auto shops, semiconductor manufacturing and even dry cleaning. The solvents evaporate into the air and drive up ozone, he explained.

Pope has given educational talks in high-ozone areas. He said these areas tend to fall in the East Valley because ozone is a daytime pollutant and during the day, the wind is most likely to blow west to east. Since ozone is colorless, one misconception people have is that just because there's no smog, the air quality must be good.

"People see outside and say it's clear outside, the sky is blue," Pope said. "But we can read it on our monitors and we can tell people what the concentration levels are. Usually sensitive people experience symptoms first when concentrations are higher. Even though they can't see it, they're affected."

Why Phoenix got an 'F' grade despite downward ozone trend

So despite the improvements, why did Phoenix receive an "F" grade from American Lung Association?

While in the long term the Phoenix area has been improving, the region is recording higher spikes in pollution, Strother said. Phoenix also recorded a higher average of "unhealthy days" in ozone and particle pollution between 2015 and 2017, the report noted.

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"We are always trying to push for stronger regulations," Strother said. "We want people to do more to help clean up the air. With the new administration, we have seen precedent in trying to seek rollbacks from some of the stronger standards we’d like to see."

Strother said American Lung Association is calling on the Trump administration and Congress to use science-based policy to mitigate the impact of climate change and ensure no community near polluting sources gets left behind.

Air quality will improve even more over time as standards are strengthened and agencies will have to meet those standards, she believes.

"We made so much progress and we need to keep making progress," Strother said.

The Trump administration's move to limit Clean Air rules would a pose great threat to that progress, she added.

Strother said he understands the concerns of pro-business interests involved, but as a member of a public health organization, her push is to protect public health.

Phoenix also saw higher particle pollution

The State of the Air report also looked at particle pollution, or PM, for particulate matter. In the report, Maricopa and Pinal counties were the only counties in Arizona to receive an "F" rating for high particle pollution days.

PM 2.5 consists of microscopic pollutants, finer than the width of a human hair. They can lodge deep into the lungs and airways, making them most harmful for children with developing lungs, the elderly with compromised lungs and people with respiratory diseases such as asthma.

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The American Lung Association found an increase of people admitted to hospitals and emergency rooms for asthma during spikes of unhealthy particle pollution, Strother said. Sources of PM 2.5 pollution include car and industry emissions, as well as smoke from wildfires or wood burning.

To reduce smoke pollution from fireplaces and backyard fires, Maricopa County offers various incentive programs. The county has also been experimenting in the past few years with portable neighborhood monitors to determine sources of wood-burning pollution more accurately, Pope said.

Slightly larger particles, like PM 10, come from dust sources — and that dust can be just as deadly.

A study released this week by the American Geophysical Union found that dust from the Southwest's desert regions and drylands contributes to air pollution and an estimated 1,300 premature deaths each year.

The study also projected the Southwest will experience more severe, decades-long droughts because of human-caused climate change. More droughts could lead to more dust. More dust could then lead to more premature deaths and hospitalizations for heart and lung diseases, said Ploy Pattanun Achakulwisut, a scientist at George Washington University.

A combination of projected population increases, disease rates and dust levels under a high greenhouse gas emissions scenario could result in 2,900 more premature deaths each year, according to the study. By 2090, the growing health damages could increase economic damages by $47 billion per year..

"Further research is needed to conclusively identify the specific health impacts related to inhaling dust particles," Achakulwisut said in an e-mail. "But the evidence so far does suggest that desert dust is a toxic component of particulate matter."

How you can help improve Phoenix's air quality

Want to reduce ozone pollution in the Valley? Here are additional suggestions from Ron Pope and Bob Huhn, communications supervisor at the Maricopa County Air Quality Department:

Commit to one day a week to carpool or public transportation

Refill your gas after dark. During the day, gas fumes evaporate and react with the sun to begin generating ozone right away.

Instead of idling at a drive-through, park your car and go inside.

Join your company's travel reduction program, which might include a ride-share system or light rail pass.

On No Burn Days, choose not to burn a fire in your fireplace or backyard. The county doesn't declare such days often, but when it does, it's because pollution concentrations are forecast to be highest and unhealthiest.

What concerns do you have about Arizona air quality? Reach the reporter at Priscilla.Totiya@azcentral.com or 602-444-8092. Follow her on Twitter: @PriscillaTotiya.

Environmental coverage on azcentral.com and in The Arizona Republic is supported by a grant from the Nina Mason Pulliam Charitable Trust. For more stories visit environment.azcentral.com or follow OurGrandAZ on Facebook, Twitter and Instagram.

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