Wildfires worsen extreme air pollution in U.S. northwest | Science News for Students

Wildfires worsen extreme air pollution in U.S. northwest

Smoke from blazes ravaging western states counteracts clean air improvements
Aug 15, 2018 — 6:45 am EST
a photo of the 2018 Carr fire from a distance

The 2018 Carr fire in northern California, seen here outside Redding, threw pollutants into the air for weeks, beginning July 23. The state reported that air quality was “unhealthy” throughout the region affected by this intense fire. One of the biggest in state history, this fire eventually burned more than 175,000 acres and destroyed more than 1,077 homes.

E.L. Karey

The northwestern United States has become an air pollution hot spot — literally. And scientists are blaming the problem on bigger and more frequent wildfires. These disasters spew plumes of fine particles that pollute the sky.

In states from Nevada to Montana, days with the most extreme air pollution are worse now than they were 30 years ago. That’s what researchers reported July 16 in Proceedings of the National Academy of Sciences.

Over the same period of time, smog and haze has tended to decrease across the rest of the country. Laws such as the Clean Air Act, which set rules to limit pollution, have helped. So have laws that limit allowable levels of pollution from vehicles and factories, says Daniel Jaffe. He is an atmospheric scientist at the University of Washington in Bothell. He also is one of the new study’s authors.

Climate change has led to a drying of western forests. This has upped the number of local wildfires. That recent increase in large western wildfires has thrown more lung-clogging pollution into the region’s air. The problem is so great now that wildfire pollution has begun overcoming the benefits of air-pollution laws in parts of the affected states, Jaffe says.

Wildfire smoke is filled with fine particles. These nanopollutants are less than 2.5 micrometers wide. (That’s about 3 one-hundredths the width of a human hair.) Such super-tiny solids and droplets can be inhaled deeply into the lungs. That can aggravate breathing problems. Children, the elderly and people with asthma face the biggest risks. But temporarily levels of pollutants in communities near wildfires can get so high that it becomes unsafe for anyone to be outside for long.

Regularly breathing high levels of these fine particles has been linked to an increased risk of chronic health conditions such as heart disease and diabetes.

“When we start to think about people’s health, [these wildfire] events matter a lot,” says Gannet Hallar. She’s an atmospheric scientist who works at the University of Utah in Salt Lake City who did not take part of the new study.

This map shows the change from 1988 to 2016 in levels of fine particulate matter (smaller than 2.5 micrometers wide) on the days with the worst air. Over most of the country, this type of air pollution has decreased. But in the northwest, wildfires are making the bad air quality days worse than they used to be. 
C. McClure and D. Jaffe/Proceedings of the National Academy of Sciences 2018

Wildfire pollution is short-lived, but bad

“Most of the year, wildfires aren't impacting air quality,” notes Jaffe. “But on some of the worst days they are.” And the blazes can hit one community hard, but leave neighboring towns largely unaffected. This intermittent and patchy nature of wildfires makes assessing their role on regional air pollution tricky, he says.

Jaffe carried out the new study with Crystal McClure. She, too, is an atmospheric scientist at the University of Washington. The two looked at daily measurements of fine particles in air at more than 100 rural monitoring sites around the United States between 1988 and 2016. In most places, the data showed a success story: cleaner air over time. But this was not true in the Northwest, an area that now gets hammered hard by wildfires every summer. 

The team compared levels of a few specific pollutants. One was black carbon, a hallmark of fires. They also looked at sulfate, a by-product of burning fossil fuels. Black carbon levels had increased over time in the Northwest; sulfate levels didn’t. This trend supported the conclusion that wildfires — not industrial activity — have had a big role in driving the air pollution trend in the western states.

Wildfires weren’t worsening air pollution on an average day in the northwest, the team found. Most days, air quality was fine. Wildfires might affect a given community for only a few days or weeks out of a year. But the bad days have been getting worse over time, the new study found.

Those particularly bad days tended to be in the summer, which is also when wildfires are at their peak.

Levels of fine particles on the handful of days with the worst air quality each year in the Northwest have increased by an average rate of 0.21 micrograms per cubic meter per year.

So, while the overall air pollution situation in the country has improved across the United States, western states now have more work to do, says Jenny Hand. She’s an atmospheric scientist at Colorado State University in Fort Collins who wasn’t part of the study. Wildfires create additional challenges beyond protecting homes and trees. Among these is figuring out how to deal with — or prevent — these more uncontrollable sources of air pollution.  

Power Words

(more about Power Words)

asthma     A disease affecting the body’s airways, which are the tubes through which animals breathe. Asthma obstructs these airways through swelling, the production of too much mucus or a tightening of the tubes. As a result, the body can expand to breathe in air, but loses the ability to exhale appropriately. The most common cause of asthma is an allergy. Asthma is a leading cause of hospitalization and the top chronic disease responsible for kids missing school.

average     (in science) A term for the arithmetic mean, which is the sum of a group of numbers that is then divided by the size of the group.

black carbon     Particles of carbon that are released when fossil fuels, wood or other carbon-based materials are burned.

carbon     The chemical element having the atomic number 6. It is the physical basis of all life on Earth. Carbon exists freely as graphite and diamond. It is an important part of coal, limestone and petroleum, and is capable of self-bonding, chemically, to form an enormous number of chemically, biologically and commercially important molecules.

chronic     A condition, such as an illness (or its symptoms, including pain), that lasts for a long time.

climate change     Long-term, significant change in the climate of Earth. It can happen naturally or in response to human activities, including the burning of fossil fuels and clearing of forests.

diabetes     A disease where the body either makes too little of the hormone insulin (known as type 1 disease) or ignores the presence of too much insulin when it is present (known as type 2 diabetes).

fossil fuel     Any fuel — such as coal, petroleum (crude oil) or natural gas — that has developed within the Earth over millions of years from the decayed remains of bacteria, plants or animals.

haze     Fine liquid or solid particles scattered through the atmosphere that make it hard to see. Haze can be caused by harmful substances such as air pollutants or by water vapor.

literally     A term that the phrase that it modifies is precisely true. For instance, to say: "It's so cold that I'm literally dying," means that this person actually expects to soon be dead, the result of getting too cold.

micrometer     (sometimes called a micron) One thousandth of a millimeter, or one millionth of a meter. It’s also equivalent to a few one-hundred-thousandths of an inch.

particle     A minute amount of something.

plume      (in environmental sciences) The movement of some gas or liquid, under the direction of gravity, winds or currents. It may be in air, soil or water. It gets its name from the fact that it tends to be long and relatively thin, shaped like a large feather.

pollutant     A substance that taints something — such as the air, water, our bodies or products. Some pollutants are chemicals, such as pesticides. Others may be radiation, including excess heat or light. Even weeds and other invasive species can be considered a type of biological pollution.

Proceedings of the National Academy of Sciences     A prestigious journal publishing original scientific research, begun in 1914. The journal's content spans the biological, physical, and social sciences. Each of the more than 3,000 papers it publishes each year, now, are not only peer reviewed but also approved by a member of the U.S. National Academy of Sciences.

risk     The chance or mathematical likelihood that some bad thing might happen. For instance, exposure to radiation poses a risk of cancer. Or the hazard — or peril — itself. (For instance: Among cancer risks that the people faced were radiation and drinking water tainted with arsenic.)

salt     A compound made by combining an acid with a base (in a reaction that also creates water). The ocean contains many different salts — collectively called “sea salt.” Common table salt is a made of sodium and chlorine.

smog     A kind of pollution that develops when chemicals react in the air. The word comes from a blend of “smoke” and “fog,” and was coined to describe pollution from burning fossil fuels on cold, damp days. Another kind of smog, which usually looks brown, develops when pollutants from cars react with sunlight in the atmosphere on hot days.

smoke     Plumes of microscopic particles that float in the air. They can be comprised of anything very small. But the best known types are pollutants created by the incomplete burning of oil, wood and other carbon-based materials.

sulfate     A family of chemical compounds that are related to sulfuric acid (H 2 SO 4 ). Sulfates occur naturally in drinking water.


Journal:​ C. McClure and D. Jaffe. US particulate matter air quality improves except in wildfire-prone areas. Proceedings of the National Academy of Sciences. Published online the week of July 16, 2018. doi: 10.1073/pnas.1804353115.