Is Air Pollution Making You Sick?

Dec 17, 2023

Though air pollution is down from decades ago, wildfire smoke and ozone have caused recent spikes in "air quality alert" days. Here's how to stay safe.

Along with warm days, summer brings two significant threats to clean air that can drive people indoors: wildfire smoke, which has blanketed the Northeast of the U.S. in recent days and frequently covers the West Coast, and ozone pollution, which is made worse by the warm sun.

Those factors often lead to alerts about air quality, with advice for certain people (and sometimes for everyone) to reduce outdoor activity and stay inside. The levels seen in New York City and other parts of the East Coast recently, due to particulate matter in smoke from Canadian wildfires, have at times reached the point where they pose potential health risks to people of all ages.

Overall, however, the air is usually still cleaner than it was decades ago. Action taken to reduce pollution levels since 1970 has had a tremendous effect. But those trends toward improvement have slowed in recent years, according to Kevin Cromar, PhD, director of the Air Quality Program and a clinical associate professor at the New York University Marron Institute of Urban Management.

In the past five years, many cities and counties—especially on the West Coast—have experienced their highest-ever average number of days with very unhealthy particle pollution, according to the American Lung Association's 2023 State of the Air report.

To better understand what people should do on these days and why we might see more of them, CR consulted a number of air pollution experts. Here's what you should know about summer air pollution—and how to protect yourself.

Air pollution has serious health effects on both the lungs and the cardiovascular system.

Current air pollution levels in the U.S., which are much better than they were before the passage of the Clean Air Act of 1970, are still responsible for more than 88,000 deaths a year, according to Robert Brook, MD, a professor of medicine at the University of Michigan who studies air pollution and health. Some studies even put that number at over 100,000.

Certain groups—including children, older adults, pregnant people, and those with heart and lung conditions—may be particularly vulnerable to experiencing the ill effects of polluted air.

A 2022 review of research on pregnant people who were exposed to wildfire smoke found that such exposure was linked to increases in pre- and post-term birth, which are associated with increased infant mortality. And a 2019 study by researchers at the National Institutes of Health found that when pregnant people were exposed to high levels of pollution in the week before delivery, their babies were significantly more likely to be admitted to the NICU.

Children are also particularly susceptible to wildfire smoke, according to a 2021 review of research, because they breathe more per kilogram of body weight and are generally more active than adults. And in a 2019 study published in the journal Proceedings of the National Academy of Sciences, the authors calculated that reducing nitrogen dioxide pollutant levels by 30 percent would have lowered asthma rates for kids in Southern California by 27.6 percent.

There are a number of different types of air pollutants, but experts typically list two major categories: particulate pollution and ozone.

Particulate pollution, which is made up of inhalable microscopic particles emitted from a variety of sources including wildfires and fossil fuels, can peak at any time of the year, depending on weather conditions and how people use energy.

On the West Coast, these levels often spike over the summer because of wildfires, says John Balmes, MD, a professor of medicine at the University of California, San Francisco, and a spokesperson for the American Lung Association (ALA). Wildfires (this time originating in Canada) have caused the recent record-setting spikes in particulate pollution on the East Coast as well. And it's early in fire season; air pollution events could continue even after current conditions subside. This is the worst start to the Canadian wildfire season on record.

Wildfire season is starting earlier and stretching later in some places, but ozone levels always spike during the summer. That's because ozone is what's called a "secondarily generated pollutant," Brook says. When sunlight hits certain pollutants—including those emitted by power plants, industrial boilers, air conditioners, and perhaps most importantly, cars—it creates ozone.

Those pollutants are emitted as people turn on their ACs to try to stay cool and as fumes are pumped out of their vehicle's exhaust pipes as they drive to work. Then they’re cooked in the hot sun, creating ozone levels that rise throughout the day. Those levels peak at some point in the afternoon and start to fall again after the sun goes down. Long, sunny days will have more ozone. That's why walking outside or trying to jog on some particularly hot days can feel like you’re trying to breathe through a pillow.

Ozone and particulate pollution are linked to cardiovascular illness and respiratory problems. Particulate pollution is more directly linked to events like heart attacks, Brook says, while there's more evidence that ozone affects lung diseases like asthma and chronic obstructive pulmonary disease (COPD). That might help explain why breathing problems are often exacerbated on hot summer days.

Present-day levels of air pollution in the U.S. are half what they were in the 1970s, according to Brook, due to stricter regulations on air pollution. Yet we still have more than twice as many deaths from air pollution (PDF) as we do from traffic accidents.

The number of record-setting air quality alert days for particulate pollution in recent years is part of a worrisome trend, according to the ALA's State of the Air report. Experts say that factors related to the changing climate as well as the political environment could put our improved air quality in jeopardy.

"That's why it's really important that we don't allow any weakening of air quality [standards]," Brook says. "We’ve made such headway."

Yet in the past decade, improvements in particulate pollution levels have slowed, according to Cromar, and there's been little to no change with regard to ozone.

Stricter fuel standards and a large transition away from coal for energy helped us get to where we are now, Cromar says. But further improvements in particulate pollution levels will require even stricter regulations, he says, and reducing ozone levels will require a coordinated effort from local, regional, and federal governments.

Plus, he says, a lot of big cities that already have high ozone levels have growing populations, which means a larger number of people will be exposed to ozone—and contribute to its formation.

At the same time, climate change will lead to more warm, sunny days and more air conditioner use, Balmes says, which will lead to more ozone. Climate change is also linked to greater intensity and frequency of wildfires, according to the Environmental Protection Agency, creating more fine particulate pollutants.

Certain steps can help you reduce your exposure to air pollution, which is particularly important on what's often referred to as an air quality action or alert day. (Different health departments use different names.) You can always check your local air quality on the EPA's AirNow website, and your local government may have additional resources or alerts for particular days.

Editor's Note: This article was originally published in July 2019. It has been updated with new research and to include more information about wildfires.

Kevin Loria

Kevin Loria is a senior reporter covering health and science at Consumer Reports. He has been with CR since 2018, covering environmental health, food safety, infectious disease, fitness, and more. Previously, Kevin was a correspondent covering health, science, and the environment at Business Insider. Kevin lives in Washington, D.C., with his wife and children. Follow him on Twitter @kevloria.