Here are some quotes from that NYTimes article:
Before deciding whether to exercise outside, we should know what inhaled smoke may do to our insides. The details are not reassuring.
Inhaling large volumes of wildfire smoke can inflame lungs, says Jennifer Stowell, a postdoctoral associate at Boston University’s School of Public Health, who has studied the health effects of wildfires. Some research suggests that wildfire smoke “may be more toxic” to the lungs than standard urban air pollution, she says, since it contains a distinct mix of particulates that activate inflammatory cells “deep in the lungs” while hindering other cells that can dampen the inflammatory response later.
Those same particles also can migrate from the lungs and “disrupt and upset the natural tone of blood vessels,” says James Hull, a sports pulmonologist at the Institute of Sport, Exercise and Health in London. In past studies, people who exercised while breathing in diesel exhaust, a pollutant somewhat similar to wildfire smoke, developed fleeting changes in how efficiently their blood vessels dilated and contracted as blood flowed through them. These changes could, over time, contribute to blood pressure problems and other cardiovascular issues.
Orange signifies “unhealthy for sensitive groups” on the color-coded Air Quality Index devised by the Environmental Protection Agency and is probably the highest alert at which it is advisable for most people to exercise outside, says Matthew Strickland, an associate professor of health sciences at the University of Nevada, Reno, who has studied links between wildfire smoke and emergency room visits.
“My opinion is that it is reasonable to exercise on ‘unhealthy for sensitive groups’ days,” he says, if you are not among those sensitive groups — such as people with asthma, the elderly and children — and “if you do not experience acute symptoms,” he says. “But I would avoid exercising outside on days classified as ‘very unhealthy’” — purple — or “hazardous” — maroon.
Most of us might assume low-intensity activities would be preferable in smoke, since we wouldn’t be breathing as hard. But, “surprisingly, there is not yet any evidence that, for a given duration, higher-intensity exercise is more harmful than lower-intensity exercise,” says Dr. Michael Koehle, the director of the Environmental Physiology Laboratory at the University of British Columbia.
Masks may help a little, says Dr. Crooks, of the Colorado School of Public Health. “An N95 respirator mask, worn properly, can filter out some of the particles,” he says. But it “will do little to protect against harmful gases in the smoke, such as carbon monoxide.” Plus, N95 masks are still in short supply because of the ongoing pandemic and, to be effective, must fit snugly against the face, which can feel intolerable during exercise. The looser facial coverings many of us wear now to lower our risk of spreading the coronavirus to others will provide negligible protection against wildfire pollutants — though they remain “a moral imperative” during the pandemic, he says.
“A ballpark estimate” is that particulate levels indoors “may be roughly half of outdoors,” depending on “how leaky a building is,” says Robert Laumbach, an associate professor at the Rutgers School of Public Health who researches wildfire smoke and health.
On days with poor air quality, exercising inside, with windows tightly closed, an air-conditioner on “recirculation mode” and, if you own one, an air purifier with HEPA filter humming, “can help to substantially reduce exposure to particulate-matter air pollution,” he says.