The sky was yellow, the sun was red, and every time I rode my bike I came home with a gritty scrim of ash in my eyes. For a week in August, Seattle had the worst air quality ever recorded in the area. (The second worst was last August.) In fact, it had the worst air quality of any big city in the world.听
As the postapocalyptic pea soup settled in, and outdoor pools closed听and sports teams canceled practices,听I tried to decide whether听I should keep going outside. The official advice from state health departments and national lung-health organizations is usually general: something like 鈥,鈥 but I wasn鈥檛 sure what that meant. Should I be doing push-ups in my living room with the windows closed and an air filter cranking? Would a few days of running outside, sucking down smoke, really do much damage?
Fires are still burning from Alaska to Arizona, and the National Interagency Fire Center reported across the West through September. As the blazes rage on, in line with听, I鈥檓 not alone in my question about exercise and exposure. The Washington state听, for example, saw more than 1,600 visits a minute during the smokiest听weeks鈥攃ompared to its听average 1,100 visits a day听before this summer鈥檚 wildfires.听
Matt Kadlec, an air-quality toxicologist at the Washington Department of Ecology, says it鈥檚 hard to give concrete answers. There are many human variables, and according to Kadlec, researchers are just beginning to look into the topic more deeply. He says there鈥檚 been an uptick in studies about the health impacts of wildfires and smoke, especially in the past five years, but a lot of it is still听inconclusive, especially because wide-ranging, variable wildfires are hard to research. For example, a听 from wildfire epidemiologist Colleen Reid surveyed existing research and found a direct correlation between a population-wide increase in respiratory illness and wildfire smoke, but she concluded that 鈥渕ore research is needed to clarify which causes of mortality may be associated with wildfire smoke, whether cardiovascular outcomes are associated with wildfire smoke, and if certain populations are more susceptible.鈥
The most common metric for pollution is the EPA鈥檚 air-quality index (AQI), which is calculated from four major air pollutants regulated by the : ozone, particle pollution, carbon monoxide, and sulfur dioxide. Kadlec says that those calculations are based on human-generated air pollution, which tends to have a slightly different composition than wildfire smoke, but they track closely enough that the AQI offers a good metric for measuring the risks posed by air quality.
Atmospheric scientist Ranil Dhammapala, who runs the , says that particulate pollution鈥攑articularly fine particles smaller than 2.5 micrometers in diameter, commonly referred to PM2.5鈥攊s most concerning. Once those tiny particles hit your lungs, they start to break down cells. Resulting health effects听can range from a sore throat or difficulty breathing to respiratory diseases like chronic obstructive pulmonary disease (COPD) and chronic bronchitis. From there, they can enter your bloodstream and potentially cause heart attacks and arrhythmia. 听
Personal health and genetics make a big difference in how your body responds to the same amount of pollution. The World Health Organization says that听25 micrograms per cubic meter of PM2.5 is the upper limit of what鈥檚 safe for people who aren鈥檛 particularly sensitive. Children, the elderly, and people who suffer from asthma or COPD have a lower threshold.
You can track levels of PM2.5, and the four other pollutants the EPA uses to gauge the AQI, on the federal site听. Kadlec says that PM2.5 levels below 12 are considered good, but听that above 20 (which equates to moderate on the AQI scale), he鈥檇听scale back on running or biking outside. Regardless of the amount of pollution, the longer your听exposure, both on a daily and a long-term level, the greater your听risk.听
A听 published in Preventive Medicine looked at the break-even point for exercising in urban air pollution, and found that, both generally听and in the short term, some exercise is better than no exercise. Researchers 诲颈诲苍鈥檛 control for genetics or other personal factors that can change susceptibility, but they found that when PM2.5 is at 50 micrograms per cubic meter鈥攚ell into the EPA鈥檚 unhealthy zone鈥攜ou won't cancel out the cardiovascular benefits of exercise until you've spent ten听hours walking or five hours biking. The harder you鈥檙e breathing, the less听time you should spend exercising outside, Kadlec says. If you鈥檙e hiking uphill or running, you鈥檒l hit that break-even point much sooner. But short periods of activity should be OK听up until the 50-microgram level. Kadlec also recommends taking periodic clean-air breaks throughout the day, ideally by keeping a room in your house clean, sealed off from the outside, and filtered with a high-efficiency particulate air filter.
If you have to work outdoors, Kadlec recommends wearing a sealed dust mask rated N95鈥攎eaning it filters 95 percent听of fine particles鈥攐r higher, and听warns that bandanas and medical masks don't provide any kind of filtration.听And听pay attention to your听upper respiratory system, Kadlec听says, because the early health impacts of pollution are physically obvious. 鈥淲e warn people that if they鈥檙e starting to cough, or if they have a headache, sore throat, or runny nose, to try to reduce their exposure. Smoke can push disease processes along, even if you feel healthy,鈥 he says.听
In Seely Lake, Montana, where ER visits for respiratory problems more than doubled during the听long,听smoky fire season of听2017, Christopher Migliaccio, a professor at the University of Montana, started following residents as part of the nation's听first long-term wildfire health-effects study. He鈥檒l continue doing so over the next few years, to try to gauge long-lasting听impacts and offer people better advice and tools to help them avoid adverse health impacts.听Dhammapala, who has been tracking historic smoke exposure, says that the reports he and his team have听received from the fire services predict more acres burning听in the immediate future. Given that forecast,听they鈥檙e trying to model how smoke distribution might grow and change, so people can make informed听decisions about their exposure.听鈥淚t would be really surprising, scientifically speaking, if it 诲颈诲苍鈥檛 have long-term effects.听But that work just hasn鈥檛 been done yet,鈥 Kadlec says.