An N95 Mask Is Your Best Outdoor Defense Against Wildfire Smoke

For the second day in a row, the eastern U.S. was enveloped in a hazy beige smog that blocked the skies and sun of early summer. Countless tiny particles from the raging Canadian wildfires—measuring 2.5 microns or less in width (30 times the diameter of a human hair)—are polluting the air. In New York City, levels of these particulates have soared to nearly 60 times the recommended guideline established by the World Health Organization, according to data collected by IQAir.

The sight and smell of obviously unclean air prompted many to dig up the masks they had used while they were still taking COVID-19 precautions and wear them outside. But how much can masks protect against wildfire particulates?

It depends on which type you wear. Experts say that N95 or KN95 masks, which are designed to filter out 95% of particles that are 0.3 microns or larger, are the most effective masks that most people have access to. Even if they can’t filter out 100% of tiny particles, they’re still worthwhile: when you inhale particulates over the short term, they can embed themselves in lung tissue and cause breathing problems by triggering asthma attacks and other respiratory symptoms, so filtering out as many as possible makes sense. Longer term exposure can cause more serious harm to the heart and lungs.

Read More: How to Stay Safe from Wildfire Smoke

On June 7, the New York City Department of Health recommended that anyone spending appreciable time outdoors—regardless of their health status—wear masks to reduce their exposure to the smoke pollutants. The health department also advised employers to limit outdoor activities for their employees, and for people with heart and lung disease to remain indoors if possible.

For people who do have to spend time outdoors, whether commuting to work or school, wearing an N95 or KN95 mask will give you the most protection from tiny smoke particles. Reusing these masks several times lowers their effectiveness, however, so starting out with fresh ones before venturing into polluted air will give you the most protection.

If you don’t have N95 or KN95 masks, then any mask you do have is better than not wearing one, said Dr. James McDonald, acting commissioner of health for New York, during a briefing. “The point is to use the best available mask you have access to,” he said. “If you have a surgical mask, that will give you some protection, but N95 and KN95 are better masks to use in times like this.”

New York health officials expect the pollution to continue lowering air quality in much of the state throughout the weekend.