While smoke from devastating wildfires in Canada blanketed much of the US, forcing millions to stay indoors, lobbyist Steve Milloy told Fox News there is "no health risk" associated with inhaling such polluted air. "We have this kind of air in India and China all the time—no public health emergency," he said. " This is like clean air in China."

Meanwhile, the US authorities issued air-quality alerts, and the US Environmental Protection Agency says about Particulate Matter (PM):

"Particulate matter contains microscopic solids or liquid droplets that are so small that they can be inhaled and cause serious health problems. Some particles less than 10 micrometers in diameter can get deep into your lungs and some may even get into your bloodstream. Of these, particles less than 2.5 micrometers in diameter, also known as fine particles or PM2.5, pose the greatest risk to health."

Source: http://web.archive.org/web/20230610030914/https://www.epa.gov/pm-pollution/particulate-matter-pm-basics