What you need to know about the loophole hiding the extent of US wildfire pollution

Exceptional events rule has become regulatory escape hatch' for states that want to meet federal air-quality standards

• Revealed: how a little-known pollution rule keeps the air dirty for millions of Americans

When smoke from the Camp fire poured down over northern California in 2018, schools across the region closed to protect kids from breathing dangerous air. When wildfires blanketed the Willamette valley with soot and ash in 2020, hundreds of Oregonians sought urgent care for shortness of breath, headaches and asthma. When Canadian wildfire smoke made its way to Michigan last year, ozone levels in Detroit spiked to levels that caused officials to warn residents sensitive to air pollution to take extra care.

In each of those cases, the US Environmental Protection Agency (EPA), the federal agency that oversees air quality, allowed local air regulators to strike the pollution caused by these events from air-quality records, using a mostly overlooked legal tool called the exceptional events rule, which allows pollution caused by uncontrollable" events to be forgiven.