This month, the US Environmental Protection Agency (EPA) proposed tightening the national standards for soot pollution (PM2.5). Strengthening controls on PM2.5 has, second to banning lead additives in gasoline, provided the greatest public health benefits of any action taken be EPA over the past 3 decades and the action proposed this month by EPA would protect public health in many communities. But a rapidly growing share of PM2.5, especially in western states, is now created by wildfire and prescribed fire rather than traditional sources such as diesel and coal combustion. Under the Clean Air Act, wildfire and prescribed fire emissions are treated very differently, creating disincentives for the use of prescribed fire. Tightening of the PM2.5 standard will limit future growth in the use of prescribed fire which may in turn increase risk and wildfire related emissions of PM2.5 in many states. In order to achieve public health goals in California and the broader west, EPA must develop new approaches to PM2.5 regulation that tighten rules for smokestacks and tailpipes while simultaneously allowing for the growth of prescribed fire.