Fire heat affects the impacts of wildfires on air pollution in the United States.

Conventional wisdom suggests that wildfires in the western United States (WUS) degrade air quality nationwide as a result of aerosol emissions and eastward transport. However, we found that heat produced by wildfires, a commonly neglected effect, can reduce fine particle concentrations (PM2.5) in the eastern United States (EUS) by an amount comparable to the increases in the WUS during the fire season. This phenomenon arises from fire heat–induced convection in the WUS and subsequent downstream meteorological changes distant from fires. Enhanced wet deposition and weakened eastward transport of fire aerosols lower PM2.5 levels in the EUS. Therefore, neglecting the effect of fire heat on PM2.5 pollution leads to an overestimate of 1200 additional premature deaths and 3.3 billion USD in economic losses, particularly in the densely populated EUS. Editor's summary: One could be excused for assuming that wildfires in the western US worsen air quality across the rest of the nation only due to smoke transport, but that would be incorrect. Instead, Ma et al. showed that extreme wildfires in the west actually reduce fine particle concentrations in the eastern US by an amount comparable to the increases that they cause in the west (see the Perspective by Qian). They attributed this unexpected effect to weakened eastward transport of fire smoke and enhanced wet removal of air pollutants caused by heat-induced convection from fires. This mechanism actually reduces deaths and economic losses nationwide. —Jesse Smith [ABSTRACT FROM AUTHOR]