Western wildfires send smoke across the country, so it sounds obvious that they always make air quality worse everywhere. New research shows that is not the whole story.

During severe fire seasons in the West, the intense heat from those fires can change weather patterns and rainfall in ways that actually lower fine particle pollution in the eastern United States. That result surprised even seasoned atmospheric scientists.

Wildfire heat and air quality

Qihan Ma of Tsinghua University and colleagues analyzed observations and climate simulations that account for the daily heat released by fires. The researchers found that strong fire heat can reduce fine particle levels in the East during the fire season.

Scientists track fine particle pollution called PM2.5, which refers to particles smaller than 2.5 micrometers across. PM2.5 gets deep into the lungs and bloodstream, and its effects include higher risks of heart and lung disease and premature death.

The results did not just point to smoke. The team showed how fire-driven heat boosts convection, the upward movement of warm air. This suppresses eastward smoke transport and increases rain that washes particles out of the air, a process called wet deposition. 

Air quality in the East and West

Observations from air monitors revealed a dipole pattern during extreme western fire events, with PM2.5 rising in the West and falling in the East by a comparable amount.

Model simulations for the full fire season showed similar contrasts of about 1.71 micrograms per cubic meter in the West and minus 1.21 micrograms per cubic meter in the East.

Satellite analysts also mapped smoke plumes over long distances during these events. NOAA confirmed that smoke often spread across parts of the East, yet many eastern monitors still recorded lower PM2.5.

To represent fire inputs day by day, the researchers used the GFED4.1s dataset, which estimates burned area, emissions, and heat release. The data helped quantify how much energy the fires pumped into the atmosphere.

The air quality and weather responses were simulated with the Community Earth System Model (CESM). To separate the drivers, the team ran simulations with smoke alone, heat alone, and with both.

Wildfires shift weather across the country

Heat from large western fires increased convective available potential energy (CAPE) over the West, which favors stronger thunderstorms. It also nudged broader circulation patterns that reshaped wind and moisture across the country.

As the central United States dried and warmed near the surface, low level pressure dropped and winds shifted toward anomalous easterlies over the eastern half of the country.

The East grew more humid and unstable, and convective rain increased, which removed more particles from the air. These heat-driven shifts can modulate long range smoke impacts.

“Heat produced by wildfires, a commonly neglected effect, can reduce fine particle concentrations in the eastern United States,” wrote Ma.

Lessons for health and policy

The results do not suggest that wildfires are harmless. The West still sees higher PM2.5 during fire season, and people there bear the brunt of smoke exposure and related health burdens.

The research shows that ignoring fire heat in national assessments can skew results. The authors report that leaving heat out of models overestimates health and economic losses by about 1,200 premature deaths and 3.3 billion dollars nationwide for the fire season.

Those numbers are driven by the East’s large population and the modeled reductions in PM2.5 when heat effects are included.

Public health guidance should still emphasize reducing exposure wherever smoke raises risk. Strategies include wearing masks during high pollution days and targeted help for sensitive groups like children, older adults, pregnant women, and those with heart or lung disease.

For modeling and policy, the message is straightforward. Future national air quality planning and wildfire risk assessments need to incorporate fire heat, not just smoke emissions, to capture regional differences accurately.

Limitations and open questions

The researchers emphasize that no model is perfect. In global models with coarse grids, convection is parameterized, meaning certain local storm processes are simplified.

The team validated a subset of cases with a superparameterized model that more explicitly resolves clouds. The results showed the same overall pattern, though the heat effects were weaker in magnitude – providing a useful constraint for future research.

Better heat estimates at subdaily timescales will also help. Averaging heat over a day can smooth out fire bursts that may drive the strongest convective responses.

Implications for daily life

People in the West should continue to prepare for smoke season and protect their lungs, because local pollution still rises during major fires.

Communities in the East should not assume they are safe, since many days still exceed health guidelines and smoke episodes remain disruptive.

The broader lesson is about getting the physics right. Accounting for heat shows how the same fires can worsen air in one region and temporarily ease it in another, and that nuance matters for equitable investments in health and resilience.

The study is published in the journal Science.

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