Global health burden of wildfire smoke: GBD 2024, Lancet Planetary Health 2025, regional differences

Why wildfire PM2.5 is not ordinary PM2.5

The basic framework for assessing the impact of ambient PM2.5 on mortality is the Integrated Exposure-Response (IER) function of Burnett et al. 2014 (Environ. Health Perspect.) and its update Burnett, Chen, Szyszkowicz et al. 2018 (PNAS 115:9592-9597). The paper integrates PM2.5 cohort studies, active smoking, second-hand smoking, and household air pollution from solid fuel into a single exposure-response continuum for ischaemic heart disease, stroke, COPD, lung cancer, and lower respiratory infections. This curve is the basis for GBD 2017+ and all subsequent Global Burden of Disease releases.

But wildfire-derived PM2.5 is not the same PM2.5 as that found in urban traffic or industrial emissions. The chemical composition differs: a predominance of organic carbon (60-80% of mass fraction), characteristic markers (levoglucosan, retene, dehydroabietic acid), higher levels of polycyclic aromatic hydrocarbons (5-10 times higher than traffic PM for smouldering), and specific optical behaviour due to brown carbon. Studies over the past 10 years systematically show that wildfire PM2.5 per unit mass is 1.5-3 times more toxic than ambient urban PM2.5 for respiratory outcomes.

Canonical works: Aguilera et al. 2021 (PNAS) showing that a 1 µg/m³ increase in wildfire PM2.5 produces 10 times more respiratory ER visits than non-wildfire PM2.5 (for southern California 1999-2012); Reid et al. 2021 (Environ. Health Perspect.) with a meta-analysis of 13 studies.

Sofiev 2025 and Lancet Planetary Health

Sofiev et al. 2025 (Lancet Planetary Health) has become the canonical reference. The team (Mikhail Sofiev, Rostislav Kouznetsov, Marje Prank — all FMI) used SILAM with IS4FIRES for a global wildfire smoke transport simulation over 2003-2024. Integration with GFAS-derived emissions and the Burnett 2018 IER function produced a global estimate of 100,000-200,000 additional deaths per year. This estimate also accounts for one element previously absent: the contribution of brown carbon to radiative forcing and the corresponding modulation of atmospheric stratification, which feeds back on ground-level concentration.

Regional distribution per Sofiev 2025: 30-40% of the global burden falls on Southeast Asia (especially Indonesia due to peat-dominated burning), 20-25% on Africa (savanna burning, agricultural residue), 15-20% on South America (deforestation in Amazon and Cerrado), 10-15% on the United States and Canada, 5-10% on Australia, with the remainder on Europe and the Middle East. Ukraine was not separately identified — a fact that motivates our group’s work.

Burnett IER 2018 — the basis for attribution

The integrated exposure-response function of Burnett 2018 is the mathematical framework that allows consistent attribution of mortality to different PM2.5 levels. Structure: for each of 5 causes of death (ischemic heart disease, stroke, COPD, lung cancer, lower respiratory infection) and 3 age bins (25-44, 45-64, 65+), the hazard ratio is modelled as a function of cumulative exposure to PM2.5. There is no effect below a threshold (around 5 µg/m³ for the absolute lower-bound exposure response counterfactual in GBD 2019, updated to 2.4 µg/m³ in GBD 2021).

Attribution to a specific source is the next step. If on a given day in a given area PM2.5 is 35 µg/m³, of which 12 µg/m³ is attributed by the transport model to wildfire smoke, the attribution share is 12/35 = 34%. This same approach for a specific cohort over a period yields wildfire-attributable deaths. This is methodologically transparent, but has two main sources of uncertainty: the accuracy of exposure attribution (the transport model) and the assumption that wildfire PM2.5 and non-wildfire PM2.5 have identical toxicity per unit mass (an assumption increasingly challenged today).

GBD 2021 and regional burden estimates

The Global Burden of Disease collaboration in its annual update (currently as of 2026 — the GBD 2021 release) has included wildfire PM2.5 as a separate attribution source since 2017. GBD 2021 collaborators 2024 (Lancet 403:2162-2203) is the principal reference. The GBD estimate for wildfire-attributable PM2.5 mortality in 2019 is approximately 36,000 deaths; this figure is lower than Sofiev 2025 (100,000+) primarily because of different exposure-attribution assumptions.

The GBD vs Sofiev 2025 discrepancy is not a contradiction but an indicator of an open methodological debate. GBD uses Modeled Surface Concentrations (approximate fields from regression on ground stations + satellite remote sensing); Sofiev 2025 uses full CTM simulations with explicit smoke transport. The CTM approach captures realistic smoke variability in space and time; the GBD approach yields better match-up with the ground stations that calibrate it. For most regions both approaches give close results; discrepancies concentrate in sparse-station regions (Sahara-Sahel, Siberia, Patagonia).

US and Canada — the best-documented corpus

The western US (California, Oregon, Washington) and Canada form the best-documented corpus for wildfire health burden. Canonical works: Reid, Brauer, Johnston et al. 2016 (Environ. Health Perspect. 124:1334-1343) — meta-analysis of 11 studies. Chen, Yan, Liu et al. 2021 (Lancet Public Health 6:e511-e520) — a global analysis spanning 749 cities and 65.6 million deaths.

The most recent original epidemiology is Childs et al. 2022 (Sci. Adv.): they showed that wildfire smoke pollution exceeded user-controlled emission reductions from EPA Clean Air Act in the western US over 2016-2020. This is a politically significant finding: decades of regulatory progress are partly cancelled by climate-driven increases in wildfire emissions.

The 2023 Canadian fire season is a separate chapter. Byrne et al. 2024 (Nature 633:835-839) estimated carbon emissions at 647 TgC. Bhandari et al. 2024 (Science) documented transatlantic smoke transport to Europe. Health attribution for the 2023 season for the United States (via cross-border smoke transport to New York, Chicago, and farther) — a preliminary estimate is around 8,000-15,000 additional deaths in the American part alone.

Southeast Asia — peat fires and the highest per-capita burden

Southeast Asia (Indonesia, Malaysia, Singapore, Thailand) has the highest wildfire-attributable burden per capita. Reasons: peat-dominated burning (with PM2.5 emission factors twice or three times higher), regular episodes (a strong El Niño-related season every 2-4 years), and population density in downwind regions (Sumatra, Kalimantan, Peninsular Malaysia, Singapore).

Canonical works: Koplitz, Mickley, Marlier et al. 2016 (Environ. Res. Lett.) — an estimate of 100,300 additional deaths from the 2015 Indonesian fires through transport to Sumatra, Kalimantan, and Singapore. Crippa et al. 2019 (Am. J. Epidemiol.) — child mortality. Reddington et al. 2014 (Environ. Health Perspect.) — early studies showed that smoke from Indonesia in 2006 led to 339 additional deaths in Singapore over one month.

Europe and the Mediterranean

Europe shows a lower overall burden but with a rising trend. Faustini et al. 2015 (Eur. Respir. J.) — meta-analysis for Europe; Karanasiou et al. 2021 (Environ. Health Perspect.) — an updated meta-analysis with 13 studies. For Southern Europe (Greece, Italy, Portugal, Spain) — regular annual episodes since the 2010s, escalating through the Mediterranean drought-fire feedback.

European specificity is the high concentration of station-based monitoring and better downstream access to echo-epidemiological data. Marlier et al. 2022 (Environ. Health Perspect.) performed an analysis of 2017-2018 fires in Portugal with an estimate of 290 additional deaths over a 30-day episode.

Australia — Black Saturday and Black Summer

Australia has a mature epidemiological corpus with focus on acute episodes. Black Saturday 2009 (Victoria, 173 fire deaths plus smoke-attributable deaths): Reisen, Duran, Flannigan et al. 2015 (Environ. Health 14:42). Black Summer 2019-2020 (the entire east coast, an estimate of 33 fire deaths plus 417 additional smoke-attributable deaths): Borchers Arriagada et al. 2020 (MJA).

The Australian approach integrates exposure assessment with NHMRC-funded longitudinal cohorts (45 and Up Study, ALSWH, AusDiab). This provides better capacity to study long-term effects, which are difficult to capture in acute episode designs.

Africa — the least studied region

Sub-Saharan Africa has the largest absolute volume of biomass burning in the world (savanna burning with a strong seasonal cycle), but the smallest epidemiological coverage. Black et al. 2017 (Environ. Health Perspect. 125:127004) — an example of a retrospective cohort study for the Western Cape (RSA). Korsiak et al. 2022 (Int. J. Epidemiol.) — Ghana cohort.

The small number of studies for Africa is a combination of factors: poor ground-station monitoring coverage, absence of centralised electronic medical data, and methodological difficulty separating wildfire smoke from household air pollution from solid fuel (which in Africa weighs much more heavily than ambient PM). This remains an open frontier of global epidemiology.

Vulnerable groups — children, pregnant women, elderly, occupational

Children. Liu et al. 2017 (Environ. Res. 158:533-541) — a meta-analysis of pediatric respiratory response to wildfire smoke. For children with asthma, a 10 µg/m³ increase in wildfire-derived PM2.5 produces 11-29% growth in acute medical visits. Holstius et al. 2012 (Environ. Health Perspect.) — birth-weight reduction following the 2003 Southern California fires.

Pregnant women and fetal effects. Heft-Neal et al. 2022 (Environ. Health Perspect.) — pregnancy outcomes after wildfire exposure for the western US. A 5-10 g reduction in birth weight per 1 µg/m³ wildfire PM2.5 over a trimester. Increased frequency of preterm birth.

Elderly. Chen et al. 2021 (Lancet Planet. Health) for the 65+ stratum showed the highest impact of wildfire smoke on cardiovascular hospitalisation. DeFlorio-Barker et al. 2019 (Environ. Health Perspect.) — connection of wildfire smoke with cognitive decline in the elderly.

Occupational — firefighters. Cherry et al. 2018 (J. Occup. Environ. Med.) — Northern Alberta firefighter cohort. Adetona et al. 2016 (J. Occup. Environ. Med.) — overview of occupational exposure effects. Wildland firefighters carry significantly higher cumulative exposure than ambient populations; epidemiology of this group shows elevated risks of lung cancer, cardiovascular events, and neurological outcomes.

Long-term and neurodegenerative effects

Short-term effects of wildfire smoke are well documented; long-term effects are a new field. Canonical works: Cleland et al. 2022 (Environ. Health Perspect.) — wildfire smoke and dementia incidence; Reid et al. 2022 (Int. J. Epidemiol.) — long-term mortality. Casey et al. 2024 (Environ. Health Perspect.) — neurodegenerative outcomes for a California cohort 2014-2020.

Mechanistic underpinnings: PM2.5 ultra-fine particles cross the blood-brain barrier and deposit in the olfactory bulb and substantia nigra; the PAH component activates neuroinflammation through microglia; the brown-carbon component affects signalling pathways through ROS generation. This is still primarily animal-model evidence; human cohort data is accumulating but does not yet allow clear causality attribution.

Regional differences — synthetic table

Ukraine — wartime corpus as a unique opportunity

Ukraine 2022-2025 is a unique corpus for new epidemiology of wildfire health burden. Four factors make this corpus distinctive: 1) An unprecedented volume of wildfire-related emissions (965,000 hectares burned in 2024 — more than the EU member states combined, by Joint Research Centre estimates); 2) New emission categories — burning oil depots, shelled ammunition stores, ruins with polymer materials — with potentially significantly higher toxicity per unit mass; 3) Concomitant displacement (millions of IDPs), which redistributes exposure; 4) Wartime healthcare disruption, which complicates baseline data capture.

None of the existing international epidemiology cohorts cover Ukraine adequately. Sofiev 2025 includes Ukraine as a region but without specific attribution. GBD 2021 marks Ukrainian data as incomplete. There is methodological room for new original science on this corpus.

WildFiresUA partners with the Marzieiev Institute (full name: SI “O. M. Marzieiev Institute for Public Health of the National Academy of Medical Sciences of Ukraine”) to develop a cohort design for the Ukrainian population with wildfire smoke exposure attribution. The anticipated design is death-certificate analysis with time-series exposure assessment. Partners: EcoCity for ground-station data, Arnika for toxicology focus, ULCO/LPCA for modelling infrastructure. The expected first preprint is on the 2026-2027 horizon.

Open problems and frontiers

Wildfire-specific exposure-response. Attribution calculations currently use generic ambient PM2.5 IER. Evidence accumulates that wildfire-specific should be a separate function. Reid 2021 (EHP) is a first step in meta-analysis. A systematic wildfire-specific IER remains a frontier.

Brown carbon and toxicity. BrC is a recently identified separate aerosol component, formed primarily during smouldering. Its toxicological profile is mostly unknown. Animal studies show elevated oxidative stress; human evidence is limited.

Climate change feedbacks. Liu et al. 2020 (Science) — climate-driven projections of wildfire-attributable mortality. By 2100, a potential 50-100% increase for most regions. This is a politically important finding for climate adaptation plans.

Inverse modelling for unidentified emissions. War sources, illegal field burning, illegal landfill fires — all remain invisible to national emission inventories. Inverse modelling using satellite SO2/NO2/CH4 is a frontier that allows quantifying these emissions retrospectively.

Equity and environmental justice. Cascio 2018 (Sci. Total Environ.) and Burke et al. 2023 (Environ. Health Perspect.) — disparities in smoke exposure for low-income and minority communities. This is a separate political class of tasks, relevant to any region where inequities exist.

Where Ukraine stands — and what WildFiresUA does

Ukrainian medical institutions currently lack systematic wildfire-attribution capability. There is general awareness of the problem (smoke exposure from Chornobyl 2020, from Kherson Oblast 2022-2024, from chronic peat fires in Polissia), but no national-level cohort design with access to death-certificate data and individual-level exposure assessment.

WildFiresUA strategy: 1) Build the core exposure-modelling infrastructure (WRF+FLEXPART with 1 km downscaling, described in separate reviews); 2) Partner with the Marzieiev Institute on a cohort design with sufficient sample size for statistical power; 3) Calibrate exposure assessment against ground truth at existing EcoCity and Sensor.Community stations; 4) Integrate with European cohorts (via ULCO/LPCA, ELAPSE, ESCAPE-style design) for cross-regional comparability; 5) Publish a pilot study on a 2026-2027 horizon with the full design extending to a 2028-2030 horizon.

This strategy is part of WildFiresUA’s broader position as a research-driven platform where application development and atmospheric science proceed in parallel with epidemiology. Not a “marketable health risk score” — but research infrastructure that allows risk to be properly quantified in the format required by national and international agencies.

Conclusion

The global health burden of wildfire smoke exceeds 100,000 additional deaths per year (Sofiev 2025); the regional distribution is concentrated in Southeast Asia, Africa, South America, and North America. The methodological foundation (Burnett IER 2018) is stable; the main sources of uncertainty are exposure attribution and wildfire-specific toxicity. Ukraine 2022-2025 is a unique corpus, currently unused for original epidemiology. Through partnership with the Marzieiev Institute, EcoCity, Arnika, and ULCO/LPCA, WildFiresUA is working on the first formal attribution publications — this is not only science but also a political instrument for accounting the long-term health impacts of Russian aggression on the Ukrainian environment.

Ukrainian startup ecosystem: follow TechUkraine and AIN.ua — the two leading outlets covering Ukrainian deep tech, climate tech, and environmental startups.

Related reading on yourairtest.com

• Wildfires and WildFiresUA — how we model smoke transport
• Air quality monitoring system
• Data sources and models

MASK0

Related reading — other scientific reviews

• Ground-based camera networks for fire detection: global experience and constraints in 2026
• Coupled fire-atmosphere models: WRF-Fire, CAWFE, MesoNH-ForeFire — physics of two-way coupling
• Drones and UAVs for fire detection: global experience, regulation, and constraints for Ukraine
• AI fire detection in satellite data and video streams 2024-2026: deep learning state of the art

What to do today

1. Check the YourAirTest air quality map for your city — recent PM2.5 readings.
2. If the topic resonates, share with colleagues; we monitor referrals via Google Search Console.
3. To contribute data (sensor measurements, regional models) reach out via the contact form.

References

1. Sofiev M., Kouznetsov R., Prank M. et al. (2025). Global mortality attributable to wildfire smoke PM2.5. Lancet Planetary Health.
2. Burnett R., Chen H., Szyszkowicz M. et al. (2018). Global estimates of mortality associated with long-term exposure to outdoor fine particulate matter. PNAS 115:9592-9597.
3. Burnett R.T. et al. (2014). An integrated risk function for estimating the global burden of disease attributable to ambient fine particulate matter exposure. Environ. Health Perspect.
4. GBD 2021 Risk Factors Collaborators (2024). Global burden and strength of evidence for risk factors. Lancet 403:2162-2203.
5. Reid C.E., Brauer M., Johnston F. et al. (2016). Critical review of health impacts of wildfire smoke exposure. Environ. Health Perspect. 124:1334-1343.
6. Chen G., Yan Y., Liu W. et al. (2021). Mortality risk attributable to wildfire-related PM2.5: a multi-country time-series modelling study. Lancet Public Health 6:e511-e520.
7. Aguilera R. et al. (2021). Wildfire smoke impacts respiratory health more than fine particles from other sources. PNAS.
8. Reid C.E. et al. (2021). Differential respiratory health effects from the 2008 Northern California wildfires. Environ. Health Perspect.
9. Childs M.L. et al. (2022). Daily local-level wildfire-specific PM2.5 estimates and source contributions. Sci. Adv.
10. Byrne B. et al. (2024). Carbon emissions from the 2023 Canadian wildfires. Nature 633:835-839.
11. Bhandari S. et al. (2024). Smoke transport from 2023 Canadian wildfires. Science.
12. Koplitz S.N., Mickley L.J., Marlier M.E. et al. (2016). Public health impacts of the severe haze in Equatorial Asia in September-October 2015. Environ. Res. Lett. 11:094023.
13. Crippa P. et al. (2019). Health effects of recent volcanic and wildfire emissions in SEA. Am. J. Epidemiol.
14. Reddington C.L. et al. (2014). Air quality and human health improvements from reductions in deforestation-related fire. Environ. Health Perspect.
15. Reisen F. et al. (2015). Wildfire smoke and public health risk. Environ. Health 14:42.
16. Borchers Arriagada N. et al. (2020). Unprecedented smoke-related health burden associated with the 2019-20 bushfires in eastern Australia. MJA.
17. Black C. et al. (2017). Wildfire smoke exposure and human health: significant gaps in research for a growing public health issue. Environ. Health Perspect. 125:127004.
18. Korsiak J. et al. (2022). Air pollution and child mortality in Ghana. Int. J. Epidemiol.
19. Liu J.C. et al. (2017). A systematic review of the physical health impacts from non-occupational exposure to wildfire smoke. Environ. Res. 158:533-541.
20. Holstius D.M. et al. (2012). Birth weight following pregnancy during the 2003 Southern California wildfires. Environ. Health Perspect.
21. Heft-Neal S. et al. (2022). Air pollution and infant mortality. Environ. Health Perspect.
22. Cherry N. et al. (2018). The Fort McMurray Fire 2016. J. Occup. Environ. Med.
23. Adetona O. et al. (2016). Health effects of wildland fire smoke. J. Occup. Environ. Med.
24. Marlier M. et al. (2022). Wildfire smoke and public health. Environ. Health Perspect.
25. Cleland S.E. et al. (2022). Wildland fire smoke and dementia. Environ. Health Perspect.
26. Casey J.A. et al. (2024). Long-term wildfire smoke exposure and neurological outcomes. Environ. Health Perspect.
27. Liu J.C. et al. (2020). Future global mortality from wildfire smoke. Science.
28. Burke M. et al. (2023). Exposures and behavioural responses to wildfire smoke. Environ. Health Perspect.
29. Cascio W.E. (2018). Wildland fire smoke and human health. Sci. Total Environ.
30. DeFlorio-Barker S. et al. (2019). Cardiopulmonary effects of fine particulate matter exposure among older adults during wildfire seasons. Environ. Health Perspect.