State of Wildfires 2025-26: Annual mean PM2.5 surface concentrations and number of days air quality exceedences due to wildfires aggregated by Continent, Biome, Country, and Administrative Region

This dataset supports the State of Wildfires 2025-26 report under review at Earth System Science Data (Burton et al., under review). It is an update of the State of Wildfires 2024-25 report (Kelley et al. 2025). The dataset provides annual means of daily regional population-weighted values for surface concentrations (in units of μg m-3) of particulate matter with an average diameter of 2.5 μm or less (PM2.5), the number of days where these values exceed the World Health Organization 24-hour mean Air Quality Guideline of 15 μg m-3, and differences between model simulations with observed and climatological fire emissions. These values are computed per region over a March–February global fire season (e.g., March 2025–February 2026), which aligns with the annual lull in the global fire calendar (see Kelley et al. 2025). Global PM2.5 surface concentrations are provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecasting System for atmospheric composition (IFS-COMPO) from model simulations with observed and climatological wildfire emissions datasets or where wildfire emissions are denied, with biomass-burning emissions prescribed from the Copernicus Atmosphere Monitoring Service (CAMS) Global Fire Assimilation System (GFAS; Kaiser et al., 2012). The complete methodology is described by Burton et al. (under review). Citation Work utilising our regional summaries should cite both Burton et al. (under review) AND the primary reference for the variable(s) of interest as follows: ECMWF (2026). IFS Documentation CY50R1 - Part 8: Atmospheric Composition. IFS Documentation. https://doi.org/10.21957/0e95cd084c Regional Analysis We performed "cookie-cutting" (spatial and temporal masking) of the above input data sets to features in each of the following regional layers (e.g. per country in the "Countries" layer). The statistics derived from cookie-cutting are listed below. Full details in Burton et al. (under review). Layer Short Form Source Biomes NA Olson et al. (2001) Ecoregions NA Olson et al. (2001) Continents NA ArcGIS Hub (2024) Continental Biomes NA See above Countries NA EU Eurostat (2020) UC Davis Global Administrative Areas (GADM) Level 1 GADM-L1 UC Davis (2022) Intergovernmental Panel on Climate Change Sixth Assessment Report (AR6) Working Group I (WGI) Reference Regions IPCC AR6 WGI Regions Iturbide et al. (2020) Global C Project Regional C Cycle Assessment and Processes (RECCAP2) Reference Regions RECCAP2 Regions Ciais et al. (2022) Global Fire Emissions Database (GFED) Basis Regions GFED Regions van der Werf et al. (2006) Citation