This dataset contains information about annual estimates of fine particulate matter (PM2.5) concentrations and trends beginning in 1998. PM2.5 refers to airborne particulate matter less than 2.5 µm in diameter; comprises several chemical and particulate constituents, including nitrate, ammonium, elemental carbons, organic carbons, silicon and sodium ions and dust, and originates from a variety of sources, including vehicle exhaust, forest fires, and industrial processes. Exposure to PM2.5 is a leading environmental risk factor for mortality and the global burden of disease.

Global and regional PM2.5 concentrations are estimated using a combination of satellite observations, chemical transport modeling, and ground-based monitoring. Annual and coarse-resolution averages correspond to a simple mean of within-grid values. Gridded datasets are provided to allow users to agglomerate data as best meets their particular needs.

Annual and monthly datasets are provided in NetCDF [.nc] format, with naming convention V6GL02.02.CNNPM25.REGION.YYYYMM_START-YYYYMM_END.nc. REGION refers to the file region (e.g. ‘Global’). YYYYMM_START and YYYYMM_END refer to the numeric start and end date of the file (e.g. for annual mean PM2.5 for 2015, YYYYMM_START is 201501 and YYYYMM_END is 201512). Gridded files use the WGS84 projection.

Variable names within these files include "lat" (latitude coordinate centers of the PM2.5 grid, "lon" (longitude coordinates centers of the PM2.5 grid), and "PM25" (gridded mean PM2.5 concentrations).

Processed summary files are available for annual global country-level means, Canada provincial-level means, China and India regional-level means, and US state-level means. Population-weighted estimates and total population describe only those people covered by the V6.GL.02.02 dataset and are provided by Gridded Population of the World, version 4 (GPWv4). Country borders are defined following the Database of Global Administrative Areas, version 3.6 (GAD3.6).