Concentrations of fine particulate matter (PM2.5)

Rationale:Air pollution consists of many pollutants, among other particulate
matter. These particles are able to penetrate deeply into the
respiratory tract and therefore constitute a risk for health by
increasing mortality from respiratory infections and diseases, lung
cancer, and selected cardiovascular diseases. Definition:
The mean annual concentration of fine suspended particles of less than
2.5 microns in diameters is a common measure of air pollution. The mean
is a population-weighted average for urban population in a country. Method of measurement:
Concentration of PM2.5 are regularly measured from fixed-site, 
population-oriented monitors located within the metropolitan areas.
High-quality measurements of PM concentration from all the monitors in
the metropolitan area can be averaged to develop a single estimate.
  Method of estimation:
Although PM is measured at many thousands of locations throughout the
world, the amount of
monitors in different geographical areas vary, with some areas having
little or no monitoring. In
order to produce global estimates at high resolution (0.1◦ grid‐cells),
additional data is required. Annual urban mean concentration of PM2.5 is
estimated with improved modelling using data integration from satellite
remote sensing, population estimates, topography and ground
measurements.