Estimates of exposures to PM2.5, ozone, and household air pollution on this website come from the Global Burden of Disease (GBD) project of the Institute for Health Metrics and Evaluation (IHME). Find more details on our methodology in the State of Global Air report.

How We Estimate PM2.5 Exposure

Fine-particle outdoor air pollution (PM2.5) consists of airborne particles measuring less than 2.5 micrometers in aerodynamic diameter, most often produced as a result of combustion. PM2.5 concentrations are measured in micrograms of particulate matter per cubic meter of air, or μg/m3.

To estimate concentrations of PM2.5, GBD scientists combine data from:

  • 10,408 air quality monitors representing urban and rural data in 116 countries,
  • Satellite observations, and
  • Global chemical transport models that use data on emissions, chemical reactions, and meteorological conditions to estimate the movement and concentration of pollutants.

To estimate PM2.5 exposures for people living in a specific area, scientists combine:

  • The number of people living within that area, and
  • The PM2.5 concentration to which they are exposed.

This method produces a population-weighted annual average concentration for a given country or region. Population-weighted annual average concentrations are better estimates of population exposures, because they give proportionately greater weight to the air pollution experienced where most people live.

How We Estimate Ozone Exposure

Ozone is formed in a chemical reaction between nitrogen oxides and volatile organic compounds in the presence of sunlight. Tropospheric ozone (at ground level) is a harmful pollutant created mostly by human activities. Stratospheric ozone (6–30 miles above Earth’s surface) is a naturally occurring beneficial layer that protects us from UV radiation. Ozone concentrations are measured in parts per billion (ppb).

To estimate global concentrations of ozone in the air near ground level, GBD scientists statistically combine data from:

  • More than 8,800 air quality monitors, and
  • Nine global chemical transport models that use data on emissions, chemical reactions, and meteorological conditions to estimate the movement and concentration of pollutants at a fine geographic scale (1 kilometer by 1 kilometer).

Our assessment focuses on: 

  • Measurements taken in the warm season in each country or region, defined as the six months with the highest average ozone levels, and
  • The highest (maximum) 8-hour daily ozone concentrations during that season. (This is the metric used to characterize exposure in the most recent epidemiological studies of ozone’s health effects.)

To estimate ozone exposures for people living in a specific area, we combined:

  • The number of people living within that area, and
  • The ozone concentration to which they are exposed.

This method evaluates human exposure to ozone in terms of the population-weighted average seasonal 8-hour daily maximum concentration for a given country or region. Population-weighted annual average concentrations are better estimates of population exposures, because they give proportionately greater weight to the air pollution experienced where most people live.

How We Estimate Household Air Pollution Exposure

Burning any type of fuel (coal, charcoal, wood, agricultural residue, dung, and liquid fuels such as kerosene) for any purpose (cooking, heating, or lighting) can potentially create household air pollution consisting of fine particulate matter (PM2.5), carbon monoxide, and other pollutants. The use of solid fuels for cooking is a major source of household air pollution, though it is not the only source. As a result, these analyses likely underestimate household air pollution in some places, especially in colder regions.

We report exposure to household air pollution as the proportion of each country’s population living in households where cooking is done with solid fuels. However, for purposes of estimating health impacts, these proportions are ultimately translated into exposures to fine particulate matter (PM2.5) in the home.

To estimate exposure to household air pollution, we combine:

  • Information from the World Health Organization (WHO) and other surveys about cooking practices and fuel use in different countries,
  • Information on the age and sex demographics of the population in each country, and
  • Indoor and personal measurements of household air pollution–related PM2.5.

To make sure that the estimated exposure to PM2.5 for each location and year represents household exposures only, GBD scientists subtract the ambient PM2.5 exposure from the household exposure for each location at the time of measurement. In this way, the analysis provides independent estimates of exposures to household pollution and to ambient PM2.5.

If you have data from your city or country that you would like to have included in the Global Burden of Disease project, please contact us at contactsoga@healtheffects.org.