Air pollution is a complex mixture of particles and gases. Their levels and composition vary from place to place, depending on what sources are present (for example, power plants, heavy industry, and traffic), weather conditions, and how they mix in the atmosphere.
One of the most widely tracked and studied components of air pollution is fine particulate matter, consisting of airborne particles that are smaller than 2.5 micrometers in aerodynamic diameter (or PM2.5). These particles are 20–30 times smaller than the width of a human hair and can be readily inhaled into the lungs. The level of PM2.5 in ambient (outdoor) air has been the most consistent predictor of early mortality (that is, people dying sooner than they would have otherwise) and increased disability (for example, feeling sick and missing school or work) in long-term studies of air pollution around the world.
Another air pollutant widely used by many governments to track air quality is ozone. Ozone is formed by chemical interactions among other pollutants in the atmosphere where we live and breathe. It is a reactive gas that, due to its ability to irritate sensitive tissues in the airways and lungs, has been associated with adverse health effects in children and adults. Its effects on the respiratory system are well established and include worsening of asthma (acute effects) and reductions in lung growth (chronic effects).
Future State of Global Air reports will include additional pollutants (such as NO2), when rigorous scientific evidence for those pollutants becomes available. See What’s Next.
Why report on the State of Global Air?
Given the importance of air pollution to human health, reporting and tracking pollutant levels over time is a first step toward finding solutions. The State of Global Air project also uses the levels of PM2.5 and ozone to estimate how air pollution affects the health of populations in countries and regions around the globe. Its unique interactive feature makes the data accessible to scientists, regulators, and citizens alike and allows them to compare air quality and health across countries and regions and to follow how they change over time.