How clean is the air you breathe?
Air pollution is a complex mixture of particles and gases. Fine particulate matter (PM2.5) is often measured as an indicator of ambient (outdoor) pollution levels. Ozone, a harmful gas, is also an important measure of ambient air pollution. The levels and composition of these pollutants vary from place to place, depending on what sources are present (e.g., power plants, heavy industry, traffic, and the household burning of solid fuels), weather conditions, and how they mix in the atmosphere. See What are the major sources of outdoor air pollution? for more information.
In addition, over a third of the world’s population is also exposed to household air pollution from the burning of solid fuels for cooking and heating in the home. For them, fine particulate matter levels in the home can exceed the air quality guidelines by as much as 20 times. The estimated combined toll from all forms of air pollution (fine particulate matter, ozone, and household, see below) can be substantial.
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. Levels of PM2.5 are measured in terms of micrograms per cubic meter of air (µg/m3). 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).
When wood, dung, peat, and other solid biomass are burned as fuels for cooking and heating, the combination of incomplete combustion and lack of ventilation can lead to high levels of exposure to particulate matter, among other pollutants, in the home. This year’s State of Global Air presents levels and trends in the proportion of the population in each country around the world that relies on solid fuels. In the Global Burden of Disease (GBD) project, these data provide a foundation for estimating exposures to fine particulate matter in these populations, which are in turn used to estimate health burden. Read the report for more details on estimating exposures to household air pollution.
Given that air pollution is a mixture of particulates and gases, no single measure of exposure to total air pollution exists. However, the State of Global Air presents the estimate of the total impact of air pollution as it is represented in the GBD project today (fine particulate matter, ozone, and household air pollution combined).
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 are first steps toward finding solutions. The State of Global Air project also uses the levels of PM2.5, ozone, and household air pollution 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.
The State of Global Air project is a joint effort by the Health Effects Institute, the Institute for Health Metrics and Evaluation (IHME), and the University of British Columbia. It is based on data from IHME's Global Burden of Disease, an extensive scientific analysis of over 300 diseases and causes of death in 195 different countries and territories, and of the 84 behavioral, dietary, environmental, and occupational risk factors that contribute to them.