Glossary

Acute lower-respiratory infections include pneumonia (infection of the lung alveoli), as well as infections affecting the airways such as acute bronchitis and bronchiolitis, influenza, and whooping cough. Such infections are a leading cause of illness and death in children and adults across the world.

A statistical technique used to make it possible to compare death or disease rates between populations with different age profiles. Without this statistical adjustment, a population that has a larger proportion of people in older age groups, for example, would appear to have a higher rate of people dying from diseases that occur in later life (for example, heart disease) than another population with greater numbers of younger people.

The share of the burden of a disease that is estimated to occur due to (“attributable to”) exposure to a particular risk factor (for example, the burden of lung disease that results from breathing air pollution versus that from smoking).

The principle of, or relationship between, cause and effect (for example, smoking causes lung cancer).

Chemical transport models (CTMs) consist of mathematical representations of the relevant physical and chemical atmospheric processes, which are solved using numerical algorithms to obtain pollutant concentrations as a function of space and time for a given set of pollutant emissions and meteorological conditions.

Chronic obstructive pulmonary disease (COPD), including chronic bronchitis and emphysema, is a lung disease characterized by chronic obstruction of lung airflow that interferes with normal breathing and is not fully reversible.

Years of healthy life lost to premature (early) death and disability (illness). DALYs are the sum of years of life lost (YLLs) and years lived with disability (YLDs). Simply expressed, one DALY is equal to one healthy year of life lost. (DALYs are higher when young people die compared with when old people die, because young people still had many years ahead of them.)

The ratio of disability-adjusted life-years (DALYs) to the population (number of people) of a particular area during a particular period of time. It is calculated in the GBD project as the number of DALYs per 100,000 people per year.

The ratio of deaths to the population (number of people) of a particular area during a particular period of time. It is calculated as the number of deaths per 100,000 people per year.

Diabetes is a chronic disease caused by the inherited and/or acquired deficiency in production of insulin by the pancreas or by the ineffectiveness of the insulin produced. Such a deficiency results in increased concentrations of glucose in the blood, which in turn damage many of the body’s systems, in particular the blood vessels and nerves. The most common types of diabetes are type 1, type 2, and gestational diabetes. Air pollution burden is estimated for type 2 diabetes.

Global regions used in the IHME analysis: Asia, Africa, America, and Europe.

Groups of countries that are geographically close and epidemiologically similar, as defined in the Global Burden of Disease (GBD) project. The “High-income North America GBD region,” for example, contains Canada and the United States of America, while the “South Asia GBD region” contains Bangladesh, Bhutan, India, Nepal, and Pakistan. See GBD regions.

Global Burden of Disease (GBD) regions are grouped into seven super-regions that exhibit similar cause-of-death patterns. The “Latin America and Caribbean super-region,” for example, contains the Caribbean, Central Latin America, Tropical Latin America, and Andean Latin America regions.

The seven super-regions are: High income; Latin America & Caribbean; Sub-Saharan Africa; North Africa & Middle East; South East Asia, East Asia & Oceania; South Asia; Central Europe, Eastern Europe & Central Asia. 

Household air pollution is a mixture of particles and gases resulting from incomplete combustion of fuels used in the home for heating and cooking. The GBD focuses on use of solid fuels (coal/ charcoal, wood, dung, agricultural residue). In many locations, HAP is also a key contributor to ambient air pollution, potentially affecting public health more broadly on national and regional spatial scales.

Ischemic heart diseases refer to heart problems caused by narrowed heart arteries. When arteries are narrowed, less blood and oxygen reach the heart muscle. Also called coronary artery disease and coronary heart disease, ischemic heart diseases can ultimately lead to a heart attack.

A statistical estimate of the expected lifespan of an individual based on a person’s year of birth, current age, and demographic factors such as sex and location, assuming that current mortality rates hold indefinitely into the future

Cancer is a disease in which cells in the body grow out of control. When cancer starts in the lungs, it is called lung cancer. Unlike normal cells, cancer cells grow without order or control, destroying the healthy lung tissue around them.

A diseased state, ill health.

The number of deaths in a given time or place.

Nitrogen dioxide. This gaseous pollutant belongs to a group of highly reactive gases known as nitrogen oxides (NOx). NO₂ is often measured as a marker for this group and for the broader traffic-related air pollution mixture.

Ozone is a gas made up of 3 oxygen atoms; it has the chemical formula O₃. Ozone found at ground level, where people live and breathe, is formed by chemical reactions between nitrogen oxides and volatile organic compounds in the presence of sunlight.  For this project, ozone levels are measured in units of parts per billion (ppb) by volume. Ozone concentrations, averaged over the summer season in each region when ozone levels tend to be highest, are used to represent the exposures experienced by human populations in those regions. 

Particulate matter less than or equal to 2.5 µm (micrometers) in aerodynamic diameter. PM_2.5 is measured in units of micrograms per cubic meter (µg/m³).

Instead of calculating average air pollution levels where all areas receive equal weight, as is typically done, population-weighted averages give weight to the areas in proportion to their population, so that greater weight is given to exposures in areas where the most people live.

Any chemical that contributes to the formation of another compound or species (e.g. ozone or PM_2.5). For example, nitrogen oxides (NO_x), sulfur oxides (SO_x), volatile organic compounds (VOCs), and ammonia (NH₃) are all precursors for the formation of PM_2.5 in the atmosphere.

Dying earlier than expected when compared to a full life expectancy. It may be characterized in numbers of deaths or as years of life lost.

Potentially modifiable causes of disease and injury. (For example, smoking is a risk factor for lung cancer. People who stop smoking reduce their risk of getting lung cancer.)

A number that identifies where countries or other geographical areas sit on the spectrum of development. Expressed on a scale of 0 to 1, SDI combines rankings of (1) the incomes per capita (how much money people earn on average), (2) average educational attainment (how many people have completed high school or university), and (3) fertility rates (how many women give birth) of all areas in the GBD study. Health outcomes are closely tied to this measure. See GBD Socio-Demographic Income regions.

A stroke occurs when the blood supply to part of the brain is suddenly interrupted or when a blood vessel in the brain bursts, spilling blood into the spaces surrounding brain cells. Brain cells die when they no longer receive oxygen and nutrients from the blood or there is sudden bleeding into or around the brain.

A range of values that reflects the “certainty” of an estimate (calculated number). Larger uncertainty intervals can result from limited data availability, small studies, and conflicting data (indicating scientists are less certain that the data are accurate). Smaller uncertainty intervals can result from extensive data availability, large studies, and data that are consistent across sources (indicating scientists are more certain that the data are accurate).

In State of Global Air, estimates of scientific uncertainty are provided for every value in the form of 95% uncertainty intervals (UIs), representing the range between the 2.5^th and 97.5^th percentiles of the distribution of possible values.

Guideline set by the World Health Organization for exposure to fine particle (PM_2.5) ozone, and nitrogen dioxide (NO₂), based on evidence of the health effects of long-term exposure to these pollutants. The guideline is set at an annual average concentration of 5 µg/m³ for PM_2.5 , 60 µg/m³ , and 10 µg/m³ for NO₂ (based on data averaged over one year). Learn more. 

• Four interim air quality targets (IT) set by the World Health Organization for annual average fine particle (PM_2.5) concentrations (based on data averaged over one year): IT-1 ≤ 35 µg/m³; IT-2 ≤ 25 µg/m³; IT-3 ≤ 15 µg/m³; and IT-4 ≤ 10 µg/m³.
   
• Three interim air quality targets set by the World Health Organization for annual average nitrogen dioxide (NO₂) concentrations (based on data averaged over one year): IT-1 ≤ 40 µg/m³; IT-2 ≤ 30 µg/m³; and IT-3 ≤ 20 µg/m³.
   
• Two interim air quality targets set by the World Health Organization for annual average nitrogen dioxide (NO₂) concentrations (daily maximum 8-hour mean ozone concentration in the six consecutive months with the highest six-month running-average ozone concentration): IT-1 ≤ 100 µg/m³ and IT-2 ≤ 70 µg/m³.
   

Groupings of countries used by the World Health Organization: African region (AFRO), European region (EURO), Region of the Americas (PAHO), South-East Asian Region (SEARO), Western Pacific Region (WPRO), and Eastern Mediterranean Region (EMRO). 

Groupings of countries used by the World Bank based on income levels: High Income, Upper Middle Income, Lower Middle Income, and Low Income. 

Groupings of countries used by the World Bank: South Asia, East Asia and Pacific, Europe and Central Asia, Latin America and Caribbean, Middle East and North Africa, Africa. See World Bank.

Years lived in less-than-ideal health. This includes health loss (illness) that may last for only a few days (for example, due to influenza), or for a lifetime (for example, reduced lung function due to asthma).

Years of life lost attributable to premature mortality (people dying before their time due to some risk factor).