Source: WHO. Country groupings. Click to enlarge.

In the past two years, the database—now covering 3,000 cities in 103 countries—has nearly doubled, with more cities measuring air pollution levels and recognizing the associated health impacts.

As urban air quality declines, the risk of stroke, heart disease, lung cancer, and chronic and acute respiratory diseases, including asthma, increases for the people who live in them.

Global urban air pollution trends. WHO was able to compare a total of 795 cities in 67 countries for levels of small and fine particulate matter (PM₁₀ and PM_2.5) during the five-year period, 2008-2013. PM₁₀ and PM_2.5 include pollutants such as sulfate, nitrates and black carbon, which penetrate deep into the lungs and into the cardiovascular system, posing the greatest risks to human health. Data was then analysed to develop regional trends.

Key trends from 2008-2013:

• Global urban air pollution levels increased by 8%, despite improvements in some regions.

• In general, urban air pollution levels were lowest in high-income countries, with lower levels most prevalent in Europe, the Americas, and the Western Pacific Region.

• The highest urban air pollution levels were experienced in low-and middle-income countries in WHO’s Eastern Mediterranean and South-East Asia Regions, with annual mean levels often exceeding 5-10 times WHO limits, followed by low-income cities in the Western Pacific Region.

• In the Eastern Mediterranean and South-East Asia Regions and low-income countries in the Western Pacific Region, levels of urban air pollution has increased by more than 5% in more than two-thirds of the cities.

• In the African Region urban air pollution data remains very sparse, however available data revealed particulate matter (PM) levels above the median. The database now contains PM measurements for more than twice as many cities than previous versions.

Most sources of urban outdoor air pollution are well beyond the control of individuals and require action by cities, as well as national and international policymakers to promote cleaner transport, more efficient energy production and waste management, WHO said.

More than half of the monitored cities in high-income countries and more than one-third in low- and middle-income countries reduced their air pollution levels by more than 5% in five years.

During the World Health Assembly, 23-28 May, Member States will discuss a road map for an enhanced global response to the adverse health effects of air pollution.

WHO’s Air Quality Guidelines offer global guidance on thresholds and limits for key air pollutants that pose health risks. The Guidelines indicate that by reducing particulate matter (PM₁₀) pollution from 70 to 20 micrograms per cubic meter (μg/m), air pollution-related deaths could be reduced by roughly 15%.

The WHO urban air quality database builds on well-established, public air quality monitoring systems as a source of reliable data in different parts of the world.

The primary source of data include official reporting from countries to WHO, and official national and sub-national reports and web sites containing measurements of PM₁₀ or PM_2.5. Measurements reported by the following regional networks were used: the Clean Air Asia for Asia and the European Environment Agency for Europe’s Air Quality e-Reporting database. In the absence of data from the previous sources, data from UN and development agencies, peer-reviewed journal articles and ground measurements compiled in the framework of the Global Burden of Disease project were used.

Annual mean concentrations of particulate matter (PM₁₀ and/or PM_2.5) based on daily measurements, or data which could be aggregated into annual means, were included in the database. In the absence of annual means measurements covering a more limited period of the year were exceptionally used.