Across the globe, more than 7 billion people (94% of the world’s population) breathe air that exceeds the World Health Organization’s (WHO) air quality guidelines. The levels are considered hazardous for 2.8 billion people, which is estimated to cause millions of deaths annually. Countries in Africa and Asia that are rapidly urbanizing have the highest levels of air pollution, and eight of the top ten countries with the highest levels of fine particulate matter (PM2.5) are in Africa.
The WHO air quality guidelines set thresholds for six pollutants in urban areas. Another indicator in the cities system tracks how many days an average urban area exceeds those thresholds for any one of the six pollutants. Of the six pollutants, PM2.5 poses a great risk to public health because the fine particles can get deep in the lungs and enter the bloodstream, which causes heart disease, strokes and respiratory illnesses.
PM2.5 can come from both primary and secondary sources. Primary sources include forest fires, windblown dust, energy power plants, vehicle exhaust, burning of waste and crops, and industrial processes, whereas secondary sources are chemical reactions between gasses in the atmosphere.
This indicator measures the annual concentrations of PM2.5 in urban areas, in alignment with Sustainable Development Goal indicator 11.6.2. In 2019, the average annual concentration of PM2.5 in urban areas globally was 33.1 micrograms per cubic meter (μg/m3). This data is weighted by population, meaning that a greater weight is assigned to air pollution experienced where more people live, which provides a better estimate of population exposures.
Between 2010 and 2013, the average annual concentrations increased, peaking in 2013 at 42.3 μg/m3. Since 2013, the concentrations have declined every year globally, so this indicator is headed in the right direction. However, concentrations have not declined in every region, with increases in Africa and the Middle East between 2010 and 2019. For example, concentrations increased in Sub-Saharan Africa from 33.9 μg/m3 in 2010 to 35.4 μg/m3 in 2019.
To reduce health risks, PM2.5 concentrations need to continue to decline globally, and start to decline in areas where it is currently increasing.