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WHO releases new Global Air Quality Guidelines

23 September 2021

The World Health Organization (WHO) released a new update of their global air quality guidelines (AQG)—for the first time since 2005—tightening most of the AQG levels.

Since the 2005 AQG update, there has been a marked increase of evidence that shows how air pollution affects different aspects of health, the WHO said. For that reason, WHO has adjusted almost all the AQGs levels downwards, warning that exceeding the new air quality guideline levels is associated with significant risks to health.

The WHO estimates that exposure to air pollution causes 7 million premature deaths per year and results in the loss of millions more healthy years of life. In children, this could include reduced lung growth and function, respiratory infections and aggravated asthma. In adults, ischaemic heart disease and stroke are the most common causes of premature death attributable to outdoor air pollution, and evidence is also emerging of other effects such as diabetes and neurodegenerative conditions. This puts the burden of disease attributable to air pollution on a par with other major global health risks such as unhealthy diet and tobacco smoking, the WHO said in a press release.

The WHO’s guidelines recommend air quality levels for 6 pollutants, where evidence has advanced the most on health effects from exposure. These so-called classical pollutants include particulate matter (PM), ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2), and carbon monoxide (CO).

WHO 2021 and 2005 air quality guidelines
PollutantAveraging time2005 AQGs2021 AQGs
PM2.5, µg/m3Annual105
24 houra2515
PM10, µg/m3Annual2015
24 houra5045
O3, µg/m3Peak seasonb-60
8 houra100100
NO2, µg/m3Annual4010
24 houra-25
SO2, µg/m324 houra2040
CO, mg/m3 24 houra-4
a 99th percentile (i.e., 3–4 exceedance days per year).
b Average of daily maximum 8-hour mean O3 concentration in the six consecutive months with the highest six-month running-average O3 concentration.

The health risks associated with particulate matter equal or smaller than 10 and 2.5 µm in diameter (PM10 and PM2.5, respectively) are of particular public health relevance. PM is primarily generated by fuel combustion in different sectors, including transport, energy, households, industry, and from agriculture. In 2013, outdoor air pollution and particulate matter were classified as carcinogenic by WHO’s International Agency for Research on Cancer (IARC).

The guidelines also highlight good practices for the management of certain types of particulate matter (for example, black carbon/elemental carbon, ultrafine particles, particles originating from sand and dust storms) for which there is currently insufficient quantitative evidence to set air quality guideline levels.

“Air pollution is a threat to health in all countries, but it hits people in low- and middle-income countries the hardest,” said WHO Director-General, Tedros Ghebreyesus. “WHO’s new Air Quality Guidelines are an evidence-based and practical tool for improving the quality of the air on which all life depends. I urge all countries and all those fighting to protect our environment to put them to use to reduce suffering and save lives.”

Disparities in air pollution exposure are increasing worldwide, particularly as low- and middle-income countries are experiencing growing levels of air pollution because of large-scale urbanization and economic development that has largely relied on the burning of fossil fuels.

In 2019, more than 90% of the global population lived in areas where concentrations exceeded the 2005 WHO air quality guideline for long term exposure to PM2.5. Almost 80% of deaths related to PM2.5 could be avoided in the world if the current air pollution levels were reduced to those proposed in the updated guideline, according to an analysis performed by WHO.

Whilst not legally-binding, the AQGs are a tool for policy-makers to guide legislation and policies, in order to reduce levels of air pollutants and decrease the burden of disease that results from exposure to air pollution worldwide.

Source: WHO