CORRESPONDENCE
26 October 2021

Air quality: WHO guidelines could deepen inequities

Forrest Lacey
1. National Center for Atmospheric Research, Boulder, Colorado, USA.
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Rajesh Kumar
1. National Center for Atmospheric Research, Boulder, Colorado, USA.
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Gabriele Pfister
1. National Center for Atmospheric Research, Boulder, Colorado, USA.
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Jean-Francois Lamarque
1. National Center for Atmospheric Research, Boulder, Colorado, USA.
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Cassandra O’Lenick
1. National Center for Atmospheric Research, Boulder, Colorado, USA.
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Guy Brasseur
1. Max Planck Institute for Meteorology, Hamburg, Germany.
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To curb the effects of anthropogenic air pollution on health, the World Health Organization (WHO) has halved its recommended limit for the annual average concentration of fine particulate matter (PM_2.5) to 5 micrograms per cubic metre. Given that 99% of the world’s population is living in areas where such small particulates exceed the WHO’s latest threshold, the contribution from natural sources of PM_2.5 — suspended atmospheric dust, for example — needs to be determined to help countries meet the guidelines.