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What are global air quality standards?
The WHO standard for PM2.5 is 10 μg/m3 annual average, and 25 μg/m3 24-hour average.
The World Health Organization (WHO) Air Quality Guidelines are the only truly global air quality standards. The WHO guidelines suggest standards and targets on air pollutants that pose health risks to humans, and act as a reference for individual countries to set their own standards. The guidelines were first published in 1987 and revised in 1997 and 2005. Each update reflects the latest scientific assessment of the health impact of air pollution.
The guidelines are intended for worldwide use, but the WHO acknowledges that countries will set their own standards based on balancing health risks, technological feasibility, economic considerations, and socio-political factors.
Air quality measurements are generally based on daily mean concentrations of particulate matter (PM) per cubic metre of air volume (m3). These concentrations are measured in micrograms per cubic metre (μg/m3). Two kinds of PM are measured: PM10 and PM2.5. PM10 is easier to measure because the particles are larger – they have a diameter of 10 microns or less – while PM2.5 particles are much smaller, with a diameter of 2.5 microns or less.
WHO guidelines measure 5 key pollutants
The WHO Air Quality Guidelines set guidelines for five types of key air pollutants: PM10, PM2.5, ozone, nitrogen dioxide, and sulphur dioxide. The guidelines are as follows, and can be used as a reference point for national standards and targets:
PM2.5: 10 μg/m3 annual average, and 25 μg/m3 24-hour average.
PM10: 20 μg/m3 annual average, and 50 μg/m3 24-hour average.
Ozone (O3): 100 μg/m3 8-hour average.
Nitrogen dioxide (NO3): 40 μg/m3 annual average, and 200 μg/m3 1-hour average.
Sulphur dioxide (SO2): 20 μg/m3 24-hour average, and 500 μg/m3 10-minute average.
These guidelines help us measure whether our air is healthy or unhealthy. If the average amount of particles is higher than the guidelines, the air is considered polluted. For example, if a city’s PM2.5 levels are higher than 25 μg/m3 over a 24-hour period, that city’s air is dangerous for humans to breathe. Achieving the guidelines set by the WHO would mean that the health effect of air pollution is significantly reduced.
Other global reference points for air quality standards include the European Union, Australia, Canada, the United States, Japan, China, and Switzerland, although some of these standards have been subjected to increasing scrutiny in recent years due to being too weak.
The WHO strongly suggests that the highest priority for air pollution monitoring is PM2.5. This is because it is a key contaminant that dramatically influences air quality and its impact on our health.