WHO revises global air quality: Basics Explained

The World Health Organisation (WHO), last month, released a revised Global Air Quality Guidelines, announcing more stringent limits for six pollutant categories —particulate matter (PM), ozone (O3), nitrogen dioxide (NO2) sulfur dioxide (SO2), and carbon monoxide (CO).

The latest WHO guidelines provide clear evidence of the damage air pollution inflicts on human health, at even lower concentrations than previously understood. The guidelines recommend new air quality levels to protect the health of populations, by reducing levels of key air pollutants, some of which also contribute to climate change.

The WHO’s revised guidelines prescribe annual PM2.5 average at 5 ug/m3, bringing it down from 2005 limits set at 10 ug/m3. PM10 annual average is now 15 ug/m3 in comparison to the earlier norm of 20 ug/m3. NO2 levels, which are primarily attributable to vehicular emissions, have been revised to 10 ug/m3, in comparison to 40 ug/m3 in 2005.

WHO Director-General Tedros Adhanom Ghebreyesus


PM2.5 means particulate matter in the air – caused by motor exhaust or anything combustible – that is less than 2.5 micrometers.

         Airborne particles are sometimes referred to as ‘particulate matter’ or ‘PM. They include dust, dirt, soot, smoke, and liquid droplets. Some particles are emitted directly into the air from a variety of sources that are either natural or related to human activity. Natural sources include bushfires, dust storms, pollens and sea spray.

           Those related to human activity include motor vehicle emissions, industrial processes (eg electricity generation, incinerators and stone crushing), unpaved roads and wood heaters.

Particles can be classified on the basis of their size, referred to as their ‘aerodynamic diameter’. ‘Coarse particles’ are those between 10 and 2.5 micrometres (µm) in diameter; ‘fine particles’ are smaller than 2.5 µm; and ‘ultrafine particles’ are smaller than 0.1 µm. Studies have linked exposure to particle pollution to a number of health problems including respiratory illnesses (such as asthma and bronchitis) and cardiovascular disease.


India has set standards for what it thinks are appropriate warnings for a particular level of pollutant. Air Quality Index(AQI) help in comparing pollution levels at a glance with a color code and a numerical value. In India, AQIs are determined based on the concentrations of pollutants, including PM2.5 (fine, respirable particles), sulphur dioxide (SO2), nitrogen dioxide (NO2) and carbon monoxide (CO).There are six AQI categories, namely: Good, Satisfactory, Moderately polluted, Poor, Very poor and Severe.

                    The Index is centered around five chief pollutants – Particulate Matter with a diameter less than 10 micrometers (PM10), Particulate Matter with a diameter of less than 2.5 micrometers (PM2.5), ozone (O3), Nitrogen Dioxide (NO2), and Carbon Monoxide (CO).


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