WHO air quality guidelines (updated)

Many guidelines regulate how to measure air pollution and control air quality in the world today. A prevailing one remains that set by the World Health Organization (WHO). The WHO air quality guidelines serve as a reference standard from which many cities manage the air pollution policies in its region. It includes guidelines that help policymakers around the globe set standards regarding air quality and how it affects the health of the residents.

Air pollution has dreaded many health conditions and has impacted many lives across the world. As of 2016, it was recorded that it has caused an estimate of about 4.2 million (premature) deaths. This mortality rate was caused by constant exposure to particulate matter of 2.5 (PM2.5) microns or smaller in diameter. Hence, WHO’s guideline remains an essential tool to set a significant standard to protect lives that may be lost from uncontrolled exposure to poor quality outdoor air.

In 2005, the WHO guidelines stated that exposure to PM2.5 (which causes cardiovascular and chronic respiratory) conditions shouldn’t exceed an average of 10µg/m3 annually, and 25µg/m3 daily (not more than three times a year). This particulate matter concentration varies from country to country; however, it remains comparable to the standard of WHO. The general guidelines set by WHO were grounded solely on air quality measurement and evaluation based on; Particulate matter (PM), Nitrogen dioxide (NO2), Ozone (O3), and Sulfur dioxide (SO2). Now the new guidelines (2021) have nearly all pollutant standards being strengthened in comparison to the air quality guidelines established in 2005. The new guidelines (2021) recommend air quality levels for 6 pollutants, where evidence has advanced the most on health effects from exposure. These classical pollutants are particulate matter (PM), ozone (O₃), nitrogen dioxide (NO₂) sulfur dioxide (SO₂) and carbon monoxide (CO). Each pollutant received a recommended AQG level based on an average time, typically annually or over a 24-hour period.



What is Particulate Matter (PM) in air pollution ?

Here’s a pollutant-by-pollutant look:

Particulate matter

Particulate matter is a universal indicator for outdoor air pollution. It has a more deadly impact on the health of people than any other air pollutant. Ranging from cardiovascular impairments to pulmonary disorders, particulate matter has put people at risk of mortality over the years by penetrating the lungs and entering the blood. The major constituents of particulate matter include nitrates, sulfates, sodium chloride, mineral dust, ammonia, water, and black carbon. It is made up of a mixture of solid and liquid pollutants suspended in the air.

The particles are either ≤PM10 (meaning it has a diameter of 10 microns or less) or PM2.5, meaning the particles have a diameter of 2.5 or smaller. PM2.5 is even riskier to the health as it can cause lung cancer once it penetrates the lung barrier. In 2005, the highest recommended average annual emission level for PM2.5 was 10 μg/m3. The 2021 revision halves that number, to just 5 μg/m3. The 24-hour level changed from 25 μg/m3 in 2005 to 15 μg/m3.

Adverse effects on health

Chronic exposure to a high concentration of small particulate matter (PM 2.5 and PM10) has adversely increased mortality and morbidity. This means that if the exposure is controlled, there will be a decrease in mortality over time. During air quality evaluation to reduce outdoor air pollution, these particulates will need to be considered. WHO specifically included this in its guidelines and limits, which will help achieve minimum exposure to PM.

Nitrogen dioxide (NO2)

Nitrogen dioxide is also a common air pollutant as it is a toxic gas that can cause inflammations to the airways after uncontrolled exposure. To make it even more health-damaging, it is a significant constituent of PM2.5, which is even riskier. Essential sources of NO2 in the air include gaseous emissions from industrial processes such as combustion, petrol generators, engines, and vehicles. NO2 can trigger asthmatic attacks and bronchitis. WHO guidelines were sharply revised from 40 to just 10 μg/m3 on average annually. A new standard level of 25 μg/m3 on average per 24-hour period was also recommended.

Ozone (O3)

Ozone at ground level isn’t the same as that in the atmosphere. It is formed from photochemical reactions with NO and other VOCs. This means that ozone concentration increases during sunny periods. Excess ozone in the atmosphere can cause lung disorders, asthmatic attacks, and other respiratory problems. In 2021 it was established a recommended AQG level of 60 μg/m3 during peak season.

Sulfur dioxide (SO2)

SO2 has an awful odor, but it is colorless. It is produced from burning fossil fuels and smelting ores that have sulfur components. It also has adverse impacts on health by declining lungs and respiratory tracts functions. The WHO’s sulfur dioxide recommendations were to raise the level from 20 μg/m3 to 40 μg/m3 in a 24-hour period

Carbon monoxide

The recommended level of 4 mg/m3 averaged over a 24-hour period is new to the 2021 guidelines.

To maintain excellent air quality in countries, all guidelines must be strictly adhered to. The policymakers must also handle the evaluation of all policies and standards.


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