The Hindu Explains | WHO updates emission recommendations

Why has the World Health Organisation (WHO) updated emission recommendations?

The WHO has updated global air pollution standards, a first since 2005. The update, in most instances, reduces the maximum permissible limits for several classes of pollutants from nitrous oxide to particulate matter (PM). This is to recognise the research in the last decade and a half that shows air pollution to be much more strongly linked to poor health than previously recognised. Since 1987, the world body has periodically issued health-based air quality guidelines to assist governments and civil society to reduce human exposure to air pollution and its adverse effects.

In 2015, the World Health Assembly adopted a resolution on air quality and health, recognising air pollution as a risk factor for non-communicable diseases such as ischaemic heart disease, stroke, chronic obstructive pulmonary disease, asthma and cancer, and the economic toll they take. “The global nature of the challenge calls for an enhanced global response. These guidelines, taking into account the latest body of evidence on the health impacts of different air pollutants, are a key step in that global response,” says WHO Director General, Tedros Adhanom Ghebreyesus.

What are the recommendations?

The existing ceiling of annual PM2.5, or particles of diameter up to 2.5 micron, as per the 2005 standards, which is what countries now follow, is 10 microgram per cubic metre. That has now been halved to five microgram per cubic metre.

The upper limit for PM2.5, for a 24-hour period is now 25 micrograms. As per the new guidelines it has been cut down to 15. The PM10, or PM of size exceeding 10 microgram, upper limit is 20 microgram and has now been revised to 15, whereas the 24-hour value has been revised from 50 to 45 microgram. There are also standards for a host of chemical pollutants, including sulphur dioxide, lead and nitrogen dioxide, ozone and carbon monoxide.

How are these new values calculated?

Committees of the WHO assessed the latest evidence on what levels of exposure certain pollutants were linked, in the published scientific literature, to health risks. Then they assessed the evidence for how much a reduction to a specific pollutant improved health. They did that for each of the selected pollutants, They compared the guideline levels of a specific pollutant across critical health outcomes and took as the final AQG (Air Quality Guidelines) level the lowest AQG level found for any of the critical health outcomes. They also finally assessed to what degree of confidence was a specific pollutant linked to a specific outcome. The bulk of the exercise lay in scanning through the vast scientific literature and deciding how many studies definitely proved a greater link between exposure to a pollutant and deteriorating health.

What do these numbers mean for India?

India’s National Ambient Air Quality standards — last revised in 2009 — specify an annual limit of 60 microgram per cubic metre for PM10 and 100 for a 24 hour period. Similarly it’s 40 for PM2.5 annually and 60 on a 24-hour period. India is thus far from meeting even the existing guidelines. The WHO guidelines also propose interim targets that can be met en route to achieving the final target. The aim of these revised numbers, which are aspirational, is for policy-makers around the world to use these guidelines to inform evidence-based legislation and policies to improve air quality and reduce the unacceptable health burden that results from air pollution. As part of improving air quality standards, India has ongoing a National Clean Air Programme that aims for a 20% to 30% reduction in PM concentrations by 2024 in 124 cities. keeping 2017 as the base year for the comparison of concentration.

How do cities in India and globally stack up?

Environmental organisation Greenpeace said in a statement that the new guidelines meant that among100 global cities, Delhi’s annual PM2.5 trends in 2020 was 16.8 times more than WHO’s revised air quality guidelines, while Mumbai’s exceeded 8-fold, Kolkata 9.4, Chennai 5.4, Hyderabad 7 fold and Ahmedabad exceeded 9.8 fold.

In comparison, Tokyo exceeded the levels by two times, New York by 1.4 times, Shanghai by 6.4 fold and Lahore by 15.8 times

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