Delhi’s PM2.5 levels remained more than twice the safe standards over the past 2 decades: Study

A joint study by IIT-Delhi and TERI showed that for 18 years, the annual average of PM2.5 levels in Delhi were more than double the safe limit.

Over the past two decades almost, the average level of PM2.5 – pollutants that can penetrate deep inside the lungs – in Delhi has remained more than two times above the annual permissible limits, says a new study by researchers from Indian Institute of Technology, Delhi and TERI.

A toxic haze engulfed Delhi for more than a week in November 2017.(HT File Photo)

While annual permissible limit of PM2.5 is 40ug/m3 according to the National Ambient Air Quality Standards, the average level of PM2.5 in Delhi has been 97.4ug/m3 between 1998 and 2005, which is more than two times the safe limit.

Delhi has been ranked the most polluted city in the world by the World Health Organization(WHO) based on the air quality data for megacities with a population of 14 million or more

The situation in the satellite towns of Faridabad, Gurgaon, Ghaziabad and Noida has been equally worse. The average level of PM2.5 in Noida was recorded to be 103.4ug/m3, which was the highest among NCR towns. Ghaziabad stands second with 101ug/m3 followed by Delhi.

“As PM2.5 measurement in India, following international protocols in a systematic manner started in 2008-2009 and there was a lack of data prior to 2012, we had to rely on satellite data. Satellite data on aerosol pollution can give us an idea of PM2.5 concentrations and exposure,” said Sagnik Dey, associate professor at Centre for Atmospheric Sciences in IIT Delhi, who lead the four-member research team.

The study titled ’18-year Ambient PM2.5 Exposure and Night Light Trends in India Cities’ has been published in the Aerosol and Air Quality Research, an international peer reviewed journal.

Hindustan Times had earlier reported that in 2016 and 2017 the average annual pollution levels (PM10 and PM2.5) in Delhi, and its satellite towns remained at least three to four times above the annual permissible limits. In 2016 a report by the World Health Organization (WHO) had stated that Delhi was the most polluted megacity in the world, followed by Cairo and Dhaka, as far as PM10 pollution was considered.

The study takes into account PM2.5 exposure and its 18-year trend (1998 – 2015) in 109 cities across India using satellite data. The researchers have categorised the cities into six classes according to their vulnerability.

“Even though Delhi is touted as one of the most polluted cities in the world, it doesn’t belong to the highest vulnerability class because of better healthcare access,” he added.

Instead, cities in UP and Bihar with annual PM2.5 exposures lower than that of Delhi, are categorised as extremely vulnerable due to combination of factors such as wide PM2.5 exposure, a high increasing trend in annual PM2.5 exposure, high population density and high baseline mortality for all diseases.

The study has warned that there are many cities where pollution is increasing faster than Delhi and NCR towns. If steps are not taken to control pollution levels in these cities it would create a Delhi-like situation.