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Pollutants are increasing in some of the world's most polluted cities

Unexpected air pollutants are on the rise in cities across India, according to a study led by the University of Birmingham. The researchers determined that fine particle pollution (PM2.5) and nitrogen dioxide (NO2) are increasing in Kanpur and Delhi.

“We wanted to demonstrate the utility of satellite observations to monitor city-wide air pollution in the UK where ground-based measurements are in abundance and in India where they are not,” said study lead author Karn Vohra.

“Our approach will be able to provide useful information about air quality trends in cities with limited surface monitoring capabilities. This is critical as the WHO estimates that outdoor air pollution causes 4.2 million deaths a year.”

The experts analyzed data from satellites which monitor the global sky on a daily basis. According to Dr. Eloise Marais of UCL, there is more than a decade of freely available observations from instruments in space to monitor and assess air quality in cities throughout the world. 

“Greater use of these in the UK, India, and beyond is paramount to successful air quality policies,” said Dr. Marais.

The researchers set out to estimate trends in a range of air pollutants in the UK and India from 2005 to 2018. The study period coincided with well-established air quality policies in the UK, and with rapid development in India.

In 2018, the World Health Organization ranked Kanpur as the most polluted city in the world. The researchers believe that the rising levels of PM2.5 and NO2 in Kanpur and Delhi are tied to increasing vehicle ownership, industrialization, and the limited effect of air pollution policies. 

Meanwhile, in London and Birmingham, the team found moderate yet continuous declines in PM2.5 and NOx, which reflect the effectiveness of policies that have been established in the UK to the target sources of these pollutants.

Furthermore, the team discovered that formaldehyde increased in Delhi, Kanpur, and London over the course of the study period. Formaldehyde is associated with sources such as industrial emissions and fuel combustion from traffic.

“We were surprised to see the increase in formaldehyde above Delhi, Kanpur and London – a clue that emissions of other volatile organic compounds may be changing, potentially driven by economic development and changes in domestic behavior,” said study co-author Professor William Bloss.

“Our results emphasise the need to monitor our air for the unexpected, and the importance of ongoing enforcement of measures for cleaner air.”

The study is published in the journal Atmospheric Chemistry and Physics.

By Chrissy Sexton, Staff Writer

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