Nobody really knows which is the most polluted city in the world

A lack of data on PM 2.5 concentrations cripples research on air pollution

air-pollution-woman-mask-walking-shut Representative image | Shutterstock

Do you feel confused when you see a ranking of the most polluted cities on the planet? Such rankings could actually be misleading, according to an analysis by researchers from the Washington University in St Louis.

According to the study, there is no data on which city has the highest concentration of PM 2.5 — fine particulate matter that is 2.5 microns or less in size — with most countries lacking monitoring of the same.

Despite growing insights in recent years on the adverse health consequences of air pollution, the lack of sufficient infrastructure for on-the-ground monitoring cripples researchers in environmental science.

Published in the journal Atmospheric Environment: X, the study highlights the dismal state of PM 2.5 monitoring across the world. With only 24 of 234 countries having more than three monitors per million inhabitants and with 141 having no regular monitoring at all, it is nearly impossible to do a reliable assessment of regional and global PM 2.5 exposure. Using India as a case study, the study points to how there is only one monitor for every 6.8 million people in the country despite 99.9 per cent of the population living in areas with PM 2.5 concentrations above the WHO Interim Target 1 guideline of 35 μg m−3.

Originating from a variety of sources like dust, vehicular emissions and other industrial activities like energy production, construction and mining, they are minuscule enough (the comparison is usually with human hair which is 70 microns in diameter) to easily lodge themselves deep into the lungs and cause heart and respiratory diseases like stroke and lung cancer among others.

According to two 2018 studies, the global mortality from exposure to PM 2.5 was estimated to be between 3-9 million deaths in 2017 alone. The costs of premature deaths due to pollution will increase from $3 trillion in 2015 to $18-25 trillion by 2060, according to the Organisation for Economic Cooperation and Development (OECD).

“The difference between the importance of this measure and the level of ground-based monitoring is shocking” said Randall Martin, corresponding author and professor in the Department of Energy, Environmental&Chemical Engineering in the McKelvey School of Engineering at Washington University in St. Louis. Co-authors include Urvashi Narain from the World Bank Group's Environment and Natural Resources Global Practice and Sagnik Dey from the Centre for Atmospheric Sciences, Indian Institute of Technology, Delhi.

Pointing to how the global mean population distance to the nearest PM 2.5 monitor being 220km makes the areas being monitored too large for any meaningful assessment of PM 2.5 exposure, the researchers propose an integrated monitoring framework consisting of varied monitoring equipment pivoted to areas with a high population density or pollution variability.

Though the researchers acknowledge the significance of ground-based measurements and monitoring, they stress how this needs to be supplemented by “innovative low-cost monitors, mobile monitoring and measurements at different points along the vertical (by aircraft, for example)”, according to the press release.

Apart from the comprehensive picture of air pollution that such a system would yield, researchers say it would also be of help in predicting air quality and consequently improving atmospheric models, especially for researchers like Martin who need accurate data to operate at the junction of remote sensing and global modelling.

“The ability to identify the location of the most polluted city in an indicator of scientific progress. It is important to be able to answer basic questions about something this important. The drive to overcome this challenge, speaks to something fundamental about our knowledge of the world around us,” said Martin.