Two Indian cities — Delhi and Kolkata — have have topped the charts of the world's most polluted cities in the latest report on global air pollution. Mumbai has been ranked 14th according to the report released by the State of Global Air. India, in fact, is home to 18 of the 20 cities with the most severe increase in PM2.5 pollution from 2010 to 2019. The latest State of Global Air Report is part of an initiative on air quality between the Health Effects Insitute and the Institute for Health Metrics and Evaluation, with inputs from the University of British Columbia.
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Meanwhile, cities where residents are exposed to PM2.5 levels that are "several-fold higher than the global averages" include Karachi, Dhaka, Beijing and Singapore.
Data from India and Indonesia show a worrisome spike in PM2.5 pollution, while China has seen the greatest improvements. The report focused on two major pollutants-- fine particulate matter (PM2.5) & nitrogen dioxide (NO2) with its focus on cities. The SoGA said that their focus was on urban areas since it is being estimated that by 2050 "almost 68% of the world's population will be living in cities and breathing urban air."
PM2.5 is highest in developing nations
The report also found that the pattern of ambient pollution was higher in developing nations. "South Asia, West Sub-Saharan Africa, and East Asia cities reported PM2.5 exposure higher than the least stringent WHO interim target (35 µg/m3)
," the report said. Cities in East Asia, South Asia, Southeast Asia, Central Asia, Middle East, North Africa and Central Europe witnessed death rates higher than the global urban median of 58 deaths/100,000 people.
Death rates of the 20 populous cities — such as Delhi, Kolkata, Mumbai, Dhaka, and Karachi— with the highest PM2.5-related death rates ranged from 77 deaths/100,000 people to 124 deaths/100,000 people.
Airborne particles measuring 2.5 µm or less in aerodynamic diameter constitute the ambient (outdoor) fine particle air pollution (PM2.5). This is caused by activities like household
burning, energy production and use, industrial activities, vehicles,
and other sources. Exposure to PM2.5 can result in heart, lung and other types of diseases, the report said.
A Lancet study published indicated that air pollution claimed 1.6 million lives in India in 2019. "The death rate due to household air pollution decreased by 64·2% from 1990 to 2019, while that due to ambient particulate matter pollution increased by 115·3% and that due to ambient ozone pollution increased by 139·2%," the report published in May this year said.
NO2 is also a cause for concern
Another pollutant that has been a cause of concern, particularly in urban areas is Nitrogen dioxide (NO2). The gaseous pollutant is a key marker of traffic-related air pollution. Beirut in Lebanon, Shenyang and Shanghai in China and Moscow in Russia, had NO2 levels exceeding even the least stringent WHO interim target of 40 µg/m3, the report said. These cities collectively are home to over 53 million people.
Suva in Fiji, Karangasem in Indonesia and Mtwapa in Kenya are among the cities that met WHO guidelines for NO2. Like them, most cities that meet the WHO mandated levels are located on the coast.
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"NO2 is particularly abundant in cities and urban areas," the report said, adding that the combustion of fossil fuels in vehicles, energy production, and industries is the leading source of NO2.
Exposure to NO2 is known to cause health conditions like asthma in children and adults and has been linked with a greater risk of hospitalisation among people with asthma. NO2 levels are high in large cities across countries of all income levels, the report said.
Lack of data
There has been lack of data and monitoring systems in most of the cities grappling with high rates of air pollution. The report said that of the 20 cities with steepest rise in PM2.5 exposures, only two (Satna and Varanasi in India) have an "official monitoring station at ground level". "This fact points to the need for improved local air quality monitoring infrastructure worldwide," the report added.
WHO's air quality guidelines
In September 2021, the World Health Organisation issued guidelines on new air quality levels to "protect the health of populations, by reducing levels of key air pollutants, some of which also contribute to climate change." The WHO noted that every year air pollution causes 7 million premature deaths. The WHO said the annual average for PM 2.5 should not exceed 5 micrograms per cubic metre of air.
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"Air pollution is a threat to health in all countries, but it hits people in low- and middle-income countries the hardest," WHO's Director-General, Dr Tedros Adhanom Ghebreyesus, said then.
"WHO's new Air Quality Guidelines are an evidence-based and practical tool for improving the quality of the air on which all life depends. I urge all countries and all those fighting to protect our environment to put them to use to reduce suffering and save lives," he said.