The world’s biggest cities are suffering from extremely hazardous levels of toxic air, which has killed more than 1.7 million people, according to a worldwide study on urban air pollution.
The latest State of Global Air report, published by US-based research organisation Health Effects Institute (HEI) on Wednesday, covers more than 7,000 cities around the world. It is the first such study to focus only on urban air pollution, as the population in the coming years is expected to be concentrated in urban areas.
The report analysed two major pollutants in the air – the widely talked about fine particulate matter (PM2.5) and the lesser-known nitrogen dioxide – and assessed their impact on public health.
In 2019, as many as 1.7 million deaths linked to PM2.5 exposure occurred in the 7,239 cities included in the analysis, with urban areas in Asia, Africa, and eastern and central Europe seeing the greatest effect on health.
PM2.5 levels continue to be extremely toxic around the world, with cities in south Asia topping the charts of worst air quality once again.
Indian cities Delhi and Kolkata have the highest concentration of PM2.5, followed by Nigeria’s Kano, Lima in Peru and Bangladesh’s capital Dhaka. Four of the 10 cities with the worst levels of fine particulate matter are in South Asia.
Two cities in China, Beijing and Chengdu, saw the highest rate of deaths due to illnesses caused by toxic air. The Chinese capital reported 124 deaths per 100,000 population in 2019 that could be attributed to PM2.5 pollution, while Chengdu reported 118 deaths.
Ukraine’s Kyiv and Kharkiv cities were next, reporting 114 deaths, and were followed by Jakarta. Delhi and Kolkata, meanwhile, reported 106 and 99 deaths and are among the 10 worst affected cities.
According to estimates by the United Nations, almost 68 per cent of the world’s population will live in cities and breathe urban air by 2050. The pace of urbanisation is particularly fast in low- and middle-income countries, where the levels of PM2.5 also remain high.
“As cities around the world rapidly grow, the impacts of air pollution on residents’ health are also expected to increase, underscoring the importance of early interventions to reduce exposures and protect public health,” said Pallavi Pant, HEI senior scientist who oversaw the report’s publication.
This is also the first time scientists have focused on the concentration of nitrogen dioxide in the air and not just the particulate matter (PM2.5), which is adding to the toxicity of the air. While PM2.5 pollution tends to get more attention in known hotspots around the world, the study notes that there is less data available for nitrogen dioxide on this global scale.
Ajay Nagpure, think tank WRI India’s head for air quality, noted that the assessment of air quality must include other harmful pollutants to be able to safely mitigate the health impacts of toxic air.
“Not only NO2 [nitrogen dioxide], we have to focus on other pollutants such as O3 [ozone] and carbon monoxide; we are currently focusing on mitigating PM2.5 only. I think we have to work in a holistic manner to formulate and implement air pollution control policies,” he said.
Nitrogen dioxide comes mainly from the burning of fuels, often in older vehicles, power plants, industrial facilities, and residential cooking and heating.
As city residents tend to live closer to busy roads with dense traffic, they are often exposed to higher nitrogen dioxide pollution than residents of rural areas.
In 2019, about 86 per cent of the more than 7,000 cities included in this report exceeded the WHO’s 10 µg/m3 guideline for nitrogen dioxide, affecting about 2.6 billion people.
The report, using data from 2010 to 2019, also found that global patterns for exposures to the two key air pollutants are strikingly different. While exposure to fine particulate, or PM2.5 pollution, tends to be higher in cities located in low- and middle-income countries, exposure to nitrogen dioxide is high across cities in high-income as well as low- and middle-income countries.
But there are many cities, especially those in high-income countries, that are reaping rewards for their efforts to improve air quality through traffic control interventions, the report showed. For instance, London’s ultra-low-emission zone delivered a 36 per cent reduction in nitrogen dioxide in the first six months after its launch in 2019.
Of the 20 cities with the largest decrease in nitrogen dioxide exposure between 2010 and 2019, as many as 18 are located in China. Cities that saw the largest increase in nitrogen dioxide exposure during this period included those in low and middle-income countries in north Africa and the Middle East, south Asia, southeast Asia and Latin America.
The lack of data on NO2 also remains a challenge because fewer countries have official air quality monitoring stations that keep a check on these levels. The report stated that among the 20 cities experiencing the largest increase in nitrogen dioxide levels between 2010 and 2019, only five have an official air quality monitoring station, and only three of those measured NO2.
The report also pointed to the growing need to reduce pollution at the source, with the help of newer technologies, by promoting green and sustainable transportation and expanding access to clean energy.