An increase in the number of people dying prematurely from exposure to polluted air is high in cities in South Asia. Among them Dhaka tops the list with 24,000 deaths annually.
Premature death defines deaths that occur before the average age of death within a certain population.
Altogether Bangladesh has had around 27,000 premature deaths due to air pollution, with Chittagong being the second highest contributor.
Around 180,000 avoidable deaths over 14 years in fast-growing tropical cities were caused by a rapid rise in air pollution, states a study the results of which were published in Science Advances in April 2022.
The study was conducted from 2005 to 2018 in over 46 tropical cities around Asia, Africa and the Middle East. They are megacities or projected to be by 2100. From Bangladesh the researchers monitored the air quality in Dhaka and Chittagong.
“We wanted to quantify long-term changes in air quality in the tropical cities which lack extensive surface monitoring to identify the real scenario of air pollution; also those which have the potential to witness even worse situations of air pollution in the coming years,” said Karn Vohra, the lead author of the paper and research fellow at University College London.
According to the study, cities in South Asia have the highest numbers of people dying prematurely from exposure to air pollution. After Dhaka, eight Indian cities made it to the list with 100,000 deaths over the years.
PM 2.5 on significant rise due to anthropogenic activities
The international team of scientists observed significant yearly increases of fine pollutants such as nitrogen dioxide (NO2), ammonia (NH3), reactive volatile organic compounds and PM 2.5.
Across all the cities, the authors found significant annual increases in pollutants directly hazardous to health of up to 14%for nitrogen dioxide (NO2) and up to 8% for fine particles (PM2.5), as well as increases in precursors of PM2.5 of up to 12% for ammonia and up to 11% for reactive volatile organic compounds.
In 14 years, Dhaka had a 20.2 increase in PM2.5, where Kolkata had the highest increase with 27.6 PM2.5 in the region.
“PM2.5 is a very crucial particle that can be formed with various components according to the atmospheric characteristics of a particular area. The size of these particles is so minuscule that they can easily enter the respiratory system, causing mild to severe airborne diseases. In the case of Dhaka, we have seen a significant rise of PM 2.5 due to anthropogenic activities caused by the rapid growth of population,” said Vohra.
NO2 increasing at an alarming rate in Chittagong
The emission of NO2 has tripled in Chittagong where the change was double in case of Dhaka in 2018 compared to 2005, the report found.
The researcher attributed construction activities such as combustion from fossil fuel and residential fuel, and emissions from vehicles, and powerplants to be the prime reasons behind the widespread rise of NO2. In the case of Chittagong, the rise of unregulated shipping activities at Chittagong port had a significant contribution to such an alarming rise of NO2.
At the same time the study has also seen an increase in non-methane volatile organic compounds (NMVOCs) in the atmosphere, which generally hail from activities, including construction, industrialization and burning of low quality fossil fuels.
Both NMVOCs and NO2 have a chemical relation in creating ozone production in the atmosphere. Currently, the ozone production of these two cities is sensitive to NO2, but the way these cities are growing, it’s very unlikely that the ozone will start forming by reacting with the NMVOCs by 2025 in Chittagong and by 2030 in Dhaka.
“The ozone gas which is present on the ground level can be formed after chemical reactions of either NO2 or NMVOCs with the ultraviolet rays of the sun. Right now, the NO2 is more persistent in creating ozone gas and the sources of NO2 are easily traceable and therefore the emission is within a controllable level. However, due to rapid anthropogenic activities, the rise of NMVOCs is giving a stark warning because tracing the sources of NMVOCs is almost impossible,” said Vohra.
“That’s why policymakers in Bangladesh have to be serious from now on so that the transition doesn’t happen,” he added.
IQAir’s 2021 World Air Quality Report also designated Dhaka as the second most air polluted city in the world. The report stated that Dhaka had an annual average PM 2.5 concentration of 78.1 µg/m3, whereas according to the WHO guideline the presence of PM2.5 can be not more than 5 µg/m3.