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Primary organics — organic particles emitted directly into the atmosphere from various sources — have been identified as the main drivers of high concentrations of PM2.5 over South Asia.
PM2.5 refers to fine particulate matter that is 2.5 micrometres or smaller and that is produced by coal power generation, wood burning, motor vehicles and other combustion sources. Exposure to these particles is a leading mortality risk factor in India and the surrounding region of South Asia.
In a new study, researchers at Washington University in St. Louis evaluated the contribution of various emission sectors and fuels to PM2.5 mass for 29 states in India and six surrounding countries: Pakistan, Bangladesh, Nepal, Bhutan, Sri Lanka and Myanmar.
They showed that over 1 million deaths in South Asia attributable to ambient PM2.5 in 2019 were primarily from residential combustion, industry and power generation. Solid biofuel is the leading fuel contributing to PM2.5-attributable mortality, followed by coal and oil and gas.
“Understanding the major contributing sources is a critical first step towards the management of this serious problem,” study co-author Michael Brauer said in a media statement.
According to Brauer, a major challenge in evaluating the impacts of PM2.5 is understanding how it is produced and distributed over time. To get this information, he and his colleagues combined global emission inventories, satellite-derived fine surface particulate matter estimates and state-of-the-art global scale modelling capabilities to develop regional simulations. They also accounted for long-range transport to understand how different emission sectors and fuels contributed to PM2.5 and associated mortality rates.
“Advances in modelling atmospheric composition with constraints from satellite remote sensing enabled our assessment of the sources of PM2.5 across South Asia,” head researcher Randall Martin said. “That helped draw our attention to large contributions from burning biofuel and coal.”
The scientists also noted that PM2.5 mass composition in South Asia is driven by primary organics across major contributing sectors. The team’s PM2.5 composition analysis can be particularly useful to develop mitigation strategies associated with particular species.
A few other notable features include high contribution from coal in central and eastern India, higher household air pollution in north-east and central India, biofuel contributions in Bangladesh and open fires in Myanmar.
“This study shows that the air pollution problem in South Asia is not just an urban scale problem, so policies targeted at urban scale development will not be enough to mitigate the national level PM2.5 exposure,” Deepangsu Chatterjee, lead author of the study, said.
Chatterjee, Martin and their co-authors suggest several strategies for future interventions throughout South Asia, including policies encouraging the replacement of traditional fuel sources with renewables.
“Policies in India in the past five to 10 years have worked toward identifying and improving air pollution concerns and associated health burden and mortality risks. Seeing these policies be effective is motivating for the South Asian population to keep moving the needle and develop strategic policies to curb the growth of air pollution,” Chatterjee said.
“Our paper provides detailed sector – fuel – and composition-based information for different states in India along with surrounding countries, which could be useful for local policymakers to eliminate PM2.5 sources associated with their specific region.”
