A group of international collaborators led by the Research Institute for Humanity and Nature (RIHN) team performed the first quantitative study of air pollution in the northwestern region of India using 29 low-cost and reliable instruments. Their study demonstrated the benefits of source region observations to link crop residue burning (CRB) and air pollution at local to regional scales.
Exposure to particulate matter less than 2.5 µm in diameter (popularly known as PM2.5) poses health hazards in cities worldwide. Although the major sources of PM2.5 are industrial, certain agricultural practices also contribute to the emission and formation of fine particles during certain seasons. CRB, a common practice in Punjab, Haryana and part of Indo-Gangetic Plain, occurs immediately after the paddy harvest in the post-monsoon period (September-November). CRB activities have increased in the past two decades partly due to rise in mechanized agriculture in the 1990s and delayed rice planting in Punjab and Haryana following the Preservation of Subsoil Water Act (2009).
Since 2010, the effects of CRB in Punjab and Haryana on the Delhi and its surrounding area (known as the national capital region - NCR) have been in the spotlight. Yet, no measurements of PM2.5 in the source regions have been conducted. To rectify this, a group of researchers conducted an intensive field campaign involving the states of Punjab, Haryana and the NCR from September 1 to November 30, 2022, using 29 Compact and Useful PM2.5 Instruments with Gas sensors (CUPI-Gs).
Continuous observations showed that the PM2.5 in the region increased gradually from less than 60 µg m-3 between October 6-10, and up to 500 µg m-3 between November 5-9. This subsequently decreased to about 100 µg m-3 between November 20-30. The Indian national air quality standards for PM2.5 are set at 40 µg/m³ for the annual average and and 60 µg m-3 for the 24-hour average. The measurements in this study demonstrated that PM2.5 values in the Punjab to NCR remained over 60 µg m-3 during mid-October to the end of November and exceeded 200 µg m-3 for the first two weeks of November at many sites.
The researchers tracked two distinct CRB plumes of PM2.5 over 500 µg m-3 from Punjab to NCR via Haryana on 2-3 and 9-11 of November, 2022. These were associated with the northwesterly monsoon. Higher concentrations observed in the southeast downwind regions indicated the presence of a secondary formation (gas to particle conversion in the atmosphere due to chemical reactions).
"Reducing air pollutants is possible through effective public awareness. Since individuals affected by air pollutants often live in areas where these pollutants are emitted, their awareness can have a direct impact, unlike the global effects of long-lived greenhouse gases," says Professor Prabir K. Patra, the current leader of the Aakash Project--a project dedicated to promoting sustainable agriculture to reduce air pollution in the Punjab region--at RIHN and the principal scientist at the Japan Agency for Marine-Earth Science and Technology (JAMSTEC).
"Despite having a limited budget, we managed to gather detailed information about the behavior of air pollutants across a wide region spanning from Punjab to NCR, thanks to the development of CUPI-G. This data is now being employed to measure air pollution in several other Asian regions," explained Professor Emeritus Yutaka Matsumi from the Institute for Space-Earth Environmental Research at Nagoya University.
The sensors used were developed by Panasonic Corporation and members at Nagoya University. "Let our efforts to build a greener and cleaner future be guided by the precision of low-cost PM2.5 monitoring, leading to cleaner air and a healthier livelihood for both rural and urban citizens," says Professor Manpreet Singh Bhatti at the Department of Botanical and Environmental Sciences, Guru Nanak Dev University.
There are many other environmental impacts of air pollution. Pollutants emitted from CRB contain significant amounts of light-absorbing aerosols, capable of altering the thermodynamics of our atmosphere and cloud properties. "High-quality data obtained from a dense measurement network offers to address these issues by combining multiple data streams and numerical models," says Dr. Pradeep Khatri, a researcher at Tohoku University.
Professor Sachiko Hayashida (RIHN), the former project leader and who supervised the measurement campaign, says, "We hope future Japan-India collaboration helps to reduce serious air pollution in this area. Aakash project is also working with Indian researchers on the ways to improve straw management without burning."
The measurement data of PM2.5 are available from the RIHN database.
Very high particulate pollution over northwest India captured by a high-density in situ sensor network
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