doi:10.1038/nindia.2018.78 Published online 25 June 2018
Air pollution from crop stubble burning in some northern states of India – an environmental menace that makes headlines every year – is not confined to the north. Scientists now have evidence from NASA’s satellite images and ground stations in India that the burning of crop residue threatens a larger region in central and south India1.
An increase in finer black carbon (BC) particles and greenhouse gases from crop residue burning (CRB) has made the Indo-Gangetic basin a global hotspot for atmospheric pollutants and a place for recurring winter haze and toxic fog, the researchers say in their report.
"While, a lot of attention is given to the impact of CRB over the Indo-Gangetic basin (IGB), relatively less is known about its effect on the greater Indian peninsula," Ramesh Singh, a professor at Chapman University in California and one of the authors, told Nature India.
The analysis based on data from multiple sources is the ‘first work of its kind’ to assess the impact of CRB over India between 2003 and2017. Their results show "an increasing influence of CRB over the eastern parts of the IGB and also over parts of central and southern India."
Mechanized harvesting leaves residues in the field in the form of stalks, stubbles, and straws that are burnt by the farmers to clear the field for the next crop. Biomass burning after harvesting for wheat (during April-May) and rice (during October-November) is a recurring problem, in the northern states of Punjab, Haryana and Uttar Pradesh. The problem becomes severe in winters when large parts of northern India choke on smog and haze triggered by large scale crop residue burning.
The researchers – Sudipta Sarkar from NASA Maryland, IIT Kanpur alumnus Ramesh Singh at the Chapman University, California, and Ph.D. student Akshansha Chauhan from Sharda University, Greater Noida, Uttar Pradesh – looked at data from multiple sources. They culled data from NASA’s Imaging Spectro-radiometer, Ozone sensor, a number of other NASA satellite observations, ground stations in Kanpur and Hyderabad and global climate models. They used the ‘Emissions Database for Global Atmospheric Research’ to assess the magnitude of methane emissions – an inevitable by-product of CRB – and NASA’s database to obtain information on BC and dust column.
Data from the Kanpur and Hyderabad ground stations showed that BC aerosol-laden winds can travel longer distances at higher altitudes and impact far off places. While dust aerosol was largely confined to its source regions of western and north-western India, "the increase in BC is more evident along the eastern IGB and central India, conforming to the north-westerly wind direction in the post-monsoon period." According to the authors, most of the changes related to CRB are seen to be restricted within the lower 2 km of the atmosphere.
"Our results clearly show an increased preponderance of BC aerosols and finer particles, during the post-monsoon and wintertime, over the eastern IGB and central India," the authors say. The implications of higher black carbon levels in the post-monsoon ambient air-quality over eastern and Central India could be ‘far-reaching’, they say.
This deterioration of air quality, the researchers note, is of “great concern, especially over the eastern IGB that is already riddled with increasing pollution from various other sources like coal mining, fossil fuel combustion, industrial output and increased vehicular traffic, all of which are contributors to BC."
1. Sarkar, S. et al. Crop residue burning in northern India: Increasing threat to greater India. J. Geophys. Res. (2018) doi: 10.1029/2018JD028428