This map, based on a model known as MERRA-2, shows how the amount of airborne black carbon, averaged for the month of November, has changed over a 12-year period from 2005 to 2016. Blue areas indicate where concentrations have decreased, while orange and red show increases. Data from research by S. Sarkar/NASA GSFC, R. Singh / Chapman University, and A. Chauhan / Sharda University Graphic: Lauren Dauphin / NASA Earth Observatory

By Kathryn Hansen
28 June 2018

(NASA) – In recent decades, northern India has been plagued by a double-dose of air pollution due to nearby sources of desert dust and increasing amounts of airborne particles from human activities. New research suggests that winds are spreading the problem, moving some of the pollution southward in ever-increasing amounts.

Black carbon is one of several components of Indian air pollution described in new research led by Sudipta Sarkar of NASA’s Goddard Space Flight Center. Black carbon is a sooty black material that comes from the incomplete combustion of things like fossil fuels and vegetation and is easily transported by winds. It can cause respiratory and cardiovascular disease if inhaled, and it can also affect climate.

The map above, based on a model known as MERRA-2, shows how the amount of airborne black carbon, averaged for the month of November, has changed over a 12-year period from 2005 to 2016. Blue areas indicate where concentrations have decreased, while orange and red show increases.

Looking at the map, the increases in central India do not stand out compared to some other areas. They were, however, surprising. “We first looked at India’s capital, Delhi, which is in the news a lot for its air pollution problems,” Sarkar said. “When we looked at whole picture, we thought ‘wow, this is happening in areas to the south, too.’”

Ground-based measurements at sites including Aurangabad confirmed what the models indicated: increases in black carbon are affecting central India in November. So where is it coming from?

Sarkar and colleagues attribute the overall rise in black carbon to the rise in the use of mechanical harvesting, which leaves behind stalks that farmers then burn before planting the next crop. Mechanical harvesting has long been performed in the north. Since 2010, the method has been expanding eastward along the foothills of Himalaya. More mechanical harvesting means more black carbon, one of the key byproducts of crop residue burning.

Sarkar and colleagues think that winds are likely the main way that this pollution is reaching central India from areas north. From mid-October through mid-November, after the monsoon, a ridge of atmospheric high pressure usually sets up over northwestern part of the country. As a result, winds during this time usually blow from northern states toward the south and east, carrying fine pollution particles from the northwest.

“Mechanical harvesting in Punjab has increased and spread to other states, so the cumulative effect is increasing with every passing year,” Sarkar said. Specifically, black carbon values over central and southern India in November increased by as much as 60 percent over the 12-year period.

Sarkar notes that there was a hint of improvement downwind after regulations were put into effect in Punjab in 2017, but researchers will need a few more years of data before they can say for sure.

Air Pollution on the Move in India


ABSTRACT: Crop residue burning (CRB) is a recurring problem, during October‐November, in the northwestern regions (Punjab, Haryana and western Uttar Pradesh) of India. The emissions from the CRB source regions spread in all directions through long‐range transport mechanisms, depending upon the meteorological conditions. In recent years, numerous studies have been carried out dealing with the impact of CRB on the air quality of Delhi and surrounding areas, especially in the Indo‐Gangetic Basin (IGB) (also referred to as Indo‐Gangetic Plain, IGP). In this paper, we present detailed analysis using both satellite and ground‐based sources, which show an increasing impact of CRB over the eastern parts of the IGB and also over parts of central and southern India. The increasing trends of finer black carbon (BC) particles and greenhouse gases have accelerated since the year 2010 onwards, which is confirmed by the observation of different wavelength dependent aerosol properties. Our study shows an increased risk to ambient air quality and an increased spatiotemporal extent of pollutants in recent years, from CRB, which could be a severe health threat to the population of these regions. This paper shows from multiple evidence, increasing effects of biomass burning on the rest of India. This is the first work of its kind that treats this issue over rest of India at depth based on data from multiple sources and shows the ever increasing menace of biomass burning to air pollution.

Crop Residue Burning in Northern India: Increasing Threat to Greater India

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