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Washington, Apr 23: Air pollution over northern India has plummeted to a 20-year-low for this time of the year, according to satellite data published by US space agency National Aeronautics and Space Administration (NASA).
The US space agency's satellite sensors observed aerosol levels at a 20-year low post the countrywide lockdown, implemented to slow the spread of the novel coronavirus.

"We knew we would see changes in atmospheric composition in many places during the lockdown," said Pawan Gupta, a Universities Space Research Association (USRA) scientist at NASA''s Marshall Space Flight Center. "But I have never seen aerosol values so low in the Indo-Gangetic Plain at this time of year," added Mr Gupta.

Acting Assistant Secretary of State for South and Central Asia Alice G Wells tweeted, "These images from NASA were taken each spring starting in 2016 and show a 20-year low in airborne particle levels over India. When India and the world are ready to work and travel again, let's not forget that collaborative action can result in cleaner air."

The data published with maps show aerosol optical depth (AOD) in 2020 compared to the average for 2016-2019. Aerosol optical depth is a measure of how light is absorbed or reflected by airborne particles as it travels through the atmosphere.

If aerosols are concentrated near the surface, an optical depth of 1 or above indicates very hazy conditions. An optical depth, or thickness, of less than 0.1 over the entire atmospheric vertical column is considered "clean." The data were retrieved by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite.

In the first few days of the lockdown, it was difficult to observe a change in the pollution signature. "We saw an aerosol decrease in the first week of the shutdown, but that was due to a combination of rain and the lockdown," said Mr Gupta.

Around March 27, heavy rain poured over vast areas of northern India and helped clear the air of aerosols. Aerosol concentrations usually increase again after such heavy precipitation.

"After the rainfall, I was really impressed that aerosol levels did not go up and return to normal. We saw a gradual decrease and things have been staying at the level we might expect without anthropogenic emissions," Mr Gupta said.

On March 25, the Indian government placed its 1.3 billion citizens under a strict lockdown to reduce the spread of COVID-19. The countrywide mandate decreased activity at factories and severely reduced car, bus, truck and airplane traffic. Every year, aerosols from anthropogenic (human-made) sources contribute to unhealthy levels of air pollution in many Indian cities.

Aerosols are tiny solid and liquid particles suspended in the air that reduce visibility and can damage the human lungs and heart.

In southern India though, the story is a little hazier. Satellite data show aerosol levels have not yet decreased to the same extent. In fact, levels seem to be slightly higher than in the past four years. The reasons are unclear but could be related to recent weather patterns, agricultural fires, winds or other factors.

"This a model scientific experiment," Robert Levy, program leader for NASA's MODIS aerosol products, said about the lockdown and its effects on pollution.

"We have a unique opportunity to learn how the atmosphere reacts to sharp and sudden reductions in emissions from certain sectors. This can help us separate how natural and human sources of aerosols affect the atmosphere," Mr Levy added.

New Delhi, Jan 29: The Supreme Court on Wednesday dismissed the plea by Mukesh Kumar Singh, one of the four death row convicts in the Nirbhaya gang rape and murder case, challenging the rejection of his mercy petition by the President.

A three-judge bench headed by Justice R Banumathi said that expeditious disposal of mercy plea by the President doesn't mean non-application of mind by him.

The court also said that alleged sufferings in prison can't be grounds to challenge the rejection of mercy petition.

The bench said all relevant material including judgments pronounced by trial court, high court and Supreme Court were placed before the President when he was considering the mercy plea of the convict.

The bench also comprising justices Ashok Bhushan and A S Bopanna rejected the contentions of the counsel appearing for Singh that entire materials of the case were not placed before the President when he was considering his mercy plea.

The bench, while referring to two files placed before it by the Centre on Tuesday, said that as per the January 15 covering letter which was sent by the Delhi government to the Ministry of Home Affairs, all relevant documents were sent.

The bench noted that detailed judgements of trial court, high court and the Supreme Court, curative petition filed by Singh, his past criminal history and his family background were sent to the Home Ministry by the Delhi government.

"All the documents were taken into consideration by the President while rejecting the mercy petition," the bench said.

The bench also dealt with submissions advanced by the convict's counsel, who had argued that the mercy plea was rejected at "lightning speed".

The bench said that if a mercy petition is expeditiously dealt with, it cannot be assumed that it has been adjudicated upon in a pre-conceived mind.