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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.

Jun 3: Emphasising that airlines are clearly the safest mode of transportation, IndiGo CEO Ronojoy Dutta on Tuesday said there is no evidence yet of coronavirus infection getting transmitted among passengers onboard an aeroplane.

His comments against the backdrop of instances of some passengers, who had taken flights after resumption of domestic air services on May 25, testing positive for coronavirus.

"Those people had the virus before they got on to the aeroplane. What is noteworthy is that they have done the tracing after that. There is no evidence of transmission onboard there... that is a very encouraging sign on the safety of airline travel," he said during an earnings call.

According to him, airlines are clearly the safest mode of transportation and there is no evidence yet of contamination on an aircraft.

"You can come in contaminated but so far there is no evidence of passing it on to a fellow passenger," he noted.

Amid concerns over the coronavirus pandemic, aviation regulator DGCA has asked airlines to ensure that to the extent possible, middle seat in flights should be kept empty.

In this regard, Dutta said the airline would keep the middle seat empty wherever it can and "where we have to fill the middle seat, we will have the extra protective gown".

To a query about possible hedging of fuel prices, he said it would be a dumb idea and that airlines adjust to ups and downs in fuel prices.

"I can't overemphasise what a dumb idea it will be for an airline to hedge fuel prices. I looked at it from different angles and it is not a good idea... we looked at hedging and we talked about it at the board level and we said no," he noted.

Chennai, Mar 25: Tamil Nadu reported its first Covid-19 death at the Rajaji Government Hospital in Madurai this morning. The 54-year-old man from Madurai had no history of travel to any coronavirus-affected state or country.

However, he did have contact with two Thai nationals who had tested positive for Covid-19 and are undergoing treatment in isolation in Erode.

"Despite our best efforts, the #COVID-19 +ve Pt at MDU, #RajajiHospital, passed away few minutes back. He had medical history of prolonged illness with steroid-dependent COPD, uncontrolled Diabetes with Hypertension,” Tamil Nadu health minister C. Vijayabaskar tweeted.

The patient tested positive for the coronavirus on March 23. Yesterday the minister had disclosed that the patient had not responded well to treatment due to his medical condition. “He has a medical history of prolonged illness with steroid dependent COPD, uncontrolled diabetes with hypertension,” he said.

As of Wednesday morning, the total number of Covid-19 infected patients in Tamil Nadu was 18, including one patient who has recovered.

The latest patients include a 65-year-old man who returned from New Zealand and is currently in isolation at a private hospital, a 55-year-old woman from Saidapet who is currently in quarantine Kilpauk Medical College Hospital, and a 25-year-old who returned from London and is undergoing treatment at the Rajiv Gandhi Government General Hospital.