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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 3: US aviation regulator Federal Aviation Administration on Thursday warned America's airlines and their pilots that there is risk involved in operating flights in Pakistan airspace due to "extremist or militant activity", according to an official document.

"Exercise caution during flight operations. There is a risk to US civil aviation operating in the territory and airspace of Pakistan due to extremist/militant activity," said the US Federal Aviation Administration (FAA) in a notice to airmen (NOTAM) dated December 30, 2019.

The NOTAM is applicable to all US-based airlines and US-based pilots.

The US regulator said in its NOTAM that there continues to be a risk to US civil aviation sector from attacks against airports and aircraft in Pakistan, particularly for aircraft on the ground and aircraft operating at low altitudes, including during the arrival and departure phases of flights.

"The ongoing presence of extremist/militant elements operating in Pakistan poses a continued risk to US civil aviation from small-arms fire, complex attacks against airports, indirect weapons fire, and anti-aircraft fire, any of which could occur with little or no warning," it said.

The FAA said that while, to date, there have been no reports of man-portable air defense systems or Manpads being used against the civil aviation sector in Pakistan, some extremist or terrorist groups operating there are suspected of having access to these Manpads.

"As a result, there is potential risk for extremists/militants to target civil aviation in Pakistan with Manpads," it said.

The regulator added that pilots or airlines must report safety or security incidents - which may happen in Pakistan - to the FAA.

Pakistan on July 16 last year opened its airspace for India after about five months of restrictions imposed in the wake of a standoff with New Delhi.

Following the Balakot airstrikes by the Indian Air Force, Pakistan had closed its airspace on February 26 last year.

Pakistan in October last year had denied India's request to allow Prime Minister Narendra Modi's VVIP flight to use its airspace for his visit to Saudi Arabia over the Jammu and Kashmir issue.