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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, Jun 14: Petrol price on Sunday was hiked by a record 62 paise per litre and that of diesel by 64 paise as oil companies for the eighth day in a row adjusted retail rates in line with cost since ending an 82-day hiatus in rate revision.

Petrol price in Delhi was hiked to Rs 75.78 per litre from Rs 75.16 while diesel rates were increased to Rs 74.03 a litre from Rs 73.39, according to a price notification of state oil marketing companies.

Rates have been increased across the country and vary from state to state depending on the incidence of local sales tax or VAT.

The 62 paise a litre increase in petrol and 64 paise hike in diesel price is the highest surge in rates since the daily price revision was started in June 2017.

This is the eighth daily increase in rates in a row since oil companies on June 7 restarted revising prices in line with costs, after ending an 82-day hiatus.

In eight hikes, petrol price has gone up by Rs 4.52 per litre and diesel by Rs 4.64 -- a record increase in rates in any eight days since the daily price revision was introduced.

The freeze in rates was imposed in mid-March soon after the government hiked excise duty on petrol and diesel to shore up additional finances.

Oil PSUs Indian Oil Corp (IOC), Bharat Petroleum Corp Ltd (BPCL) and Hindustan Petroleum Corp Ltd (HPCL), instead of passing on the excise duty hikes to customers, adjusted them against the fall in the retail rates that was warranted because of international oil prices falling to two-decade lows.

The government had first raised excise duty on petrol and diesel by Rs 3 per litre each on March 14 and then again on May 5 by a record Rs 10 per litre in case of petrol and Rs 13 on diesel. The two hikes gave the government Rs 2 lakh crore in additional tax revenues.

State-owned fuel retailers IOC, BPCL and HPCL had frozen petrol and diesel prices since March 16, as if anticipating the government move and set off gains they accrued from continuing drop in international oil prices against the excise duty hike.

They, however, promptly passed the increase in local sales tax or VAT by state governments such as Rs 1.67 increase in VAT on petrol and Rs 7.10 in diesel by the Delhi government on May 4.

The total incidence of excise duty on petrol has risen to Rs 32.98 per litre and that on diesel to Rs 31.83. The excise tax on petrol was Rs 9.48 per litre when the Narendra Modi government took office in 2014 and that on diesel was Rs 3.56 a litre.

The government had between November 2014 and January 2016 raised excise duty on petrol and diesel on nine occasions to take away gains arising from plummeting global oil prices.

In all, duty on petrol rate was hiked by Rs 11.77 per litre and that on diesel by 13.47 a litre in those 15 months that helped government's excise mop up more than double to Rs 2,42,000 crore in 2016-17 from Rs 99,000 crore in 2014-15.

It cut excise duty by Rs 2 in October 2017 and by Rs 1.50 a year later. But it raised excise duty by Rs 2 per litre in July 2019.

It again raised excise duty on March 14 by Rs 3 per litre.