People exercise by the Arabian sea on a smoggy day in Mumbai, India, January 12, 2021. REUTERS/Francis Mascarenhas

People commute in a Mumbai Monorail on a smoggy morning in Mumbai, India, January 7, 2021. REUTERS/Niharika Kulkarni

Mumbai Monorail passes through a slum area on a smoggy morning in Mumbai, India, January 7, 2021. REUTERS/Niharika Kulkarni

A combination picture shows a portion of Kathmandu valley, during a smoggy day on January 5, 2021, and after the smog was cleared away a day after, as the air quality of Kathmandu reached hazardous levels, in Nepal, January 6, 2021. REUTERS/Navesh Chitrakar

A portion of Kathmandu valley is pictured during a smoggy morning as the air quality of Kathmandu reaches hazardous levels, Nepal January 5, 2021. Picture taken January 5, 2021. REUTERS/Navesh Chitrakar

A portion of Kathmandu valley is pictured during a smoggy morning as the air quality of Kathmandu reaches hazardous levels, Nepal January 5, 2021. REUTERS/Navesh Chitrakar

A general view of a street during a smoggy evening as the air quality of Kathmandu reaches hazardous levels, Nepal January 4, 2021. REUTERS/Navesh Chitrakar

People commute on motorbikes during a smoggy evening as the air quality of Kathmandu reaches hazardous levels, Nepal January 4, 2021. REUTERS/Navesh Chitrakar

A general view of the Lodhi Garden on a smoggy morning in New Delhi, India, December 23, 2020. REUTERS/Anushree Fadnavis TPX IMAGES OF THE DAY

A person walks a dog in a garden on a smoggy morning in New Delhi, India, December 23, 2020. REUTERS/Anushree Fadnavis

A woman walks in a garden on a smoggy morning in New Delhi, India, December 23, 2020. REUTERS/Anushree Fadnavis

A man rides a scooter on a smoggy morning in New Delhi, India, December 23, 2020. REUTERS/Anushree Fadnavis

A man walks along a road on a smoggy morning in New Delhi, India, December 23, 2020. REUTERS/Anushree Fadnavis

People walk near India Gate on a smoggy afternoon in New Delhi, India, November 15, 2020. REUTERS/Adnan Abidi

A man rows a makeshift boat across Yamuna river on a smoggy morning in New Delhi, India, November 15, 2020. REUTERS/Adnan Abidi TPX IMAGES OF THE DAY

A rickshaw puller waits for customers on a smoggy morning in the old quarters of Delhi, India, November 10, 2020. REUTERS/Danish Siddiqui

A man transports goods on his bicycle on a smoggy morning in the old quarters of Delhi, India, November 10, 2020. REUTERS/Danish Siddiqui

People arrive to visit the Red Fort on a smoggy morning in the old quarters of Delhi, India, November 10, 2020. REUTERS/Danish Siddiqui

An office-goer walks past a traffic signal near various federal government ministries on a smoggy morning in New Delhi, India, November 10, 2020. REUTERS/Danish Siddiqui

A man transports goods on his cycle cart near the parliament on a smoggy morning in New Delhi, India, November 10, 2020. REUTERS/Danish Siddiqui

A paramilitary personal stands guard near the parliament on a smoggy morning in New Delhi, India, November 10, 2020. REUTERS/Danish Siddiqui

Traffic moves on a smoggy morning in New Delhi, India, November 9, 2020. REUTERS/Danish Siddiqui

Traffic moves on a flyover along a residential area on a smoggy morning in New Delhi, India, November 9, 2020. REUTERS/Danish Siddiqui

A homeless family warm themselves by a fire along a road on a smoggy morning in New Delhi, India, November 9, 2020. REUTERS/Danish Siddiqui

A man rides a bicycle along a highway on a smoggy morning in New Delhi, India, October 30, 2020. REUTERS/Anushree Fadnavis

Men are seen on a skywalk near Delhi-Meerut Expressway on a smoggy day in New Delhi, India, October 30, 2020. REUTERS/Anushree Fadnavis TPX IMAGES OF THE DAY

Vehicles are seen on a highway on a smoggy morning in New Delhi, India, October 30, 2020. REUTERS/Anushree Fadnavis

A man prays on the banks of Yamuna river, on a smoggy morning in New Delhi, India, October 28, 2020. REUTERS/Anushree Fadnavis

A man feeds seagulls as he stands on the banks of Yamuna river, on a smoggy morning in New Delhi, India October 24, 2020. REUTERS/Adnan Abidi TPX IMAGES OF THE DAY

Traffic moves on a smoggy morning in New Delhi, India, October 23, 2020. REUTERS/Danish Siddiqui

Traffic moves on a smoggy morning in New Delhi, India, October 23, 2020. REUTERS/Danish Siddiqui

Ragpickers collect recyclables from a dump yard on a smoggy morning in New Delhi, India, October 23, 2020. REUTERS/Danish Siddiqui

People walk near India Gate on a smoggy morning in New Delhi, India, October 22, 2020. REUTERS/Anushree Fadnavis

A man exercises at a promenade on a smoggy day in Mumbai, India, October 20, 2020. REUTERS/Francis Mascarenhas

A boy jumps into Yamuna river while a man looks on during a smoggy morning in the old quarters of Delhi, India October 17, 2020. REUTERS/Adnan Abidi TPX IMAGES OF THE DAY

A man prays on the banks of Yamuna river on a smoggy morning in the old quarters of Delhi, India October 17, 2020. REUTERS/Adnan Abidi

People ride a boat across Yamuna river on a smoggy morning in the old quarters of Delhi, India October 17, 2020. REUTERS/Adnan Abidi

The Chinese national flag flies at half-mast at Tiananmen Square in Beijing, as China holds a national mourning for those who died of the coronavirus disease (COVID-19), on the Qingming tomb sweeping festival, April 4, 2020. REUTERS/Carlos Garcia Rawlins TPX IMAGES OF THE DAY

The Chinese national flag flies at half-mast at Tiananmen Square in Beijing, as China holds a national mourning for those who died of the coronavirus disease (COVID-19), on the Qingming tomb sweeping festival, April 4, 2020. REUTERS/Carlos Garcia Rawlins

The village of Kronberg (foreground) and the city of Frankfurt are seen on a hazy morning from a hill near Kronberg, Germany, March 26, 2020, as the spread of the coronavirus disease (COVID-19) continues. REUTERS/Kai Pfaffenbach

Mountains are seen shrouded in haze near Gloucester, New South Wales, Australia, February 19, 2020. Picture taken February 19, 2020. REUTERS/Loren Elliott

A general view of boats amid dense fog and mist in the background during morning hours at China Creek area in Karachi, Pakistan January 17, 2020. REUTERS/Akhtar Soomro

A woman walks under the Brankov bridge amidst dense fog and smog in Belgrade, Serbia, January 15, 2020. REUTERS/Marko Djurica

A man walks amidst dense fog and smog in Belgrade, Serbia, January 15, 2020. REUTERS/Marko Djurica

Smoke haze hangs around Parliament House in Canberra, Australia January 12, 2020. REUTERS/Tracey Nearmy

Smoke haze hangs around Parliament House in Canberra, Australia January 12, 2020. REUTERS/Tracey Nearmy

Burnt power lines are seen in Mallacoota, Victoria, Australia January 10, 2020. Picture taken January 10, 2020. REUTERS/Tracey Nearmy

The Duomo cathedral is pictured amidst dense fog and smog in Milan, Italy, January 8, 2020. REUTERS/Flavio Lo Scalzo

Birds fly next to electricity pylons on a smoggy morning in the old quarters of Delhi, India, December 12, 2019. REUTERS/Anushree Fadnavis

An Air India passenger plane passes the sun on a smoggy morning in Ahmedabad, India, December 4, 2019. REUTERS/Amit Dave

People walk outside the Red Fort on a smoggy morning in the old quarters of Delhi, India, November 15, 2019. REUTERS/Anushree Fadnavis

Tourists are seen with protective masks on a smoggy morning in the old quarters of Delhi, India, November 15, 2019. REUTERS/Anushree Fadnavis

A woman crosses a railway line on a smoggy morning in New Delhi, India, November 15, 2019. REUTERS/Anushree Fadnavis

Sun shines through steam rising from chimneys of a power plant in Moscow, Russia November 13, 2019. REUTERS/Maxim Shemetov TPX IMAGES OF THE DAY

Children wear masks on a smoggy morning in New Delhi, India, November 13, 2019. REUTERS/Anushree Fadnavis

A woman sits with a child in a park near India Gate, on a smoggy morning, in New Delhi, India, November 13, 2019. REUTERS/Anushree Fadnavis

A woman crosses a road on a smoggy morning in New Delhi, India, November 12, 2019. REUTERS/Anushree Fadnavis

An air traffic control tower is pictured on a smoggy morning at the Indira Gandhi International Airport in New Delhi, India, November 12, 2019. REUTERS/Anushree Fadnavis

People ride a boat across Yamuna river on a smoggy morning in the old quarters of Delhi, India November 11, 2019. REUTERS/Adnan Abidi TPX IMAGES OF THE DAY

A man cleans a pond on a smoggy morning in New Delhi, India November 11, 2019. REUTERS/Adnan Abidi