A man walks along a pedestrian bridge as the sun rises behind him during a smoggy morning amidst the ongoing air pollution in Kathmandu, Nepal April 7, 2021. REUTERS/Navesh Chitrakar

People exercise during a smoggy morning amidst the ongoing air pollution in Kathmandu, Nepal April 7, 2021. REUTERS/Navesh Chitrakar

A general view of a portion of Kathmandu valley during a smoggy day as the air quality of Kathmandu reaches hazardous levels, Nepal April 6, 2021. REUTERS/Navesh Chitrakar

A girl holding a balloon looks towards the sky during a smoggy day as the government has ordered schools to close for four days after the air pollution climbed to hazardous levels, forcing millions of students to stay home across the country, in Kathmandu, Nepal March 30, 2021. REUTERS/Navesh Chitrakar

Sun sets during a smoggy evening as the air quality of Kathmandu reaches hazardous levels, Nepal March 30, 2021. REUTERS/Navesh Chitrakar

Children sit on the branch of a dead tree during a smoggy day as the government has ordered schools to close for four days after the air pollution climbed to hazardous levels, forcing millions of students to stay home across the country, in Kathmandu, Nepal March 30, 2021. REUTERS/Navesh Chitrakar

A general view of a street during a smoggy day as the government has ordered schools to close for four days after the air pollution climbed to hazardous levels, forcing millions of students to stay home across the country, in Kathmandu, Nepal March 30, 2021. REUTERS/Navesh Chitrakar

A portion of Kathmandu valley is pictured during a smoggy day as the government has ordered schools to close for four days after the air pollution climbed to hazardous levels, forcing millions of students to stay home across the country, in Kathmandu, Nepal March 30, 2021. REUTERS/Navesh Chitrakar

A couple naps on a smoggy day, amid the coronavirus pandemic, at a Han river park in Seoul, South Korea, March 15, 2021. REUTERS/Kim Hong-Ji

People enjoy a picnic on a smoggy day, amid the coronavirus pandemic, at a Han river park in Seoul, South Korea, March 15, 2021. REUTERS/Kim Hong-Ji

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

A combination picture shows a view of the Italian Alps standing amidst dense fog and smog January 8, 2020, (top) and the same view pictured during coronavirus disease (COVID-19) outbreak, in Milan, Italy, in Milan, Italy, April 17, 2020. REUTERS/Flavio Lo Scalzo

A general view shows buildings during high levels of pollution in Mexico City, as the spread of the coronavirus disease (COVID-19) continues in Mexico City, Mexico April 19, 2020. REUTERS/Carlos Jasso

A general view shows buildings during high levels of pollution in Mexico City, as the coronavirus disease (COVID 19) continues in Mexico City, Mexico April 19, 2020. REUTERS/Carlos Jasso

A general view shows buildings during high levels of pollution in Mexico City, as the spread of the coronavirus disease (COVID-19) continues in Mexico City, Mexico April 19, 2020. REUTERS/Carlos Jasso

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