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

An auto-rickshaw moves past the India Gate on a smoggy morning in New Delhi, India November 11, 2019. REUTERS/Adnan Abidi

A man paddles a home-made boat across Yamuna river on a smoggy morning in the old quarters of Delhi, India November 11, 2019. REUTERS/Adnan Abidi

A man uses his handkerchief to cover his face as he walks on a road on a smoggy morning in New Delhi, India November 11, 2019. REUTERS/Adnan Abidi

A mosquito net bed is covered with bed sheets for Mohammad Islam's grand children who live under a flyover, on a smoggy evening in New Delhi, India, November 7, 2019. Picture taken on November 7, 2019. REUTERS/Adnan Abidi

Abida, daughter of Mohammad Islam, who lives under a flyover prepares a bed for her family on a smoggy evening in New Delhi, India, November 7, 2019. Picture taken on November 7, 2019. REUTERS/Adnan Abidi

Abida, daughter of Mohammad Islam, who lives under a flyover holds her eight-month-old daughter as she arranges kitchen utensils on a smoggy evening in New Delhi, India, November 7, 2019. Picture taken on November 7, 2019. REUTERS/Adnan Abidi

Mohammad Islam, who lives under a flyover, stands next to his wife with his daughter, who is preparing dinner on a smoggy evening in New Delhi, India, November 7, 2019. Picture taken on November 7, 2019. REUTERS/Adnan Abidi

Mohammad Islam, who lives under a flyover, plays with his grand-daughter on a smoggy evening in New Delhi, India, November 7, 2019. Picture taken on November 7, 2019. REUTERS/Adnan Abidi

Grandson of Mohammad Islam, who lives under a flyover, sits on his fathers cart on a smoggy evening in New Delhi, India, November 7, 2019. Picture taken on November 7, 2019. REUTERS/Adnan Abidi

A man pushes a handcart as vehicles are seen at a traffic junction on a smoggy morning in New Delhi, India, November 7, 2019. REUTERS/Danish Siddiqui

A woman wearing a mask crosses a traffic junction on a smoggy morning in New Delhi, India, November 7, 2019. REUTERS/Danish Siddiqui

A man wearing a protective mask crosses a traffic junction on a smoggy morning in New Delhi, India, November 7, 2019. REUTERS/Danish Siddiqui

A man receives a shave from a roadside barber wearing a protective mask on a smoggy morning in New Delhi, India, November 7, 2019. REUTERS/Danish Siddiqui

Schoolboys wearing protective masks walk towards their school on a smoggy morning in New Delhi, India, November 7, 2019. REUTERS/Adnan Abidi

A schoolgirl wearing a protective mask holds her father's hand as she waits for her school bus on a smoggy morning in New Delhi, India, November 7, 2019. REUTERS/Adnan Abidi

A schoolgirl wearing a protective mask looks on as she waits for her school bus on a smoggy morning in New Delhi, India, November 7, 2019. REUTERS/Adnan Abidi

A schoolgirl wearing a protective mask looks on as she waits for her school bus on a smoggy morning in New Delhi, India, November 7, 2019. REUTERS/Adnan Abidi

A girl waits to cross the railway line on a smoggy morning in New Delhi, India, November 5, 2019. REUTERS/Anushree Fadnavis

A traffic policeman wears a mask to protect himself from air pollution at a junction during restrictions on private vehicles based on registration plates, on a smoggy morning in New Delhi, India, November 4, 2019. REUTERS/Danish Siddiqui

A policewoman wears a mask to protect herself from air pollution at a junction during restrictions on private vehicles based on registration plates on a smoggy morning in New Delhi, India, November 4, 2019. REUTERS/Danish Siddiqui TPX IMAGES OF THE DAY

A volunteer from civil defence holds a placard with information regarding restrictions on private vehicles based on registration plates on a smoggy morning in New Delhi, India, November 4, 2019. REUTERS/Danish Siddiqui

A Hindu family leaves after worshiping the Sun god during the Hindu religious festival of Chhath Puja on a smoggy morning in New Delhi, India, November 3, 2019. REUTERS/Adnan Abidi

People pose for pictures as they stand amidst the foam covering the polluted Yamuna river on a smoggy morning in New Delhi, India, November 3, 2019. REUTERS/Adnan Abidi

People walk on a smoggy morning in New Delhi, November 3, 2019. REUTERS/Adnan Abidi

Hindu devotees leave after worshipping the Sun god during the Hindu religious festival of Chatth Puja on a smoggy morning in New Delhi, India, November 3, 2019. REUTERS/Adnan Abidi

A man wearing a mask walks on a smoggy morning in New Delhi, November 3, 2019. REUTERS/Adnan Abidi

Hindu devotees leave after worshiping the Sun god during the Hindu religious festival of Chatth Puja on a smoggy morning in New Delhi, India, November 3, 2019. REUTERS/Adnan Abidi

A crow sits on a barricade in front of India Gate amidst smog in New Delhi, November 3, 2019. REUTERS/Adnan Abidi

A Hindu woman prays on the banks of the Yamuna river to worship the Sun god during the Hindu religious festival of Chhath Puja on a smoggy evening in New Delhi, India, November 2, 2019. REUTERS/Anushree Fadnavis

Hindu devotees gather on the banks of the Yamuna river to worship the Sun god during the Hindu religious festival of Chhath Puja on a smoggy evening in New Delhi, India, November 2, 2019. REUTERS/Anushree Fadnavis

A Hindu woman prays on the banks of the Yamuna river to worship the Sun god during the Hindu religious festival of Chhath Puja on a smoggy evening in New Delhi, India, November 2, 2019. REUTERS/Anushree Fadnavis

Hindu devotees gather on the banks of the Yamuna river to worship the Sun god during the Hindu religious festival of Chhath Puja on a smoggy evening in New Delhi, India, November 2, 2019. REUTERS/Anushree Fadnavis

Hindu devotees gather on the banks of the Yamuna river to worship the Sun god during the Hindu religious festival of Chhath Puja on a smoggy evening in New Delhi, India, November 2, 2019. REUTERS/Anushree Fadnavis

A man is seen on a skywalk near Delhi - Meerut Expressway on a smoggy day in New Delhi, India, November 2, 2019. REUTERS/Anushree Fadnavis

A man paddles a boat in the waters of the Yamuna river near the Signatue bridge on a smoggy evening in New Delhi, India, November 1, 2019. REUTERS/Anushree Fadnavis

Birds fly as people commute near India's Presidential Palace on a smoggy day in New Delhi, India, November 1, 2019. REUTERS/Anushree Fadnavis TPX IMAGES OF THE DAY

People walk on the Rajpath on a smoggy day in New Delhi, India, November 1, 2019. REUTERS/Anushree Fadnavis

People rest in a park near the India Gate war memorial on a smoggy day in New Delhi, India, November 1, 2019. REUTERS/Anushree Fadnavis

People wear masks on a smoggy evening in New Delhi, India, October 31, 2019. REUTERS/Anushree Fadnavis

A man paddles a home-made boat across Yamuna river on a smoggy afternoon in the old quarters of Delhi, India, October 30, 2019. REUTERS/Adnan Abidi

Birds fly next to electricity pylons on a smoggy afternoon in the old quarters of Delhi, India, October 30, 2019. REUTERS/Adnan Abidi

Birds fly next to electricity pylons on a smoggy afternoon in the old quarters of Delhi, India, October 30, 2019. REUTERS/Adnan Abidi TPX IMAGES OF THE DAY

A man wearing a mask runs past the India Gate on a smoggy morning in New Delhi, India, October 28, 2019 REUTERS/Adnan Abidi

A man rides a cycle past the India Gate on a smoggy morning in New Delhi, India, October 28, 2019 REUTERS/Adnan Abidi

A man paddles a home-made boat across Yamuna river on a smoggy morning in New Delhi, October 28, 2019. REUTERS/Adnan Abidi

A man wearing a mask rides a cycle on a smoggy morning in New Delhi, India, October 28, 2019 REUTERS/Adnan Abidi

Women walk in front of India's Presidential Palace on a smoggy morning in New Delhi, India, October 27, 2019. REUTERS/Altaf Hussain TPX IMAGES OF THE DAY

A woman wearing a mask walks inside a park on a smoggy morning in New Delhi, India, October 27, 2019. REUTERS/Altaf Hussain