This story is part of CBC News special coverage of climate change issues in connection with the United Nations climate change conference (COP21) being held in Paris from Nov. 30 to Dec. 11.

Beijing blanketed in worst smog of the year

While Chinese President Xi Jinping joined other world leaders in Paris for climate talks, schools in Beijing kept children indoors, highways closed and factories scaled back work because of thick, smelly smog that cut visibility to mere metres in the Chinese capital on Monday.

Beijing bad air quality Nov 30 2015 CCTV building

People in the Chinese capital complained of a smoky, pungent odour that led many to wear tight-fitting face masks like this one. (Kevin Frayer/Getty)

Beijing bad air quality Nov 30 2015 CHINA-SMOG

The last time Beijing issued an orange alert (the second-highest danger level on a four-tier scale) was in February 2014. (Jason Lee/Reuters)

The matter with atmospheric particulate matter

The concentration of hazardous particulate matter (known as PM2.5 particles) in the air exceeded 600 micrograms per cubic metre in places inside Beijing's urban centre, while readings as high as 976 micrograms were recorded at monitoring sites in some suburban areas.

Beijing bad air quality Nov 30 2015 masked dog walker

The World Health Organization considers anything above 25 micrograms per cubic metre on a 24-hour average to be unsafe. (Kevin Frayer/Getty)

Red alert too disruptive

Critics inside the country say authorities held back from issuing a red alert because China's highest warning is too disruptive, requiring at least half of the vehicles on highways to be pulled off the road and the suspension of schools.

Beijing bad air quality Nov 30 2015 hide your kids

A baby peers out from inside a stranded vehicle on a highway between Beijing and Hebei, which also reported extremely polluted air Monday. The highway was closed due to smog. (Damir Sagolj/Reuters)

Beijing bad air quality Nov 30 2015 kite flier

Thick smog didn't stop this man from getting out with his kite in Baoding on Monday. The northern city, located in Hebei province neighbouring Beijing, was the most polluted city in China in the first half of 2015, according to the country's Ministry of Environmental Protection. (Damir Sagolj/Reuters)

Winter is worst for air pollution

An early cold snap in November meant winter heating — much of which is generated by coal-fired plants and wood fires for many poorer residents — was contributing to a worsening of air quality, which deteriorated over the weekend. 

Beijing bad air quality Nov 30 2015 heavy pollution during Paris talks

Beijing has vowed to clean up its notoriously foul air and had been doing fairly well this year, with generally cleaner air than in 2014 — the last time Beijing issued an orange alert. (Kim Kyung-Hoon/Reuters)

Beijing bad air quality Nov 30 2015 smoggy overpass

While air quality plummeted in Beijing, representatives of the governments of more than 190 countries, including China, were meeting in Paris for the COP21 climate talks, which began Monday. (Lintao Zhang/Getty)

Winter is coming to New Delhi, too

Indian Prime Minister Narendra Modi left similar conditions in New Delhi as he departed for the Paris climate summit.

The Indian capital, which typically suffers a deterioration of air quality in the winter, was blanked in a particularly thick cloud of hazardous, choking smog on Monday. 

New Delhi Nov 30 2015 bad air high tension wires low visibility

High tension electric wires disappear into the haze on an extra-smoggy Monday in New Delhi. (Anindito Mukherjee/Reuters)

Too little, too late?

Initiatives to clean up Delhi's air have hit roadblocks in the past. A directive this year to ban all vehicles older than 15 years has been delayed and previous city governments have often ignored court orders to address pollution woes.

India New Delhi half marathon Nov 29 2015

Thick smog didn't stop participants from running the Delhi Half Marathon on Sunday. (Altaf Qadri/Associated Press)