Smog solutions: How 6 cities are attempting to deal with dangerous air pollution
Beijing and New Delhi are notorious offenders when it comes to air pollution, but they're not alone
Smog has been blanketing parts of Italy in recent weeks, marring usually picturesque skylines with a sickly grey haze and causing cities to temporarily ban cars and even wood-burning pizza ovens.
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But Italy is by no means alone in its fight against air pollution. Thick smog draped over cities across Europe and Asia in December — in part the result of little precipitation and too much air pollution.
Here's a look at the smog situation some cities are currently contending with.
Bicyclists had free rein of Milan's streets Monday as a six-hour ban on private cars was implemented in a bid to alleviate persistent smog.
Pollution levels in Italy's business capital have exceeded levels considered healthy for more than 30 days straight, prompting officials to ban private cars from 10 a.m. until 4 p.m. Monday through Wednesday of this week.
Officials said that private motorists widely respected the ban on its first day, but faced steep fines if they did not.
Rome, which is also battling smog, has been enforcing alternate-day driving based on odd and even numbers on licence plates, while Florence has announced limits on automobile access to the historic centre through New Year's Eve.
The lack of rain and wind have worsened pollution levels in Italy, particularly in the mostly land-locked and industrial northern Po River Valley, where at least 10 cities have taken steps to limit auto traffic.
Milan's car ban falls during a holiday week, with many residents out of town and many businesses closed, and it is accompanied by a measure that allows passengers to use public transport all day for €1.50 ($1.60) on what is normally a single-ride ticket.
Sarajevo, Bosnia and Herzegovina
In Sarajevo, the capital of Bosnia and Herzegovina, authorities have also suggested that drivers use their vehicles less, asking residents to adopt alternate means of transportation and to reduce their movement outdoors, particularly during morning and evening hours.
Red Cross workers and other volunteers have been handing out face masks to residents opting to go out despite the warning.
The air pollution forced authorities to shut down schools in Sarajevo last Thursday, prompting an early winter break. (Students in the country usually start their holidays just before New Year's.)
Nestled in a basin among the mountains, Sarajevo is prone to heavy fog that can quickly turn to smog when mixed with high air pollution.
The Chinese capital issued two smog-related red alerts in December, as did several other cities in China.
Red alerts are triggered when the air quality index is forecast to exceed 200 — a level considered heavily polluted — for three or more consecutive days. And while readings of 200 are very high, some parts of Beijing have recorded levels over 900.
Industrial coal-burning, construction, factory work and millions of cars on the roads have contributed to hazardous smog levels in recent years. As the world's biggest carbon emitter, China still depends on coal for more than 60 per cent of its electricity.
Traffic restrictions in Beijing — including a numbered licence-plate system used to alternate access to roadways — are easily circumvented by people who simply cover their real licence plates with fake ones or those bought or borrowed in other cities or provinces.
Other Chinese cities, such as Shanghai, have also spent December amid rampant air pollution. Scientific studies attribute 1.4 million premature deaths per year to China's smog, or almost 4,000 per day.
Smog shrouded the Iranian capital of Tehran earlier this month, with the city's 14 million residents being warned to stay indoors when possible.
Schools were closed and soccer matches postponed because of the poor air quality, which is largely due to outdated vehicles, traffic worsened by aging infrastructure and inconsistent enforcement of emissions regulations.
Thousands of deaths from respiratory illnesses have been linked to Iran's smog, prompting a government pledge three years ago to tackle the country's air pollution.
Like Sarajevo, Tehran is surrounded by mountains, shielding the city from cleansing winds. Pollution also becomes more severe in the winter as cold air prevents smog from rising.
Home to a fast-growing population, New Delhi was named the most polluted city in 2014 by the World Health Organization.
An additional 12 Indian cities also ranked among the worst 20, with air pollution contributing to more than 600,000 deaths in the country annually.
To combat the heavy smog that seems to be a daily fact of life in the Indian capital, the country's top court issued several orders earlier this month, including a temporary ban on the sale of large diesel vehicles and stiff levies on trucks entering New Delhi.
Trucks more than 10 years old are banned from entering New Delhi and its nearby suburbs. Private cars more than a decade old were banned at an earlier date.
New Delhi will also experiment with alternate-day driving allowances for private cars in the new year, using the odd-or-even licence plate model.
Diesel vehicles, construction dust and the burning of crops on neighbouring farmland all contribute to New Delhi's air pollution woes. Unlike Beijing, New Delhi has no formal alert system to warn residents about high levels of air pollution.
Incheon, South Korea
South Korea's smog is largely blamed on blowover from China, but the country's reliance on coal plants is also at fault.
While South Korea scrapped plans for four coal-fired power plants as part of its pledge at the recent Paris climate summit, it still plans to build 20 new plants by 2021.
The capital of Seoul and the nearby coastal city of Incheon often experience a thick haze in the hot summer months and again in late fall, when home heating is turned on in South Korea and China.
An estimated 1,600 deaths are linked to air pollution in the country each year.
With files from Reuters, The Associated Press and European Pressphoto Agency