When a thick, grey smog descended over Beijing and nearby cities last month, the overwhelming response it triggered among residents was a sense of deja vu.
The worst air pollution to hit the capital in a year prompted the authorities to issue a five-day red alert for Beijing and 22 other cities that imposed school shutdowns and forced half of all private cars off the roads. But for many residents like Ms Kaylene Hong, 28, the smog has become seasonal in recent years.
With northern China experiencing its coldest winter since 2012, demand for heating has surged.
Most of it continues to be met by coal-fired power plants which, together with heavy industry's use of coal, emit fine dust that accounts for roughly half of the country's PM2.5 (or fine particulate matter) pollution.
A secondary contributor is emissions from vehicles.
Coupled with high humidity and a lack of winds - the capital is surrounded on three sides by mountains - the high density of particles in the air causes the acrid smog now symbolic of a Beijing winter.
"I wore a mask everywhere, avoided outdoor activities, and turned on the two air purifiers I have at home 24/7," said Ms Hong, a communications manager who is Singaporean. "Life didn't come to a standstill because of the red alert but when I finally saw blue skies after five days, I felt like jumping for joy."
Like Ms Hong, many took comfort that the seasonal smog was not as bad as in 2015, when Beijing authorities issued two red alerts within a fortnight, or the "airpocalypse" of 2013 that saw the air quality readings climb to as high as 993.
Smog-inspired devices a clear winner in China
The smog might have cast a pall over year-end festivities in much of China, but it has also brought out the creative and entrepreneurial streak in some people.
Knowing that many in China are eager to track air quality not just outdoors but also at home or in the office, local start-up Origins Technology created the Laser Egg, a grapefruit-size device that monitors PM2.5 levels.
The 499-yuan (S$104) device, which promises accurate, real- time air quality monitoring using a technology called laser scattering, was sold out within days of the authorities issuing a smog red alert.
"We saw a similar trend (a year ago), so we specifically stocked up with much larger quantities this time, but we still managed to run out," said CEO Liam Bates, who told The Straits Times the company has sold "tens of thousands of units" in the past few months.
Canadian company Vitality Air, which began selling bags of fresh Rocky Mountain air as a joke in 2015, was also inundated with thousands of orders from China, even though prices start at US$23 (S$33) for a three-litre canister.
It even began facing competition from an Australian outfit, Green and Clean Air, that is offering air from well-known holiday spots such as Tasmania and Bondi beach in Sydney.
The recurrent smog has also inspired a raft of gallows art.
Shanghai activist Zhang Lingling teamed up with a perfume maker friend to create a "smog perfume" that sought to recreate the caustic mix of dust and sulphur that had hit China, and asked unsuspecting strangers to try it in a bid to raise awareness about the pollution crisis.
Meanwhile, a man in Hubei, surnamed Gong, has built a "smog cannon" which he hopes will make people realise the urgency of cleaning up the environment.
And a Beijing designer has turned the now ubiquitous face mask into a fashion accessory. Graphic designer Wang Zhijun came to global attention after he deconstructed a limited-edition pair of Kanye West-designed Yeezy sneakers to make a face mask. It attracted a US$5,000 bid on eBay China.
Lim Yan Liang
This time, the readings exceeded 400 (in the "hazardous" range) at the height of last month's "airpocalypse". An orange alert was issued for the latest bout of air pollution, forecast to last until Thursday, despite a brief respite in Beijing and nearby Tianjin yesterday.
But beneath the resignation was an undercurrent of exasperation that the problem will persist for years to come, despite the central government's efforts to fight it as efforts to move away from coal have been hampered by other priorities.
Four years after Premier Li Keqiang declared war on air pollution, and three after President Xi Jinping called pollution China's biggest challenge, the government has set into motion ambitious plans aimed at eventually shaking off the moniker of "world's largest polluter".
China still uses as much coal as the rest of the world combined - it more than tripled coal burning between 2000 and 2013, and the dirty fuel still accounts for 70 per cent of its energy mix.
But at a time when climate denialist Donald Trump is about to enter the White House, China looks set to overtake the United States as the global thought leader - and doer - in renewable energy.
China's demand for coal has continued to fall after peaking in 2014, in what some experts say is a long-term trend owing to shifts in the Chinese economy towards services and the government's crackdown on pollution.
And while it began 2015 already boasting the world's largest installed capacity of wind and solar power, it invested another US$103 billion (S$149 billion) in renewable energy that year, according to the latest Renewables Global Status Report.
This is more than the investments for the US and Europe combined, noted the International Energy Agency (IEA), and essentially meant China built two wind turbines and a football field's worth of solar panels every hour that year.
The central government has also issued a series of edicts ordering sharp curbs on air pollution, mandating ambitious targets such as a reduction of as much as 33 per cent of PM2.5 emissions by the end of this year for the most affected cities like Shijiazhuang and Tangshan in industrial Hebei province, which surrounds Beijing.
The problem with this rosy picture? The faltering economy.
China's annual growth fell to 6.7 per cent in the first three quarters of 2016, the slowest rate seen in 25 years.
While it has pushed hard in recent years to expand its services sector, much of the growth was in finance and real estate that now face government action to curb asset bubbles.
Slow reform in areas such as healthcare and education meant the sector as a whole has failed to make up for lost growth elsewhere.
And despite the growth in renewable energy capacity, regional grid operators still prioritise coal due to the glut of coal-fired capacity.
"This unspoken coal-favouring protectionist measure is an important limiting factor to renewable outputs," principal consultant on China power Frank Yu at research consultancy Wood Mackenzie told Bloomberg.
Slowing growth has also forced the government to revert to its old playbook of trying to stimulate growth through heavy industry.
Greenpeace East Asia noted that record stimulus and infrastructure spending by the government in the second quarter of 2016 led to greater steel production in Hebei that caused PM2.5 levels in the region to be worse than in 2015.
Six of the 10 worst-performing cities in China in terms of air quality in the first 10 months of 2016 were in Hebei.
"The government is now caught in the dilemma of having to choose between GDP growth and environment protection, and they are quite obviously putting growth first," said East Asian Institute (EAI) senior research fellow Chen Gang.
A growing middle class and soaring demand for cars have also led to vehicle emissions becoming a key contributor to the smog.
In Beijing, such emissions have outstripped those from industries to become the number one contributor of pollutants, according to data from the Beijing Municipal Environmental Monitoring Center.
The Chinese capital today has more cars than Singapore has people, with the car population expected to reach six million by the end of the year, even after the government in 2011 began to restrict the number of licence plates issued.
In a trend that echoes mid-1990s American tastes, Chinese consumers are also buying more petrol-guzzling sport utility vehicles.
Sales in this category grew by 40 per cent year-on-year in 2015.
Throw in a powerful oil lobby that has resisted the central government's push to raise fuel and emission standards and one begins to understand how China's air has stayed stubbornly rancid.
"China's energy market is dominated by its own companies, which wield significant influence that has allowed them to resist implementing new standards controls, and that's why you have low-quality oil and coal," said China environmental politics expert Wu Fengshi at Nanyang Technological University.
In the meantime, expatriates are thinking of greener pastures.
Among them is Ms Corinne Yeoh, 26, a Malaysian baker who came from Singapore last year after her husband found a job in Beijing.
Noting how her Chinese friends were trying to leave the capital because of the pollution, she said: "It struck me that maybe I shouldn't stay here for too long."
Until China solves these twin root causes of its air pollution - overreliance on coal and a growing car market coupled with substandard petrol - the smog is likely to return year after year, even when the 2022 Winter Olympics that Beijing is hosting rolls around, said EAI's Dr Chen.
"The government can achieve an 'Apec blue' by temporarily shutting down nearby factories and power plants but this doesn't solve the fundamental causes of the pollution," he added, referring to the clean air Beijing residents enjoyed during 2014's Asia-Pacific Economic Cooperation summit.
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