Chinese authorities ordered new measures to curb choking air pollution this week, amid growing public alarm at the density of harmful micro-particles hovering over about 15 per cent of the country.
Beijing and many other northern cities have been notorious for their winter smog, caused by a combination of air pollution and weather conditions, for decades.
But growing affluence and a recent focus on harmful micro-particles, known as PM2.5, have prompted local governments, following the lead of the US embassy in Beijing, to issue 24-hour monitoring reports on air quality.
Online consumers have clamoured for all kinds of dust protectors, from simple surgical masks to colourful printed ones, cycling masks and heavy-duty industrial respirators. Many people who can afford them have bought imported air filters for their homes.
One 29-year-old woman in the Chinese capital told dpa she was "seriously thinking of leaving Beijing" because of its air pollution.
"I used to jog every day but I've stopped because of the weather (and smog)," said the woman, who asked to be identified only by her surname, Bao.
"I have to check the smog index from my mobile phone every day and I have to change my schedule each day according to the level," she said.
"If it's heavy I don't go out, and if it's medium level I wear a mask to go out."
Bao said she had also "cooked some soups to cleanse the lungs" after searching online for traditional recipes based on Chinese medicine.
Beijing's PM2.5 concentration reached a high of 490 micrograms per cubic metre early Tuesday, keeping it in the "hazardous" band, according to the US embassy's air-quality index.PM2.5 refers to particles smaller than 2.5 micrometres, which pose a serious health hazard because they can be embedded deep into the lungs.
The city's PM2.5 level Tuesday was nearly 20 times the daily maximum exposure of 25 micrograms per cubic metre recommended by the World Health Organization.
It recorded a PM2.5 peak of 900 micrograms in January 2013.Major Beijing hospitals have reported increases of up to 40 per cent in asthma and emphysema cases since the start of this year.
The city government issued an orange alert - the second-highest level- on Saturday, urging Beijing's 20 million residents to reduce outdoor activities, keep windows closed and wear masks.
The capital and other heavily polluted northern cities have tried measures including reducing the number of cars allowed onto the road seach day, and suspending production at large factories on days when heavy air pollution is recorded.
But environmental experts said Beijing's air pollution comes mainly from vehicle emissions and coal smoke drifting over from nearby industrial areas.
State media said China used about 4 billion tonnes of coal last year, up from 1.4 billion tonnes on 2003 and accounting for nearly 50 percent of global consumption.
The ruling Communist Party has allowed relatively open debate on air pollution in recent years, for what it considers a safe, non-political topic.
During a visit to Beijing by US Secretary of State John Kerry last week, China and the United States pledged cooperation on "the urgent need for action to meet the twin challenges" of reducing the impact of climate change and cutting emissions from fossil fuels.
"It is not at others' demand but our own will," state media quoted President Xi Jinping as saying of measures to curb air pollution.
"We have already taken a lot of measures and will take more in the future," Xi told Kerry.
The government issued an action plan last year to increase the use of natural gas and non-fossil energy sources in place of coal, to control energy prices through taxes and close the most-polluting factories. It also promotes the use of low-emission coal technology and provides subsidies to local governments that succeed in reducing pollution.It promised to cut the density of PM2.5 by 25 per cent in Beijing and at least 10 per cent in other cities by 2017. The package of measures reflects the party's long-term plan to rebalance China's economy away from its reliance on export-oriented factories and construction for its rapid growth.
Despite the government's commitment, coal will remain China's main fuel for several decades and smog masks will remain standard winter wear for many in the polluted northern regions.