Beijing's first-ever red alert for air pollution this week shows how far China has to go until its urban dwellers can breathe clean air.
Still, some progress has already been achieved.
The red alert was triggered because the forecast for the government's air quality index was for the reading to reach or exceed 200 for three days.
At a number from 200-300, the government considers the air heavily polluted and to have noticeable effects even on healthy people.
And while readings of 200 are very high, in some parts of Beijing they have been over 900.
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Even with such hazardous air, Dong Liansai, Greenpeace's climate and energy campaigner, regards Beijing's red alert this past week as a welcome sign, indicative of a different attitude by the local government. (Though he says authorities should have issued a red alert the previous week, when air quality was just as bad in Beijing.)
Dong, who holds a masters degree in environmental health from Emory University in the U.S., told CBC News that breathing outside in Beijing right now is uncomfortable, even for a healthy person like himself.
He notes that the smog affects a huge area of northern China, not just Beijing. Some sources says the affected area is the size of Spain.
This latest "airpocalypse" in China arises from a combination of factors, including a temperature inversion and low wind speeds.
Inversions happen where the normal condition of cool air above and warm air below gets reversed, and are not unusual in north China at this time of year.
A side effect is that these inversions usually lead to high levels of particulate matter becoming trapped in the cold air, closer to the ground, while the cold in turn leads to the burning of more coal, the main source of air pollution in China, to provide heat and electricity.
What's in the air
The current, high air quality index results in China are driven by the concentration of dangerous particulate matter in the air — fine particles with a diameter of 2.5 micrometres or less. By comparison, human hair has a diameter of 17 to 181 micrometres.
These particles, known as PM2.5, are small enough to penetrate to the gas-exchange regions of the lungs (and the smallest can even pass through the lungs)
More and more particles lodging in the lungs and elsewhere in the human body lead to cardiovascular diseases, cancers and other health problems, resulting in premature death, scientists say.
The World Health Organization classifies airborne particulate matter as a Group One carcinogen.
Beijing's average for the first half of 2015 was 77.8 micrograms per cubic metre of air, well above China's standard of 35.
Even at that high number, 45 other cities in China had worse air quality.
A 2013 European study estimates than an increase of 10 micrograms in a cubic metre leads to a 36 per cent increase in the lung cancer rate.
However, China's scary air quality may be getting better. "There's already some improvements and progress in improving air quality, not only in Beijing but also in other cities in China," Dong says.
Government taking action
In response to public pressure, China has introduced a new series of emissions standards, a new environmental protection law and a new air pollution law that will take effect in 2016.
What's more, Dong says a drop in coal consumption this year has also led to better AQI results.
He says Greenpeace's most recent analysis of Chinese city data shows a 12 per cent drop on average in PM2.5 in the first nine months of 2015 compared to 2014.
Even with that improvement, China's PM2.5 level stands at four times WHO's recommended limit, and Dong says that nearly four out of five cities don't even meet China's own, less stringent limit for PM2.5.
He says China needs a national cap on coal consumption to improve its air quality.
The country is opening four new coal plants per week, even though electricity demand is not growing very rapidly, Dong notes.
He would also like to see China beef up its already extensive renewable energy program.
China invested $90 billion US in renewables in 2014. "In the first quarter of 2015, it built more solar than exists in the whole of France and has built up the world's biggest wind power industry, all in less than a decade," says Dong.
And this change in direction seems to be having a global impact, according to a study published this week in the science journal Nature Climate Change.
That study looked at global carbon dioxide emissions and found that the rapid growth in emissions that began in 2000 has "slowed dramatically in the past two years," despite continued economic growth.
"The slower growth in emissions was attributed largely to a drop in coal consumption in China," the authors say.
'Airpocalypse' grips Beijing
Left, is a view of Tiananmen Square on a smoggy Dec. 1. At right, the same scene two days later after a shift in the weather temporarily cleared the skies. This week, Beijing is blanketed in choking smog once again, prompting the first ever red alert for air pollution.