People wearing protective masks walk on an overpass during the evening rush hour amid the heavy smog after Beijing issued its first red alert for air pollution Dec. 7, 2015. REUTERS/Jason Lee

Believe it or not, the air quality in the Chinese capital is actually improving. Just not very fast.

On Monday, the Beijing municipal government issued its first “red alert” for smog, urging schools to close, restricting traffic and closing down construction sites for three days starting Tuesday.

The decision underlines what everybody knows: decades of unbridled economic growth, corruption and utter disregard for environmental safety have combined to produce some of the deadliest air in planetary history.

Read: Air pollution in China is killing 1.6 million people a year.

But what is perhaps less well known is that the capital’s air is heading for what could be its best year in more than a decade.

And perhaps, somewhere in the choking smog that settled over Beijing this week, there is the smallest sliver of a silver lining: at least the government is finally taking some action, in response to public pressure.

Heavy smog has settled over Beijing from Sunday night and is forecast to intensify through Thursday, prompting the government to impose the highest level of alert on its four-color scale for the first time.

Yet by the city’s terrible standards, the air quality has actually been far worse: concentration of PM2.5 small particles were measured at 224 micrograms per cubic meter at 8 p.m., classified merely as “very unhealthy” by international guidelines, which recommend that people with heart or lung disease, older adults and children to avoid all physical activity outdoors.

Last week, the concentration of PM2.5 had been much higher – more than 500 micrograms per cubic meter at one point, worse than “hazardous” and pretty much off the scale as far as those guidelines go.

That's more than 20 times World Health Organization recommended levels -- yet the city government’s alert level had been maintained at “orange.”

The government, perhaps reluctant to incur the economic costs that a red alert would have entailed, came in for heavy criticism on social media – and implicitly from the central government – for failing to impose a red alert last week.

On Sunday, Environmental Protection Minister Chen Jining vowed to punish agencies and officials for any failure to quickly implement a pollution emergency response plan, the state-run Global Times tabloid reported.

“This year is still on track to be by far the best for air pollution on record, but the fact that these horrendous episodes can still happen shows how far there is to go to solve the problem,” said Lauri Myllyvirta, an energy campaigner at Greenpeace International. He said he was looking at satellite data since 2003 and U.S. Embassy data since 2009.

Despite a fall-off in coal consumption linked to a slowdown in Chinese industry, coal use remains “massive” in the provinces surrounding Beijing, while power plants and factories are still violating emissions standards, he said.

Read: China confronts the pain of kicking its coal addiction

“The episodes show that it is absolutely crucial to ramp up reductions in coal use, as well as enforcement of strict emission limits for power plants and industry, even with the leveling off of growth in manufacturing sectors,” he said.

Myllyvirta said the worst episodes occur when slow-moving air masses spend days accumulating pollution in the industrial heartland before reaching Beijing.

Here's a map that shows the wind patterns that are bringing the pollution to Beijing, from Greenpeace analysis using the U.S. NOAA Hysplit model.

“On a positive note, it is commendable that Beijing officials initiated the alert based on forecasts before the pollution levels rose to extreme range,” said Myllyvirta. “This is something that they have found hard to do in the past.”

Under the rules, cars with odd and even number plates will be kept off the roads on alternate days, and some industrial enterprises will have to close. On social media, some users welcomed the move to impose a red alert, but others remained unconvinced that the government would impose costs on powerful industrial vested interests.

“Can you not treat us like we are fools,” one user posted. “Dare you close down all the coal and chemical enterprises tomorrow?”

Last week, there was even more anger about an issue that ranks toward the top of Chinese citizens' concerns.

“The perks of China’s development are not shared by all its citizens, but its ill effects are tasted by everyone,” one user wrote in a post later deleted by censors. “Without moral and legal restraints, development could be a disaster.”

Xu Jing contributed to this report.

A couple and their child wearing masks walk past the China Central Television (CCTV) Tower shrouded in smog in Beijing, Dec. 7, 2015. EPA/HOW HWEE YOUNG