Stagnant winds and heavy traffic emissions are likely to blame for the temporary spike. But China is no stranger to dirty air. The noxious gray that frequently blankets its major cities reflects China's reliance – some would say, over-reliance – on coal.
In 2010, coal made up nearly 80 percent of China's power output, according to the International Energy Agency. The industrializing nation accounts for almost half of global coal demand. India comes in at a distant second – burning 12 percent of the world's total – making China the undisputed king of coal.
China's economy has almost certainly benefited from this relatively cheap fossil fuel, but coal has not exactly fostered breathable air or pristine views in Chinese cities.
"In Beijing, we talk about air purifiers the way that teen-age boys talk about cars," wrote New Yorker staff writer and Beijing resident Evan Osnos, in a Monday dispatch from the opaque city. "More than once, I’ve gone into a friend’s apartment and put an admiring hand on a top-of-the-line, IQAir HealthPro, and said, 'Niiiice.'"
Coal comes from fossilized plant life, taking millions of years of applied heat and pressure to form. Throughout the process, it picks up impurities like sulfur and heavy metals from the soil and sediment around it. When the carbon-based mineral is burned to generate electricity, these impurities are released into the air.
In the United States, coal plants have used technology to eliminate the release of 99 percent or more of soot-forming particulate matter, according to the US Department of Energy's National Energy Technology Laboratory (NETL). The stringent rules imposed by the Clean Air Act of 1970 pushed coal companies to use special scrubbers to knock out sulfur and nitrogen oxides – both of which contribute to acid rain and reduced visibility.
But in China, environmentalists have criticized the government for failing to act on air quality issues. It wasn't until December, when China's environmental ministry first announced specific goals to reduce levels of particulate matter – according to the Wall Street Journal – aiming to reduce them by 5 percent each year in major cities and industrial areas through 2015. Last summer, the Financial Times reported on Beijing's multibillion dollar effort to replace its coal-fired plants with natural-gas plants by the end of 2013.
This weekend's alarming peak may accelerate the government's push for clearer skies. Government officials who previously downplayed the pollution as mere "fog," held news conferences and discussed the issue openly over the past days, according to various news organizations.
"I think there's been a very big change," Beijing environmental campaigner Ma Jun told the AP. "Given the public's ability to spread this information, especially on social media, the government itself has to make adjustments."