The blue skies enjoyed by Chinese citizens during the 26th annual Asia-Pacific Economic Cooperation (APEC) summit in Beijing are gone, and the dreaded smog is back.

As China bid farewell to APEC leaders who left at the end of the conference last week, so too did it say goodbye to the clear skies enjoyed during the week of the summit.

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In preparation for the conference, China enacted a series of strict emission restrictions to keep the air clean for its guests. In Beijing and the surrounding regions, including Hebei, Tianjin, Shandong and Inner Mongolia, the government halted emission-heavy production and put a limit on the number of cars allowed on the road.

Nearly 4,000 factories were ordered to close or cut production in Hebei Province during the week-long summit, reports Global Times.

But the factories are back on, as is Beijng's central heating, which was turned on this Saturday. That means that heavily smoggy days will likely become increasingly common during the winter months.

The thick blanket of smog draped over China's major cities and industrial areas has been suspected of helping cause a recent surge in Chinese citizens being diagnosed with lung cancer.

Beijing municipal health authorities said last year that the number of lung cancer patients per 100,000 people jumped 60 percent to 63.09 in 2011 from 39.52 in 2002.

Now that APEC is over, the smog could return even heavy than before as some factories could work overtime to make up for lost production from when they had to shut down during the summit.

But at least Chinese citizens can look forward to another temporary moment of clear skies. As China was just recently named host for the G-20 summit in 2016, many are hoping for a week of "G-20 blue," according to Global Times.

TagsGoodbye APEC Blue Skies Hello Smog, Asia-Pacific Economic Cooperation, APEC, APEC summit, APEC blue, Pollution, Environment