Heavy smog covered the skies above Beijing over the weekend, causing flights to be canceled and streets unpassable.
The heavy smog started on Saturday but cleared on Monday. However, meteorologists warned that gray skies will return on Tuesday due to the cold weather.
Smog warnings were issued since mid-December. Many factories were forced to scale back production, especially in northern parts of Beijing where much of coal and steel are produced.
The Beijing local government issued an orange warning on air pollution on Monday. The government also banned heavy construction trucks to travel on the roads.
According to the World Health Organization, "a pollution index that measures the average concentration of small breathable particles, known as PM2.5, dropped to just over 100 micrograms per cubic meter in Beijing early on Monday from more than 500 on Sunday night. The safe recommended level of PM2.5 is 10 micrograms per cubic meter."
The dangerous levels of air particles are classified by the U.S. government as life-threatening and would cause "serious aggravation of heart and lung disease and premature mortality in persons with cardiopulmonary diseases and the elderly, and increased respiratory effects in the general population."
In 2014, experts thought that the smog was going to be a major challenge for China.
Tao Xie, professor of political science, at Beijing Foreign Studies University, wrote: "This new 'great leap forward' in pollution could be as disastrous as the Great Leap Forward of the 1950s when a push to industrialize and collectivize caused a famine that reportedly killed millions of people."
The government has been trying to lessen the production of coal through strict monitoring and sanctioning of more than 500 companies.
About 10,000 vehicle owners were also penalized this year due to vehicle smoke emissions.