China maintained the yellow alert issued two days ago, because smog in most of the northern regions shows no signs of reduction. Last Saturday morning, the levels of particulate matter (PM) 2.5 documented in most parts in Beijing were between 260 and 400 mg per cubic meter.

PM 2.5 is a term for particles in the atmosphere with the size of 2.5 microns or less.

Before the cold front manages to disperse the pollution, several regions, including Shaanxi, Henan, Hebei and Shandong will be experiencing heavy smog. In the south, heavy rains are expected to endure, said the National Meteorological Center.

The country's four-tier weather warning system includes red (most severe), orange, yellow and blue. A red alert is issued when pollutants in the air go beyond the 200 level on the weather warning system's index for three consecutive days. The U.S. government deems air quality that is beyond 200 very unhealthy.

Last Dec. 7, 2015, Beijing received its very first red alert warning when the smog got worst. The city, with over 22 million residents, faced what could be the worst smog incident in Beijing. Authorities were forced to close schools and issued restrictions on traffic and factory production.

In late February, reports said that Beijing is planning to create a network of "ventilation corridors" to thwart the increasing smog levels. The plan is to build a 1,640-foot-wide ventilation corridor that can connect several 262-foot-wide secondary paths.

The goal of these man-made tunnels is to break the heat circulation in cities highly affected by the air pollution. Apart from eliminating pollutants, the ventilation corridor will improve air flow and cool the air.

"The wind can blow away heat and pollutants, easing the urban heat island effect and air pollution," said Wang Fei, the city's urban planning committee deputy head.

According to a recent study presented during the American Association for the Advancement of Science 2016 meeting, air pollution-related illnesses (cardiovascular diseases and stroke) lead to 5.5 million deaths, making it the fourth leading cause of death globally.

In 2013 alone, 1.4 million people died in India due to air pollution-related disease, while China had 1.6 million, of which 366,000 are coal-related.

The report found that 55 percent (roughly 3 million) of the cases occur in countries with large populations.

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