China's Ministry of Environmental Protection said the latest bout of smog to hit the capital has come despite a number of proactive measures being put in place by the government over the past 12 months.

You can say hazy skies this winter have been quite the rarity. A marked improvement from autumn and winter in 2013 to 2016. And in 2017, the overall air quality in the nation improved drastically.

LIU BINGJIANG, SPOKESMAN MINISTRY OF ENVIRONMENTAL PROTECTION "The average concentration of PM10 in prefecture-level cities and above was 75 micrograms per cubic meter, which is about 22% lower than that in 2013. The average concentrations of PM2.5 in Beijing, Tianjin, Hebei, Yangtze River Delta and Pearl River Delta decreased by about 40%, 34% and 28% comparing with that in 2013. The annual average concentration of PM2.5 in Beijing has dropped from 89 to 58 micrograms per cubic meter."

In the previous year, Beijing's weather has been through a dramatic change. The reduction of PM2.5 levels in 2017 equalled the total reduction recorded from 2012 to 2016 -- a four year period! But what led to the vast improvement in Beijing's air quality this year? And what was the government doing to reduce air pollution in the nation before 2017?

LIU BINGJIANG, SPOKESMAN MINISTRY OF ENVIRONMENTAL PROTECTION "We had to accurately control haze. We needed a targeted policy. We were making efforts in carrying out research and solving technical problems. Pollution control is not one day of work. It is the cumulative effort."

Although the air quality across China is currently at a favorable level, it still has a long way to go. In some regions, heavy air pollution is still prominent. With coal-based transport and emissions of pollutants relatively abundant, overall air pollution control in China is still a work in progress. As Liu said, there should always be a sense of urgency when the sky is blue, and confidence when it's gray.