And just like that, Beijing's air pollution problem is back.

China's Victory Day was held Thursday,Sept.3 to celebrate the 70th anniversary of World War II's end, marking Japan's defeat. Beijing had such perfect blue skies (nicknamed "military blue") that day, providing the perfect backdrop for the celebration. However, no more than 24 hours after the festivities ended,the blue sky disappear. According to an independent air-quality monitoring results, air pollution levels have risen sharply during the night.

This isn't the first time that the country experienced a tremendous shift in air quality. Back in 2014, during the APEC summit, Beijing also had clear, blue skies during the two weeks that world leaders were gathered in the city. When the summit ended, the haze returned.

China has always had an air pollution problem so it was an incredible treat for anyone to catch a glimpse of blue skies. The days leading up the celebration also had blue skies so many from Beijing have started gotten used to the sight, which was brought about by government mandate to get millions of cars off roads and shut down or scale back operations in thousands of steel mills, power plants and factories in the city and the surrounding areas. However, when these pollution control measures were lifted, the blue skies disappeared as well.

By midday Friday, Beijing's air quality index read 158, with some portions of the city reporting up to 180. Particulate matter (PM 2.5) level, on the other hand, was recorded at 70. According to guidelines from the World Health Organization, a PM 2.5 level deemed safe should be at 25 during the course of a 24-hour period.

"All kinds of vehicles will be back out there, and the city is totally jammed. The pollution is back, and the view from high buildings is fuzzy," said Li Ming, CEO for Xiaomi.

It was raining by Friday afternoon, however, helping ease some of the pollution. It is not clear if the Chinese government had engaged in cloud-seeding efforts to clear the sky as it had in the past during important events, although the weather had been rainy the last few days before Victory Day.

Photo: Kevin Dooley | Flickr

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