SEPTEMBER 4, 2015 3:08 AM September 4, 2015 3:08 am 
 
 
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Just hours after China’s Victory Day extravaganza on Thursday, when splendid blue skies framed a parade of thousands of troops marching through central Beijing to celebrate the end of World War II, the city’s air was filling again with dirt. An independent air-quality monitoring site showed pollution levels rising sharply from midnight.
 
Air pollution is a political issue in China, and anger at the problem is high. On Friday, many Beijing residents were asking, Why? And perhaps more pertinent, How?
 
This is the how different Beijing looked before the parade and the day after:
 
By midday on Friday, the air-quality index was back to a more normal “unhealthy” reading of 158, and in some parts of the city it was up to 180. The level of dangerous fine particulate matter, or PM 2.5, was at 70. The World Health Organization’s safety guideline for PM 2.5 is 25 over a 24-hour period.
 
Here is the reading from noon on Thursday:
 
Some residents said they thought the abrupt shift was tied to the parade and not to the damper weather that had been forecast, pointing to the lifting of extensive pollution control measures shortly after the soldiers cleared out on Thursday. By Friday afternoon, rain was falling.
 
“From today until the 6th, Beijing won’t be controlling the number of cars on the streets,” wrote Citizen Big Li, or Li Ming, the chief operating officer of the mobile phone maker Xiaomi, on his Sina Weibo account. “All kind of vehicles will be back out there, and the city totally jammed. The pollution is back, and the view from high buildings is fuzzy.”
 
A person with the online handle About That Day answered: “Dare I ask where yesterday’s cloudless skies came from? At the blink of an eye, Beijing is back to its original state. Could it be that yesterday’s aircraft and tanks had anything to do with it?”
 
“God is blessing our party! The parade might have happened in this weather!” a recent graduate of Peking University wrote in a WeChat message circulated among friends. He did not wish to be named.
As reported in The New York Times’s coverage of the parade, the Beijing Meteorological Bureau had been operating under “special wartime working conditions” since Aug. 10 to deliver precise weather information and other services.
 
It is unclear if the government engaged in cloud-seeding to clear the skies, as it has in the past for important events, though there was rain in and around Beijing in the days before the parade.
 
What is known: China ordered more than 10,000 factories, power plants and steel mills in Beijing and six surrounding provinces and cities to close or scale back production during the early part of the week, to ensure cleaner air. The result was unusually clean skies residents dubbed “military parade blue.”
 
And now they are open again.
 
Vanessa Piao contributed research.