Beijing Announces Cleanest Month in 9 Years?

May 14th, 2009. Note:
Thanks to Vance for flagging the editorial mistake by China Daily. This is the "cleanest April" in 9 years.

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Blue Skies are Shining on Beijingers ! says China Daily

The city experienced 23 blue sky days in April, 2009 (a blue sky day = day with API less than 100).

Question: Why is this the cleanest month in 9 years,
August 2008, 30 days with average API of 56;
September, 2008, 29 days with average API of 56;
August 2006, 30 days with average API of 74;

and April 2009, 23 days with average API of 84?

See statistical Beijing Air Pollution Index (API) analysis @ Room with a View

Also see

• Air Quality Monitoring in Asia
• Air Quality Index in Urban Centers
• Environmental assessment of Beijing 2008 Olympic Games (UNEP)
• Dust Storms, Fires, and Haze Pollution in Asia
• Particulate Pollution in Asia
  
• Articles on air pollution and climate on "China Dialogue"
• More new cars are registered in 2009 in Beijing, China
  
• Transport Emissions Inventory for China
• Photo Diary of Air Pollution in Beijing
• Sensing air quality in Beijing (Interactive Maps)
• Beijing still hazy !!
• Air pollution in Beijing