[The Beijing EPB] spent much of their press conference Friday responding to doubts about the veracity of their numbers. Last year an American environmental consultant pointed out that the official numbers showed a disproportionately high number of days that fell just within the official target for a “blue sky day.” Yu Jianhua, head of Beijing’s environmental monitoring center, said the local government used emergency measures such as closing down construction sites on days when it expected pollution would exceed targets. That led to the high number of days just under the cutoff, Yu said.
This is the first time I’ve seen the Beijing EPB both directly acknowledge that a statistical anomaly in the number of blue sky days exists and provide a concrete reason why. The statistical anomaly I’m referring to can be be seen in this figure, from a 2008 report by environmental consultant Steven Andrews. The graph appears to show data biasing right around the “blue sky day” cut-off point (in this case, a PM10 concentration of 150 ug/m3).
It has been interesting to watch the evolving responses from the EPB to Mr. Andrews’ discovery – from official data – of what appears to be blatant data massaging to achieve an artificial result. In February 2008, Beijing EPB spokesperson Du Shaozhong infamously responded to criticisms of data manipulation with, “this phenomenon does not exist. ” By July 2008, in a press conference before the Olympics, the Beijing EPB response had shifted to the bewildering “some convenience maybe taken in very adverse situations to improve the air quality within 9 square kilometers so that the API can remain at or below 100.” (The WSJ reported on this response the following day.)
Now, however, we have a definitive claim from the Beijing EPB that the preponderance of API values just below the blue sky day cut-off point resulted from emergency measures taken on days which were predicted to be dangerously close to the limit.
As is so often the case in China, this reponse only makes me ask more questions. Questions like:
- Why didn’t the Beijing EPB admit this last year, as soon as Mr. Andrews’ report came out?
- How are such accurate predictions made? Can we have more details on the program, like which factories or construction sites were closed?
- Why do this at all? Is there really a critical human health benefit to a 99 API day as opposed to a 101 day? (Answer: not really, since where we need to be is below 20.)
- Why were these emergency shut-downs conducted from 2003-2007, but not in 2008?
- Was this program really conducted in dozens of cities around China?
I can keep asking questions of course, but I think it’s time now to invoke Occam’s Razor in support of the more obvious conclusion…
More info in related posts on this blog:
October 2008: problems with the blue sky day metric
March 2009: looking for biasing in 2008 blue sky day data
June 2009: new report shows widespread air quality data manipulation
Final note: I am playing catch up on posting after falling behind the last few weeks with the site redesign and work distractions. Apologies in advance that some of the commentary will be on “old” (e.g., from July) news.