A China Daily report today mentions Beijing’s 2010 Blue Sky Day target as 266. This is the first time I’ve seen the target referenced; I’m not sure how/when they set or publicize them. Perhaps they are in Beijing’s Five Year Plan. Does anyone know?

This China Daily report also mentions Beijing’s 2009 Blue Sky Day total, 285, representing the first time I’ve seen it mentioned in English-language domestic media (although Xinhua covered the accomplishment in Chinese on 1/1.)

Recent targets and totals are shown below. Note that the 2010 target is below the number of Blue Sky Days achieved in both 2008 and 2009.

Happy New Year (a few hours early)!!! For my last post of the year, here is some overall analysis of Beijing’s air quality over the past 12 months.

First, the numbers. As usual, I’m working from air quality data downloaded from the Ministry of Environmental Protection’s datacenter. (Direct link to Beijing’s data is here.) There is a bug in the system that prevents the query function from working properly, but you can still scroll through the data and download it manually through copy and paste.

The datacenter reports 363 data points for 2009; 2/18 and 11/14 are mysteriously missing. Assuming those two days were Blue Sky Days yields a Blue Sky Day count of 285 and a calculated average PM10 concentration of 120 ug/m3.

For anyone who is new to this blog or who needs a refresher, a Blue Sky Day is a day with an Air Pollution Index (API) of 100 or below, which means that the air quality meets China’s National Grade II air quality standard – theoretically “excellent” or “good” air quality. China tallies annual number of Blue Sky Days as a consumer-friendly and easily-understood measure of air quality progress, although the metric is prone to gaming and scientifically meaningless.

PM10 means particulate matter of size 10 microns or smaller, also called “inhalable particles.” In 2009, PM10 was the reported dominant pollutant on 97% of days with an API above 50. (No dominant pollutant is reported on days with an API 50 or below.) I back-calculated PM10 from API using formulas and assumptions described here.

Trends of Blue Sky Days and PM10 concentration since 2000 are shown here:

The Good News: The good news isn’t really that good, but in the interest of balance here are some positive perspectives. First, Beijing’s count of 285 Blue Sky Days in 2009 is well above that of 2008 (274), and also well above the goal of 259. This will keep the trending up in official reporting and for boosting public morale; I imagine this fact will be spun as success / progress in the Chinese media in the days to come. I suppose another bit of good news is that Beijing has achieved what appears to be an improvement over 2008 without the boost of two months of extreme traffic restrictions and factory closures implemented last year during the Olympic period.

The Bad News: My calculated average PM10 concentration in Beijing for 2009 is 120.2 ug/m3, which less than a 1% reduction from 2008’s average. In other words, from the perspective of average particulate matter concentration, there was no improvement in air quality in Beijing from 2008 to 2009. This shows the danger of using “number of Blue Sky Days” as a metric for air quality evaluation – just because the number of Blue Sky Days increases doesn’t mean that air quality has improved.

Interestingly, as a thought experiment, let’s suppose that China’s air quality goal was that all cities should meet the Grade I air quality standard, meaning that a Blue Sky Day would have an API of 50 or below as opposed to an API of 100 or below. If we count these days (shown in the graph above in light blue), we actually see that 2009 was worse than 2008; 2008 had 62 Grade I days, while 2009 had only 47.

Most importantly, regardless of how you spin the data, Beijing’s 2009 level of inhalable particulate matter was still 20% higher than China’s own air quality standard and six times higher than the WHO’s recommended annual PM10 standard. What this means, of course, is that our work continues to be cut out for us moving into 2010 and beyond.

Related post:  Summary of Beijing’s 2008 air quality

Although a little late, I do want to highlight a rather unexpected comment from the Beijing EPB at a press conference in early July. As reported in the Time blog:

[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.