Monday, October 27, 2008

more on the datacenter

The Ministry of Environmental Protection's old air quality site hasn't been updated since 10/19, leading me to believe that the new online datacenter is here to stay. I finally had a chance to look through it in some depth today, and discovered some cool features. Unfortunately, the site is only in Chinese right now, but I'll keep checking and report back if an English version comes online. Also, it only works in Internet Explorer (not Firefox) on my computer, and even then still gives some weird scripting error messages.

In any case, here is a screen capture of the main interface:

The home page shows the Air Pollution Index (API) for 86 major cities in China, along with a pie chart displaying fractions of cities meeting various air quality grades. (In the screen shot above, 25 cities have "excellent" (优) air quality while 59 have "good" (良).) The bar graph below shows the 10 best API ratings across China each day. Congrats to Beijing for being 6th yesterday! The air quality data for the cities auto-scrolls on the home page; the complete list is presented here.

Besides additional air quality info (which I will discuss in detail below), the site features:

- Weekly water quality monitoring info for major river basins in China (全国主要流域重点断面水质自动监测周报), including some pretty detailed water quality analysis. (I'm no water expert, but from glancing through the data it seems both extensive and depressing.);
- A list of nature reserves in China (全国自然保护区名录);
- A list of companies in China that have received certification for environmental labeling (环境标志产品认证), though to be honest I'm not sure what this is used for;
- A search engine for environment-related scientific standards (科技标准查询), including links to the original documents;
- Some detailed info on solid waste management in China (限制类固体废物进口 and 自动类固体废物进口.)

My mouse goes directly to the air quality data, though, so let's explore that further...

First of all, as I mentioned in my last post, clicking on each city brings up a city-specific page, such as this one for Beijing:

At the top of this page, you can query past API data for any city you choose. In the results of the daily query, there is at least one new feature that was not previously available, and that is the presenting of the forecasted high and low API's for each day in parallel with the actual API. (Those in Beijing will remember last Friday's crazy winds; that day's actual API of 14 was a welcome, far cry from the predictions of 51-71!) There is also a graph of the last 30 days of API's.

Besides the city-specific sites, the following pages are available:

- A database of past air quality forecasts for each city (重点城市空气质量预报);
- An air quality analysis page (重点城市空气质量分析). There is some really cool stuff on this page - including the ability to rank and compare different cities in China against each other - and as such I think it deserves its own post. Therefore, rather than write more about it now, I'm going to save further explanation for another, more in-depth post about that page specifically. Also:

a) I can't imagine there are all that many people who got this far in this post anyway;
b) For those who did get this far, I want to make sure you have an excuse to come back to this blog; and,
c) It's time for me to leave the office...

Monday, October 20, 2008

I just noticed today a new feature on the website of the Ministry of Environmental Protection:

My browser is giving me some errors loading the pages, so it seems they are still doing some debugging, but so far it seems interesting. The pie chart above displays fraction of Chinese cities meeting different air quality levels today.

There are also links to city specific sites (e.g. Beijing) that automatically display a graph of the last 30 days of API data for each city:

(Note the 10/18 pollution spike I mentioned in my last post).

Historical API data is also now hosted on the new site, here: (The use of the term "test run" in the URL leads me to believe this is temporary, but we'll see; in any case the old API site has not yet been updated today so this is the only source of current data for now.)

pollution increases after the olympics

We are now one month past the end of the temporary air pollution reduction policies put in place for the Olympics and Paralympics. As expected, pollution levels have gone up. But how much? Using PM10 concentrations as an indicator, I estimate that the air quality in Beijing for the past month has been around 24% worse than it was during the two-month Olympic period. The pollution has actually been worse this past month than it was during the same period in 2007, though still significantly better than the same period in 2006:

It should be noted, though, that the averages over this past month are slightly skewed by the extreme pollution of this past Saturday (October 18th), when the API shot up to 174 (PM10 concentration 298 ug/m^3). This was the first day with an API above 150 since June.

Saturday's brutal - but short-lived - high pollution event raised a question in my mind that I'm not sure the answer to. From a health perspective, should we worry more about these short-lived extreme pollution spikes or long-term elevated baseline levels? For PM10 specifically, the WHO gives both daily and annual targets (50 and 20 ug/m^3, respectively). Granted, Beijing's air quality regularly exceeds both, but which is likely to cause more damage?

Lastly, it should be noted about the above table that I have done a direct conversion from API to PM10 concentration using the formulas at the bottom of this post, although this is an imperfect system because China does not list the primary pollutant for APIs below 50. Given the fact that PM10 is almost always the primary pollutant when the API is above 50, I think it's a reasonable approximation.

Tuesday, October 14, 2008

new vehicle restriction policy in beijing

I know, I'm a little late to the party on writing about this, so apologies for that.

As of yesterday, a new policy is in effect in Beijing to keep 800,000 cars off the roads every day. Though not nearly as far-reaching as the odd/even car ban implemented during the Olympics, the basic concept is the same: forbid certain cars from driving inside Beijing's fifth ring road depending on the last digit of their license plates. According to this policy, vehicles whose license plate numbers end in 1 and 6 may not drive on Mondays, 2 and 7 on Tuesdays, 3 and 8 on Wednesdays, 4 and 9 on Thursdays, and 5 and 0 on Fridays (though supposedly the prohibited driving days will change each month). There are no restrictions on the weekends. Additionally, the government has supposedly eliminated 30% of government cars, though the details on how are a bit hazy.

I'm curious to see what the results of this policy will be, both from a pollution perspective and a congestion perspective. My initial reaction on the former is that it won't have a huge effect, largely because cars are not the largest source of pollution in Beijing anyway. I wonder, then, if the ban is somewhat symbolic, a response to the loud public calls for the government to do something to signify a clear commitment not to let the pollution return to pre-Olympic levels.

Or maybe we are just seeing one step in a broad, coordinated series of policies designed to ween car-addicted Beijingers back to transit, bikes, and walking...

More info:

problems with the "blue sky day" metric

Late last month, consultant Steven Q. Andrews published an excellent report with detailed analysis of the publicly reported daily API data for Beijing. His key findings, which were first published as an op-ed in the Wall Street Journal (and subsequently covered by the New York Times, Time, and others), are as follows (quoted from the report's abstract):
Here I show that reported improvements in air quality [in Bejiing] for 2006–2007 over 2002 levels can be attributed to (a) a shift in reported daily PM10 concentrations from just above to just below the national standard, and (b) a shift of monitoring stations in 2006 to less polluted areas.
Many people, including Mr. Andrews, have been asking me my opinion on the findings of the report. Here, I will try to summarize what I consider to be the most impressive and surprising results, while also commenting on what the report's results do - and don't - show.

Summary: Statistical analysis of reported API frequency shows clear data biasing to reach Blue Sky Day targets, and, as such, I think effectively invalidates the use of annual number of Blue Sky Days as an air quality measure. This is an extremely impressive finding that I hope the Chinese government will respond to appropriately, both by reconsidering the use of the Blue Sky Day metric altogether and investigating how such bias was introduced and eliminating it in the future.

However, I caution against using this finding alone to make broader, sweeping assumptions about Beijing's air quality changes over the last five or ten years. Specifically, Mr. Andrews' report should not be used as proof that any and all recent improvements in air quality in Beijing have been simply the result of "gaming the numbers" as opposed to actual improvements. While Mr. Andrews' results regarding numbers of Blue Sky Days are dramatic, his analysis of pollutant concentrations in recent years focuses on only one pollutant, PM10, and shows concerning, but not dramatic, discrepancies to the officially reported data. Additionally, when discussing PM10, it should be noted that controlling concentrations of particulate is well known to be one of the biggest air quality challenges faced by Beijing, and that trends of PM10 concentration should not necessarily be equated with trends of other pollutants or even trends of overall air quality.

Finally, while I think Mr. Andrews' analysis normalizing air quality data across multiple years by accounting for the moving of monitoring stations is excellent, correct, and appropriate, I do not think it proves deliberate deceit about air quality (as the Blue Sky Day biasing does).


Blue Sky Day Data Biasing

First of all, to me, the most impressive graph in the report is this one, showing the dramatically higher frequency of reported PM10 concentration just below the Blue Sky Day cut-off than just above (Figure 2 from Mr. Andrews' report):

Equally impressive is this statement from the report:
While 52% of the days with a city API between 96 and 105 (PM10 = 142–160 μg m−3) were reported as ‘Blue Sky’ days in 2001, 98% of the days in this range were ‘Blue Sky’ days in 2006, and 93% of days in the range were ‘Blue Sky’ days in 2007.
This seems to show, unequivocally, that there is bias in the reported data around the Blue Sky Day cut-off point. From this data, it appears that the use of the number of Blue Sky Days metric is not reliable as an indicator of Beijing's air quality improvement. Therefore, I will stop using it as such and will edit a previous post on this blog that references it. I would hope that, in time, Beijing will recognize this clear bias and take steps towards identifying how it is introduced and preventing it in the future. At the same time, detailed investigations into potential biasing of other pollutant data should also be conducted (though it seems less likely that such biasing would have occurred, given the fact that the biasing appears to be related to meeting Blue Sky Day targets, for which PM10 is usually the limiting factor).

Moving of Monitoring Stations

The second issue Mr. Andrews raises is the moving of monitoring stations. While I find his analysis here to be fascinating and correct, I'm not convinced that his results prove that the moving of the monitoring stations was driven by the desire to lower artificially air pollution levels by measuring in less polluted areas. He mentions that the new monitoring regulations put into effect in 2006 included "new specifications...regarding the minimum distance from roadways that air pollution should be monitored." I don't know enough about international monitoring to know if perhaps these new standards were designed simply to bring China's monitoring better in line with international standards? Whatever the case, Mr. Andrews' point that different measuring systems were used is valid:
It has been widely reported that the number of ‘Blue Sky’ days in Beijing increased from 100 in 1998 to 246 in 2007, but these reported trends encompass a period during which air quality was evaluated in three different ways: (1) 1998– 1999, based on the 1996 Chinese national ambient air quality standards (2) 2000–2005, based on the 2000 revisions of the Chinese national ambient air quality standards and using the 1984–2005 monitoring station locations (3) 2006–2007, based on the 2000 revisions of the Chinese national ambient air quality standard and using the 2006–2007 monitoring station locations.
Ideally, officially reported data in the future should note the change in monitoring methodology on graphs showing data from both periods.

Impacts on Pollutant Concentration

As Mr. Andrews points out in the report, the Blue Sky Day metric is a "policy-relevant metric," and, "an effective communication facilitate greater public understanding." In other words, it is not a scientific metric, insofar as the cut-off point of API = 100 is rather arbitrary. Evaluating the effect of the aforementioned bias and monitoring station location change on reported vs. actual air quality requires analyzing pollutant concentrations.

Using a methodology to eliminate the reporting bias and normalize across similar reporting stations, Mr. Andrews' ran a new concentration analysis for PM10 and generated the following results:
In 2006, an annual average PM10 concentration of 161 μg m−3 was reported, however, if the monitoring station used from 1984 to 2005 continued to be used in 2006, the concentration would be ∼167 μg m−3—an average concentration ∼6 μg m−3 higher than reported. In 2007, an annual average PM10 concentration of 149 μg m−3 was reported, however, if the original monitoring stations continued to be used in 2007, the concentration would be ∼161 μg m−3—an average concentration of ∼12 μg m−3 higher than reported.
Stated differently, he concludes that Beijing's 2006 and 2007 reported values for PM10 were about 3.6% and 7.5% lower, respectively, than they would have been without data biasing or moving of monitoring stations. While this is concerning, the results are not nearly as dramatic as the difference in Blue Sky Days, as shown in Mr. Andrews' report (Figure 3 from the report):

In the above graph, note that the difference in Blue Sky Days (shown as columns) is much greater than the difference in PM10 concentration (shown as red lines). Note also that while the trending on Blue Sky Days changes dramatically based on the new analysis (increasing 2001-2005, decreasing 2005-2007), the trending on PM10 does not show a large change under the new analysis.


As I mentioned earlier, Mr. Andrews' result regarding the biasing of annual numbers of Blue Sky Days is powerful and dramatic. However, I'm not sure the result regarding 2006-2007 concentrations of PM10 is as dramatic, especially given the fact that PM10 has notoriously been one of the most difficult pollutants for Beijing to control. The Beijing EPB's own data show a 2007 PM10 concentration of 149 um/m3, higher than 2003 and 2005. While adjusting the concentration data according to Mr. Andrews' analysis may be important, doing so does not qualitatively change the 2001-2007 PM10 trends in Beijing.

Mr. Andrews concludes his report:
Although nine continuous years of air quality improvement has been reported in Beijing between 1998 and 2007, my analysis finds that these improvements, as indicated by the annual number of ‘Blue Sky’ days, are due to irregularities in the monitoring and reporting of air quality and not to less polluted air. Reported variations in air quality that occur as a result of changes in monitoring station locations or air quality standards, should be considered as inconsistencies in the metrics and not as actual changes in air quality.
While I agree with his analysis showing data biasing in the numbers of annual Blue Sky Days over the past few years, I think it is critical to clarify that such biasing does not mean that there was no improvement whatsoever in Beijing air quality over the last decade.