Great news! Today is Beijing’s 36th consecutive Blue Sky Day, a day whose Air Pollution Index (API) is 100 or below, indicating “excellent” or “good” air quality. As far as I can tell, this is the longest consecutive streak of Blue Sky Days in Beijing for at least ten years. Previously, there were only three streaks of 30 days or longer, one in 2006 and two during the Olympics.

Although we have seen gaming of the Blue Sky Day metric in the past, in this case both the data and public observation support dramatically cleaner air quality over January 2011 than in months and years past.

On the data side, for the 36-day period December 23, 2010 to January 27, 2011, I calculated an average particulate matter concentration of around 64 ug/m3 in Beijing. (API to PM10 concentration methodology here.) While this is still well above the WHO’s recommended annual limit of 20 ug/m3, this pollution level is less than half of that over the same period in 2009-2010, and is actually on par with the pollution levels during the Olympic (57 ug/m3) and Paralympic (71 ug/m3) periods, which were widely regarded as successful.

Looking at the data another way, an astonishing 18 of the past 36 days have been Grade I “excellent” air quality days in Beijing, which means the API is 50 or below. In 2001, Beijing only had 12 Grade I air quality days the entire year.

From a public observation perspective, I offer up for evidence the conversation I mentioned in my last post which made me start thinking about the streak, this e-mail I received two days ago from another friend:

I’ve been meaning to ask but since pretty much Christmas Eve I feel like has been the best stretch of air quality since I landed here…even better than the Olympics (which I caught the tail end of). My general air quality test is how well I can see the mountains from Tsinghua or Andingmen bridge. Rarely has there been a miss. I must have clearly seen stars all but a handful of nights and I can’t think of a day that’s looked polluted from start to finish. Are my eyes merely deceiving? Is the wind just being very helpful? Or has there actually been a drop locally?

and finally, the Beijing Air feature from the Asia Society, which features daily pictures, monthly averages, and weekly comparisons of Beijing’s air quality with that of New York. Here’s the past week comparison between Beijing (top row) and New York (bottom row):

They note, “This week has been by far the cleanest in terms of both blue-ness and air quality stable performance. Even New York looked less impressive.”

So why has the air quality been so uncharacteristically good recently? Unfortunately, I have no data-backed theories, although I would guess it’s a combination of existing pollution control programs and standards beginning to bear fruit, economic slowdown prior to the Chinese New Year holiday, and really favorable weather patterns that have prevented any pollution from building up. (Perhaps the lack of pollution build-up is also related to similar weather patterns that have prevented any measurable precipitation in Beijing since October 23rd.)  Regardless, it’s a great air quality start to 2011. Let’s see how much longer the streak can go.

Over the past few weeks in Beijing, the air quality has seemed uncharacteristically good. In fact, Beijing has had 25 consecutive Blue Sky Days – days for which the Air Pollution Index has been at 100 or below, representing “good” or “excellent” air quality. This morning a friend remarked that she couldn’t remember any other time when the air quality has been this good for so long continuously. I decided to investigate her claim.

Here’s what I found. Going back to 2001, I only found 6 streaks of 25 or more consecutive Blue Sky Days. They were as follows:

6/24/06 – 7/28/06 (35 days)
7/31/06 – 8/24/06 (25 days)
1/21/08 – 2/18/08 (29 days)
7/28/08 – 8/28/08 (32 days)
8/30/08 – 9/29/08 (31 days)
8/19/10 – 9/14/10 (27 days)

The two streaks in the summer of 2008 were clearly linked to the temporary pollution reduction policies put in place for the Olympics and Paralympics. I’m not sure what caused the other streaks, especially the excellent summer of 2006.

The current streak began on 12/23/10. Let’s see how long it can go! Track it yourself here at the MEP datacenter.

Happy New Year! For each of the past two years around this time (link to 2008, link to 2009), I’ve posted a summary of the previous year’s air quality in Beijing. This post contains some data and notes on 2010.

My data source, as always, is the datacenter of the Ministry of Environmental Protection, which archives historical Beijing air quality data here. (Note that I’m using the daily averages, not the recently released hourly data.) All I’m doing is copying the data into Excel, then parsing it and doing some conversions to look for patterns. The most important conversion is converting Air Pollution Index (API) to ambient particulate matter (PM) concentration, using the equations described here. This is important for two reasons. First, the conversion allows for averaging, which should not be done with API data directly. Second, ambient PM concentration is a much better indicator of the health impact of air pollution in Beijing, allowing for direct comparison to international air quality standards and existing health effect studies.

Now on to the data. The datacenter reports 363 data points for 2010 (3/15 and 5/21 are missing). Assuming those two days were Blue Sky Days yields a Blue Sky Day count of 286 and a calculated average PM10 concentration of 122 ug/m3. The Blue Sky Day count of 286 has been confirmed by the Beijing EPB, but the PM10 concentration value probably won’t be released for another few months.

As a reminder, Blue Sky Days are days for which the API is at or below 100, which China deems “excellent” or “good” air quality. Cities count the annual number of Blue Sky Days as an easily-understood measure of air quality progress, although the metric has been gamed in the past and is actually scientifically meaningless.

This figure shows trends of Beijing’s Blue Sky Days and PM10 concentration since 2000:

The Bad News: Beijing’s air pollution levels, as represented by ambient particulate matter concentration, have remained flat for the past three years, actually getting slightly worse from 2009 to 2010. This is consistent with results reported in mid-2010. Beijing’s air quality still does not meet China’s own air quality standard, and is six times worse than the recommended particulate matter target set by the WHO.

The Good News: Beijing’s 286 Blue Sky Days in 2010 far exceeded its target (266), and miraculously managed to beat last year’s total by just one day. In addition, there was a slight increase in the number of Grade I (”excellent”) air quality days as compared with 2009 (as shown in the above graph in light blue). This is dramatic turn-around from the way things looked in the first half of the year. Given that over 700,000 vehicles were sold in Beijing in 2010, I suppose the fact that the pollution didn’t get even worse can be viewed in some respects as a success.

Beijing’s Environmental Protection Bureau really struggled to call 2010 a success. On December 31st, they released a short note stating, “今年我市空气质量二级和好于二级的天数累计达到286天，占78.4%，比去年多1天，实现了空气质量连续12年持续改善,” meaning, “This year, the number of days in our city meeting the Grade II or better air quality standard totaled 286, representing 78.4% of all days, one more than last year. This has realized 12 consecutive years of air quality improvement.” The last statement is highly dubious, especially given my preliminary conclusion that the average PM10 concentration was higher in 2010 than 2009. It will be interesting to see how and if the EPB’s statements change when the PM numbers are released in the environmental annual report later this year.

Related posts:
Summary of Beijing’s 2009 air quality
Summary of Beijing’s 2008 air quality

Earlier this month, the Economist featured a nice piece about the ineffectiveness of current efforts to improve China’s environmental quality, including some discussion of recent decreases in air quality. The authors cite the official Ministry of Environmental Protection announcement for overall air quality averages in cities across the country, but run their own numbers for Beijing specifically, arriving at this conclusion:

Residents of Beijing, who hoped the clear skies they enjoyed during the 2008 Olympic Games would persist, have also resumed their grumbling. Smog is back with a vengeance…

Official data show a diminishing share of grade 1 (“excellent”) air-quality days since the games.

The claim is supported with this chart:

This chart caught my attention because it’s the first time I’ve seen “percentage of Grade 1 air quality days” used as an indicator of air quality. Usually, data for Grade 1 and Grade 2 are presented together. The reason is because China’s ambient air quality standard calls for urban air quality to meet only the Grade 2 level. (”Blue Sky Days” are days which have Grade 1 (excellent) or Grade 2 (good) air quality by the Chinese standards.) Charting percentage of days meeting Grade 1 or Grade 2 yields a very different impression:

Using this metric of Grade 1 or 2, there is no apparent decrease in air quality from 2008 to 2009, the drop from 2009 to 2010 seems minimal, and the overall situation appears much less dire (the percentage of passing days floats above 70% as opposed to 10%).

Two questions come to mind here. First, is it misleading for the Economist to use this unconventional metric? Maybe. The article neither describes what Grade 1 means nor justifies why “percentage of Grade 1 days” is an appropriate / better indicator of air quality, although Grade 2 is discredited using an comparison to the BeijingAir Twitter feed:

The American embassy in Beijing, to the annoyance of local officials, issues frequent air-quality readings for its part of the city. These, based on the presence of fine particulates, mostly ranged from “moderate” to “unhealthy” in the 24 hours after midday on July 31st. But the government called that period grade 2, or “good”. Incredibly, to anyone familiar with China’s perennially grey urban landscapes, fully 91% of days in 113 big cities in the first half of this year were described as “blue sky”.

Second question: is it correct to talk about percentage of Grade 1 days? That’s tough to answer. The technical answer is no, it’s not, because any use of “number of days” or “percentage of days” meeting a single standard is statistically meaningless. (For a short and nerdy explanation of this, see this post). That having been said, though, I do believe that scrutinizing Beijing’s air quality by looking at Grade 1 – instead of Grades 1 and 2 – days provides a much more reasonable snapshot of the actual air quality in the city. For one thing, China’s air quality limits for Grade 1 are much closer to internationally-recognized standards. For another, one would assume that there is lower risk for data manipulation around the Grade 1/2 border than around the Grade 2/3 border.

I raised the idea of looking closer at Grade 1 earlier this year. Maybe it’s time for a more in depth analysis, but I’ll save that for another post.

Last week, multiple media outlets (including Xinhua, the New York Times, and the Wall Street Journal) reported on MEP’s admission of worsening air quality during the first half of 2010. Here, I will take a closer look at how this was reported, what exactly this means, and what is happening in Beijing specifically.

First of all, the original announcement from MEP is here (Chinese only). Both Xinhua* and the Wall Street Journal made major mistakes in their reporting of the announcement. Both reported that the average atmospheric particulate level rose to 0.091 mg/m^3 from 0.002 mg/m^3 last year. This is incorrect. Doesn’t anyone check original sources any more? The MEP report says “可吸入颗粒物浓度同比上升0.002毫克/立方米。” This means that the PM level is 0.002 mg/m^3 higher than last year’s, not that last year’s value was 0.002 mg/m^3. Someone pointed this out in the comments section of the Wall Street Journal article (which claims the increase is “humongous”), but it still hasn’t been corrected.

The Wall Street Journal also made the mistake of claiming that “the first half of 2010 had the worst air quality since 2005.” This is also not true. MEP’s announcement, which the WSJ story links to, says, “自2005年以来，环保重点城市空气质量优良天数比例首次出现下降，可吸入颗粒物浓度首次上升。” The correct interpretation here is that the first half of 2010 is the first period since 2005 that there has been a decrease in air quality from one year to the next. In other words, the trend of improving air quality has changed. At least Xinhua got this one right:

Economic recovery has partly caused the country’s air quality to fall in the first half of the year, the first such fall since 2005, figures from environmental authorities showed on Monday…”It was the first time for these cities to record a fall in the number of days with good air quality and a rise in the concentration of inhalable particles since 2005,” ministry spokesman Tao Detian said.

Unfortunately, the WSJ’s mistakes are already bouncing around the blogosphere.

Of course, despite the mistakes I’ve pointed out, the story is still quite significant. After years of official statistics showing improving air quality, MEP’s air quality data now shows a very slight increase in ambient particulate matter concentration. The data MEP gives are average pollution levels for 113 major cities, which is a little strange, since pollution levels vary widely across China. Although the averages are an interesting snapshot (and it is significant that MEP is reporting this bad news), these averages are not very meaningful; they say nothing about regional trends / changes or population exposure. This is an important area for more detailed research.

MEP’s announcement also gives averages in percentages of days meeting Class I and II air quality standards (so-called “Blue Sky Days“), but this metric is meaningless, as described previously on this blog.

What is more interesting is looking at data on individual cities. After all, most people spend most of their time in a single city. Plus, local and regional pollution control programs may vary from place to place. For Beijing specifically, I ran my own analysis of Beijing’s API data for the first half of the year using data I downloaded from MEP’s datacenter. After converting API to PM10 concentration using the methodology described here, I calculated the average PM10 concentration for the first half of 2010 in Beijing to be 124 ug/m^3. I also produced the following figure:

The figure shows that Beijing’s air quality, using average PM10 concentration as an indicator, has not shown improvement over the period 2008-2010. This trend is a continuation of the stagnant pollution levels I described earlier this year. Although MEP’s 113-city average (91 ug/m^3) is below China’s ambient air quality standard (100 ug/m^3), Beijing’s air quality remains well above China’s own standard, which is well, well above the WHO’s.

For those of you keeping track of Blue Sky Days, the Beijing EPB announced that there were 140 Blue Sky Days in the first half of the year, which, despite the increase in air pollution, somehow means Beijing is still on track to meet its Blue Sky Day goal. But this is a subject for another post.

Anyone who read this blog over the period 2008 to 2009 will know that I often repeated a two-part mantra: Beijing’s air quality is getting better, but we have a long way to go. I always felt that acknowledging the first part was critical to making progress working with China, and I was happy to see the New York Times article last October making this exact claim (headline: “Beijing’s Air is Cleaner, but Far from Clean;” my analysis here) It is frustrating and sad that this is no longer the case, even by China’s official data.

*To be fair to Xinhua, their mistake was only one word. Their report states, “The amount of inhalable particles, a major air pollution index, was also 0.091 milligrams per cubic meter in these cities, rising from 0.002 milligrams per cubic meter over the same period last year, the ministry reported.” The problem in this sentence is the one word “from,” which significantly changes the meaning (from incorrect to correct) if removed.