“crazy bad” air quality in beijing

crazy bad aqi chartI’ve taken the liberty of updating the US EPA’s AQI colors chart

A few days ago, the US embassy’s BeijingAir Twitter feed, which automatically reports Beijing’s hourly air quality, made headlines across the web by announcing that the air quality was “crazy bad.” Although the wording was quickly revised to the more politically-palatable “beyond index,” the impact was immediate. “Crazy bad” air was all the buzz of the blogosphere and at social events over the weekend; I have a feeling “crazy bad” would make it onto Beijing’s Word of the Year list, if there were such a thing. MyHealthBeijing‘s Dr. Richard St. Cyr even suggested “Crazy Bad” T-shirts.

In this post, I’ll look a little closer at the data behind the Crazy Bad incident to see what we can learn. The graph below shows hourly and daily data from the BeijingAir Twitter feed along with official air quality data from the Ministry of Environmental Protection (available here, Chinese only). For clarity, I show all data in terms of particulate matter concentration, not standardized index. (I’ve converted MEP’s reported API numbers to PM concentration; for background on the difference and methodology, see this post.) Note that MEP’s data is reported for a 24-hour period from noon to noon, which is why the daily data changes at noon each day. The break in the red corresponds to the BeijingAir Twitter feed not reporting any data for a couple of days after the Crazy Bad incident.

crazy bad

This graph reveals some really fascinating info:

1) The Crazy Bad spike on Thursday and Friday last week was both preceded and followed by gorgeous, wonderfully clean weekend days. On 11/15, the air quality was, by all accounts, “good.” By 11/18, though, the air pollution had steadily risen to what the US calls “hazardous“/”crazy bad,” and China calls “heavily polluted” (“重污染”). After the steep rise, the air quality improved just as dramatically; MEP’s reported PM10 numbers dropped 297 points – from 334 to 37 – from 11/21 to 11/22 alone. This demonstrates just how quickly the air quality can change in Beijing – both for better and for worse.

Why did it change so quickly? The start of the heating season on 11/15? Possibly, although that wouldn’t explain the sudden drop beginning 11/20. To be honest, the answer is probably less dramatic: weather. Most day-to-day pollution changes in Beijing are caused by changes in temperature and wind patterns. If there are a few days of static air, or light winds blowing from the southeast and trapping pollution against the mountains to the north and the west, the pollution builds up very quickly. I should find the time to post separately about this.

2) MEP’s air quality data tracked the embassy’s with reasonable consistency. This is actually encouraging; we should be grateful at least for some degree of accuracy and transparency with official data. There are some differences, but we shouldn’t expect them to track exactly. This is because the MEP data is an average of multiple sites across the city, while the embassy data is just a single point. Plus, they are measuring slightly different things.

In the past, we have seen situations where rapid and very short-term pollution spikes highlighted by the BeijingAir hourly readings were not reflected in daily MEP averages, but that doesn’t appear to have happened here.

(As I point this out, though, I should also note that I do not intend to make excuses for or to justify China’s current reporting mechanism. For the record, I would like to see at least three immediate changes to China’s air quality reporting: hourly release of data, more representative descriptions of health impacts, and some sort of real-time alert system for at-risk populations to avoid exposure.)

Lastly, a few data highlights for the numbers geeks out there (background on international standards here):

US EPA daily ambient air quality standard for PM2.5: 35 ug/m^3
Peak PM2.5 concentration reported by BeijingAir, 11/19: 557 ug/m^3

WHO recommended daily limit for PM10 exposure: 50 ug/m^3
China daily ambient air quality standard for PM10: 150 ug/m^3
Peak PM10 concentration reported by MEP, 11/19: 430 ug/m^3

12 Responses to ““crazy bad” air quality in beijing”

  1. You’re breathing it wrong.

    Sent from my ChiPad

  2. Antonio says:

    What I think is: what is the credibility of a measure made by the Embassy of a country that never signed Kioto Protocol and is ALWAYS criticizing China for everything, real or not?

    I guess Americans are very happy of themselves, but for the rest of the world, their country is quite more dangerous than China…

  3. Vance says:


    It’s a fair question. The unprofessional use of the term “crazy bad” here certainly undermines the embassy’s credibility, and makes one question their true motives (e.g. providing accurate data to concerned residents or taking pop shots at China?).

    However, I should point out that, although I agree that the US has little or no credibility when it comes to international climate negotiations, in this case we’re talking about local air pollution, which is a different issue. The US has decades of experience in monitoring, reporting, and controlling air pollution, so I think it’s important to consider that experience separately from their approach to climate change.


  4. I think the US Embassy’s feed has provided an invaluable service to the community these last couple years. Many schools depend on their hourly feeds to make appropriate action plans for their children, and many Beijingers have used the feed to make better health decisions (whether to wear a mask that day, whether or not to walk outside etc). I am constantly telling my patients about their feed, and it is universally appreciated. Kudos to them!

  5. Vance says:

    Dr. Saint Cyr:

    I completely agree. The service is invaluable, and a wonderful tool for the Beijing community, especially at-risk populations. I should clarify my previous comment to say that I personally do not question the motives of the embassy, only that I can see how one might misconstrue the “crazy bad” incident into just another example of arrogant US criticism of China.


  6. Thanks for this very cool post, Vance. And especially that graph — it is indeed comforting that the MEP concentrations match…so can you please help explain the usual disconnect between those raw data and the published AQI? Perhaps you have a previous piece on this, but what would that same chart above look like with AQI instead of raw concentration? Or also another graph overlay with “warning” levels. Or is is always hard to do since it’s a different comparison, PM10 to 2.5?

  7. Vance says:

    Dr. Saint Cyr:

    The disconnect could be caused by at least four reasons I can think of. The reality is probably a combination of all of these:

    1) MEP measures PM10, while the embassy measures PM2.5. In theory, PM2.5 is a subset of PM10, so the PM2.5 number should always be lower than the PM10 number, but there could be differences in measurement methodology. I’m not sure what methods and technologies are used by MEP vs. the embassy.

    2) MEP averages over many stations, while the embassy measures only one station. I would generally expect the average to be lower since it encompasses some urban sites where the pollution levels are lower.

    3) MEP averages over 24 hours, whereas the embassy reports one hour at a time. If pollution levels drop overnight, for example, a daily average would appear lower that what you might expect based on what you saw during the daylight hours.

    4) The MEP data (or, to be fair, the embassy data) could be incorrect for any of a variety of reasons.

    Hope this helps. Anyway, with the new hourly reports from MEP, it looks like we’re about to have a ton more data to start exploring, so these questions might be moot!


    More / similar analysis in this post: http://www.livefrombeijing.com/2009/06/more-info-on-beijings-618-air-quality/

  8. elizabeth wilson says:

    This is great stuff. I’m giving a presentation tomorrow and this and (credit to you) will be a big part of it. Seeing this data up close is so interesting. Are similar data available for other Chinese cities (think Taiyuan….).

    At any rate, I hope all is well.

  9. Vance says:


    Daily MEP data is available for over a 100 cities in China, including Taiyuan. (The direct link for Taiyuan is here: http://datacenter.mep.gov.cn/TestRunQian/air/airCityMain.jsp?city=%CC%AB%D4%AD.)

    Last week, MEP also started hourly reported for these cities, but even if they are storing that in a publicly accessible database it only goes back to last Thursday!

    In any case, let me know what your specific needs are and I’m happy to help.


  10. Louie Cheng says:


    Great to see some actual trends and this is the first time I’ve seen actual PM2.5 data mapped directly against PM10 for China air. I wish that we had PM2.5 reporting for Shanghai, but I haven’t found any source yet. Must be all that government money you guys have :)

    In Shanghai, the PM2.5 numbers for clients we’ve tested recently indoors has averaged around 130-230ug/m3. Do you have any data around comparative numbers up there in Beijing? Given the relatively higher PM10 and the degree to which PM2.5 tracks, I would expect then PM2.5 indoor numbers to be also comparatively higher in Beijing.

    Turn on those HEPA filters guys!

    Also, I notice that you are using the 24-hr EPA standard. Assuming that we are looking at this over the long-term, instead of as a short term exposure limit (like in the workplace), wouldn’t the annual (and much lower — 15 instead of 35 ug/m3) standard be more relevant to the average joe?

    – Louie

  11. Vance says:


    Thanks for the comments and questions. Some quick responses:

    – I actually ran some similar PM2.5 and PM10 comparative analysis in June of last year; check out this post: http://www.livefrombeijing.com/2009/06/us-embassy-outed-as-source-of-beijingair-twitter-feed/

    – Maybe you should write to the US consulate in Shanghai about setting up a PM2.5 monitor there…

    – Those PM2.5 numbers are shockingly high. Is that really what we are breathing indoors in China? I’ve done very little research into indoor air quality.

    – It’s true that the yearly standard is ultimately more important. The only reason I showed the daily standard here is because I felt it was the most fair when looking at only one day’s data. When I aggregate over a month or more I compare against the yearly target.


  12. Glenn says:

    The AQI hit a new high/low tonight . It broke 600ppm

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