how long can beijing’s good air quality streak last?

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.

4 Responses to “how long can beijing’s good air quality streak last?”

  1. Simon LIU says:

    In Beijing, the Sept normally comes with good weather due to the currency flow and pressure, and during the Jan-Feb CNY period, for 10-14 days, far less people stayed in Beijing and less communte to work.
    So no surprise to witness the streaks during these periods, you will repeatly obeserve this pattern.

  2. Simon LIU says:

    I believe that in London, or NYC, during the Xmas period, the API should be better than the average of other daysin winter. Since many work force are out of town for holidays or family reunion.
    Surprisingly, HK API is somehow getting worse and worse, not even better than Shanghai.

  3. Simon LIU says:

    If I am not wrong, Beijng AQI measures PM10 instead of PM2.5, if this means all particles bigger than 10 or 2.5, the PM2.5 index number should be larger than PM10’s.
    The air in BJ in many days feels like to breathe in a blanket of chemical gas, esp some humid and lower pressure summer days, windy and dusty spring days, Sulphur smelly winter. And all year long vehicle exhausted gas from the traffic congestion.

  4. Vance says:


    Thanks for the comments. It’s a good point that a lot of activity slows down over the CNY period, although we have also seen times in the past where all the fireworks displays have increased pollution levels (e.g. Let’s see what happens when and if this current streak lasts until the official holiday beginning 2/2.

    Regarding PM10 and PM2.5, these metrics actually measure all pollution below a certain size cutoff, which means that PM2.5 is a subset of PM10. In other words, the PM2.5 reading should always be below the PM10 reading if sampled consistently.


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