beijing breaks record for longest streak of consecutive blue sky days – best air quality in years

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):

asia society jan 11 1
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.

5 Responses to “beijing breaks record for longest streak of consecutive blue sky days – best air quality in years”

  1. elpato says:

    Next week the temperatures are set to go up to +10 celsius. If this means that there is a shift in prevailing air currents we should very quickly see a return to the pea soup. Certainly the blue skies have been as dramatic as the pea soups were dreadful during so much of the rest of the year. As traffic has certainly not decreased in Beijing, nor has construction, most likely the blue skies are linked to the bitter and dry winter. I hope we can get nice weather without choking to death, but I am not willing to put a wager on it.

  2. Ethan says:

    Amen. Since I got here a few weeks ago I’ve been amazed at how many gorgeous, sunny days we’ve had. Really takes much of the bite out of the chill outside.

  3. Eugene says:

    One of my greatest memories of Beijing was looking westward out the 9th floor window at the Peruvian Consulate in the Sanlitun Diplomatic Building at sunset in early January, 2006. It was super cold, with a strong north wind, and the sky was beautifully blue and clear with snow shimmering on the city and the mountains to the west!

  4. It has been really nice! As for why, my personal view is the unusual weather pattern — it’s definitely windier in general each day, and I notice because I bike to work each day. We’re stuck in an unusually dry and windy weather pattern.

    By the way, Vance, have you had the time to compare the new Beijing AQI numbers with the US Embassy’s data?

  5. Not So Fast says:

    Has anyone noticed that it has not precipitated since at least mid-October? Just saying…

Leave a Reply