final day of temporary air quality measures

Prior to the Games, a major question asked on this blog and elsewhere was, "Will Beijing's efforts to control the air quality work?" (Some analysts even boldly predicted that they wouldn't.) And now, here we are, on September 20th, 2008 - the final day of the temporary environmental policies implemented by the Beijing government to control air quality during the Olympic and Paralympic period - with a resounding "yes" answer to that question.

Through the banning of over half the cars on the roads, the temporary closing of factories, the shutting down of construction in the city, and a little luck from the weather (on second thought, not luck), Beijing managed over the past two months to reduce air pollution by around 50% (analysis at the bottom of this post) and yield the cleanest air the city has seen in ten years.

Let's look one last time at the graph of daily Air Pollution Index during the Olympic period:


And some averages:

Average API, Two-month Olympic period, 7/20/08 - 9/20/08: 62
Average API, Olympics, 8/8/08 - 8/24/08: 49
Average API, Paralympics, 9/6/08 - 9/17/08: 59

According to my analysis, these numbers are comparable to the air quality during the 1984 Los Angeles Olympics (in that previous post, I estimated that the air quality during the Los Angeles Olympics would have rated as a Chinese API of 59).

To get a better sense of just how much better Beijing's air actually was from 7/20 - 9/20 of this year, it makes sense to convert the numbers from API back into particulate matter concentration (explanation at bottom of this post), and compare those numbers against some past data.

The following table shows average API and PM10 concentrations for some selected time periods over the past three years (2006 and 2007 PM10 data from Beijing EPB environmental annual reports):

--
Update 10/20/08: Found a minor mistake in the first version of the PM10 data I showed below; fixed now.
---

From this data, we can calculate that, according to PM10 concentrations, Beijing's air during the two-month Olympic period was:

-- 44% less polluted than the first half of 2008;
-- 40% less polluted than the same period in 2007;
-- 47% less polluted than all of 2007;
-- 51% less polluted than all of 2006.

These numbers are comparable to the Beijing EPB's statement that concentrations of major pollutants were cut by 45% during the month of August.

Lastly, for a different perspective on the impact of the temporary air quality control policies, I wanted to show API data over a much longer time period. The following graph shows daily API readings from the beginning of 2006 to today:


I find this graph fascinating (granted, I'm an engineer). Two key observations jump out at me: first, the average API during the Olympic period is clearly lower than any previous periods of comparable length. Second, perhaps more interestingly, the extreme variability has been reduced tremendously; specifically, Beijing succeeded in prevented any severe spikes in air pollution that were so common in previous periods.

Which, of course, leaves me wondering: how long before we see another one of those dreaded spikes?