Thanks to Deep Lung and Osmo for pointing out this change in the list of the Beijing Environmental Protection Bureau’s monitoring stations. I assume this is the agency that passes the daily API value to SEPA for its national listing, so it is important to understand how the value is calculated.
Pre-2008 there were 27 stations in the list (for example 25 Oct 2007) and from this year there are still 27 stations (for example 8 Jan 2008). Note that the first line in both lists is the average; it looks like this is the number that SEPA uses for Beijing- although it does not seem to be the normal average of (sum/number of stations), maybe they use the actual PM10 values to calculate the average and convert to API afterwards.
However, more interestingly, if we look at the above picture, we see that the number of stations in the central districts have decreased:
- Dongcheng: 2 to 1
- Chaoyang: 3 to 2
- Fengtai: 3 to 2
And extra stations in Miyun, Daxing, and Yangqing. So the sum remains 27 stations, but 3 rather central locations have been removed, and 3 created in the outlying districts where the API is usually lower, so the average will definitely be lower from day 1; seems like a rather cheap trick doesn’t it?