The trend in 2008: down and up
Looking at the graph below, we can see the daily API values for Beijing in 2008 in blue, and a black trend line based on a moving average over 10 days. The first half of the year was similar to what we have seen over the past years, with an average of around 100, with severe peaks above that. However, from June the trend was downwards, reflecting the success of the efforts for clean air during the Olympic Games. The trendline even dipped under the 50 line, which is considered acceptable air quality, around mid-August.
Unfortunately the trend since August has been upwards again, as a result of lifting the temporary restrictions (traffic, industry). Let’s look at the monthly averages:
- August: 56
- September: 57
- October: 75
- November: 80
- December: 98
- January: 82
- February: 90 (first 6 days)
So despite the relatively good air of the summer of 2008, December seemed back to normal (read: very unhealthy). The yearly average API for 2008 stood at 87, which is certainly significantly better than the values around 100 we have been seeing over the last few years.
Of course this is all based on officially reported data. The issue of their reliability remains; as we have discussed last year, there is something strange about the absence of API values of 101 and 102, which statistically is extremely unlikely.
Of course this is related to the concept of ’blue sky days’ which are counted as having an API of 100 or less, and which are an important policy performance indicator. So imagine the pressure on man and machine when the value comes out as 101 or 102.. It Just Does Not Happen, and some things never change.