googling with keywords, “Beijing sandstorms” gets over 99,000 hits discussing all these alarming stories of environmental degradation. One of these sandstorms occured as recently as July of 2008.
Here are couple of links:
http://www.chinapost.com.tw/china/local%20news/beijing/2008/03/19/147845/Beijing-shrouded.htm
http://www.youtube.com/watch?v=myVNx1RNbxE

How does wind impact all this? I get the sense that there is no wind in Beijing, at least it looks calm on most days. Is there a wind correlation?

And below are the “official” Max, Min, Median and Averages for PM10 for these same days (computed by Finder!) and the last column lists BBC’s reading (snapshot) of PM10:

Date Min Max Median Avg BBC-PM10
12/08/08 20 48 31 31.37 41
11/08/08 10 52 39 35.4 54
10/08/08 55 94 81 79.44 278
9/08/08 55 94 81 79.56 110
8/08/08 84 100 94 93.52 156
7/08/08 80 108 94 94.07 191
6/08/08 65 95 87 85.41 186
5/08/08 78 114 90 90.19 104

Only in last two days have the BMEPB data in the same range as BBC’s.
Here is BBC’s version of how they measure PM10 levels:
http://www.bbc.co.uk/blogs/thereporters/jamesreynolds/2008/07/pollution_problem.html
and
http://news.bbc.co.uk/2/hi/asia-pacific/7498198.stm

More updates follow over the next several days.

Further Beijing/Beijing province is landlocked and its likely that the air-pollution may have drifted in from cities in the surrounding provinces of Tianjin and Hubei.
See for eg. this aerial photo from a USNSF project:
http://www.nsf.gov/news/news_summ.jsp?cntn_id=112022&govDel=USNSF_51

Thanks to recent downpours, the PM10 levels have plummeted to what WHO considers as safe.