HK Air Pollution Varies with Weather

I saw a recent item in the South China Morning Post, saying that even though June 2008 was the wettest month on record for Hong Kong, pollution levels were still high; said to have surprised experts.

Just had quick look at data on Env Protection Dept website - and can see that for the general stations, air pollution was mostly medium or low: at Tap Mun, say, air pollution was low for 564 hours. But at roadside stations, air pollution was always medium or high - not low for even one hour.
So, air pollution at roadsides not readily swept out by rain and/or winds off the sea - but seems the Pearl River Delta filth does indeed get carried/washed away with such weather. This seems right to me - as lately had scintillatingly clear days, when not raining, by contrast to typical smog.

Checking December last year, when air drier, winds more off mainland, see very different picture. Still bad at roadsides, of course, tho not a massive shift: mostly high, sometimes very high.
But at general stations, see a major shift: just 13 hours in total (12 at Tap Mun, one at Tai Po) with low air pollution, otherwise moderate or (mainly) high, with tens of hours of very high air pollution.
Here, seeing shift to pollution over Hong Kong being from Pearl River Delta. Can see this by eye, too, as air woefully murky during dry conditions with northerly breezes/light winds.