Here's a graph from the government that gave me a shock. It shows that the pollution we generate in Hong Kong fell significantly between 1990 (on the left) and 2007 :
How can that be, when we all know that air quality has got much worse?
Compare it with the Batgung Smog Index for the same years:
In the early 1990s, as we produced more pollutants the amount of smoggy weather (the red line) also increased. But in the mid 1990's there was an important change: we cut our emissions of pollutants, yet the amount of smog just kept on rising.
So since the mid-1990s, we've lost control of the smog. It now depends on levels of pollutants that are produced outside Hong Kong, ie in southern China.
But we still see claims that local emissions are the source of our air-quality problems:
I think we're disagreeing because we're really talking about two different things. Let's clear that up first, by turning to the government for their description of the problem :
The two greatest challenges are local street-level pollution and regional smog. Diesel vehicles, particularly trucks, buses and light buses, are the main source of street-level pollution. Smog is caused by a combination of pollutants mainly from motor vehicles, industry and power plants in Hong Kong and the Pearl River Delta.
Instead of talking about 'Hong Kong's poor air quality', let's be clear we're really talking about two different issues:
If we can agree on that, we can move past the argument about whether our air-quality problems are caused by local, or regional pollution: Street-level pollution is a result of local, diesel vehicles, while the smog is mainly caused by pollution from outside Hong Kong.
Then on to the important question, which of those two should we fix first?