Batgung

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 [1]:

How can that be, when we all know that air quality has got much worse?

Compare it with the Batgung Smog Index[2] 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:

• HK Magazine, June 12, 2009
  At the beginning of this month, levels recorded at all 11 general monitoring stations were above World Health Organisation (WHO) guidelines. This despite the low-wind [sic] speeds recorded by the Observatory, which Greenpeace campaigner Prentice Woo Wai-Muk said revealed that it was surely being produced locally.
  
  
• Albert Cheng in his SCMP column, 15^th Aug 2009
  Hongkongers have for many years blamed the city's poor air quality on the polluting factories on the other side of the border. Indeed, many of these factories have suspended operation since the economic downturn began last year. But, despite this, our air quality remains atrocious, which has unequivocally proved that the pollution is local.

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 [3]:

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:

• Local street-level pollution
• Regional smog

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?

References:

1. These are the government's estimates of Sulphur Dioxide (SO2) produced in Hong Kong over the years 1990-2007. The graphs for other pollutants vary slightly in shape, but all end at much lower values in 2007 than in 1990. See them all here. 
2. This line shows the Batgung Smog Index, derived from the Observatory's 'number of hours of reduced visibility' figures. Full details. 
3. GovHK: Air Quality in Hong Kong