Where does Hong kong's air pollution come from?

Last month saw several articles in the media with headlines like:

Hong Kong producing most of its own pollution (AFP)

Local sources blamed for most air pollution woes (HK Standard)

If they are true, were earlier claims about regional pollution affecting us just a smokescreen? We’d certainly need to focus our efforts on reducing local sources of pollution, instead of those over the border. But if they’re wrong, we risk diverting people’s attention from the real source of the problem.

Unfortunately, they’re wrong.

Both articles were covering a report and press release issued by a local think tank, Civic Exchange. Neither document directly says that ‘Hong Kong Produces Most of its own pollution’. But for several reasons they make it easy for readers to reach this misunderstanding.

First the press release, which is probably what most of the media focused on. It starts with the headline:



53%? So over half of our air pollution comes from local sources?

No – but it’s an easy mistake to make. Yes, for over half (53%) of the days in a year more of our air pollution comes from local sources than from regional sources (ie those in Guangdong). BUT, on the days when most of our pollution comes from the regional sources, overall pollution levels are higher. So, over a whole year, more of the pollution (other studies put it at 60-70%) comes from regional than local sources.

Then how about that second headline? That also suggests a lot more is under our control. But what would be a ‘dramatic improvement’?

I expect it to mean an end to, or at least a significant cut in the number of days when thick smog blankets all of Hong Kong. It’s that combination of high pollution levels, the fact I can see it, and the feeling there’s nowhere to escape that makes me want to pack my bags and leave.

But even eliminating all locally produced pollution would have little effect on those smoggy days, since they’re usually days when ‘regional pollution’ predominates. Also, even on the worst local-pollution days, the high levels tend to be concentrated in just a few areas of Hong Kong. On the worst of the regional-pollution days, it affects all Hong Kong, giving that ‘no escape’ feeling.

If you then go on to read the full report, there’s another pitfall awaiting you.

It classifies polluted days as belonging to one of five different pollution patterns. There are three patterns where regional pollution dominates, and two when most pollution comes from local sources. The study gives charts showing typical pollution levels at different sites around Hong Kong. Here I’ve brought the readings for Mong Kok together:

So you’d probably rate the days with the ‘Local Vehicle / Power Plant’ pattern as having the worst pollution? But if you squint at the numbers you’ll find the readings are drawn to different scales. If we use the same scales for each chart, we get quite a different result:

I’m in two minds about the report. On one hand it seems unfair to criticize it. It makes an important point that pollution levels are under our control most of the year. It also gives good recommendations (I especially like the measures to reduce pollution from shipping) that will help make Hong Kong’s air cleaner.

But on the down side it seems very easy to misinterpret, giving readers unrealistic expectations for the benefits of local changes … 53% reductions! The ‘wrong’ interpretation is exactly what has been reported by several local and international media. When actual improvements turn out to be far less dramatic than expected, it leads to confusion at best, or disappointment and cynicism at worst.

It would have been better to focus on the results of the study that are smaller scale, and improvements that can realistically be achieved, eg the effects of pollution from shipping on the areas around the container port, and the measures to reduce them. Not such a news-grabbing headline perhaps, but one where it is true to say the area can ‘dramatically improve local air quality despite regional pollution’.

Getting rid of those smoggy days is still going to need lots of help from our friends across the border.


Further info: Has misinterpretation really been a problem, or am I imagining problems where none exist? We can take a look at how the report and press release have been reported in the press to see how they have been interpreted, and the type of expectations they set.

I ran a google search for “civic exchange institute for the environment pollution”, and found the following references to these documents in the first 20 results:

  • Clean Air Initiative: Headline: “[…] local sources are the primary influence on Hong Kong’s air quality and not regional sources.”
  • AFP (A worldwide press agency, so this article was also shown on several other news sites such as Yahoo News): “Hong Kong producing most of its own pollution: study HONG KONG (AFP) — Most of the pollution blighting Hong Kong is produced in the city itself rather than neighbouring southern China, according to a study released Wednesday which contradicts previous research.”
  • The HK Standard: Headline “Local sources blamed for most air pollution woes”
  • Clear The Air: '"Dirty Sky Days" More than half are from Hong Kong sources’
  • The Economist: “However, a new report […] finds that in 2006 Hong Kong's air pollution was caused more often by local sources (road traffic, coal-fired power stations and ships) than by factories in southern China. Local emissions were the main cause of pollution on 192 days; those from the Pearl River Delta on the mainland on 132 days. The other 41 days had low pollution.

    This does not necessarily contradict the government's findings. Pollution from the mainland may well be worse measured by volume, so more pollution probably does come from the mainland (where many factories are owned by Hong Kong firms). But the findings do suggest that Hong Kong can itself do more to improve its air.”

So, a well-balanced article from the Economist, and the Standard’s article is also more balanced than the headline suggests. But the incorrect ‘Hong Kong producing most of its own pollution’ interpretation is more common.



I'm a moderately new reader. Excellent insight! It's more regional than I had expected.

I've been asked to compare the air quality of Taipei and HK, and I told him that I felt Taipei's ground-level (i.e. roadside) air quality is worse, but that HK's regional air (smog) is worse.

Interesting, and disappointing

MrB's really on to something, I think -- I also find it very disappointing that an organization like this would mess with the scale of its charts in order to create the effect they want -- i.e. making all of their modes of pollution sources look equally bad -- but it's hard to imagine why they wouldn't otherwise stick to one scale.

One insight I did gather from the report: the fact that the 'Regional west' air is so much worse than the 'regional east' air. It's been my knee-jerk observation/assumption over my years here that the western parts of HK suffer from really bad air more often than the eastern areas do. And this study does seem to lend some credence to this. Understandably, I guess, if there's regional pollution flowing into HK from the west, then the western parts of HK are going to suffer more. If you're interested in this, it's worth downloading the report itself in .pdf, and taking a look at the satellite photo they provide of the 'regional west' pollution pattern (Figure 6 on p. 20 in the appendices) -- it's pretty striking.

Mr Tall

How long can China pollute for free?

An article on MSN talks about the current problems pollution is causing in China, and suggests some of the limits that will cause the China government to take action.


Air Pollution Charts

"I also find it very disappointing that an organization like this would mess with the scale of its charts in order to create the effect they want".
Readers and viewers of graphs should always read the scales on the X-Y axis before looking at the curves or bars on the graphs. In Powerpoint presentation when time is limited, the presenter should describe the scales before going into its contents.
Where a group of charts are presented simultaneously for comparison purposes, the same scale for all charts are preferrable, but this is not always the ideal.
As with engineering, financial and medical charts, air pollution charts don't need to start at zero values or have idential scales.
In my 40 years of engineering work, manipulating the scales of graphs have been necessary on some occasions and has never invited accusations of skewing the story or facts. Sometimes, it is essential to do it to enhance your presentation without bias or causing misunderstanding.

Air Pollution Charts

How's this for pollution? Not only can I not see Kowloon today (well, just barely) but I had to shut all my windows because the air has a serious foul stench to it.

Not sure you could doctor any scales or charts to show a bright side to this, I guess I just live in the wrong region of Hong Kong.

Air Pollution Chart

Sometimes a picture is worth a thousand words and your photo may indeed be one of them. However, the poor visibility could have been caused by fog or mist. Good thing you mentioned the foul and stench smelling air and I have no doubt of your comments.
Is this a "region" pollution or site-specific which would be attributed to HK-Kowloon's factories, car exhausts and poor sanitation including sewage treatment.
Showing charts is a small part of the story. Can they do a mass-balance analysis by measuring and analyzing air movements and the pollution particle-loadings into and out of the city?


Further to a comment I made in my own blog a few days ago - there are 60,000 factories just over our borders which are owned by HK residents ... it's not 'THEM' it's 'US' causing the pollution.

Who owns the factories?

The predominant winds during the summer are southerly wind, SE, then SW, in that order. Easterly wind also occurs but I stay indoor because of the rain.
Now that autumn (and soon winter) is here, there will be more northerly wind which means you will be seeing and breathing in (more) the pollution from Kowloon and mainland factories.

Who owns the factories?

Another report from Civic Exchange is a good read if you're looking for more information about this. eg the opening statement states:

Hong Kong is the largest source of outside investment in Guangdong’s manufacturing with more than 53,000 plants there in 2003. So far, however, we have to conclude that the Hong Kong owners and managers of a large share of Guangdong’s manufacturing have not faced up to their responsibility for much of the air pollution Hong Kong imports from across the border.

Here is the full report: "Owing up to Responsibility for Manufacturing Contributions to the Pearl River Delta’s Poor Air Quality"


53% ?

The misleading interpretation of the Civic Exchange report continues. In the current (May 16, 2008) copy of HK Magazine, the 'Why aren't we greener?" article quotes the Chairman of Clear the Air as saying "53 percent of our air pollution is locally generated", which as we showed above is not the case.

The full paragraph reads:

"53 percent of our air pollution is locally generated", says Christian Masset, Chairman of Clear the Air. "Which means 53 percent of the responsibility - and 53 percent of the opportunity for change - lies at home."

Ironically, later in the article is a section titled "Government Denial", which starts:

If the government's refusal to act on the above sources doesn't underscore enough of its dismissive attitude, one need only consuider their misleading statements and false characterizations for confirmation.