So You Thought Hong Kong’s Pollution Comes From Mainland China?

Air pollution is a serious problem in Hong Kong, and Hong Kongers often complain that the worst of it comes from Mainland China. Is that fact or a convenient scapegoat? After all, Hong Kong is a densely populated developed city with one of the busiest ports in the World – it is likely that they have their own sources of pollution. I set out to find data on where exactly Hong Kong’s air pollution comes from.


How Much of Hong Kong’s Pollution Is Local?

One way to answer this question is see what happens to Hong Kong’s air pollution when the wind blows from the Mainland. To do that, I analyzed data on Hong Kong’s PM2.5 and wind direction and speed from 2016 to 2018.



Where Hong Kong’s Pollution Comes From

Anytime the wind blows from the West-North-West to East-North-East (the arrows below), Hong Kong’s air is coming from Mainland China. If most of Hong Kong’s air pollution is coming from China, we should see air pollution spikes whenever the wind comes from that direction.

Hong Kong's Pollution map


Does Wind Direction Affect PM2.5?

When the wind was blowing from directions not from Mainland China, the average PM2.5 level was 25 micrograms. In contrast, when the wind was blowing from Mainland China, the PM2.5 level was 29 micrograms, which is a 15% increase.

wind direction increased Hong Kong's Pollution by 15%

How wind affects Hong Kong's Pollution

This data gives two (somewhat contradictory) takeaways:

  • Yes, Hong Kong’s air pollution is 15% worse when the wind blows from the Mainland.
  • However, even when no air is coming from the Mainland, Hong Kong still averages more than twice the WHO annual limit of 10 micrograms.

Thus, even without the influence of the Mainland, Hong Kong still has significant sources of air pollution from within.


Does Wind Speed Affect PM2.5?

When there was no wind, the PM2.5 level averaged 24 micrograms. This is a few times over the WHO’s annual limit of 10 micrograms. This proves that even without external influence, Hong Kong’s pollution is still significant.

I repeated the analysis of PM2.5 level at low and high wind speeds and came up with the same conclusion (see details here).


Bottomline: Wind direction and speed marginally affect air pollution in Hong Kong. When wind blows from Mainland China, PM2.5 levels in Hong Kong increases 10 – 20%. However, the main sources of air pollution still come from within the city. Hong Kong should take measures to reduce their own sources of air pollution.


Caveat: This data is for particulate pollution. Particulate “affects more people than any other pollutants,” but there are also gas pollutants like ozone and NO2. According to this data, Hong Kong also has unsafe levels of NO2, SO2, and ozone.


If I were in Hong Kong, I would protect myself from air pollution by following these measures.

Breathe safe, Hong Kong!



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