Is China to blame for Seoul’s air pollution?

Air pollution is a serious problem in Seoul, which South Koreans have often blamed China for. Is that fact or a convenient scapegoat? After all, Seoul is a densely populated, developed city that depends on coal power plants. South Korea certainly has its own sources of pollution. To get to the bottom of it, I analyzed where exactly Seoul’s air pollution comes from.

 

factory smog

 

How much of Seoul’s pollution is local?

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

 

Seoul PM2.5 Wind direction

 

Wind Analysis

Anytime the wind blows from the South-West to North-North-East direction (the arrows below), Seoul’s air is getting at least some air from China. If most of Seoul’s air pollution is coming from China, we should see air pollution spike whenever the wind comes from that direction.

 

Seoul PM2.5 Wind direction map china

 

Does wind direction affect Seoul PM2.5?

When the wind was NOT blowing from the direction of China, the average PM2.5 level was 25 micrograms. In contrast, when the wind was blowing from China, the PM2.5 level was 27 micrograms—an 8% increase.

 

Seoul PM2.5 Wind from china

 

The highest spike happens when the wind is from the northwest—the direction of Pyongyang and Liaoning. Yet Seoul also sees higher pollution when air comes from east-southeast—other parts of South Korea.

 

Seoul PM2.5 Wind direction from china

 

This data gives three (somewhat contradictory) takeaways:

  • Yes, Seoul’s air pollution is 8% worse when the wind blows from China.
  • However, even when no air is coming from China, Seoul still averages more than twice the WHO annual limit of 10 micrograms.
  • When the air is blowing from east-southeast (ESE) i.e., from other parts of South Korea, Seoul’s PM2.5 increases.

Thus, even without the influence of China, Seoul still has significant sources of air pollution from within.

 

A mystery: Where’s that ESE pollution coming from?

Air from China raises pollution 8%, but air from the ESE increases it even more—12%.

Currently, we don’t know where exactly this spike in pollution from the ESE originates. Besides the East Sea, a possible source outside of South Korea would be Japan. However, the provinces of Fukuoka, Hiroshima and Osaka that lie in the ESE have much cleaner recorded air than Seoul.

Thus, it is very likely that the ESE pollution originates within South Korea.

 

Does wind speed affect PM2.5?

Another way to ask this question is to ask what happens when there’s no wind. When there was no wind, the PM2.5 level averaged 24 micrograms, which is 8% below Seoul’s average PM2.5. Thus, PM2.5 in Seoul is largely similar, even with no wind.

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: When wind blows from China, Seoul’s PM2.5 increases 8%, which suggests that most of Seoul’s pollution still comes from home.

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

 

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

Breathe safe, Seoul!

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