This article includes supplemental data for the main article “Is China to blame for Seoul’s air pollution?”
This supplemental data will show how high and low wind speeds affect the PM2.5 levels. Ultimately, this supplemental article draws the same conclusion as the main article.
Does Wind Speed Affect PM2.5?
What if particulate matter can only be transported at high speeds? In order to test if wind speed affects PM2.5, I repeated the analysis for PM2.5 data at wind speeds below average and above average.
The data shows that lower wind speeds in Seoul almost always correlated with lower PM2.5 levels, regardless of the wind direction.
However, this also shows that air pollution was significant even without strong winds blowing PM2.5 from China. This means that there are PM2.5 sources within Seoul as well.
When the wind was blowing at higher speeds from the direction of China, the PM2.5 level was about 9% higher than average. However, when the wind was blowing at higher speeds from the East and East-South-East directions, the PM2.5 level was about 23% higher. This agrees with the findings in the main article—that some pollution comes from China, but the majority still originates in South Korea.