Every Monday I get to tool around the port of Imabari for an hour or so while waiting for a ferry to take me out to a little island within spitting distance of Hiroshima Prefecture.
Lately it has been smokey or hazy most times when I go to the port. Around where I live, I attribute it to a combination of local farmers burning unwanted stalks and husks and such, or to the cemetery burning whatever it is they burn. At the port there's no such excuse.
Today when I went to the waterfront, however, it was fine and clear.
When I got to Iwagijima, I remarked to my driver how clear it was. He told me that it was because the kousa (黄砂) or yellow dust blowing in from China had recently abated, thanks to strong winds and rain blowing up from Taiwan.
Now I know the real reason Japanese all wear surgical masks in the springtime. Pollen, sure. But I suspect radioactive Gobi dust to be the number one culprit. They just don't want to scare me by telling me the truth. (That's China in the video link, if you click on it, not Japan.)