You know the dust has blown in from China when:

The morning dawns bright and clear except for the clear part, not so much. This was the view from my hotel room yesterday.

By lunchtime your contacts feel like they've been in for sixteen hours.

You blow your nose and get black gunk. Mind you, you don't do this in public in Asia--they don't mind sniffing at all, but think blowing is disgusting, which is the exact opposite of how I was raised--so think twice before ordering that wonderfully-piping-painfully-hot spicy soup.

You've probably read in the news about dust storms from China affecting Japan and Korea. It's true. Deforestation and lack of forestation in the first place combined with strong winds have been making Asia one gritty, dusty place lately.