One year the sandstorm was so thick it painted the sky orange. Even if you sealed all the windows, the next day your tables and floors would be covered by sand. The spring wind blows it in from the Gobi Desert. The smog, by contrast, has many culprits: fossil fuels, coal, heavy industry, too many cars. People in Beijing hate the wind for bringing the sand but love it for blowing the smog away.
Read more about The Sandstorms in Beijing