In many areas of China, the phenomenon of haze weather combined with fog becomes disastrous weather, which is collectively called "haze weather". The fog in three towns of Wuhan began in June 1 1.

A. Smog is a big dust particle and a solid substance; Instead of a large number of small water droplets or ice crystals floating in the near-surface air layer; So, A is wrong;

B, the essence of fog is small water droplets, and the essence of haze is small solid particles; So fog and haze are two different weather phenomena; Therefore, B is correct;

C, the essence of fog is small water droplets, and the essence of haze is small solid particles; So fog and haze are two different concepts; So, c is wrong;

D, fog is water vapor in the air, which liquefies into liquid when it is cold; So, d is wrong;

So choose B.