Fog and haze can reduce visibility, among which

A, a large number of firecrackers will cause a sharp increase in inhalable particles in the air in a short time, which is correct;

B, "fog" and "haze" can reduce visibility, but they are not the same natural phenomenon, so they are wrong;

C, automobile exhaust contains a lot of air pollutants, which is an important reason for the formation of haze weather, so it is correct;

D air pollution is serious in foggy days, so it is correct to reduce outdoor activities.

So choose B.