Hazy weather in China

A. Sulfur dioxide is the main component of acid rain and has little effect on the formation of smog, so A is wrong;

B. Nitrogen dioxide is the main component of acid rain and has little effect on the formation of smog, so B is wrong;

C. Inhalable particulate matter (PM2.5) belongs to atmospheric pollutants and is the main cause of haze weather, so C is correct;

D. carbon dioxide is not an atmospheric pollutant, nor is it a gas that causes haze weather, so d is wrong;

So choose C.