The weather in Texas is 65438+ 10 month.

A, increasing the intensity of changing coal into electricity and gas, and promoting the use of clean energy can improve air quality;

B, strengthening the renewal of old motor vehicles and improving exhaust emission standards can improve air quality;

C, reducing students' outdoor exercise time and avoiding respiratory diseases has nothing to do with improving air quality;

D, limiting the setting off of firecrackers in festivals and reducing the emission of harmful gases can improve air quality.

So choose C.