If you would look at our pictures again, the air is clear and the sky is blue. That is one of the major reasons that I like to ride in Yunnam, perhaps that is because of the high altitude and less densely populated. You get clear blue sky in Tibet too.
With regard to air pollution, I always take a 3M mask of grading N95 with me when I go cycling in China just in case. Covering with a handkerchief wouldn't make much difference.