How is the air pollution in Oct. for the Yangtze River, Shanghai, Xian, and Beijing?

According to the situation of last October, the air condition along Yangtze River and in Shanghai is mainly excellent.
In Beijing, there are 4 days marking lightly-polluted and 5 days of Heavily-polluted condition.
Xian went through nearly half of month of lightly polluted environment.

What kind of a mask should I get for polluted days and where would I get this mask? I do have some lung sensitivities and don't want to end up in the hospital so I need as accurate as can be on the pollution risks. How will I know once in China what the daily pollution index is?

Masks that can filter out pm2.5 practicles are recommended. They can be purchased in big pharmacies in CN. I know an APP called 'Fresh Ideas' that can tell you the in-time air condition. You can download it on your phone.