[1] Lanzhou Univ, Sch Publ Hlth, Inst Epidemiol & Stat, Lanzhou 73000, Peoples R China
[2] Gen Hosp PLA, Beijing 100853, Peoples R China
[3] Lanzhou Univ, Coll Atmospher Sci, Lanzhou 730000, Peoples R China
[4] Chengdu Univ Informat Technol, Sch Atmospher Sci, Chengdu 610225, Peoples R China