in the mid-1980 's , precipitation in sichuan had become significantly acid -lrb- in 1989 the ph of rain in chongqing had fallen to 4.21 -rrb- , and acid rain was abundant in the chengdu and chongqing regions ; as a result , the huashan pines at fengjie , the firs of mount emei , and the masson pines in the hills south of chongqing have been damaged over an area of more than 100,000 mu .