Fig. 1: Spatial distribution of averaged tropospheric HCHO VCD from 2013 to 2021 and altitude of Tibet in 3D view.

A Spatial distribution of averaged tropospheric HCHO VCD in Tibet from 2013 to 2021 in 3D view. B Altitude distribution map of Tibet in 3D view. The area framed by a thick black line is Tibet. The rectangles from left to right are the western region (red), central region (blue), and eastern region (black). The cities in figure from left to right are Xigaze, Lhasa, Shannan, Nagqu, Nyingchi, and Qamdo. For follow-up studies, we also show the approximate extent of southern region (violet) in Tibet with lower altitude and further south India assam (orange).