(A) Representative scanning electronic microscope (SEM) for particles detained on the fiber filter membrane, which were collected from airborne pollution in seven different locations, including Nanjing City (Qixia, Jiangning, Pukou, Gulou, and Gaochun) in Jiangsu Province, Suzhou City in Anhui Province, and Tieling City in Liaoning Province (named as QX, JN, PK, GL, GC, SZ, and TL) and tobacco smoke particle (TSP). Scale bar = 5 μm. (B) Representative transmission electron microscopy (TEM) images for detached particles from filter membrane in panel (A). Scale bar = 100 nm. Images are representative of three independent experiments.