Figure 1

Morphology of PM2.5 particles.
(a) large area image of as-collected PM2.5 on the filamentary filter. (b) and (c) SEM images of a particle with flat and rough top surface, respectively. (d) SEM image of the PM2.5 transferred on a Silicon substrate. Inset, zoom-in SEM image of an Iron-rich particle. The scale bars are 20 μm for image (a) 2 μm for image (b) 1 μm for image (c) 40 μm for image (d).