(a)
(b)
(c)
(d)
Figure 7: The distribution of relative error of PM2.5 estimation over the mass concentrations measured by TEOM in case of (a) SDS011 (Nova Fitness), (b) ZH03A (Winsen), (c) PMS7003 (Plantower), and (d) OPC-N2 (Alphasense). Please note the different scales on the -axes.