(a)
(b)
(c)
(d)
Figure 4: Scatterplots of sensor unit outputs versus the mean values of the 1-minute averaged data: (a) SDS011 (Nova Fitness), (b) ZH03A (Winsen), (c) PMS7003 (Plantower), and (d) OPC-N2 (Alphasense). Dashed lines denote the ideal relationship.