FIG. 4.

The risk index (I_risk) maps of the classroom for an infector in the front of the classroom with (a) no box fan air cleaner placed (case A), (b) the air cleaner placed in the front of the classroom (case A1), (c) in the middle of the classroom near the horizontal unit ventilator (HUV) (case A2), (d) in the middle but away from the HUV (case A3), and (e) in the back of the classroom (case A4). The wall contour maps show the spatially averaged I_risk (${\overline{I}}_{\mathrm{risk}})$ along x, y, and z directions, respectively. The I_risk distribution at x-y plane at the breathing level of a sitting individual (1.2 m) is also provided. The contour of ${\overline{I}}_{\mathrm{risk}}\ge 1$ and $I_{\mathrm{risk}}\ge 10$ mark the regions of high-risk (relatively) in the space. The I_risk scales are consistent between different figure types but not between the two types: spatially averaged (top) and breathing level sections (bottom). Note that the human figures in (a) are used for illustration purposes and only the infector is modeled as a cuboid in the simulation.