Figure 1.

 Schematic diagram of a test room and time course of changes in concentration of ClO₂ gas. (a) Schematic diagram of bacteria and viruses on the glass surface in a test room. The microbes in the wet state on the glass dishes were placed at the centre of the room. The 0·8 m given in a parenthesis in the figure shows the height of glass dishes with the microbes placed above the floor. (b) Time course of changes in concentration of ClO₂ gas in the test room. The graph presents the mean of eight experiments; each error bar indicates the SD. The background level of ClO₂ gas in ordinary air was below 0·01 ppmv.