論文雑誌「Indoor Air」のカバーピクチャーを制作しました［産業技術総合研究所］

Air exchange rates and advection–diffusion of CO₂ and aerosols in a route bus for evaluation of infection risk
Naohide Shinohara, Koichi Tatsu, Naoki Kagi, Hoon Kim, Jun Sakaguchi, Isamu Ogura, Yoshiko Murashima, Hiromu Sakurai, Wataru Naito

As COVID-19 continues to spread, infection risk on public transport is concerning. Air exchange rates (ACH) and advection–diffusion of CO₂ and particles were determined in a route bus to evaluate the infection risk. ACH increased with bus speed whether windows were open or closed, and ACH were greater when more windows were open. With two open windows, ACH was greater when a front and rear window were open than when two rear windows were open. With both front and rear ventilation fans set to exhaust, ACH was more than double that when both were set to supply. With air conditioning (AC) off, CO₂ and particles spread proportionally at the same rate from a source, whereas with the AC on, the spread rate of particles was about half that of CO₂, because particles might be trapped by a prefilter on the AC unit. Infection risk can be reduced by equipping AC unit with an appropriate filter. Calculations with a modified Wells–Riley equation showed that average infection risk was reduced by 92% in the moving bus with windows open comparing to with windows closed. When the bus was moving with windows closed, exhaust fan operation reduced the average risk by 35%.
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