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. 2023 Nov 21;8(1):148-160.
doi: 10.20411/pai.v8i1.619. eCollection 2023.

Carbon Dioxide Monitoring Demonstrates Variations in the Quality of Ventilation on Public Transportation Buses and University Student Shuttle Vans and Identifies Effective Interventions

David Henry Greentree  1   2 , Brigid M Wilson  3   4 , Curtis J Donskey  3   4
Affiliations

Carbon Dioxide Monitoring Demonstrates Variations in the Quality of Ventilation on Public Transportation Buses and University Student Shuttle Vans and Identifies Effective Interventions

David Henry Greentree et al. Pathog Immun. .

Abstract

Background: There is a risk for transmission of severe acute respiratory syndrome 2 (SARS-CoV-2) and other respiratory viruses in motor vehicles, particularly if ventilation is inadequate.

Methods: We used carbon dioxide monitoring to examine the quality of ventilation in several public transportation buses and in university student shuttle vans in the Cleveland metro area during peak and non-peak travel times. Carbon dioxide levels above 800 parts per million (ppm) were considered an indicator of suboptimal ventilation for the number of people present. In the shuttle vans, we evaluated the impact of an intervention to improve ventilation.

Results: In large articulated buses with 2 ventilation systems, carbon dioxide concentrations never exceeded 800 ppm, whereas in standard buses with 1 ventilation system concentrations rose above 800 ppm during peak travel times and on some trips during non-peak travel times. In shuttle vans, the ventilation system was not turned on during routine operation, and carbon dioxide levels rose above 800 ppm on all trips during peak and non-peak travel times. In the shuttle vans, an intervention involving operation of the existing ventilation system resulted in a significant reduction in carbon dioxide levels (mean concentration, 1,042 no intervention versus 785 with intervention; P < 0.001).

Conclusions: Our findings demonstrate substantial variability in the quality of ventilation in public transportation buses and university shuttle vans. There is a need for efforts to assess and optimize ventilation in motor vehicles used for public transportation to reduce the risk for aerosol-mediated transmission of respiratory viruses. Carbon dioxide monitoring may provide a useful tool to assess and improve ventilation.

Keywords: COVID-19; SARS-CoV-2; carbon dioxide; transportation; ventilation.

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Conflict of interest statement

C.J.D has received research grants from Clorox, Pfizer, and Ecolab. All other authors report no conflicts of interest relevant to this article.

Figures

Figure 1.
Figure 1.
Map of Cleveland, Ohio, area with highlighted public transportation routes. The green line shows the articulated bus route. The blue lines show the standard bus routes. The red, orange, and pink lines show the shuttle van routes.
Figure 2.
Figure 2.
Carbon dioxide concentrations and passenger numbers over time during 6 individual trips, including 1 during peak travel time and 1 during non-peak travel time for the articulated bus (A), standard bus (B), and shuttle van (C). Abbreviations: CO2, carbon dioxide; ppm, parts per million; min, minutes.
Figure 3.
Figure 3.
Comparison of carbon dioxide concentrations during non-peak vs peak travel times in each of the vehicle types. Solid rectangles indicate second quartile (50% of values). Horizontal lines within rectangles indicate median values and X markers indicate mean values. Whiskers indicate lower and upper quartiles. Abbreviations: CO2, carbon dioxide; ppm, parts per million.
Figure 4.
Figure 4.
Correlation between the concentration of carbon dioxide and the percentage of maximum recommended passenger occupancy during peak (A) and non-peak (B) travel times for the 3 types of vehicles. Abbreviations: CO2, carbon dioxide; ppm, parts per million.
Figure 5.
Figure 5.
Concentrations of carbon dioxide during the 4 intervention trips in comparison to the 4 no intervention trips. Abbreviation: CO2, carbon dioxide
See this image and copyright information in PMC

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