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This chapter reframes carbon dioxide (CO2) from a comfort-based indoor air quality metric into a biologically meaningful surrogate for ventilation adequacy and airborne infection risk. Because pathogens such as SARS-CoV-2, tuberculosis bacilli, and fungal spores are invisible to occupants, effective prevention depends on measurable proxies that reveal the hidden dynamics of air dilution and rebreathed exposure. CO2, produced universally by human metabolism and exhaled at predictable concentrations, provides a practical biomarker for estimating the fraction of air previously breathed by others and therefore the probability of pathogen accumulation. The chapter integrates physiology, building science, and epidemiology to explain how CO2 generation varies with activity, vocalization, and occupancy, and how these variations interact with ventilation performance. It traces the historical evolution of CO2 standards from Pettenkofer’s nineteenth-century odor threshold to contemporary pandemic-era targets focused on infection resilience. The Rudnick–Milton “rebreathed air fraction” framework is used to demonstrate how simple CO2 measurements can be translated into quantitative estimates of biological risk, while field evidence from schools, healthcare settings, and transport environments illustrates real-world associations between elevated CO2 and adverse health outcomes. Crucially, the chapter also addresses the limitations of CO2 as a proxy. Spatial heterogeneity, transient dynamics, sensor inaccuracies, metabolic variability, and the decoupling effect introduced by HEPA filtration can all distort interpretation if not properly understood. Technological considerations—such as the superiority of NDIR sensors over eCO2 devices, calibration drift, and optimal placement strategies—are examined to support reliable implementation. The discussion extends to policy, legal accountability, and the emerging role of smart buildings, where continuous CO2 monitoring, IoT integration, and public display of air-quality data may redefine expectations of healthy indoor environments. Ultimately, the chapter argues that CO2 is neither a direct virus detector nor a flawless metric, but remains the most accessible and actionable tool for making airborne risk visible and operationalizing ventilation as a public health intervention.

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Surrogate for Ventilation for Infection Control: Using Carbon Dioxide Biomarker

  • 章节

  • 发表日期：

    2026年

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  • Raja Singh,
  • Nirupam Madaan,
  • Anil Dewan

摘要

This chapter reframes carbon dioxide (CO2) from a comfort-based indoor air quality metric into a biologically meaningful surrogate for ventilation adequacy and airborne infection risk. Because pathogens such as SARS-CoV-2, tuberculosis bacilli, and fungal spores are invisible to occupants, effective prevention depends on measurable proxies that reveal the hidden dynamics of air dilution and rebreathed exposure. CO2, produced universally by human metabolism and exhaled at predictable concentrations, provides a practical biomarker for estimating the fraction of air previously breathed by others and therefore the probability of pathogen accumulation. The chapter integrates physiology, building science, and epidemiology to explain how CO2 generation varies with activity, vocalization, and occupancy, and how these variations interact with ventilation performance. It traces the historical evolution of CO2 standards from Pettenkofer’s nineteenth-century odor threshold to contemporary pandemic-era targets focused on infection resilience. The Rudnick–Milton “rebreathed air fraction” framework is used to demonstrate how simple CO2 measurements can be translated into quantitative estimates of biological risk, while field evidence from schools, healthcare settings, and transport environments illustrates real-world associations between elevated CO2 and adverse health outcomes. Crucially, the chapter also addresses the limitations of CO2 as a proxy. Spatial heterogeneity, transient dynamics, sensor inaccuracies, metabolic variability, and the decoupling effect introduced by HEPA filtration can all distort interpretation if not properly understood. Technological considerations—such as the superiority of NDIR sensors over eCO2 devices, calibration drift, and optimal placement strategies—are examined to support reliable implementation. The discussion extends to policy, legal accountability, and the emerging role of smart buildings, where continuous CO2 monitoring, IoT integration, and public display of air-quality data may redefine expectations of healthy indoor environments. Ultimately, the chapter argues that CO2 is neither a direct virus detector nor a flawless metric, but remains the most accessible and actionable tool for making airborne risk visible and operationalizing ventilation as a public health intervention.