Development and validation of a methodology to measure exhaled carbon dioxide (CO2) and control indoor air renewal

The measurement of CO2 has positioned itself as a low-cost and straightforward technique to indirectly control indoor air quality, allowing the reduction of the concentration of potentially pathogen-loaded aerosols to which we are exposed. However, on numerous occasions, bad practice limits the technique for CO2 level interpreting and does not apply methodologies that guarantee air renewal. This work proposes a new methodology for measuring and controlling CO2 levels for indoor air in shared spaces. The proposed methodology is based on three stages: diagnosis, correction protocols, and monitoring/control/surveillance (MCS). The procedure is explained using a cultural center as an actual base case study. Additionally, the procedure was validated by implementing 40 voluntary commercial spaces in Zaragoza (Spain). Standardization of methods is suggested so that the measurement of CO2 becomes an effective strategy to control the airborne transmission of pathogens and thus prevent future Covid-19 outbreaks and novel pandemics. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This research was funded by the Aragon Health Research Institute: Crowfunding Investiga COVID-19 (CoviBlock). This work was partly funded by Federacion de Empresarios de Comercio y Servicios de Zaragoza (ECOS Zaragoza) ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All data produced in the present work are contained in the manuscript