A real-time web tool for monitoring and mitigating indoor airborne COVID-19 transmission risks at city scale

•CityRPI: city-scale interactive website for real-time tracking indoor airborne infection risks in north american cities.•Users are allowed to input customized building specific information for their own building assessment.•New archetype building library developed for urban scale risk assessments.•Urban scale energy analysis for evaluations of energy costs of risk mitigation measures.•Doubling outdoor air ventilation rate is the least effective strategy with a 10–60% peak urban energy demand increase. Airborne transmission of aerosols contributes to a large portion of the SARS-CoV-2 spread indoors. This study develops a real-time interactive web-based platform for the public to compare various strategies to curb indoor airborne transmission of COVID-19 in different archetype buildings at a city scale. Although many countries have started vaccination and a gradual re-opening, because of emerging new variants of the virus and the possibility of future pandemics, a lively updated tool for monitoring and mitigation of infection risk is essential. As a demonstration, we evaluated the impacts of six mitigation measures on the infection risks in various building types in a city. It shows that the same strategy could perform quite differently, depending on building types and properties. All strategies are shown to reduce the infection risk but wearing a mask and reducing exposure time are the most effective strategies in many buildings, with around 60% reduction. Doubling the minimum required outdoor air ventilation rate is not as effective as other strategies to reduce the risk. It also causes considerable penalties on energy consumption. Therefore, new building ventilation standards, control actions, and design criteria should be considered to mitigate the infection risk and save energy.