Airborne transmission of SARS-CoV-2 mostly occurs indoors, and effective mitigation strategies for specific building types are needed. Most guidance provided during the pandemic focused on general strategies that may not be applicable for all buildings. A systematic evaluation of infection risk mitigation strategies for different public and commercial buildings would facilitate their reopening process as well as post-pandemic operation. This study evaluates engineering mitigation strategies for five selected US Department of Energy prototype commercial buildings (i.e., Medium Office, Large Office, Small Hotel, Stand-Alone Retail, and Secondary School). The evaluation applied the multizone airflow and contaminant simulation software, CONTAM, with a newly developed CONTAM-quanta approach for infection risk assessment. The zone-to-zone quanta transmission and quanta fate were analyzed. The effectiveness of mechanical ventilation, and in-duct and in-room air treatment mitigation strategies were evaluated and compared. The efficacy of mitigation strategies was evaluated for full, 75%, 50% and 25% of design occupancy of these buildings under no-mask and mask-wearing conditions. Results suggested that for small spaces, in-duct air treatment would be insufficient for mitigating infection risks and additional in-room treatment devices would be needed. To avoid assessing mitigation strategies by simulating every building configuration, correlations of individual infection risk as a function of building mitigation parameters were developed upon extensive parametric studies.

Sea-breeze circulation can mitigate urban overheating in coastal cities, but its effectiveness during extreme heatwaves (HWs) remains insufficiently quantified, particularly regarding the balance between cooling intensity and inland penetration. This study evaluates the impact of sea-breeze circulation on outdoor thermal comfort and heat-exposure risk across metropolitan Sydney during multiple HWs and paired non-HW periods. High-resolution Weather Research and Forecasting (WRF) simulations, coupled with a single-layer urban canopy model (SLUCM), were conducted over three nested domains with horizontal resolution down to 0.5 km using LCZ-informed urban parameters. Three major HW events in 2017, 2019, and 2020 were examined, together with five-day pre- and post-event reference periods. Results show that HWs intensified the coastal–inland Universal Thermal Climate Index (UTCI) gradient to about 10 °C, compared with 5–7 °C during non-HW periods, while the cooling benefit remained highly localized. During HWs, strong synoptic offshore winds substantially restricted the inland penetration of sea-breeze circulation, confining the main mitigation effect to a narrow coastal strip. Although cooling intensity was greatest near the coastline, the confrontation between sea breezes and hot continental air masses created an abrupt thermal transition and a spatial mismatch in heat relief. As a result, inland regions experienced about 20% greater heat exposure, whereas coastal areas remained relatively buffered, with increases below 8%. This study provides a transferable, health-relevant quantification of sea-breeze cooling decay with coastal distance and offers useful evidence for distance-based thermal zoning in coastal cities