Influence of Urban Form, Weather and Population on Outdoor Airborne Infection Risk: Implications in Greater London for SARS-CoV-2

Although airborne infectious disease transmission outdoors is possible, particularly in densely built urban areas with limited ventilation, the role of urban morphology and neighborhood climate heterogeneity in modulating the risk remains poorly quantified. We couple an urban climate model (SUEWS) and a modified Wells-Riley framework to develop a transferable neighborhood-scale approach for mapping outdoor airborne infection risk across morphologically diverse neighborhoods, factoring in urban form, population distribution and meteorologically driven viral infectivity decay. We demonstrate this framework by applying it to SARS-CoV-2 in Greater London. Considering outdoor urban ventilation alone, estimated risk follows a diurnal cycle and peaks at night. Including population distribution, daytime risk in busy commercial centers is up to 7.23 times higher than nighttime. Infectivity decay from ultraviolet B (UVB) exposure reduces risk by 35–45% in less dense areas and up to 99% in high built-density neighborhoods. Despite this mitigation, the highest risks persist in high-rise, high-workplace-density districts (e.g., City of London and Westminster), while lower-rise areas (e.g., Lambeth and Croydon) exhibit reductions exceeding 90%. For SARS-CoV-2, these findings demonstrate strong intraurban heterogeneity in outdoor airborne infection risk in Greater London. More broadly, the transferable framework supports high-resolution mapping to inform targeted, place-based public health interventions.