Towards dynamic urban environmental exposure assessments: a case study of the Brussels Capital Region

This study proposes a multi-dimensional dynamic exposure assessment methodology for outdoor environments, which incorporates factors such as heat, cold, air pollution, sky view factor, and greenery, along with population dynamics. Utilizing high spatiotemporal resolution data, the dynamic exposure assessment captures temporal and spatial variations in urban environmental exposures and evaluates the effectiveness of green infrastructure and urban planning features in mitigating environmental stressors. This approach offers novel insights compared to conventional static exposure assessments, which rely on fixed census-based population data and overlook diurnal and seasonal variability. Focusing on the Brussels Capital Region (BCR), the study analyzed exposure during the two hottest days and the annual average for the year 2011. The indicators of Mean Radiant Temperature (Tmrt) and Universal Thermal Comfort Index (UTCI) for day and night were computed for all soft mobility routes - non-motorized urban pathways used by pedestrians, cyclists, e-scooter users, etc - located in the BCR. For the hottest days, the results showed that 1/260% and 1/240% of the soft mobility routes are exposed to moderate (26 to 32 °C UTCI) and strong heat stress (above 32 °C UTCI), respectively. For the annual average, we calculated the difference between the dynamic and static exposure assessment methods. The results indicate that the static method underest mates heat exposure by 1/251%, cold exposure by 1/210%, and air pollution and greenery exposure by 1/28%. These findings support urban design policies by highlighting soft mobility routes that need strategic planning to reduce exposure risks.