Evaluation of City-Scale Disparities in PM_2.5 Exposure Using Hyper-Localized Taxi-Based Mobile Monitoring

Efforts have been directed to pollution control of fine particles (PM_2.5) because exposure to PM_2.5 could result in adverse health effects. However, PM_2.5 exposure disparities persisted even with largely declined concentrations. Here, we applied taxi-based measurements to characterize hyper-localized PM_2.5 exposures (30 m resolution) in Xi'an in December 2019 and July 2020. A big data set was derived from the taxi-based measurements (∼6 × 10⁶ hourly PM_2.5) and was used to evaluate the performance of existing regulatory measurements in urban and rural regions. Results from regulatory measurements tend to alleviate PM_2.5 exposure disparities compared with taxi-based measurements. The taxi-based measurements reported higher population-weighted average (PWA) exposure in December 2019 (90 μg/m³) and July 2020 (27 μg/m³) compared to regulatory measurements (76 and 24 μg/m³ in December and July, respectively) with a wider range of relative disparities. Results indicate that the urban region would be overrepresented by regulatory measurements, where regulatory measurements reported that 60.0-84.7% of inhabitants were exposed to PM_2.5 higher than PWA, while taxi-based ones reported a smaller portion (22.6-35.2%). Significant seasonal variability in PM_2.5 exposure levels was found by taxi-based measurements but not regulatory measurements. The results highlight the need for providing complementary measurements (e.g., low-cost) for exposure assessment because the rural regions could be disproportionately exposed and overlooked by existing regulatory measurements.