Impact of Warehouse Expansion on Ambient PM2.5 and EC Levels in Southern California's Disadvantaged Communities: A Two-Decade Analysis

Over the past two decades, the surge in warehouse construction near seaports and in 44 economically lower-cost land areas has intensified product transportation and e45 commerce activities, particularly affecting air quality and health in nearby socially 46 disadvantaged communities. This study, spanning from 2000 to 2019 in Southern 47 California, investigated the relationship between ambient concentrations of PM2.5 and 48 elemental carbon (EC) and the proliferation of warehouses. Utilizing satellite-driven 49 estimates of annual mean ambient pollution levels at the zip code level and linear mixed 50 effect models, significant associations were found between warehouse characteristics 51 such as rentable building area (RBA), number of loading docks (LD), and parking 52 spaces (PS), and increases in PM2.5 and EC concentrations. After adjusting for 53 demographic covariates, an Interquartile Range (IQR) increase of the RBA, LD, and PS 54 were associated with a 0.20 µg/m³ (95% CI = [0.17, 0.22], p < 0.001), 0.12 µg/m³ (95% 55 CI = [0.10, 0.13], p < 0.001), and 0.22 µg/m³ (95% CI = [0.19, 0.25], p < 0.001) increase 56 in PM2.5, respectively. For EC concentrations, an IQR increase of RBA, LD, and PS 57 were each associated with a 0.026 µg/m³ (95% CI = [0.024, 0.028], p < 0.001), 0.014 58 µg/m³ (95% CI = [0.013, 0.015], p < 0.001), and 0.026 µg/m³ (95% CI = [0.024, 0.029], p 59 < 0.001) increase. The study also highlighted that disadvantaged populations, including 60 racial/ethnic minorities, individuals with lower education levels, renters, and lower61 income earners, were disproportionately affected by higher pollution levels.