Hybrid land use regression modeling for estimating spatio-temporal exposures to PM_2.5, BC, and metal components across a metropolitan area of complex terrain and industrial sources

Land use regression (LUR) modeling has become a common method for predicting pollutant concentrations and assigning exposure estimates in epidemiological studies. However, few LUR models have been developed for metal constituents of fine particulate matter (PM_2.5) or have incorporated source-specific dispersion covariates in locations with major point sources. We developed hybrid AERMOD LUR models for PM_2.5, black carbon (BC), and steel-related PM_2.5 constituents lead, manganese, iron, and zinc, using fine-scale air pollution data from 37 sites across the Pittsburgh area. These models were designed with the aim of developing exposure estimates for time periods of interest in epidemiology studies. We found that the hybrid LUR models explained greater variability in PM_2.5 (R² = 0.79) compared to BC (R² = 0.59) and metal constituents (R² = 0.34-0.55). Approximately 70% of variation in PM_2.5 was attributable to temporal variance, compared to 36% for BC, and 17-26% for metals. An AERMOD dispersion covariate developed using PM_2.5 industrial emissions data for 207 sources was significant in PM_2.5 and BC models; all metals models contained a steel mill-specific PM_2.5 emissions AERMOD term. Other significant covariates included industrial land use, commercial and industrial land use, percent impervious surface, and summed railroad length.