Spatioseasonal Variability and Correlations of Particle-Bound Organophosphate Esters in Providence, Rhode Island

The concentrations of organophosphate esters (OPEs) in atmospheric particulate matter (PM) collected every 6 days at two sites across Providence, Rhode Island (Providence College, PC, and the Port of Providence, Port) are reported for the first time. Of the 31 OPEs in the target analyte list, 23 were detected in either total suspended particulate (TSP) and PM less than 2.5 μm in aerodynamic diameter (PM_2.5), including six "novel" OPEs never before reported in the US. Notably, this study represents the longest, most comprehensive report of OPEs in PM_2.5 in the US. Median total OPE concentrations (∑₂₃OPE) were similar between sites (PC TSP: 600 pg m^-3; PC PM_2.5: 751 pg m^-3; Port TSP: 689 pg m^-3; Port PM_2.5: 889 pg m^-3), though the sites proved statistically different when compared by size fraction (p < 0.05), likely due to the variety of sources contributing to ∑₂₃OPE. Tris-[(2R)-1-chloro-2-propyl] phosphate (TCPP) was the most prominent OPE in samples, with chlorinated OPEs dominating sample profiles regardless of site and size fraction. Select OPEs were significantly (p < 0.05) correlated with each other, suggesting similar sources in the area, though several deviations examined suggest source differences despite sites being 6.5 km apart. Meteorological parameters were also examined, with temperature proving an important factor for OPEs in both TSP and PM_2.5, but relative humidity only affecting PM_2.5 samples. Seasonal differences were also noted, with autumn and summer ∑₂₃OPE concentrations significantly higher than winter and spring. Daily intensives during autumn and spring also showed high day-to-day variability in OPE concentrations, with summer night samples providing some of the highest OPE concentrations observed in the study. It is possible that traditional 1-in-6 or 1-in-12-day sampling schemes with samplers in one location in a city are not adequately characterizing OPEs in the atmosphere and more intensive strategies are needed for the best understanding of OPE ambient concentrations to better characterize their effects on human health in urban areas.