Spatioseasonal Variations and Partitioning Behavior of Organophosphate Esters in the Great Lakes Atmosphere

Organophosphate esters (OPEs) were measured in atmospheric vapor and particle samples collected at six sites in the Laurentian Great Lakes basin every 12 days from January to December 2017 (inclusive). Median total OPE concentrations (∑OPEs) ranged from 41.2 pg/m³ at Eagle Harbor, Michigan to 1320 pg/m³ at Cleveland, Ohio. Tris(1-chloro-2-propyl) phosphate (TCIPP) was the most abundant OPE measured in these samples and contributed 26% to ∑OPE concentrations. The spatial distribution of OPEs among the sites suggests that OPEs with longer atmospheric half-lives and relatively high octanol-air partitioning coefficients (K_OA) are likely to have a greater potential to undergo long-range atmospheric transport. OPE particle-phase partitioning fraction (Φ) significantly and positively correlated with K_OA, but declined with increasing relative humidity. Φ values varied seasonally and were lower in the summer for volatile OPEs. In addition, samples collected in the summer had significantly higher levels of ∑OPEs than samples collected in the winter. The estimated dry deposition flow of ∑OPEs to the Great Lakes was 1.22 tons/year, exceeding the corresponding flows reported for polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and organochlorine pesticides (OCPs).