Brominated Persistent Organic Pollutants in Cloud/Fog Water: First Field Observations of Scavenging Behavior

Cloud/fogwater represents critical but understudied pathways for the cycling and deposition of persistent organic pollutants (POPs). This study presents the first field-based measurements of brominated POPs (Br-POPs), including polybrominated diphenyl ethers (PBDEs) and polybrominated dibenzo-<i>p</i>-dioxins and furans (PBDD/Fs), in cloud/fogwater, revealing their multiphase behavior and scavenging dynamics during 2018-2020 Northeast monsoon seasons in northern Taiwan. BDE-209 dominated the homologue distribution, with median concentrations of 7.5 × 10³ pg L^-1 (maximum: 7.1 × 10⁴ pg L^-1) in the particulate fraction and 1.3 × 10³ pg L^-1 (maximum: 2.0 × 10⁴ pg L^-1) in the aqueous fraction of cloud/fogwater in 2018, higher than in 2019, suggesting the combined influence of a stronger Northeast monsoon, enhanced scavenging efficiency, and long-range atmospheric transport. Multiphase partitioning analysis demonstrated that gas-aqueous, gas-aerosol, and aqueous-insoluble particle exchanges did not attain equilibrium during fog events, consistent with the short atmospheric residence time of cloud/fog droplets. Scavenging ratios and coefficients indicated efficient incorporation of Br-POPs into cloud/fog droplets, with lower-brominated congeners preferentially associated with the aqueous phase and highly brominated species with the particle phase. These findings highlight cloud/fogwater as an effective pathway for atmospheric removal and deposition of Br-POPs and its role in regional contaminant cycling.