Direct measurements and comparisons of dry deposition fluxes and velocities of PCDD/Fs with two samplers

Abstract

Polychlorinated dibenzo-p-dioxins/furans (PCDD/Fs) are toxic and persistent pollutants that raise concerns due to their accumulative characteristics in the environments and biota. Atmospheric PCDD/Fs can enter various recipient environments and impact the entire ecosystem, thereby arousing more attention. Dry deposition is deemed the dominant migration pathway of atmospheric PCDD/Fs owing to their predominant distributions in the particulate phase. So far, however, there is no universally accepted method and device for dry deposition sampling. Here, we selected two widely used dry deposition samplers that work in different modes, water surface sampler (WSS) and wet-dry deposition sampler (WDDS), and investigated their differences in dry deposition sampling of PCDD/Fs. The average monthly total (∑17 PCDD/Fs) dry deposition fluxes (FP) in the particulate phase measured with the WSS and WDDS were 314 ± 158 pg/m2-day (36.6 ± 24.6 pg I-TEQ/m2-day) and 108 ± 39.4 pg/m2-day (11.4 ± 5.21 pg I-TEQ/m2-day), respectively. The difference between flux values indicated their collection efficiencies and artifacts during the sample collection. Higher dry deposition fluxes were measured in winter. This was mainly due to higher atmospheric levels of PCDD/Fs in colder months. The highest and lowest values of PCDD/Fs in both samplers were observed for OCDD and 2,3,4,6,7,8-HxCDF, respectively. This could indicate parallel collection characteristics of both samplers. A high-volume air sampler was used simultaneously with the WSS to determine the ambient air concentrations. Then, dry deposition velocities (Vd) were calculated by dividing the dry deposition fluxes (Fp) by the particulate phase concentrations (Cp) for each PCDD/F congener. The mean dry deposition velocity for PCDD/F congeners was determined with the WSS and WDDS 1.71 ± 0.88 cm/s and 0.64 ± 0.39 cm/s, respectively. Furthermore, the study underscored that water surfaces and shorter sampling periods provided more reliable values for particulate PCDD/F deposition than steel surfaces with prolonged exposure due to the degradation and volatilization effects observed on the latter.