Atmospheric wet deposition monitoring of PCDD/Fs in an urban site: Fluxes, rain concentrations and washout ratios?

Abstract

The fate of atmospheric pollutants can partly be explained by deposition phenomena occurring either wet or dry. This investigation reported the wet deposition flux values of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) utilizing a wet deposition sampler (WDS) in a densely populated urban center in T & uuml;rkiye between June 2022 and July 2023. The particulate phase in precipitation was captured on a filter, while the dissolved phase was sorbed onto the XAD-2 resin in the WDS. The experimental findings revealed that the average total PCDD/F (& sum;17PCDD/F) wet deposition flux, measured on a monthly basis, exhibited values of 2030 f 660 pg/m2-day (n = 12) and 397 f 186 pg/m2-day (n = 11) for the particulate and dissolved phases, respectively. These results demonstrated that PCDD/Fs were significantly removed from the atmosphere through rainfall. Among the compounds, the most dominant congener was OCDD (744 f 463 pg/m2-day in particulate and 107 f 45 pg/m2-day dissolved phase). However, regarding TEQ units, the highest flux belonged to 2,3,7,8TCDD (3.9 f 1.2 pg I-TEQ/m2-day for particulate and 4.3 f 3.0 pg I-TEQ/m2-day for dissolved phase). Rainwater samples revealed that & sum;17PCDD/F concentrations in the particulate phase (68.5 f 44.3 pg/L) significantly exceeded those in the dissolved phase (12.4 f 5.7 pg/L). The washout ratios for particulate and dissolved phases were calculated using the rainwater and atmospheric concentrations of PCDD/Fs. These ratios ranged between 1.44 x 104 and 3.76 x 105 for particulate phases and from 8.41 x 103 to 8.75 x 105 for dissolved phases. Consequently, the washout rates of 4- and 5-chlorinated compounds were lower than those of 7- and 8-chlorinated compounds. During the winter months, an increase in the PCDD/F pollution level was observed, leading to higher detections of PCDD/Fs in wet deposition compared to other seasons. However, this situation was not mirrored in the concentrations found in rainwater. The frequency of precipitation and the high volume of rainwater during the colder months resulted in lower concentrations.