Atmospheric Bulk Deposition of PCDD/Fs in an Urban Area: Fluxes, Temporal Changes and Comparisons

This study investigates the bulk deposition fluxes of PCDD/Fs in an urban area over four seasons. The samples were named bulk-dry and bulk-wet, respectively. Bulk-dry samples referred to no precipitation during the sampling period. The study employed a bulk deposition sampler (BDS), with bulk-dry deposition fluxes averaging 52.3 ± 23.7 pg/m²/day (4.29 ± 2.38 pg I-TEQ/m²-day). These results were higher than those of studies in the background regions due to increased pollution from anthropogenic activities. Additionally, the study estimated dry deposition velocities, with an average value of 0.25 ± 0.14 cm/s. This average value was smaller than the determined deposition velocities obtained from another sampler placed side-by-side. The difference mainly came from sampling duration and sampler characteristics. Moreover, bulk-wet deposition fluxes were evaluated separately, with particulate and dissolved phase deposition rates averaging 63.3 ± 16.8 pg/m²-day and 67.7 ± 9.7 pg/m²-day, respectively. Based on our search, the dissolved and particulate phases were evaluated separately in bulk samples for the first time. The collected rainwater samples were analyzed, and washout ratios were calculated. The results were different from the results obtained using a wet deposition sampler. In conclusion, the bulk results gave rough values rather than exact ones. However, BDSs have no energy necessity, are easy to use, and inexpensive. Seasonal variations in deposition fluxes were also observed, with higher fluxes recorded during colder months, attributed to increased emissions from incomplete combustion. The study also examined the compound profiles of PCDD/Fs, revealing that OCDD is the most prevalent congener in both bulk-dry and bulk-wet depositions.