Modification and Evalution of a Water Surface Sampler to Investigate the Dry Deposition and Air Water Exchange of Polychlorinated Bipheyls (PCBs)

Tez Türü: Doktora

Tezin Yürütüldüğü Kurum: Illinois Institute of Technology, Çevre Mühendisliği, Amerika Birleşik Devletleri

Tez Danışmanı: Prof. Thomas M. Holsen

Tezin Onay Tarihi: 1997

Tezin Dili: İngilizce

Desteklendiği Program: Diğer

Özet:

Dry deposition is an effective removal mechanism for polychlorinated biphenyls (PCBs) from the atmosphere. In this study a new analytical technique was developed to characterize the transport and deposition of PCBs in the environment. This technique featured a modified water surface sampler (WSS) in conjunction with greased surrogate surfaces and traditional high-volume sampler.

Ambient air samples were collected with a high-volume sampler in Chicago, IL from June to October 1995 to determine concentrations and gas/particle partitionings of PCBs. The total PCB concentration was about 1.9 ng/m³ and on average 95% of the total PCB concentration was in the vapor phase.

The partitioning between gas and particulate phase was modeled using the Junge-Pankow model. The measured particle phase concentration for low molecular weight (MW) PCBs was lower than those predicted by Junge-Pankow model while the opposite case was observed for the high MW PCBs.

The PCB dry deposition fluxes were measured with knife-edge surrogate surfaces and a water surface sampler (WSS). The knife-edge surface measured particulate phase deposition and the WSS measured both particulate and gas phase deposition. The average flux to the WSS and plate were about 1200 and 240 ng/m²-d, respectively. In general, medium molecular weight PCBs were dominant.

Average dry deposition velocities, calculated dividing the fluxes by the concentrations, for both the particle and gas phases were calculated to be 6.5 cm/s and 0.7 cm/s, respectively. The difference between the dry deposition velocities is due to the different deposition phenomena affecting the particulate and gas phases. A modified two-film gas-exchange model which depends on wind speed, water temperature, and properties of PCBs, was used to predict the overall gas phase mass transfer coefficient compared well with the measured values.