Persistent organic pollutants in the atmosphere over the marine boundary layer of the North Pacific Ocean and adjacent Arctic regions : sources, trends and processes
Persistent organic pollutants (POPs) are substances that are persistent and toxic and can affect both humans and wildlife. Once these compounds are released into the environment, they can migrate through the atmosphere and be transported to the regions where these chemicals have never been used, lik...
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| Format: | Thesis |
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City University of Hong Kong
2011
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| Online Access: | http://hdl.handle.net/2031/6577 http://lib.cityu.edu.hk/record=b4086483 |
| Summary: | Persistent organic pollutants (POPs) are substances that are persistent and toxic and can affect both humans and wildlife. Once these compounds are released into the environment, they can migrate through the atmosphere and be transported to the regions where these chemicals have never been used, like the Arctic. During the long range atmospheric transport, POPs show the tendency to deposit, condense and accumulate in the cold Arctic ecosystem. Hence, long range spatial surveys are necessary and effective to understanding the large scale distribution, long range atmospheric transport (LRAT) and sources of these substances in the North Pacific Ocean and adjacent Arctic regions. On the other hand, environmental events and climate change can alter the exposure levels of marine ecosystems through a variety of means including changes in long range transport and re-emission of these pollutants via biomass burning and the melting of the sea ice. In order to obtain current levels of POPs, identify the source areas and factors influencing the long range atmospheric transport, and reveal the potential influence of environmental events and climate change on atmospheric levels of these pollutants in the North Pacific Ocean and the adjacent Arctic Ocean, air samples were collected aboard the research expedition icebreaker XueLong (Snow Dragon) as part of the 2008 Chinese Arctic Research Expedition Program. Concentrations of polychlorinated biphenyls (PCBs), hexachlorobenzene (HCB), hexachlorocyclohexanes (HCHs), dichlorodiphenyltrichloroethane (DDTs), chlordanes and hexabromocyclododecanes (HBCD) were analyzed in all of the samples. In the current study, levels of HBCDs were less than the limits of detection for all the air samples, indicating that the levels of HBCD in the oceanic atmosphere over the North Pacific Ocean and the Arctic Ocean were low, and that the atmosphere may not be the major pathway for the long range transport of HBCD from Eurasia to the Arctic region. ΣPCBs in the atmosphere ranged from 22.0 to 520 pg m-3 with an average concentration of 240±160 pg m-3. Tri-PCBs, tetra-PCBs and penta-PCBs were the most abundant homologues, contributing 30±13%, 53±13% and 16±6% of total PCBs in all samples. The highest concentration was observed over the Japan Sea, while the lowest concentration was measured at the highest latitude in the Arctic Ocean. Relatively high levels of PCBs over the North Pacific Ocean were observed in samples collected near land masses. Air mass back trajectories indicated these samples might be influenced by the atmospheric transport of PCBs from nearby source regions. Homologue composition and latitudinal trends of PCBs indicated that during the long range atmospheric transport, the lighter PCB congeners would be transported and deposited in colder regions like the Bering Sea, while the heavier PCB congeners would be deposited closer to sources. The concentration of HCB was greater than the method detection limit (MDL) in all the samples and ranged from 24 to180 pg m-3, with an average concentration of 88 pg m-3. Levels of HCB in East Asia were relatively higher than levels over the North Pacific Ocean, indicating that East Asia may be a potential source region of HCB to the North Pacific Ocean. The concentrations of HCB exhibited an increasing trend at the North Pacific Ocean and the adjacent Arctic Ocean, indicating the global fractionation of HCB. HCH concentrations were analyzed in all of the samples. The average concentrations over the entire period were 33±16, 5.4±3.0, and 13±7.5 pg m-3 for α-, β- and γ-HCH, respectively. Compared to previous studies in the same areas, total ΣHCH levels declined by more than ten times compared to those observed in the 1990s, but were approximately four times higher than those measured by the 2003 China Arctic Research Expedition, suggesting the recent increase of atmospheric ΣHCH. Because of the continuing use of lindane, ratios of α/ γ-HCH showed an obvious decrease in the North Pacific and Arctic regions compared with those of the 2003 Chinese Arctic Research Expedition. ΣDDTs concentrations collected during the expedition varied substantially, ranging from 2.0 to 110 pg m-3 with an average concentration of 36±31 pg m-3. The fresh inputs of p,p'-DDT and o,p'-DDT indicated by DDT/DDE ratios and the relatively higher levels of p,p'-DDT and o,p'-DDT observed in East Asia and the North Pacific Ocean may reflect direct transport of these compounds from the adjacent continent where there may still be continuing usage of DDT-related compounds. The ratios of o,p'-DDT/p,p'-DDT were higher than that in technical DDT, but much lower than those observed in air samples from China, indicating that the atmosphere, during the present study, was likely influenced by a mixture of DDT-containing products. The concentrations of Σchlordanes varied between 1.8 and 11 pg m-3, with an average of 5.4 ± 2.6 pg m-3. Trans-chlordane (TC) and cis-chlordane (CC) were the most abundant among the chlordanes isomers, accounting for 40% and 39%, respectively of the total chlordane for all samples. The TC/CC ratios measured in all samples were lower than in the technical mixture, reflecting the main influence by weathered chlordane. Sampling sites with low levels of TC and CC often have relatively low TC/CC ratios, and may be influenced by older air masses. As the usage and production of most of POPs have been widely banned or restricted around the world, in addition to significant reductions in primary emissions of these substances recently, the relative importance of secondary re-emission is expected to increase. In the current study, most the organochlorine pesticides presented high levels during the end of July when the sampling ship was sailing over the Bering Sea. Satellite data indicated that there were great fires over the Siberia in July of 2008. Satellite data of smoke emissions, CO distribution and air mass back trajectories were used to identify the influence of biomass burning emissions to the levels of pesticides in Bering Sea. The result indicated that the occurrences of fires in Siberia during July 2008 might have made a significant contribution to high levels of DDT and HCH observed in the atmosphere of the North Pacific Ocean during our expedition. In Arctic regions, the levels of most organochlorine pollutants in the floating sea ice region were higher than those measured in the open sea area and packed ice region. In the areas covered by seasonal and multiyear ice, these chemicals showed decreasing trends with increasing ice concentration. This phenomenon implied that the volatilization of these pollutants accumulated in snow pack, sea ice, and the Arctic Ocean might have accelerated during the summer as ice coverage in the Arctic region decreased in response to global climate change. CityU Call Number: TD196.O73 W8 2011 xxv, 179 leaves : ill. 30 cm. Thesis (Ph.D.)--City University of Hong Kong, 2011. Includes bibliographical references (leaves 140-167) |
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