The influence of gaseous species in the accurate determination of particulate phase mercury in the atmosphere.

摘要

Man's extraction of mercury from the earth's crust has resulted in a large perturbation of the natural biogeochemical cycle of this element. This has been manifested through bioaccumulation of atmospherically deposited mercury in the food chain. Since mercury is known to be toxic, it is crucial to study its atmospheric behavior in order to preserve public health and prevent ecosystem demise.; Particulate phase mercury was collected in Detroit, MI during periods in 2000–2002 to gain further insight into how gaseous species influence the sampling of this phase in an urban environment. This study focused on reactive gaseous mercury and ozone, both of which were found to have an impact on the sampling. Specifically, a significantly higher amount of particulate mercury was collected on a filter which had not been denuded of reactive gaseous mercury (RGM) when compared to one that was. The RGM leads to a positive artifact in the measurement of particulate phase mercury and indicates that any further measurements of this phase must utilize a denuder during collection. A study on the influence of ozone during sampling of particulate mercury shows that elevated levels of ozone may result in a reaction with gaseous elemental mercury producing reactive gaseous mercury which sorbs to the particulate mercury and biases the measurement. This phenomenon was not observed at lower atmospheric levels of ozone and further study is necessary, in particular, to examine whether removal of elemental mercury from the sample stream will prevent this reaction during times when ozone levels are elevated.; A fully automated instrument was used to obtain near real-time speciated mercury measurements at three sites in Michigan. These measurements were combined with meteorological and chemical parameters in order to understand the atmospheric behavior of mercury at higher time resolutions. Results from a factor analysis show a high degree of correlation between elemental mercury and nitrogen oxides and suggests a common combustion source for both. Reactive gaseous mercury was found to be highly correlated with ozone and particulate matter but it was not possible to identify a source.; As part of this study, a new method combining thermal release analysis and mass spectrometry has enabled a tentative chemical identification of particulate mercury. Most samples were tentatively identified as containing mercuric chloride HgCl₂.; This work delineates the complexity of particulate mercury and indicates that great caution is imperative during sampling, analysis and data interpretation of this phase. Further study is necessary to continue to resolve the best sampling approach to the measurement of this species in the atmosphere.