Biomedical subjects

Yushan Su

Publications and source records attributed to Yushan Su.

4 recordsLinked to original sources

PubMed2006

Spatial and seasonal variations of Hexachlorocyclohexanes (HCHs) and hexachlorobenzene (HCB) in the Arctic atmosphere.

Weekly high-volume air samples were collected between 2000 and 2003 at six Arctic sites, i.e., Alert, Kinngait, and Little Fox Lake (LFL) in Canada, Point Barrow in Alaska, Valkarkai in Russia, and Zeppelin in Norway. Hexachlorocyclohexanes (HCHs) and hexachlorobenzene (HCB) were quantified in all samples. Comparison showed that alpha-HCH and HCB were homogeneously distributed in the circumpolar atmosphere and uniform throughout the seasons. However, significantly higher atmospheric concentrations of alpha-HCH and HCB and strongertemperature dependence of alpha-HCH and gamma-HCH were found at LFL in Yukon (YK), which is unique among the sites by virtue of its high altitude and low latitude, resulting in higher precipitation rates and summer temperatures. Strong temperature dependence of alpha- and gamma-HCH at this location suggests that secondary emissions, i.e., re-evaporation from surfaces, were more important at this site than others. It is hypothesized that a higher precipitation rate at LFL facilitated the transfer of alpha-HCH from the atmosphere to surface media when technical HCH was still in use worldwide. On the other hand, higher temperature at LFL enhanced reevaporation to the atmosphere after the global ban of technical HCH. In contrast to alpha-HCH and HCB, larger spatial and seasonal differences were seen for gamma-HCH (a currently used pesticide), which likely reflect the influence of different primary contaminant sources on different Arctic locations. Fugacity ratios suggest a net deposition potential of HCB from air to seawater, whereas seawater/air exchange direction of alpha-HCH varies in the circumpolar environment.

Air Pollutants↗

PubMed2006

Regressing gas/particle partitioning data for polycyclic aromatic hydrocarbons.

Polycyclic aromatic hydrocarbons (PAHs) were measured in the rural atmosphere of Southern Ontario, Canada from October 2001 to November 2002. Sixty seven pairs of gaseous and particle-bound concentrations of PAHs were determined concurrently in a forest and a clearing. The gas/particle partitioning behavior of the PAHs was investigated by fitting the original Junge-Pankow equation to the fraction in the particle phase phi for each set of measured data, either allowing the slope m to deviate from -1 (two-parameter model) or not (one-parameter model). This fitting procedure was judged more robust than linear logarithmic regressions involving the gas/particle partition coefficient, because the latter is sensitive to the applied blank correction, tends to ignore a significant amount of analytical information, and gives undue weight to more uncertain data points. The experimental data fit was good for both nonlinear models, and discrepancies between experimental data and models and between models are mostly related to sampling/experimental artifacts. In particular, samples taken close to the freezing point appear to suffer from blow-off artifacts. Applying slopes m different from -1 appears only justified if it can be assured that a second parameter indeed provides a better fit and that this better fit is not due to experimental, analytical, or statistical artifacts. The magnitude of the differences in the model fitting parameters between sampling events is consistent with the reported variability in the nature and concentration of atmospheric particles. Statistical tests on the regression results indicate that the gas/particle partitioning was not significantly different between the forest and the clearing.

Air Pollutants↗

PubMed2005

Does the forest filter effect prevent semivolatile organic compounds from reaching the Arctic?

Forests act as efficient filters for many airborne semivolatile organic compounds (SOCs). However, most simulations of an organic chemical's long-range transport in the atmosphere do not account for this filter effect. In this study, forests are introduced into an existing zonally averaged global distribution model (Globo-POP) to investigate how such a change affects a chemical's potential to undergo long range transport and accumulation in the Arctic, as quantified by the Arctic contamination potential (ACP). Simulation results indicate that the ACP of a "space" of perfectly persistent hypothetical organic chemicals, defined by log KOA and log KAW, is reduced by introducing forests in the global model. Depending on partition characteristics, this reduction can be as large as a factor of 2. Model calculations also indicate that it is mostly the boreal forests, specifically boreal deciduous forests, which play a key role in this respect. Sensitivity analyses establish the deposition velocity to boreal forests, especially for gaseous compounds, as one of the most influential parameters controlling this global forest filter effect. The extent of the effect is further sensitive to the forest density and precipitation rate in the boreal zone, and the degradation rates of the chemical. Specifically, degradation in the forest canopy may enhance the effect and further reduce an SOC's long range transport to remote regions. Simulations for three PCB congeners suggest that forests may reduce concentrations in air, ocean, and freshwater at the expense of increased concentrations in forest soils and may lead to substantially increased overall global residence times.

Air↗

PubMed2004

Quantifying the global fractionation of polychlorinated biphenyls.

Due to the wide range of their physical-chemical properties, polychlorinated biphenyls (PCBs) have played an important role in the derivation of the global fractionation hypothesis, which predicts changes in the composition of persistent organic pollutant mixtures with latitude. Recent historical emission estimates, the derivation of an internally consistent property data set, in combination with a zonally averaged global fate and transport model, allow a quantitative investigation of the compositional shifts PCBs experience as a function of environmental compartment, latitude and time. Model simulations reproduce the higher relative abundance of lighter PCB congeners with increasing latitude, observed in air and soil, and quantify the relative importance of partitioning, persistence and emissions in establishing PCB patterns. Compositional variations consistent with global fractionation, as well as inverted concentration profiles with higher levels in the Arctic than at lower latitudes, are consistent with only minor fractions of the global PCB inventory being transferred northward.

Arctic Regions↗