A Dynamic Model To Study the Exchange of Gas-Phase Persistent Organic Pollutants between Air and a Seasonal Snowpack
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- 作者：Kaj M. Hansen ; Crispin J. Halsall ; and Jesper H. Christensen
- 刊名：Environmental Science & Technology
- 出版年：2006
- 出版时间：April 15, 2006
- 年：2006
- 卷：40
- 期：8
- 页码：2644 - 2652
- 全文大小：272K
- 年卷期：v.40,no.8(April 15, 2006)
- ISSN：1520-5851
文摘
An arctic snow model was developed to predict theexchange of vapor-phase persistent organic pollutantsbetween the atmosphere and the snowpack over a winterseason. Using modeled meteorological data simulatingconditions in the Canadian High Arctic, a single-layer snowpack was created on the basis of the precipitationrate, with the snow depth, snow specific surface area,density, and total surface area (TSA) evolving throughoutthe annual time series. TSA, an important parameteraffecting the vapor-sorbed quantity of chemicals in snow,was within a factor of 5 of measured values. Net fluxesfor fluorene, phenanthrene, PCB-28 and -52, and 
- and
-HCH (hexachlorocyclohexane) were predicted on the basisof their wet deposition (snowfall) and vapor exchangebetween the snow and atmosphere. Chemical fluxes werefound to be highly dynamic, whereby deposition wasrapidly offset by evaporative loss due to snow settling(i.e., changes in TSA). Differences in chemical behaviorover the course of the season (i.e., fluxes, snow concentrations) were largely dependent on the snow/air partitioncoefficients (Ksa). Chemicals with relatively higher Ksa valuessuch as - and -HCH were efficiently retained withinthe snowpack until later in the season compared to fluorene,phenathrene, and PCB-28 and -52. Average snow and airconcentrations predicted by the model were within a factorof 5-10 of values measured from arctic field studies,but tended to be overpredicted for those chemicals withhigher Ksa values (i.e., HCHs). Sensitivity analysis revealedthat snow concentrations were more strongly influencedby Ksa than either inclusion of wind ventilation of the snowpackor other changes in physical parameters. Importantly,the model highlighted the relevance of the arctic snowpackin influencing atmospheric concentrations. For the HCHs,evaporative fluxes from snow were more pronounced in Apriland May, toward the end of the winter, providing evidencethat the snowpack plays an important role in influencingthe seasonal increase in air concentrations for thesecompounds at this time of year.
- and-HCH (hexachlorocyclohexane) were predicted on the basisof their wet deposition (snowfall) and vapor exchangebetween the snow and atmosphere. Chemical fluxes werefound to be highly dynamic, whereby deposition wasrapidly offset by evaporative loss due to snow settling(i.e., changes in TSA). Differences in chemical behaviorover the course of the season (i.e., fluxes, snow concentrations) were largely dependent on the snow/air partitioncoefficients (Ksa). Chemicals with relatively higher Ksa valuessuch as - and -HCH were efficiently retained withinthe snowpack until later in the season compared to fluorene,phenathrene, and PCB-28 and -52. Average snow and airconcentrations predicted by the model were within a factorof 5-10 of values measured from arctic field studies,but tended to be overpredicted for those chemicals withhigher Ksa values (i.e., HCHs). Sensitivity analysis revealedthat snow concentrations were more strongly influencedby Ksa than either inclusion of wind ventilation of the snowpackor other changes in physical parameters. Importantly,the model highlighted the relevance of the arctic snowpackin influencing atmospheric concentrations. For the HCHs,evaporative fluxes from snow were more pronounced in Apriland May, toward the end of the winter, providing evidencethat the snowpack plays an important role in influencingthe seasonal increase in air concentrations for thesecompounds at this time of year.