Atmospheric transport of persistent semi-volatile organic chemicals to the Arctic and cold condensation in the mid-troposphere – Part 2: 3-D modeling of episodic atmospheric transport

摘要

Two 3-dimensional global atmospheric transport models forpersistent organic pollutants (POPs) have been employed to investigate theassociation between the large-scale atmospheric motions and polewardtransports of persistent semi-volatile organic chemicals (SVOCs). We examinethe modeled daily air concentration of α- and γ-hexachlorocyclohexane(HCH) over a period from 1997 through 1999 duringwhich a number of episodic atmospheric transport events were detected inthis modeling study. These events provide modeling evidence for improvingthe interpretation on the cold condensation effect and poleward atmospherictransport of SVOCs in the mid-troposphere. Two episodic transport events ofγ-HCH (lindane) to the high Arctic (80–90° N), one from Asianand another from Eurasian sources, are reported in this paper. Both eventssuggest that the episodic atmospheric transports occurring in themid-troposphere (e.g. from 3000 m to 5500 m height) are driven byatmospheric horizontal and vertical motions. The association of thetransport events with atmospheric circulation is briefly discussed. Strongsoutherly winds, forced by the evolution of two semi-permanent high pressuresystems over mid-high latitudes in the Northern Hemisphere, play animportant role in the long-range transport (LRT) of HCHs to the highlatitudes from its sources. Being consistent with the cold condensationeffect and poleward atmospheric transport in a mean meridional atmosphericcirculation simulated by a 2-D atmospheric transport model, as reported bythe first part of this study, this modeling study indicates that coldcondensation is likely occurring more intensively in the mid-tropospherewhere rapid declining air temperature results in condensed phase of thechemical over and near its source regions and where stronger winds conveythe chemical more rapidly to the polar region during the episodic polewardatmospheric transport events.