Measurement Technique for the Determination of Photolyzable
JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 102, NO. D13, PAGES 15,999-16,004,JULY 20, 1997 Measurement techniquefor the determination of photolyzable chlorine and bromine in the atmosphere G. A. Impey,P. B. Shepson,• D. R. Hastie,L. A. Bartie• Departmentof Chemistryand Centre for AtmosphericChemistry, York University,Toronto, Ontario, Canada Abstract. A techniquehas been developed to enablemeasurement of photolyzablechlorine and bromineat tracelevels in the troposphere.In thismethod, ambient air is drawnt•ough a cylindricalflow cell, whichis irradiatedwith a Xe arc lamp. In the reactionvessel of the photoactivehalogen detector (PHD), photolyrically active molecules Clp (including C12, HOC1, C1NO,C1NO2, and C1ONO2) and Brp (including Br2, HOBr, BrNO, BrNO2, and BrONO2) are photolyzed,and the halogenatoms produced react with properieto form stablehalogenated products.These products are thensampled and subsequently separated and detected by gas chromatography.The systemis calibratedusing low concentrationmixtures of C12and Br2 in air from commerciallyavailable permeation sources. We obtaineddetection limits of 4 pptv and 9 pptv as Br2 andC12, respectively, for 36 L samples. 1. Introduction (or C12)in the Arctic, largely as a result of the lack of suitable analyticalmethodologies. This paperreports the developmentof The episodicdestruction of groundlevel ozonein the Arctic at a measurementtechnique for the determinationof rapidly sunriseis a phenomenonthat hasbeen observed for many years. photolyzingchlorine (referred to hereas Clp) and bromine (Brp) With the onsetof polar sunrise,ozone levels are often observed speciesat pansper trillion by volume(pptv) mixingratios in the to drop from a backgroundconcentration of •40 ppbv to almost atmosphere.Impey et al. [this issue]discuss the resultsobserved zero on a timescaleof a day or less [Barrie et al., 1988] for from a field studyconducted in the Canadianhigh Arctic at Alert, periodsof 1-10 days.
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