An investigation of the interaction of carbonyl ... - Wiley Online Library

GEOPHYSICAL RESEARCH LETTERS, VOL. 27, NO. 15, PAGES 2241-2244, AUGUST 1, 2000

An Investigation of the Interaction of Carbonyl Compounds with the Snowpack TaraLinCouch •, AnnLouise Sumner • TerraM Dassau • andPaulB Shepson •'2 Departments of IChemistry and2Earth andAtmospheric Sciences, Purdue University, WestLafayette, Indiana, 47907, USA

Richard E. Honrath Department of Civil andEnvironmental Engineering, MichiganTechnological University,Houghton, Michigan,49931, USA

inconsistentwith loss from the snowpack via snow grain

Alert, Nunavut (Sumner and Shepson, 1999), and that NOx is photochemicallyproduced in the snowpack in Greenland (Honrath et al., 1999). Honrath et al. (1999) and Sumner and Shepson(1999) discussthe possibilitythat photochemistryin the snowpack could generate free radicals, which, in turn, could participatein the oxidationof other species. Theseobservations demonstratethe potential role of the snowpackin processing troposphericgasesin snow-coveredregions. To investigatethe importance and influence of the snowpack on gas phase concentrations of carbonylcompounds,measurements of HCHO, CH3CHO, and CH3C(O)CH3 were conductedin ambient air and snowpackair in the Upper Peninsulaof Michigan as part of the SnowNitrogen and Oxidantsin Winter (SNOW99) study.

metamorphism.The data also imply that formaldehyde is not hydratedin the snowgrainsurfacelayer.

Experimental Methods

Abstract. Measurementsof formaldehyde,acetaldehyde,and acetonein ambientand snowpackair wereconductedasa partof the SNOW99 studyin northernMichigan. Vertical profilesof ambientandsnowpackair illustratelargeconcentration gradients

throughthetop-10 cm of the snowpack, implyinga positiveflux of thesespeciesfrom the surface. Snowchamberexperiments that involvedflushinga snow-filled34L Teflon-linedchamber with zero air at 20 slpm indicatedthat releasefrom the snow followedfirst orderkinetics,with decayconstants of 0.19, 0.44,

and 0.34 hr-• for formaldehyde, acetaldehyde, and acetone, respectively.Althoughit is likely that temperature dependent adsorption/desorption processes play a role, the data are not

Introduction

Investigating the chemicalcomposition andprocesses within ice andsnowhasrecentlybecomean activeresearch area(•Volff and Bales,1996;Dibb and Jaffrezo,1997), due,in part,to the historicalclimatic and chemicalrecordthat lies within the glacial

ice cores (Neffel et al., 1995; Staffelbachet al., 1991). Deposition of atmospheric species to thesnowsurface tendsto

All measurements were conductedfrom January9 to January 17, 1999, in a rural forest locatedoutsideof Ahmeek, Michigan (47.35ø N, 88.40ø W). This site and the 34 liter Teflon-coated flow-throughsnow chamberused for experimentsare described by Honrath et al. (this issue). Gas phaseHCHO measurements were conductedusinga continuousflow injectionanalysissystem (Fan and Dasgupta, 1994) as describedby Sumnerand Shepson (1999). CH3CHO and CI-I3C(O)CH3 were measuredusing an automatedGC/MS sampling system(Sram et al., 1998). We

concentratethem near the snow/atmosphere interface,creating estimate absolute uncertainties for the determination of these conditionsfavorableto further chemicaland/or photochemical carbonylcompoundsof +20%, with a precisionof +2% for processing. HCHO and +5% for CH3CHO and CH3C(O)CH3.

Formaldehyde (HCHO), acetaldehyde (CH•CHO), and acetone (CH•C(O)CH•)areall directlyemitted fromcombustion andbiogenic sources (•arneke,et al., 1999;•4rlander et al., Results 1995a, b; Fall et al., 1999) but are also produced from the Vertical Profiles through the Snowpack photooxidation of anthropogenic and biogenichydrocarbons. To conduct measurementsof the vertical profiles of the Thesecompounds canbefoundin appreciable quantities evenin remoteregions(Shepsonet al., 1996) due to long-range concentrationsof these speciesin the air above and within the transport, especially in winter,of the carbonylcompoundssnowpack,a 5cm diameterhole wasboredwith a cleanPVC pipe themselves or their precursors. It has been shownthat throughfresh undisturbedsnow down to the snowpackbaseat formaldehyde is elevatedin the snowpack interstitial air in 60 cm (heights are expressedrelative to the snow/atmosphere Greenland (Fuhreret al., 1996;Hutterliet al., 1999a)andat interface).PFA-Teflon inlet lineswerethencarefullyplacedinto the hole at variousdepths. The top of the hole was then covered INow at Departmentof Chemistry,PurdueUniversity,West with a piece of Teflon film, to restrictair flow from above the Lafayette,Indiana,47907, USA. snowpack surface. Simultaneous HCHO, CH•CHO, and 2Alsoat Department of Earthand Atmospheric Science, Purdue CH3C(O)CH3 measurementswere conductedfrom-60 cm to University,West Lafayette,Indiana,47907, USA. +170 cm, resultingin the verticalprofilesshownin Figure 1. All three compoundsexhibit a substantialincreasein concentration Copyright2000 by the AmericanGeophysical Union. relativeto ambientair immediatelybelow the snowsurface. This large gradient implies a flux of these reactive carbonyl compounds out of the snowpack(Waddingtonet al., 1996).

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