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The Canadian Arctic Atmospheric Chemistry Experiment Validation Campaignshave been carried out at Eureka, Nunavut (80.05° N, 86.42° W) duringthe polar sunrise period since 2004. During the International Polar Year(IPY) springs of 2007 and 2008, three ground-based Fourier transforminfrared (FTIR) spectrometers were operated simultaneously. This paperpresents a comparison of trace gas measurements of stratosphericallyimportant species involved in ozone depletion, namely O3, HCl,ClONO2, HNO3 and HF, recorded with these three spectrometers.Total column densities of the gases measured with the new Canadian Networkfor the Detection of Atmospheric Change (CANDAC) Bruker 125HR are shown toagree to within 3.5% with the existing Environment Canada Bomem DA8measurements. After smoothing both of these sets of measurements to accountfor the lower spectral resolution of the University of Waterloo PortableAtmospheric Research Interferometric Spectrometer for the Infrared(PARIS-IR), the measurements were likewise shown to agree with PARIS-IR towithin 7%. Concurrent measurements of these gases were also made with thesatellite-based Atmospheric Chemistry Experiment Fourier TransformSpectrometer (ACE-FTS) during overpasses of Eureka during these timeperiods. While one of the mandates of the ACE satellite mission is to studyozone depletion in the polar spring, previous validation exercises haveidentified the highly variable polar vortex conditions of the spring periodto be a challenge for validation efforts. In this work, comparisons betweenthe CANDAC Bruker 125HR and ACE-FTS have been used to develop strictcriteria that allow the ground- and satellite-based instruments to beconfidently compared. When these criteria are taken into consideration, theobserved biases between the ACE-FTS and ground-based FTIR spectrometer arenot persistent for both years and are generally insignificant, though smallpositive biases of ~5%, comparable in magnitude to those seen inprevious validation exercises, are observed for HCl and HF in 2007, andnegative biases of −15.3%, −4.8% and −1.5% are seen forClONO2, HNO3 and O3 in 2008

atmospheric measurement techniques

Four Fourier transform spectrometers and the Arctic polar vortex: instrument intercomparison and ACE-FTS validation at Eureka during the IPY springs of 2007 and 2008