A new Bruker IFS 125HR Fourier transform spectrometer has been installed at the Polar Environment Atmospheric Research Laboratory at Eureka, Nunavut, Canada (80.05°N, 86.42°W). This instrument will become the Network for the Detection of Atmospheric Composition Change’s (NDACC’s) primary instrument at Eureka, replacing the existing Bomem DA8 Fourier transform spectrometer, and will operate throughout the sunlit parts of the year. This paper introduces the new instrument and describes the retrieval procedure, including a comprehensive error analysis. Total columns of O3, HCl, HF, HNO3, N2O, CH4, and CO are presented for the first full year of measurements (2007). Perturbations in the total column resulting from the presence of the Arctic polar vortex over Eureka and the chemical processes within it are visible, as are annual cycles driven by photochemistry and dynamics. Enhancements in the CO total column resulting from specific biomass burning smoke events can also be seen. An intercomparison between the existing Bomem DA8 and the new Bruker IFS 125HR was carried out in July 2007 and is presented here. The total columns derived from the two instruments are shown to be in excellent agreement, with mean differences for all gases of less than 2.3%.

G lobal climate change is visibly and tangibly manifested through the Arctic cryospheric system: sea ice loss, earlier spring snowmelts, thawing permafrost, retreating glaciers, and coastal erosion. While not as visibly manifest, the role of the atmosphere is also a critical component in determining the trajectory of the Arctic system. The atmosphere not only drives change, but is reciprocally being modified through a complex web of feedbacks, and is the fast-track mechanism for the transport of energy and moisture through the global system that links climate and weather. For decades, it has been recognized that fundamental components of the atmospheric system such as clouds, atmospheric trace gases, aerosols, and atmosphere-surface exchange processes compose some of the major uncertainties that limit the diagnostic or predictive skill of coupled atmosphere-ice-ocean-terrestrial models (IPCC 2013, chapter 9). Arctic nations have responded in recent decades by establishing  A micrometeorological tower in Tiksi, Russia is used to determine the atmospheric-surface energy balance. (Photo credit: Vasily Kustov)

Abstract. The Optical Spectrograph and Infra-Red Imager System (OSIRIS) and the Atmospheric Chemistry Experiment (ACE) have been taking measurements from space since 2001 and 2003, respectively. This paper presents intercomparisons between ozone and NO 2 measured by the ACE and OSIRIS satellite instruments and by groundbased instruments at the Polar Environment Atmospheric Research Laboratory (PEARL), which is located at Eureka, Canada (80 • N, 86 • W) and is operated by the Canadian Network for the Detection of Atmospheric Change (CANDAC). The ground-based instruments included in this study are four zenith-sky differential optical absorption spectroscopy (DOAS) instruments, one Bruker Fourier transform infrared spectrometer (FTIR) and four Brewer spectrophotometers.Ozone total columns measured by the DOAS instruments were retrieved using new Network for the Detection of Atmospheric Composition Change (NDACC) guidelines and agree to within 3.2 %. The DOAS ozone columns agree with the Brewer spectrophotometers with mean relative differences that are smaller than 1.5 %. This suggests that for these instruments the new NDACC data guidelines were successful in producing a homogenous and accurate ozone dataset at 80 • N. Satellite 14-52 km ozone and 17-40 km NO 2 partial columns within 500 km of PEARL were calculated for ACE-FTS Version 2.2 (v2.2) plus updates, ACE- C. Adams et al.: Validation of ACE and OSIRISand Optimal Estimation v3.0 NO 2 data products. The new ACE-FTS v3.0 and the validated ACE-FTS v2.2 partial columns are nearly identical, with mean relative differences of 0.0 ± 0.2 % and −0.2 ± 0.1 % for v2.2 minus v3.0 ozone and NO 2 , respectively. Ozone columns were constructed from 14-52 km satellite and 0-14 km ozonesonde partial columns and compared with the ground-based total column measurements. The satellite-plus-sonde measurements agree with the ground-based ozone total columns with mean relative differences of 0.1-7.3 %. For NO 2 , partial columns from 17 km upward were scaled to noon using a photochemical model. Mean relative differences between OSIRIS, ACE-FTS and ground-based NO 2 measurements do not exceed 20 %. ACE-MAESTRO measures more NO 2 than the other instruments, with mean relative differences of 25-52 %. Seasonal variation in the differences between NO 2 partial columns is observed, suggesting that there are systematic errors in the measurements and/or the photochemical model corrections. For ozone spring-time measurements, additional coincidence criteria based on stratospheric temperature and the location of the polar vortex were found to improve agreement between some of the instruments. For ACE-FTS v2.2 minus Bruker FTIR, the 2007-2009 spring-time mean relative difference improved from −5.0 ± 0.4 % to −3.1 ± 0.8 % with the dynamical selection criteria. This was the largest improvement, likely because both instruments measure direct sunlight and therefore have well-characterized lines-of-sight compared with scattered sunlight measurements. For NO 2 , the addition of a ±1 • latitude co...

Two of the ten instruments involved in the campaign, both Fourier transform spectrometers (FTSs), were operated simultaneously, recording atmospheric solar absorption spectra. The first instrument was an ABB Bomem DA8 high-resolution infrared FTS. The second instrument was the Portable Atmospheric Research Interferometric Spectrometer for the Infrared (PARIS-IR), the ground-based version of the satelliteborne FTS on the ACE satellite (ACE-FTS). From the measurements collected by these two ground-based instruments, total column densities of seven stratospheric trace gases (O 3 , HCl, ClONO 2 , HF, HNO 3 , NO 2 , and NO) were retrieved using the optimal estimation method and these results were compared. Since the two instruments sampled the same portions of atmosphere by synchronizing observations during the campaign and used consistent retrieval parameters, the biases in retrieved columns from the two spectrometers represent the instrumental differences. Mean differences in total column densities of O 3 , HCl, ClONO 2 , HF, HNO 3 , and NO 2 from the observations between PARIS-IR and the DA8 FTS are 2.8 %, −3.2 %, −4.3 %, −1.5 %, −1.9 %, and −0.1 %, respectively. Partial column results from the ground-based Correspondence to: K. A. Walker (kwalker@atmosp.physics.utoronto.ca) spectrometers were also compared with partial columns derived from ACE-FTS version 2.2 (including updates for O 3 ) profiles. Mean differences in partial column densities of O 3 , HCl, ClONO 2 , HF, HNO 3 , NO 2 , and NO from the measurements between ACE-FTS and the DA8 FTS are −5.9 %, −8.5 %, −11.8 %, −0.9 %, −6.6 %, −21.6 % and −7.6 % respectively. Mean differences in partial column densities of O 3 , HCl, ClONO 2 , HF, HNO 3 , NO 2 from the measurements between ACE-FTS and the PARIS-IR are −5.2 %, −4.6 %, −2.3 %, −4.7 %, 5.7 % and −11.9 %, respectively. This work provides further evidence of the reliability of ACE-FTS measurements from the first three years of on-orbit observations. Column densities of O 3 , HCl, ClONO 2 , and HNO 3 from the three FTSs were normalized with respect to HF and used to compare the time evolution of the chemical constituents in the atmosphere over Eureka during spring 2006.

Abstract. As a consequence of dynamically variable meteorological conditions, springtime Arctic ozone levels exhibit significant interannual variability in the lower stratosphere. In winter 2011, the polar vortex was strong and cold for an unusually long time. Our research site, located at Eureka, Nunavut, Canada (80.05 • N, 86.42 • W), was mostly inside the vortex from October 2010 until late March 2011. The Bruker 125HR Fourier transform infrared spectrometer installed at the Polar Environment Atmospheric Research Laboratory at Eureka acquired measurements from 23 February to 6 April during the 2011 Canadian Arctic Atmospheric Chemistry Experiment Validation Campaign. These measurements showed unusually low ozone, HCl, and HNO 3 total columns compared to the previous 14 yr. To remove dynamical effects, we normalized these total columns by the HF total column. The normalized values of the ozone, HCl, and HNO 3 total columns were smaller than those from previous years, and confirmed the occurrence of chlorine activation and chemical ozone depletion. To quantify the chemical ozone loss, a three-dimensional chemical transport model, SLIMCAT, and the passive subtraction method were used. The chemical ozone depletion was calculated as the mean percentage difference between the measured ozone and the SLIMCAT passive ozone, and was found to be 35 %.