Abstract. We use aircraft observations of carbon monoxide (CO) from the NASA ARCTAS and NOAA ARCPAC campaigns in

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%.

Based on model simulations of O 3 and HNO 3 tagged by source type and region, we find that the anthropogenic pollution from the Northern Hemisphere is the dominant source of O 3 and HNO 3 in the Arctic at pressures greater than 400 hPa, and that the stratospheric influence is the principal contribution at pressures less 400 hPa. During the summer, intense Russian fire emissions contribute some amount to the tropospheric columns of both gases over the American sector of the Arctic. North American fire emissions (California and Canada) also show an important impact on tropospheric ozone in the Arctic boundary layer.Additional analysis of tropospheric O 3 measurements from ground-based FTIR and from the IASI satellite sounder made at the Eureka (Canada) and Thule (Greenland) polar sites during POLARCAT has been performed using the tagged contributions. It demonstrates the capability of these instruments for observing pollution at northern high latitudes. Differences between contributions from the sources to the tropospheric columns as measured by FTIR and IASI are discussed in terms of vertical sensitivity associated with these instruments. The first analysis of O 3 tropospheric columns observed by the IASI satellite instrument over the Arctic is also provided. Despite its limited vertical sensitivity in the lowermost atmospheric layers, we demonstrate that IASI is capable of detecting low-altitude pollution transported into the Arctic with some limitations.

Abstract. Vertical profiles of NO 2 and NO have been obtained from solar occultation measurements by the Atmospheric Chemistry Experiment (ACE), using an infrared Fourier Transform Spectrometer (ACE-FTS) and (for NO 2 ) an ultraviolet-visible-near-infrared spectrometer, MAESTRO (Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation). In this paper, the quality of the ACE-FTS version 2.2 NO 2 and NO and the MAESTRO version 1.2 NO 2 data are assessed using other solar occultation measurements (HALOE, SAGE II, SAGE III, POAM III, SCIAMACHY), stellar occultation measurements (GOMOS), limb measurements (MIPAS, OSIRIS), nadir measurements (SCIA-MACHY), balloon-borne measurements (SPIRALE, SAOZ) and ground-based measurements (UV-VIS, FTIR). Time differences between the comparison measurements were reduced using either a tight coincidence criterion, or where possible, chemical box models. ACE-FTS NO 2 and NO and the MAESTRO NO 2 are generally consistent with the correlative data. The ACE-FTS and MAESTRO NO 2 volume mixing ratio (VMR) profiles agree with the profiles from other satellite data sets to within about 20% between 25 and 40 km, with the exception of MIPAS ESA (for ACE-FTS) and SAGE II (for ACE-FTS (sunrise) and MAESTRO) and suggest a negative bias between 23 and 40 km of about 10%. MAESTRO reports larger VMR values than the ACE-FTS. In comparisons with HALOE, ACE-FTS NO VMRs typically (on average) agree to ±8% from 22 to 64 km and to +10% from 93 to 105 km, with maxima of 21% and 36%, respectively. Partial column comparisons for NO 2 show that there is quite good agreement between the ACE instruments and the FTIRs, with a mean difference of +7.3% for ACE-FTS and +12.8% for MAESTRO.

Abstract. Time series of total column abundances of hydrogen chloride (HCl), chlorine nitrate (ClONO2), and hydrogen fluoride (HF) were determined from ground-based Fourier transform infrared (FTIR) spectra recorded at 17 sites belonging to the Network for the Detection of Atmospheric Composition Change (NDACC) and located between 80.05° N and 77.82° S. By providing such a near-global overview on ground-based measurements of the two major stratospheric chlorine reservoir species, HCl and ClONO2, the present study is able to confirm the decrease of the atmospheric inorganic chlorine abundance during the last few years. This decrease is expected following the 1987 Montreal Protocol and its amendments and adjustments, where restrictions and a subsequent phase-out of the prominent anthropogenic chlorine source gases (solvents, chlorofluorocarbons) were agreed upon to enable a stabilisation and recovery of the stratospheric ozone layer. The atmospheric fluorine content is expected to be influenced by the Montreal Protocol, too, because most of the banned anthropogenic gases also represent important fluorine sources. But many of the substitutes to the banned gases also contain fluorine so that the HF total column abundance is expected to have continued to increase during the last few years. The measurements are compared with calculations from five different models: the two-dimensional Bremen model, the two chemistry-transport models KASIMA and SLIMCAT, and the two chemistry-climate models EMAC and SOCOL. Thereby, the ability of the models to reproduce the absolute total column amounts, the seasonal cycles, and the temporal evolution found in the FTIR measurements is investigated and inter-compared. This is especially interesting because the models have different architectures. The overall agreement between the measurements and models for the total column abundances and the seasonal cycles is good. Linear trends of HCl, ClONO2, and HF are calculated from both measurement and model time series data, with a focus on the time range 2000–2009. This period is chosen because from most of the measurement sites taking part in this study, data are available during these years. The precision of the trends is estimated with the bootstrap resampling method. The sensitivity of the trend results with respect to the fitting function, the time of year chosen and time series length is investigated, as well as a bias due to the irregular sampling of the measurements. The measurements and model results investigated here agree qualitatively on a decrease of the chlorine species by around 1% yr−1. The models simulate an increase of HF of around 1% yr−1. This also agrees well with most of the measurements, but some of the FTIR series in the Northern Hemisphere show a stabilisation or even a decrease in the last few years. In general, for all three gases, the measured trends vary more strongly with latitude and hemisphere than the modelled trends. Relative to the FTIR measurements, the models tend to underestimate the decreasing chlorine trends and to overestimate the fluorine increase in the Northern Hemisphere. At most sites, the models simulate a stronger decrease of ClONO2 than of HCl. In the FTIR measurements, this difference between the trends of HCl and ClONO2 depends strongly on latitude, especially in the Northern Hemisphere.

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...

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 %.

Bruker 125HR are shown to agree to within 3.5% with the existing Environment Canada Bomem DA8 measurements. After smoothing both of these sets of measurements to account for the lower spectral resolution of the University of Waterloo Portable Atmospheric Research Interferometric Spectrometer for the Infrared (PARIS-IR), the measurements were likewise shown to agree with PARIS-IR to within 7%. Concurrent measurements of these gases were also made with the satellite-based Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) during overpasses of Eureka during these time periods. While one of the mandates of the ACE satellite mission is to study ozone depletion in the polar spring, previous validation exercises have identified the highly variable polar vortex conditions of the spring period to be a challenge for validation efforts. In this Correspondence to: R. L. Batchelor (rbatchelor@atmosp.physics.utoronto.ca) work, comparisons between the CANDAC Bruker 125HR and ACE-FTS have been used to develop strict criteria that allow the ground-and satellite-based instruments to be confidently compared. When these criteria are taken into consideration, the observed biases between the ACE-FTS and ground-based FTIR spectrometer are not persistent for both years and are generally insignificant, though small positive biases of ∼5%, comparable in magnitude to those seen in previous validation exercises, are observed for HCl and HF in 2007, and negative biases of −15.3%, −4.8% and −1.5% are seen for ClONO 2 , HNO 3 and O 3 in 2008.