Abstract
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 NO2 measured by the ACE and OSIRIS satellite instruments and by ground-based 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 NO2 partial columns within 500 km of PEARL were calculated for ACE-FTS Version 2.2 (v2.2) plus updates, ACE-FTS v3.0, ACE-MAESTRO (Measurements of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) v1.2 and OSIRIS SaskMART v5.0x ozone and Optimal Estimation v3.0 NO2 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 NO2, 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 NO2, partial columns from 17 km upward were scaled to noon using a photochemical model. Mean relative differences between OSIRIS, ACE-FTS and ground-based NO2 measurements do not exceed 20%. ACE-MAESTRO measures more NO2 than the other instruments, with mean relative differences of 25–52%. Seasonal variation in the differences between NO2 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 NO2, the addition of a ±1° latitude coincidence criterion improved spring-time intercomparison results, likely due to the sharp latitudinal gradient of NO2 during polar sunrise. The differences between satellite and ground-based measurements do not show any obvious trends over the missions, indicating that both the ACE and OSIRIS instruments continue to perform well.
Highlights
Consistent long-term measurements of ozone and NO2 are essential for the characterization of ozone depletion and recovery
Since the University of Toronto GBS (UT-GBS) and Polar Environment Atmospheric Research Laboratory (PEARL)-GBS are very similar instruments and data were analyzed with the same settings, their columns agree within an average of 1 % for ozone, NO2 retrieved in the visible region (NO2-vis), and NO2 retrieved in the UV region (NO2-UV)
The GBS differential SCDs (DSCDs) were retrieved using the wavelength-corrected Greenblatt et al (1990) O4 cross-section, which was recommended by NDACC in 2009, while the System D’Analyse par Observations Zenithales (SAOZ) DSCDs were retrieved with the Hermans (2004) cross-section, which was included in the Hendrick et al (2011) NDACC recommendations
Summary
Consistent long-term measurements of ozone and NO2 are essential for the characterization of ozone depletion and recovery. While ozone and NO2 data products from both satellites have been validated (e.g. Brohede et al, 2008; Degenstein et al, 2009; Dupuy et al, 2009; Kerzenmacher et al, 2008), continued assessment assures long-term consistency within the datasets. Measurements included in this study were taken at the PEARL Ridge Lab (80.05◦ N, 86.42◦ W) and the Eureka Weather Station (79.98◦ N, 85.93◦ W), which is located 15 km from the Ridge Lab. Since August 2006, CANDAC instruments have recorded measurements of ozone and NO2, using ground-based zenith-sky differential optical absorption spectroscopy (DOAS) instruments and a Bruker Fourier transform infrared spectrometer (FTIR), when sunlight and weather permitted. Brewer spectrophotometer measurements were taken year-round for 2004– 2011 by Environment Canada, with support from the Canadian Arctic ACE Validation Campaigns and CANDAC This yields a multi-year dataset that can be used for long-term validation of satellite measurements. Details of the instrumentation and data analysis methods are described in the sections below
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