Atmospheric Chemistry Experiment Instruments Research Articles

Updated validation of ACE and OSIRIS ozone and NO2 measurements in the Arctic using ground-based instruments at Eureka, Canada

This paper presents long-term intercomparisons (2003–2017) between ozone and NO2 measured by the Optical Spectrograph and Infra-Red Imager System (OSIRIS) and the Atmospheric Chemistry Experiment (ACE) satellite instruments, and by ground-based instruments at the Polar Environment Atmospheric Research Laboratory (PEARL), near Eureka, Nunavut, Canada (80∘N, 86∘W). The ground-based instruments include four zenith-sky differential optical absorption spectroscopy (DOAS) instruments, two Fourier transform infrared (FTIR) spectrometers, and a Brewer spectrophotometer. Comparisons of 14–52 km ozone partial columns show good agreement between OSIRIS v5.10 and ACE-FTS v3.5/3.6 data (1.2%), while ACE-MAESTRO v3.13 ozone is smaller than the other two datasets by 6.7% and 5.9%, respectively. Satellite profiles were extended to the surface using ozonesonde data, and the resulting columns agree with the ground-based datasets with mean relative differences of 0.1–12.0%. For NO2, 12–40 km partial columns from ACE-FTS v3.5/3.6 and 12–32 km partial columns from OSIRIS v6.0 (scaled to 40 km) agree with ground-based partial columns with mean relative differences of 0.7–33.2%. Dynamical coincidence criteria improved the ACE to ground-based FTIR ozone comparisons, while little to no improvements were seen for other instruments, and for NO2. A ± 1∘ latitude criterion modestly improved the spring and fall NO2 comparisons. The results of this study are consistent with previous validation exercises. In addition, there are no significant drifts between the satellite datasets, or between the satellites and the ground-based measurements, indicating that the OSIRIS and ACE instruments continue to perform well.

Variations in middle atmospheric water vapor from 2004 to 2013

AbstractWe show measurements of middle atmospheric water vapor as measured by two ground‐based Water Vapor Millimeter‐wave Spectrometer instruments and three satellite‐based instruments: the Aura Microwave Limb Sounder, the Atmospheric Chemistry Experiment (ACE), and the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). We also show CH4 measurements from the MIPAS and ACE instruments and use these to help interpret the H2O variations. We find that interannual changes in stratospheric H2O of ~0.5 ppmv, observed from Table Mountain, California, at 26 km and 40 km from 2010 to 2012, are caused primarily by dynamically driven changes in CH4 during this period. The interannual variations in H2O observed over Mauna Loa, Hawaii, are shown to be quite similar to the average variations observed over 50°S–50°N in the lower mesosphere; thus, we conclude that a single ground‐based microwave instrument can provide a useful estimate of interannual globally averaged lower mesospheric H2O variations, even when such changes are as small as ~0.2–0.3 ppmv. We find that the increase of ~0.2–0.3 ppmv in H2O in the lower mesosphere since 2006 is qualitatively consistent with an increase in tropical tropopause temperature since around 2001.

Validation of ACE and OSIRIS ozone and NO<sub>2</sub> measurements using ground-based instruments at 80° N

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.

Validation of NO<sub>2</sub> and NO from the Atmospheric Chemistry Experiment (ACE)

Abstract. Vertical profiles of NO2 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 NO2) 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 NO2 and NO and the MAESTRO version 1.2 NO2 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 (SCIAMACHY), 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 NO2 and NO and the MAESTRO NO2 are generally consistent with the correlative data. The ACE-FTS and MAESTRO NO2 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 NO2 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.

Atmospheric chemistry experiment (ACE): Analytical chemistry from orbit

ACE is a Canadian-led satellite mission that is measuring the concentrations of more than 30 atmospheric constituents by absorption spectroscopy using the Sun as a light source. The principal goal of the ACE mission is to make measurements that will improve understanding of the chemical and dynamic processes that control the distribution of ozone in the upper troposphere and stratosphere. The ACE instruments are an infrared Fourier transform spectrometer (FTS), a UV/visible/near IR spectrograph and a two-channel solar imager, all working in solar occultation mode. The high-resolution (0.02 cm −1) FTS is the primary instrument on the satellite, and it covers the mid-infrared spectral region (750–4400 cm −1).