| 1. |
- Blumenstock, T., et al.
(författare)
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Characterization and potential for reducing optical resonances in Fourier transform infrared spectrometers of the Network for the Detection of Atmospheric Composition Change (NDACC)
- 2021
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Ingår i: Atmospheric Measurement Techniques. - : Copernicus GmbH. - 1867-1381 .- 1867-8548. ; 14:2, s. 1239-1252
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Tidskriftsartikel (refereegranskat)abstract
- Although optical components in Fourier transform infrared (FTIR) spectrometers are preferably wedged, in practice, infrared spectra typically suffer from the effects of optical resonances ("channeling") affecting the retrieval of weakly absorbing gases. This study investigates the level of channeling of each FTIR spectrometer within the Network for the Detection of Atmospheric Composition Change (NDACC). Dedicated spectra were recorded by more than 20 NDACC FTIR spectrometers using a laboratory mid-infrared source and two detectors. In the indium antimonide (InSb) detector domain (1900-5000 cm-1), we found that the amplitude of the most pronounced channeling frequency amounts to 0.1 ‰ to 2.0 ‰ of the spectral background level, with a mean of (0:68±0:48) ‰ and a median of 0.60 ‰. In the mercury cadmium telluride (HgCdTe) detector domain (700-1300 cm-1), we find even stronger effects, with the largest amplitude ranging from 0.3 ‰ to 21 ‰ with a mean of (2:45±4:50) ‰ and a median of 1.2 ‰. For both detectors, the leading channeling frequencies are 0.9 and 0.11 or 0.23 cm-1 in most spectrometers. The observed spectral frequencies of 0.11 and 0.23 cm-1 correspond to the optical thickness of the beam splitter substrate. The 0.9 cm-1 channeling is caused by the air gap in between the beam splitter and compensator plate. Since the air gap is a significant source of channeling and the corresponding amplitude differs strongly between spectrometers, we propose new beam splitters with the wedge of the air gap increased to at least 0.8. We tested the insertion of spacers in a beam splitter's air gap to demonstrate that increasing the wedge of the air gap decreases the 0.9 cm-1 channeling amplitude significantly. A wedge of the air gap of 0.8 reduces the channeling amplitude by about 50 %, while a wedge of about 2 removes the 0.9 cm-1 channeling completely. This study shows the potential for reducing channeling in the FTIR spectrometers operated by the NDACC, thereby increasing the quality of recorded spectra across the network.
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| 2. |
- Brodie, Juliet, et al.
(författare)
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The future of the northeast Atlantic benthic flora in a high CO2 world
- 2014
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Ingår i: Ecology and Evolution. - : John Wiley & Sons. - 2045-7758. ; 4:13, s. 2787-2798
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Tidskriftsartikel (refereegranskat)abstract
- Seaweed and seagrass communities in the northeast Atlantic have been profoundly impacted by humans, and the rate of change is accelerating rapidly due to runaway CO2 emissions and mounting pressures on coastlines associated with human population growth and increased consumption of finite resources. Here, we predict how rapid warming and acidification are likely to affect benthic flora and coastal ecosystems of the northeast Atlantic in this century, based on global evidence from the literature as interpreted by the collective knowledge of the authorship. We predict that warming will kill off kelp forests in the south and that ocean acidification will remove maerl habitat in the north. Seagrasses will proliferate, and associated epiphytes switch from calcified algae to diatoms and filamentous species. Invasive species will thrive in niches liberated by loss of native species and spread via exponential development of artificial marine structures. Combined impacts of seawater warming, ocean acidification, and increased storminess may replace structurally diverse seaweed canopies, with associated calcified and noncalcified flora, with simple habitats dominated by noncalcified, turf-forming seaweeds.
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| 3. |
- Cantos, Irene Pardo, et al.
(författare)
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Determination and analysis of time series of CFC-11 (CCl3F) from FTIR solar spectra, in situ observations, and model data in the past 20 years above Jungfraujoch (46 degrees N), Lauder (45 degrees S), and Cape Grim (40 degrees S) stations
- 2022
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Ingår i: Environmental Science: Atmospheres. - : Royal Society of Chemistry (RSC). - 2634-3606. ; 2:6, s. 1487-1501
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Tidskriftsartikel (refereegranskat)abstract
- The atmospheric concentration of CFC-11 (CCl3F) has declined in response to the phase-out of its production by the Montreal Protocol. Nevertheless, this atmospheric concentration decline suffered a slow-down around 2012 due to emissions from non-reported production. Since CFC-11 is one of the most important ozone-depleting chlorofluorocarbons (CFCs), its continuous monitoring is essential. We present the CFC-11 total column time series (2000-2020) retrieved in a consistent way from ground-based high-resolution solar absorption Fourier transform infrared (FTIR) spectra. These observations were recorded at two remote stations of the Network for the Detection of Atmospheric Composition Change (NDACC): the Jungfraujoch station (Northern Hemisphere) and the Lauder station (Southern Hemisphere). These time series are new. They were produced using improved line parameters and merged considering the instrument changes and setup modifications. Afterwards, they were compared with Cape Grim station in situ surface observations conducted within the Advanced Global Atmospheric Gases Experiment (AGAGE) network and with total column datasets calculated by the TOMCAT/SLIMCAT 3-D chemical transport model. Trend analyses were performed, using an advanced statistical tool, in order to identify the timing and magnitude of the trend change in both hemispheres. The observations are consistent with the model results and confirm the slowdown in the CFC-11 atmospheric concentration decay, since approximate to 2011 in the Northern Hemisphere, and since approximate to 2014 in the Southern Hemisphere.
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| 4. |
- Minganti, Daniele, et al.
(författare)
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Evaluation of the N2O Rate of Change to Understand the Stratospheric Brewer-Dobson Circulation in a Chemistry-Climate Model
- 2022
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Ingår i: Journal of Geophysical Research: Atmospheres. - 2169-8996 .- 2169-897X. ; 127:22
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Tidskriftsartikel (refereegranskat)abstract
- The Brewer-Dobson Circulation (BDC) determines the distribution of long-lived tracers in the stratosphere; therefore, their changes can be used to diagnose changes in the BDC. We evaluate decadal (2005–2018) trends of nitrous oxide (N2O) in two versions of the Whole Atmosphere Chemistry-Climate Model (WACCM) by comparing them with measurements from four Fourier transform infrared (FTIR) ground-based instruments, the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS), and with a chemistry-transport model (CTM) driven by four different reanalyses. The limited sensitivity of the FTIR instruments can hide negative N2O trends in the mid-stratosphere because of the large increase in the lowermost stratosphere. When applying ACE-FTS measurement sampling on model datasets, the reanalyses from the European Center for Medium Range Weather Forecast (ECMWF) compare best with ACE-FTS, but the N2O trends are consistently exaggerated. The N2O trends obtained with WACCM disagree with those obtained from ACE-FTS, but the new WACCM version performs better than the previous above the Southern Hemisphere in the stratosphere. Model sensitivity tests show that the decadal N2O trends reflect changes in the stratospheric transport. We further investigate the N2O Transformed Eulerian Mean (TEM) budget in WACCM and in the CTM simulation driven by the latest ECMWF reanalysis. The TEM analysis shows that enhanced advection affects the stratospheric N2O trends in the Tropics. While no ideal observational dataset currently exists, this model study of N2O trends still provides new insights about the BDC and its changes because of the contribution from relevant sensitivity tests and the TEM analysis.
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| 5. |
- Revell, Laura E., et al.
(författare)
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The effectiveness of N2O in depleting stratospheric ozone
- 2012
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 39, s. L15806-
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Tidskriftsartikel (refereegranskat)abstract
- Recently, it was shown that of the ozone-depleting substances currently emitted, N2O emissions (the primary source of stratospheric NOx) dominate, and are likely to do so throughout the 21st century. To investigate the links between N2O and NOx concentrations, and the effects of NOx on ozone in a changing climate, the evolution of stratospheric ozone from 1960 to 2100 was simulated using the NIWA-SOCOL chemistry-climate model. The yield of NOx from N2O is reduced due to stratospheric cooling and a strengthening of the Brewer-Dobson circulation. After accounting for the reduced NOx yield, additional weakening of the primary NOx cycle is attributed to reduced availability of atomic oxygen, due to a) stratospheric cooling decreasing the atomic oxygen/ozone ratio, and b) enhanced rates of chlorine-catalyzed ozone loss cycles around 2000 and enhanced rates of HOx-induced ozone depletion. Our results suggest that the effects of N2O on ozone depend on both the radiative and chemical environment of the upper stratosphere, specifically CO2-induced cooling of the stratosphere and elevated CH4 emissions which enhance HOx-induced ozone loss and remove the availability of atomic oxygen to participate in NOx ozone loss cycles. Citation: Revell, L. E., G. E. Bodeker, D. Smale, R. Lehmann, P. E. Huck, B. E. Williamson, E. Rozanov, and H. Struthers (2012), The effectiveness of N2O in depleting stratospheric ozone, Geophys. Res. Lett., 39, L15806, doi:10.1029/2012GL052143.
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| 6. |
- Risi, Camille, et al.
(författare)
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Process-evaluation of tropospheric humidity simulated by general circulation models using water vapor isotopologues : 1. Comparison between models and observations
- 2012
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 117, s. D05303-
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Tidskriftsartikel (refereegranskat)abstract
- The goal of this study is to determine how H2O and HDO measurements in water vapor can be used to detect and diagnose biases in the representation of processes controlling tropospheric humidity in atmospheric general circulation models (GCMs). We analyze a large number of isotopic data sets (four satellite, sixteen ground-based remote-sensing, five surface in situ and three aircraft data sets) that are sensitive to different altitudes throughout the free troposphere. Despite significant differences between data sets, we identify some observed HDO/H2O characteristics that are robust across data sets and that can be used to evaluate models. We evaluate the isotopic GCM LMDZ, accounting for the effects of spatiotemporal sampling and instrument sensitivity. We find that LMDZ reproduces the spatial patterns in the lower and mid troposphere remarkably well. However, it underestimates the amplitude of seasonal variations in isotopic composition at all levels in the subtropics and in midlatitudes, and this bias is consistent across all data sets. LMDZ also underestimates the observed meridional isotopic gradient and the contrast between dry and convective tropical regions compared to satellite data sets. Comparison with six other isotope-enabled GCMs from the SWING2 project shows that biases exhibited by LMDZ are common to all models. The SWING2 GCMs show a very large spread in isotopic behavior that is not obviously related to that of humidity, suggesting water vapor isotopic measurements could be used to expose model shortcomings. In a companion paper, the isotopic differences between models are interpreted in terms of biases in the representation of processes controlling humidity.
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| 7. |
- Sha, Mahesh Kumar, et al.
(författare)
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Validation of methane and carbon monoxide from Sentinel-5 Precursor using TCCON and NDACC-IRWG stations
- 2021
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Ingår i: Atmospheric Measurement Techniques. - : Copernicus GmbH. - 1867-1381 .- 1867-8548. ; 14:9, s. 6249-6304
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Tidskriftsartikel (refereegranskat)abstract
- The Sentinel-5 Precursor (S5P) mission with the TROPOspheric Monitoring Instrument (TROPOMI) on board has been measuring solar radiation backscattered by the Earth's atmosphere and surface since its launch on 13 October 2017. In this paper, we present for the first time the S5P operational methane (CH4) and carbon monoxide (CO) products' validation results covering a period of about 3 years using global Total Carbon Column Observing Network (TCCON) and Infrared Working Group of the Network for the Detection of Atmospheric Composition Change (NDACC-IRWG) network data, accounting for a priori alignment and smoothing uncertainties in the validation, and testing the sensitivity of validation results towards the application of advanced co-location criteria. We found that the S5P standard and bias-corrected CH4 data over land surface for the recommended quality filtering fulfil the mission requirements. The systematic difference of the bias-corrected total column-averaged dry air mole fraction of methane (XCH4) data with respect to TCCON data is -0.26 +/- 0.56 % in comparison to -0.68 +/- 0.74 % for the standard XCH4 data, with a correlation of 0.6 for most stations. The bias shows a seasonal dependence. We found that the S5P CO data over all surfaces for the recommended quality filtering generally fulfil the missions requirements, with a few exceptions, which are mostly due to co-location mismatches and limited availability of data. The systematic difference between the S5P total column-averaged dry air mole fraction of carbon monoxide (XCO) and the TCCON data is on average 9.22 +/- 3.45 % (standard TCCON XCO) and 2.45 +/- 3.38 % (unscaled TCCON XCO). We found that the systematic difference between the S5P CO column and NDACC CO column (excluding two outlier stations) is on average 6.5 +/- 3.54 %. We found a correlation of above 0.9 for most TCCON and NDACC stations. The study shows the high quality of S5P CH4 and CO data by validating the products against reference global TCCON and NDACC stations covering a wide range of latitudinal bands, atmospheric conditions and surface conditions.
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