Case Studies of Stratospheric Nitrogen, Chlorine and Iodine Photochemistry Based on Balloon Borne UV/visible and IR Absorption Spectroscopy

Nitrogen and halogen bearing compounds play an important role in catalytic loss of stratospheric ozone. Balloon borne spectroscopic measurements of the vertical distribution of the most important nitrogen, chlorine and iodine containing species are used to estimate the quality of state-of-the-art instruments and retrieval algorithms and to gain new insights into stratospheric photochemistry. A comparison study between observations of O3 and NO2 in the UV/visible and infrared spectral ranges involving the DOAS and LPMA balloon borne instruments and the satellite borne SCIAMACHY instrument yields reasonable agreement. The variety of trace gases measured by the LPMA/DOAS balloon payload allows for investigation of the budget and partitioning of stratospheric nitrogen and chlorine under several geophysical conditions. Comparison of the observations with the 3-D chemical transport model (CTM) SLIMCAT indicates that the ratio between short- and long-lived nitrogen containing species is overestimated by the model. For a high-latitude winter scenario the 1-D stratospheric chemistry model LABMOS is constrained by the observations in order to test recently published updates of the reaction kinetics of the ClO-ClO and ClO-BrO catalytic cycles with respect to model-measurement agreement and ozone loss rates. The latter are enhanced by 20% to 25% when using the kinetic updates. The determination of upper limits for IO and OIO corroborate earlier findings of the budget of stratospheric iodine in high- and mid-latitudes and extend the data base to tropical latitudes. Given the measured IO and OIO upper limits, model calculations show that total gaseous iodine in the lower tropical stratosphere is less abundant than (0.32 ± 0.11) ppt or (0.38 ± 0.10) ppt depending on whether OIO photolysis occurs or does not

Retrievals of atmospheric CO_2 from simulated space-borne measurements of backscattered near-infrared sunlight: accounting for aerosol effects

Retrievals of atmospheric carbon dioxide (CO_2) from space-borne measurements of backscattered near-infrared sunlight are hampered by aerosol and cirrus cloud scattering effects. We propose a retrieval approach that allows for the retrieval of a few effective aerosol parameters simultaneously with the CO_2 total column by parameterizing particle amount, height distribution, and microphysical properties. Two implementations of the proposed method covering different spectral bands are tested for an ensemble of simulated nadir observations for aerosol (and cirrus) loaded scenes over low- and mid-latitudinal land surfaces. The residual aerosol-induced CO_2 errors are mostly below 1% up to aerosol optical thickness 0.5. The proposed methods also perform convincing for scenes where cirrus clouds of optical thickness 0.1 overlay the aerosol

Antiarrhythmic effect of ischemic preconditioning during low-flow ischemia: The role of bradykinin and sarcolemmal versus mitochondrial ATP-sensitive K+ channels

Abstract. : Short episodes of ischemia (ischemic preconditioning) protect the heart against ventricular arrhythmias during zero-flow ischemia and reperfusion. However, in clinics, many episodes of ischemia present a residual flow (low-flow ischemia). Here we examined whether ischemic preconditioning protects against ventricular arrhythmias during and after a low-flow ischemia and, if so, by what mechanism(s). Isolated rat hearts were subjected to 60 min of low-flow ischemia (12% residual coronary flow) followed by 60 min of reperfusion. Ischemic preconditioning was induced by two cycles of 5 min of zero-flow ischemia followed by 5 and 15 min of reperfusion, respectively. Arrhythmias were evaluated as numbers of ventricular premature beats (VPBs) as well as incidences of ventricular tachycardia (VT) and ventricular .brillation (VF) during low-flow ischemia and reperfusion. Ischemic preconditioning significantly reduced the number of VPBs and the incidence of VT and of VF during low-flow ischemia. This antiarrhythmic effect of preconditioning was abolished by HOE 140 (100 nM), a bradykinin B2 receptor blocker. Similar to preconditioning, exogenous bradykinin (10 nM) reduced the number of VPBs and the incidence of VT and of VF during low-flow ischemia. Furthermore, the antiarrhythmic effects of both ischemic preconditioning and bradykinin were abolished by glibenclamide (1 µM), a non-specific blocker of ATP-sensitive K+ (KATP) channels. Finally, the antiarrhythmic effects of both ischemic preconditioning and bradykinin were abolished by HMR 1098 (10 µM), a sarcolemmal KATP channel blocker but not by 5-hydroxydecanoate (100 µM), a mitochondrial KATP channel blocker. In conclusion, ischemic preconditioning protects against ventricular arrhythmias induced by low-flow ischemia, and this protection involves activation of bradykinin B2 receptors and subsequent opening of sarcolemmal but not of mitochondrial KATP channel

Tropical methane emissions: A revised view from SCIAMACHY onboard ENVISAT

Methane retrievals from near-infrared spectra recorded by the SCIAMACHY instrument onboard ENVISAT hitherto suggested unexpectedly large tropical emissions. Even though recent studies confirm substantial tropical emissions, there were indications for an unresolved error in the satellite retrievals. Here we identify a retrieval error related to inaccuracies in water vapor spectroscopic parameters, causing a substantial overestimation of methane correlated with high water vapor abundances. We report on the overall implications of an update in water spectroscopy on methane retrievals with special focus on the tropics where the impact is largest. The new retrievals are applied in a four-dimensional variational (4D-VAR) data assimilation system to derive a first estimate of the impact on tropical CH_4 sources. Compared to inversions based on previous SCIAMACHY retrievals, annual tropical emission estimates are reduced from 260 to about 201 Tg CH_4 but still remain higher than previously anticipated

Shipborne measurements of XCO2_{2}, XCH4_{4}, and XCO above the Pacific Ocean and comparison to CAMS atmospheric analyses and S5P/TROPOMI

Measurements of atmospheric column-averaged dry-air mole fractions of carbon dioxide (XCO2), methane (XCH4), and carbon monoxide (XCO) have been collected across the Pacific Ocean during the Measuring Ocean REferences 2 (MORE-2) campaign in June 2019. We deployed a shipborne variant of the EM27/SUN Fourier transform spectrometer (FTS) on board the German RN Sonne which, during MORE-2, crossed the Pacific Ocean from Vancouver, Canada, to Singapore. Equipped with a specially manufactured fast solar tracker, the FTS operated in direct-sun viewing geometry during the ship cruise reliably delivering solar absorption spectra in the shortwave infrared spectral range (4000 to 11000 cm(-1)). After filtering and bias correcting the dataset, we report on XCO2, XCH4, and XCO measurements for 22 d along a trajectory that largely aligns with 30 degrees N of latitude between 140 degrees W and 120 degrees E of longitude. The dataset has been scaled to the Total Carbon Column Observing Network (TCCON) station in Karlsruhe, Germany, before and after the MORE-2 campaign through side-by-side measurements. The la repeatability of hourly means of XCO2, XCH4, and XCO is found to be 0.24 ppm, 1.1 ppb, and 0.75 ppb, respectively. The Copernicus Atmosphere Monitoring Service (CAMS) models gridded concentration fields of the atmospheric composition using assimilated satellite observations, which show excellent agreement of 0.52 +/- 0.31 ppm for XCO2, 0.9 +/- 4.1 ppb for XCH4, and 3.2 +/- 3.4 ppb for XCO (mean difference +/- SD, standard deviation, of differences for entire record) with our observations. Likewise, we find excellent agreement to within 2.2 +/- 6.6 ppb with the XCO observations of the TROPOspheric MOnitoring Instrument (TROPOMI) on the Sentinel-5 Precursor satellite (S5P). The shipborne measurements are accessible at https://doi.org/10.1594/PANGAEA.917240 (Knapp et al., 2020)

Pressure broadening in the 2ν3 band of methane and its implication on atmospheric retrievals

N2-broadened half widths and pressure shifts were obtained for transitions in the 2ν3 methane band. Laboratory measurements recorded at 0.011 cm$^{-1}$ resolution with a Bruker 120 HR Fouriertransform spectrometer were analysed from 5860 to 6185 cm$^{-1}$. A 140 cm gas cell was filled with methane at room temperature and N2 as foreign gas at pressures ranging from 125 to 900 hPa. A multispectrum nonlinear constrained least squares approach based on Optimal Estimation was applied to derive the spectroscopic parameters by simultaneously fitting laboratory spectra at different ambient pressures assuming a Voigt line-shape. At room temperature, the half widths ranged between 0.030 and 0.071 cm$^{-1}$ atm$^{-1}$, and the pressure shifts varied from –0.002 to –0.025 cm$^{-1}$ atm$^{-1}$ for transitions up to J´´=10. Especially for higher rotational levels, we find systematically narrower lines than HITRAN predicts. The Q and R branch of the new set of spectroscopic parameters is further tested with ground based direct sun Fourier transform infrared (FTIR) measurements where systematic fit residuals reduce by about a factor of 3–4. We report the implication of those differences on atmospheric methane measurements using high-resolution ground based FTIR measurements as well as low-resolution spectra from the Scanning Imaging Absorption SpectroMeter for Atmospheric ChartographY (SCIAMACHY) instrument onboard ENVISAT. We find that for SCIAMACHY, a latitudinal and seasonally varying bias of about 1% can be introduced by erroneous broadening parameters

Spectral sizing of a coarse-spectral-resolution satellite sensor for XCO2

Verifying anthropogenic carbon dioxide (CO$_{2}$) emissions globally is essential to inform about the progress of institutional efforts to mitigate anthropogenic climate forcing. To monitor localized emission sources, spectroscopic satellite sensors have been proposed that operate on the CO$_{2}$ absorption bands in the shortwave-infrared (SWIR) spectral range with ground resolution as fine as a few tens of meters to about a hundred meters. When designing such sensors, fine ground resolution requires a trade-off towards coarse spectral resolution in order to achieve sufficient noise performance. Since fine ground resolution also implies limited ground coverage, such sensors are envisioned to fly in fleets of satellites, requiring low-cost and simple design, e.g., by restricting the spectrometer to a single spectral band. Here, we use measurements of the Greenhouse Gases Observing Satellite (GOSAT) to evaluate the spectral resolution and spectral band selection of a prospective satellite sensor with fine ground resolution. To this end, we degrade GOSAT SWIR spectra of the CO$_{2}$ bands at 1.6 (SWIR-1) and 2.0 μm (SWIR-2) to coarse spectral resolution, without a further addition of noise, and we evaluate single-band retrievals of the column-averaged dry-air mole fractions of CO$_{2}$ (XCO$_{2}$) by comparison to ground truth provided by the Total Carbon Column Observing Network (TCCON) and by comparison to global “native” GOSAT retrievals with native spectral resolution and spectral band selection. Coarsening spectral resolution from GOSAT’s native resolving power of > 20000 to the range of 700 to a few thousand makes the scatter of differences between the SWIR-1 and SWIR-2 retrievals and TCCON increase moderately. For resolving powers of 1200 (SWIR-1) and 1600 (SWIR-2), the scatter increases from 2.4 (native) to 3.0 ppm for SWIR-1 and 3.3 ppm for SWIR-2. Coarser spectral resolution yields only marginally worse performance than the native GOSAT configuration in terms of station-to-station variability and geophysical parameter correlations for the GOSAT–TCCON differences. Comparing the SWIR-1 and SWIR-2 configurations to native GOSAT retrievals on the global scale, however, reveals that the coarseresolution SWIR-1 and SWIR-2 configurations suffer from some spurious correlations with geophysical parameters that characterize the light-scattering properties of the scene such as particle amount, size, height and surface albedo. Overall, the SWIR-1 and SWIR-2 configurations with resolving powers of 1200 and 1600 show promising performance for future sensor design in terms of random error sources while residual errors induced by light scattering along the light path need to be investigated further. Due to the stronger CO$_{2}$ absorption bands in SWIR-2 than in SWIR-1, the former has the advantage that measurement noise propagates less into the retrieved XCO$_{2}$ and that some retrieval information on particle scattering properties is accessible