scholarly journals Global distribution of CO<sub>2</sub> in the upper troposphere and stratosphere

2017 ◽  
Vol 17 (6) ◽  
pp. 3861-3878 ◽  
Author(s):  
Mohamadou Diallo ◽  
Bernard Legras ◽  
Eric Ray ◽  
Andreas Engel ◽  
Juan A. Añel
Keyword(s):  
Upper Troposphere ◽  
Model Driven ◽  
Mixing Ratios ◽  
Satellite Validation ◽  
Time Period ◽  
Stratospheric Circulation ◽  
Carbon Dioxide Co2 ◽  
Inversion Modelling ◽  
Good Agreement

Abstract. In this study, we construct a new monthly zonal mean carbon dioxide (CO2) distribution from the upper troposphere to the stratosphere over the 2000–2010 time period. This reconstructed CO2 product is based on a Lagrangian backward trajectory model driven by ERA-Interim reanalysis meteorology and tropospheric CO2 measurements. Comparisons of our CO2 product to extratropical in situ measurements from aircraft transects and balloon profiles show remarkably good agreement. The main features of the CO2 distribution include (1) relatively large mixing ratios in the tropical stratosphere; (2) seasonal variability in the extratropics, with relatively high mixing ratios in the summer and autumn hemisphere in the 15–20 km altitude layer; and (3) decreasing mixing ratios with increasing altitude from the upper troposphere to the middle stratosphere ( ∼ 35 km). These features are consistent with expected variability due to the transport of long-lived trace gases by the stratospheric Brewer–Dobson circulation. The method used here to construct this CO2 product is unique from other modelling efforts and should be useful for model and satellite validation in the upper troposphere and stratosphere as a prior for inversion modelling and to analyse features of stratosphere–troposphere exchange as well as the stratospheric circulation and its variability.

scholarly journals A comparison of DOAS observations by the CARIBIC aircraft and the GOME-2 satellite of the 2008 Kasatochi volcanic SO<sub>2</sub> plume

2010 ◽  
Vol 10 (1) ◽  
pp. 523-558
Author(s):  
K.-P. Heue ◽  
C. A. M. Brenninkmeijer ◽  
T. Wagner ◽  
K. Mies ◽  
B. Dix ◽  
...  
Keyword(s):  
Wind Speed ◽  
Volcanic Plume ◽  
Upper Troposphere ◽  
Wind Speeds ◽  
Satellite Validation ◽  
Civil Aircraft ◽  
Comparison Of The Results ◽  
Slight Discrepancy ◽  
Good Agreement

Abstract. The 2008 Kasatochi volcanic eruption emitted ≈1.5–2.5 Tg SO2 into the upper troposphere and lower stratosphere. Parts of the main volcanic plume (gases and particles) reached central Europe a week after the eruption and were detected there by the CARIBIC (Civil Aircraft for Regular investigation of the Atmosphere based on an Instrument Container) flying observatory. The plume was also observed by the GOME-2 satellite instrument, only a few hours after the CARIBIC aircraft had crossed the plume, thus giving a unique opportunity to compare results. Trajectories and local wind speeds are investigated in detail using the GOME-2 and CARIBIC observations for better comparison of the results from these two observational systems. A comparison of the spatial pattern with the local observations of the wind speed and the trajectory model TRAJKS showed a slight discrepancy, which has to be considered for satellite validation. Hence, it appears that detailed analyses of wind speeds are required. Emitted and secondary particles, partly measured and sampled by the CARIBIC in situ instruments, affected the DOAS SO2 measurements, of both CARIBIC and GOME-2. Overall GOME-2 and the CARIBIC SO2 measurements agree very well. The major uncertainties remain the actual wind speed needed to properly correct for the advection of the plume between the different overpass times, and to smaller degree the effect of aerosol. The good agreement can be seen as validation for both GOME-2 and CARIBIC DOAS observations and is also a basis for future common projects.

scholarly journals Observations of the 2008 Kasatochi volcanic SO<sub>2</sub> plume by CARIBIC aircraft DOAS and the GOME-2 satellite

2010 ◽  
Vol 10 (10) ◽  
pp. 4699-4713 ◽  
Author(s):  
K.-P. Heue ◽  
C. A. M. Brenninkmeijer ◽  
T. Wagner ◽  
K. Mies ◽  
B. Dix ◽  
...  
Keyword(s):  
Wind Speed ◽  
Volcanic Plume ◽  
Upper Troposphere ◽  
Wind Speeds ◽  
Satellite Validation ◽  
Civil Aircraft ◽  
Comparison Of The Results ◽  
Slight Discrepancy ◽  
Good Agreement

Abstract. The 2008 Kasatochi volcanic eruption emitted ≈1.5–2.5 Tg SO2 into the upper troposphere and lower stratosphere. Parts of the main volcanic plume (gases and particles) reached central Europe a week after the eruption and were detected there by the CARIBIC (Civil Aircraft for Regular investigation of the Atmosphere based on an Instrument Container) flying observatory. The plume was also observed by the GOME-2 satellite instrument, only a few hours after the CARIBIC aircraft had crossed the plume, thus giving a unique opportunity to compare results. Trajectories and local wind speeds are investigated in detail using the GOME-2 and CARIBIC observations for better comparison of the results from these two observational systems. A comparison of the satellite spatial pattern with the local observations of the wind speed and the trajectory model TRAJKS showed a slight discrepancy, which has to be considered for satellite validation. Hence, it appears that detailed analyses of wind speeds are required. Emitted and secondary particles, partly measured and sampled by the CARIBIC in situ instruments, affected the DOAS SO2 measurements, of both CARIBIC and GOME-2. Overall GOME-2 and the CARIBIC SO2 measurements agree very well. The major uncertainties remain the actual wind speed needed to properly correct for the advection of the plume between the different overpass times and effects of aerosols on DOAS retrievals. The good agreement can be seen as validation for both GOME-2 and CARIBIC DOAS observations.

scholarly journals Level 2 processing for the imaging Fourier transform spectrometer GLORIA: derivation and validation of temperature and trace gas volume mixing ratios from calibrated dynamics mode spectra

2015 ◽  
Vol 8 (6) ◽  
pp. 2473-2489 ◽  
Author(s):  
J. Ungermann ◽  
J. Blank ◽  
M. Dick ◽  
A. Ebersoldt ◽  
F. Friedl-Vallon ◽  
...  
Keyword(s):  
Fourier Transform ◽  
Horizontal Resolution ◽  
Trace Gas ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Ionization Mass ◽  
Fourier Transform Spectrometer ◽  
Upper Troposphere ◽  
Mixing Ratios

Abstract. The Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) is an airborne infrared limb imager combining a two-dimensional infrared detector with a Fourier transform spectrometer. It was operated aboard the new German Gulfstream G550 High Altitude LOng Range (HALO) research aircraft during the Transport And Composition in the upper Troposphere/lowermost Stratosphere (TACTS) and Earth System Model Validation (ESMVAL) campaigns in summer 2012. This paper describes the retrieval of temperature and trace gas (H2O, O3, HNO3) volume mixing ratios from GLORIA dynamics mode spectra that are spectrally sampled every 0.625 cm−1. A total of 26 integrated spectral windows are employed in a joint fit to retrieve seven targets using consecutively a fast and an accurate tabulated radiative transfer model. Typical diagnostic quantities are provided including effects of uncertainties in the calibration and horizontal resolution along the line of sight. Simultaneous in situ observations by the Basic Halo Measurement and Sensor System (BAHAMAS), the Fast In-situ Stratospheric Hygrometer (FISH), an ozone detector named Fairo, and the Atmospheric chemical Ionization Mass Spectrometer (AIMS) allow a validation of retrieved values for three flights in the upper troposphere/lowermost stratosphere region spanning polar and sub-tropical latitudes. A high correlation is achieved between the remote sensing and the in situ trace gas data, and discrepancies can to a large extent be attributed to differences in the probed air masses caused by different sampling characteristics of the instruments. This 1-D processing of GLORIA dynamics mode spectra provides the basis for future tomographic inversions from circular and linear flight paths to better understand selected dynamical processes of the upper troposphere and lowermost stratosphere.

scholarly journals Origins and characterization of CO and O<sub>3</sub> in the African upper troposphere

2021 ◽  
Author(s):  
Victor Lannuque ◽  
Bastien Sauvage ◽  
Brice Barret ◽  
Hannah Clark ◽  
Gilles Athier ◽  
...  
Keyword(s):  
Wind Shear ◽  
Asian Monsoon ◽  
Shear Zones ◽  
Hadley Cell ◽  
Trade Winds ◽  
Air Masses ◽  
Upper Troposphere ◽  
Mixing Ratios ◽  
Hadley Cells

Abstract. Between December 2005 and 2013, the In-service Aircraft for a Global Observing System (IAGOS) program produced almost daily in situ measurements of CO and O3 between Europe and southern Africa. IAGOS data combined with measurements from the IASI instrument onboard the Metop-A satellite (2008–2013) are used to characterize meridional distributions and seasonality of CO and O3 in the African upper troposphere (UT). The FLEXPART particle dispersion model and the SOFT-IO model which combines the FLEXPART model with CO emission inventories are used to explore the sources and origins of the observed transects of CO and O3. We focus our analysis on two main seasons: December to March (DJFM) and June to October (JJASO). These seasons have been defined according to the position of Intertropical Convergence Zone (ITCZ), determined using in situ measurements from IAGOS. During both seasons, the UT CO meridional transects are characterized by maximum mixing ratios located 10° from the position of the ITCZ above the dry regions inside the hemisphere of the strongest Hadley cell (132 to 165 ppb at 0–5° N in DJFM and 128 to 149 ppb at 3–7° S in JJASO), and decreasing values south- and north-ward. The O3 meridional transects are characterized by mixing ratio minima of ~ 42–54 ppb at the ITCZ (10–16° S in DJFM and 5–8° N in JJASO) framed by local maxima (~ 53–71 ppb) coincident with the wind shear zones North and South of the ITCZ. O3 gradients are strongest in the hemisphere of the strongest Hadley cell. IASI UT O3 distributions in DJFM have revealed that the maxima are a part of a crescent-shaped O3 plume above the Atlantic Ocean around the Gulf of Guinea. CO emitted at the surface is transported towards the ITCZ by the trade winds and then convectively uplifted. Once in the upper troposphere, CO enriched air masses are transported away from the ITCZ by the upper branches of the Hadley cells and accumulate within the zonal wind shear zones where the maximum CO mixing ratios are found. Anthropogenic and fires both contribute, by the same order of magnitude, to the CO budget of the African upper troposphere. Local fires have the highest contribution, drive the location of the observed UT CO maxima, and are related to the following transport pathway: CO emitted at the surface is transported towards the ITCZ by the trade winds and further convectively uplifted. Then UT CO enriched air masses are transported away from the ITCZ by the upper branches of the Hadley cells and accumulate within the zonal wind shear zones where the maxima are located. Anthropogenic CO contribution is mostly from Africa during the entire year, with a low seasonal variability, and is related to similar transport circulation than fire air masses. There is also a large contribution from Asia in JJASO related to the fast convective uplift of polluted air masses in the Asian monsoon region which are further westward transported by the tropical easterly jet (TEJ) and the Asian monsoon anticyclone (AMA). O3 minima correspond to air masses that were recently uplifted from the surface where mixing ratios are low at the ITCZ. The O3 maxima correspond to old high altitude air masses uplifted from either local or long distance area of high O3 precursor emissions (Africa and South America during all the year, South Asia mainly in JJASO), and must be created during transport by photochemistry. This analysis of meridional transects contribute to a better understanding of distributions of CO and O3 in the intertropical African upper troposphere and the processes which drive these distributions. Therefore, it provides a solid basis for comparison and improvement of models and satellite products in order to get the good O3 for the good reasons.

The Airyx 2D SkySpec instrument: MAX-DOAS measurements of tropospheric NO2 and HCHO in Munich and the comparison to satellite observations

2020 ◽  
Author(s):  
Johannes Lampel ◽  
Ka Lok Chan ◽  
Denis Pöhler ◽  
Matthias Wiegner ◽  
Carlos Alberti ◽  
...  
Keyword(s):  
Pearson Correlation ◽  
Satellite Observations ◽  
Optical Absorption Spectroscopy ◽  
Aerosol Extinction ◽  
Aerosol Formation ◽  
Mixing Ratios ◽  
Monitor Data ◽  
Sun Light ◽  
Good Agreement

&lt;p&gt;We present the Airyx 2D SkySpec Instrument: A commercially available two-dimensionally scanning Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) setup for the observations of trace gases using spectral measurements of scattered sun light and optionally also direct sun light. The waterproof design of the scanner unit is designed for long-term outdoor deployment. Temperature stabilisation of the spectrometers and automatic calibration spectra measurement are used to ensure high-quality measurement data over months and years of observations.&lt;/p&gt;&lt;p&gt;We show 2.5 years of measurements in Munich. Vertical columns and vertical distribution profiles of aerosol extinction coefficient, NO&lt;sub&gt;2&lt;/sub&gt; and HCHO are retrieved from the 2D MAX-DOAS observations. The measured surface aerosol extinction coefficients and NO&lt;sub&gt;2&lt;/sub&gt; mixing ratios are compared to in-situ monitor data. The retrieved surface NO&lt;sub&gt;2&lt;/sub&gt; mixing ratios show good agreement with in-situ monitor data with a Pearson correlation coefficient (R) of 0.91. Good agreement (R= 0.80) is also found for AOD when compared to sun-photometer measurements. Tropospheric vertical column densities (VCDs) of NO2 and HCHO derived from the MAX-DOAS measurements are also used to validate OMI and TROPOMI satellite observations. Monthly averaged data show good correlation, however, satellite observations are on average 30% lower than the MAX-DOAS measurements. Furthermore, the 2D MAX-DOAS observations are used to investigate the spatio-temporal characteristic of NO2 and HCHO in Munich. Analysis of the relations among aerosol, NO&lt;sub&gt;2&lt;/sub&gt; and HCHO show higher aerosol to HCHO ratios in winter indicating a longer atmospheric lifetime of aerosol and HCHO. The analysis also suggests that secondary aerosol formation is the major source of aerosols in Munich.&lt;/p&gt;

scholarly journals The global middle-atmosphere aerosol model MAECHAM5-SAM2: comparison with satellite and in-situ observations

2010 ◽  
Vol 3 (3) ◽  
pp. 1359-1421
Author(s):  
R. Hommel ◽  
C. Timmreck ◽  
H. F. Graf
Keyword(s):  
Sulphuric Acid ◽  
Middle Atmosphere ◽  
Stratospheric Aerosol ◽  
Aerosol Layer ◽  
Upper Troposphere ◽  
Mixing Ratios ◽  
Fine Mode ◽  
In Situ Observations ◽  
Polar Stratosphere

Abstract. In this paper we investigate results from a middle-atmosphere aerosol-climate model which has been developed to study the evolution of stratospheric aerosols. Here we focus on the stratospheric background period and evaluate several key quantities of the global dispersion of stratospheric aerosols and their precursors with observations and other model studies. It is shown that the model fairly well reproduces in situ observations of the aerosol size and number concentrations in the upper troposphere and lower stratosphere (UT/LS). Compared to measurements from the limb-sounding SAGE II satellite instrument, modelled integrated aerosol quantities are more biased the lower the moment of the aerosol population. Both findings are consistent with earlier work analysing the quality of SAGE II retrieved e.g. aerosol surface area densities from the volcanically unperturbed stratosphere (SPARC/ASAP, 2006; Thomason et al., 2008; Wurl et al., 2010). The model suggests that new particles are formed over large areas of the LS, albeit nucleation rates in the upper troposphere are at least one order of magnitude larger than those in the stratosphere. Hence, we suggest that both tropospheric sulphate aerosols and particles formed in situ in the LS are maintaining the stability of the stratospheric aerosol layer also in the absence of direct stratospheric emissions from volcanoes. Particle size distributions are clearly bimodal, except in the upper branches of the stratospheric aerosol layer where aerosols evaporate. Modelled concentrations of condensation nuclei (CN) are lesser than measured in regions of the aerosol layer where aerosol mixing ratios are largest, due to an overpredicted particle growth by coagulation. Transport regimes of tropical stratospheric aerosol have been identified from modelled aerosol mixing ratios and correspond to those deduced from satellite extinction measurements. We found that convective updraft in the Asian Monsoon region significantly contributes to both stratospheric aerosol load and size. The timing of formation and descend of layers of fine mode particles in the winter and spring polar stratosphere (CN layer) are reproduced by the model. Far above the tropopause where nucleation is inhibited due to with height increasing stratospheric temperatures, planetary wave mixing transports significant amounts of fine mode particles from the polar stratosphere to mid-latitudes. In those regions enhanced condensation rates of sulphuric acid vapour counteracts the evaporation of aerosols, hence prolonging the aerosol lifetime in the upper branches of the stratospheric aerosol layer. Measurements of the aerosol precursors SO2 and sulphuric acid vapour are fairly well reproduced by the model throughout the stratosphere.

scholarly journals First-Year Operation of a New Water Vapor Raman Lidar at the JPL Table Mountain Facility, California

2008 ◽  
Vol 25 (8) ◽  
pp. 1454-1462 ◽  
Author(s):  
Thierry Leblanc ◽  
I. Stuart McDermid ◽  
Robin A. Aspey
Keyword(s):  
Water Vapor ◽  
Current System ◽  
First Year ◽  
Raman Lidar ◽  
Upper Troposphere ◽  
Mixing Ratios ◽  
Table Mountain ◽  
Lidar Measurements ◽  
Better Than ◽  
Good Agreement

Abstract A new water vapor Raman lidar was recently built at the Table Mountain Facility (TMF) of the Jet Propulsion Laboratory (JPL) in California and more than a year of routine 2-h-long nighttime measurements 4–5 times per week have been completed. The lidar was designed to reach accuracies better than 5% anywhere up to 12-km altitude, and with the capability to measure water vapor mixing ratios as low as 1 to 10 ppmv near the tropopause and in the lower stratosphere. The current system is not yet fully optimized but has already shown promising results as water vapor profiles have been retrieved up to 18-km altitude. Comparisons with Vaisala RS92K radiosondes exhibit very good agreement up to at least 10 km. They also revealed a wet bias in the lidar profiles (or a dry bias in the radiosonde profiles), increasing with altitude and becoming significant near 10 km and large when approaching the tropopause. This bias cannot be explained solely by well-known too-dry measurements of the RS92K in the upper troposphere and therefore must partly originate in the lidar measurements. Excess signal due to residual fluorescence in the lidar receiver components is among the most likely candidates and is subject to ongoing investigation.

scholarly journals Total column CO<sub>2</sub> measurements at Darwin, Australia – site description and calibration against in situ aircraft profiles

2010 ◽  
Vol 3 (2) ◽  
pp. 989-1021 ◽  
Author(s):  
N. M. Deutscher ◽  
D. W. T. Griffith ◽  
G. W. Bryant ◽  
P. O. Wennberg ◽  
G. C. Toon ◽  
...  
Keyword(s):  
Nir Spectroscopy ◽  
Solar Observatory ◽  
Total Carbon ◽  
Relative Precision ◽  
Mixing Ratios ◽  
Clear Sky ◽  
The World ◽  
Total Column ◽  
Good Agreement

Abstract. An automated Fourier Transform Spectroscopic (FTS) solar observatory was established in Darwin, Australia in August 2005. The laboratory is part of the Total Carbon Column Observing Network, and measures atmospheric column abundances of CO2 and O2 and other gases. Measured CO2 columns were calibrated against integrated aircraft profiles obtained during the TWP-ICE campaign in January–February 2006, and show good agreement with calibrations for a similar instrument in Park Falls, Wisconsin. A clear-sky low airmass relative precision of 0.1% is demonstrated in the CO2 and O2 retrieved column-averaged volume mixing ratios. The 1% negative bias in the FTS XCO2 relative to the World Meteorological Organization (WMO) calibrated in situ scale is within the uncertainties of the NIR spectroscopy and analysis.

scholarly journals Evaluation of balloon and satellite water vapour measurements in the Southern tropical UTLS during the HIBISCUS campaign

2007 ◽  
Vol 7 (3) ◽  
pp. 6037-6075 ◽  
Author(s):  
N. Montoux ◽  
A. Hauchecorne ◽  
J.-P. Pommereau ◽  
G. Durry ◽  
B. Morel ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Water Vapour ◽  
Transport Model ◽  
Tunable Diode Laser ◽  
Upper Troposphere ◽  
Satellite Systems ◽  
Mixing Ratios ◽  
Tropical Tropopause ◽  
Dry Bias

Abstract. Among the objectives of the HIBISCUS campaign was the study of water vapour in the tropical upper troposphere and lower stratosphere (UTLS) by balloon borne in situ and remote sensing, offering a unique opportunity for evaluating the performances of balloon and satellite water vapour data available at the southern tropics in February-April 2004. Instruments evaluated include balloon borne in situ tunable diode laser spectrometer (μ SDLA) and surface acoustic wave hygrometer (SAW), and remote sensing with a near IR spectrometer (SAOZ) flown on a circumnavigating long duration balloon. The satellite systems available are those of AIRS/AMSU (v4), SAGE-II (v6.2), HALOE (v19), MIPAS (v4.62) and GOMOS (v6.0). In the stratosphere between 20–25 km, three satellite instruments, HALOE, SAGE-II and MIPAS, are showing very consistent results (nearly constant mixing ratios), while AIRS, GOMOS and the SAOZ balloon are displaying a slight increase with altitude. Considering the previous studies, the first three appear the most precise at this level, HALOE being the less variable (5%), close to the atmospheric variability shown by the REPROBUS/ECMWF Chemistry-Transport model. The three others are showing significantly larger variability, AIRS being the most variable (35%), followed by GOMOS (25%) and SAOZ (20%). Lower down in the Tropical Tropopause Layer between 14–20 km, HALOE and SAGE-II are showing marked minimum mixing ratios around 17–19 km, not seen by all others. For HALOE, this might be related to an altitude registration error already identified on ozone, while for SAGE-II, a possible explanation could be the persistence of the dry bias displayed by previous retrieval versions, not completely removed in version 6.2. On average, MIPAS is consistent with AIRS, GOMOS and SAOZ, not displaying the dry bias observed in past versions, but a fast degradation of precision below 20 km. Compared to satellites, the μ SDLA measurements shows systematically larger humidity although this conclusion may be biased by the fact that the balloon flights were carried out intentionally next or above strong convective systems where remote observations from space are difficult. In the upper troposphere below 14 km, all remote sensing measurements (except MIPAS of limited precision, and AIRS/AMSU) become rare, dry biased and less variable compared to ECMWF, but particularly HALOE and SAGE-II. The main reason for that is the frequent masking by clouds within which no remote measurements could be performed except by the AMSU microwave. Water vapour remote sensing profiles are representative of cloud free conditions only and thus dryer and less variable on average than ECMWF and AIRS/AMSU. Always in the upper troposphere, two in-situ instruments, μ SDLA and SAW, flown on the same balloon agree each other, displaying water vapour mixing ratios 100–200% larger than that of HALOE and MIPAS, which could be explained by the large ice supersaturation of the layer up to the tropopause, hardly detectable from the orbit.

scholarly journals Assimilation of TES CO into a global CTM: first results

2006 ◽  
Vol 6 (6) ◽  
pp. 11727-11743 ◽  
Author(s):  
N. A. D. Richards ◽  
Q. Li ◽  
K. W. Bowman ◽  
J. R. Worden ◽  
S. S. Kulawik ◽  
...  
Keyword(s):  
Transport Model ◽  
Model Simulation ◽  
Three Dimensional ◽  
Model Bias ◽  
Upper Troposphere ◽  
First Results ◽  
Assimilation Scheme ◽  
Co Observations ◽  
Good Agreement

Abstract. We present results from the first assimilation of carbon monoxide (CO) observations from the Tropospheric Emission Spectrometer (TES) into a global three-dimensional (3-D) chemistry and transport model (CTM). A sequential sub-optimal Kalman filter assimilation scheme (Khattatov et al., 2000) was applied to assimilate TES CO profiles during November 2004 into the GEOS-Chem global 3-D CTM. The assimilation results were compared with MOPITT and MOZAIC observations. The assimilation significantly improves model simulation of CO in the middle to upper troposphere, where the MOPITT versus model bias was reduced by up to two-thirds. Assimilation results show higher levels of CO in the southern tropics, consistent with MOPITT observations. We find good agreement between the TES assimilated model estimates of CO and in situ measurements from the MOZAIC program, which shows a negative bias of up to 10 ppbv in middle and upper tropospheric TES CO. The results demonstrate how assimilation can be used for non-coincident validation of TES CO profile retrievals.

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