scholarly journals Global tropospheric halogen (Cl, Br, I) chemistry and its impact on oxidants

2021 ◽  
Vol 21 (18) ◽  
pp. 13973-13996
Author(s):  
Xuan Wang ◽  
Daniel J. Jacob ◽  
William Downs ◽  
Shuting Zhai ◽  
Lei Zhu ◽  
...  
Keyword(s):  
Marine Boundary Layer ◽  
Transport Model ◽  
Ph Dependence ◽  
Primary Source ◽  
Mixing Ratio ◽  
Chemical Transport Model ◽  
Oxidation Of Methane ◽  
Aircraft Observations ◽  
Chlorine Radicals ◽  
Global Mean

Abstract. We present an updated mechanism for tropospheric halogen (Cl + Br + I) chemistry in the GEOS-Chem global atmospheric chemical transport model and apply it to investigate halogen radical cycling and implications for tropospheric oxidants. Improved representation of HOBr heterogeneous chemistry and its pH dependence in our simulation leads to less efficient recycling and mobilization of bromine radicals and enables the model to include mechanistic sea salt aerosol debromination without generating excessive BrO. The resulting global mean tropospheric BrO mixing ratio is 0.19 ppt (parts per trillion), lower than previous versions of GEOS-Chem. Model BrO shows variable consistency and biases in comparison to surface and aircraft observations in marine air, which are often near or below the detection limit. The model underestimates the daytime measurements of Cl2 and BrCl from the ATom aircraft campaign over the Pacific and Atlantic, which if correct would imply a very large missing primary source of chlorine radicals. Model IO is highest in the marine boundary layer and uniform in the free troposphere, with a global mean tropospheric mixing ratio of 0.08 ppt, and shows consistency with surface and aircraft observations. The modeled global mean tropospheric concentration of Cl atoms is 630 cm−3, contributing 0.8 % of the global oxidation of methane, 14 % of ethane, 8 % of propane, and 7 % of higher alkanes. Halogen chemistry decreases the global tropospheric burden of ozone by 11 %, NOx by 6 %, and OH by 4 %. Most of the ozone decrease is driven by iodine-catalyzed loss. The resulting GEOS-Chem ozone simulation is unbiased in the Southern Hemisphere but too low in the Northern Hemisphere.

scholarly journals Global tropospheric halogen (Cl, Br, I) chemistry and its impact on oxidants

2021 ◽  
Author(s):  
Xuan Wang ◽  
Daniel J. Jacob ◽  
William Downs ◽  
Shuting Zhai ◽  
Lei Zhu ◽  
...  
Keyword(s):  
Marine Boundary Layer ◽  
Transport Model ◽  
Ph Dependence ◽  
Primary Source ◽  
Mixing Ratio ◽  
Chemical Transport Model ◽  
Oxidation Of Methane ◽  
Aircraft Observations ◽  
Chlorine Radicals ◽  
Global Mean

Abstract. We present an updated mechanism for tropospheric halogen (Cl + Br + I) chemistry in the GEOS-Chem global atmospheric chemical transport model and apply it to investigate halogen radical cycling and implications for tropospheric oxidants. Improved representation of HOBr heterogeneous chemistry and its pH dependence in our simulation leads to less effective recycling and mobilization of bromine radicals, and enables the model to include mechanistic sea salt aerosol debromination without generating excessive BrO. The resulting global mean tropospheric BrO mixing ratio is 0.19 ppt, lower than previous versions of GEOS-Chem. Model BrO shows variable consistency and biases in comparison to surface and aircraft observations in marine air, which are often near or below the detection limit. The model underestimates the daytime measurements of Cl2 and BrCl from the ATom aircraft campaign over the Pacific and Atlantic, which if correct would imply a very large missing primary source of chlorine radicals. Model IO is highest in the marine boundary layer and uniform in the free troposphere, with a global mean tropospheric mixing ratio of 0.08 ppt, and shows consistency with surface and aircraft observations. The modeled global mean tropospheric concentration of Cl atoms is 630 cm−3, contributing 0.8 % of the global oxidation of methane, 14 % of ethane, 8 % of propane, and 7 % of higher alkanes. Halogen chemistry decreases the global tropospheric burden of ozone by 11 %, NOx by 6 %, and OH by 4 %. Most of the ozone decrease is driven by iodine-catalyzed loss. The resulting GEOS-Chem ozone simulation is unbiased in the Southern Hemisphere but too low in the Northern Hemisphere.

scholarly journals A global off-line model of size-resolved aerosol microphysics: I. Model development and prediction of aerosol properties

2005 ◽  
Vol 5 (8) ◽  
pp. 2227-2252 ◽  
Author(s):  
D. V. Spracklen ◽  
K. J. Pringle ◽  
K. S. Carslaw ◽  
M. P. Chipperfield ◽  
G. W. Mann
Keyword(s):  
Boundary Layer ◽  
Sulfuric Acid ◽  
Size Distribution ◽  
Marine Boundary Layer ◽  
Transport Model ◽  
Model Development ◽  
Aerosol Size Distribution ◽  
Chemical Transport Model ◽  
Cloud Processing ◽  
Nucleation Mechanisms

Abstract. A GLObal Model of Aerosol Processes (GLOMAP) has been developed as an extension to the TOMCAT 3-D Eulerian off-line chemical transport model. GLOMAP simulates the evolution of the global aerosol size distribution using a sectional two-moment scheme and includes the processes of aerosol nucleation, condensation, growth, coagulation, wet and dry deposition and cloud processing. We describe the results of a global simulation of sulfuric acid and sea spray aerosol. The model captures features of the aerosol size distribution that are well established from observations in the marine boundary layer and free troposphere. Modelled condensation nuclei (CN>3nm) vary between about 250–500 cm-3 in remote marine boundary layer regions and are generally in good agreement with observations. Modelled continental CN concentrations are lower than observed, which may be due to lack of some primary aerosol sources or the neglect of nucleation mechanisms other than binary homogeneous nucleation of sulfuric acid-water particles. Remote marine CN concentrations increase to around 2000–10 000 cm

scholarly journals Observing atmospheric formaldehyde (HCHO) from space: validation and intercomparison of six retrievals from four satellites (OMI, GOME2A, GOME2B, OMPS) with SEAC<sup>4</sup>RS aircraft observations over the Southeast US

2016 ◽  
Author(s):  
Lei Zhu ◽  
Daniel J. Jacob ◽  
Patrick S. Kim ◽  
Jenny A. Fisher ◽  
Karen Yu ◽  
...  
Keyword(s):  
Transport Model ◽  
Research Groups ◽  
Chemical Transport Model ◽  
Shape Factors ◽  
Aircraft Observations ◽  
Volatile Organic ◽  
Satellite Retrievals ◽  
Mass Factor ◽  
The Mean ◽  
Southeast Us

Abstract. Formaldehyde (HCHO) column data from satellites are widely used as a proxy for emissions of volatile organic compounds (VOCs), but validation of the data has been extremely limited. Here we use highly accurate HCHO aircraft observations from the NASA SEAC4RS campaign over the Southeast US in August–September 2013 to validate and intercompare six operational and research retrievals of HCHO columns from four different satellite instruments (OMI, GOME2A, GOME2B and OMPS) and three different research groups. The GEOS-Chem chemical transport model provides a common intercomparison platform. We find that all retrievals capture the HCHO maximum over Arkansas and Louisiana, reflecting high emissions of biogenic isoprene, and are consistent in their spatial variability over the Southeast US (r = 0.4–0.8 on a 0.5° × 0.5° grid) as well as their day-to-day variability (r = 0.5–0.8). However, all satellite retrievals are biased low in the mean by 20–51 %, which would lead to corresponding bias in estimates of isoprene emissions from the satellite data. The smallest bias is for OMI-BIRA, which has the highest corrected slant columns and the lowest scattering weights in its air mass factor (AMF) calculation. Correcting the assumed HCHO vertical profiles (shape factors) used in the AMF calculation would further reduce the bias in the OMI-BIRA data. We conclude that current satellite HCHO data provide a reliable proxy for isoprene emission variability but with a low mean bias due both to the corrected slant columns and the scattering weights used in the retrievals.

scholarly journals Ethane, ethyne and carbon monoxide concentrations in the upper troposphere and lower stratosphere from ACE and GEOS-Chem: a comparison study

2011 ◽  
Vol 11 (4) ◽  
pp. 13099-13139 ◽  
Author(s):  
G. González Abad ◽  
N. D. C. Allen ◽  
P. F. Bernath ◽  
C. D. Boone ◽  
S. D. McLeod ◽  
...  
Keyword(s):  
Carbon Monoxide ◽  
Atmospheric Chemistry ◽  
Transport Model ◽  
Chemical Mechanism ◽  
Chemical Transport Model ◽  
Spectrometer Data ◽  
Chemistry Experiment ◽  
Global Mean ◽  
Tropospheric Concentrations ◽  
Good Agreement

Abstract. Near global upper tropospheric concentrations of carbon monoxide (CO), ethane (C2H6) and ethyne (C2H2) from ACE (Atmospheric Chemistry Experiment) Fourier transform spectrometer on board the Canadian satellite SCISAT-1 are presented and compared with the output from the Chemical Transport Model (CTM) GEOS-Chem. The retrievals of ethane and ethyne from ACE have been improved for this paper by using new sets of microwindows compared with those for previous versions of ACE data. With the improved ethyne retrieval we have been able to produce a near global upper tropospheric distribution of C2H2 from space. Carbon monoxide, ethane and ethyne concentrations retrieved using ACE spectra show the expected seasonality linked to variations in the anthropogenic emissions and destruction rates as well as seasonal biomass burning activity. The GEOS-Chem model was run using the dicarbonyl chemistry suite, an extended chemical mechanism in which ethyne is treated explicitly. Seasonal cycles observed from satellite data are well reproduced by the model output, however the simulated CO concentrations are found to be systematically biased low over the Northern Hemisphere. An average negative global mean bias of 12% and 7% of the model relative to the satellite observations has been found for CO and C2H6 respectively and a positive global mean bias of 1% has been found for C2H2. ACE data are compared for validation purposes with MkIV spectrometer data and Global Tropospheric Experiment (GTE) TRACE-A campaign data showing good agreement with all of them.

scholarly journals New constraints on biogenic emissions using satellite-based estimates of carbon monoxide fluxes

2019 ◽  
Vol 19 (21) ◽  
pp. 13569-13579 ◽  
Author(s):  
Helen M. Worden ◽  
A. Anthony Bloom ◽  
John R. Worden ◽  
Zhe Jiang ◽  
Eloise A. Marais ◽  
...  
Keyword(s):  
Carbon Monoxide ◽  
Transport Model ◽  
A Priori ◽  
Primary Source ◽  
Biogenic Emissions ◽  
Chemical Production ◽  
Chemical Transport Model ◽  
Ozone Monitoring Instrument ◽  
Top Down ◽  
Decadal Scale

Abstract. Biogenic non-methane volatile organic compounds (NMVOCs) emitted from vegetation are a primary source for the chemical production of carbon monoxide (CO) in the atmosphere, and these biogenic emissions account for about 18 % of the global CO burden. Partitioning CO fluxes to different source types in top-down inversion methods is challenging; typically a simple scaling of the posterior flux to prior flux values for fossil fuel, biogenic and biomass burning sources is used. Here we show top-down estimates of biogenic CO fluxes using a Bayesian inference approach, which explicitly accounts for both posterior and a priori CO flux uncertainties. This approach re-partitions CO fluxes following inversion of Measurements Of Pollution In The Troposphere (MOPITT) CO observations with the GEOS-Chem model, a global chemical transport model driven by assimilated meteorology from the NASA Goddard Earth Observing System (GEOS). We compare these results to the prior information for CO used to represent biogenic NMVOCs from GEOS-Chem, which uses the Model of Emissions of Gases and Aerosols from Nature (MEGAN) for biogenic emissions. We evaluate the a posteriori biogenic CO fluxes against top-down estimates of isoprene fluxes using Ozone Monitoring Instrument (OMI) formaldehyde observations. We find similar seasonality and spatial consistency in the posterior CO and top-down isoprene estimates globally. For the African savanna region, both top-down CO and isoprene seasonality vary significantly from the MEGAN a priori inventory. This method for estimating biogenic sources of CO will provide an independent constraint on modeled biogenic emissions and has the potential for diagnosing decadal-scale changes in emissions due to land-use change and climate variability.

scholarly journals Vertical distributions of N<sub>2</sub>O isotopocules in the equatorial stratosphere

2018 ◽  
Vol 18 (2) ◽  
pp. 833-844 ◽  
Author(s):  
Sakae Toyoda ◽  
Naohiro Yoshida ◽  
Shinji Morimoto ◽  
Shuji Aoki ◽  
Takakiyo Nakazawa ◽  
...  
Keyword(s):  
High Latitude ◽  
Lower Stratosphere ◽  
Transport Model ◽  
Three Dimensional ◽  
Vertical Gradient ◽  
Mixing Ratio ◽  
Residual Circulation ◽  
Chemical Transport Model ◽  
Eastern Equatorial Pacific ◽  
Middle Stratosphere

Abstract. Vertical profiles of nitrous oxide (N2O) and its isotopocules, isotopically substituted molecules, were obtained over the Equator at altitudes of 16–30 km. Whole air samples were collected using newly developed balloon-borne compact cryogenic samplers over the eastern equatorial Pacific in 2012 and Biak Island, Indonesia, in 2015. They were examined in the laboratory using gas chromatography and mass spectrometry. The mixing ratio and isotopocule ratios of N2O in the equatorial stratosphere showed a weaker vertical gradient than the previously reported profiles in the subtropical and mid-latitude and high-latitude stratosphere. From the relation between the mixing ratio and isotopocule ratios, further distinct characteristics were found over the Equator: (1) observed isotopocule fractionations (ε values) in the middle stratosphere (25–30 km or [N2O] < ca. 260 nmol mol−1) are almost equal to ε values reported from broadband photolysis experiments conducted in the laboratory; (2) ε values in the lower stratosphere (< ca. 25 km or [N2O] > ca. 260 nmol mol−1) are about half of the experimentally obtained values, being slightly larger than those observed in the mid-latitude and high-latitude lower stratosphere ([N2O] > ca. 170 nmol mol−1). These results from the deep tropics suggest the following. (i) The timescale for quasi-horizontal mixing between tropical and mid-latitude air in the tropical middle stratosphere is sufficiently slow relative to the tropical upwelling rate that isotope fractionation approaches the Rayleigh limit for N2O photolysis. (ii) The air in the tropical lower stratosphere is exchanged with extratropical air on a timescale that is shorter than that of photochemical decomposition of N2O. Previously observed ε values, which are invariably smaller than those of photolysis, can be explained qualitatively using a three-dimensional chemical transport model and using a simple model that assumes mixing of “aged” tropical air and extratropical air during residual circulation. Results show that isotopocule ratios are useful to examine the stratospheric transport scheme deduced from tracer–tracer relations.

scholarly journals Constraining remote oxidation capacity with ATom observations

2020 ◽  
Vol 20 (13) ◽  
pp. 7753-7781 ◽  
Author(s):  
Katherine R. Travis ◽  
Colette L. Heald ◽  
Hannah M. Allen ◽  
Eric C. Apel ◽  
Stephen R. Arnold ◽  
...  
Keyword(s):  
Northern Hemisphere ◽  
Transport Model ◽  
Model Bias ◽  
Chemical Transport Model ◽  
Oxidation Capacity ◽  
Oxidation Of Methane ◽  
Photolysis Frequencies ◽  
Measurement Uncertainties ◽  
Reactive Trace Gases ◽  
Minimal Bias

Abstract. The global oxidation capacity, defined as the tropospheric mean concentration of the hydroxyl radical (OH), controls the lifetime of reactive trace gases in the atmosphere such as methane and carbon monoxide (CO). Models tend to underestimate the methane lifetime and CO concentrations throughout the troposphere, which is consistent with excessive OH. Approximately half of the oxidation of methane and non-methane volatile organic compounds (VOCs) is thought to occur over the oceans where oxidant chemistry has received little validation due to a lack of observational constraints. We use observations from the first two deployments of the NASA ATom aircraft campaign during July–August 2016 and January–February 2017 to evaluate the oxidation capacity over the remote oceans and its representation by the GEOS-Chem chemical transport model. The model successfully simulates the magnitude and vertical profile of remote OH within the measurement uncertainties. Comparisons against the drivers of OH production (water vapor, ozone, and NOy concentrations, ozone photolysis frequencies) also show minimal bias, with the exception of wintertime NOy. The severe model overestimate of NOy during this period may indicate insufficient wet scavenging and/or missing loss on sea-salt aerosols. Large uncertainties in these processes require further study to improve simulated NOy partitioning and removal in the troposphere, but preliminary tests suggest that their overall impact could marginally reduce the model bias in tropospheric OH. During the ATom-1 deployment, OH reactivity (OHR) below 3 km is significantly enhanced, and this is not captured by the sum of its measured components (cOHRobs) or by the model (cOHRmod). This enhancement could suggest missing reactive VOCs but cannot be explained by a comprehensive simulation of both biotic and abiotic ocean sources of VOCs. Additional sources of VOC reactivity in this region are difficult to reconcile with the full suite of ATom measurement constraints. The model generally reproduces the magnitude and seasonality of cOHRobs but underestimates the contribution of oxygenated VOCs, mainly acetaldehyde, which is severely underestimated throughout the troposphere despite its calculated lifetime of less than a day. Missing model acetaldehyde in previous studies was attributed to measurement uncertainties that have been largely resolved. Observations of peroxyacetic acid (PAA) provide new support for remote levels of acetaldehyde. The underestimate in both model acetaldehyde and PAA is present throughout the year in both hemispheres and peaks during Northern Hemisphere summer. The addition of ocean sources of VOCs in the model increases cOHRmod by 3 % to 9 % and improves model–measurement agreement for acetaldehyde, particularly in winter, but cannot resolve the model summertime bias. Doing so would require 100 Tg yr−1 of a long-lived unknown precursor throughout the year with significant additional emissions in the Northern Hemisphere summer. Improving the model bias for remote acetaldehyde and PAA is unlikely to fully resolve previously reported model global biases in OH and methane lifetime, suggesting that future work should examine the sources and sinks of OH over land.

scholarly journals Validation of TES methane with HIPPO aircraft observations: implications for inverse modeling of methane sources

2011 ◽  
Vol 11 (10) ◽  
pp. 27887-27911
Author(s):  
K. J. Wecht ◽  
D. J. Jacob ◽  
S. C. Wofsy ◽  
E. A. Kort ◽  
J. R. Worden ◽  
...  
Keyword(s):  
Simulation Experiment ◽  
Transport Model ◽  
Observation System ◽  
Chemical Transport Model ◽  
Surface Type ◽  
Upper Troposphere ◽  
The Pacific ◽  
Standard Product ◽  
Aircraft Observations ◽  
Better Than

Abstract. We validate satellite methane observations from the Tropospheric Emission Spectrometer (TES) with 151 aircraft vertical profiles over the Pacific from the HIAPER Pole-to-Pole Observation (HIPPO) program. We find that a collocation window of ±750 km and ±24 h does not introduce significant error in comparing TES and aircraft profiles. We validate both the TES standard product (V004) and an experimental product with two pieces of information in the vertical (V005). We determine a V004 mean bias of 65.7 ppb with residual standard deviation of 44.2 ppb. For V005 we determine mean biases (residual standard deviations) in the lower and upper troposphere of 18.2 (31.1) and 49.4 (33.2) ppb, respectively. TES errors show no significant dependence on latitude or surface type. Even when V005 cannot retrieve two pieces of information it still performs better than V004. An observation system simulation experiment (OSSE) with the GEOS-Chem chemical transport model (CTM) and its adjoint shows that TES V004 has only limited value for constraining methane sources. Our successful validation of V005 encourages its production as a standard retrieval to replace V004.

scholarly journals Episodes of cross-polar transport in the Arctic troposphere during July 2008 as seen from models, satellite, and aircraft observations

2010 ◽  
Vol 10 (11) ◽  
pp. 26361-26410 ◽  
Author(s):  
H. Sodemann ◽  
M. Pommier ◽  
S. R. Arnold ◽  
S. A. Monks ◽  
K. Stebel ◽  
...  
Keyword(s):  
Transport Model ◽  
Chemical Transport ◽  
The Arctic ◽  
Actual State ◽  
Chemical Transport Model ◽  
Horizontal Structure ◽  
Model Simulations ◽  
Aircraft Observations ◽  
Total Column ◽  
Aircraft Data

Abstract. During the POLARCAT summer campaign in 2008, two episodes (2–5 July and 7–10 July 2008) occurred where low-pressure systems traveled from Siberia across the Arctic Ocean towards the North Pole. The two cyclones had extensive smoke plumes embedded in their associated air masses, creating an excellent opportunity to use satellite and aircraft observations to validate the performance of atmospheric transport models in the Arctic, which is a challenging model domain due to numerical and other complications. Here we compare transport simulations of carbon monoxide (CO) from the Lagrangian transport model FLEXPART, the Eulerian chemical transport model TOMCAT, and for numerical aspects the limited-area chemical transport model WRF-Chem. Retrievals of total column CO from the IASI passive infrared sensor onboard the MetOp-A satellite are used as a total column CO reference for the two simulations. Main aspect of the comparison is how realistic horizontal and vertical structures are represented in the model simulations. Analysis of CALIPSO lidar curtains and in situ aircraft measurements provide further independent reference points to assess how reliable the model simulations are and what the main limitations are. The horizontal structure of mid-latitude pollution plumes agrees well between the IASI total column CO and the model simulations. However, finer-scale structures are too quickly diffused in the Eulerian models. Aircraft data suggest that the satellite data are biased high, while TOMCAT and WRF-Chem are biased low. FLEXPART fits the aircraft data rather well, but due to added background concentrations the simulation is not independent from observations. The multi-data, multi-model approach allows separating the influences of meteorological fields, model realisation, and grid type on the plume structure. In addition to the very good agreement between simulated and observed total column CO fields, the results also highlight the difficulty to identify a data set that most realistically represents the actual state of the atmosphere.

scholarly journals Interpreting aerosol lifetimes using the GEOS-Chem model and constraints from radionuclide measurements

2013 ◽  
Vol 13 (12) ◽  
pp. 32391-32421 ◽  
Author(s):  
B. Croft ◽  
J. R. Pierce ◽  
R. V. Martin
Keyword(s):  
Boundary Layer ◽  
Nuclear Power ◽  
Transport Model ◽  
Chemical Transport Model ◽  
Removal Rates ◽  
Mean Lifetime ◽  
The Mean ◽  
Removal Processes ◽  
Global Mean ◽  
Mean Lifetimes

Abstract. Aerosol removal processes control global aerosol abundance, but the rate of that removal remains uncertain. A recent study of aerosol-bound radionuclide measurements after the Fukushima Dai-Ichi nuclear power plant accident documents 137Cs removal (e-folding) times of 10.0 to 13.9 days, suggesting that mean aerosol lifetimes in the range of 3–7 days in global models might be too short by a factor of two. In this study, we attribute this discrepancy to differences between the e-folding and mean aerosol lifetimes. We implement a~simulation of 137Cs and 133Xe into the GEOS-Chem chemical transport model and examine the removal rates for the Fukushima case. We find a~general consistency between modelled and measured e-folding times. The simulated 137Cs global burden e-folding time is about 14 days. However, the simulated mean lifetime of aerosol-bound 137Cs over a 6 month post-accident period is only 1.8 days. We find that the mean lifetime depends strongly on the removal rates in the first few days after emissions, before the aerosols leave the boundary layer and are transported to altitudes and latitudes where lifetimes with respect to wet removal are longer by a few orders of magnitude. We present sensitivity simulations that demonstrate the influence of differences in altitude and location of the radionuclides on the mean lifetime. Global mean lifetimes are shown to strongly depend on the altitude of injection. The global mean 137Cs lifetime is more than one order of magnitude greater for the injection at 7 km than into the boundary layer above the Fukushima site. Instantaneous removal rates are slower during the first few days after the emissions for a free tropospheric vs. boundary layer injection and this strongly controls the mean lifetimes. Global mean aerosol lifetimes for the GEOS-Chem model are 3–6 days, which is longer than for the 137Cs injected at the Fukushima site (likely due to precipitation shortly after Fukushima emissions), but about the same as the mean lifetime of 3.9 days for the 137Cs emissions injected with a uniform spread through the model's Northern Hemisphere boundary layer. Despite the reasonable global mean agreement of GEOS-Chem with measurement e-folding times, site by site comparisons yield differences of up to a factor of two, which suggest possible deficiencies in either the model transport, removal processes or the representation of 137Cs removal, particularly in the tropics and at high latitudes. There is an ongoing need to develop constraints on aerosol lifetimes, but these measurement-based constraints must be carefully interpreted given the sensitivity of mean and e-folding times to both mixing and removal processes.

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