24 research outputs found
What Can 14CO Measurements Tell Us about OH?
Get PDFThe possible use of 14CO measurements to constrain hydroxyl radical (OH) concentrations in the atmosphere is investigated. 14CO is mainly produced in the upper atmosphere from cosmic radiation. Measurements of 14CO at the surface show lower concentrations compared to the upper atmospheric source region, which is the result of oxidation by OH. In this paper, the sensitivity of 14CO mixing ratio
surface measurements to the 3-D OH distribution is assessed with the TM5 model. Simulated 14CO mixing ratios agree within a few molecules 14COcm-3 (STP) with existing measurements at five locations worldwide. The simulated cosmogenic 14CO distribution appears mainly sensitive to the assumed upper atmospheric 14C source function, and to a lesser extend to model resolution. As a next step, the sensitivity of 14CO measurements to OH is calculated with the adjoint TM5 model. The results indicate that 14CO measurements
taken in the tropics are sensitive to OH in a spatially confined region that varies strongly over time due to meteorological variability. Given measurements with an accuracy of 0.5 molecules 14COcm-3 STP, a good characterization of the cosmogenic 14CO fraction, and assuming perfect transport modeling, a single 14CO measurement may constrain OH to 0.2¿0.3×106 moleculesOHcm-3 on time scales of 6 months
and spatial scales of 70×70 degrees (latitude×longitude) between the surface and 500 hPa. The sensitivity of 14CO measurements
to high latitude OH is about a factor of five higher. This is in contrast with methyl chloroform (MCF) measurements, which show the highest sensitivity to tropical OH, mainly due to the temperature dependent rate constant of the MCF¿OH reaction. A logical next step will be the analysis of existing 14CO measurements in an inverse modeling framework. This paper presents the required mathematical framework for such an analysis.JRC.H.2-Climate chang
Development of an atmospheric N2O isotopocule model and optimization procedure, and application to source estimation
Get PDFThis paper presents the development of an atmospheric N2O isotopocule model based on a chemistry-coupled atmospheric general circulation model (ACTM). We also describe a simple method to optimize the model and present its use in estimating the isotopic signatures of surface sources at the hemispheric scale. Data obtained from ground-based observations, measurements of firn air, and balloon and aircraft flights were used to optimize the long-term trends, interhemispheric gradients, and photolytic fractionation, respectively, in the model. This optimization successfully reproduced realistic spatial and temporal variations of atmospheric N2O isotopocules throughout the atmosphere from the surface to the stratosphere. The very small gradients associated with vertical profiles through the troposphere and the latitudinal and vertical distributions within each hemisphere were also reasonably simulated. The results of the isotopic characterization of the global total sources were generally consistent with previous one-box model estimates, indicating that the observed atmospheric trend is the dominant factor controlling the source isotopic signature. However, hemispheric estimates were different from those generated by a previous two-box model study, mainly due to the model accounting for the interhemispheric transport and latitudinal and vertical distributions of tropospheric N2O isotopocules. Comparisons of time series of atmospheric N2O isotopocule ratios between our model and observational data from several laboratories revealed the need for a more systematic and elaborate intercalibration of the standard scales used in N2O isotopic measurements in order to capture a more complete and precise picture of the temporal and spatial variations in atmospheric N2O isotopocule ratios. This study highlights the possibility that inverse estimation of surface N2O fluxes, including the isotopic information as additional constraints, could be realized
17O18O and 18O18O in ice core O2 from Greenland: implications to reconstruct past atmospheric photochemistry
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<p>Abundances of <sup>17</sup>O<sup>18</sup>O and <sup>18</sup>O<sup>18</sup>O (also called clumped isotopes and denoted by Δ<sub>35</sub> and Δ<sub>36</sub>) of O<sub>2</sub>  in firn and ice core air are novel tracers that can be useful to study past changes in atmospheric photochemistry and temperature. We present Δ<sub>35</sub> and Δ<sub>36</sub> values measured in firn and ice core air O<sub>2</sub> from North Greenland (NEEM; 77.45°N 51.06°W). The aim is to reconstruct the preindustrial-industrial, Holocene and glacial-interglacial variation in the tropospheric ozone photochemistry and temperature. Measurements of Δ<sub>35</sub> and Δ<sub>36</sub> are carried out using a high-resolution stable isotope ratio mass spectrometer Thermo Fisher 253 ULTRA[1]. Our measurements of Δ<sub>35</sub> and Δ<sub>36</sub>  across past air, from archive samples, to the modern-day show significant changes in the atmospheric photochemistry via ozone burdening and stratospheric- tropospheric transport processes. We will present the measurement results along with a detailed discussion on the dominant process using explicit dynamic simulations of ∆<sub>36 </sub>in the AC-GCM EMAC model [2,3,4].</p><p> </p>
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17O18O and 18O18O in ice core O2 from Greenland: implications to reconstruct past atmospheric photochemistry
No full textSensitivity of PARASOL multi-angle photopolarimetric aerosol retrievals to cloud contamination
Get PDFAn important problem in satellite remote sensing of aerosols is related to the need to perform an adequate cloud screening. If a cloud screening is applied that is not strict enough, the ground scene has the probability of residual cloud cover which causes large errors on the retrieved aerosol parameters. On the other hand, if the cloud-screening procedure is too strict, too many clear sky cases, especially near-cloud scenes, will falsely be flagged cloudy. The detrimental effects of cloud contamination as well as the importance of aerosol cloud interactions that can be studied in these near-cloud scenes call for new approaches to cloud screening. Multi-angle multi-wavelength photopolarimetric measurements have a unique capability to distinguish between scattering by (liquid) cloud droplets and aerosol particles. In this paper the sensitivity of aerosol retrievals from multi-angle photopolarimetric measurements to cloud contamination is investigated and the ability to intrinsically filter the cloud-contaminated scenes based on a goodness-of-fit criteria is evaluated. Hereto, an aerosol retrieval algorithm is applied to a partially clouded over-ocean synthetic data set as well as non-cloud-screened over-ocean POLDER-3/PARASOL observations. It is found that a goodness-of-fit filter, together with a filter on the coarse mode refractive index (m(r)(coarse) > 1.335) and a cirrus screening, adequately rejects the cloud-contaminated scenes. No bias or larger SD are found in the retrieved parameters for this intrinsic cloud filter compared to the parameters retrieved in a priori cloud-screened data set (using MODIS/AQUA cloud masks) of PARASOL observations. Moreover, less high-aerosol load scenes are misinterpreted as cloud contaminated. The retrieved aerosol optical thickness, single scattering albedo and Angstrom exponent show good agreement with AERONET observations. Furthermore, the synthetic retrievals give confidence in the ability of the algorithm to correctly retrieve the micro-physical aerosol parameters
Influence of 3D effects on 1D aerosol retrievals in synthetic, partially clouded scenes
No full textAn important challenge in aerosol remote sensing is to retrieve aerosol properties in the vicinity of clouds and in cloud contaminated scenes. Satellite based multi-wavelength, multi-angular, photo-polarimetric instruments are particularly suited for this task as they have the ability to separate scattering by aerosol and cloud particles. Simultaneous aerosol/cloud retrievals using 1D radiative transfer codes cannot account for 3D effects such as shadows, cloud induced enhancements and darkening of cloud edges. In this study we investigate what errors are introduced on the retrieved optical and micro-physical aerosol properties, when these 3D effects are neglected in retrievals where the partial cloud cover is modeled using the Independent Pixel Approximation. To this end a generic, synthetic data set of PARASOL like observations for 3D scenes with partial, liquid water cloud cover is created. It is found that in scenes with random cloud distributions (i.e. broken cloud fields) and either low cloud optical thickness or low cloud fraction, the inversion algorithm can fit the observations and retrieve optical and micro-physical aerosol properties with sufficient accuracy. In scenes with non-random cloud distributions (e.g. at the edge of a cloud field) the inversion algorithm can fit the observations, however, here the retrieved real part of the refractive indices of both modes is biased
Characteristics, sources and evolution of fine aerosol (PM1) at urban, coastal and forest background sites in Lithuania
No full textThe chemical and isotopic composition of organic aerosol (OA) samples collected on PM1 filters was determined as a function of desorption temperature to investigate the main sources of organic carbon and the effects of photochemical processing on atmospheric aerosol. The filter samples were collected at an urban (54°38′ N, 25°18′ E), coastal (55°55′ N, 21°00′ E) and forest (55°27′ N, 26°00’ E) site in Lithuania in March 2013. They can be interpreted as winter-time samples because the monthly averaged temperature was −4 °C. The detailed chemical composition of organic compounds was analysed with a thermal desorption PTR-MS. The mass concentration of organic aerosol at the forest site was roughly by a factor of 30 lower than at the urban and coastal site. This fact could be an indication that in this cold month the biogenic secondary organic aerosol (SOA) formation was very low. Moreover, the organic aerosol collected at the forest site was more refractory and contained a larger fraction of heavy molecules with m/z > 200. The isotopic composition of the aerosol was used to differentiate the two main sources of organic aerosol in winter, i.e. biomass burning (BB) and fossil fuel (FF) combustion. Organic aerosol from biomass burning is enriched in 13C compared to OA from fossil fuel emissions. δ13COC values of the OA samples showed a positive correlation with the mass fraction of several individual organic compounds. Most of these organic compounds contained nitrogen indicating that organic nitrogen compounds formed during the combustion of biomass may be indicative of BB. Other compounds that showed negative correlations with δ13COC were possibly indicative of FF. These compounds included heavy hydrocarbons and were on the average less oxidized than the bulk organic carbon. The correlation of δ13COC and the O/C ratio was positive at low but negative at high desorption temperatures at the forest site. We propose that this might be due to photochemical processing of OA. This processing can lead to accumulation of carbon in the more refractory organic fraction that is depleted in 13C compared with the less refractory organic fraction. Detailed laboratory experiments are necessary to further investigate the aging of aerosol particles before firm conclusions can be drawn
Application of the large-scale flux chamber for quantification of methane release rate at Transylvanian gas fields.
No full text&lt;p&gt;The oil and gas (O&amp;G) sector contributes significantly to the anthropogenic part of the methane cycle in the atmosphere while having the most effective opportunities for emission mitigation with technically feasible and cost-effective options. Romania is a key O&amp;G producer within the EU Region of Transylvania with its active gas fields being in the focus of the second measurement campaign in the ROMEO project. Teams from European collaborations were deploying various techniques (GPM, OTM-33A, High Flow Sampler, Tracer release) for quantifications of the methane emission rates. In June of 2021, AGH deployed the large-scale flux chamber with help of scientists from&amp;#160; UBB, Romania, &amp;#160;and in cooperation with local O&amp;G operator &amp;#8211; Rom-Gas. Construction was designed and built to be used in the case of small gas installations like the single Christmas tree and was tested intensively during this campaign. A hemispheric structure with a diameter of 6 meters and volume of approximately 55 m&lt;sup&gt;3&lt;/sup&gt; was used to check the tightness of different gas wells in suitable conditions (size, terrain, meteorology). The methane concentration increase was measured by the OA-ICOS technique. We used an LGR MGGA-918 analyser while additional airflow and air mixing inside the chamber were provided with additional ventilators.&lt;/p&gt;
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&lt;p&gt;In this presentation, methane emission rates calculations based on deployments of large-scale flux chambers in Transylvania will be compared to other techniques. Verification of the chamber was developed using controlled release tests of methane and acetylene. Moreover, the estimated uncertainty of the measurement technique will be presented. Finally, the potential for use of a large-scale flux chamber as a direct ground based measurement technique and complementary to other direct and indirect techniques will be discussed.&lt;/p&gt;
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&lt;p&gt;The research results presented in this paper have been developed with the use of equipment financed from the funds of the &quot;Excellence Initiative - Research University&quot; program at AGH University of Science and Technology. The authors thank all the members of the ROMEO campaign, in particular, Thomas Roeckmann for providing an opportunity to be part of this measurement campaign.&lt;/p&gt;</jats:p
Stable isotopic composition of CO, H2 and CH4 in the troposphere and lower stratosphere: results from the ATom-WAS samples
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&lt;p&gt;The NASA Atmospheric Tomography Mission (ATom) aimed to improve the understanding of atmospheric composition through global scale aircraft sampling campaigns in different seasons. The flights included continuous profiling between 0.2 and 12 km over the Atlantic and Pacific Oceans.&lt;/p&gt;&lt;p&gt;A large number of samples were taken using the Whole Air sampler (WAS, UC Irvine, CA). In a selection of these samples, we measured the stable isotopic composition of CO, H&lt;sub&gt;2&lt;/sub&gt; and CH&lt;sub&gt;4&lt;/sub&gt;. The samples cover remote clean air from different latitudes, from troposphere and lower stratosphere, and air influenced by specific (pollution) sources or processes.&lt;/p&gt;&lt;p&gt;We will give an overview of the data available and the main characteristics. We observe large variations in the isotopic composition, showing the large scale influence of tropospheric sources and sinks, but also stratospheric processing. The three gas species are mainly affected by the same sources and processes but in different ways, thus giving complementary information on the atmospheric processes.&lt;/p&gt;
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Carbon isotope ratios suggest no additional methane from boreal wetlands during the rapid Greenland Interstadial 21.2
No full textSamples from two Greenland ice cores (NEEM and NGRIP) have been measured for methane carbon isotope ratios (δ13C-CH4) to investigate the CH4 mixing ratio anomaly during Greenland Interstadial (GI) 21.2 (85,000 years before present). This extraordinarily rapid event occurred within 150 years, comprising a CH4 mixing ratio pulse of 150 ppb (∼25%). Our new measurements disclose a concomitant shift in δ13C-CH4 of 1‰. Keeling plot analyses reveal the δ13C of the additional CH4 source constituting the CH4 anomaly as -56.8 ± 2.8‰, which we confirm by means of a previously published box model. We propose tropical wetlands as the most probable additional CH4 source during GI-21.2 and present independent evidence that suggests that tropical wetlands in South America and Asia have played a key role. We find no evidence that boreal CH4 sources, such as permafrost degradation, contributed significantly to the atmospheric CH4 increase, despite the pronounced warming in the Northern Hemisphere during GI-21.2
