Effect of local and regional sources on the isotopic composition of nitrous oxide in the tropical free troposphere and tropopause layer

Measurements and models of the spatiotemporal variability of surface N 2O mixing ratios and isotopic compositions are increasingly used to constrain the global N2O budget. However, large variability observed on the small spatial scales of soil chambers and shipboard sampling, which appears to be very sensitive to local environmental conditions, has made extrapolation to the global scale difficult. In this study, we present measurements of the isotopic composition of N2O (δ 15Nbulk, δ15N, δ15N, and δ18O) from whole-air samples collected at altitudes of 0.5 to 19km by the NASA DC-8 and WB-57 aircraft during the Costa Rica-Aura Validation Experiment (CR-AVE) and the Tropical Composition, Cloud and Climate Coupling Experiment (TC4) campaigns in January-February 2006 and July-August 2007, respectively. The vertical profiles of isotopic composition showed predictable, repeating patterns consistent with the influence of a surface source at lower altitudes and the influence of stratospheric photochemistry in the lower stratosphere. Their correlations with marine tracers at lower altitudes are consistent with a predominantly oceanic source, although a soil source cannot be ruled out. Measurements in a combustion plume revealed a strong depletion in 15N at the central nitrogen atom (i.e., low δ15N values), providing new information on N2O isotopic compositions from combustion. This new data set demonstrates that a coherent picture of the isotopic composition of tropospheric N2O is possible at currently attainable precisions and that its variations from 0.5 km to the lower stratosphere are a useful tool in investigating the sources and distributions of this important greenhouse gas. Copyright 2010 by the American Geophysical Union

Extreme deuterium enrichment in stratospheric hydrogen and the global atmospheric budget of H_2

Molecular hydrogen (H_2) is the second most abundant trace gas in the atmosphere after methane (CH_4). In the troposphere, the D/H ratio of H_2 is enriched by 120‰ relative to the world's oceans. This cannot be explained by the sources of H_2 for which the D/H ratio has been measured to date (for example, fossil fuels and biomass burning). But the isotopic composition of H_2 from its single largest source—the photochemical oxidation of methane—has yet to be determined. Here we show that the D/H ratio of stratospheric H2 develops enrichments greater than 440‰, the most extreme D/H enrichment observed in a terrestrial material. We estimate the D/H ratio of H_2 produced from CH_4 in the stratosphere, where production is isolated from the influences of non-photochemical sources and sinks, showing that the chain of reactions producing H_2 from CH_4 concentrates D in the product H_2. This enrichment, which we estimate is similar on a global average in the troposphere, contributes substantially to the D/H ratio of tropospheric H_2

Isotopic ordering in atmospheric O2 as a tracer of ozone photochemistry and the tropical atmosphere

The distribution of isotopes within O2 molecules can be rapidly altered when they react with atomic oxygen. This mechanism is globally important: while other contributions to the global budget of O2 impart isotopic signatures, the O(3P) + O2 reaction resets all such signatures in the atmosphere on subdecadal timescales. Consequently, the isotopic distribution within O2 is determined by O3 photochemistry and the circulation patterns that control where that photochemistry occurs. The variability of isotopic ordering in O2 has not been established, however. We present new measurements of 18O18O in air (reported as Δ36 values) from the surface to 33 km altitude. They confirm the basic features of the clumped-isotope budget of O2: Stratospheric air has higher Δ36 values than tropospheric air (i.e., more 18O18O), reflecting colder temperatures and fast photochemical cycling of O3. Lower Δ36 values in the troposphere arise from photochemistry at warmer temperatures balanced by the influx of high-Δ36 air from the stratosphere. These observations agree with predictions derived from the GEOS-Chem chemical transport model, which provides additional insight. We find a link between tropical circulation patterns and regions where Δ36 values are reset in the troposphere. The dynamics of these regions influences lapse rates, vertical and horizontal patterns of O2 reordering, and thus the isotopic distribution toward which O2 is driven in the troposphere. Temporal variations in Δ36 values at the surface should therefore reflect changes in tropospheric temperatures, photochemistry, and circulation. Our results suggest that the tropospheric O3 burden has remained within a ±10% range since 1978

Large and unexpected enrichment in stratospheric ^(16)O^(13)C^(18)O and its meridional variation

The stratospheric CO_2 oxygen isotope budget is thought to be governed primarily by the O(1D)+CO_2 isotope exchange reaction. However, there is increasing evidence that other important physical processes may be occurring that standard isotopic tools have been unable to identify. Measuring the distribution of the exceedingly rare CO_2 isotopologue ^(16)O^(13)C^(18)O, in concert with ^(18)O and ^(17)O abundances, provides sensitivities to these additional processes and, thus, is a valuable test of current models. We identify a large and unexpected meridional variation in stratospheric 16O13C18O, observed as proportions in the polar vortex that are higher than in any naturally derived CO_2 sample to date. We show, through photochemical experiments, that lower ^(16)O^(13)C^(18)O proportions observed in the midlatitudes are determined primarily by the O(1D)+CO_2 isotope exchange reaction, which promotes a stochastic isotopologue distribution. In contrast, higher ^(16)O^(13)C^(18)O proportions in the polar vortex show correlations with long-lived stratospheric tracer and bulk isotope abundances opposite to those observed at midlatitudes and, thus, opposite to those easily explained by O(1D)+CO_2. We believe the most plausible explanation for this meridional variation is either an unrecognized isotopic fractionation associated with the mesospheric photochemistry of CO_2 or temperature-dependent isotopic exchange on polar stratospheric clouds. Unraveling the ultimate source of stratospheric ^(16)O^(13)C^(18)O enrichments may impose additional isotopic constraints on biosphere–atmosphere carbon exchange, biosphere productivity, and their respective responses to climate change

O_3-N_2O correlations from the Atmospheric Chemistry Experiment: revisiting a diagnostic of transport and chemistry in the stratosphere

Our knowledge of stratospheric O3-N2O correlations is extended, and their potential for model-measurement comparison assessed, using data from the Atmospheric Chemistry Experiment (ACE) satellite and the Canadian Middle Atmosphere Model (CMAM). ACE provides the first comprehensive data set for the investigation of interhemispheric, interseasonal, and height-resolved differences of the O_3-N_2O correlation structure. By subsampling the CMAM data, the representativeness of the ACE data is evaluated. In the middle stratosphere, where the correlations are not compact and therefore mainly reflect the data sampling, joint probability density functions provide a detailed picture of key aspects of transport and mixing, but also trace polar ozone loss. CMAM captures these important features, but exhibits a displacement of the tropical pipe into the Southern Hemisphere (SH). Below about 21 km, the ACE data generally confirm the compactness of the correlations, although chemical ozone loss tends to destroy the compactness during late winter/spring, especially in the SH. This allows a quantitative comparison of the correlation slopes in the lower and lowermost stratosphere (LMS), which exhibit distinct seasonal cycles that reveal the different balances between diabatic descent and horizontal mixing in these two regions in the Northern Hemisphere (NH), reconciling differences found in aircraft measurements, and the strong role of chemical ozone loss in the SH. The seasonal cycles are qualitatively well reproduced by CMAM, although their amplitude is too weak in the NH LMS. The correlation slopes allow a "chemical" definition of the LMS, which is found to vary substantially in vertical extent with season

Arthrosis deformans van het kaakgewricht: een klinisch en röntgenologisch onderzoek

INLEIDING De aandoening van het kaakgewricht, gekenmerkt door knappen, pijn en bewegingsbeperking, is in de literatuur onder vele namen bekend. De meest voorkomende zijn: Costen's syndroom, pijn-dysfunctiesyndroom, mandibular joint syndrome of -disorder, chronische Kiefergelenkerkrankung en temporomandibular joint arthrosis. Ook wordt vaak ccn van dt bovengenoemde symptomen gebruikt om het gehele ziektebeeld aan te duiden. Het grote aantal omschrijvingen is een gevolg van de bezwaren, die bij velen bestaan tegen het gebruik van de term arthrosis deformans. Dit is immers in het algemeen een gewrichtsaandoening, die bij de oudere mens voorkomt en samengaat met duidelijke rontgenologische afwijkingen. De genoemde kaakgewrichtsklachten komen daarentegen meestal op jeugdiger leeftijd voor en een afwijking op de rontgenfoto wordt bij het eerste onderzoek vaak niet waargenomen. De klinische symptomen passen echter zeer wel bij het beeld van een arthrosis, zoals deze aan andere gewrichten voorkomt. Het zeer gevarieerde klinische beeld bij het kaakgewricht is toe te schrijven aan de discus met zijn gecompliceerd bewegingsmechanisme. Er bestaan mijns inziens dan ook geen bezwaren tegen het gebruik van de term arthrosis voor deze chronische aandoening van het kaakgewricht, die niet berust op een infectie of een neoplasma en geen congenitale afwijking is. Uitgebreide histologische onderzoekingen hebben aangetoond, dat bij zeer velen reeds op vrij jeugdige leeftijd degcneratieve veranderingen in de articlilerende oppervlakken van het kaakgewricht aanwezig kunnen zijn. Men moet zich er echter van bewust zijn, dat geen afwijkingen op de röntgenfoto zijn waar te nemen, zolang deze veranderingen tot het kraakbeen zijn beperkt. Door het verschil van mening over de ware aard van dc afwijking zijn er sinds de publicaties van GOODFRIEND en COSTEN, ruim 30 jaar geleden, zoveel theorieen ontwikkeld, dat de behoefte om zelf een oordeel over deze materie te hebben, zich deed gevoelen. De problemen bij de behandeling van deze patienten in het Militair Kaakchirurgisch Centrum te Utrecht in 1955, doch vooral de voordrachten van LINDBLOM en STEINHARDT, in 1956 gehouden voor de Nederlandse Vereniging van Tandartsen, hebben mijn belangstelling voor deze afwijking gewekt. Tijdens een verblijf aan de kliniek van Prof. STE1NHARDT te Bremen, werd de basis gelegd voor een onderzoek, waarvan de resultaten zijn neergelegd in dit proefschrift. Gedurende de periode 1956-1963 werden 400 patienten, die zich primair meldden voor onderzoek en behandeling van hun kaakgewrichtsklachten, in de Kliniek voor Mondheelkunde van het Academisch Ziekenhuis te Groningen onderzocht. Hierin is tevens begrepen een gering aanul, dat reeds lang op de kliniek bekend was. Bovendien werden acht patienten, die primair voor een kaakluxatie waren behandeld, na gcruime tijd nog eens gecontroleerd op arhrotische veranderingen. Hetzelfde geschiedde met zestien patienten met een contusie van het kaakgewricht. Om een indruk te krijgen van de veranderingen, welke de vcrschillendc vormen van reuma in het kaakgewricht kunnen veroorzaken, werden twaalf patienten met reumatoide arthritis, drie met spondylitis ankylopoetica, twee met psoriasis arthropatica en een met lupus erythematodes onderzocht. Ook werden drie patienten gecontroleerd, die aan acuut reuma hadden geleden. Teneinde een 20 goed mogelijk overzicht en een uniformiteit in de beoordeling te krijgen, werden het onderzoek en de behandeling van de genoemde 400 patienten zoveel mogelijk in één hand gehouden. Vrijwel allen werden zij na verloop van tijd een of meerdere malen gecontroleerd: de controle-periode varieerde van 1 tot 12 jaar en bedroeg meestal 2 tot 5 jaar. Het onderzoek geschiedde in alle gevallen poliklinisch De patienten, die zich op het spreekuur meldden, werden globaal onderzocht, waarna een afspraak werd gemaakt voor een meer gedetailleerd onderzoek. Dit laatste geschiedde aan de hand van een uitgebreid onderzoekschema (zie Bijlage I). Bij de diverse controles werd meestal een verkort schema gebruikt. hetwelk alleen die punten bevatte, waarbij veranderingen zouden kunnen zijn opgetreden, Het spreekt vanze1f dat bij het kaakgewrichtsonderzock eveneens werd gelet op andere afwijkingen, welke in het gebied van mond en kaken kunnen voorkomen. Een meer gedetailleerde bespreking van de in het onderzoekschema genoemde punten en de hiermede verband houdende problemen, wordt gegeven in de desbetreffende hoofdstukken

Protein Targeting of L1CAM Mutants in Cultured Neurons

The correct targeting of proteins to axons and dendrites of neurons is essential for the proper development of the nervous system. L1CAM is an axonally-targeted protein responsible for multiple aspects of neuronal development. L1CAM mutations are known to result in a developmental syndrome characterized by cognitive and motor disabilities. We investigated the cellular distribution of known L1CAM mutant proteins, P941L and D544N, in cultured embryonic chick forebrain neurons to test the hypothesis that aberrant protein targeting of these mutants plays a role in the developmental abnormalities associated with the syndrome. Preliminary data suggests that the P941L L1CAM mutant is targeted normally to the axon suggesting that downstream signaling events are abnormal. In contrast, the D544N L1CAM mutant does not appear to reach the cell surface of the neuron

The diurnal variation of hydrogen, nitrogen, and chlorine radicals: implications for the heterogeneous production of HNO_2

In situ measurements of hydrogen, nitrogen, and chlorine radicals obtained through sunrise and sunset in the lower stratosphere during SPADE are compared to results from a photochemical model constrained by observed concentrations of radical precursors and environmental conditions. Models allowing for heterogeneous hydrolysis of N_(2)O_(5) on sulfate aerosols agree with measured concentrations of NO, NO_(2), and ClO throughout the day, but fail to account for high concentrations of OH and HO_(2) observed near sunrise and sunset. The morning burst of [OH] and [HO_(2)] coincides with the rise of [NO] from photolysis of NO_(2), suggesting a new source of HO_(x) that photolyzes in the near UV (350 to 400 nm) spectral region. A model that allows for the heterogeneous production of HNO_(2) results in an excellent simulation of the diurnal variations of [OH] and [HO_(2)]

The distribution of hydrogen, nitrogen, and chlorine radicals in the lower stratosphere: Implications for changes in O_3 due to emission of NO_y from supersonic aircraft

In situ measurements of hydrogen, nitrogen, and chlorine radicals obtained in the lower stratosphere during SPADE are compared to results from a photochemical model that assimilates measurements of radical precursors and environmental conditions. Models allowing for heterogeneous hydrolysis of N_2O_5 agree well with measured concentrations of NO and ClO, but concentrations of HO_2 and OH are underestimated by 10 to 25%, concentrations of NO_2 are overestimated by 10 to 30%, and concentrations of HCl are overestimated by a factor of 2. Discrepancies for [OH] and [HO_2] are reduced if we allow for higher yields of O(^1D) from O_3 photolysis and for heterogeneous production of HNO_2. The data suggest more efficient catalytic removal of O_3 by hydrogen and halogen radicals relative to nitrogen oxide radicals than predicted by models using recommended rates and cross sections. Increases in [O_3] in the lower stratosphere may be larger in response to inputs of NO_y from supersonic aircraft than estimated by current assessment models