scholarly journals Correcting the impact of the isotope composition on the mixing ratio dependency of water vapour isotope measurements with cavity ring-down spectrometers

2020 ◽  
Vol 13 (6) ◽  
pp. 3167-3190
Author(s):  
Yongbiao Weng ◽  
Alexandra Touzeau ◽  
Harald Sodemann
Keyword(s):  
Water Vapour ◽  
Isotope Composition ◽  
Data Interpretation ◽  
Polar Regions ◽  
Mixing Ratio ◽  
Mixing Ratios ◽  
Δ18o And Δd ◽  
Isotope Composition Of Water ◽  
The Impact ◽  
Cavity Ring Down

Abstract. Recent advances in laser spectroscopy enable high-frequency in situ measurements of the isotope composition of water vapour. At low water vapour mixing ratios, however, the measured stable water isotope composition can be substantially affected by a measurement artefact known as the mixing ratio dependency, which is commonly considered independent of the isotope composition. Here we systematically investigate how the mixing ratio dependency, in a range from 500 to 23 000 ppmv of three commercial cavity ring-down spectrometers, is affected by the isotope composition of water vapour. We find that the isotope composition of water vapour has a substantial and systematic impact on the mixing ratio dependency for all three analysers, particularly at mixing ratios below 4000 ppmv. This isotope composition dependency can create a deviation of ±0.5 ‰ and ±6.0 ‰ for δ18O and δD, respectively, at ∼2000 ppmv, resulting in about 2 ‰–3 ‰ deviation for the d-excess. An assessment of the robustness of our findings shows that the overall behaviour is reproducible over up to 2 years for different dry gas supplies, while being independent of the method for generating the water vapour and being the first order of the evaluation sequence. We propose replacing the univariate mixing ratio dependency corrections with a new, combined isotope composition–mixing ratio dependency correction. Using aircraft- and ship-based measurements in an Arctic environment, we illustrate a relevant application of the correction. Based on our findings, we suggest that the dependency on the isotope composition may be primarily related to spectroscopy. Repeatedly characterising the combined isotope composition–mixing ratio dependency of laser spectrometers when performing water vapour measurements at high elevations, on aircraft, or in polar regions appears critical to enable reliable data interpretation in dry environments.

scholarly journals Impact of isotope composition on the humidity dependency correction of water vapour isotope measurements with infra-red cavity ring-down spectrometers

2019 ◽  
Author(s):  
Yongbiao Weng ◽  
Alexandra Touzeau ◽  
Harald Sodemann
Keyword(s):  
Water Vapour ◽  
Isotope Composition ◽  
Spectroscopic Techniques ◽  
Substantial Impact ◽  
Cold Environments ◽  
Dry Conditions ◽  
Low Humidity ◽  
Δ18o And Δd ◽  
The Impact ◽  
Cavity Ring Down

Abstract. Advances in laser spectroscopic techniques now enable high-frequency in situ measurements of the water vapour isotope composition on platforms such as ship and aircraft. However, the isotope compositions and the d-excess measured by this technique can be substantially affected by water concentrations, especially at low humidity. This measurement artefact is known as the "humidity dependency", and is commonly corrected for uniformly across all isotope compositions. Here we systematically investigate the behaviour of the humidity dependency on three commercial cavity ring-down spectrometers for different water standards within a humidity range of 500 to 23'000 ppmv. We find that the isotope compositions of measured water do have a substantial impact on the shape of the humidity dependency at low humidity (below 4'000 ppmv). This isotope composition dependency can, for example, create an offset of ±0.5 and ±6 ‰ for δ18O and δD at ~2'000 ppmv in the case of a Picarro L2130-i, resulting in an offset of 2–3 ‰ for the d-excess. We show that the combined isotope composition–humidity dependency can be expressed by a surface function, which allows to build a correction framework. The impact of this correction is illustrated for a case of aircraft measurements and ship-based measurements in cold environments. A ystematic assessment of the robustness of our findings for three laser spectrometers shows overall constant behaviour with time (for periods ranging from one month to two years), independent of the method of characterisation (discrete liquid injection and continuous vapour streaming), dry gas supply (N2 and synthetic air), or the sequence of humidity levels. Based on our analysis, we recommend a procedure for the characterisation and subsequent correction of the combined isotope composition–humidity dependency for this type of laser spectrometers when performing water vapour measurements in cold and dry conditions.

scholarly journals Evaluation of MUSICA IASI tropospheric water vapour profiles using theoretical error assessments and comparisons to GRUAN Vaisala RS92 measurements

2018 ◽  
Vol 11 (9) ◽  
pp. 4981-5006 ◽  
Author(s):  
Christian Borger ◽  
Matthias Schneider ◽  
Benjamin Ertl ◽  
Frank Hase ◽  
Omaira E. García ◽  
...  
Keyword(s):  
Water Vapour ◽  
Degrees Of Freedom ◽  
Global Climate ◽  
Atmospheric Temperature ◽  
Systematic Difference ◽  
Polar Regions ◽  
Mixing Ratio ◽  
Random Errors ◽  
The Tropics ◽  
Dry Bias

Abstract. Volume mixing ratio water vapour profiles have been retrieved from IASI (Infrared Atmospheric Sounding Interferometer) spectra using the MUSICA (MUlti-platform remote Sensing of Isotopologues for investigating the Cycle of Atmospheric water) processor. The retrievals are done for IASI observations that coincide with Vaisala RS92 radiosonde measurements performed in the framework of the GCOS (Global Climate Observing System) Reference Upper-Air Network (GRUAN) in three different climate zones: the tropics (Manus Island, 2° S), mid-latitudes (Lindenberg, 52° N), and polar regions (Sodankylä, 67° N). The retrievals show good sensitivity with respect to the vertical H2O distribution between 1 km above ground and the upper troposphere. Typical DOFS (degrees of freedom for signal) values are about 5.6 for the tropics, 5.1 for summertime mid-latitudes, 3.8 for wintertime mid-latitudes, and 4.4 for summertime polar regions. The errors of the MUSICA IASI water vapour profiles have been theoretically estimated considering the contribution of many different uncertainty sources. For all three climate regions, unrecognized cirrus clouds and uncertainties in atmospheric temperature have been identified as the most important error sources and they can reach about 25 %. The MUSICA IASI water vapour profiles have been compared to 100 individual coincident GRUAN water vapour profiles. The systematic difference between the data is within 11 % below 12 km altitude; however, at higher altitudes the MUSICA IASI data show a dry bias with respect to the GRUAN data of up to 21 %. The scatter is largest close to the surface (30 %), but never exceeds 21 % above 1 km altitude. The comparison study documents that the MUSICA IASI retrieval processor provides H2O profiles that capture the large variations in H2O volume mixing ratio profiles well from 1 km above ground up to altitudes close to the tropopause. Above 5 km the observed scatter with respect to GRUAN data is in reasonable agreement with the combined MUSICA IASI and GRUAN random errors. The increased scatter at lower altitudes might be explained by surface emissivity uncertainties at the summertime continental sites of Lindenberg and Sodankylä, and the upper tropospheric dry bias might suggest deficits in correctly modelling the spectroscopic line shapes of water vapour.

scholarly journals Diagnosis of processes controlling water vapour in the tropical tropopause layer by a Lagrangian cirrus model

2007 ◽  
Vol 7 (2) ◽  
pp. 5515-5552 ◽  
Author(s):  
C. Ren ◽  
A. R. MacKenzie ◽  
C. Schiller ◽  
G. Shur ◽  
V. Yushkov
Keyword(s):  
Water Vapour ◽  
Specific Humidity ◽  
Mixing Ratio ◽  
Total Water ◽  
Water Mixing ◽  
Tropical Tropopause Layer ◽  
Mixing Ratios ◽  
Aircraft Flight ◽  
Tropical Tropopause ◽  
Ecmwf Model

Abstract. We have developed a Lagrangian air-parcel cirrus model (LACM), to diagnose the processes controlling water in the tropical tropopause layer (TTL). LACM applies parameterised microphysics to air parcel trajectories. The parameterisation includes the homogeneous freezing of aerosol droplets, the growth/sublimation of ice particles, and sedimentation of ice particles, so capturing the main dehydration mechanism for air in the TTL. Rehydration is also considered by resetting the water vapour mixing ratio in an air parcel to the value at the point in the 4-D analysis/forecast data used to generate the trajectories, but only when certain conditions, indicative of convection, are satisfied. These conditions are imposed to confine what processes contribute to rehydration. The conditions act to restrict rehydration of the Lagrangian air parcels to regions where convective transport of water vapour from below is significant, at least to the extent that the analysis/forecast captures this process. The inclusion of hydration and dehydration mechanisms in LACM results in total water fields near tropical convection that have more of the "stripey" character of satellite observations of high cloud, than do either the ECMWF analysis or trajectories without microphysics. The mixing ratios of total water in the TTL, measured by a high-altitude aircraft over Brazil (during the TROCCINOX campaign), have been reconstructed by LACM using trajectories generated from ECMWF analysis. Two other Lagrangian reconstructions are also tested: linear interpolation of ECMWF analysed specific humidity onto the aircraft flight track, and instantaneous dehydration to the saturation vapour pressure over ice along trajectories. The reconstructed total water mixing ratios along aircraft flight tracks are compared with observations from the FISH total water hygrometer. Process-oriented analysis shows that modelled cirrus cloud events are responsible for dehydrating the air parcels coming from lower levels, resulting in total water mixing ratios as low as 2 μmol/mol. Without adding water back to some of the trajectories, the LACM and instantaneous-dehydration reconstructions have a dry bias. The interpolated-ECMWF reconstruction does not suffer this dry bias, because convection in the ECMWF model moistens air parcels dramatically, by pumping moist air upwards. This indicates that the ECMWF model captures the gross features of the rehydration of air in the TTL by convection. Overall, the ECMWF models captures well the exponential decrease in total water mixing ratio with height above 250 hPa, so that all the reconstruction techniques capture more than 75% of the variance in the measured total water mixing ratios over the depth of the TTL. We have therefore developed a simple method for re-setting the total water in LACM using the ECMWF-analysed specific humidity in regions where the model predicts convection. By picking up the main contributing processes to dehydration and rehydration in the TTL, LACM reconstructs total water mixing ratios along aircraft flight tracks at the top of the TTL, close to the cold point, that are always in substantially better agreement with observations than instantaneous-dehydration reconstructions, and better than the ECMWF analysis for regions of high relative humidity and cloud.

scholarly journals Validation of Aura MLS retrievals of temperature, water vapour and ozone in the upper troposphere and lower–middle stratosphere over the Tibetan Plateau during boreal summer

2016 ◽  
Author(s):  
X. L. Yan ◽  
J. S. Wright ◽  
X. D. Zheng ◽  
N. Livesey ◽  
H. Vömel ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Water Vapour ◽  
Boreal Summer ◽  
The Tibetan Plateau ◽  
Mixing Ratio ◽  
Upper Troposphere ◽  
Mixing Ratios ◽  
Dry Bias ◽  
Temperature Water ◽  
Middle Stratosphere

Abstract. We validate Aura Microwave Limb Sounder (MLS) version 3 (v3) and version 4 (v4) retrievals of summertime temperature, water vapour and ozone in the upper troposphere and lower–middle stratosphere (UTLS; 10–316 hPa) against balloon soundings collected during the Study of Ozone, Aerosols and Radiation over the Tibetan Plateau (SOAR-TP). Mean v3 and v4 profiles of temperature, water vapour and ozone in this region during the measurement campaigns are almost identical through most of the stratosphere (10–68 hPa), but differ in several respects in the upper troposphere and tropopause layer. Differences in v4 relative to v3 include slightly colder mean temperatures from 100–316 hPa, smaller mean water vapour mixing ratios in the upper troposphere (215–316 hPa), and a more vertically homogeneous profile of mean ozone mixing ratios below the climatological tropopause (100–316 hPa). These changes substantially improve agreement between ozonesondes and MLS ozone retrievals in the upper troposphere, but slightly worsen existing cold and dry biases in the upper troposphere. Aura MLS v3 and v4 temperature profiles contain significant cold biases relative to collocated temperature measurements in several layers of the lower–middle stratosphere (mean biases of −1.3 to −1.8 K centered at 10–12 hPa, 26–32 hPa and 68– 83 hPa) and in the upper troposphere (mean biases of approximately −2.3±0.3 K in v3 and −2.6±0.4 K in v4 between 147 and 261 hPa). MLS v3 and v4 profiles of water vapour volume mixing ratio generally compare well with collocated measurements, with a slight dry bias (v4: −8±4%) near 22–26 hPa, a slight wet bias (v4: +12±5%) near 68–83 hPa, and a more substantial dry bias (v4: −32±11%) in the upper troposphere (121–261 hPa). MLS v3 and v4 retrievals of ozone volume mixing ratio are biased high relative to collocated ozonesondes through most of the stratosphere (18–83 hPa), but are biased low at 100 hPa. The largest positive biases in ozone retrievals are located at 83 hPa (approximately +70%); this peak was not identified by earlier validations and may be regionally or seasonally specific. Ozone retrievals are substantially improved in v4 relative to v3, with smaller biases in the tropopause layer, reduced variance below 68 hPa, larger data yields, and smoother gradients in the vertical profile of ozone biases in the upper troposphere.

scholarly journals Measurement report: Variability in the composition of biogenic volatile organic compounds in a Southeastern US forest and their role in atmospheric reactivity

2021 ◽  
Vol 21 (20) ◽  
pp. 15755-15770
Author(s):  
Deborah F. McGlynn ◽  
Laura E. R. Barry ◽  
Manuel T. Lerdau ◽  
Sally E. Pusede ◽  
Gabriel Isaacman-VanWertz
Keyword(s):  
Volatile Organic Compounds ◽  
Organic Compounds ◽  
Growing Season ◽  
Mixing Ratio ◽  
Biogenic Volatile Organic Compounds ◽  
Mixing Ratios ◽  
Southeastern Us ◽  
Atmospheric Reactivity ◽  
Volatile Organic ◽  
The Impact

Abstract. Despite the significant contribution of biogenic volatile organic compounds (BVOCs) to organic aerosol formation and ozone production and loss, there are few long-term, year-round, ongoing measurements of their volume mixing ratios and quantification of their impacts on atmospheric reactivity. To address this gap, we present 1 year of hourly measurements of chemically resolved BVOCs between 15 September 2019 and 15 September 2020, collected at a research tower in Central Virginia in a mixed forest representative of ecosystems in the Southeastern US. Mixing ratios of isoprene, isoprene oxidation products, monoterpenes, and sesquiterpenes are described and examined for their impact on the hydroxy radical (OH), ozone, and nitrate reactivity. Mixing ratios of isoprene range from negligible in the winter to typical summertime 24 h averages of 4–6 ppb, while monoterpenes have more stable mixing ratios in the range of tenths of a part per billion up to ∼2 ppb year-round. Sesquiterpenes are typically observed at mixing ratios of <10 ppt, but this represents a lower bound in their abundance. In the growing season, isoprene dominates OH reactivity but is less important for ozone and nitrate reactivity. Monoterpenes are the most important BVOCs for ozone and nitrate reactivity throughout the year and for OH reactivity outside of the growing season. To better understand the impact of this compound class on OH, ozone, and nitrate reactivity, the role of individual monoterpenes is examined. Despite the dominant contribution of α-pinene to total monoterpene mass, the average reaction rate of the monoterpene mixture with atmospheric oxidants is between 25 % and 30 % faster than α-pinene due to the contribution of more reactive but less abundant compounds. A majority of reactivity comes from α-pinene and limonene (the most significant low-mixing-ratio, high-reactivity isomer), highlighting the importance of both mixing ratio and structure in assessing atmospheric impacts of emissions.

scholarly journals Long-term observation of mass-independent oxygen isotope anomaly in stratospheric CO<sub>2</sub>

2008 ◽  
Vol 8 (20) ◽  
pp. 6189-6197 ◽  
Author(s):  
S. Kawagucci ◽  
U. Tsunogai ◽  
S. Kudo ◽  
F. Nakagawa ◽  
H. Honda ◽  
...  
Keyword(s):  
Oxygen Isotope ◽  
Middle Atmosphere ◽  
Isotope Composition ◽  
Mixing Ratio ◽  
Least Squares Regression ◽  
Air Samples ◽  
Mixing Ratios ◽  
Long Term Observation ◽  
Isotope Correlation ◽  
Middle Stratosphere

Abstract. Stratospheric and upper tropospheric air samples were collected during 1994–2004 over Sanriku, Japan and in 1997 over Kiruna, Sweden. Using these archived air samples, we determined the triple oxygen-isotope composition of stratospheric CO2 and the N2O mixing ratio. The maximum Δ17OCO2 value of +12.2‰, resembling that observed previously in the mesosphere at 60 km height, was found in the middle stratosphere over Kiruna at 25.6 km height, suggesting that upper stratospheric and mesospheric air descended to the middle stratosphere through strong downward advection. A least-squares regression analysis of our observations on a δ18OCO2−δ17OCO2 plot (r2>0.95) shows a slope of 1.63±pm0.10, which is similar to the reported value of 1.71±0.06, thereby confirming the linearity of three isotope correlation with the slope of 1.6–1.7 in the mid-latitude lower and middle stratosphere. The slope decrease with increasing altitude and a curvy trend in three-isotope correlation reported from previous studies were not statistically significant. Using negative linear correlations of Δ17OCO2 and δ18OCO2 with the N2O mixing ratio, we quantified triple oxygen-isotope fluxes of CO2 to the troposphere as +48‰ GtC/yr (Δ17OCO2) and +38‰ GtC/yr (δ18OCO2) with ~30% uncertainty. Comparing recent model results and observations, underestimation of the three isotope slope and the maximum Δ17OCO2 value in the model were clarified, suggesting a smaller O2 photolysis contribution than that of the model. Simultaneous observations of δ18OCO2, δ17OCO2, and N2O mixing ratios can elucidate triple oxygen isotopes in CO2 and clarify complex interactions among physical, chemical, and photochemical processes occurring in the middle atmosphere.

scholarly journals Impact of convection on the upper-tropospheric composition (water vapor and ozone) over a subtropical site (Réunion island; 21.1° S, 55.5° E) in the Indian Ocean

2020 ◽  
Vol 20 (14) ◽  
pp. 8611-8626 ◽  
Author(s):  
Damien Héron ◽  
Stéphanie Evan ◽  
Jérôme Brioude ◽  
Karen Rosenlof ◽  
Françoise Posny ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Local Maximum ◽  
Reunion Island ◽  
Mixing Ratio ◽  
Southwest Indian Ocean ◽  
Air Masses ◽  
Upper Troposphere ◽  
Mixing Ratios ◽  
Réunion Island ◽  
The Impact

Abstract. Observations of ozonesonde measurements of the NDACC/SHADOZ (Network for the Detection of Atmospheric Composition Change and the Southern Hemisphere ADditional OZonesondes) program and humidity profiles from the daily Météo-France radiosondes at Réunion island (21.1∘ S, 55.5∘ E) from November 2013 to April 2016 were analyzed to identify the origin of wet upper-tropospheric air masses with low ozone mixing ratio observed above the island, located in the southwest Indian Ocean (SWIO). A seasonal variability in hydration events in the upper troposphere was found and linked to the convective activity within the SWIO basin. In the upper troposphere, ozone mixing ratios were lower (mean of 57 ppbv) in humid air masses (RH > 50 %) compared to the background mean ozone mixing ratio (73.8 ppbv). A convective signature was identified in the ozone profile dataset by studying the probability of occurrence of different ozone thresholds. It was found that ozone mixing ratios lower than 45 to 50 ppbv had a local maximum of occurrence between 10 and 13 km in altitude, indicative of the mean level of convective outflow. Combining FLEXPART Lagrangian back trajectories with METEOSAT-7 infrared brightness temperature products, we established the origin of convective influence on the upper troposphere above Réunion island. It has been found that the upper troposphere above Réunion island is impacted by convective outflows in austral summer. Most of the time, deep convection is not observed in the direct vicinity of the island, but it is observed more than 1000 km away from the island, in the tropics, either from tropical storms or the Intertropical Convection Zone (ITCZ). In November and December, the air masses above Réunion island originate, on average, from central Africa and the Mozambique Channel. During January and February the source region is the northeast of Mozambique and Madagascar. Those results improve our understanding of the impact of the ITCZ and tropical cyclones on the hydration of the upper troposphere in the subtropics in the SWIO.

scholarly journals Investigating the source, transport, and isotope composition of water vapor in the planetary boundary layer

2016 ◽  
Vol 16 (8) ◽  
pp. 5139-5157 ◽  
Author(s):  
Timothy J. Griffis ◽  
Jeffrey D. Wood ◽  
John M. Baker ◽  
Xuhui Lee ◽  
Ke Xiao ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Water Vapor ◽  
Planetary Boundary Layer ◽  
Isotope Composition ◽  
Convective Precipitation ◽  
Mixing Ratio ◽  
Rayleigh Distillation ◽  
Water Vapor Mixing Ratio ◽  
Isotope Composition Of Water ◽  
Tall Tower

Abstract. Increasing atmospheric humidity and convective precipitation over land provide evidence of intensification of the hydrologic cycle – an expected response to surface warming. The extent to which terrestrial ecosystems modulate these hydrologic factors is important to understand feedbacks in the climate system. We measured the oxygen and hydrogen isotope composition of water vapor at a very tall tower (185 m) in the upper Midwest, United States, to diagnose the sources, transport, and fractionation of water vapor in the planetary boundary layer (PBL) over a 3-year period (2010 to 2012). These measurements represent the first set of annual water vapor isotope observations for this region. Several simple isotope models and cross-wavelet analyses were used to assess the importance of the Rayleigh distillation process, evaporation, and PBL entrainment processes on the isotope composition of water vapor. The vapor isotope composition at this tall tower site showed a large seasonal amplitude (mean monthly δ18Ov ranged from −40.2 to −15.9 ‰ and δ2Hv ranged from −278.7 to −113.0 ‰) and followed the familiar Rayleigh distillation relation with water vapor mixing ratio when considering the entire hourly data set. However, this relation was strongly modulated by evaporation and PBL entrainment processes at timescales ranging from hours to several days. The wavelet coherence spectra indicate that the oxygen isotope ratio and the deuterium excess (dv) of water vapor are sensitive to synoptic and PBL processes. According to the phase of the coherence analyses, we show that evaporation often leads changes in dv, confirming that it is a potential tracer of regional evaporation. Isotope mixing models indicate that on average about 31 % of the growing season PBL water vapor is derived from regional evaporation. However, isoforcing calculations and mixing model analyses for high PBL water vapor mixing ratio events ( >  25 mmol mol−1) indicate that regional evaporation can account for 40 to 60 % of the PBL water vapor. These estimates are in relatively good agreement with that derived from numerical weather model simulations. This relatively large fraction of evaporation-derived water vapor implies that evaporation has an important impact on the precipitation recycling ratio within the region. Based on multiple constraints, we estimate that the summer season recycling fraction is about 30 %, indicating a potentially important link with convective precipitation.

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