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The molecules feeding life's emergence are thought to have been provided through the hydrothermal interactions of convecting carbonic ocean waters with minerals comprising the early Hadean oceanic crust. Few laboratory experiments have simulated ancient hydrothermal conditions to test this conjecture. We used the JPL hydrothermal flow reactor to investigate CO

Real-time monitoring of exhaled carbon dioxide (CO2), also known as capnography, is a valuable hospital tool for assessing patient health during anesthesia and in both the emergency department and critical care units. The fundamental measurement is referred to as end-tidal carbon dioxide concentration that reflects pulmonary gas exchange of CO2representing systemic metabolism. The shape of the exhaled CO2concentration for individual inhalation/exhalation breath cycles can offer additional information regarding lung function, airway obstruction, alveolar ventilation, and worsening disease. The most frequent use is to indicate appropriate placement of an endotracheal tube but and it is also employed in the assessment of disease severity and response to treatment (e.g. asthma). Other applications include outpatient monitoring with oxygen supplementation (nasal cannula) and continuous positive airway pressure control for sleep apnea. As technology has evolved, CO2measurements have become more mobile; capnography systems are now used by emergency medical services personnel for verifying proper placement of airway devices in 'pre-hospital' environments. The use of CO2diagnostics has evolved to identify breathing system disruptions in 'on-demand' regulator/masks equipment, both in medical and occupational settings. Most recently, miniaturized tunable laser spectroscopy sensors have been implemented for assessing pilot breathing in high-performance military aircraft. This editorial describes the use of CO2breath sensors and proposes some new applications based on miniaturized sensors that can be directly inserted into breathing masks.

With the availability of high-power (milliwatts) single-mode tunable laser sources that operate at room temperature across the infrared (IR) region, tunable laser spectrometers have seen an explosion of growth in applications that include commercial, Earth and planetary science, and medical and industrial sensing. While the laser sources themselves have shown steady improvement, the detection architecture of using a single-element detector at one end of a multipass cell has remained unchanged over the last few decades. We present here an innovative new approach using a detector array coupled to an IR-transmissive mirror to image all or part of the multipass spot pattern of the far mirror and record spectra for each pixel. This novel approach offers improved sensitivity, increased dynamic range, laser power normalization, contaminant subtraction, resilience to misalignment, and reduces the instrument power requirement by avoiding the need for “fringe-wash” heaters. With many tens of pixels representing each spot during the laser spectral scan, intensity and optical fringe amplitude and phase information are recorded. This allows selection and manipulation (e.g., co-addition, subtraction) of the pixel output spectra to minimize optical interference fringes thereby increasing sensitivity. We demonstrate a factor of ∼ 20 sensitivity improvement over traditional single-element detection. Dynamic range increase of a factor of ∼ 100 is also demonstrated through spot selection representing different pathlengths. Additionally, subtracting the spectrum of the first spot from that of the higher pass normalizes the laser power and removes the contribution of contaminant gas and fringes in the fore-optics region. These initial results show that this imaging method is particularly advantageous for multi-channel laser spectrometers, and, once the image field is analyzed, pixel selection can be used to minimize data rate and volume collection requirements. This technique could be beneficial to enhanced-cavity detection schemes.

Tunable laser spectroscopy (TLS) near 2683 nm was used to measure carbon dioxide and water vapor inside a pilot mask during jet fighter flights. Measurement frequency was 100 Hz in order to capture breathing profiles and other gas flow dynamics. Analysis of the full inhalation and exhalation breathing cycle allowed precise monitoring of breathing performance and interaction of the pilot with the life-support system. Measurements revealed dynamic phenomena pertaining to mechanical gas flow and pilot respiration that may be used to understand gas delivery stresses imposed upon the pilot and pilot physiology during flight. Typically, such measurements are made with non-dispersive infrared instrumentation for only carbon dioxide with intrinsic challenges regarding time and optical resolution. The TLS approach is a major advance because the sensor is placed directly into the mask improving its time response and enabling use of water vapor measurements that are less impacted from memory effects. This article presents the implementation of TLS and shows highly time-resolved pilot breathing data for high-performance aircraft tests.

This paper describes a data quality aware framework for developing a repeatable flight mission design for fugitive methane sniffing missions using fixed wing small unmanned aerial systems (sUAS) in rural areas. The design outlines general aircraft requirements & performance characteristics as well as overviews required sensors and their performance & data quality considerations. Using Gaussian plume models, atmospheric stability and detection experiments from previous works - we outline a mission design that focuses on detection of downwind plume using a two flux plane flight path. This mission design aims to aid future efforts in improving flux quantification accuracy, uncertainty and comparison between individual experiments.

The conceptual model of Cabeco de Vide mineral waters, issuing at the contact metamorphism zone developed by the local mafic/ultramafic pluton, is described. These mineral waters discharge with a temperature between 17 and 20°C, show a very alkaline pH (up to 11.8), and have: Na-Cl/Ca-OH facies; dry residuum ≈ 200mg/L; Ctotal < 3.0mg/L; and extremely low Mg2+ and silica concentrations (< 0.3 and 6.5mg/L, respectively). CH4 isotopic composition (-24.4 o/oo < δ13C-CH4 < -14.0 o/oo and -285 o/oo < δ2H-CH4 < -218 o/oo) falls in the range of typical abiotic gas. In the case of Cabeco de Vide mineral waters, the understanding of the resource will help to preserve the mineral water quality, creating public interest.

15 páginas.--10 figuras.-- 2 tablas.-- 87 referencias.-- Supplementary data related to this article can be found at https://doi.org/10.1016/j.apgeochem.2018.07.011., Continental active serpentinization of ultramafic rocks is today recognized as a key process triggering a sequence of phenomena involving the passage from inorganic, to organic and metabolic reactions. These may have a role in the origin of life, and may explain the occurrence of abiotic hydrocarbons on Earth and other planets. Production of hyperalkaline waters and abiotic methane (CH4) are two critical steps in this sequence. They were described independently by specific hydrogeological and geochemical models. Here, we update and combine these models into a unified scheme using and integrating geological, hydrogeological, hydrogeochemical, gas-geochemical and microbial analyses acquired from 2002 to 2014 in the Cabeço de Vide (CdV) study site, Portugal. The hyperalkaline (pH > 10.5), Na-Cl/Ca-OH mineral water of CdV evolve from groundwater-peridotite interaction (serpentinization) generating hydrogen (H2), which, according to multiple theoretical, laboratory and field evidence, likely reacted with CO2 within metal- (catalyst) rich rocks, abiotically producing CH4 (up to 1.2 mg/L; -24.4°/oo < δ13C-CH4 < -14.0°/oo and -285°/oo < δ2H-CH4 < -218°/oo). The hyperalkaline water hosts hydrogen oxidizing bacteria “Serpentinomonas” which may explain the paucity of H2 observed in the dissolved gas. The CdV gas-rich mineral waters ascend along a fault at the boundary of the peridotite intrusion. Temporal changes of pH and CH4 concentration result from episodic mixing with shallower Mg-HCO3-type waters. Soil-gas analyses show that methane migrates to the surface along the fault, also independently from the water emergences, consistently with non-aqueous abiotic CH4 production. Our integrated model is generally compatible with observations from other gas-bearing continental serpentinization sites., This study was supported by FCT/MEC (PIDDAC) funds under the scope of the Project PTDC/AAG-MAA/2891/2012, CERENA/IST acknowledges the FCT (the Portuguese Science and Technology Foundation) support through the UID/ECI/04028/2013 Project and C2TN/IST author gratefully acknowledge the FCT support through the UID/Multi/04349/2013. The study on gas origin and emission, performed by INGV, was supported by the Deep Carbon Observatory – Deep Energy community. Work performed at the Jet Propulsion Laboratory, California Institute of Technology, was done under contract with NASA and funded by the NASA Astrobiology Institute (grants 08- NAI5-0021 and 13-13NAI7_2-0024). The authors would like to thank Benjamin Tutolo and an anonymous reviewer for their comments and suggestions in order to improve a previous draft of the manuscript. The authors also would like to thank José Teixeira and Helder Chaminé for redrawing Figs. 1 and 12. The authors also would like to thank L. Rocha, Technical Director of Cabeço de Vide thermal spa, for his support during field work campaigns. Special thanks to the Junta de Freguesia of Cabeço de Vide for all the logistical support during this study. No competing financial interests exist

Accurate and precise measurements of wind are important for understanding atmospheric transport, especially when trying to localize and quantify natural gas emissions from pipeline leaks. This work looks at the applicability of measuring wind speed and direction with mini ultrasonic anemometers on-board small unmanned aerial systems. The 'prop wash effect' from propeller air intake mixing of the wind is quantified through experiments for a multi-rotor platform in a low cost wind tunnel (LCWT). Trisonica and FT742SM sensors are compared through wind tunnel experiments for accuracy confirmation. The validation of measuring wind conditions on-board is compared with accepted estimation techniques for VTOL and fixed wing platforms.

Variable levels of methane in the martian atmosphere have eluded explanation partly because the measurements are not repeatable in time or location.We report in situ measurements at Gale crater made over a 5-year period by the Tunable Laser Spectrometer on the Curiosity rover.The background levels of methane have a mean value 0.41 ± 0.16 parts per billion by volume (ppbv) (95% confidence interval) and exhibit a strong, repeatable seasonal variation (0.24 to 0.65 ppbv).This variation is greater than that predicted from either ultraviolet degradation of impact-delivered organics on the surface or from the annual surface pressure cycle.The large seasonal variation in the background and occurrences of higher temporary spikes (∼7 ppbv) are consistent with small localized sources of methane released from martian surface or subsurface reservoirs., The authors thank the reviewers for constructive comments that greatly improved the manuscript. The research described here was carried out in part at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (NASA). Funding: Funding from NASA’s Planetary Science Division is acknowledged by authors C.R.W., P.R.M., S.K.A., G.J.F., C.M., C.P.M., M.H.W., M.G.T., A.S., D.A., C.H.H., R.V.G., A.P., J.L.E., D.P.G., J.C.P., D.K., L.E.C., J.P.-G., S.C.R.R., M.D.S., D.M.H., M.L., J.C., R.W.Z., and A.R.V. R.N.-G. acknowledges funding from the National Autonomous University of Mexico and Consejo Nacional de Ciencia y Tecnología. J.E.M. and C.L.S. acknowledge funding from the Canadian Space Agency MSL participating scientist program. S.P.Sc. acknowledges funding from the UK Space Agency. A.-M.H. acknowledges funding from the Finnish Academy under grant 310509. J.P.-G. acknowledges funding from the Spanish Ministry of Economy and Competitiveness under contract ESP2016-79612-C3-1-R. Author contributions: C.R.W. and P.R.M. performed TLS-SAM instrument design, build, and testing (IDBT); surface operations (SO); test-bed activities (TBA); data analysis (DA); data correlations (DC); and science interpretation (SI). G.J.F. and C.M. performed IDBT, SO, TBA, and DA. S.K.A., J.E.M., C.P.M., C.L.S., A.S., D.A., B.S., P.J.C., C.F., P.-Y.M., R.V.G., C.H.H., A.P., J.L.E., D.P.G., S.P.Sa., and R.W.Z. performed SI. J.C. and A.R.V. performed SO. J.C.P., D.K., and L.E.C. performed IDBT. G.M., J.M.-T., J.G.-E., M.-P.Z., M.G.T., S.P.Sc., R.N.-G., A.V.-R., H.K., D.V.-M., M.D.S., A.-M.H., M.G., D.M.H., and M.L. performed DC. J.P.-G. and S.C.R.R. performed DC and SI. Competing interests: No potential conflicts of interest exist for any of the listed authors. Data and materials availability: The data described in this paper are publicly available from NASA’s Planetary Data System (PDS) under an arrangement with the Mars Science Laboratory (MSL) project at http://pds-geosciences.wustl.edu/missions/msl/sam. htm, under the run numbers given in table S2.

A miniature in-situ CH4 concentration measurement instrument based upon tunable laser spectroscopy (TLS) was developed and applied in numerous field campaigns. The instrument, a 3.4 μm laser spectrometer developed at NASA Jet Propulsion Lab (JPL), is lightweight (250g), low power (< 8 W), and high sensitivity (10 ppb s−1). The payload was further developed and integrated onto a small UAV at UC Merced, rendering an overall payload weight of 400 g and real-time data acquisition. The remarkable characteristics of the instrument and prior investigative work regarding sensor placement yielded excellent trial and field results, which are presented in this work.

We describe a versatile mid-infrared (Mid-IR) spectroscopy system developed to measure the concentration of a wide range of gases with an ultra-low sample size. The system combines a rapidly-swept external cavity quantum cascade laser (ECQCL) with a hollow fiber gas cell. The ECQCL has sufficient spectral resolution and reproducibility to measure gases with narrow features (e.g., water, methane, ammonia, etc.), and also the spectral tuning range needed to measure volatile organic compounds (VOCs), (e.g., aldehydes, ketones, hydrocarbons), sulfur compounds, chlorine compounds, etc. The hollow fiber is a capillary tube having an internal reflective coating optimized for transmitting the Mid-IR laser beam to a detector. Sample gas introduced into the fiber (e.g., internal volume = 0.6 ml) interacts strongly with the laser beam, and despite relatively modest path lengths (e.g., L ~ 3 m), the requisite quantity of sample needed for sensitive measurements can be significantly less than what is required using conventional IR laser spectroscopy systems. Example measurements are presented including quantification of VOCs relevant for human breath analysis with a sensitivity of ~2 picomoles at a 1 Hz data rate.

Acquiring accurate measurements of water vapor at the low mixing ratios (

We report a new case of methane (CH4) of apparent abiotic origin in continental serpentinized ultramafic rocks. Multiple analytical techniques, on-site and in the laboratory, revealed methane and ethane degassing from hyperalkaline (pH > 11) Ca2+–OH− mineral waters in boreholes drilled in the Alter-do-Chao igneous intrusion, at Cabeco de Vide, in mainland Portugal. The C and H isotopic composition of CH4 (δ13C ∼ −20‰; δ2H: −283‰) suggests a dominant abiotic origin, although minor thermogenic contributions cannot be excluded. Similarly, low methane-to-ethane ratios suggest a predominantly non-microbial source, consistent with previous microbiological data showing the lack of methanogenic archaea in these waters. Heavier hydrocarbons, CO2 and H2 are below detection limits. This case study confirms that CH4 from serpentinized ultramafic rocks can be transported by hyperalkaline fluids linked to deep circulation of meteoric waters. Maximum depth of Cabeco de Vide serpentinized rocks is less than 1 km, and present temperatures are likely lower than 50 °C. Serpentinization and related gas formation may have occurred at any time during thermal evolution of the igneous intrusion, so gas formation temperature cannot be easily determined. This case is an opportunity to test thermometry provided by CH4 isotopologue analyses. The existence of methane in continental serpentinized igneous rocks is more widespread than previously thought and petroleum systems with similar serpentinized ultramafics in reservoir rocks may have traces of the observed 13C-enriched CH4.

The NASA ER-2 aircraft sampled the lower stratosphere over North America during the field mission for the NASA Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS). This study reports observations of convectively influenced air parcels with enhanced water vapor in the overworld stratosphere over the summertime continental United States and investigates three case studies in detail. Water vapor mixing ratios greater than 10 ppmv, which is much higher than the background 4 to 6 ppmv of the overworld stratosphere, were measured by the JPL Laser Hygrometer (JLH Mark2) at altitudes between 16.0 and 17.5 km (potential temperatures of approximately 380 to 410 K). Overshooting cloud tops (OTs) are identified from a SEAC4RS OT detection product based on satellite infrared window channel brightness temperature gradients. Through trajectory analysis, we make the connection between these in situ water measurements and OT. Back trajectory analysis ties enhanced water to OT 1 to 7 days prior to the intercept by the aircraft. The trajectory paths are dominated by the North American monsoon (NAM) anticyclonic circulation. This connection suggests that ice is convectively transported to the overworld stratosphere in OT events and subsequently sublimated; such events may irreversibly enhance stratospheric water vapor in the summer over Mexico and the United States. A regional context is provided by water observations from the Aura Microwave Limb Sounder (MLS).

In light of recent U.S. Federal Aviation Administration (FAA) notices, there is a surge in the research and development of the ‘micro’ class sUAS for commercial purposes. Natural gas production and distribution companies in particular are making an effort to develop aerial leak detection methods with sUAS. These efforts require a comprehensive evaluation of sUAS capabilities and the environmental disturbances introduced by the sUAS in order to accurately utilize data collected via onboard in situ methane gas sensors. Though many commercially available sUAS are on the market, the shape and arrangement of any system has significant impact on the aircraft's ability to accurately sense gas leaks. This paper explores using a 3DRobotics Iris+ quadcopter for gas sensing, paying particular attention to propeller disturbances introduced by the sUAS. The paper defines certain operating conditions in which the influence of propellers can be ignored. These results can be used in gas leak applications by examining the overall airflow dynamics of a commercially available rotary sUAS.

Inclusion of line-mixing into spectroscopic models is required for precise and accurate dry-mole-fraction column CO 2 retrievals from a satellite instrument. We measure first-order line-mixing parameters of thirteen 12 CO 2 20 0 1 3 ←00 0 0 CO 2 transitions near 2.05 μm using tunable laser spectroscopy. We also report line position measurements of twelve 13 CO 2 and 18 OCO transitions in this spectral region. By incorporating line-mixing into a simple atmospheric model, we show how biases in CO 2 retrievals can be generated if line-mixing is ignored.

Of water and methane on Mars The Curiosity rover has been collecting data for the past 2 years, since its delivery to Mars (see the Perspective by Zahnle). Many studies now suggest that many millions of years ago, Mars was warmer and wetter than it is today. But those conditions required an atmosphere that seems to have vanished. Using the Curiosity rover, Mahaffy et al. measured the ratio of deuterium to hydrogen in clays that were formed 3.0 to 3.7 billion years ago. Hydrogen escapes more readily than deuterium, so this ratio offers a snapshot measure of the ancient atmosphere that can help constrain when and how it disappeared. Most methane on Earth has a biological origin, so planetary scientists have keenly pursued its detection in the martian atmosphere as well. Now, Webster et al. have precisely confirmed the presence of methane in the martian atmosphere with the instruments aboard the Curiosity rover at Gale crater. Science , this issue p. 412 , p. 415 ; see also p. 370

As universal products of biological processes, volatile organic sulfur compounds such as methyl mercaptan (CH3SH) may be essential in the search for signs of life on Mars and in exoplanet atmospheres. Methyl mercaptan is implicated in the origin of life at sites of low-temperature hydrothermal activity driven by serpentinization. Serpentinization may occur on Mars, in icy satellite oceans, and in other small wet bodies to a greater extent than on Earth, with important implications for life. We characterized absorption features in pure laboratory sample spectra of CH3SH using the Carbon Isotope Laser Spectrometer (CILS), an infrared ( 3.27 μ m ) tunable diode laser spectrometer with capabilities nearly identical to those of the Tunable Laser Spectrometer (TLS) instrument on the Mars Science Laboratory. The molecular species proves detectable by CILS and TLS at the sensitivities approaching the level of parts per trillion with pre-concentration. These measurements demonstrate the possibility for detection of methyl mercaptan, with implications for its possible use as an in situ biosignature for Earth-based and extraterrestrial exploration.

We present results of early validation studies using retrieved atmospheric profiles from the Earth Observing System Microwave Limb Sounder (MLS) instrument on the Aura satellite. "Global" results are presented for MLS measurements of atmospheric temperature, ozone, water vapor, hydrogen chloride, nitrous oxide, nitric acid, and carbon monoxide, with a focus on the January-March 2005 time period. These global comparisons are made using long-standing global satellites and meteorological datasets, as well as some measurements from more recently launched satellites. Comparisons of MLS data with measurements from the Ft. Sumner, NM, September 2004 balloon flights are also presented. Overall, good agreement is obtained, often within 5% to 10%, but we point out certain issues to resolve and some larger systematic differences; some artifacts in the first publicly released MLS (version 1.5) dataset are noted. We comment briefly on future plans for validation and software improvements.

Rate coefficients for the reaction HO_2 + NO_2 + N_2 → HO_2NO_2 + N_2 (reaction 1) were measured using simultaneous near-IR and UV spectroscopy from 220 to 298 K and from 45 to 200 Torr. Using the data acquired in the present experiment, the low-pressure and high-pressure limit rate constants for reaction 1 were determined to be k_o = (2.1 ± 0.1) × 10^(-31) × (T/300)^(-(3.1±0.3)) cm^6 molecule^(-2) s^(-1) and k∞ = (2.4 ± 0.1) × 10^(-12) × (T/300))^(-(1.9±0.5)) cm^3 molecule^(-1) s^(-1), using the expressions for rate constants adopted by the NASA data evaluation panel (F_c = 0.6). The reaction rate was significantly enhanced in the presence of methanol due to a chaperone effect involving an HO_2·CH_3OH complex. Enhancement parameters for this process were quantified as a function of temperature. During the course of our studies, we observed an unexpected time-dependent UV absorption unaccounted for in previous examinations of reaction 1 that employed UV spectroscopy to monitor HO_2. We show that this absorption, which may have led to errors in those prior studies, is due to the process NO_2 + NO_2 ⇄ N_2O_4 (reaction 3). Using UV−visible spectroscopy, we determine k_(-3) to be (36 ± 10) s^(-1) at 231 K and 100 Torr using the NASA-recommended equilibrium constant for the dimerization of NO_2. This represents the first measurement of k_(-3) at T < 250 K.

Of water and methane on Mars The Curiosity rover has been collecting data for the past 2 years, since its delivery to Mars (see the Perspective by Zahnle). Many studies now suggest that many millions of years ago, Mars was warmer and wetter than it is today. But those conditions required an atmosphere that seems to have vanished. Using the Curiosity rover, Mahaffy et al. measured the ratio of deuterium to hydrogen in clays that were formed 3.0 to 3.7 billion years ago. Hydrogen escapes more readily than deuterium, so this ratio offers a snapshot measure of the ancient atmosphere that can help constrain when and how it disappeared. Most methane on Earth has a biological origin, so planetary scientists have keenly pursued its detection in the martian atmosphere as well. Now, Webster et al. have precisely confirmed the presence of methane in the martian atmosphere with the instruments aboard the Curiosity rover at Gale crater. Science , this issue p. 412 , p. 415 ; see also p. 370

H 2 O, CO 2 , SO 2 , O 2 , H 2 , H 2 S, HCl, chlorinated hydrocarbons, NO, and other trace gases were evolved during pyrolysis of two mudstone samples acquired by the Curiosity rover at Yellowknife Bay within Gale crater, Mars. H 2 O/OH-bearing phases included 2:1 phyllosilicate(s), bassanite, akaganeite, and amorphous materials. Thermal decomposition of carbonates and combustion of organic materials are candidate sources for the CO 2 . Concurrent evolution of O 2 and chlorinated hydrocarbons suggests the presence of oxychlorine phase(s). Sulfides are likely sources for sulfur-bearing species. Higher abundances of chlorinated hydrocarbons in the mudstone compared with Rocknest windblown materials previously analyzed by Curiosity suggest that indigenous martian or meteoritic organic carbon sources may be preserved in the mudstone; however, the carbon source for the chlorinated hydrocarbons is not definitively of martian origin.

The AquaVIT-1 Intercomparison of Atmospheric Water Vapor Measurement Techniques was conducted at the aerosol and cloud simulation chamber AIDA at the Karlsruhe Institute of Technology, Germany, in October 2007. The overall objective was to intercompare state-of-the-art and prototype atmospheric hygrometers with each other and with independent humidity standards under controlled conditions. This activity was conducted as a blind intercomparison with coordination by selected referees. The effort was motivated by persistent discrepancies found in atmospheric measurements involving multiple instruments operating on research aircraft and balloon platforms, particularly in the upper troposphere and lower stratosphere where water vapor reaches its lowest atmospheric values (less than 10 ppm). With the AIDA chamber volume of 84 m3, multiple instruments analyzed air with a common water vapor mixing ratio, either by extracting air into instrument flow systems, locating instruments inside the chamber, or sampling the chamber volume optically. The intercomparison was successfully conducted over 10 days during which pressure, temperature, and mixing ratio were systematically varied (50 to 500 hPa, 185 to 243 K, and 0.3 to 152 ppm). In the absence of an accepted reference instrument, the reference value was taken to be the ensemble mean of a core subset of the measurements. For these core instruments, the agreement between 10 and 150 ppm of water vapor is considered good with variation about the reference value of about ±10% (±1σ). In the region of most interest between 1 and 10 ppm, the core subset agreement is fair with variation about the reference value of ±20% (±1σ). The upper limit of precision was also derived for each instrument from the reported data. These results indicate that the core instruments, in general, have intrinsic skill to determine unknown water vapor mixing ratios with an accuracy of at least ±20%. The implication for atmospheric measurements is that the substantially larger differences observed during in-flight intercomparisons stem from other factors associated with the moving platforms or the non-laboratory environment. The success of AquaVIT-1 provides a template for future intercomparison efforts with water vapor or other species that are focused on improving the analytical quality of atmospheric measurements on moving platforms.

Mars' Atmosphere from Curiosity The Sample Analysis at Mars (SAM) instrument on the Curiosity rover that landed on Mars in August last year is designed to study the chemical and isotopic composition of the martian atmosphere. Mahaffy et al. (p. 263 ) present volume-mixing ratios of Mars' five major atmospheric constituents (CO 2 , Ar, N 2 , O 2 , and CO) and isotope measurements of 40 Ar/ 36 Ar and C and O in CO 2 , based on data from one of SAM's instruments, obtained between 31 August and 21 November 2012. Webster et al. (p. 260 ) used data from another of SAM's instruments obtained around the same period to determine isotope ratios of H, C, and O in atmospheric CO 2 and H 2 O. Agreement between the isotopic ratios measured by SAM with those of martian meteorites, measured in laboratories on Earth, confirms the origin of these meteorites and implies that the current atmospheric reservoirs of CO 2 and H 2 O were largely established after the period of early atmospheric loss some 4 billion years ago.

[1] Recent studies have suggested that CH4 emissions in Los Angeles and other large cities may be underestimated. We utilized stable isotopes (13C and D) and radiocarbon (14C) to investigate sources of CH4 in Los Angeles, California. First, we made measurements of δ13C and δD of various CH4 sources in urban areas. Fossil fuel CH4 sources (oil refineries, power plants, traffic, and oil drilling fields) had δ13C values between −45 and −30‰ and dD values between −275 and −100‰, whereas biological CH4 (cows, biofuels, landfills, sewage treatment plants, and cattle feedlots) had δ13C values between −65 and −45‰ and δD values between −350 and −275‰. We made high-altitude observations of CH4 concentration using continuous tunable laser spectroscopy measurements combined with isotope analyses (13C, 14C, and D) of discrete samples to constrain urban CH4 sources. Our data indicate that the dominant source of CH4 in Los Angeles has a δ13C value of approximately −41.5‰ and a δD value between −229 and −208‰. Δ14C of CH4 in urban air samples ranged from +262 to +344‰ (127.1 to 134.9 pMC), depleted with respect to average global background CH4. We conclude that the major source of CH4 in Los Angeles is leakage of fossil fuels, such as from geologic formations, natural gas pipelines, oil refining, and/or power plants. More research is needed to constrain fluxes of CH4 from natural gas distribution and refining, as this flux may increase with greater reliance on natural gas and biogas for energy needs.

[1] Water vapor in the subtropical troposphere plays an important role in the radiative balance, the distribution of precipitation, and the chemistry of the Earth's atmosphere. Measurements of the water vapor mixing ratio paired with stable isotope ratios provide unique information on transport processes and moisture sources that is not available with mixing ratio data alone. Measurements of the D/H isotope ratio of water vapor from Mauna Loa Observatory over 4 weeks in October–November 2008 were used to identify components of the regional hydrological cycle. A mixing model exploits the isotope information to identify water fluxes from time series data. Mixing is associated with exchange between marine boundary layer air and tropospheric air on diurnal time scales and between different tropospheric air masses with characteristics that evolve on the synoptic time scale. Diurnal variations are associated with upslope flow and the transition from nighttime air above the marine trade inversion to marine boundary layer air during daytime. During easterly trade wind conditions, growth and decay of the boundary layer are largely conservative in a regional context but contribute ∼12% of the nighttime water vapor at Mauna Loa. Tropospheric moisture is associated with convective outflow and exchange with drier air originating from higher latitude or higher altitude. During the passage of a moist filament, boundary layer exchange is enhanced. Isotopic data reflect the combination of processes that control the water balance, which highlights the utility for baseline measurements of water vapor isotopologues in monitoring the response of the hydrological cycle to climate change.

The Jet Propulsion Laboratory Carbon Dioxide Laser Absorption Spectrometer (CO2LAS) utilizes Integrated Path Differential Absorption (IPDA) at 2.05 μm to obtain CO 2 column mixing ratios weighted heavily in the boundary layer. CO2LAS employs a coherent detection receiver and continuous-wave Th:Ho:YLF laser transmitters with output powers around 100 milliwatts. An offset frequency-locking scheme coupled to an absolute frequency reference enables the frequencies of the online and offline lasers to be held to within 200 kHz of desired values. We describe results from 2009 field campaigns when CO2LAS flew on the Twin Otter. We also describe spectroscopic studies aimed at uncovering potential biases in lidar CO 2 retrievals at 2.05 μm.

We report airborne measurements of CO(2) column abundance conducted during two 2009 campaigns using a 2.05 μm laser absorption spectrometer. The two flight campaigns took place in the California Mojave desert and in Oklahoma. The integrated path differential absorption (IPDA) method is used for the CO(2) column mixing ratio retrievals. This instrument and the data analysis methodology provide insight into the capabilities of the IPDA method for both airborne measurements and future global-scale CO(2) measurements from low Earth orbit pertinent to the NASA Active Sensing of CO(2) Emissions over Nights, Days, and Seasons mission. The use of a favorable absorption line in the CO(2) 2 μm band allows the on-line frequency to be displaced two (surface pressure) half-widths from line center, providing high sensitivity to the lower tropospheric CO(2). The measurement repeatability and measurement precision are in good agreement with predicted estimates. We also report comparisons with airborne in situ measurements conducted during the Oklahoma campaign.

We present a climatology of O3, CO, and H2O for the upper troposphere and lower stratosphere (UTLS), based on a large collection of high-resolution research aircraft data taken between 1995 and 2008. To group aircraft observations with sparse horizontal coverage, the UTLS is divided into three regimes: the tropics, subtropics, and the polar region. These regimes are defined using a set of simple criteria based on tropopause height and multiple tropopause conditions. Tropopause-referenced tracer profiles and tracer-tracer correlations show distinct characteristics for each regime, which reflect the underlying transport processes. The UTLS climatology derived here shows many features of earlier climatologies. In addition, mixed air masses in the subtropics, identified by O3-CO correlations, show two characteristic modes in the tracer-tracer space that are a result of mixed air masses in layers above and below the tropopause (TP). A thin layer of mixed air (1–2 km around the tropopause) is identified for all regions and seasons, where tracer gradients across the TP are largest. The most pronounced influence of mixing between the tropical transition layer and the subtropics was found in spring and summer in the region above 380 K potential temperature. The vertical extent of mixed air masses between UT and LS reaches up to 5 km above the TP. The tracer correlations and distributions in the UTLS derived here can serve as a reference for model and satellite data evaluation.

The Aura Validation Experiment (AVE) focuses on validating Aura satellite measurements of important atmospheric trace gases using ground-based, aircraft, and balloon-borne instruments. Global satellite observations of CO from the Tropospheric Emission Spectrometer (TES) on the EOS Aura satellite have been ongoing since September 2004. This paper discusses CO validation experiments during the Oct-AVE (2004 Houston, Texas) and CR-AVE (2006 San Jose, Costa Rica) campaigns. The coincidences in location and time between the satellite observations and the available in situ profiles for some cases are not ideal. However, the CO distribution patterns in the two validation flight areas are shown to have very little variability in the aircraft and satellite . observations, thereby making them suitable for validation comparisons. TES CO profiles, which typically have a retrieval uncertainty of 10-20%, are compared with in situ CO measurements from NASA Ames Research Center's Argus instrument taken on board the WB-57F aircraft during Oct-AVE. TES CO retrievals during CR-AVE are compared with in situ measurements from Jet Propulsion Laboratory's Aircraft Laser Infrared Absorption Spectrometer (ALIAS) instrument as well as with the Argus instrument, both taken on board the WB-57F aircraft. During CR-AVE, the average overall difference between ALIAS and Argus CO was 4%, with the ALIAS measurement higher. During individual flights, 2-min time-averaged differences between the two in situ instruments had standard deviation of 14%. The TES averaging kernels and a priori constraint profiles for CO are applied to the in situ data for proper comparisons to account for the reduced vertical resolution and the influence of the a priori in the satellite-derived profile. In the TES sensitive pressure range, approx.700-200 hPa, the in situ profiles and TES profiles agree within 5-10%, less than the variability in CO distributions obtained by both TES and the aircraft instruments in the two regions. TES CO is slightly lower than in situ measurements in the Houston area (midlatitudes) and slightly higher than in situ CO measurements in the Costa Rica region (tropical).

The Earth Observing System (EOS) Microwave Limb Sounder (MLS) aboard the Aura satellite has provided daily global HCl profiles since August 2004. We provide a characterization of the resolution, random and systematic uncertainties, and known issues for the version 2.2 MLS HCl data. The MLS sampling allows for comparisons with many (similar to 1500 to more than 3000) closely matched profiles from the Halogen Occultation Experiment (HALOE) and Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS). These data sets provide HCl latitudinal distributions that are, overall, very similar to those from (coincident) MLS profiles, although there are some discrepancies in the upper stratosphere between the MLS and HALOE gradients. As found in previous work, MLS and ACE HCl profiles agree very well (within similar to 5%, on average), but the MLS HCl abundances are generally larger (by 10-20%) than HALOE HCl. The bias versus HALOE is unlikely to arise mostly from MLS, as a similar systematic bias (of order 15%) is not observed between average MLS and balloon-borne measurements of HCl, obtained over Fort Sumner, New Mexico, in 2004 and 2005. At the largest pressure (147 hPa) for MLS HCl, a high bias (similar to 0.2 ppbv) is apparent in analyses of low to midlatitude data versus in situ aircraft chemical ionization mass spectrometry (CIMS) HCl measurements from the Aura Validation Experiment (AVE) campaigns in 2004, 2005, and 2006; this bias is also observed in comparisons of MLS and aircraft HCl/O-3 correlations. Good agreement between MLS and CIMS HCl is obtained at 100 to 68 hPa. The recommended pressure range for MLS HCl is from 100 to 0.15 hPa.

Global satellite observations of ozone and carbon monoxide from the Microwave Limb Sounder (MLS) on the EOS Aura spacecraft are discussed with emphasis on those observations in the 215-100 hPa region (the upper troposphere and lower stratosphere). The precision, resolution and accuracy of the data produced by the MLS "version 2.2'' processing algorithms are discussed and quantified. O-3 accuracy is estimated at similar to 40 ppbv + 5% (similar to 20 ppbv + 20% at 215 hPa) while the CO accuracy is estimated at similar to 30 ppbv + 30% for pressures of 147 hPa and less. Comparisons with expectations and other observations show good agreements for the O3 product, generally consistent with the systematic errors quoted above. In the case of CO, a persistent factor of similar to 2 high bias is seen at 215 hPa. However, the morphology is shown to be realistic, consistent with raw MLS radiance data, and useful for scientific study. The MLS CO data at higher altitudes are shown to be consistent with other observations.

[1] The validation of version 2.2 (v2.2) H2O measurements from the Earth Observing System (EOS) Microwave Limb Sounder (Aura MLS) on the Aura satellite are presented. Results from comparisons made with Aqua Atmospheric Infrared Sounder (AIRS), Vaisala radiosondes, frost point hygrometer, and WB57 aircraft hygrometers are presented. Comparisons with the Aura MLS v1.5 H2O, Goddard global modeling and assimilation office Earth Observing System analyses (GEOS-5) are also discussed. For H2O mixing ratios less than 500 ppmv, the MLS v2.2 has an accuracy better than 25% between 316 and 147 hPa. The precision is 65% at 316 hPa that reduces to 25% at 147 hPa. This performance is better than expected from MLS measurement systematic error analyses. MLS overestimates H2O for mixing ratios greater than 500 ppmv which is consistent with a scaling error in either the calibrated or calculated MLS radiances. The validation of the accuracy of MLS v2.2 H2O from 121 to 83 hPa which is expected to be better than 15% cannot be confirmed at this time because of large disagreements among the hygrometers used in the AVE campaigns. The precision of the v2.2 H2O from 121 to 83 hPa is 10–20%. The vertical resolution is 1.5–3.5 km depending on height. The horizontal resolution is 210 × 7 km2 along and perpendicular to the Aura orbit track, respectively. Relative humidity is calculated from H2O and temperature. The precision, accuracy, and spatial resolution are worse than for H2O.

In situ observations in a tropical subvisible cirrus cloud during the Costa Rica Aura Validation Experiment on 2 February 2006 show the presence of condensed-phase nitric acid. The cloud was observed near the tropopause at altitudes of 16.3–17.7 km in an extremely cold (183–191 K) and dry (.lt. 5 ppm H2O) air mass. Relative humidities with respect to ice ranged from 150–250% throughout most of the cloud. Optical particle measurements indicate the presence of ice crystals as large as 90 μm in diameter. Condensed HNO3/H2O molar ratios observed in the cloud particles were 1–2 orders of magnitude greater than ratios observed previously in cirrus clouds at similar HNO3 partial pressures. Nitric acid trihydrate saturation ratios were 10 or greater during much of the cloud encounter, indicating that HNO3 may be present in the cloud particles as a stable condensate and not simply physically adsorbed on or trapped in the particles

Sulfur isotope measurements offer comprehensive information on the origin and history of natural materials. Tunable laser spectroscopy is a powerful analytical technique for isotope analysis that has proven itself readily adaptable for in situ terrestrial and planetary measurements. Measurements of delta(34)S in SO2 were made using tunable laser spectroscopy of combusted gas samples from six sulfur-bearing solids with delta(34)S ranging from -34 to +22 per thousand (also measured with mass spectrometry). Standard deviation between laser and mass spectrometer measurements was 3.7 per thousand for sample sizes of 200 +/- 75 nmol SO(2). Although SO(2)(g) decreased 9% over 15 min upon entrainment in the analysis cell from wall uptake, observed fractionation was insignificant (+0.2 +/- 0.6 per thousand). We also describe a strong, distinct (33)SO(2) rovibrational transition in the same spectral region, which may enable simultaneous delta(34)S and Delta(33)S measurements.

Aircraft and balloon in situ measurements of CH4 and HCl using cw distributed feedback (DFB) interband cascade (IC) lasers are reported. In the stratosphere and upper troposphere, sensitivity toward CH4 and HCl is better than 10 ppbv (1 s) and 90 pptv (50 s), respectively. These are the first flight measurements of trace gas-phase species using cw DFB IC lasers.

Near-infrared spectroscopy was used to monitor HO_2 formed by pulsed laser photolysis of Cl_2−O_2−CH_3OH−N_2 mixtures. On the microsecond time scale, [HO_2] exhibited a time dependence consistent with a mechanism in which [HO_2] approached equilibrium via HO_2 + HO_3OH^M⇆_M HO_2·CH_3OH (3, −3). The equilibrium constant for reaction 3, Kp, was measured between 231 and 261 K at 50 and 100 Torr, leading to standard reaction enthalpy and entropy values (1 σ) of Δ_rH°_(246K) = −37.4 ± 4.8 kJ mol^(-1) and Δ_rS°_(246K) = −100 ± 19 J mol^(-1) K^(-1). The effective bimolecular rate constant, k_3, for formation of the HO_2·CH_3OH complex is 2.8^(+7.5)_(-2.0)·10^(-15)·exp[(1800 ± 500)/T] cm^3 molecule^(-1) s^(-1) at 100 Torr (1 σ). Ab initio calculations of the optimized structure and energetics of the HO_2·CH_3OH complex were performed at the CCSD(T)/6-311++G(3df,3pd)//MP2(full)/6-311++G(2df,2pd) level. The complex was found to have a strong hydrogen bond (D_e = 43.9 kJ mol^(-1)) with the hydrogen in HO_2 binding to the oxygen in CH_3OH. The calculated enthalpy for association is Δ_rH°_(245K) = −36.8 kJ mol^(-1). The potentials for the torsion about the O_2−H bond and for the hydrogen-bond stretch were computed and 1D vibrational levels determined. After explicitly accounting for these degrees of freedom, the calculated Third Law entropy of association is Δ_rS°_(245K) = −106 J mol^(-1) K^(-1). Both the calculated enthalpy and entropy of association are in reasonably good agreement with experiment. When combined with results from our previous study (Christensen et al. Geophys. Res. Lett. 2002, 29; doi:10.1029/2001GL014525), the rate coefficient for the reaction of HO_2 with the complex, HO_2 + HO_2·CH_3-OH, is determined to be (2.1 ± 0.7) × 10^(-11) cm^3 molecule^(-1) s^(-1). The results of the present work argue for a reinterpretation of the recent measurement of the HO_2 self-reaction rate constant by Stone and Rowley (Phys. Chem. Chem. Phys. 2005, 7, 2156). Significant complex concentrations are present at the high methanol concentrations used in that work and lead to a nonlinear methanol dependence of the apparent rate constant. This nonlinearity introduces substantial uncertainty in the extrapolation to zero methanol.

Type-II interband cascade lasers are efficient and compact mid-infrared (3-5 μm) light sources with many applications such as gas sensing and environmental monitoring. Significant progress toward such a goal has recently been made in terms of achieving low threshold current densities (e.g. ∼8 A/cm 2 at 80 K), high temperature operation (e.g. 325 K in pulsed and 217 K in cw modes), and continuous wave operation of single-mode distributed feedback (DFB) lasers. These DFB lasers have been integrated into laboratory spectrometers for detection of gases such as CH 4 and HCl. One laser was flown on a high-altitude balloon instrument and measured HCl profiles in the stratosphere as part of Aura satellite instrument validation. We review the recent progress of Sb-based mid-IR IC lasers and address the requirements for further improvements in their performance.

[1] This paper provides an initial assessment of the accuracy of the Atmospheric Infrared Sounder (AIRS) water vapor retrievals from 500 to 100 mbar. AIRS satellite measurements are compared with accurate aircraft (NASA WB57) and balloon in situ water vapor measurements obtained during the NASA Pre-Aura Validation Experiment (Pre-AVE) in Costa Rica during Jan. 2004. AIRS retrieval (each pressure level of a single footprint) of water vapor amount agrees with the in situ measurements to ∼25% or better if matched closely in time (1 hr) and space (50–100 km). Both AIRS and in situ measurements observe similar significant variation in moisture amount over a two-day period, associated with large-scale changes in weather patterns.

The development of interband cascade lasers from concept to packaged devices is briefly reviewed. The application of a single-mode, mid-IR (3.27-µm) interband cascade laser packaged with a thermoelectric cooler for field measurements of methane and water is described.

Supersaturations, microphysics and nitric acid partitioning in a very cold subvisible tropical cirrus cloud observed on 2 February 2006, during the field campaign CR-AVE, are studied by comparing a simulated set of possible cloud development scenarios with the in situ observations. The scenario that best matches the observations is a cirrus cloud forming by heterogeneous freezing of a small number of ice nuclei with subsequent unimpeded mass accommodation of water on ice. Variation of the freezing process, the accommodation coefficient or the amount of available water leads to simulated clouds that differ microphysically from the observed cloud in important respects. In particular, the simulations suggest that heterogeneous ice nucleation or another freezing mechanism producing only a low number of ice crystals could be an important process for cold cirrus cloud formation, possibly explaining the frequent observations of high supersaturations inside the cirrus cloud in this temperature regime.