Trends in atmospheric halogen containing gases since 2004

The changes in the atmospheric concentration of 16 halogenated gases in the atmosphere have been determined using measurements made by the Atmospheric Chemistry Experiment Fourier transform spectrometer (ACE-FTS). ACE-FTS has been used to measure the change in concentration between 2004 and 2010 of CCl₄, CF₄, CCl₃F (CFC-11), CCl₂F₂ (CFC-12), C₂Cl₃F₃ (CFC-113), CH₃Cl, ClONO₂, COF₂, COCl₂, COClF, CHF₂Cl (HCFC-22), CH₃CCl₂F (HCFC-141b), CH₃CClF₂ (HCFC-142b), HCl, HF and SF₆ between 30°N and 30°S. ACE-FTS measurements were compared to surface measurements made by the AGAGE network and output from the SLIMCAT three-dimensional (3-D) chemical transport model, which is constrained by similar surface data. ACE-FTS measurements of CFCs show declining trends which agree with both AGAGE and SLIMCAT values. There are problems with the ACE-FTS retrievals of CFC-113 and HCFCs, with work currently ongoing to correct these problems. At lower altitudes the volume mixing ratio (VMR) of these species increase with altitude. This is due to problems with the retrievals at high beta angle (the angle between the orbital plane and the Earth-Sun vector). Although some of the retrievals have problems, we are confident that the trends are generally reliable. The concentrations of HCFCs appear to be increasing with ACE-FTS, SLIMCAT and AGAGE all showing positive trends. ACE-FTS measurements of the decomposition products (COFCl and COCl₂) do not show any significant trends. SLIMCAT data show a negative trend for COFCl which corresponds to the decrease in CFC-11, its assumed major source, during this time. COF₂ measurements from ACE-FTS show an increasing trend, while SLIMCAT shows a decreasing trend again linked to its assumed production from CFCs. ClONO₂ is highly photosensitive, thus the ACE-FTS occultations have been divided into local morning and evening occultations. Evening measurements of ClONO₂ show a decreasing trend in VMR, while morning measurements show an increasing trend. The reason for this difference is not understood at this time. The SLIMCAT output used in this study was not saved as local sunrise and sunset: therefore, only 24 h mean fields are available for ClONO₂. These SLIMCAT data show a decreasing trend. SLIMCAT and ACE-FTS both show an increasing trend in the VMR of HF and a decreasing trend in the VMR of HCl. These results illustrate the success of the Montreal Protocol in reducing ozone depleting substances. The reduction in anthropogenic chlorine emissions has led to a decrease in the VMR of stratospheric HCl. The replacement of CFCs with HCFCs has led to an increase in the VMR of HF in the stratosphere. As chlorine-containing compounds continue to be phased out and replaced by fluorine-containing molecules, it is likely that total atmospheric fluorine will continue increasing in the near future.     

Trend of lower stratospheric methane (CH4) from atmospheric chemistry experiment (ACE) and atmospheric trace molecule spectroscopy (ATMOS) measurements

The long-term trend of methane (CH₄) in the lower stratosphere has been estimated for the 1985-2008 time period by combining spaceborne solar occultation measurements recorded with high spectral resolution Fourier transform spectrometers (FTSs). Volume mixing ratio (VMR) FTS measurements from the ATMOS (atmospheric trace molecule spectroscopy) FTS covering 120-10 hPa (∼16-30 km altitude) at 25°N-35°N latitude from 1985 and 1994 have been combined with Atmospheric Chemistry Experiment (ACE) SCISAT-1 FTS measurements covering the same latitude and pressure range from 2004 to 2008. The CH₄ trend was estimated by referencing the VMRs to those measured for the long-lived constituent N₂O to account for the dynamic history of the sampled airmasses. The combined measurement set shows that the VMR increase measured by ATMOS has been replaced by a leveling off during the ACE measurement time period. Our conclusion is consistent with both remote sensing and in situ measurements of the CH₄ trend obtained over the same time span.     

Measurements of long-term changes in atmospheric OCS (carbonyl sulfide) from infrared solar observations

Multi-decade atmospheric OCS (carbonyl sulfide) infrared measurements have been analyzed with the goal of quantifying long-term changes and evaluating the consistency of the infrared atmospheric OCS remote-sensing measurement record. Solar-viewing grating spectrometer measurements recorded in April 1951 at the Jungfraujoch station (46.5°N latitude, 8.0°E longitude, 3.58 km altitude) show evidence for absorption by lines of the strong ν₃ band of OCS at 2062 cm⁻¹. The observation predates the earliest previously reported OCS atmosphere remote-sensing measurement by two decades. More recent infrared ground-based measurements of OCS have been obtained primarily with high-resolution solar-viewing Fourier transform spectrometers (FTSs). Long-term trends derived from this record span more than two decades and show OCS columns that have remained constant or have decreased slightly with time since the Mt. Pinatubo eruption, though retrievals assuming different versions of public spectroscopic databases have been impacted by OCS ν₃ band line intensity differences of ∼10%. The lower stratospheric OCS trend has been inferred assuming spectroscopic parameters from the high-resolution transmission (HITRAN) 2004 database. Volume mixing ratio (VMR) profiles measured near 30°N latitude with high-resolution solar-viewing FTSs operating in the solar occultation mode over a 22 years time span were combined. Atmospheric Trace MOlecucle Spectroscopy (ATMOS) version 3 FTS measurements in 1985 and 1994 were used with Atmospheric Chemistry Experiment (ACE) measurements during 2004-2007. Trends were calculated by referencing the measured OCS VMRs to those of the long-lived constituent N₂O to account for variations in the dynamic history of the sampled airmasses. Means and 1-sigma standard deviations of VMRs (in ppbv, or 10⁻⁹ per unit air volume) averaged over 30-100 hPa from measurements at 25-35°N latitude are 0.334±0.089 ppbv from 1985 (ATMOS Spacelab 3 measurements), 0.297±0.094 ppbv from 1994 ATLAS 3 measurements, 0.326±0.074 ppbv from ACE 2004 measurements, 0.305±0.096 ppbv from ACE 2005 measurements, 0.328±0.074 from ACE 2006 measurements, and 0.305±0.090 ppbv from ACE measurements through August 2007. Assuming these parameters, we conclude that there has been no statistically significant trend in lower stratospheric OCS over the measurement time span. We discuss past measurement sets, quantify the impact of changes in infrared spectroscopic parameters on atmospheric retrievals and trend measurements, and discuss OCS spectroscopic uncertainties of the current ν₃ band parameters in public atmospheric databases.     

Spectroscopic detection of COClF in the tropical and mid-latitude lower stratosphere

We report retrievals of COClF (carbonyl chlorofluoride) based on atmospheric chemistry experiment (ACE) solar occultation spectra recorded at tropical and mid-latitudes during 2004-2005. The COClF molecule is a temporary reservoir of both chlorine and fluorine and has not been measured previously by remote sensing. A maximum COClF mixing ratio of (10^-12 per unit volume, 1 sigma) is measured at 28 km for tropical and subtropical occultations (latitudes below 20^° in both hemispheres) with lower mixing ratios at both higher and lower altitudes. Northern hemisphere mid-latitude mixing ratios (30-50°N) resulted in an average profile with a peak mixing ratio of , 1 sigma, at 27 km, also decreasing above and below that altitude. We compare the measured average profiles with the one reported set of in situ lower stratospheric mid-latitude measurements from 1986 and 1987, a previous two-dimensional (2-D) model calculation for 1987 and 1993, and a 2-D-model prediction for 2004. The measured average tropical profile is in close agreement with the model prediction; the northern mid-latitude profile is also consistent, although the peak in the measured profile occurs at a higher altitude (2.5-4.5 km offset) than in the model prediction. Seasonal average 2-D-model predictions of the COClF stratospheric distribution for 2004 are also reported.     

Long-term trend in CHF2Cl (HCFC-22) from high spectral resolution infrared solar absorption measurements and comparison with in situ measurements

The average tropospheric volume mixing ratio of CHF₂Cl (HCFC-22) has been retrieved from a time series of high spectral resolution ground-based infrared solar absorption spectra recorded with the McMath Fourier transform spectrometer located at the U.S. National Solar Observatory facility on Kitt Peak in southern Arizona (31.9°N, 111.6°W, 2.09 km altitude) for the time period October 1987–November 2002. The retrievals are based on fits to the well-isolated, unresolved 2ν₆ Q branch at 829.05 cm⁻¹ and the SFIT2 retrieval algorithm. The measured daily averages show a near linear rise per year in the mean tropospheric volume mixing ratio as a function of time with a best fit yielding an average increase rate of (5.66±0.15) parts per trillion (10⁻¹²) by volume per year, corresponding to (6.47±0.17)%yr⁻¹, 1 sigma, at the beginning of the time series. The tropospheric mixing ratios retrieved from the solar spectra have been compared with monthly average surface flask sampling measurements from the Climate Monitoring and Diagnostic Laboratory (CMDL) station at Niwot Ridge, Colorado (40.0°N, 105.5°W, 3013 m altitude), archived measurement from the same location, and early CMDL northern hemisphere Pacific cruise measurements. The average ratio of the retrieved tropospheric mixing ratio relative to the CMDL surface mixing ratio is 1.053 for the overlapping 1987 to 2002 time period. The retrieved mean tropospheric mixing ratio is consistent with the surface measurements within the errors estimated for the remote sensing observations.     

First global observations of atmospheric COClF from the Atmospheric Chemistry Experiment mission

Carbonyl chlorofluoride (COClF) is an important reservoir of chlorine and fluorine in the Earth's atmosphere. Satellite-based remote sensing measurements of COClF, obtained by the Atmospheric Chemistry Experiment (ACE) for a time period spanning February 2004 through April 2007, have been used in a global distribution study. There is a strong source region for COClF in the tropical stratosphere near 27 km. A layer of enhanced COClF spans the low- to mid-stratosphere over all latitudes, with volume mixing ratios of 40-100 parts per trillion by volume, largest in the tropics and decreasing toward the poles. The COClF volume mixing ratio profiles are nearly zonally symmetric, but they exhibit a small hemispheric asymmetry that likely arises from a hemispheric asymmetry in the parent molecule CCl₃F. Comparisons are made with a set of in situ stratospheric measurements from the mid-1980s and with predictions from a 2-D model.     

Detection of elevated tropospheric hydrogen peroxide (H2O2) mixing ratios in atmospheric chemistry experiment (ACE) subtropical infrared solar occultation spectra

We report measurements of hydrogen peroxide (H₂O₂) profiles from infrared solar occultation spectra recorded at 0.02 cm⁻¹ resolution by the atmospheric chemistry experiment (ACE) during 2004 and 2005. Mixing ratios as high as 1.7 ppbv (1 ppbv=1×10⁻⁹ per unit volume) were measured in the subtropical troposphere. Back trajectories, fire count statistics, and simultaneous measurements of other species from the same occultation provide evidence that the elevated H₂O₂ mixing ratios originated from a young biomass-burning plume. The ACE time series show only a few cases with elevated H₂O₂ mixing ratios likely because of the short lifetime of H₂O₂ and the limited sampling during biomass-burning time periods.     

Tropospheric emission spectrometer (TES) and atmospheric chemistry experiment (ACE) measurements of tropospheric chemistry in tropical southeast Asia during a moderate El Niño in 2006

High spectral resolution Fourier transform spectrometer (FTS) measurements of tropospheric carbon monoxide (CO) distributions show mixing ratios over Indonesia during October 2006 of ∼200 ppbv (10⁻⁹ per unit volume) in the middle troposphere. The elevated emissions were caused by intense and widespread Indonesian peat and forest fire emissions elevated compared to other years by the impact of a moderate El Niño/Soutern Oscillation (ENSO) event, which delayed that year's monsoon season and produced very dry conditions. Moderate resolution imaging spectrometer (MODIS) fire counts, atmospheric chemistry experiment (ACE) measurements of elevated mixing ratios of fire emission products and near infrared extinction, and back trajectory calculations for a sample measurement location near the time of maximum emissions provide additional evidence that the elevated 2006 emissions resulted primarily from the Indonesia fires. Lower CO mixing ratios measured by ACE and fewer MODIS fire counts in Indonesia during October 2005 indicate lower emissions than during 2006. Coincident profiles from the ACE agree within the uncertainties with those from the tropospheric emission spectrometer (TES) for pressure ranges and time periods with good TES sensitivity after accounting for its lower vertical sensitivity compared with the ACE FTS.     

Long-term evolution in the tropospheric concentration of chlorofluorocarbon 12 (CCl2F2) derived from high-spectral resolution infrared solar absorption spectra: retrieval and comparison with in situ surface measurements

The average tropospheric volume mixing ratios of chlorofluorocarbon 12 (CCl₂F₂) have been retrieved from high-spectral resolution ground-based infrared solar-absorption spectra recorded from March 1982 to October 2003 with the McMath Fourier transform spectrometer at the US National Solar Observatory facility on Kitt Peak in southern Arizona (31.9°N, 111.6°W, 2.09 km altitude). The retrievals are based on fits to the unresolved ν₈ band Q-branches near using the SFIT2 retrieval algorithm. The annual increase rate was equal to (16.88±1.37) parts per trillion (10^-12) by volume at the beginning of the time series, March 1982, or (4.77±0.04)%, 1 sigma, declining progressively to (2.49±1.24) parts per trillion, by volume at the end, October 2003, or (0.46±0.24)%, 1 sigma. Average tropospheric mixing ratios from the solar spectra have been compared with average surface flask and in situ sampling measurements from the Climate Monitoring and Diagnostics Laboratory (CMDL) station at Niwot Ridge, CO, (USA) (40.0°N, 105.5°W, 3013 m altitude). The average ratio and standard deviation of the monthly means of the retrieved tropospheric mixing ratios relative to the CMDL surface mixing ratios is (1.01±0.03) for the overlapping time period. Both datasets demonstrate the progressive impact of the Montreal protocol and its strengthening amendments on the trend of CCl₂F₂, though a tropospheric decrease has yet to be observed.     

Effect of silane addition on acetylene ignition behind reflected shock waves

Ignition delay time and species profile measurements are reported for the combustion of C₂H₂/O₂/Ar mixtures with and without the addition of silane for temperatures between 1040 and 2320 K and pressures near 1 atm. Characteristic times, namely ignition time and time to peak, were determined from the time histories of CH* (A²Δ → X²Π) and OH* (A²Σ⁺ → X²Π) emission near 430 and 307 nm, respectively. For the cases without silane, there is good agreement between the present data and some recent acetylene oxidation results. Small SiH₄ additions (<10% of the fuel) reduced the ignition time in stoichiometric mixtures by as much as 75% for shocks near 1800 K. Similar reductions were seen in the fuel-lean mixture, although the effect was less temperature dependent. Several detailed chemical kinetics mechanisms of hydrocarbon oxidation were compared to the ignition delay-time data and species profiles for C₂H₂/O₂/Ar mixtures without silane. All models under-predicted ignition time for the 98% diluted stoichiometric mixture but matched the fuel-lean ignition data somewhat better. Two of the models displayed the shift in activation energy at lower temperatures seen in the data, although no one model was able to reproduce all ignition times over the entire range of mixtures and conditions.     

An efficient analytical approach for calculating line mixing in atmospheric remote sensing applications

Collisional coupling between energy states in a molecule undergoing an optical transition can alter the line shape associated with the transition, an effect known as line mixing. Accounting for this effect in the analysis of remote sensing measurements of Earth's atmosphere by the Atmospheric Chemistry Experiment (ACE) yields reduced residuals, which leads to improved performance in the volume mixing ratio retrievals for some molecules. Analytical expressions are presented for the imaginary components of the polynomial ratios from the Humlicek algorithm, which provides approximate solutions to the complex probability function. These imaginary components are employed in the calculation of line mixing using the Rosenkranz first order approximation. Examples of line mixing in ACE measurements are presented, including a set of CH₄ lines that exhibit both line mixing and speed dependence. An efficient, analytical approach is proposed for calculating line shapes with a combination of line mixing and speed dependence. FORTRAN routines for calculating line mixing effects are provided as a supplement to the paper.     

Pressure broadening coefficients of induced by for Venus atmosphere

Carbon dioxide (CO₂) induced pressure broadening coefficients of water vapor (H₂O) lines have been determined using a terahertz time-domain spectrometer (TDS). Thirty-two rotational transitions of H₂O were observed in the spectral range of 18– (550–3050 GHz) for the first time. Using TDS allows one to measure absorption spectra with one order of magnitude better precision than Fourier transform spectrometer in this frequency region. The precision of our broadening coefficient measurements was 2.4% in average. The measured CO₂ induced pressure broadening coefficients are compared to those calculated by the complex Robert–Bonamy formalism. The difference between the measurement and the theoretical estimation was in the range of -10.7% to +19.0% confirming the credibility of the theoretical approach. The impact on retrieval of water vapor abundance was examined by performing inversion analysis on H₂O spectra of Venus atmosphere obtained with the Submillimeter Wave Astronomy Satellite. In this example case, the retrieved water vapor mixing ratio reduces by half at the altitude region of 70–85 km when applying the newly measured broadening coefficient compared to the air-broadening coefficient, and changes by 5% compared to that estimated by the complex Robert–Bonamy formalism.     

Multi-decade measurements of the long-term trends of atmospheric species by high-spectral-resolution infrared solar absorption spectroscopy

Solar absorption spectra were recorded for the first time in 5 years with the McMath Fourier transform spectrometer at the US National Solar Observatory on Kitt Peak in southern Arizona, USA (31.91°N latitude, 111.61°W longitude, 2.09 km altitude). The solar absorption spectra cover 750-1300 and 1850-5000 cm⁻¹ and were recorded on 20 days during March-June 2009. The measurements mark the continuation of a long-term record of atmospheric chemical composition measurements that have been used to quantify seasonal cycles and long-term trends of both tropospheric and stratospheric species from observations that began in 1977. Fits to the measured spectra have been performed, and they indicate the spectra obtained since return to operational status are nearly free of channeling and the instrument line shape function is well reproduced taking into account the measurement parameters. We report updated time series measurements of total columns for six atmospheric species and their analysis for seasonal cycles and long-term trends. As an example, the time series fit shows a decrease in the annual increase rate in Montreal-Protocol-regulated chlorofluorocarbon CCl₂F₂ from 1.51±0.38% yr⁻¹ at the beginning of the time span to −1.54±1.28% yr⁻¹ at the end of the time span, 1 sigma, and hence provides evidence for the impact of those regulations on the trend.     

Contemporary carbon-14 in lemongrass oil

Liquid scintillation counting ofp- cymene, derived from lemongrass oil, has provided information on the world-wide increase in C¹⁴ since 1954. By June 1959, the activity in the tropospheric atmosphere and in the rapidly equilibrating biosphere is measured to have increased by 26·8 per cent in the northern hemisphere and 19·7 per cent in the southern hemisphere. The shape of the relationship between activity and time is essentially linear, with two sections of quite different slope.     

Speed-dependent Voigt profile for water vapor in infrared remote sensing applications

The Voigt profile does not provide a sufficiently accurate representation of the line shape for air-broadened H₂O vapor over a significant range of conditions commonly encountered in atmospheric remote sensing. A speed-dependent Voigt profile yields much improved residuals in the analysis of water from infrared measurements collected by the atmospheric chemistry experiment (ACE), a satellite mission for remote sensing of the Earth's atmosphere. An analytical expression is presented for the rapid calculation of the speed-dependent Voigt profile.     

A study of electronic states near the interface in ferroelectric-semiconductor heterojunction prepared by rf sputtering of PbTiO3

Interface states in the ferroelectric-semiconductor junction have been investigated from analyses of DLTS andC-V data. Two trap levels are located at 0.21 and 0.36 eV below the conduction band near the silicon side of the interface in the MFS (Metal-Ferroelectric-Semiconductor) structure. The interface states density has been drastically reduced by putting an oxide layer between ferroelectric and semiconductor with certain heat treatment in H₂ atmosphere at 500 °C. It has been found that the MFMOS (Metal-Ferroelectric-Metal-Oxide-Semiconductor) structure shows the least interface states density (less than 10¹¹cm^–2eV^–1) with the maximal dielectric constant of PbTiO₃ thin films.     

Investigation on infrared laser absorption spectroscopy measurement of acetylene trace quantities

A laser-based infrared spectrometer was developed for use in high-resolution spectroscopic analysis of trace gases in the atmosphere. Continuous wave, broadly tunable coherent infrared radiation was generated from 8 to 19 μm in a gallium selenide crystal by laser difference-frequency mixing. Measurements of acetylene trace concentrations using laser absorption spectroscopy are reported. The measurements have been performed by using the P(21), Q(11), and R(9) lines of the ν₅ band, respectively, in order to investigate optimal detection conditions: a trade-off choice between higher line absorption strength for sensitive detection and better spectral discrimination from lines overlapping for open path trace-gas monitoring applications. Minimum detectable concentrations are compared under different experimental conditions. The ν₅ R(9) line seems to be close to optimum in terms of absorption strength and freedom from spectral interference for spectroscopic detection of acetylene trace concentration at atmospheric pressure.     

N2O and O3 arctic column amounts from PARIS-IR observations: Retrievals, characterization and error analysis

Ground-based solar absorption infrared spectra were recorded in the Canadian Arctic during the early spring of 2004 using a moderate-resolution Fourier transform spectrometer, the Portable Atmospheric Research Interferometric Spectrometer for the Infrared (PARIS-IR). As part of the Canadian Arctic Atmospheric Chemistry Experiment (ACE) validation campaign, the PARIS-IR instrument recorded solar absorption spectra of the atmosphere from February to March 2004 as the Sun returned to the Arctic Stratospheric Ozone Observatory (AStrO) near Eureka, Nunavut, Canada (80.05°N, 86.42°W). In this paper, we briefly outline the PARIS-IR instrument configuration and data acquisition in the high Arctic. We discuss the retrieval methodology, characterization and error analysis associated with total and partial column retrievals. We compare the PARIS-IR measurements of N₂O and O₃ column amounts with those from the Fourier transform spectrometer (ACE-FTS) onboard the Canadian SCISAT-1 satellite and the ozonesonde data obtained at Eureka during the validation campaign.     

Diode Laser Spectroscopy of Water Vapor in 1.8 μM: Line Profile Measurements

A diode laser spectrometer has been used for high accuracy H₂O line profile measurements near 5475 cm⁻¹. Measured lineshapes have been least-squares fitted by Voigt profile with a floating Gaussian component. Gaussian component pressure dependence resulting from the Dicke narrowing effect is observed. Line intensities, self- and air-induced broadenings, and shifts of five water vapor lines are presented.     

Accumulation of magnetic field energy in an active region due to the alpha-effect

The problem of accumulation of magnetic field energy in an active region (AR) as the energy of electric currents in the AR atmosphere is not yet completely clear. Along with the commonly accepted concept of generation of electric current systems in an AR due to large- scale shearing motions at the photospheric level [1,2], another possibility of magnetic field energy accumulation has recently been proposed theoretically [3]. Assuming that the AR magnetic field evolves via a sequence of force- free configurations, Seehafer shows that the energy of small- scale field and velocity fluctuations can be transformed into that of large-scale current systems of an AR (alpha-effect). The necessary condition for the alpha-effect to exist is the presence of the sign- dominant current helicity H _c =B · (?×B) in the volume is considered. The purpose of this paper is to clarify the fulfillment of this condition in various ARs. Based on the measurements of magnetic field vector in 40 active regions of the maximum of the 22nd cycle we calculated the current helicity of the field B_z · (?×B) _z in the photosphere and obtained the following results. In 36 ARs we found a significant imbalance of the current helicity of the field (5 to 75%) such that in 33 ARs the excess of the current helicity was positive in the southern hemisphere and negative in the northern hemisphere. Therefore, in ARs the necessary condition for transfer of the energy of small-scale fluctuations of the field and velocity into the energy of large- scale electric currents in ARs is fulfilled rather frequently.