bluuebunny/crossref_metadata_2025 huggingface dataset:
Retrieval of temperature, H2O, O3, HNO3, CH4, N2O, ClONO2 and ClO from MIPAS reduced resolution nominal mode limb emission measurements
Authors: von Clarmann T. , Höpfner M. , Kellmann S. , Linden A. , Chauhan S. , Funke B. , Grabowski U. , Glatthor N. , Kiefer M. , Schieferdecker T. , Stiller G. P. , Versick S.
Published: April 2010

Abstract. Retrievals of temperature, H2O, O3, HNO3, CH4, N2O, ClONO2 and ClO from MIPAS reduced spectral resolution nominal mode limb emission measurements outperform retrievals from respective full spectral resolution measurements both in terms of altitude resolution and precision. The estimated precision (including measurement noise and propagation of uncertain parameters randomly varying in the time domain) and altitude resolution are typically 0.5–1.4 K and 2–3.5 km for temperature between 10 and 50 km altitude, and 5–6%, 2–4 km for H2O below 30 km altitude, 4–5%, 2.5–4.5 km for O3 between 15 and 40 km altitude, 3–8%, 3–5 km for HNO3 between 10 and 35 km altitude, 5–8%, 2–3 km for CH4 between 15 and 35 km altitude, 5–10%, 3 km for N2O between 15 and 35 km altitude, 8–14%, 2.5–9 km for ClONO2 below 40 km, and larger than 35%, 3–7 km for ClO in the lower stratosphere. As for the full spectral resolution measurements, the reduced spectral resolution nominal mode horizontal sampling (410 km) is coarser than the horizontal smoothing (often below 400 km), depending on species, altitude and number of tangent altitudes actually used for the retrieval. Thus, aliasing might be an issue even in the along-track domain. In order to prevent failure of convergence, it was found to be essential to consider horizontal temperature gradients during the retrieval.
Chlorine activation by N2O5: simultaneous, in situ detection of ClNO2 and N2O5 by chemical ionization mass spectrometry
Authors: Kercher J. P. , Riedel T. P. , Thornton J. A.
Published: April 2010

Abstract. We report a new method for the simultaneous in situ detection of nitryl chloride (ClNO2) and dinitrogen pentoxide (N2O5) using chemical ionization mass spectrometry (CIMS). The technique relies on the formation and detection of iodide ion-molecule clusters, I(ClNO2)− and I(N2O5)−. The novel N2O5 detection scheme is direct. It does not suffer from high and variable chemical interferences, which are associated with the typical method of nitrate anion detection. We address the role of water vapor, CDC electric field strength, and instrument zero determinations, which influence the overall sensitivity and detection limit of this method. For both species, the method demonstrates high sensitivity (>1 Hz/pptv), precision (~10% for 100 pptv in 1 s), and accuracy (~20%), the latter ultimately determined by the nitrogen dioxide (NO2) cylinder calibration standard and characterization of inlet effects. For the typically low background signals (<10 Hz) and high selectivity, we estimate signal-to-noise (S/N) ratios of 2 for 1 pptv in 60 s averages, but uncertainty associated with the instrumental zero currently leads to an ultimate detection limit of ~5 pptv for both species. We validate our approach for the simultaneous in situ measurement of ClNO2 and N2O5 while on board the R/V Knorr as part of the ICEALOT 2008 Field Campaign.
Determination of particulate matter vertical columns using satellite observations
Authors: Kokhanovsky A. A. , Prikhach A. S. , Katsev I. L. , Zege E. P.
Published: April 2010

Abstract. A new technique to retrieve the particulate matter vertical columns from spaceborne observations is described. The method is based on the measurements of the spectral aerosol optical thickness (AOT). The spectral slope of the derived aerosol optical thickness is used to infer the size of particles, which is needed (along with the absolute value of AOT) to determine corresponding vertical columns. The technique is applied to the case of a cloudless atmosphere over Germany and results are compared with ground-based observations. Several assumptions are made in the retrieval process such as the prescribed phase function, single scattering albedo, the refractive index of aerosol, and the half-width of the size distribution.
Design and performance of an automatic regenerating adsorption aerosol dryer for continuous operation at monitoring sites
Authors: Tuch T. M. , Haudek A. , Müller T. , Nowak A. , Wex H. , Wiedensohler A.
Published: April 2010

Abstract. Sizes of aerosol particles depend on the relative humidity of their carrier gas. Most monitoring networks require therefore that the aerosol is dried to a relative humidity below 50% r.H. to ensure comparability of measurements at different sites. Commercially available aerosol dryers are often not suitable for this purpose at remote monitoring sites. Adsorption dryers need to be regenerated frequently and maintenance-free single column Nafion dryers are not designed for high aerosol flow rates. We therefore developed an automatic regenerating adsorption aerosol dryer with a design flow rate of 1 m3/h. Particle transmission efficiency of this dryer has been determined during a 3 week experiment. The lower 50% cut-off was found to be smaller than 3 nm at the design flow rate of the instrument. Measured transmission efficiencies are in good agreement with theoretical calculations. One dryer has been successfully deployed in the Amazon river basin. We present data from this monitoring site for the first 6 months of measurements (February 2008–August 2008). Apart from one unscheduled service, this dryer did not require any maintenance during this time period. The average relative humidity of the dried aerosol was 27.1+/−7.5% r.H. compared to an average ambient relative humidity of nearly 80% and temperatures around 30°C. This initial deployment demonstrated that these dryers are well suitable for continuous operation at remote monitoring sites under adverse ambient conditions.
Greenhouse gas analysis of air samples collected onboard the CARIBIC passenger aircraft
Authors: Schuck T. J. , Brenninkmeijer C. A. M. , Slemr F. , Xueref-Remy I. , Zahn A.
Published: April 2010

Abstract. CARIBIC (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container) is a long-term atmospheric measurement program based on the use of a comprehensive scientific instrument package aboard a commercial passenger aircraft. In addition to real-time measurements, whole air sampling is performed regularly at cruising altitudes in the tropical middle troposphere and the extra-tropical UT/LS region. Air samples are analyzed for greenhouse gases, NMHCs, halocarbons, and trace gas isotopic composition. The routinely performed greenhouse gas analysis comprises gas chromatography measurements of CO2, CH4, N2O and SF6. The air sampling procedure, the GC system and its performance are described. Comparisons with similar systems employed in other laboratories and a comparison with results from a CO2 in-situ analyzer that is also part of the CARIBIC instrumentation are shown. In addition, the time series of CO2, obtained from the collection of 684 samples at latitudes between 30° N and 56° N on 21 round trips out of Germany to different destinations in Asia between November 2005 and October 2008, is presented. A time shift in the seasonal cycle of about one month was observed between the upper troposphere and the tropopause region. For two sets of return flights from Germany to the Philippines the relationship between the four greenhouse gases is briefly discussed.
A flow-tube based laser-induced fluorescence instrument to measure OH reactivity in the troposphere
Authors: Ingham T. , Goddard A. , Whalley L. K. , Furneaux K. L. , Edwards P. M. , Seal C. P. , Self D. E. , Johnson G. P. , Read K. A. , Lee J. D. , Heard D. E.
Published: April 2010

Abstract. A field instrument utilising the artificial generation of OH radicals in a sliding injector flow-tube reactor with detection by laser-induced fluorescence spectroscopy has been developed to measure the rate of decay of OH by reaction with its atmospheric sinks. The OH reactivity instrument has been calibrated using known concentrations of CO, NO2 and single hydrocarbons in a flow of zero air, and the impact of recycling of OH via the reaction HO2+NO→OH+NO2 on the measured OH reactivity has been quantified. As well as a detailed description of the apparatus, the capabilities of the new instrument are illustrated using representative results from deployment in the semi-polluted marine boundary layer at the Weybourne Atmospheric Observatory, UK, and in a tropical rainforest at the Bukit Atur Global Atmospheric Watch station, Danum Valley, Borneo.
A single gas chromatograph for accurate atmospheric mixing ratio measurements of CO2, CH4, N2O, SF6 and CO
Authors: van der Laan S. , Neubert R. E. M. , Meijer H. A. J.
Published: April 2010

Abstract. We present an adapted gas chromatograph capable of measuring simultaneously and semi-continuously the atmospheric mixing ratios of the greenhouse gases CO2, CH4, N2O and SF6 and the trace gas CO with high precision and long-term stability. The novelty of our design is that all species are measured with only one device, making it a very cost-efficient system. No time lags are introduced between the measured mixing ratios. The system is designed to operate fully autonomously which makes it ideal for measurements at remote and unmanned stations. Only a small amount of sample air is needed, which makes this system also highly suitable for flask air measurements. In principle, only two reference cylinders are needed for daily operation and only one calibration per year against international WMO standards is sufficient to obtain high measurement precision and accuracy. The system described in this paper is in use since May 2006 at our atmospheric measurement site Lutjewad near Groningen, The Netherlands at 6°21´ E, 53°24´N, 1 m a.s.l. Results show the long-term stability of the system. Observed measurement precisions at our remote research station Lutjewad were: ±0.04 ppm for CO2, ±0.8 ppb for CH4, ±0.8 ppb for CO, ±0.3 ppb for N2O, and ±0.1 ppt for SF6. The ambient mixing ratios of all measured species as observed at station Lutjewad for the period of May 2007 to August 2008 are presented as well.
Airborne multi-axis DOAS measurements of atmospheric trace gases on CARIBIC long-distance flights
Authors: Dix B. , Brenninkmeijer C. A. M. , Frieß U. , Wagner T. , Platt U.
Published: April 2010

Abstract. A DOAS (Differential Optical Absorption Spectroscopy) instrument was implemented and operated onboard a long-distance passenger aircraft within the framework of the CARIBIC project (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container). The instrument was designed to keep weight, size and power consumption low and to comply with civil aviation regulations. It records spectra of scattered light from three viewing directions (nadir, 10° above and below horizon) using a miniaturized telescope system. The telescopes are integrated in the main pylon of the inlet system which is mounted at the belly of the aircraft. Fibre bundles transmit light from the telescopes to spectrograph-detector units inside the DOAS container instrument. The latter is part of the removable CARIBIC instrument container, which is installed monthly on the aircraft for a series of measurement flights. During 30 flight operations within three years, measurements of HCHO, HONO, NO2, BrO, O3 and the oxygen dimer O4 were conducted. All of these trace gases except BrO could be analysed with a 30 s time resolution. HONO was detected for the first time in a deep convective cloud over central Asia, while BrO, NO2 and O3 could be observed in tropopause fold regions. Biomass burning signatures over South America could be seen and measurements during ascent and descent provided information on boundary layer trace gas profiles (e.g. NO2 or HCHO).
Airborne lidar reflectance measurements at 1.57 μm in support of the A-SCOPE mission for atmospheric CO2
Authors: Amediek A. , Fix A. , Ehret G. , Caron J. , Durand Y.
Published: April 2010

Abstract. The characteristics of the lidar reflectance of the Earth's surface is an important issue for the IPDA lidar technique (integrated path differential absorption lidar) which is the proposed method for the spaceborne measurement of atmospheric carbon dioxide within the framework of ESA's A-SCOPE project. Both, the absolute reflectance of the ground and its variations have an impact on the measurement sensitivity. The first aspect influences the instrument's signal to noise ratio, the second one can lead to retrieval errors, if the ground reflectance changes are strong on small scales. The investigation of the latter is the main purpose of this study. Airborne measurements of the lidar ground reflectance at 1.57 μm wavelength were performed in Central and Western Europe, including many typical land surface coverages as well as the open sea. The analyses of the data show, that the lidar ground reflectance is highly variable on a wide range of spatial scales. However, by means of the assumption of laser footprints in the order of several tens of meters, as planned for spaceborne systems, and by means of an averaging of the data it was shown, that this specific retrieval error is well below 1 ppm (CO2 column mixing ratio), and so compatible with the sensitivity requirements of spaceborne CO2 measurements. Several approaches for upscaling the data in terms of the consideration of larger laser footprints, compared to the one used here, are shown and discussed. Furthermore, the collected data are compared to MODIS ground reflectance data.
Assessment of the performance of a compact concentric spectrometer system for Atmospheric Differential Optical Absorption Spectroscopy
Authors: Whyte C. , Leigh R. J. , Lobb D. , Williams T. , Remedios J. J. , Cutter M. , Monks P. S.
Published: April 2010

Abstract. A breadboard demonstrator of a novel UV/VIS grating spectrometer has been developed based upon a concentric arrangement of a spherical meniscus lens, concave spherical mirror and curved diffraction grating suitable for a range of atmospheric remote sensing applications from the ground or space. The spectrometer is compact and provides high optical efficiency and performance benefits over traditional instruments. The concentric design is capable of handling high relative apertures, owing to spherical aberration and comma being near zero at all surfaces. The design also provides correction for transverse chromatic aberration and distortion, in addition to correcting for the distortion called "smile", the curvature of the slit image formed at each wavelength. These properties render this design capable of superior spectral and spatial performance with size and weight budgets significantly lower than standard configurations. This form of spectrometer design offers the potential for exceptionally compact instrument for differential optical absorption spectroscopy (DOAS) applications from LEO, GEO, HAP or ground-based platforms. The breadboard demonstrator has been shown to offer high throughput and a stable Gaussian line shape with a spectral range from 300 to 450 nm at 0.5 nm resolution, suitable for a number of typical DOAS applications.
Use of O2 airglow for calibrating direct atomic oxygen measurements from sounding rockets
Authors: Hedin J. , Gumbel J. , Stegman J. , Witt G.
Published: April 2010

Abstract. Accurate knowledge about the distribution of atomic oxygen is crucial for many studies of the mesosphere and lower thermosphere. Direct measurements of atomic oxygen by the resonance fluorescence technique at 130 nm have been made from many sounding rocket payloads in the past. This measurement technique yields atomic oxygen profiles with good sensitivity and altitude resolution. However, accuracy is a problem as calibration and aerodynamics make the quantitative analysis challenging. Most often, accuracies better than a factor 2 are not to be expected from direct atomic oxygen measurements. As an example, we present results from the NLTE (Non Local Thermodynamic Equilibrium) sounding rocket campaign at Esrange, Sweden, in 1998, with simultaneous O2 airglow and O resonance fluorescence measurements. O number densities are found to be consistent with the nightglow analysis, but only within the uncertainty limits of the resonance fluorescence technique. Based on these results, we here describe how better atomic oxygen number densities can be obtained by calibrating direct techniques with complementary airglow photometer measurements and detailed aerodynamic analysis. Night-time direct O measurements can be complemented by photometric detection of the O2 (b1∑g+−X3∑g-) Atmospheric Band at 762 nm, while during daytime the O2 (a1Δg−X3∑g-) Infrared Atmospheric Band at 1.27 μm can be used. The combination of a photometer and a rather simple resonance fluorescence probe can provide atomic oxygen profiles with both good accuracy and good height resolution.
Continuous measurements of atmospheric oxygen and carbon dioxide on a North Sea gas platform
Authors: van der Laan-Luijkx I. T. , Neubert R. E. M. , van der Laan S. , Meijer H. A. J.
Published: April 2010

Abstract. A new atmospheric measurement station has been established on the North Sea oil and gas production platform F3, 200 km north off the Dutch coast (5°51' N, 4°44' E). Atmospheric concentrations of O2 and CO2 are continuously measured using fuel cell technology and compact infrared absorption instruments, respectively. Furthermore, the station includes an automated air flask sampler for laboratory analysis of the atmospheric concentrations of CO2, CH4, CO and O2 and isotope measurements of δ13C, δ18O and Δ14C from CO2. This station is the first fixed sea based station with on-site continuous O2 and CO2 measurements and therefore yields valuable information about the CO2 uptake in coastal marine regions, specifically the North Sea. This paper presents the measurement station and the used methodologies in detail. In comparison to land-based stations, the data show low day-to-day variability, as they are practically free of nightly inversions as well as human influences, due to the station's remoteness. Therefore, the data set collected at this measurement station serves directly as background data for the coastal northwest European region. Additionally, the first data are presented showing the seasonal cycle as expected during August 2008 through June 2009. Furthermore, some short-term O2 and CO2 signals are presented. The observations at the platform include several large and fast changing negative atmospheric O2 excursions without an accompanying change in the CO2 signal, which most likely indicate marine O2 uptake.
Analysis of non-methane hydrocarbons in air samples collected aboard the CARIBIC passenger aircraft
Authors: Baker A. K. , Slemr F. , Brenninkmeijer C. A. M.
Published: April 2010

Abstract. The CARIBIC project (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container) is a long-term monitoring program making regular atmospheric measurements from an instrument container installed monthly aboard a passenger aircraft. Typical cruising altitudes of the aircraft allow for the study of the free troposphere and the extra-tropical upper troposphere as well as the lowermost stratosphere. CARIBIC measurements include a number of real time analyses as well as the collection of aerosol and whole air samples. These whole air samples are analyzed post-flight for a suite of trace gases, which includes non-methane hydrocarbons (NMHC). The NMHC measurement system and its analytical performance are described here. Precision was found to vary slightly by compound, and is less than 2% for the C2–C6 alkanes and ethyne, and between 1% and 6% for C7–C8 alkanes and aromatic compounds. Preliminary results from participation in a Global Atmospheric Watch (WMO) VOC audit indicate accuracies within the precision of the system. Limits of detection are 1 pptv for most compounds, and up to 3 pptv for some aromatics. These are sufficiently low to measure mixing ratios typically observed in the upper troposphere and lowermost stratosphere for the longer-lived NMHC, however, in air samples from these regions many of the compounds with shorter lifetimes (<5 days) were frequently below the detection limit. Observed NMHC concentrations span several orders of magnitude, dependent on atmospheric region and air mass history, with concentrations typically decreasing with shorter chemical lifetimes.
Aerosol quantification with the Aerodyne Aerosol Mass Spectrometer: detection limits and ionizer background effects
Authors: Drewnick F. , Hings S. S. , Alfarra M. R. , Prevot A. S. H. , Borrmann S.
Published: April 2010

Abstract. Systematic laboratory experiments were performed to investigate quantification of various species with two versions of the Aerodyne Aerosol Mass Spectrometer, a Q-AMS and a c-ToF-AMS. Here we present a new method to continuously determine the detection limits of the AMS analyzers during regular measurements, yielding DL information under various measurement conditions. Minimum detection limits range from 0.03 μg m−3 (nitrate, sulfate, and chloride) up to 0.5 μg m−3 (organics) for the Q-AMS. Those of the c-ToF-AMS are found between 0.003 μg m−3 (nitrate, sulfate) and 0.03 μg m−3 (ammonium, organics). The DL values found for the c-ToF-AMS were ~10 times lower than those of the Q-AMS, mainly due to differences in ion duty cycle. Effects causing an increase of the detection limits include long-term instrument contamination, measurement of high aerosol mass concentrations and short-term instrument history. The self-cleaning processes which reduce the instrument background after measurement of large aerosol concentrations as well as the influences of increased instrument background on mass concentration measurements are discussed. Finally, improvement of detection limits by extension of averaging time intervals, selected or reduced ion monitoring, and variation of particle-to-background measurement ratio are investigated.
Comparison of NLC particle sizes derived from SCIAMACHY/Envisat observations with ground-based LIDAR measurements at ALOMAR (69° N)
Authors: von Savigny C. , Robert C. E. , Baumgarten G. , Bovensmann H. , Burrows J. P.
Published: April 2010

Abstract. SCIAMACHY, the Scanning Imaging Absorption spectroMeter for Atmospheric CHartographY provides measurements of limb-scattered solar radiation in the 220 nm to 2380 nm wavelength range since summer 2002. Measurements in the UV spectral range are well suited for the retrieval of particle sizes of noctilucent clouds (NLCs) and have been used to compile the largest existing satellite data base of NLC particle sizes. This paper presents a comparison of SCIAMACHY NLC size retrievals with the extensive NLC particle size data set based on ground-based LIDAR measurements at the Arctic LIDAR Observatory for Middle Atmosphere Research (ALOMAR, 69° N, 16° E) for the Northern Hemisphere NLC seasons 2003 to 2007. Most of the presented SCIAMACHY NLC particle size retrievals are based on cylindrical particles and a Gaussian particle size distribution with a fixed width. If the differences in spatial as well as vertical resolution between SCIAMACHY and the ALOMAR LIDAR are taken into account, very good agreement is found. The mean particle size derived from SCIAMACHY limb observations for the ALOMAR overpasses in 2003 to 2007 is 56.2 nm with a standard deviation of 12.5 nm, and the LIDAR observations yield a value of 54.2 nm with a standard deviation of 17.4 nm.
Chlorine activation by N2O5: simultaneous, in situ detection of ClNO2 and N2O5 by chemical ionization mass spectrometry
Authors: Kercher J. P. , Riedel T. P. , Thornton J. A.
Published: April 2010

Abstract. We report a new method for the simultaneous in situ detection of nitryl chloride (ClNO2) and dinitrogen pentoxide (N2O5) using chemical ionization mass spectrometry (CIMS). The technique relies on the formation and detection of iodide ion-molecule clusters, I(ClNO2)− and I(N2O5)−. The novel N2O5 detection scheme is direct. It does not suffer from high and variable chemical interferences, which are associated with the typical method of nitrate anion detection. We address the role of water vapor, electric field strength, and instrument zero determinations, which influence the overall sensitivity and detection limit of this method. For both species, the method demonstrates high sensitivity (>1 Hz/pptv), precision (~10% for 100 pptv in 1 s), and accuracy (~20%), the latter ultimately determined by the nitrogen dioxide (NO2) cylinder calibration standard and characterization of inlet effects. For the typically low background signals (<10 Hz) and high selectivity, we estimate signal-to-noise (S/N) ratios of 2 for 1 pptv in 60 s averages, but uncertainty associated with the instrumental zero currently leads to an ultimate detection limit of ~5 pptv for both species. We validate our approach for the simultaneous in situ measurement of ClNO2 and N2O5 while on board the Research Vessel (RV) Knorr as part of the ICEALOT 2008 Field Campaign.
Reviewing the development of a ground-based FTIR water vapour profile analysis
Authors: Schneider M. , Hase F.
Published: April 2010

Abstract. Analytic algorithms effectively applied for ground-based infrared remote sensing of many different atmospheric trace gases can be rather ineffective for the remote sensing of tropospheric water vapour profiles. Reasons are the large vertical gradient and variability of water vapour as well as its large concentrations. We review the most important features of analysis and radiative transfer modeling required for monitoring tropospheric water vapour profiles by ground-based FTIR experiments. These are: a fit of a variety of different water vapour lines with different strength, a logarithmic scale inversion, a speed dependent Voigt line shape model, and a joint temperature profile inversion. Furthermore, the introduction of an interspecies constraint allows for a monitoring of HDO/H2O ratio profiles.
Use of O2 airglow for calibrating direct atomic oxygen measurements from sounding rockets
Authors: Hedin J. , Gumbel J. , Stegman J. , Witt G.
Published: April 2010

Abstract. Accurate knowledge about the distribution of atomic oxygen is crucial for many studies of the mesosphere and lower thermosphere. Direct measurements of atomic oxygen by the resonance fluorescence technique at 130 nm have been made from many sounding rocket payloads in the past. This measurement technique yields atomic oxygen profiles with good sensitivity and altitude resolution. However, accuracy is a problem as calibration and aerodynamics make the quantitative analysis challenging. In general, accuracies better than a factor 2 are not to be expected from direct atomic oxygen measurements. As an example, we present results from the NLTE (non local thermodynamic equilibrium) sounding rocket campaign at Esrange, Sweden, in 1998, with simultaneous O2 airglow and O resonance fluorescence measurements. O number densities are found to be consistent with the nightglow analysis, but only within the uncertainty limits of the resonance fluorescence technique. Based on these results, we here describe how better atomic oxygen number densities can be obtained by calibrating direct techniques with complementary airglow photometer measurements and detailed aerodynamic analysis. Night-time direct O measurements can be complemented by photometric detection of the O2 (b1Σg+−X3Σg−) atmospheric band at 762 nm, while during daytime the O2 (a1Δg−X3Σg−) infrared atmospheric band at 1.27 μm can be used. The combination of a photometer and a rather simple resonance fluorescence probe can provide atomic oxygen profiles with both good accuracy and good height resolution.
Airborne lidar reflectance measurements at 1.57 μm in support of the A-SCOPE mission for atmospheric CO2
Authors: Amediek A. , Fix A. , Ehret G. , Caron J. , Durand Y.
Published: April 2010

Abstract. The characteristics of the lidar reflectance of the Earth's surface is an important issue for the IPDA lidar technique (integrated path differential absorption lidar) which is the proposed method for the spaceborne measurement of atmospheric carbon dioxide within the framework of ESA's A-SCOPE project. Both, the absolute reflectance of the ground and its variations have an impact on the measurement sensitivity. The first aspect influences the instrument's signal to noise ratio, the second one can lead to retrieval errors, if the ground reflectance changes are strong on small scales. The investigation of the latter is the main purpose of this study. Airborne measurements of the lidar ground reflectance at 1.57 μm wavelength were performed in Central and Western Europe, including many typical land surface coverages as well as the open sea. The analyses of the data show, that the lidar ground reflectance is highly variable on a wide range of spatial scales. However, by means of the assumption of laser footprints on the order of several tens of meters, as planned for spaceborne systems, and by means of an averaging of the data it was shown, that this specific retrieval error is compatible with the sensitivity requirements of spaceborne CO2 measurements.
Quality assessment of Izaña's upper-air water vapour measurement techniques: FTIR, Cimel, MFRSR, GPS, and Vaisala RS92
Authors: Schneider M. , Romero P. M. , Hase F. , Blumenstock T. , Cuevas E. , Ramos R.
Published: April 2010

Abstract. At the Izaña Atmospheric Research Centre water vapour amounts are measured routinely by different techniques since many years. We intercompare the total precipitable water vapour amounts measured between 2005 and 2009 by a Fourier Transform Infrared (FTIR) spectrometer, a Multifilter rotating shadow-band radiometer (MFRSR), a Cimel sunphotometer, a Global Positioning System (GPS) receiver, and daily radiosondes (Vaisala RS92). In addition we intercompare the water vapor profiles measured by the FTIR and the radiosondes. The long-term intercomparison assures that our study well represents the large water vapour variabilities that occur in the troposphere and allows a reliable empirical quality assessment for the different water vapour dataset. We examine how the data quality of the different techniques depends on atmospheric conditions and estimate the dry bias of the techniques which are restricted to clear sky observations.
Continuous measurements of atmospheric oxygen and carbon dioxide on a North Sea gas platform
Authors: Luijkx I. T. , Neubert R. E. M. , van der Laan S. , Meijer H. A. J.
Published: April 2010

Abstract. A new atmospheric measurement station has been established on the North Sea oil and gas production platform F3, 200 km north off the Dutch coast (54°51' N, 4°44' E). Atmospheric mixing ratios of O2 and CO2 are continuously measured using fuel cell technology and compact infrared absorption instruments, respectively. Furthermore, the station includes an automated air flask sampler for laboratory analysis of the atmospheric mixing ratios of CO2, CH4, CO and O2 and isotope measurements of δ13C, δ18O and Δ14C from CO2. This station is – to our knowledge – the first fixed sea based station with on-site continuous O2 and CO2 measurements and therefore yields valuable additional information about the CO2 uptake in coastal marine regions, specifically the North Sea. This paper presents the measurement station and the used methodologies in detail. Additionally, the first data is presented showing the seasonal cycle as expected during August 2008 through June 2009. In comparison to land-based stations, the data show low day-to-day variability, as they are practically free of nightly inversions. Therefore, the data set collected at this measurement station serves directly as background data for the coastal northwest European region. Additionally, some short-term O2 and CO2 signals are presented, including very large (over 200 per meg) and fast negative atmospheric O2 excursions.
Field inter-comparison of eleven atmospheric ammonia measurement techniques
Authors: von Bobrutzki K. , Braban C. F. , Famulari D. , Jones S. K. , Blackall T. , Smith T. E. L. , Blom M. , Coe H. , Gallagher M. , Ghalaieny M. , McGillen M. R. , Percival C. J. , Whitehead J. D. , Ellis R. , Murphy J. , Mohacsi A. , Junninen H. , Pogany A. , Rantanen S. , Sutton M. A. , Nemitz E.
Published: April 2010

Abstract. Eleven instruments for the measurement of ambient concentrations of atmospheric ammonia gas (NH3), based on eight different measurement methods were inter-compared above an intensively managed agricultural field in late summer 2008 in S. Scotland. To test the instruments over a wide range of concentrations, the field was fertilised with urea midway through the experiment, leading to an increase in the average concentration from 10 to 100 ppbv. The instruments deployed included three wet-chemistry systems, one with offline analysis (annular rotating batch denuder, RBD) and two with online-analysis (Annular Denuder sampling with online Analysis, AMANDA; AiRRmonia), two Quantum Cascade Laser Absorption Spectrometers (a large-cell dual system, DUAL-QCLAS, and a compact system, c-QCLAS), two photo-acoustic spectrometers (WaSul-Flux, Nitrolux-100), a Cavity Ring Down Spectrosmeter (CRDS), a Chemical Ionisation Mass Spectrometer (CIMS), an ion mobility spectrometer (IMS) and an Open-Path Fourier Transform Infra-Red (OP-FTIR) spectroscopy. Each instrument was compared with each other and with the average concentration of all instruments. An overall good agreement of hourly average concentrations between the instruments (R2>0.84), was observed for NH3 concentrations at the field of up to 120 ppbv with the slopes against the average ranging from 0.67 (DUAL-QCLAS) to 1.13 (AiRRmonia) with intercepts of –0.74 ppbv (RBD) to +2.69 ppbv (CIMS). More variability was found for performance for lower concentrations (<10 ppbv). Here the overruling factors affecting measurement precision are (a) the inlet design, (b) the state of inlet filters (where applicable), and (c) the quality of gas-phase standards (where applicable). By reference to the fast (1 Hz) instruments deployed during the study, it was possible to characterize the response times of the slower instruments.
Retrieval of temperature, H2O, O3, HNO3, CH4, N2O, ClONO2 and ClO from MIPAS reduced resolution nominal mode limb emission measurements
Authors: von Clarmann T. , Höpfner M. , Kellmann S. , Linden A. , Chauhan S. , Funke B. , Grabowski U. , Glatthor N. , Kiefer M. , Schieferdecker T. , Stiller G. P. , Versick S.
Published: April 2010

Abstract. Retrievals of temperature, H2O, O3, HNO3, CH4, N2O, ClONO2 and ClO from MIPAS reduced spectral resolution nominal mode limb emission measurements outperform retrievals from respective high spectral resolution measurements both in terms of altitude resolution and precision. The estimated precision (including measurement noise and propagation of uncertain parameters randomly varying in the time domain) and altitude resolution are typically 0.5–1.4 K and 3 km for temperature between 10 and 50 km altitude, and 5–6%, 2–4 km for H2O below 30 km altitude, 4–5%, 3–4.5 km for O3 between 15 and 40 km altitude, 3–8%, 3–5 km for HNO3 between 10 and 35 km altitude, 5–8%, 3 km for CH4 between 15 and 35 km altitude, 5–10%, 3 km for N2O between 15 and 35 km altitude, 8–14%, 2.5–9 km for ClONO2 below 40 km, and larger than 35%, 5–6 km for ClO in the lower stratosphere. As for the high spectral resolution measurements, the reduced spectral resolution nominal mode horizontal sampling (410 km) is coarser than the horizontal smoothing (often below 400 km), depending on species, altitude and number of tangent altitudes actually used for the retrieval. Thus, aliasing might be an issue even in the along-track domain. In order to prevent failure of convergence, it was found to be essential to consider horizontal temperature gradients during the retrieval.
Seasonal distribution of aerosol properties over Europe and their impact on UV irradiance
Authors: Chubarova N. Y.
Published: April 2010

Abstract. Using the aerosol optical thickness at 550 nm (τ550) from MODIS (collection 5) combined with the aerosol products from the ground-based AERONET network, key aerosol parameters have been obtained with 1 degree resolution over Europe. Additional tests have revealed a satisfactory quality of the MODIS data, except in a few cases. Quality assured AERONET data are used for evaluating the Angstrom exponent, single scattering albedo and asymmetry factor, and for validating the final aerosol optical thickness in the UV spectral region. A method for extrapolating the aerosol parameters into the UV spectral region is discussed. The aerosol optical thickness distributions are considered together with meteorological fields from NOAA_NCEP_CPC_CAMS_OPI climatology. The τ340 is shown to vary significantly from approximately 0.01 to 0.9 depending on the season and location. Permanent elevated aerosol loading over several industrial areas is observed, which agrees with the output of chemical transport models. Using radiative transfer modeling, monthly mean UV loss due to aerosol was estimated. The absolute decrease in UV indices varies from less than 0.1 to 1.5. The relative UV attenuation has large spatial and temporal variations (from −1% to −17%) with a minimum towards the northwest and maxima over several southern local areas (Northern Italy, etc.) during the warm period.
A comparison of spectrophotometric and denuder based approaches for the determination of gaseous molecular iodine
Authors: Chance R. J. , Shaw M. , Telgmann L. , Baxter M. , Carpenter L. J.
Published: April 2010

Abstract. The presence of molecular iodine in the atmosphere is thought to have implications for both climate and human nutritional health, but measurement of the gas at low concentrations requires technically demanding techniques that are not widely accessible. Here, starch coated denuder tubes and solvent traps coupled with spectrophotometric detection are evaluated and compared as relatively cheap and straightforward methods to measure gaseous molecular iodine at environmentally relevant concentrations. Denuder tubes were found to give unacceptably low and highly variable recoveries of molecular iodine from a test gas source, with values ranging from 1 to 62%. Blank concentrations were also high, being equivalent to a gas phase concentration of 5 pptv under typical operating conditions. Ethanol and hexane solvent traps gave much better performance. Optimisation of the hexane solvent trap method gave 100% recovery and an atmospheric limit of detection of 70 pptv, which is within the range of concentrations observed in the coastal marine atmosphere.
A low power automated MAX-DOAS instrument for the Arctic and other remote unmanned locations
Authors: Carlson D. , Donohoue D. , Platt U. , Simpson W. R.
Published: April 2010

Abstract. Multiple Axis Differential Optical Absorption Spectrometer (MAX-DOAS) systems are inherently very simple instruments, which have been shown to provide extremely useful information about a wide variety of environmental parameters. In order to exploit the potential of the technique we have developed a new field-deployable MAX-DOAS system that is automated and uses little power (<3 W). This new instrument utilizes a fully enclosed scan head that protects all moving parts and optics from harsh environments. Instrument diagnostics, such as tilt monitoring and frost accumulation detection and removal, are integrated into the main data acquisition program, which then acts to remedy problems that were discovered. This full automation and data quality checking make this instrument ideal for long-term deployment at remote, unmanned locations around the world, such as in polar regions or in the monitoring of trace gas emissions from volcanoes. This instrument was recently integrated into an ice-tethered autonomous buoy and tested in Elson Lagoon, near Barrow, Alaska to monitor halogen chemistry in the Arctic. During this investigation differential slant column densities (dSCDs) of BrO up to 6×1014 molecules/cm2 were observed. Typical spectral fit residual RMS optical densities were less than 6×10−4 for solar zenith angles (SZA) < 80° and a 6-min integration time. Here we describe the design concepts and performance of this new MAX-DOAS instrument through detailed analyses of spectral quality, power usage, possible instrument response biases, and typical instrument operations.
Analysis of non-methane hydrocarbons in air samples collected aboard the CARIBIC passenger aircraft
Authors: Baker A. K. , Slemr F. , Brenninkmeijer C. A. M.
Published: April 2010

Abstract. The CARIBIC project (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container) is a long-term monitoring program making regular atmospheric measurements from an instrument container installed monthly aboard a passenger aircraft. Typical cruising altitudes of the aircraft allow for the study of the free troposphere and the extra-tropical upper troposphere as well as the lowermost stratosphere. CARIBIC measurements include a number of real time analyses as well as the collection of aerosol and whole air samples. These whole air samples are analyzed post-flight for a suite of trace gases, which includes non-methane hydrocarbons (NMHC). The NMHC measurement system and its analytical performance are described here. Precision was found to vary slightly by compound, and is less than 2% for the C2–C6 alkanes and ethyne, and between 1 and 6% for C7–C8 alkanes and aromatic compounds. Preliminary results from participation in a Global Atmospheric Watch (WMO) VOC audit indicate accuracies within the precision of the system. Limits of detection are 1 pptv for most compounds, and up to 3 pptv for some aromatics. These are sufficiently low to measure mixing ratios typically observed in the upper troposphere and lowermost stratosphere for the longer-lived NMHC, however, in air samples from these regions many of the compounds with shorter lifetimes (<5 d) were frequently below the detection limit. Observed NMHC concentrations span many orders of magnitude, dependent on atmospheric region and air mass history, with concentrations typically decreasing with shorter chemical lifetimes.
The MIPAS2D database of MIPAS/ENVISAT measurements retrieved with a multi-target 2-dimensional tomographic approach
Authors: Dinelli B. M. , Arnone E. , Brizzi G. , Carlotti M. , Castelli E. , Magnani L. , Papandrea E. , Prevedelli M. , Ridolfi M.
Published: April 2010

Abstract. We present a multi-year database of atmospheric state parameters retrieved for the upper tropospheric to mesospheric region from satellite measurements with a 2-dimensional tomographic approach. The full mission of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) instrument, on board the European Space Agency ENVISAT satellite, is analyzed with the Geofit Multi-Target Retrieval (GMTR) system to obtain the MIPAS2D database with atmospheric fields of pressure, temperature and volume mixing ratio of MIPAS main targets H2O, O3, HNO3, CH4, N2O, and NO2. The database covers both the MIPAS nominal observation mode measured at Full Resolution (FR) from July 2002 to March 2004 and the nominal observation mode of the new configuration, measured at Optimized Resolution (OR) and introduced in 2005. Further to the main targets, minor species N2O5, ClONO2, COF2, CFC-11, and CFC-12 for the FR mission only have been included in MIPAS2D to enhance its applicability in studies of stratospheric chemistry. The database is continuously updated with the analysis of the ongoing measurements that are planned to last until the end of 2013. The GMTR algorithm is operated on a fixed vertical grid coincident with the tangent altitudes of the FR nominal mode, spanning the altitude range from 6 to 68 km. In the horizontal domain, FR measurements are retrieved on both the observational grid and an equispaced 5 latitudinal-degrees grid which is made possible by the 2-dimensional retrieval algorithm. The analysis of MIPAS OR observations is operated on the same altitude-latitude fixed retrieval grid used for the FR measurements. This choice provides a homogeneous database in altitude and latitude, over the whole globe, covering to date about seven years of measurements. The equispaced latitudinal grid provides a new and convenient layout for the much needed synergetic studies of data from various instrumental and modeling sources. MIPAS2D is available to the scientific community through the two web sites http://www.mbf.fci.unibo.it/mipas2d.html, and http://www.isac.cnr.it/~rss/mipas2d.htm.
Detection of multi-layer and vertically-extended clouds using A-train sensors
Authors: Joiner J. , Vasilkov A. P. , Bhartia P. K. , Wind G. , Platnick S. , Menzel W. P.
Published: April 2010

Abstract. The detection of multiple cloud layers using satellite observations is important for retrieval algorithms as well as climate applications. In this paper, we describe a relatively simple algorithm to detect multiple cloud layers and distinguish them from vertically-extended clouds. The algorithm can be applied to coincident passive sensors that derive both cloud-top pressure from the thermal infrared observations and an estimate of solar photon pathlength from UV, visible, or near-IR measurements. Here, we use data from the A-train afternoon constellation of satellites: cloud-top pressure, cloud optical thickness, and the multi-layer flag from the Aqua MODerate-resolution Imaging Spectroradiometer (MODIS) and the optical centroid cloud pressure from the Aura Ozone Monitoring Instrument (OMI). The cloud classification algorithms applied with different passive sensor configurations compare well with each other as well as with data from the A-train CloudSat radar. We compute monthly mean fractions of pixels containing multi-layer and vertically-extended clouds for January and July 2007 at the OMI spatial resolution (12 km×24 km at nadir) and at the 5 km×5 km MODIS resolution for infrared cloud retrievals. There are seasonal variations in the spatial distribution of the different cloud types. The fraction of pixels containing distinct multi-layer cloud is a strong function of the pixel size. Globally averaged, these fractions are approximately 20% and 5% for OMI and MODIS, respectively. These fractions may be significantly higher or lower depending upon location. There is a much smaller resolution dependence for fractions of pixels containing vertically-extended clouds (~20% for OMI and slightly less for MODIS globally), suggesting larger spatial scales for these clouds. We also find significantly higher fractions of vertically-extended clouds over land as compared with ocean, particularly in the tropics and summer hemisphere.