bluuebunny/crossref_metadata_2025 huggingface dataset:
Aerodynamic gradient measurements of the NH3-HNO3-NH4NO3 triad using a wet chemical instrument: an analysis of precision requirements and flux errors
Authors: Wolff V. , Trebs I. , Ammann C. , Meixner F. X.
Published: April 2010

Abstract. The aerodynamic gradient method is widely used for flux measurements of ammonia, nitric acid, particulate ammonium nitrate (the NH3-HNO3-NH4NO3 triad) and other water-soluble reactive trace compounds. The surface exchange flux is derived from a measured concentration difference and micrometeorological quantities (turbulent exchange coefficient). The significance of the measured concentration difference is crucial for the significant determination of surface exchange fluxes. Additionally, measurements of surface exchange fluxes of ammonia, nitric acid and ammonium nitrate are often strongly affected by phase changes between gaseous and particulate compounds of the triad, which make measurements of the four individual species (NH3, HNO3, NH4+, NO3− necessary for a correct interpretation of the measured concentration differences. We present here a rigorous analysis of results obtained with a multi-component, wet-chemical instrument, able to simultaneously measure gradients of both gaseous and particulate trace substances. Basis for our analysis are two field experiments, conducted above contrasting ecosystems (grassland, forest). Precision requirements of the instrument as well as errors of concentration differences and micrometeorological exchange parameters have been estimated, which, in turn, allows the establishment of thorough error estimates of the derived fluxes of NH3, HNO3, NH4+, and NO3−. Derived median flux errors for the grassland and forest field experiments were: 39% and 50% (NH3), 31% and 38% (HNO3), 62% and 57% (NH4+), and 47% and 68% (NO3−), respectively. Additionally, we provide the basis for using field data to characterize the instrument performance, as well as subsequent quantification of surface exchange fluxes and underlying mechanistic processes under realistic ambient measurement conditions.
A method for improved SCIAMACHY CO2 retrieval in the presence of optically thin clouds
Authors: Reuter M. , Buchwitz M. , Schneising O. , Heymann J. , Bovensmann H. , Burrows J. P.
Published: April 2010

Abstract. An optimal estimation based retrieval scheme for satellite based retrievals of XCO2 (the dry air column averaged mixing ratio of atmospheric CO2) is presented enabling accurate retrievals also in the presence of thin clouds. The proposed method is designed to analyze near-infrared nadir measurements of the SCIAMACHY instrument in the CO2 absorption band at 1580 nm and in the O2-A absorption band at around 760 nm. The algorithm accounts for scattering in an optically thin cirrus cloud layer and at aerosols of a default profile. The scattering information is mainly obtained from the O2-A band and a merged fit windows approach enables the transfer of information between the O2-A and the CO2 band. Via the optimal estimation technique, the algorithm is able to account for a priori information to further constrain the inversion. Test scenarios of simulated SCIAMACHY sun-normalized radiance measurements are analyzed in order to specify the quality of the proposed method. In contrast to existing algorithms for SCIAMACHY retrievals, the systematic errors due to cirrus clouds with optical thicknesses up to 1.0 are reduced to values below 4 ppm for most of the analyzed scenarios. This shows that the proposed method has the potential to reduce uncertainties of SCIAMACHY retrieved XCO2 making this data product potentially useful for surface flux inverse modeling.
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, 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). For the first time, we use data from the CloudSat radar to evaluate the results of a multi-layer cloud detection scheme. The cloud classification algorithms applied with different passive sensor configurations compare well with each other as well as with data from CloudSat. 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 used for infrared cloud retrievals. There are seasonal variations in the spatial distribution of the different cloud types. The fraction of cloudy pixels containing distinct multi-layer cloud is a strong function of the pixel size. Globally averaged, these fractions are approximately 20% and 10% 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 higher fractions of vertically-extended clouds over land as compared with ocean, particularly in the tropics and summer hemisphere.
Development of an autonomous sea ice tethered buoy for the study of ocean-atmosphere-sea ice-snow pack interactions: the O-buoy
Authors: Knepp T. N. , Bottenheim J. , Carlsen M. , Carlson D. , Donohoue D. , Friederich G. , Matrai P. A. , Netcheva S. , Perovich D. K. , Santini R. , Shepson P. B. , Simpson W. , Valentic T. , Williams C. , Wyss P. J.
Published: April 2010

Abstract. A buoy based instrument platform (the "O-buoy") was designed, constructed, and field tested for year-round measurement of ozone, bromine monoxide, carbon dioxide, and meteorological variables over Arctic sea ice. The O-buoy operated in an autonomous manner with daily, bi-directional data transmissions using Iridium satellite communication. The O-buoy was equipped with three power sources: primary lithium-ion battery packs, rechargeable lead acid packs, and solar panels that recharge the lead acid packs, and can fully power the O-buoy during summer operation. This system was designed to operate under the harsh conditions present in the Arctic, with minimal direct human interaction, to aid in our understanding of the atmospheric chemistry that occurs in this remote region of the world. The current design requires approximately yearly maintenance limited by the lifetime of the primary power supply. The O-buoy system was field tested in Elson Lagoon, Barrow, Alaska from February to May 2009, and deployed in the Beaufort Sea in October 2009. Here, we describe the design and present preliminary data.
Development of a Bioaerosol single particle detector (BIO IN) for the Fast Ice Nucleus CHamber FINCH
Authors: Bundke U. , Reimann B. , Nillius B. , Jaenicke R. , Bingemer H.
Published: April 2010

Abstract. In this work we present the setup and first tests of our new BIO IN detector. This detector was constructed to classify atmospheric ice nuclei (IN) for their biological content. It is designed to be coupled to the Fast Ice Nucleus CHamber FINCH. If one particle acts as an ice nucleus, it will be at least partly covered with ice at the end of the development section of the FINCH chamber. The device combines an auto-fluorescence detector and a circular depolarization detector for simultaneous detection of biological material and discrimination between water droplets, ice crystals and non activated large aerosol particles. The excitation of biological material with UV light and analysis of auto-fluorescence is a common principle used for flow cytometry, fluorescence microscopy, spectroscopy and imaging. The detection of auto-fluorescence of airborne single particles demands some more experimental effort. However, expensive commercial sensors are available for special purposes, e.g. size distribution measurements. But these sensors will not fit the specifications needed for the FINCH IN counter (e.g. high sample flow of up 10 LPM). The newly developed -low cost- BIO IN sensor uses a single high-power UV LED for the electronic excitation instead of much more expensive UV lasers. Other key advantages of the new sensor are the low weight, compact size, and the little effect on the aerosol sample, which allows it to be coupled with other instruments for further analysis. The instrument will be flown on one of the first missions of the new German research aircraft "HALO" (High Altitude and LOng range).
Modelling Ag-particle activation and growth in a TSI WCPC model 3785
Authors: Stratmann F. , Herrmann E. , Petäjä T. , Kulmala M.
Published: April 2010

Abstract. In this work, we modelled activation and growth of silver particles in the water-operated TSI model 3785 water condensation particle counter (WCPC). Our objective was to investigate theoretically how various effects influence the counting efficiency of this CPC. Coupled fluid and particle dynamic processes were modelled with the computational fluid dynamics (CFD) code FLUENT in combination with the Fine Particle Model (FPM) to obtain profiles of temperature, vapour concentration, nucleation rate, and particle size. We found that the counting efficiency of the TSI 3785 for small particles might be affected by the presence of larger particles. Moreover, homogeneous nucleation processes can significantly influence counting efficiency.
Retrieval of tropospheric column densities of NO2 from combined SCIAMACHY nadir/limb measurements
Authors: Beirle S. , Kühl S. , Puķīte J. , Wagner T.
Published: April 2010

Abstract. The SCIAMACHY instrument onboard the ESA satellite ENVISAT allows measurements of various atmospheric trace gases, such as NO2. A unique feature of SCIAMACHY is that measurements are made alternately in limb and nadir mode. The limb measurements provide an opportunity for directly determining stratospheric column densities (CDs), which are needed to extract tropospheric CDs from the total CD measurements performed in (quasi simultaneous) nadir geometry. Here we discuss the potential and limitations of SCIAMACHY limb measurements for estimating stratospheric CDs of NO2 in comparison to a simple reference sector method, and the consequences for the resulting tropospheric CDs. A direct, absolute limb correction scheme is presented that improves spatial patterns of tropospheric NO2 column densities at high latitudes, but results in artificial zonal stripes at low latitudes. Subsequently, a relative limb correction scheme is introduced that successfully reduces stratospheric artefacts in the tropospheric data product without introducing new ones. This relative limb correction scheme is rather simple, robust, and, in essence, based on measurements alone. The effects of the different stratospheric estimation schemes on tropospheric CDs are discussed with respect to zonal and temporal dependencies. In addition, we define error quantities from the nadir/limb measurements that indicate remaining systematic errors as a function of latitude and day. Our new suggested stratospheric estimation scheme, the relative limb correction, improves mean tropospheric slant CDs significantly, e.g. from −1×1015 molec/cm2 (using a reference sector method) to ≈0 in the Atlantic ocean, and from +1×1015 molec/cm2 to ≈0 over Siberia, at 50° N in January 2003–2008.
Continuous quality assessment of atmospheric 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 Observatory, water vapour amounts have been measured routinely by different techniques for many years. We intercompare the total precipitable water vapour (PWV) 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). The long-term characteristics of our study allows a reliable and extensive empirical quality assessment of long-term validity, which is an important prerequisite when applying the data to climate research. We estimate a PWV precision of 1% for the FTIR, about 10% for the MFRSR, Cimel, and GPS (when excluding rather dry conditions), and significantly better than 15% for the RS92 (the detection of different airmasses avoids a better constrained estimation). We show that the MFRSR, Cimel and GPS data quality depends on the atmospheric conditions (humid or dry) and that the restriction to clear-sky observations introduces a significant dry bias in the FTIR and Cimel data. In addition, we intercompare the water vapour profiles measured by the FTIR and the Vaisala RS92, which allows the conclusion that both experiments are able to detect lower to upper tropospheric water vapour mixing ratios with a precision of better than 15%.
Tomographic retrieval approach for mesoscale gravity wave observations by the PREMIER Infrared Limb-Sounder
Authors: Ungermann J. , Hoffmann L. , Preusse P. , Kaufmann M. , Riese M.
Published: April 2010

Abstract. PREMIER is one of three candidates for ESA's 7th Earth Explorer mission that are currently undergoing feasibility studies. The main mission objective of PREMIER is to quantify processes controlling atmospheric composition in the mid/upper troposphere and lower stratosphere, a region of particular importance for climate change. To achieve this objective, PREMIER will employ the first satellite Fourier transform infrared limb-imager with a 2-D detector array combined with a millimetre-wave limb-sounder. The infrared limb-imager can be operated in a high spatial resolution mode ("dynamics mode") for observations of small-scale structures in atmospheric temperatures and trace gas fields with unprecedented 3-D sampling (0.5 km in the vertical direction, 50 km along track, 25 km across track). In this paper, a fast tomographic retrieval scheme is presented, which is designed to fully exploit the high-resolution radiance observations of the dynamics mode. Based on a detailed analysis of the "observational filter", we show that the dynamics mode provides unique information on global distributions of gravity waves (GW). The achievable vertical resolution for GW observations has values between the vertical sampling (0.5 km) of the dynamics mode and the vertical field of view (about 0.75 km). The horizontal across track resolution corresponds to the horizontal across track sampling of 25 km. Since the achievable along track horizontal resolution is about 70 km, the dynamics mode will provide GW limb-observations with a horizontal resolution comparable to nadir sounders. Compared to previous observations, PREMIER will therefore considerably extend the range of detectable GWs in terms of horizontal and vertical wavelength.
High-accuracy continuous airborne measurements of greenhouse gases (CO2 and CH4) using the cavity ring-down spectroscopy (CRDS) technique
Authors: Chen H. , Winderlich J. , Gerbig C. , Hoefer A. , Rella C. W. , Crosson E. R. , Van Pelt A. D. , Steinbach J. , Kolle O. , Beck V. , Daube B. C. , Gottlieb E. W. , Chow V. Y. , Santoni G. W. , Wofsy S. C.
Published: April 2010

Abstract. High-accuracy continuous measurements of greenhouse gases (CO2 and CH4) during the BARCA (Balanço Atmosférico Regional de Carbono na Amazônia) phase B campaign in Brazil in May 2009 were accomplished using a newly available analyzer based on the cavity ring-down spectroscopy (CRDS) technique. This analyzer was flown without a drying system or any in-flight calibration gases. Water vapor corrections associated with dilution and pressure-broadening effects for CO2 and CH4 were derived from laboratory experiments employing measurements of water vapor by the CRDS analyzer. Before the campaign, the stability of the analyzer was assessed by laboratory tests under simulated flight conditions. During the campaign, a comparison of CO2 measurements between the CRDS analyzer and a nondispersive infrared (NDIR) analyzer on board the same aircraft showed a mean difference of 0.22±0.09 ppm for all flights over the Amazon rain forest. At the end of the campaign, CO2 concentrations of the synthetic calibration gases used by the NDIR analyzer were determined by the CRDS analyzer. After correcting for the isotope and the pressure-broadening effects that resulted from changes of the composition of synthetic vs. ambient air, and applying those concentrations as calibrated values of the calibration gases to reprocess the CO2 measurements made by the NDIR, the mean difference between the CRDS and the NDIR during BARCA was reduced to 0.05±0.09 ppm, with the mean standard deviation of 0.23±0.05 ppm. The results clearly show that the CRDS is sufficiently stable to be used in flight without drying the air or calibrating in flight and the water corrections are fully adequate for high-accuracy continuous airborne measurements of CO2 and CH4.
Measurements of greenhouse gases and related tracers at Bialystok tall tower station in Poland
Authors: Popa M. E. , Gloor M. , Manning A. C. , Jordan A. , Schultz U. , Haensel F. , Seifert T. , Heimann M.
Published: April 2010

Abstract. Quasi-continuous, in-situ measurements of atmospheric CO2, O2/N2, CH4, CO, N2O, and SF6 have been performed since August 2005 at the tall tower station near Bialystok, in Eastern Poland, from five heights up to 300 m. Besides the in-situ measurements, flask samples are filled approximately weekly and measured at Max-Planck Institute for Biogeochemistry for the same species and, in addition, for H2, Ar/N2 and the stable isotopes 13C and 18O in CO2. The in-situ measurement system was built based on commercially available analysers: a LiCor 7000 for CO2, a Sable Systems "Oxzilla" FC-2 for O2, and an Agilent 6890 gas chromatograph for CH4, CO, N2O and SF6. The system was optimized to run continuously with very little maintenance and to fulfill the precision requirements of the CHIOTTO project. The O2/N2 measurements in particular required special attention in terms of technical setup and quality assurance. The evaluation of the performance after more than three years of operation gave overall satisfactory results, proving that this setup is suitable for long term remote operation with little maintenance. The precision achieved for all species is within or close to the project requirements. The comparison between the in-situ and flask sample results, used to verify the accuracy of the in-situ measurements, showed no significant difference for CO2, O2/N2, CH4 and N2O, and a very small difference for SF6. The same comparison however revealed a statistically significant difference for CO, of about 6.5 ppb, for which the cause could not be fully explained. From more than three years of data, the main features at Bialystok have been characterized in terms of variability, trends, and seasonal and diurnal variations. CO2 and O2/N2 show large short term variability, and large diurnal signals during the warm seasons, which attenuate with the increase of sampling height. The trends calculated from this dataset, over the period August 2005 to December 2008, are 2.02±0.46 ppm/year for CO2 and −23.2±2.5 per meg/year for O2/N2. CH4, CO and N2O show also higher variability at the lower sampling levels, which in the case of CO is strongly seasonal. Diurnal variations in CH4, CO and N2O mole fractions can be observed during the warm season, due to the periodicity of vertical mixing combined with the diurnal cycle of anthropogenic emissions. We calculated increase rates of 10.1±4.4 ppb/year for CH4, (−8.3)±5.3 ppb/year for CO and 0.67±0.08 ppb/year for N2O. SF6 shows only few events, and generally no vertical gradients, which suggests that there are no significant local sources. A weak SF6 seasonal cycle has been detected, which most probably is due to the seasonality of atmospheric circulation. SF6 increased during the time of our measurement at an average rate of 0.29±0.01 ppt/year.
Minimizing light absorption measurement artifacts of the Aethalometer: evaluation of five correction algorithms
Authors: Collaud Coen M. , Weingartner E. , Apituley A. , Ceburnis D. , Fierz-Schmidhauser R. , Flentje H. , Henzing J. S. , Jennings S. G. , Moerman M. , Petzold A. , Schmid O. , Baltensperger U.
Published: April 2010

Abstract. The aerosol light absorption coefficient is an essential parameter involved in atmospheric radiation budget calculations. The Aethalometer (AE) has the great advantage of measuring the aerosol light absorption coefficient at several wavelengths, but the derived absorption coefficients are systematically too high when compared to reference methods. Up to now, four different correction algorithms of the AE absorption coefficients have been proposed by several authors. A new correction scheme based on these previously published methods has been developed, which accounts for the optical properties of the aerosol particles embedded in the filter. All the corrections have been tested on six datasets representing different aerosol types and loadings and include multi-wavelength AE and white-light AE. All the corrections have also been evaluated through comparison with a Multi-Angle Absorption Photometer (MAAP) for four datasets lasting between 6 months and five years. The modification of the wavelength dependence by the different corrections is analyzed in detail. The performances and the limits of all AE corrections are determined and recommendations are given.
Ozone sonde cell current measurements and implications for observations of near-zero ozone concentrations in the tropical upper troposphere
Authors: Vömel H. , Diaz K.
Published: April 2010

Abstract. Laboratory measurements of the Electrochemical Concentration Cell (ECC) ozone sonde cell current using ozone free air as well as defined amounts of ozone reveal that background current measurements during sonde preparation are neither constant as a function of time, nor constant as a function of ozone concentration. Using a background current, measured at a defined timed after exposure to high ozone may often overestimate the real background, leading to artificially low ozone concentrations in the upper tropical troposphere, and may frequently lead to operator dependent uncertainties. Based on these laboratory measurements an improved cell current to partial pressure conversion is proposed, which removes operator dependent variability in the background reading and possible artifacts in this measurement. Data from the Central Equatorial Pacific Experiment (CEPEX) have been reprocessed using the improved background treatment based on these laboratory measurements. In the reprocessed data set near-zero ozone events no longer occur. At Samoa, Fiji, Tahiti, and San Cristóbal, nearly all near-zero ozone concentrations occur in soundings with larger background currents. To a large extent, these events are no longer observed in the reprocessed data set using the improved background treatment.
Toward a standardised thermal-optical protocol for measuring atmospheric organic and elemental carbon: the EUSAAR protocol
Authors: Cavalli F. , Viana M. , Yttri K. E. , Genberg J. , Putaud J.-P.
Published: April 2010

Abstract. Thermal-optical analysis is a conventional method for determining the carbonaceous aerosol fraction and for classifying it into organic carbon, OC, and elemental carbon, EC. Unfortunately, the different thermal evolution protocols in use can result in a wide elemental carbon-to-total carbon variation by up to a factor of five. In Europe, there is currently no standard procedure for determining the carbonaceous aerosol fraction which implies that data from different laboratories at various sites are of unknown accuracy and cannot be considered comparable. In the framework of the EU-project EUSAAR (European Supersites for Atmospheric Aerosol Research), a comprehensive study has been carried out to identify the causes of differences in the EC measured using different thermal evolution protocols; thereby the major positive and negative biases affecting thermal-optical analysis have been isolated and minimised to define an optimised protocol suitable for European aerosols. Our approach to improve the accuracy of the discrimination between OC and EC was essentially based on four goals. Firstly, charring corrections rely on faulty assumptions – e.g. pyrolytic carbon is considered to evolve completely before native EC throughout the analysis –, thus we have reduced pyrolysis to a minimum by favoring volatilisation of OC. Secondly, we have minimised the potential negative bias in EC determination due to early evolution of light absorbing carbon species at higher temperatures in the He-mode, including both native EC and combinations of native EC and pyrolytic carbon potentially with different specific attenuation cross section values. Thirdly, we have minimised the potential positive bias in EC determination resulting from the incomplete evolution of OC during the He-mode which then evolves during the He/O2-mode, potentially after the split point. Finally, we have minimised the uncertainty due to the position of the OC/EC split point on the FID response profile by introducing multiple desorption steps in the He/O2-mode. Based on different types of carbonaceous PM encountered across Europe, we have defined an optimised thermal evolution protocol, the EUSAAR_2 protocol, as follows: step 1 in He, 200 °C for 120 s; step 2 in He 300 °C for 150 s; step 3 in He 450 °C for 180 s; step 4 in He 650 °C for 180 s. For steps 1–4 in He/O2, the conditions are 500 °C for 120 s, 550 °C for 120 s, 700 ° C for 70 s, and 850 °C for 80 s, respectively.
Surface features on Sahara soil dust particles made visible by atomic force microscope (AFM) phase images
Authors: Helas G. , Andreae M. O.
Published: April 2010

Abstract. We show that atomic force microscopy (AFM) phase images can reveal surface features of soil dust particles, which are not evident using other microscopic methods. The non-contact AFM method is able to resolve topographical structures in the nanometer range as well as to uncover repulsive atomic forces and attractive van der Waals' forces, and thus gives insight to surface properties. Though the method does not allow quantitative assignment in terms of chemical compound description, it clearly shows deposits of distinguishable material on the surface. We apply this technique to dust aerosol particles from the Sahara collected over the Atlantic Ocean and describe micro-features on the surfaces of such particles.
Characterization of a thermodenuder- particle beam mass spectrometer system for the study of organic aerosol volatility and composition
Authors: Faulhaber A. E. , Thomas B. M. , Jimenez J. L. , Jayne J. T. , Worsnop D. R. , Ziemann P. J.
Published: April 2010

Abstract. This paper describes the development and evaluation of a method for measuring the vapor pressure distribution and volatility-dependent mass spectrum of organic aerosol particles using a thermodenuder-particle beam mass spectrometer. The method is well suited for use with the widely used Aerodyne Aerosol Mass Spectrometer (AMS) and other quantitative aerosol mass spectrometers. The data that can be obtained are valuable for modeling organic gas-particle partitioning and for gaining improved composition information from aerosol mass spectra. The method is based on an empirically determined relationship between the thermodenuder temperature at which 50% of the organic aerosol mass evaporates (T50) and the organic component vapor pressure at 25°C (P25). This approach avoids the need for complex modeling of aerosol evaporation, which normally requires detailed information on aerosol composition and physical properties. T50 was measured for a variety of monodisperse, single-component organic aerosols with known P25 values and the results used to create a log P25 vs. T50 calibration curve. Experiments and simulations were used to estimate the uncertainties in P25 introduced by variations in particle size and mass concentration as well as mixing with other components. A vapor pressure distribution and volatility-dependent mass spectrum were then measured for laboratory-generated secondary organic aerosol particles. Vaporization profiles from this method can easily be converted to a volatility basis set representation, which shows the distribution of mass vs. saturation concentration and the gas-particle partitioning of aerosol material. The experiments and simulations indicate that this method can be used to estimate organic aerosol component vapor pressures to within approximately an order of magnitude and that useful mass-spectral separation based on volatility can be achieved.
Measurement of atmospheric sesquiterpenes by proton transfer reaction-mass spectrometry (PTR-MS)
Authors: Kim S. , Karl T. , Helmig D. , Daly R. , Rasmussen R. , Guenther A.
Published: April 2010

Abstract. The ability to measure sesquiterpenes (SQT; C15H24) by a Proton-Transfer-Reaction Mass Spectrometer (PTR-MS) was investigated with SQT standards, prepared by a capillary diffusion method, and the estimated mixing ratios, derived from the counts of product ions and proton transfer reaction constants were intercompared with measured mixing ratios, measured by a complementary Gas Chromatograph (GC) coupled to a Flame Ionization Detector (GC-FID). Product ion distributions due to soft-ionization occurring in a selected ion drift tube via proton transfer were measured as a function of collision energies. Results after the consideration of the mass discrimination of the PTR-MS system suggest that quantitative SQT measurements within 20% accuracy can be achieved with PTR-MS if two major product ions (m/z 149+ and 205+) out of seven major product ions (m/z 81+, 95+, 109+, 123+, 135+, 149+ and 205+) are accounted for. Bicyclic sesquiterpenes, i.e. β-caryophyllene and α-humulene, showed considerable fragmentation causing the accuracy of their analysis to be reduced to 50% if only the parent ion (m/z 205) is considered. These findings were applied to a field dataset collected above a deciduous forest at the PROPHET (Program for Research on Oxidants: Photochemistry, Emissions, and Transport) research station in 2005. Inferred Average daytime ecosystem scale mixing ratios (fluxes) of isoprene, sum of monoterpenes (MT), and sum of SQT exhibited values of 15 μg m−3 (4.5 mg m−2 h−1), 1.2 μg m−3 (0.21 mg m−2 h−1) and 0.0016 μg m−3 (0.10 mgm−2 h−1) respectively. A range of MT and SQT reactivities with respect to the OH radical was calculated and compared to an earlier study inferring significantly underestimated OH reactivities due to unknown terpenes above this deciduous forest. The results indicate that MT and SQT can resolve ~30% of missing OH reactivity, reported from this site.
Influence of particle charging on TEOM measurements in the presence of an electrostatic precipitator
Authors: Meyer N. K. , Lauber A. , Nussbaumer T. , Burtscher H.
Published: April 2010

Abstract. The efficiency of an electrostatic precipitator (ESP) for reducing wood combustion emissions was investigated. Real-time measurements were conducted by directly reading the change in frequency of the tapered element in a Thermo Scientific 1400a TEOM. The measurements have been shown to be influenced by the charge on the aerosols reaching the tapered element such that the TEOM overestimates mass concentration. This electrostatic effect was cross-checked with particle number concentration measurements where no influence was observed. Placing a radioactive neutraliser prior to the TEOM leads to agreement between observed ESP efficiencies as measured by both the TEOM and a CPC.
A cavity ring down/cavity enhanced absorption device for measurement of ambient NO3 and N2O5
Authors: Schuster G. , Labazan I. , Crowley J. N.
Published: April 2010

Abstract. An inexpensive, compact instrument for the sensitive measurement of NO3 and N2O5 in ambient air at high time resolution is described. Light from a red-emitting laser diode (≈662 nm) is coupled off-axis into an optical resonator defined by two highly reflective mirrors to achieve effective absorption paths exceeding 20 km. Light leaking from the cavity is detected either as single ring-down events over ≈200 μs following rapid switching of the laser intensity at 200 Hz (Cavity Ring Down mode), or as an integrated intensity (Cavity Enhanced Absorption mode). The operational conditions, detection limits and total uncertainty for the prototype device for NO3 and N2O5 detection/monitoring are assessed and the first measurements in ambient air and from an environmental chamber are described.
A new airborne tandem platform for collocated measurements of microphysical cloud and radiation properties
Authors: Frey W. , Eichler H. , de Reus M. , Maser R. , Wendisch M. , Borrmann S.
Published: April 2010

Abstract. A new airborne tandem measurement platform for cloud-radiation interaction studies is introduced in this paper. It consists of a Learjet 35A research aircraft and the AIRcraft TOwed Sensor Shuttle (AIRTOSS), which is an instrumented drag-body towed by the Learjet. Currently, the AIRTOSS is instrumented with a Cloud Imaging Probe (CIP) for measuring cloud microphysical properties and an Inertial Navigation System (INS) for measurements of flight attitudes. The cable dragging AIRTOSS can be as long as four kilometres. Thus, truly collocated measurements in two altitudes above, in, and below clouds can be obtained. Results from first test flights with Learjet and AIRTOSS are reported here. The flights were performed from Hohn Airport, Germany. Specific manoeuvres were flown to test the aerodynamic behaviour of the drag-body and to investigate the suitability of AIRTOSS for high-precision irradiance measurements which require a stable flight attitude of AIRTOSS. The flight attitude data show that AIRTOSS is sensitive to several flight manoeuvres such as curves, altitude and airspeed changes, and also to changes of towing cable length. The effects of these manoeuvres on the attitude angles of AIRTOSS have been quantified. Maximum roll angle deviations were observed during curve flight. Even small changes in heading can lead to high roll angles (one degree change in heading causes a change in roll angle of about eight degrees). The pitch angle varies during climb or dive periods, extending or retracting of towing cable, acceleration or deceleration, and even when flying at too low or too high true airspeed depending on altitude. Values of pitch angle between −5° (dive) and 8° (climb and retracting towing cable) have been observed. While change in attitude is not problematic for cloud particle property measurements it is for radiation measurements. Here, the deviation from the horizontal should be no more than 3° to avoid large errors. When keeping the above mentioned flight parameters constant, sufficiently stable flight conditions can be maintained to perform high-quality irradiance measurements with AIRTOSS in future experiments. During this test campaign also observations of cloud microphysical data as for example droplet number concentrations and size distributions with the AIRTOSS in stratocumulus clouds were performed to prove the compliance with scientific needs. Simultaneous radiation measurements of the clouds have been made. The measurements of internal operational data of AIRTOSS as well as the first atmospheric data demonstrate the suitability of this tandem platform for detailed cloud microphysics and radiation interaction studies.
Water vapor total column measurements using the Elodie Archive at Observatoire de Haute Provence from 1994 to 2004
Authors: Sarkissian A. , Slusser J.
Published: April 2010

Abstract. Water vapor total column measurements at Observatoire de Haute Provence (5°42' E, +43°55' N), south of France, were obtained using observations of astronomical objects made between July 1994 and December 2004 on the 193-cm telescope with the high-resolution spectrometer Elodie. Spectra of stars, nebulae, and other astronomical objects were taken regularly during 10 years. More than 18 000 spectra from 400 nm to 680 nm are available on-line in the Elodie Archive. This archive, usually explored by astronomers, contains information to study the atmosphere of the Earth. Water vapor absorption lines appear in the visible in delimited bands that astronomers often avoid for their spectral analysis. We used the Elodie Archive with two objectives: firstly, to retrieve seasonal variability and long-term trend of atmospheric water vapor, and secondly, to remove signatures in spectra for further astronomical or geophysical use. The tools presented here are developed following, when possible, formats and standards recommended by the International Virtual Observatory Alliance.
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% RH 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 weeks experiment. The lower 50% cut-off was found to be below 3 nm at the design flow rate of the instrument. Measured transmission efficiencies are in good agreement with theoretical calculations. One drier has been successfully deployed in the Amazonas river basin. From this monitoring site, we present data from 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% RH 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.
Cloud detection for MIPAS using singular vector decomposition
Authors: Hurley J. , Dudhia A. , Grainger R. G.
Published: April 2010

Abstract. Clouds are increasingly recognised for their influence on the radiative balance of the Earth and the implications that they have on possible climate change, as well as in air pollution and acid-rain production. However, clouds remain a major source of uncertainty in climate models. Satellite-borne high-resolution limb sounders, such as the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) onboard ENVISAT, provide information on clouds, especially optically thin clouds, which have been difficult to observe in the past. The aim of this work is to develop, implement and test a reliable cloud detection method for infrared spectra measured by MIPAS. Current MIPAS cloud detection methods used operationally have been developed to detect thick cloud filling more than 30% of the measurement field-of-view (FOV). In order to resolve thin clouds, a new detection method using Singular Vector Decomposition (SVD) is formulated and tested. A rigorous comparison of the current operational and newly-developed detection methods for MIPAS is carried out – and the new SVD detection method has been proven to be much more reliable than the current operational method, and very sensitive even to thin clouds only marginally filling the MIPAS FOV.
Water vapor δ2H and δ18O measurements using off-axis integrated cavity output spectroscopy
Authors: Sturm P. , Knohl A.
Published: April 2010

Abstract. We present a detailed assessment of a commercially available water vapor isotope analyzer (WVIA, Los Gatos Research, Inc.) for simultaneous in-situ measurements of δ2H and δ18O in water vapor. This method, based on off-axis integrated cavity output spectroscopy, is an alternative to the conventional water trap/isotope ratio mass spectrometry (IRMS) techniques. We evaluate the analyzer in terms of precision, memory effects, concentration dependence, temperature sensitivity and long-term stability. A calibration system based on ink jet technology is used to characterize the performance and to calibrate the analyzer. Our results show that the precision at an averaging time of 15 s is 0.16‰ for δ2H and 0.08‰ for δ18O. The isotope ratios are strongly dependent on the water mixing ratio of the air. Taking into account this concentration dependence as well as the temperature sensitivity of the instrument we obtained a long-term stability of the water isotope measurements of 0.38‰ for δ2H and 0.25‰ for δ18O. The accuracy of the WVIA was further assessed by comparative measurements using IRMS and a dew point generator indicating a linear response in isotopic composition and H2O concentrations. The WVIA combined with a calibration system provides accurate high resolution water vapor isotope measurements and opens new possibilities for hydrological and ecological applications.
Development of an autonomous sea ice tethered buoy for the study of ocean-atmosphere-sea ice-snow pack interactions: the O-buoy
Authors: Knepp T. N. , Bottenheim J. , Carlsen M. , Carlson D. , Donohoue D. , Friederich G. , Matrai P. M. , Netcheva S. , Perovich D. K. , Santini R. , Shepson P. B. , Simpson W. , Stehle R. , Valentic T. , Williams C. , Wyss P. J.
Published: April 2010

Abstract. A buoy based instrument platform (the "O-buoy") was designed, constructed, and field tested for year-round measurement of ozone, bromine monoxide, carbon dioxide, and meteorological variables over Arctic sea ice. The O-buoy operated in an autonomous manner with daily, bi-directional data transmissions using Iridium satellite communication. The O-buoy was equipped with three power sources: primary lithium-ion battery packs, rechargeable lead acid packs, and solar panels that recharge the lead acid packs, and can fully power the O-buoy during summer operation. This system was designed to operate under the harsh conditions present in the Arctic, with minimal direct human interaction, to aid in our understanding of the atmospheric chemistry that occurs in this remote region of the world. The current design requires approximately yearly maintenance limited by the lifetime of the primary power supply. The O-buoy system was field tested in Elson Lagoon, Barrow, Alaska from February to May 2009, and here we describe the design and present preliminary data.
Laboratory-generated primary marine aerosol via bubble-bursting and atomization
Authors: Fuentes E. , Coe H. , Green D. , McFiggans G.
Published: April 2010

Abstract. A range of bubble and sea spray aerosol generators has been tested in the laboratory and compared with ocean measurements. We have shown that the method of generation has a significant influence on the properties of the aerosol particles produced. Hence, the validity of a generation system to mimic atmospheric aerosol is dependent on its capacity of generating bubbles and particulate in a realistic manner. A bubble-bursting aerosol generator consisting in the production of bubbles by the impingement of water jets on seawater was shown to best reproduce the real oceanic bubble and aerosol distributions signatures. Two aeration methods and a plunging-water jet system were tested as bubble-bursting aerosol generators for comparison with a standard nebulizer. The methods for aerosol production were evaluated by analysing the bubble spectrum generated by the bubble-bursting systems and the submicron size distribution, hygroscopicity and cloud condensation nucleus activity of the aerosols generated by the different techniques. Significant differences in the bubble spectrum and aerosol properties were observed when using different aerosol generators. The hygroscopicity and cloud condensation nucleus activity of aerosols generated by the different methods were similar when a sample of purely inorganic salts was used as a parent seawater solution; however, significant differences in the aerosol properties were found when biogenic organics were incorporated in the seawater samples. The presence of organics in the aerosol caused suppression of the growth factor at humidities above 75% RH and an increase in the critical supersaturation when compared with the case without organics. Unequal extent of these effects was observed for aerosols generated by the different methods of particle production. While the highest reductions of the growth factor were observed for the plunging-water jet aerosol, the largest effect on the critical supersaturation was obtained for the atomization-generated particles. The results of this work show that the aerosol generation mechanism affects the particles organic enrichment, thus the behaviour of the produced aerosols strongly depends on the laboratory aerosol generator employed.
Development of a bioaerosol single particle detector (BIO IN) for the fast ice nucleus chamber FINCH
Authors: Bundke U. , Reimann B. , Nillius B. , Jaenicke R. , Bingemer H.
Published: April 2010

Abstract. In this work we present the setup and first tests of our new BIO IN detector. This detector is designed to classify atmospheric ice nuclei (IN) for their biological content. Biological material is identified via its auto-fluorescence (intrinsic fluorescence) after irradiation with UV radiation. Ice nuclei are key substances for precipitation development via the Bergeron–Findeisen process. The level of scientific knowledge regarding origin and climatology (temporal and spatial distribution) of IN is very low. Some biological material is known to be active as IN even at relatively high temperatures of up to –2°C (e.g. pseudomonas syringae bacteria). These biological IN could have a strong influence on the formation of clouds and precipitation. We have designed the new BIO IN sensor to analyze the abundance of IN of biological origin. The instrument will be flown on one of the first missions of the new German research aircraft ''HALO'' (High Altitude and LOng Range).