bluuebunny/crossref_metadata_2025 huggingface dataset:
MS/MS studies for the selective detection of isomeric biogenic VOCs using a Townsend Discharge Triple Quadrupole Tandem MS and a PTR-Linear Ion Trap MS
Authors: Müller M. , Mielke L. H. , Breitenlechner M. , McLuckey S. A. , Shepson P. B. , Wisthaler A. , Hansel A.
Published: April 2010

Abstract. We performed MS/MS investigations of biogenic volatile organic compounds (BVOC) using a triple quadrupole tandem mass spectrometer (QqQ-MS) equipped with a Townsend Discharge ion source and a Proton Transfer Reaction Linear Ion Trap (PTR-LIT) mass spectrometer. Both instruments use H2O chemical ionization to produce protonated molecular ions. Here we report a study of the application of these instruments to determine methyl vinyl ketone (MVK) and methacrolein (MACR) and a series of monoterpenes (α-pinene, β-pinene, 3-carene, limonene, myrcene, ocimene) and sesquiterpenes (humulene and farnesene). Both instruments achieved sub-ppb detection limits in the single MS mode and in the MS/MS mode for differentiating MVK and MACR. Collision induced dissociation (CID) of protonated monoterpenes and sesquiterpenes was studied under the high-energy, single-to-few collision conditions of the QqQ-MS instrument and under the low-energy, multiple collision conditions of the PTR-LIT. Differences and similarities in the breakdown curves obtained are discussed. In addition, we performed MS4 of protonated limonene to illustrate the analytical power of the PTR-LIT. In spite of the progress we have made, the selective on-line mass-spectrometric detection of individual monoterpenes or sesquiterpenes in complex mixtures currently does not yet seem to be possible.
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 for atmospheric research 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 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 coma 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 an exceptionally compact instrument for differential optical absorption spectroscopy (DOAS) applications particularly from space (LEO, GEO orbits) and from HAPs 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 better than 0.5 nm resolution, suitable for a number of typical DOAS applications.
Determination of oceanic ozone deposition by ship-borne eddy covariance flux measurements
Authors: Bariteau L. , Helmig D. , Fairall C. W. , Hare J. E. , Hueber J. , Lang E. K.
Published: April 2010

Abstract. A fast response ozone analyzer based on the ozone-nitric oxide chemiluminescence method was integrated into the NOAA-ESRL flux system to achieve the first ship-borne, direct ozone flux measurements over the open ocean. Air was collected from an inlet at 18 m height over the ocean surface mounted to the bow-jackstaff and via a 30 m-long sampling line to the ozone instrument on the ship deck. A "puff" system was used for accurate and regular determination of the sample transport time (lag) between the inlet and the chemical analyzer. A Nafion-membrane dryer facilitated removal of fast water vapor fluctuations, which eliminated the need for quenching and density correction of the ozone signal. The sampling-analyzer system was found to have a ~0.25–0.40 s response time at a sensitivity of ~2800 counts s−1 per ppbv of ozone. Quality control and data filtering procedures for eliminating data that did not meet measurement requirements were critically evaluated. The new ozone flux system was deployed during several cruises aboard the NOAA Ship Ronald H. Brown, and evaluated using results obtained during several research cruises off the coasts of the North and South America continents.
Determining the sea-air flux of dimethylsulfide by eddy correlation using mass spectrometry
Authors: Blomquist B. W. , Huebert B. J. , Fairall C. W.
Published: April 2010

Abstract. Mass spectrometric measurement of DMS by atmospheric pressure ionization with an isotopically labeled standard (APIMS-ILS) is a sensitive method with sufficient bandpass for direct flux measurements by eddy correlation. Use of an isotopically labeled internal standard greatly reduces instrumental drift, improving accuracy and precision. APIMS-ILS has been used in several recent campaigns to study ocean-atmosphere gas transfer and the chemical budget of DMS in the marine boundary layer. This paper provides a comprehensive description of the method and errors associated with DMS flux measurement from ship platforms. The APIMS-ILS instrument used by most groups today has a sensitivity of 100–200 counts s−1 pptv−1, which is shown to be more than sufficient for flux measurement by eddy covariance. Mass spectral backgrounds (blanks) are determined by stripping DMS from ambient air with gold. The instrument is found to exhibit some signal loss, with a half-power frequency of ≈1 Hz, but a correction based on an empirically determined instrument response function is presented. Standard micrometeorological assumptions of steady state and horizontal uniformity are found to be appropriate for DMS flux measurement, but rapid changes in mean DMS mixing ratio serve as a warning that measured flux may not represent the true surface flux. In addition, bias in surface flux estimates arising from the flux gradient are not generally significant, but conditions of lowered inversion and high surface flux may lead to a significant difference between measured flux and true surface flux. The effects of error in motion corrections and of vertical motion within the surface layer concentration gradient are discussed and the estimated maximum error from these effects is ≤18%.
Measurement of relative humidity dependent light scattering of aerosols
Authors: Fierz-Schmidhauser R. , Zieger P. , Wehrle G. , Jefferson A. , Ogren J. A. , Baltensperger U. , Weingartner E.
Published: April 2010

Abstract. Relative humidity (RH) influences the water content of aerosol particles and therefore has an important impact on the particles' ability to scatter visible light. The RH dependence of the particle light scattering coefficient (σsp) is therefore an important measure for climate forcing calculations. We built a humidification system for a nephelometer which allows the measurement of σsp at a defined RH in the range of 40–90%. This RH conditioner consists of a humidifier followed by a dryer, which enables us to measure the hysteresis behavior of deliquescent aerosol particles. In this paper we present the set-up of a new humidified nephelometer, a detailed characterization with well defined laboratory generated aerosols, and a first application in the field by comparing our instrument to another humidified nephelometer. Monodisperse ammonium sulfate and sodium chloride particles were measured at four different dry particle sizes. Agreement between measurement and prediction based on Mie theory was found for both σsp and f(RH)=σsp(RH)/σsp(dry) within the range of uncertainty. The two humidified nephelometers measuring at a rural site in the Black Forest (Germany) often detected different f(RH), probably caused by the aerosol hysteresis behavior: when the aerosol was metastable, therefore was scattering more light, only one instrument detected the higher f(RH).
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 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.
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. 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).
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 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 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, for the first time, 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.
Mobile MAX-DOAS observations of tropospheric trace gases
Authors: Wagner T. , Ibrahim O. , Shaiganfar R. , Platt U.
Published: April 2010

Abstract. From Multi-Axis- (MAX-) DOAS observations information on tropospheric trace gases close to the surface and up to the free troposphere can be obtained. Usually MAX-DOAS observations are performed at fixed locations, which allows to retrieve the diurnal variation of tropospheric species at that location. Alternatively, MAX-DOAS observations can also be made on mobile platforms like cars, ships or aircrafts. Then, in addition to the vertical (and temporal) distribution, also the horizontal variation of tropospheric trace gases can be measured. Such information is important for the quantitative comparison with model simulations, study of transport processes, and for the validation of tropospheric trace gas products from satellite observations. However, for MAX-DOAS observations from mobile platforms, the standard analysis techniques for MAX-DOAS observations can usually not be applied, because the probed airmasses can change rapidly between successive measurements. In this study we introduce a new technique which overcomes these problems and allows the exploitation of the full information content of mobile MAX-DOAS observations. Our method can also be applied to MAX-DOAS observations made at fixed locations in order to improve the accuracy especially in cases of strong winds. We apply the new technique to MAX-DOAS observations made during an automobile trip from Brussels to Heidelberg.
Optical properties of different aerosol types: seven years of combined Raman- elastic backscatter lidar measurements in Thessaloniki, Greece
Authors: Giannakaki E. , Balis D. S. , Amiridis V. , Zerefos C.
Published: April 2010

Abstract. We present our combined Raman/elastic backscatter lidar observations which were carried out at the EARLINET station of Thessaloniki, Greece, during the period 2001–2007. The largest optical depths are observed for Saharan dust and smoke aerosol loads. For "local" and "continental polluted" aerosols the measurements indicate moderate aerosol loads. However, measurements associated with the "local" path show lower values of free tropospheric contribution (37% versus 46% for "continental polluted") and thus, enhanced aerosol load within the Planetary Boundary Layer. The lowest value of aerosol optical depth is observed for "continental clean" aerosols. The largest lidar ratios, of the order of 70 sr are found for biomass burning aerosols. A significant and distinct correlation between lidar ratio and backscatter related Ångström exponent values was estimated for well defined aerosol categories, which provides a statistical measure of the lidar ratio's dependency on aerosol-size, which is a useful tool for elastic lidar systems. Scatter plot between lidar ratio values and Ångström exponent values for "local" and "continental polluted" aerosols does not show a significant correlation, with a large variation in both parameters possibly due to variable absorption characteristics of these aerosols. Finally for "clean continental" aerosols we found constantly low lidar ratios almost independent of size.
On the improvement of NO2 satellite retrievals – aerosol impact on the airmass factors
Authors: Leitão J. , Richter A. , Vrekoussis M. , Kokhanovsky A. , Zhang Q. J. , Beekmann M. , Burrows J. P.
Published: April 2010

Abstract. The accurate determination of nitrogen dioxide (NO2) tropospheric vertical columns from satellite measurements depends, partly, on the airmass factor (AMF) used. A sensitivity study was performed with the radiative transfer model SCIATRAN to better understand the impact of aerosols in the calculation of NO2 AMFs. This influence was studied by varying the NO2 and aerosol vertical distributions, as well as physical and optical properties of the particles. The key factors for these calculations were identified as the relation between trace gas and aerosol vertical profiles, the optical depth of the aerosol layer, and single scattering albedo. Overall it was found that aerosol mixed with the trace gas increases the measurements' sensitivity. The largest change, a factor of ~2 relative to the situation without aerosols, was found when a low layer of aerosol (600 m) was combined with a homogenous NO2 layer of 1.0 km. A layer of aerosol above the NO2 will usually reduce the sensitivity of the satellite measurement, a situation found mostly for runs with discrete elevated aerosol layers representative for long-range transport of aerosols that can generate a decrease of the AMF values of up to 70%. The use of measured aerosol profiles and modelled NO2 resulted, generally, in a much smaller changes of AMF relative to the pure Rayleigh case. Exceptions are some events of elevated layers with high aerosol optical depth that lead to a strong decrease of the AMF values. These results highlight the importance of aerosols in the retrieval of tropospheric NO2 columns from space and indicate the need for detailed information on aerosol properties and vertical distribution.
Validation of CALIPSO space-borne-derived aerosol vertical structures using a ground-based lidar in Athens, Greece
Authors: Mamouri R. E. , Amiridis V. , Papayannis A. , Giannakaki E. , Tsaknakis G. , Balis D. S.
Published: April 2010

Abstract. We present initial aerosol validation results of the space-borne lidar CALIOP retrievals -onboard the CALIPSO satellite-, using coincident observations performed with a ground-based lidar in Athens, Greece (37.9° N, 23.6° E). A multi-wavelength ground-based backscatter/Raman lidar system is operating since 2000 at the National Technical University of Athens (NTUA) in the framework of the European Aerosol Research LIdar NETwork (EARLINET), the first lidar network for tropospheric aerosol studies on a continental scale. Since July 2006, a total of 40 coincidental aerosol ground-based lidar measurements were performed over Athens during CALIPSO overpasses. The duration of the ground-based lidar measurements was approximately two hours, centred on the satellite overpass time. From the statistical analysis of the ground-based/satellite correlative lidar measurements, a mean bias of the order of 22% for daytime measurements and of 8% for nighttime measurements with respect to the CALIPSO profiles was found for altitudes between 3 and 10 km. The mean bias becomes much larger for altitudes lower that 3 km (of the order of 60%) which is attributed to the decrease of the CALIOP signal-to-noise ratio, as well as to the incomplete overlap height region of the ground based lidar and finally to the distance between the two instruments, resulting to the observation of possibly different air masses. In cases of aerosols layers underlying cirrus clouds, comparison results for aerosol tropospheric profiles become worst, illustrating the limitations of space-borne downward-looking lidar measurements due to strong signal attenuations.
The benefit of limb cloud imaging for tropospheric infrared limb sounding
Authors: Adams S. , Spang R. , Preusse P. , Heinemann G.
Published: April 2010

Abstract. Advances in detector technology enable a new generation of infrared limb sounders to measure 2-D images of the atmosphere. A proposed limb cloud imager (LCI) mode will measure clouds with very high spatial resolution. For the inference of temperature and trace gas distributions, detector pixels of the LCI have to be combined into super-pixels which provide the required signal-to-noise ratio and information content for the retrievals. This study examines the extent to which tropospheric coverage can be improved in comparison to limb sounding using a fixed field of view with the size of the super-pixels, as in conventional limb sounders. The study is based on cloud topographies derived from (a) IR brightness temperatures (BT) of geostationary weather satellites in conjunction with ECMWF temperature profiles and (b) ice and liquid water content data of the Consortium for Small-scale Modeling-Europe (COSMO-EU) of the German Weather Service. Limb cloud images are simulated by matching the cloud topography with the limb sounding line of sight (LOS). The analysis of the BT data shows that the reduction of the spatial sampling along the track has hardly any effect on the gain in information. The comparison between BT and COSMO-EU data identifies the strength of both data sets, which are the representation of the horizontal cloud extent for the BT data and the reproduction of the cloud amount for the COSMO-EU data. The results of the analysis of both data sets show the great advantage of the cloud imager. However, because both cloud data sets do not present the complete fine structure of the real cloud fields in the atmosphere it is assumed that the results tend to underestimate the increase in information. In conclusion, real measurements by such an instrument may result in an even higher benefit for tropospheric limb retrievals.
A new method for the simulation of the Ring effect in observations of scattered sun light
Authors: Wagner T. , Beirle S. , Deutschmann T.
Published: April 2010

Abstract. We present a new technique for the quantitative simulation of the "Ring effect" for scattered light observations from various platforms and under different atmospheric situations. The method is based on radiative transfer calculations at only one wavelength λ0 in the wavelength range under consideration, and is thus computationally fast. The strength of the Ring effect is calculated from statistical properties of the photon paths for a given situation, which makes Monte Carlo radiative transfer models in particular appropriate. We quantify the Ring effect by the so called rotational Raman scattering probability, the probability that an observed photon has undergone a rotational Raman scattering event. The Raman scattering probability is independent from the spectral resolution of the instrument and can easily be converted into various definitions used to characterise the strength of the Ring effect. We compare the results of our new method to the results of previous studies and in general good quantitative agreement is found. In addition to the simulation of the Ring effect, we developed a detailed retrieval strategy for the analysis of the Ring effect based on DOAS retrievals, which allows the precise determination of the strength of the Ring effect for a specific wavelength while using the spectral information within a larger spectral interval around the selected wavelength. Using our new technique, we simulated synthetic satellite observation of an atmospheric scenario with a finite cloud illuminated from different sun positions.
Design and construction of a simple Knudsen Effusion Mass Spectrometer (KEMS) system for vapour pressure measurements of low volatility organics
Authors: Booth A. M. , Markus T. , McFiggans G. , Percival C. J. , Mcgillen M. R. , Topping D. O.
Published: April 2010

Abstract. A design of and initial results from a Knudsen Effusion Mass Spectrometer (KEMS) are presented. The design was adapted from high temperature alloy studies with a view to using it to measure vapour pressures for low volatility organics. The system uses a temperature controlled cell with an effusive orifice. This produces a molecular beam which is sampled by a quadropole mass spectrometer with electron impact ionization calibrated to a known vapour pressure. We have determined P298 and ΔHsub of the first 5 unsaturated straight chain dicarboxylic acids: 2.15±1.19×10−2 Pa and 75±19 kJ mol−1 respectively for Oxalic acid, 5.15±0.76×10−4 Pa and 91±4 kJ mol−1 for Malonic acid, 9.19±2.26×10−5 Pa and 93±6 kJ mol−1 for Succinic acid, 4.21±1.66×10−4 Pa and 123±22 kJ mol−1 for Glutaric acid and 5.21±3.84×10−6 Pa and 125±40 kJ mol−1 for Adipic acid.
A Relaxed Eddy Accumulation (REA)-GC/MS system for the determination of halocarbon fluxes
Authors: Hornsby K. E. , Flynn M. J. , Dorsey J. R. , Gallagher M. W. , Chance R. , Jones C. E. , Carpenter L. J.
Published: April 2010

Abstract. Very short lived halocarbons (VSLH) play an important role in the transport of halogen atoms to the troposphere and lower stratosphere. Here we describe the development of a relaxed eddy accumulation system using gas chromatography coupled to a mass spectrometer (REA-GC/MS) to determine surface fluxes of VSLH with a time resolution of about 0.5 h. Laboratory tests showed that use of a common inlet for upward, downward and deadband flow paths resulted in mixing of upward and downward moving air masses, therefore we recommend the use of separate inlets. The modified system underwent field trials at Mace Head on the west coast of Ireland, where there are dense kelp beds known to emit a range of halocarbons. Over a 16 h period in mid-September 2007, the mean fluxes obtained were 51.7±5.9, 2.9±0.4 and 0.9±0.1 nmol m−2 day−1 for CH2Br2, CH2ICl and CH2IBr, respectively.
An intercomparison of GC-FID and PTR-MS toluene measurements in ambient air under conditions of enhanced monoterpene loading
Authors: Ambrose J. L. , Haase K. , Russo R. S. , Zhou Y. , White M. L. , Frinak E. K. , Jordan C. , Mayne H. R. , Talbot R. , Sive B. C.
Published: April 2010

Abstract. Toluene was measured using both a gas chromatographic system (GC), with a flame ionization detector (FID), and a proton transfer reaction-mass spectrometer (PTR-MS) at the AIRMAP atmospheric monitoring station Thompson Farm (THF) in rural Durham, NH during the summer of 2004. Simultaneous measurements of monoterpenes, including α- and β-pinene, camphene, Δ3-carene, and d-limonene, by GC-FID demonstrated large enhancements in monoterpene mixing ratios relative to toluene, with median and maximum enhancement ratios of ~2 and ~30, respectively. A detailed intercomparison among the GC-FID and PTR-MS toluene measurements was conducted to test the specificity of PTR-MS for atmospheric toluene measurements under conditions often dominated by biogenic emissions. We derived quantitative estimates of potential interferences in the PTR-MS toluene measurements related to sampling and analysis of monoterpenes, including fragmentation of the monoterpenes and some of their primary carbonyl oxidation products via reactions with H3O+, O2+ and NO+ in the PTR-MS drift tube. The PTR-MS and GC-FID toluene measurements were in good quantitative agreement and the two systems tracked one another well from the instrumental limits of detection to maximum mixing ratios of ~0.5 ppbv. Discrepancies in the measured mixing ratios were not well correlated with enhancements in the monoterpenes. Better quantitative agreement between the two systems was obtained by correcting the PTR-MS measurements for contributions from monoterpene fragmentation in the PTR-MS drift tube; however, the improvement was minor. Interferences in the PTR-MS measurements from fragmentation of the monoterpene oxidation products pinonaldehyde, caronaldehyde and α-pinene oxide were also likely negligible. The results from THF suggest that toluene can be reliably quantified by PTR-MS using our operating conditions under the ambient compositions probed. This work extends the range of field conditions under which PTR-MS validation studies have been conducted.
A sea surface reflectance model for (A)ATSR, and application to aerosol retrievals
Authors: Sayer A. M. , Thomas G. E. , Grainger R. G.
Published: April 2010

Abstract. A model of the sea surface bidirectional reflectance distribution function (BRDF) is presented for the visible and near-IR channels (over the spectral range 550 nm to 1.6 μm) of the dual-viewing Along-Track Scanning Radiometers (ATSRs). The intended application is as part of the Oxford-RAL Aerosols and Clouds (ORAC) retrieval scheme. The model accounts for contributions to the observed reflectance from whitecaps, sun-glint and underlight. Uncertainties in the parametrisations used in the BRDF model are propagated through into the forward model and retrieved state. The new BRDF model offers improved coverage over previous methods, as retrievals are possible into the sun-glint region, through the ATSR dual-viewing system. The new model has been applied in the ORAC aerosol retrieval algorithm to process Advanced ATSR (AATSR) data from September 2004 over the south-eastern Pacific. The assumed error budget is shown to be generally appropriate, meaning the retrieved states are consistent with the measurements and a priori assumptions. The resulting field of aerosol optical depth (AOD) is compared with colocated MODIS-Terra observations, AERONET observations at Tahiti, and cruises over the oceanic region. MODIS and AATSR show similar spatial distributions of AOD, although MODIS reports values which are larger and more variable. It is suggested that assumptions in the MODIS aerosol retrieval algorithm may lead to a positive bias in MODIS AOD of order 0.01 at 550 nm over ocean regions where the wind speed is high.
Capability of multi-viewing-angle photo-polarimetric measurements for the simultaneous retrieval of aerosol and cloud properties
Authors: Hasekamp O. P.
Published: April 2010

Abstract. An important new challenge in the field of multi-angle photopolarimetric satellite remote sensing is the retrieval of aerosol properties under cloudy conditions. In this paper the possibility has been explored to perform a simultaneous retrieval of aerosol and cloud properties for partly cloudy scenes and for fully cloudy scenes where the aerosol layer is located above the cloud, using multi-angle photo-polarimetric measurements. Also, for clear sky conditions a review is given of the capabilities of multi-angle photo-polarimetric measurements in comparison with other measurement types. It is shown that already for clear sky conditions polarization measurements are highly important for the retrieval of aerosol optical and microphysical properties over land surfaces with unknown reflection properties. Furthermore, it is shown that multi-angle photo-polarimetric measurements have the capability to distinguish between aerosols and clouds, and thus facilitate a simultaneous retrieval of aerosol and cloud properties. High accuracy (0.002–0.004) of the polarimetric measurements plays an essential role here.
Synergy between CALIOP and MODIS instruments for aerosol monitoring: application to the Po Valley
Authors: Royer P. , Raut J.-C. , Ajello G. , Berthier S. , Chazette P.
Published: April 2010

Abstract. We propose here a synergy between Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations/Cloud-Aerosol LIdar with Orthogonal Polarization (CALIPSO/CALIOP) and Moderate Resolution Imaging Spectroradiometer (MODIS) onboard Aqua and Terra in order to retrieve aerosol optical properties over the Po Valley from June 2006 to February 2009. Such an approach gives simultaneously access to the aerosol extinction vertical profile and to the equivalent backscatter-to-extinction ratio at 532 nm (BER, inverse of the lidar ratio). The choice of the Po valley has been driven by the great occurrences of pollutant events leading to a mean MODIS-derived aerosol optical thickness of 0.27(±0.17) at 550 nm over a large area of ~120 000 km2. In such area, a significant number of CALIOP level-1 vertical profiles can be averaged (~200 individual laser shots) leading to a signal-to-noise ratio greater than 10 in the planetary boundary layer (PBL) sufficient to perform a homemade inversion of the mean lidar profiles. The mean BER (together with the associated variabilities) over the Po Valley retrieved from the coupling between CALIOP/MODIS-Aqua and CALIOP/MODIS-Terra are ~0.014(±0.003) sr−1 and ~0.013(±0.004) sr−1, respectively. The total uncertainty on BER retrieval has been assessed to be ~0.003 sr−1 using a Monte Carlo approach. These mean BER values retrieved have been compared with those given by the level-2 operational products of CALIOP ~0.016(±0.003) sr−1. The values we assessed appear close to what is expected above urban area. A seasonal cycle has been observed with higher BER values in spring, summer and fall, which can be associated to dust event occurring during this period. In most of cases, the mean aerosol extinction coefficient in the PBL diverges significantly between the level-2 operational products and the result of our own inversion procedure. Indeed, mean differences of 0.10 km−1 (~50%) and 0.13 km−1 (~60%) have been calculated using MODIS-Aqua/CALIOP and MODIS-Terra/CALIOP synergies, respectively. Such differences may be due to the identification of the aerosol model by the operational algorithm and thus to the choice of the BER.
Continuous low-maintenance CO2/CH4/H2O measurements at the Zotino Tall Tower Observatory (ZOTTO) in Central Siberia
Authors: Winderlich J. , Chen H. , Höfer A. , Gerbig C. , Seifert T. , Kolle O. , Kaiser C. , Lavrič J. V. , Heimann M.
Published: April 2010

Abstract. The Zotino Tall Tower Observatory in Central Siberia (ZOTTO, 60°48' N, 89°21' E) is an excellent location to monitor the continental carbon cycle. Since April 2009, a fully automated low maintenance measurement system based on a cavity ring-down spectroscopy (CRDS) analyzer is installed at the site to measure continuously carbon dioxide (CO2) and methane (CH4) from six heights up to 301 m a.g.l. Buffer volumes in each air line remove short term CO2 and CH4 mixing ratio fluctuations associated with turbulence, and allow continuous, near-concurrent measurements from all six tower levels. Instead of drying the air sample, the simultaneously measured water vapor is used to correct the dilution and pressure-broadening effects for the accurate determination of dry air CO2 and CH4 mixing ratios. The stability of the water vapor correction was demonstrated by repeated laboratory and field tests. The effect of molecular adsorption in the wet air lines was shown to be negligible. The low consumption of four calibration tanks that need recalibration only on decadal timescale further reduces maintenance. The measurement precision (accuracy) of 0.04 ppm (0.09 ppm) for CO2 and 0.3 ppb (1.5 ppb) for CH4 is compliant with the WMO recommendations. The data collected during the 2009 vegetation period reveals a seasonal cycle amplitude of 26.4 ppm at the 301 m level.
Prediction of tropical cyclonegenesis over the South China Sea using SSM/I satellite
Authors: Zhang C. , Zhang Q. , Wang L.
Published: April 2010

Abstract. We propose a method for predicting tropical cyclonegenesis over the South China Sea (SCS) based on the total latent heat release (TLHR) derived from the Special Sensor Microwave/Imager(SSM/I) satellite observations. A threshold value (3×1014 W) for distinguishing the non-developing and developing tropical disturbances is obtained based on the analysis for 25 developing and 43 non-developing tropical disturbances over the SCS during 2000 to 2005. One simple idealized model is further designed to verify that mean TLHR of 3×1014 W within 500 km of the center of tropical disturbance could maintain and develop the tropical disturbance, by heating the air at the upper level and dropping the sea level pressure by 3.2 hPa. A real time testing prediction of tropical cyclonegenesis over the SCS was conducted for the year of 2007 and 2008 using this threshold value of TLHR. We find that the method is successful in detecting the formation of tropical cyclones for 80% of all tropical disturbances over the SCS during 2007 and 2008.
Optical properties of a heated aerosol in an urban atmosphere: a case study
Authors: Backman J. , Virkkula A. , Petäjä T. , Aurela M. , Frey A. , Hillamo R.
Published: April 2010

Abstract. Light absorption measurements most commonly rely on filter-based measurement techniques. These methods are disturbed by light scattering constituents in the aerosol phase deposited on the filters. The light scattering material changes the optical path of light in the filter matrix increasing the light absorption of the filter. Measurement equipment interpret this wrongly as light absorption by the aerosol. Most light scattering constituents in a sub-micron aerosol are volatile by their nature and they can be volatilized by heating the sample air. This volatilisation significantly alters the optical properties of the urban aerosol and was studied during a short field campaign with two groups of equipment measuring in parallel for six days in April 2009 at the SMEAR III station in Helsinki. When heated, the light scattering constituents were evaporated thus reducing the single-scattering albedo (ω0) of the aerosol by as much as 0.4. With less light scattering constituents in the aerosol phase the mass absorption cross section (MAC) of soot was calculated to be 13.5±0.5 m2 g−1 at λ=545 nm. An oven was set to scan different temperatures which revealed the volatility of the urban aerosol at different temperatures as well as the single-scattering albedo's dependence on the non-volatile volume fraction remaining (NVFR). At 50 °C 79±13% of the volume remained while only 46±8% remained at 150 °C and just 23±6% at 280 °C. At 50 °C ω0 was 0.65±0.06, at 150 °C ω0=0.54±0.06 and at 280 °C ω0=0.33±0.06. We found that absorption coefficients measured at different temperatures showed a temperature dependency possibly indicating initially different mixing states of the non-volatile constituents.
Towards the development of standard reference materials for soot measurements – Part 1: Tailored graphitized soot
Authors: Popovicheva O. , Subramanian R. , Baumgardner D. , Kok G. , Cary R. , Vlasenko E. , Khokhlova T. , Shonija N. , Kireeva E.
Published: April 2010

Abstract. The lack of standard reference materials for calibrating, troubleshooting and intercomparing instruments that measure the properties of black carbon, commonly referred to as soot, has been a major obstacle that hinders improved understanding of how climate and health is impacted by this ubiquitous component of the atmosphere. A different approach is offered here as a means of constructing precisely controlled material with fractions of organic carbon (OC) on the surface of elemental carbon (EC) whose structure reflects that of combustion particles found in the atmosphere. The proposed soot reference material (SRM) uses elemental carbon as a basis substrate for surface coatings of organic compounds that are representative of main classes of organics identified in the coverage of soot produced by fossil fuel burning. A number of methods are used to demonstrate the quality and stability of the reference EC and SRM. Comparison of the nominal fraction of OC deposited on the EC substrate with the fraction measured with thermal/optical analysis (TOA) shows excellent agreement. Application of this type of reference material for evaluating the different methods of carbon analysis may help resolve differences that currently exist between comparable measurement techniques when trying to separate OC and EC from ambient samples.
On differentiating ground clutter and insect echoes from Doppler weather radars using archived data
Authors: Rennie S. J. , Illingworth A. J. , Dance S. L.
Published: April 2010

Abstract. Normally wind measurements from Doppler radars rely on the presence of rain. During fine weather, insects become a potential radar target for wind measurement. However, it is difficult to separate ground clutter and insect echoes when spectral or polarimetric methods are not available. Archived reflectivity and velocity data from repeated scans provide alternative methods. The probability of detection (POD) method, which maps areas with a persistent signal as ground clutter, is ineffective when most scans also contain persistent insect echoes. We developed a clutter detection method which maps the standard deviation of velocity (SDV) over a large number of scans, and can differentiate insects and ground clutter close to the radar. Beyond the range of persistent insect echoes, the POD method more thoroughly removes ground clutter. A new, pseudo-probability clutter map was created by combining the POD and SDV maps. The new map optimised ground clutter detection without removing insect echoes.
Development and characterization of a High-Temperature Proton-Transfer-Reaction Mass Spectrometer (HT-PTR-MS)
Authors: Mikoviny T. , Kaser L. , Wisthaler A.
Published: April 2010

Abstract. We have developed a High-Temperature Proton-Transfer-Reaction Mass Spectrometer (HT-PTR-MS) in which both the ion source and the ion drift tube can be continuously operated at temperatures up to 250 °C. The instrument was characterized in a high E/N-mode (130 Td) and in a low E/N-mode (87 Td) at an operating temperature of 200 °C. Instrumental sensitivities and 2σ-detection limits were on the order of 50–110 cps/ppb and 100 ppt (1 s signal integration time), respectively. The HT-PTR-MS is primarily intended for measuring "sticky" or semi-volatile trace gases. Alternatively, it may be coupled to a particle collection/thermal desorption apparatus to measure particle-bound organics in near real-time. In view of these applications, we have measured instrumental response times for a series of reference compounds. 1/e2-response times for dimethyl sulfoxide, ammonia and monoethanolamine were in the sub-second to second regime. 1/e2-response times for levoglucosan, oxalic acid and cis-pinonic acid ranged from 8 to 370 s.
A performance assessment of the World Wide Lightning Location Network (WWLLN) via comparison with the Canadian Lightning Detection Network (CLDN)
Authors: Abreu D. , Chandan D. , Holzworth R. H. , Strong K.
Published: April 2010

Abstract. The World Wide Lightning Location Network (WWLLN) uses globally-distributed Very Low Frequency (VLF) receivers in order to observe lightning around the globe. Its objective is to locate as many global strokes as possible, with high temporal and spatial (<10 km) accuracy. Since detection is done in the VLF range, signals from high peak current lightning strokes are able to propagate up to ~104 km before being detected by the WWLLN sensors, allowing for receiving stations to be sparsely spaced. Through a comparison with measurements made by the Canadian Lightning Detection Network (CLDN) between May and August 2008 over a 4° latitude by 4° longitude region centered on Toronto, Canada, this study found that WWLLN detection was most sensitive to high peak current lightning strokes. Events were considered shared between the two networks if they fell within 0.5 ms of each other. Using this criterion, 19 128 WWLLN strokes (analyzed using the Stroke_B algorithm) were shared with CLDN lightning strokes, producing a detection efficiency of 2.8%. The peak current threshold for WWLLN detection is found to be ~20 kA, with the detection efficiency increasing to ~70% at peak currents of ±120 kA. The detection efficiency is seen to have a clear diurnal dependence, with a higher detection efficiency at local midnight than at local noon; this is attributed to the difference in the thickness of the ionospheric D-region between night and day. The mean time difference (WWLLN – CLDN) between shared events was −6.44 μs with a standard deviation of 35 μs, and the mean absolute location accuracy was 7.24 km with a standard deviation of 6.34 km. These results are generally consistent with previous comparison studies of the WWLLN with other regional networks around the world. Additional receiver stations are continuously being added to the network, acting to improve this detection efficiency.
The ground-based MW radiometer OZORAM on Spitsbergen – description and validation of stratospheric and mesospheric O3-measurements
Authors: Palm M. , Hoffmann C. G. , Golchert S. H. W. , Notholt J.
Published: April 2010

Abstract. This manuscript introduces the OZORAM ground based millimeter wave radiometer. The instrument is deployed to the high Arctic (79° N, 12° E) for measurements of O3 in the upper stratosphere and lower mesosphere. The discussion covers measurements taken since late 2006. To investigate instrumental biases, the results from September 2008 till spring 2009 are compared to O3 profiles derived from measurements of two instruments onboard polar orbiting satellites, MLS onboard EOS-AURA and SABER onboard TIMED. The agreement is within 20% in the stratosphere and 40% in the mesosphere. The deviations show strong systematic and oscillating features, for which the error discussion of the ground based instrument/measurement gives possible explanations. Nonetheless, expected features like the diurnal cycle and O3 enhancements due to stratospheric warmings are readily observed, which could not originally be taken for granted given the large deviation from the satellite data. The nature of the oscillatory deviation is further studied. This study points to a systematic error in the radiative transfer modeling caused by imperfect spectroscopic data.