bluuebunny/crossref_metadata_2025 huggingface dataset:
Seasonal distribution of aerosol properties over Europe and their impact on UV irradiance
Authors: Chubarova N. Y.
Published: April 2010

Abstract. Using the aerosol optical thickness at 550 nm (τ550) from MODIS (collection 5) for the 2000–2008 period combined with the aerosol products from the ground-based AERONET network since 1996, monthly mean values of key aerosol parameters have been obtained with 1 degree resolution over Europe. Additional tests have revealed a satisfactory quality of the MODIS data, except in a few cases. Quality assured AERONET data are used for evaluating the Angstrom exponent, single scattering albedo and asymmetry factor, and for validating the final aerosol optical thickness in the UV spectral region. A method for extrapolating the aerosol parameters into the UV spectral region is discussed. The aerosol optical thickness distributions are considered together with meteorological fields from NOAA_NCEP_CPC_CAMS_ OPI climatology. The τ340 is shown to vary significantly from approximately 0.01 to 0.9 depending on the season and location. Permanent elevated aerosol loading over several industrial areas is observed, which agrees with the output of chemical transport models. Using radiative transfer modeling, monthly mean UV loss due to aerosol was estimated. The absolute decrease in UV indices varies from less than 0.1 to 1.5. The relative UV attenuation has large spatial and temporal variations (−1%–−17%) with a minimum towards the northwest and maxima over several southern local areas (Northern Italy, etc.) during the warm period.
Non-Gaussian Bayesian retrieval of tropical upper tropospheric cloud ice and water vapour from Odin-SMR measurements
Authors: Rydberg B. , Eriksson P. , Buehler S. A. , Murtagh D. P.
Published: April 2010

Abstract. Improved Odin-SMR retrievals of upper tropospheric water are presented. The new retrieval algorithm retrieves humidity and cloud ice mass simultaneously and takes into account of cloud inhomogeneities. Both these aspects are introduced for microwave limb sounding inversions for the first time. A Bayesian methodology is applied allowing for a formally correct treatment of non-unique retrieval problems involving non-Gaussian statistics. Cloud structure information from CloudSat is incorporated into the retrieval algorithm. This removes a major limitation of earlier inversion methods where uniform cloud layers were assumed and caused a systematic retrieval error. The core part of the retrieval technique is the generation of a database that must closely represent real conditions. Good agreement with Odin-SMR observations indicates that this requirement is met. The retrieval precision is determined to be about 5–17% RHi and 65% for humidity and cloud ice mass, respectively. For both quantities, the vertical resolution is about 5 km and the best retrieval performance is found between 11 and 15 km. New data show a significantly improved agreement with CloudSat cloud ice mass retrievals, at the same time consistency with the Aura MLS humidity results is maintained. The basics of the approach presented can be applied for all passive cloud observations and should be of broad interest. The results can also be taken as a demonstration of the potential of down-looking sub-mm radiometry for global measurements of cloud ice properties.
Cloud sensitivity studies for stratospheric and lower mesospheric ozone profile retrievals from measurements of limb-scattered solar radiation
Authors: Sonkaew T. , Rozanov V. V. , von Savigny C. , Rozanov A. , Bovensmann H. , Burrows J. P.
Published: April 2010

Abstract. Clouds in the atmosphere play an important role in reflection, absorption and transmission of solar radiation and thus affect trace gas retrievals. The main goal of this paper is to examine the sensitivity of stratospheric and lower mesospheric ozone retrievals from limb-scattered radiance measurements to clouds using the SCIATRAN radiative transfer model and retrieval package. The retrieval approach employed is optimal estimation, and the considered clouds are vertically and horizontally homogeneous. Assuming an aerosol-free atmosphere and Mie phase functions for cloud particles, we compute the relative error of ozone profile retrievals in a cloudy atmosphere if clouds are neglected in the retrieval. To access altitudes from the lower stratosphere up to the lower mesosphere, we combine the retrievals in the Chappuis and Hartley ozone absorption bands. We find significant cloud sensitivity of the limb ozone retrievals in the Chappuis bands at lower stratospheric altitudes. The relative error in the retrieved ozone concentrations gradually decreases with increasing altitude and becomes negligible above approximately 40 km. The parameters with the largest impact on the ozone retrievals are cloud optical thickness, ground albedo and solar zenith angle. Clouds with different geometrical thicknesses or different cloud altitudes have a similar impact on the ozone retrievals for a given cloud optical thickness value, if the clouds are outside the field of view of the instrument. The effective radius of water droplets has a small influence on the error, i.e., less than 0.5% at altitudes above the cloud top height. Furthermore, the impact of clouds on the ozone profile retrievals was found to have a rather small dependence on the solar azimuth angle (less than 1% for all possible azimuth angles). For the most frequent cloud types, the total error is below 6% above 15 km altitude, if clouds are completely neglected in the retrieval. Neglecting clouds in the ozone profile retrievals generally leads to a low bias for a low ground albedo and to a high bias for a high ground albedo, assuming that the ground albedo is well known.
Response of the Nevzorov hot wire probe in clouds dominated by droplet conditions in the drizzle size range
Authors: Schwarzenboeck A. , Mioche G. , Armetta A. , Herber A. , Gayet J.-F.
Published: April 2010

Abstract. During the airborne research mission ASTAR 2004 (Arctic Study of Tropospheric Aerosols, Clouds and Radiation) performed over the island of Svalbard in the Arctic a constant-temperature hot-wire Nevzorov Probe designed for aircraft measurements, has been used onboard the aircraft POLAR 2. The Nevzorov probe measured liquid water (LWC) and total condensed water content (TWC) in supercooled liquid and partly mixed phase clouds, respectively. As for other hotwire probes the calculation of LWC and/or TWC (and thus the ice water content IWC) has to take into account the collection efficiencies of the two separate sensors for LWC and TWC which both react differently with respect to cloud phase and what is even more difficult to quantify with respect to the size of ice and liquid cloud particles. The study demonstrates that during pure liquid cloud sequences the ASTAR data set of the Nevzorov probe allowed to improve the quantification of the collection efficiency, particularly of the LWC probe part with respect to water. The improved quantification of liquid water content should lead to improved retrievals of IWC content. Simultaneous retrievals of LWC and IWC are correlated with the asymmetry factor derived from the Polar Nephelometer instrument.
Laboratory-generated primary marine aerosol via bubble-bursting and atomization
Authors: Fuentes E. , Coe H. , Green D. , de Leeuw G. , McFiggans G.
Published: April 2010

Abstract. A range of bubble and sea spray aerosol generators has been tested in the laboratory and compared with oceanic measurements from the literature. 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 for generating bubbles and particles in a realistic manner. A bubble-bursting aerosol generator which produces bubbles by water impingement was shown to best reproduce the oceanic bubble spectral shapes, which confirms previous findings. Two porous bubblers 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 aerosols generated by the different methods exhibited similar hygroscopicity and cloud condensation nucleus activity behaviour when a sample of purely inorganic salts was used as a parent seawater solution; however, significant differences in the aerosol properties were found when using samples of filtered natural seawater enriched with biogenic organics. 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 with respect to the generation from artificial seawater devoid of organics. The extent of the effect of organics on the aerosol properties varied depending on the method of particle production. The results of this work indicate 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. Comparison between bubble lifetimes in several laboratory simulations and the oceanic conditions indicated that it would require a considerable extension of the dimensions of the currently used bubble-bursting laboratory systems in order to replicate the characteristic oceanic bubble lifetimes. We analyzed the implications derived from the reduced bubble residence times in scaled systems, regarding marine surfactants adsorption on rising bubbles, and found that adsorption equilibrium is reached on a timescale much shorter than the bubble lifetime in small-scale laboratory generators. This implies that adsorption of marine surface-active material is not limited by surfactant transport to the bubble surface.
Intercomparison of measurements of NO2 concentrations in the atmosphere simulation chamber SAPHIR during the NO3Comp campaign
Authors: Fuchs H. , Ball S. M. , Bohn B. , Brauers T. , Cohen R. C. , Dorn H.-P. , Dubé W. P. , Fry J. L. , Häseler R. , Heitmann U. , Jones R. L. , Kleffmann J. , Mentel T. F. , Müsgen P. , Rohrer F. , Rollins A. W. , Ruth A. A. , Kiendler-Scharr A. , Schlosser E. , Shillings A. J. L. , Tillmann R. , Varma R. M. , Venables D. S. , Villena Tapia G. , Wahner A. , Wegener R. , Wooldridge P. J. , Brown S. S.
Published: April 2010

Abstract. NO2 concentrations were measured by various instruments during the NO3Comp campaign at the atmosphere simulation chamber SAPHIR at Forschungszentrum Jülich, Germany, in June 2007. Analytical methods included photolytic conversion with chemiluminescence (PC-CLD), broadband cavity ring-down spectroscopy (BBCRDS), pulsed cavity ring-down spectroscopy (CRDS), incoherent broadband cavity-enhanced absorption spectroscopy (IBB\\-CEAS), and laser-induced fluorescence (LIF). All broadband absorption spectrometers were optimized for the detection of the main target species of the campaign, NO3, but were also capable of detecting NO2 simultaneously with reduced sensitivity. NO2 mixing ratios in the chamber were within a range characteristic of polluted, urban conditions, with a maximum mixing ratio of approximately 75 ppbv. The overall agreement between measurements of all instruments was excellent. Linear fits of the combined data sets resulted in slopes that differ from unity only within the stated uncertainty of each instrument. Possible interferences from species such as water vapor and ozone were negligible under the experimental conditions.
Elemental analysis of aerosol organic nitrates with electron ionization high-resolution mass spectrometry
Authors: Rollins A. W. , Fry J. L. , Hunter J. F. , Kroll J. H. , Worsnop D. R. , Singaram S. W. , Cohen R. C.
Published: April 2010

Abstract. Four hydroxynitrates (R(OH)R'ONO2) representative of atmospheric volatile organic compound (VOC) oxidation products were synthesized, nebulized and sampled into an Aerodyne High Resolution Time of Flight Aerosol Mass Spectrometer (HR-ToF-AMS). The resulting mass spectrum was used to evaluate calibration factors for elemental analysis of organic nitrates by AMS, and to determine the distribution of nitrogen in the detected fragments in a search for an AMS signature of organic nitrates. We found that 30% of the detected nitrogen mass is in the NO+ and NO2+ fragments, 12% at NHx+ fragments, 5% at CxHyOzN+ fragments, and 53% at various CxHyN+ fragments. Elemental analysis indicated that nitrogen was detected with higher efficiency than carbon and hydrogen, but oxygen was detected with reduced efficiency compared to previously reported results for a suite of organics which did not include organic nitrates. The results are used to suggest the maximum corrections to ambient O:C and N:C ratios based on AMS measurements.
Characterizing a Quantum Cascade Tunable Infrared Laser Differential Absorption Spectrometer (QC-TILDAS) for measurements of atmospheric ammonia
Authors: Ellis R. A. , Murphy J. G. , Pattey E. , van Haarlem R. , O'Brien J. M. , Herndon S. C.
Published: April 2010

Abstract. A compact, fast-response Quantum Cascade Tunable Infrared Laser Differential Absorption Spectrometer (QC-TILDAS) for measurements of ammonia (NH3) has been evaluated under both laboratory and field conditions. Absorption of radiation from a pulsed, thermoelectrically cooled QC laser occurs at reduced pressure in a 0.5 L multiple pass absorption cell with an effective path length of 76 m. Detection is achieved using a thermoelectrically-cooled Mercury Cadmium Telluride (HgCdTe) infrared detector. A novel sampling inlet was used, consisting of a short, heated, quartz tube with a hydrophobic coating to minimize the adsorption of NH3 to surfaces. The inlet contains a critical orifice that reduces the pressure, a virtual impactor for separation of particles, and additional ports for delivering NH3-free background air and calibration gas standards. The level of noise in this instrument has been found to be 0.23 ppb at 1 Hz. The sampling technique has been compared to the results of a conventional lead salt Tunable Diode Laser Absorption Spectrometer (TDLAS) during a laboratory intercomparison. The effect of humidity and heat on the surface interaction of NH3 with sample tubing was investigated at mixing ratios ranging from 30–1000 ppb. Humidity was seen to worsen the NH3 time response and considerable improvement was observed when using a heated sampling line. A field intercomparison of the QC-TILDAS with a modified Thermo 42CTL chemiluminescence-based analyzer was also performed at Environment Canada's Centre for Atmospheric Research Experiments (CARE) in the rural town of Egbert, ON between May–July 2008. Background tests and calibrations using two different permeation tube sources and an NH3 gas cylinder were regularly carried out throughout the study. Results indicate a very good correlation at 1 min time resolution (R2 = 0.93) between the two instruments at the beginning of the study, when regular background subtraction was applied to the QC-TILDAS. An overall good correlation of R2 = 0.85 was obtained over the entire two month data set, where the majority of the spread can be attributed to differences in inlet design and background subtraction methods.
μDirac: an autonomous instrument for halocarbon measurements
Authors: Gostlow B. , Robinson A. D. , Harris N. R. P. , O'Brien L. M. , Oram D. E. , Mills G. P. , Newton H. M. , Yong S. E. , A Pyle J.
Published: April 2010

Abstract. We describe a new instrument (μDirac) capable of measuring halocarbons in the atmosphere. Portability, power efficiency and autonomy were critical design requirements and the resulting instrument can be readily deployed unattended on a range of platforms: long duration balloon, aircraft, ship and ground-based stations. The instrument is a temperature programmed gas chromatograph with electron capture detector (GC-ECD). The design requirements led to μDirac being built in-house with several novel features. It currently measures a range of halocarbons (including short-lived tracers having biogenic and anthropogenic sources) with measurement precision relative standard deviations ranging from ± 1% (CCl4) to ± 9% (CH3I). The prototype instrument was first tested in 2005 and the instrument has been proved in the field on technically challenging aircraft and ground-based campaigns. Results from an aircraft and a ground-based deployment are described.
Four Fourier transform spectrometers and the Arctic polar vortex: instrument intercomparison and ACE-FTS validation at Eureka during the IPY springs of 2007 and 2008
Authors: Batchelor R. L. , Kolonjari F. , Lindenmaier R. , Mittermeier R. L. , Daffer W. , Fast H. , Manney G. , Strong K. , Walker K. A.
Published: April 2010

Abstract. The Canadian Arctic Atmospheric Chemistry Experiment Validation Campaigns have been carried out at Eureka, Nunavut (80.05° N, 86.42° W) during the polar sunrise period since 2004. During the International Polar Year (IPY) springs of 2007 and 2008, three ground-based Fourier transform infrared (FTIR) spectrometers were operated simultaneously. This paper presents a comparison of trace gas measurements of stratospherically important species involved in ozone depletion, namely O3, HCl, ClONO2, HNO3 and HF, recorded with these three spectrometers. Total column densities of the gases measured with the new Canadian Network for the Detection of Atmospheric Change (CANDAC) Bruker 125HR are shown to agree to within 3.5% with the existing Environment Canada Bomem DA8 measurements. After smoothing both of these sets of measurements to account for the lower spectral resolution of the University of Waterloo Portable Atmospheric Research Interferometric Spectrometer for the Infrared (PARIS-IR), the measurements were likewise shown to agree with PARIS-IR to within 7%. Concurrent measurements of these gases were also made with the satellite-based Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) during overpasses of Eureka during these time periods. While one of the mandates of the ACE satellite mission is to study ozone depletion in the polar spring, previous validation exercises have identified the highly variable polar vortex conditions of the spring period to be a challenge for validation efforts. In this work, comparisons between the CANDAC Bruker 125HR and ACE-FTS have been used to develop strict criteria that allow the ground- and satellite-based instruments to be confidently compared. When these criteria are taken into consideration, the observed biases between the ACE-FTS and ground-based FTIR spectrometer are not persistent for both years and are generally insignificant, though small positive biases of ~5%, comparable in magnitude to those seen in previous validation exercises, are observed for HCl and HF in 2007, and negative biases of −15.3%, −4.8% and −1.5% are seen for ClONO2, HNO3 and O3 in 2008.
Intercomparison study of six HTDMAs: results and general recommendations for HTDMA operation
Authors: Duplissy J. , Gysel M. , Sjogren S. , Meyer N. , Good N. , Kammermann L. , Michaud V. , Weigel R. , Martins dos Santos S. , Gruening C. , Villani P. , Laj P. , Sellegri K. , Metzger A. , McFiggans G. B. , Wehrle G. , Richter R. , Dommen J. , Ristovski Z. , Baltensperger U. , Weingartner E.
Published: April 2010

Abstract. We report on an intercomparison of six different hygroscopicity tandem differential mobility analysers (HTDMAs). These HTDMAs are used worldwide in laboratory experiments and field campaigns to measure the water uptake of aerosol particles and were never intercompared. After an investigation of the different design of the instruments with their advantages and inconveniencies, the methods for calibration, validation and data analysis are presented. Measurements of nebulised ammonium sulphate as well as of secondary organic aerosol generated from a smog chamber were performed. Agreement and discrepancies between the instrument and to the theory are discussed, and final recommendations for a standard instrument are given, as a benchmark for laboratory or field experiments to ensure a high quality of HTDMA data.
Six years of total ozone column measurements from SCIAMACHY nadir observations
Authors: Lerot C. , Van Roozendael M. , van Geffen J. , van Gent J. , Fayt C. , Spurr R. , Lichtenberg G. , von Bargen A.
Published: April 2010

Abstract. Total O3 columns have been retrieved from six years of SCIAMACHY nadir UV radiance measurements using SDOAS, an adaptation of the GDOAS algorithm previously developed at BIRA-IASB for the GOME instrument. GDOAS and SDOAS have been implemented by the German Aerospace Center (DLR) in the version 4 of the GOME Data Processor (GDP) and in version 3 of the SCIAMACHY Ground Processor (SGP), respectively. The processors are being run at the DLR processing centre on behalf of the European Space Agency (ESA). We first focus on the description of the SDOAS algorithm with particular attention to the impact of uncertainties on the reference O3 absorption cross-sections. Second, the resulting SCIAMACHY total ozone data set is globally evaluated through large-scale comparisons with results from GOME and OMI as well as with ground-based correlative measurements. The various total ozone data sets are found to agree within 2% on average. However, a negative trend of 0.2–0.4%/year has been identified in the SCIAMACHY O3 columns; this probably originates from instrumental degradation effects that have not yet been fully characterized.
Methodology and calibration for continuous measurements of biogeochemical trace gas and O2 concentrations from a 300-m tall tower in central Siberia
Authors: Kozlova E. A. , Manning A. C. , Kisilyakhov Y. , Seifert T. , Heimann M.
Published: April 2010

Abstract. We present an integrated system for measuring atmospheric concentrations of CO2, O2, CH4, CO, and N2O in central Siberia. Our project aims to demonstrate the feasibility of establishing long-term, continuous, high precision atmospheric measurements to elucidate greenhouse gas processes from a very remote mid-continental boreal environment. Air is sampled from five heights on a custom-built 300-m tower. Common features to all species' measurements include air intakes, an air drying system, flushing procedures, and data processing methods. Calibration standards are shared among all five measured species as a result of extending and optimising a proven methodology for long-term O2 calibration. Our system achieves the precision and accuracy requirements specified by the European Union's "CarboEurope" and "ICOS" (Integrated Carbon Observing System) programmes in the case of CO2, O2, and CH4, while CO and N2O require some further improvements. We found that it is not possible to achieve these high precision measurements without skilled technical assistance on-site, primarily because of 2–3 month delays in access to data and diagnostic information. We present results on the stability of reference standards in high pressure cylinders. We also found that some previous methods do not mitigate fractionation of O2 in a sample airstream to a satisfactory level.
Broadband Cavity Enhanced Differential Optical Absorption Spectroscopy (CE-DOAS) – applicability and corrections
Authors: Platt U. , Meinen J. , Pöhler D. , Leisner T.
Published: April 2010

Abstract. Atmospheric trace gas measurements by cavity assisted long-path absorption spectroscopy are an emerging technology. An interesting approach is the combination of CEAS with broad band light sources, the broad-band CEAS (BB-CEAS). BB-CEAS lends itself to the application of the DOAS technique to analyse the derived absorption spectra. While the DOAS approach has enormous advantages in terms of sensitivity and specificity of the measurement, an important implication is the reduction of the light path by the trace gas absorption, since cavity losses due to absorption by gases reduce the quality (Q) of the cavity. In fact, at wavelength, where the quality of the BB-CEAS cavity is dominated by the trace gas absorption (esp. at very high mirror reflectivity), the light path will vary inversely with the trace gas concentration and the strength of the band will become nearly independent of the trace gas concentration c in the cavity, rendering the CEAS Method useless for trace gas measurements. Only in the limiting case where the mirror reflectivity determines Q at all wavelength, the strength of the band as seen by the BB-CEAS instrument becomes proportional to the concentration c. We investigate these relationships in detail and present methods to correct for the cases between the two above extremes, which are of course the important ones in practice.
Determination of particulate matter vertical columns using satellite observations
Authors: Kokhanovsky A. A. , Prikhach A. S. , Katsev I. L. , Zege E. P.
Published: April 2010

Abstract. A new technique to retrieve the particulate matter vertical columns from spaceborne observations is described. The method is based on the measurements of the spectral aerosol optical thickness (AOT). The spectral slope of the derived aerosol optical thickness is used to infer the size of particles, which is needed (along with the absolute value of AOT) to determine corresponding vertical columns. The technique is applied to the case of a cloudless atmosphere over Germany and results are compared with ground-based observations.
Particle Loss Calculator – a new software tool for the assessment of the performance of aerosol inlet systems
Authors: von der Weiden S.-L. , Drewnick F. , Borrmann S.
Published: April 2010

Abstract. Most aerosol measurements require an inlet system to transport aerosols from a select sampling location to a suitable measurement device through some length of tubing. Such inlet systems must be optimized to minimize aerosol sampling artifacts and maximize sampling efficiency. In this study we introduce a new multifunctional software tool (Particle Loss Calculator, PLC) that can be used to quickly determine aerosol sampling efficiency and particle transport losses due to passage through arbitrary tubing systems. The software employs relevant empirical and theoretical relationships found in established literature and accounts for the most important sampling and transport effects that might be encountered during deployment of typical, ground-based ambient aerosol measurements. The software treats non-isoaxial and non-isokinetic aerosol sampling, aerosol diffusion and sedimentation as well as turbulent inertial deposition and inertial deposition in bends and contractions of tubing. This software was validated through comparison with experimentally determined particle losses for several tubing systems bent to create various diffusion, sedimentation and inertial deposition properties. As long as the tube geometries are not "too extreme", agreement is satisfactory. We discuss the conclusions of these experiments, the limitations of the software and present three examples of the use of the Particle Loss Calculator in the field.
In-situ measurements of oxygen, carbon monoxide and greenhouse gases from Ochsenkopf tall tower in Germany
Authors: Thompson R. L. , Manning A. C. , Gloor E. , Schultz U. , Seifert T. , Hänsel F. , Jordan A. , Heimann M.
Published: April 2010

Abstract. We present 2.5 years of in-situ measurements of CO2, O2, CH4, CO, N2O and SF6 mixing ratios sampled from 23, 90 and 163 m above ground on the Ochsenkopf tower in the Fichtelgebirge range, Germany (50°01´49´´ N, 11°48´30´´ E, 1022 m a.s.l.). In addition to the in-situ measurements, flask samples are taken at Ochsenkopf at approximately weekly intervals and are subsequently analysed for the same species, as well as H2, and the stable isotopes, δ13C, δ18O in CO2. The in-situ measurements of CO2 and O2 from 23 m show substantial diurnal variations that are modulated by biospheric fluxes, combustion of fossil fuels, and by diurnal changes in the planetary boundary layer height. Measurements from 163 m exhibit only very weak diurnal variability, as this height (1185 m a.s.l.) is generally above the nocturnal boundary layer. CH4, CO, N2O and SF6 show little diurnal variation even at 23 m owing to the absence of any significant diurnal change in the fluxes and the absence of any strong local sources or sinks. From the in-situ record, the seasonal cycles of the gas species have been characterized and the multi-annual trends determined. Because the record is short, the calculation of the trend is sensitive to inter-annual variations in the amplitudes of the seasonal cycles. However, for CH4 a significant change in the growth-rate was detected for 2006.5–2008.5 as compared with the global mean from 1999 to 2006 and is consistent with other recent observations of a renewed increasing global growth rate in CH4 since the beginning of 2007.
Response of the Nevzorov hot wire probe in Arctic clouds dominated by very large droplet sizes
Authors: Schwarzenboeck A. , Mioche G. , Armetta A. , Herber A. , Gayet J.-F.
Published: April 2010

Abstract. During the airborne research mission ASTAR 2004 (Arctic Study of Tropospheric Aerosols, Clouds and Radiation) performed over the island of Svalbard in the Arctic a constant-temperature hot-wire Nevzorov Probe designed for aircraft measurements, has been used onboard the aircraft POLAR 2. The Nevzorov probe measured liquid water (LWC) and total condensed water content (TWC) in supercooled liquid and partly mixed phase clouds, respectively. As for other hotwire probes the calculation of LWC and/or TWC (and thus the ice water content IWC) has to take into account the collection efficiencies of the two separate sensors for LWC and TWC which both react differently with respect to cloud phase and what is even more difficult to quantify with respect to the size of ice and liquid cloud particles. The study demonstrates that during pure liquid cloud sequences the ASTAR data set of the Nevzorov probe allowed to improve the quantification of the collection efficiency, particularly of the LWC probe part with respect to water. The improved quantification of liquid water content should lead to improved retrievals of IWC content. Simultaneous retrievals of LWC and IWC are correlated with the asymmetry factor derived from the Polar Nephelometer instrument.
Water vapour total columns from SCIAMACHY spectra in the 2.36 μm window
Authors: Schrijver H. , Gloudemans A. M. S. , Frankenberg C. , Aben I.
Published: April 2010

Abstract. The potential of the shortwave infrared channel of the atmospheric spectrometer SCIAMACHY on Envisat to provide accurate measurements of total atmospheric water vapour columns is explored. It is shown that good quality results can be obtained for cloud free scenes above the continents using the Iterative Maximum Likelihood Method. In addition to the standard cloud filter employed in this method, further cloud screening is obtained by comparing simultaneously retrieved methane columns with values expected from models. A novel method is used to correct for the scattering effects introduced in the spectra by the ice layer on the detector window. The retrieved water vapour total columns for the period 2003–2007 are compared with spatially and temporally collocated values from the European Centre for Mid-Range Weather Forecast (ECMWF) data. The observed differences for individual measurements have standard deviations not higher than 0.3 g/cm2 and an absolute mean value smaller than 0.01 g/cm2 with some regional excursions. The use of recently published spectroscopic data for water vapour led to a significant improvement in the agreement of the retrieved water vapour total columns and the values derived from ECMWF data. This analysis thus provides independent verification of the new spectroscopic information using atmospheric data.
Relationship between the NO2 photolysis frequency and the solar global irradiance
Authors: Trebs I. , Bohn B. , Ammann C. , Rummel U. , Blumthaler M. , Koenigstedt R. , Meixner F. X. , Fan S. , Andreae M. O.
Published: April 2010

Abstract. Representative values of the atmospheric NO2 photolysis frequency, (j(NO2)), are required for the adequate calculation and interpretation of NO and NO2 concentrations and exchange fluxes near the surface. Direct measurements of j(NO2) at ground level are often not available in field studies. In most cases, modeling approaches involving complex radiative transfer calculations are used to estimate j(NO2) and other photolysis frequencies for air chemistry studies. However, important input parameters for accurate modeling are often missing, most importantly with regard to the radiative effects of clouds. On the other hand, solar global irradiance ("global radiation", G) is nowadays measured as a standard parameter in most field experiments and in many meteorological observation networks around the world. A linear relationship between j(NO2) and G was reported in previous studies and has been used to estimate j(NO2) from G in the past 30 years. We have measured j(NO2) using spectro- or filter radiometers and G using pyranometers side-by-side at several field sites. Our results cover a solar zenith angle range of 0–90°, and are based on nine field campaigns in temperate, subtropical and tropical environments during the period 1994–2008. We show that a second-order polynomial function (intercept=0): j(NO2)=(1+α)×(B1×G+B2×G2), with α defined as the site-dependent UV-A surface albedo and the polynomial coefficients (including uncertainty ranges): B1=(1.47±0.03)×10−5 W−1 m2 s−1 and B2=(−4.84±0.31)×10−9 W−2 m4 s−1 can be used to estimate ground-level j(NO2) directly from G, independent of solar zenith angle under all atmospheric conditions. The absolute j(NO2)↓ residual of the empirical function is ±6×10−4 s−1 (95.45% confidence level). The relationship is valid for sites below 800 m a.s.l. and under low background albedo conditions. It is not valid in alpine regions, above snow or ice and sandy or dry soil surfaces. Our function can be applied to estimate chemical life times of the NO2 molecule with respect to photolysis, and is useful for surface-atmosphere exchange and photochemistry studies close to the ground, e.g., above fields with short vegetation and above forest canopies.
Minimizing light absorption measurement artifacts of the Aethalometer: evaluation of five correction algorithms
Authors: Collaud Coen M. , Weingartner E. , Apituley A. , Ceburnis D. , Flentje H. , Henzing J. S. , Jennings S. G. , Moerman M. , Petzold A. , Schmidhauser R. , 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.
Development and application of a new mobile LOPAP instrument for the measurement of HONO altitude profiles in the planetary boundary layer
Authors: Häseler R. , Brauers T. , Holland F. , Wahner A.
Published: April 2010

Abstract. The LOPAP (long path absorption) technique has been shown to be very sensitive for the detection of nitrous acid (HONO) in the atmosphere. However, current instruments were mainly built for ground based applications. Therefore, we designed a new LOPAP instrument to be more versatile for mobile measurements and to meet the requirements for airborne application. The detection limit of the new instrument is below 1 ppt at a time resolution of 5 to 7 min. As a first test, the instrument was successfully employed during the ZEPTER-1 campaign in July 2007 on board of the Zeppelin NT airship. During 15 flights on six days we measured HONO concentration profiles over southwest Germany, predominantly in the range between 100 m and 650 m above ground level. On average, a mixing ratio of 34 ppt was observed, almost independently of height. Within a econd campaign, ZEPTER-2 in fall 2008, higher HONO mixing ratios were observed in the Lake Constance area.
μDirac: an autonomous instrument for halocarbon measurements
Authors: Gostlow B. , Robinson A. D. , Harris N. R. P. , O'Brien L. M. , Oram D. E. , Mills G. P. , Newton H. M. , Pyle J. A.
Published: April 2010

Abstract. We describe a new instrument (μDirac) capable of measuring halocarbons in the atmosphere. Portability, power efficiency and autonomy were critical requirements in the design, and the resulting instrument can be readily deployed unattended on a range of platforms: long duration balloon, aircraft, ship and ground based stations. The instrument is a temperature programmed gas chromatograph with electron capture detector (GC-ECD). The design requirements led to μDirac being built in-house with several novel features. It currently measures a range of halocarbons (CFCs and shorter-lived halocarbons having biogenic and anthropogenic sources) with measurement precisions ranging from ∼1% sd (CCl4) to ∼9% sd (CH3I). Since the prototype instrument was first tested in 2005 the instrument has been proved in the field on technically challenging aircraft and ground based campaigns. Results from one aircraft and two ground-based deployments are described.
Sources of uncertainty in eddy covariance ozone flux measurements made by dry chemiluminescence fast response analysers
Authors: Muller J. B. A. , Percival C. J. , Gallagher M. W. , Fowler D. , Coyle M. , Nemitz E.
Published: April 2010

Abstract. Eddy covariance ozone flux measurements are the most direct way to estimate ozone removal near the surface. Over vegetated surfaces, high quality ozone fluxes are required to probe the underlying processes for which it is necessary to separate the flux into the components of stomatal and non-stomatal deposition. Detailed knowledge of the processes that control non-stomatal deposition is limited and more accurate ozone flux measurements are needed to quantify this component of the deposited flux. We present a systematic intercomparison study of eddy covariance ozone flux measurements made using two fast response dry chemiluminescence analysers. Ozone deposition was measured over a well characterised managed grassland near Edinburgh, Scotland, during August 2007. A data quality control procedure specific to these analysers is introduced. Absolute ozone fluxes were calculated based on the relative signals of the dry chemiluminescence analysers using three different calibration methods and the results are compared for both analysers. It is shown that the error in the fitted parameters required for the flux calculations provides a substantial source of uncertainty in the fluxes. The choice of the calculation method itself can also constitute an uncertainty in the flux as the calculated fluxes by the three methods do not agree within error at all times. This finding highlights the need for a consistent and rigorous approach for comparable data-sets, such as e.g. in flux networks. Ozone fluxes calculated by one of the methods were then used to compare the two analysers in more detail. This systematic analyser comparison reveals half-hourly flux values differing by up to a factor of two at times with the difference in mean hourly flux ranging from 0 to 23% with an error in the mean daily flux of ±12%. The comparison of analysers shows that the agreement in fluxes is excellent for some days but that there is an underlying uncertainty as a result of variable analyser performance and/or non-linear behaviour of disc sensitivity.
Intercomparison of measurements of NO2 concentrations in the atmosphere simulation chamber SAPHIR during the NO3Comp campaign
Authors: Fuchs H. , Ball S. M. , Bohn B. , Brauers T. , Cohen R. C. , Dorn H.-P. , Dubé W. P. , Fry J. L. , Häseler R. , Heitmann U. , Jones R. L. , Kleffmann J. , Mentel T. F. , Müsgen P. , Rohrer F. , Rollins A. W. , Ruth A. A. , Kiendler-Scharr A. , Schlosser E. , Shillings A. J. L. , Tillmann R. , Varma R. M. , Venables D. S. , Villena Tapia G. , Wahner A. , Wegener R. , Wooldridge P. J. , Brown S. S.
Published: April 2010

Abstract. NO2 concentrations were measured by various instruments during the NO3Comp campaign at the atmosphere simulation chamber SAPHIR at Forschungszentrum Jülich, Germany, in June 2007. Analytic methods included photolytic conversion with chemiluminescence (PC-CLD), broadband cavity ring-down spectroscopy (BBCRDS), pulsed cavity ring-down spectroscopy (CRDS), incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS), and laser-induced fluorescence (LIF). All broadband absorption spectrometers were optimized for the detection of the main target species of the campaign, NO2, but were also capable of detecting NO2 simultaneously with reduced sensitivity. NO2 mixing ratios in the chamber were within a range characteristic of polluted, urban conditions, with a maximum mixing ratio of approximately 75 ppbv. The overall agreement between measurements of all instruments was excellent. Linear fits of the combined data sets resulted in slopes that differ from unity only within the stated uncertainty of each instrument. Possible interferences from species such as water vapor and ozone were negligible under the experimental conditions.
A new CF-IRMS system for the quantification of the stable isotopes of carbon monoxide from ice cores and small air samples
Authors: Wang Z. , Mak J. E.
Published: April 2010

Abstract. A new simultaneous analysis technique for stable isotope ratios (δ13C and δ18O) of atmospheric carbon monoxide (CO) from ice core samples and small air samples is presented, based on an on-line cryogenic vacuum extraction followed by continuous-flow isotope ratio mass spectrometry (CF-IRMS). The CO extraction system includes two multi-loop cryogenic cleanup traps, a chemical oxidant for oxidation to CO2, a cryogenic collection trap, a cryofocusing unit, purification by gas chromatography, and subsequent injection into a Finnigan Delta Plus IRMS. Analytical precision of 0.2‰(±1σ) for δ13C and 0.6‰(±1σ) for δ18O can be obtained for 100 mL (STP) air sample with CO mixing ratio ranging from 60 to 140 ppbv (~268–625 pmol CO). Six South Pole ice core samples with depth ranging from 133 to 177 m are also processed for CO isotope analysis based on a wet extraction line attached to the above cryogenic vacuum system. This is the first report on measuring isotope ratios of CO in ice core samples.
A model of aerosol evaporation kinetics in a thermodenuder
Authors: Cappa C. D.
Published: April 2010

Abstract. Aerosol thermodenuders provide a measure of particle volatility. The information provided by a thermodenuder is fundamentally related to the kinetics of evaporation and condensation within the device. Here, a time-dependent, multi-component model of particle and gas-phase mass transfer in a thermodenuder is described. This model explicitly accounts for the temperature profile along the length of a typical thermodenuder and distinguishes between the influence of the heating section and of the adsorbent denuder section. It is shown that "semi-volatile" aerosol is particularly sensitive to the inclusion of the adsorbent denuder in the model. As expected, the mass loss from particles through the thermodenuder is directly related to the compound vapor pressure, although the assumptions regarding the enthalpy of vaporization are shown to also have a large influence on the overall calculated mass thermograms. The model has been validated by comparison with previously measured mass thermograms for single-component aerosols and is shown to provide reasonable semi-quantitative agreement. The model that has been developed here can be used to provide quantitative understanding of aerosol volatility measurements of single and multi-component aerosol made using thermodenuders.
Elemental analysis of aerosol organic nitrates with electron ionization high-resolution mass spectrometry
Authors: Rollins A. W. , Fry J. L. , Hunter J. F. , Kroll J. H. , Worsnop D. R. , Singaram S. W. , Cohen R. C.
Published: April 2010

Abstract. Four hydroxynitrates (R(OH)R'ONO2) representative of atmospheric volatile organic compound (VOC) oxidation products were synthesized, nebulized and sampled into an Aerodyne High Resolution Time of Flight Aerosol Mass Spectrometer (HR-ToF-AMS). The resulting mass spectrum was used to evaluate calibration factors for elemental analysis of organic nitrates by AMS, and to determine the distribution of nitrogen in the detected fragments in a search for an AMS signature of organic nitrates. We find that 30% of the detected nitrogen mass is in the NO+ and NO2+ fragments, 12% at NHx+ fragments, 5% at CxHyOzN+ fragments, and 53% at various CxHyN+ fragments. Elemental analysis indicated that nitrogen was detected with higher efficiency than carbon and hydrogen, but oxygen was detected with reduced efficiency compared to previously reported results for a suite of organics which did not include organic nitrates. The results are used to suggest the maximum corrections to ambient O:C and N:C ratios based on AMS measurements.
Retrieval of SO2 from thermal infrared satellite measurements: correction procedures for the effects of volcanic ash
Authors: Corradini S. , Merucci L. , Prata A. J.
Published: April 2010

Abstract. The simultaneous presence of SO2 and ash in a volcanic plume can lead to a significant error in the SO2 columnar abundance retrieval when multispectral Thermal InfraRed (TIR) data are used. The ash particles within the plume with effective radii (from 1 to 10 μm) reduce the Top Of Atmosphere (TOA) radiance in the entire TIR spectral range, including the channels used for SO2 retrieval. The net effect is a significant SO2 overestimation. In this work the interference of ash is discussed and two correction procedures for satellite SO2 volcanic plume retrieval in the TIR spectral range are developed to achieve an higher computation speed and a better accuracy. The ash correction can be applied when the sensor spectral range includes the 7.3 and/or 8.7 μm SO2 absorption bands, and the split window bands centered around 11 and 12 μm required for ash retrieval. This allows the possibility of a simultaneous estimation of both volcanic SO2 and ash in the same data set. The proposed ash correction procedures have been applied to the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Spin Enhanced Visible and Infrared Imager (SEVIRI) measurements. Data collected during the 24 November 2006 Mt. Etna eruption have been used to illustrate the technique. The SO2 and ash estimations are carried out by using a least squares fit method and the Brightness Temperature Difference (BTD) procedures, respectively. The simulated TOA radiance Look-Up Table (LUT) needed for the SO2 columnar abundance and the ash retrievals have been computed using the MODTRAN 4 Radiative Transfer Model. The results show the importance of the ash correction on SO2 retrieval at 8.7 μm – the SO2 columnar abundance corrected by the ash influence is less than one half of the values retrieved without the correction. The ash correction on SO2 retrieval at 7.3 μm is much less important and only significant for low SO2 columnar abundances. Results also show that the simplified and faster correction procedure underestimates the ash correction compared with the more time consuming but more accurate correction procedure. Such underestimation is greater for instruments having better ground pixel resolution, i.e. greater for MODIS than for SEVIRI.