bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of the pathways of tropospheric nitrophenol formation using a multiphase model
Authors: Harrison M. A. J. , Heal M. R. , Cape J. N.
Published: April 2010

Abstract. Phenols are a major class of volatile organic compounds (VOC) whose reaction within, and partitioning between, the gas and liquid phases affects their lifetime within the atmosphere, the local oxidising capacity, and the extent of production of nitrophenols, which are toxic chemicals. In this work, a zero-dimension box model was constructed to quantify the relative nitration pathways, and partitioning into the liquid phase, of mono-aromatic compounds in order to help elucidate the formation pathways of 2- and 4-nitrophenol in the troposphere. The liquid phase contributed significantly to the production of nitrophenols for liquid water content (Lc) values exceeding 3×10-9, and for a range of assumed liquid droplet diameter, even though the resultant equilibrium partitioning to the liquid phase was much lower. For example, in a ''typical'' model scenario, with Lc=3×10-7, 58% of nitrophenol production occurred in the liquid phase but only 2% of nitrophenol remained there, i.e. a significant proportion of nitrophenol observed in the gas phase may actually be produced via the liquid phase. The importance of the liquid phase was enhanced at lower temperatures, by a factor ~1.5–2 at 278 K cf. 298 K. The model showed that nitrophenol production was particularly sensitive to the values of the rate coefficients for the liquid phase reactions between phenol and OH or NO3 reactions, but insensitive to the rate coefficient for the reaction between benzene and OH, thus identifying where further experimental data are required.
Large decadal scale changes of polar ozone suggest solar influence
Authors: Sinnhuber B.-M. , von der Gathen P. , Sinnhuber M. , Rex M. , König-Langlo G. , Oltmans S. J.
Published: April 2010

Abstract. Long-term measurements of Arctic ozone show an unexpectedly large decadal scale variability in the mid-stratosphere during winter. Negative ozone anomalies are strongly correlated with the flux of energetic electrons in the radiation belt, which is modulated by the 11-year solar cycle. The magnitude of the observed decadal ozone changes (≈20%) is much larger than any previously reported solar cycle effect in the atmosphere up to this altitude. The early-winter ozone anomalies subsequently propagate downward into the lower stratosphere and may even influence total ozone and meteorological conditions during spring. These findings suggest a previously unrecognized mechanism by which solar variability impacts on climate through changes in polar ozone.
Inverse modelling of the spatial distribution of NOx emissions on a continental scale using satellite data
Authors: Konovalov I. B. , Beekmann M. , Richter A. , Burrows J. P.
Published: April 2010

Abstract. The recent important developments in satellite measurements of the composition of the lower atmosphere open the challenging perspective to use such measurements as independent information on sources and sinks of atmospheric pollutants. This study explores the possibility to improve estimates of gridded NOx emissions used in a continental scale chemistry transport model (CTM), CHIMERE, by employing measurements performed by the GOME and SCIAMACHY instruments. We set-up an original inverse modelling scheme that not only enables a computationally efficient optimisation of the spatial distribution of seasonally averaged NOx emissions (during summertime), but also allows estimating uncertainties of input data and a priori emissions. The key features of our method are (i) replacement of the CTM by a set of empirical models describing the relationships between tropospheric NO2 columns and NOx emissions with sufficient accuracy, (ii) combination of satellite data for tropospheric NO2 columns with ground based measurements of near surface NO2 concentrations, and (iii) evaluation of uncertainties of the a posteriori emissions by means of a special Bayesian Monte-Carlo experiment which is based on random sampling of errors of both NO2 columns and emission rates. We have estimated the uncertainty in a priori emissions based on the EMEP emission inventory to be about 1.9 (in terms of the geometric standard deviation) and found the uncertainty in a posteriori emissions obtained from our inverse modelling scheme to be significantly lower (about 1.4). It is found also that a priori NOx emission estimates are probable to be persistently biased in many regions of Western Europe, and that the use of a posteriori emissions in the CTM improves the agreement between the modelled and measured data.
The use of tunnel concentration profile data to determine the ratio of NO2/NOx directly emitted from vehicles
Authors: Yao X. , Lau N. T. , Chan C. K. , Fang M.
Published: April 2010

Abstract. Recently, it is reported that primary vehicular NO2/NOx ratio to be 10–30% and primary vehicular NO2 has raised much interest and concern in the control of NO2 in urban areas. In this study, primary vehicular NO2/NOx ratio in Hong Kong was investigated based on intensive long tunnel (3.7–4 km in length) experiments where concentration profiles of air pollutants along the entire lengths of the tunnels were obtained. Long tunnels were selected because of the inherent low O3 concentrations in the partially enclosed environment. In addition the concentrations of pollutants from vehicles are high. Thus, the NO2 measured inside long tunnels would be more representative of the primary NO2 emitted by vehicles and contribution due to atmospheric transformation would be limited. This dataset was supported by a long-term on-road air quality dataset (June 2002–August 2003). Both datasets were obtained using the Mobile Real-time Air Monitoring Platform (MAP). The primary on-road vehicular NO2/NOx ratio was less than 2%, detected in the mid sections of tunnels investigated, where O3 concentration was at a minimum. In sections of the tunnels (entrance and exit) where O3 concentrations were relatively high, the NO2/NOx ratio could be as high as 19%. Long-term (annual average) on-road air quality data in open air yielded NO2/NOx ratios up to 28%. Thus, it is apparent that directly emitted NO2 from vehicles is not significant in atmospheric NO2 concentration. A simple model was used to segregate the contribution of background NO2 and transformed NO2 measured in vehicle plumes.
A scaling analysis of ozone photochemistry: I Model development
Authors: Ainslie B. , Steyn D. G.
Published: April 2010

Abstract. A scaling analysis has been used to capture the integrated behaviour of several photochemical mechanisms for a wide range of precursor concentrations and a variety of environmental conditions. The Buckingham Pi method of dimensional analysis was used to express the relevant variables in terms of dimensionless groups. These grouping show maximum ozone, initial NOx and initial VOC concentrations are made non-dimensional by the average NO2 photolysis rate (jav) and the rate constant for the NO-O3 titration reaction (kNO); temperature by the NO-O3 activation energy (ENO) and Boltzmann constant (k) and total irradiation time by the cumulative javΔt photolysis rate (π3). The analysis shows dimensionless maximum ozone concentration can be described by a product of powers of dimensionless initial NOx concentration, dimensionless temperature, and a similarity curve directly dependent on the ratio of initial VOC to NOx concentration and implicitly dependent on the cumulative NO2 photolysis rate. When Weibull transformed, the similarity relationship shows a scaling break with dimensionless model output clustering onto two straight line segments, parameterized using four variables: two describing the slopes of the line segments and two giving the location of their intersection. A fifth parameter is used to normalize the model output. The scaling analysis, similarity curve and parameterization appear to be independent of the details of the chemical mechanism, hold for a variety of VOC species and mixtures and a wide range of temperatures and actinic fluxes.
Validation of SCIAMACHY AMC-DOAS water vapour columns
Authors: Noël S. , Buchwitz M. , Bovensmann H. , Burrows J. P.
Published: April 2010

Abstract. A first validation of water vapour total column amounts derived from measurements of the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) in the visible spectral region has been performed. For this purpose, SCIAMACHY water vapour data have been determined for the year 2003 using an extended version of the Differential Optical Absorption Spectroscopy (DOAS) method, called Air Mass Corrected (AMC-DOAS). The SCIAMACHY results are compared with corresponding water vapour measurements by the Special Sensor Microwave Imager (SSM/I) and with model data from the European Centre for Medium-Range Weather Forecasts (ECMWF). In confirmation of previous results it could be shown that SCIAMACHY derived water vapour columns are typically slightly lower than both SSM/I and ECMWF data, especially over ocean areas. However, these deviations are much smaller than the observed scatter of the data which is caused by the different temporal and spatial sampling and resolution of the data sets. For example, the overall difference with ECMWF data is only −0.05 g/cm2 whereas the typical scatter is in the order of 0.5 g/cm2. Both values show almost no variation over the year. In addition, first monthly means of SCIAMACHY water vapour data have been computed. The quality of these monthly means is currently limited by the availability of calibrated SCIAMACHY spectra. Nevertheless, first comparisons with ECMWF data show that SCIAMACHY (and similar instruments) are able to provide a new independent global water vapour data set.
The semianalytical cloud retrieval algorithm for SCIAMACHY – I. The validation
Authors: Kokhanovsky A. A. , Rozanov V. V. , Nauss T. , Reudenbach C. , Daniel J. S. , Miller H. L. , Burrows J. P.
Published: April 2010

Abstract. A recently developed cloud retrieval algorithm for the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) is briefly presented and validated using independent and well tested cloud retrieval techniques based on the look-up-table approach for MODeration resolutIon Spectrometer data. The results of the cloud top height retrievals using measurements in the oxygen A-band by an airborne crossed Czerny-Turner spectrograph and the Global Ozone Monitoring Experiment (GOME) instrument are compared with those obtained from airborne dual photography and retrievals using data from Along Track Scanning Radiometer (ATSR-2), respectively.
Combustion characteristics of water-insoluble elemental and organic carbon in size selected ambient aerosol particles
Authors: Wittmaack K.
Published: April 2010

Abstract. Combustion of elemental carbon (EC) and organic carbon (OC) contained in ambient aerosol matter was explored using scanning electron microscopy (SEM) in combination with energy dispersive X-ray analysis (EDX). To ease identification of the particles of interest and to avoid or at least reduce interaction with simultaneously sampled inorganic oxides and salts, the approach used in this work differed in two ways from commonly applied procedures. First, rather than using a mixture of particles of vastly different sizes, as in PM10 or PM2.5, aerosol matter was collected in a 5-stage impactor. Second, the water soluble fraction of the collected matter was removed prior to analysis. Diesel soot particles, which appeared in the well-known form of chain-type aggregates, constituted the major fraction of EC. In contrast, OC containing particles were observed in a variety of shapes, including a sizable amount of bioaerosol matter appearing mostly in the size range above about 1 µm. During heating in ambient air for 1 h, diesel soot particles were found to be stable up to 480°C, but complete combustion occurred in a narrow temperature interval between about 490 and 510°C. After diesel soot combustion, minute quantities of ''ash'' were observed in the form of aggregated tiny particles with sizes less than 10 nm. These particles could be due to elemental or oxidic contaminants of diesel soot. Combustion of OC was observed over a wide range of temperatures, from well below 200°C to at least 500°C. Incompletely burnt bioaerosol matter was still found after heating to 600°C. The results imply that the EC fraction in aerosol matter can be overestimated significantly if the contribution of OC to a thermogram is not well separated.
Validation of ENVISAT/SCIAMACHY columnar methane by solar FTIR spectrometry at the Ground-Truthing Station Zugspitze
Authors: Sussmann R. , Stremme W. , Buchwitz M. , de Beek R.
Published: April 2010

Abstract. Methane total-vertical column retrievals from ground-based solar FTIR measurements at the Permanent Ground-Truthing Station Zugspitze (47.42° N, 10.98° E, 2964 m a.s.l.), Germany are used to validate column averaged methane retrieved from ENVISAT/SCIAMACHY spectra by WFM-DOAS (WFMD) version 0.4 and 0.41 for 153 days in 2003. Smoothing errors are estimated to be below 0.10% for FTIR and 0.14% for SCIAMACHY-WFMD retrievals and can be neglected for the assessment of observed bias and day-to-day-scatter. In order to minimize the altitude-difference effect, dry-air column averaged mixing ratios (XCH4) have been utilized. From the FTIR-time series of XCH4 an atmospheric day-to-day variability of 1% was found, and a sinusoidal annual cycle with a ≈1.6% amplitude. To obtain the WFMD bias, a polynomial fitted to the FTIR series was used as a reference. The result is WFMD v0.4/FTIR=1.008±0.019 and WFMD v0.41/FTIR=1.058±0.008. WFMD v0.41 was significantly improved by a time-dependent bias correction. It can still not capture the natural day-to-day variability, i.e., the standard deviation calculated from the daily-mean values is 2.4% using averages within a 2000-km radius, and 2.7% for a 1000-km radius. These numbers are dominated by a residual time-dependent bias in the order of 3%/month. The latter can be reduced, e.g., from 2.4% to 1.6% as shown by an empirical time-dependent bias correction. Standard deviations of the daily means, calculated from the individual measurements of each day, are excluding time-dependent biases, thus showing the potential precision of WFMD daily means, i.e., 0.3% for a 2000-km selection radius, and 0.6% for a 1000-km selection radius. Therefore, the natural variability could be captured under the prerequisite of further advanced time-dependent bias corrections, or the use of other channels, where the icing issue is less prominent.
On the effects of hydrocarbon and sulphur-containing compounds on the CCN activation of combustion particles
Authors: Petzold A. , Gysel M. , Vancassel X. , Hitzenberger R. , Puxbaum H. , Vrochticky S. , Weingartner E. , Baltensperger U. , Mirabel P.
Published: April 2010

Abstract. The European PartEmis project (''Measurement and prediction of emissions of aerosols and gaseous precursors from gas turbine engines'') was focussed on the characterisation and quantification of exhaust emissions from a gas turbine engine. A comprehensive suite of aerosol, gas and chemi-ion measurements were conducted under different combustor operating conditions and fuel sulphur concentrations. Combustion aerosol characterisation included on-line measurements of mass and number concentration, size distribution, mixing state, thermal stability of internally mixed particles, hygroscopicity, cloud condensation nuclei (CCN) activation potential, and off-line analysis of chemical composition. Modelling of CCN activation of combustion particles was conducted using microphysical and chemical properties obtained from the measurements as input data. Based on this unique data set, the role of sulphuric acid coatings on the combustion particles, formed in the cooling exhaust plume through either direct condensation of gaseous sulphuric acid or coagulation with volatile condensation particles nucleating from gaseous sulphuric acid, and the role of the organic fraction for the CCN activation of combustion particles was investigated. It was found that particles containing a large fraction of non-volatile organic compounds grow significantly less at high relative humidity than particles with a lower content of non-volatile OC. Also the effect of the non-volatile OC fraction on the potential CCN activation is significant. While a coating of water-soluble sulphuric acid increases the potential CCN activation, or lowers the activation diameter, respectively, the non-volatile organic compounds, mainly found at lower combustion temperatures, can partially compensate this sulphuric acid-related enhancement of CCN activation of carbonaceous combustion aerosol particles.
Comparisons between SCIAMACHY and ground-based FTIR data for total columns of CO, CH4, CO2 and N2O
Authors: Dils B. , De Mazière M. , Blumenstock T. , Buchwitz M. , de Beek R. , Demoulin P. , Duchatelet P. , Fast H. , Frankenberg C. , Gloudemans A. , Griffith D. , Jones N. , Kerzenmacher T. , Kramer I. , Mahieu E. , Mellqvist J. , Mittermeier R. L. , Notholt J. , Rinsland C. P. , Schrijver H. , Smale D. , Strandberg A. , Straume A. G. , Stremme W. , Strong K. , Sussmann R. , Taylor J. , van den Broek M. , Wagner T. , Warneke T. , Wiacek A. , Wood S.
Published: April 2010

Abstract. Total column amounts of CO, CH4, CO2 and N2O retrieved from SCIAMACHY nadir observations in its near-infrared channels have been compared to data from a ground-based quasi-global network of Fourier-transform infrared (FTIR) spectrometers. The SCIAMACHY data considered here have been produced by three different retrieval algorithms, WFM-DOAS (version 0.4, 0.41 for CH4), IMAP-DOAS (version 0.9) and IMLM (version 5.5) and cover the January to December 2003 time period. Comparisons have been made for individual data, as well as for monthly averages. To maximize the number of reliable coincidences that satisfy the temporal and spatial collocation criteria, the SCIAMACHY data have been compared with a temporal 3rd order polynomial interpolation of the ground-based data. Particular attention has been given to the question whether SCIAMACHY observes correctly the seasonal and latitudinal variability of the target species. The ensemble of comparisons, discussed in this paper, demonstrate the capability of SCIAMACHY, using any of the three algorithms, to deliver products for the target species under consideration, which are already useful for qualitative geophysical studies on a global scale. It is expected that the remaining uncertainties in the data products will decrease in future versions of the algorithm to also allow more quantitative investigations on a regional scale.
Technical note: A stratospheric climatology for O3, H2O and CH4 derived from HALOE measurements
Authors: Grooß J.-U. , Russell J. M.
Published: April 2010

Abstract. The Halogen Occultation Experiment (HALOE) on board the Upper Atmosphere research satellite (UARS) has observed mixing ratios of important trace species in the stratosphere over more than a decade since 1991. Here we present a climatology for the stratosphere compiled from the HALOE data for ozone, H2O and CH4 for the period from 1991 to 2002. In this approach, the data are averaged over equivalent latitude instead of latitude in order to correctly reproduce the gradients at the transport barriers like the polar vortex edge. The climatology is compiled for 5 degree equivalent latitude bins. The seasonal dependence is taken into account by choosing intervals of one month. The climatology is available as an electronic supplement.
Estimates of lightning NOx production from GOME satellite observations
Authors: Boersma K. F. , Eskes H. J. , Meijer E. W. , Kelder H. M.
Published: April 2010

Abstract. Tropospheric NO2 column retrievals from the Global Ozone Monitoring Experiment (GOME) satellite spectrometer are used to quantify the source strength and 3D distribution of lightning produced nitrogen oxides (NOx=NO2+NO2). A sharp increase of NO2 is observed at convective cloud tops with increasing cloud top height, consistent with a power-law behaviour with power 5±2. Convective production of clouds with the same cloud height are found to produce NO2 with a ratio 1.6/1 for continents compared to oceans. This relation between cloud properties and NO2 is used to construct a 10:30 local time global lightning NO2 production map for 1997. An extensive statistical comparison is conducted to investigate the capability of the TM3 chemistry transport model to reproduce observed patterns of lightning NO2 in time and space. This comparison uses the averaging kernel to relate modelled profiles of NO2 to observed NO2 columns. It exploits a masking scheme to minimise the interference of other NOx sources on the observed total columns. Simulations are performed with two lightning parametrisations, one relating convective preciptation (CP scheme) to lightning flash distributions, and the other relating the fifth power of the cloud top height (H5 scheme) to lightning distributions. The satellite-retrieved NO2 fields show significant correlations with the simulated lightning contribution to the NO2 concentrations for both parametrisations. Over tropical continents modelled lightning NO2 shows remarkable quantitative agreement with observations. Over the oceans however, the two model lightning parametrisations overestimate the retrieved NO2 attributed to lightning. Possible explanations for these overestimations are discussed. The ratio between satellite-retrieved NO2 and modelled lightning NO2 is used to rescale the original modelled lightning NOx production. Eight estimates of the lightning NOx production in 1997 are obtained from spatial and temporal correlation methods, from cloud-free and cloud-covered observations, and from two different lightning parametrisations. Accounting for a wide variety of random and possible systematic errors, we estimate the global NOx production from lightning to be in the range 1.1–6.4 TgN in 1997.
Boundary layer structure and decoupling from synoptic scale flow during NAMBLEX
Authors: Norton E. G. , Vaughan G. , Methven J. , Coe H. , Brooks B. , Gallagher M. , Longley I.
Published: April 2010

Abstract. This paper presents an overview of the meteorology and planetary boundary layer structure observed during the NAMBLEX field campaign to aid interpretation of the chemical and aerosol measurements. The campaign has been separated into five periods corresponding to the prevailing synoptic condition. Comparisons between meteorological measurements (UHF wind profiler, Doppler sodar, sonic aneometers mounted on a tower at varying heights and a standard anemometer) and the ECMWF analysis at 10 m and 1100 m identified days when the internal boundary layer was decoupled from the synoptic flow aloft. Generally the agreement was remarkably good apart from during period one and on a few days during period four when the diurnal swing in wind direction implies a sea/land breeze circulation near the surface. During these periods the origin of air sampled at Mace Head would not be accurately represented by back trajectories following the winds resolved in ECMWF analyses. The wind profiler observations give a detailed record of boundary layer structure including an indication of its depth, average wind speed and direction. Turbulence statistics have been used to assess the height to which the developing internal boundary layer, caused by the increased surface drag at the coast, reaches the sampling location under a wide range of marine conditions. Sampling conducted below around 10m will be impacted by emission sources at the shoreline in all wind directions and tidal conditions, whereas sampling above 15m is unlikely to be affected in any of the wind directions and tidal heights sampled during the experiment.
On the isolation of elemental carbon for micro-molar 14C accelerator mass spectrometry; evaluation of alternative isolation procedures, and accuracy assurance using a hybrid isotopic particulate carbon reference material
Authors: Currie L. A. , Kessler J. D.
Published: April 2010

Abstract. The primary objective of the research reported here has been the development of an hybrid reference material (RM) to serve as a test of accuracy for elemental carbon (EC) isotopic (14C) speciation measurements. Such measurements are critically important for the quantitative apportionment of fossil and biomass sources of ''soot'' (EC), the tracer of fire that has profound effects on health, atmospheric visibility, and climate. Previous studies of 14C-EC measurement quality, carried out with NIST SRM 1649a (Urban Dust), showed a range of results, but since the ''truth'' was not known for this natural matrix RM, one had to rely on isotopic-chemical consistency evidence (14C in PAH, EC) of measurement validity (Currie et al., 2002). Components of the new Hybrid RM (DiesApple), however, have known 14C and EC composition, and they are nearly orthogonal (isotopically and chemically). NIST SRM 2975 (Forklift Diesel Soot) has little or no 14C, and its major compositional component is EC. SRM 1515 (Apple Leaves) has the 14C content of biomass-C, and it has little or no EC. Thus, the hybrid RM can serve as an absolute isotopic test for the absence of EC-mimicking pyrolysis-C from SRM 1515 in the EC isolate of the hybrid RM, together with testing for conservation of its dominant soot fraction through the isolation procedure.
Ice nucleation by surrogates for atmospheric mineral dust and mineral dust/sulfate particles at cirrus temperatures
Authors: Archuleta C. M. , DeMott P. J. , Kreidenweis S. M.
Published: April 2010

Abstract. This study examines the potential role of some types of mineral dust and mineral dust with sulfuric acid coatings as heterogeneous ice nuclei at cirrus temperatures. Commercially-available nanoscale powder samples of aluminum oxide, alumina-silicate and iron oxide were used as surrogates for atmospheric mineral dust particles, with and without multilayer coverage of sulfuric acid. A sample of Asian dust aerosol particles was also studied. Measurements of ice nucleation were made using a continuous-flow ice-thermal diffusion chamber (CFDC) operated to expose size-selected aerosol particles to temperatures between −45 and −60°C and a range of relative humidity above ice-saturated conditions. Pure metal oxide particles supported heterogeneous ice nucleation at lower relative humidities than those required to homogeneously freeze sulfuric acid solution particles at sizes larger than about 50 nm. The ice nucleation behavior of the same metal oxides coated with sulfuric acid indicate heterogeneous freezing at lower relative humidities than those calculated for homogeneous freezing of the diluted particle coatings. The effect of soluble coatings on the ice activation relative humidity varied with the respective uncoated core particle types, but for all types the heterogeneous freezing rates increased with particle size for the same thermodynamic conditions. For a selected size of 200 nm, the natural mineral dust particles were the most effective ice nuclei tested, supporting heterogeneous ice formation at an ice relative humidity of approximately 135%, irrespective of temperature. Modified homogeneous freezing parameterizations and theoretical formulations are shown to have application to the description of heterogeneous freezing of mineral dust-like particles with soluble coatings.
Atmospheric methanol measurement using selective catalytic methanol to formaldehyde conversion
Authors: Solomon S. J. , Custer T. , Schade G. , Soares Dias A. P. , Burrows J.
Published: April 2010

Abstract. A novel atmospheric methanol measurement technique, employing selective gas-phase catalytic conversion of methanol to formaldehyde followed by detection of the formaldehyde product, has been developed and tested. The effects of temperature, gas flow rate, gas composition, reactor-bed length, and reactor-bed composition on the methanol conversion efficiency of a molybdenum-rich, iron-molybdate catalyst [Mo-Fe-O] were studied. Best results were achieved using a 1:4 mixture (w/w) of the catalyst in quartz sand. Optimal methanol to formaldehyde conversion (>95% efficiency) occurred at a catalyst housing temperature of 345°C and an estimated sample-air/catalyst contact time of <0.2 s. Potential interferences arising from conversion of methane and a number of common volatile organic compounds (VOC) to formaldehyde were found to be negligible under most atmospheric conditions and catalyst housing temperatures. Using the new technique, atmospheric measurements of methanol were made at the University of Bremen campus from 1 to 15 July 2004. Methanol mixing ratios ranged from 1 to 5 ppb with distinct maxima at night. Formaldehyde mixing ratios, obtained in conjunction with methanol by periodically bypassing the catalytic converter, ranged from 0.2 to 1.6 ppb with maxima during midday. These results suggest that selective, catalytic methanol to formaldehyde conversion, coupled with existing formaldehyde measurement instrumentation, is an inexpensive and effective means for monitoring atmospheric methanol.
A method for detecting the presence of organic fraction in nucleation mode sized particles
Authors: Vaattovaara P. , Räsänen M. , Kühn T. , Joutsensaari J. , Laaksonen A.
Published: April 2010

Abstract. New particle formation and growth has a very important role in many climate processes. However, the overall knowlegde of the chemical composition of atmospheric nucleation mode (particle diameter, d<20 nm) and the lower end of Aitken mode particles (d≤50 nm) is still insufficient. In this work, we have applied the UFO-TDMA (ultrafine organic tandem differential mobility analyzer) method to shed light on the presence of organic fraction in the nucleation mode size class in different atmospheric environments. The basic principle of the organic fraction detection is based on our laboratory UFO-TDMA measurements with organic and inorganic compounds. Our laboratory measurements indicate that the usefulness of the UFO-TDMA in the field experiments would arise especially from the fact that atmospherically the most relevant inorganic compounds do not grow in subsaturated ethanol vapor, when particle size is 10nm in diameter and saturation ratio is about 86% or below it. Furthermore, internally mixed particles composed of ammonium bisulfate and sulfuric acid with sulfuric acid mass fraction ≤33% show no growth at 85% saturation ratio. In contrast, 10 nm particles composed of various organic compounds of atmospheric relevance are able to grow in those conditions. These discoveries indicate that it is possible to detect the presence of organics in atmospheric nucleation mode sized particles using the UFO-TDMA method. In the future, the UFO-TDMA is expected to be an important aid to describe the composition of atmospheric newly-formed particles.
Size distribution of EC and OC in the aerosol of Alpine valleys during summer and winter
Authors: Jaffrezo J.-L. , Aymoz G. , Cozic J.
Published: April 2010

Abstract. Collections of samples were conducted for the determination of the size distributions of EC and OC during the intensive sampling campaigns of the POVA program, in two Alpine valleys of the French Alps, in summer and in winter. The comparison of concentrations obtained for samples collected in parallel with impactor- and filter-based methods indicates that the correction of pyrolysis seems to work for the impactor samples despite non even deposits. The size distributions of the concentrations of EC and OC present large evolutions between winter and summer, and between a suburban and a rural site. In winter, an overwhelming proportion of the mass fraction of both species is found in the droplet and accumulation modes, often (but not always) in association with sulfate and other chemical species resulting from secondary formation processes. Some indications of gas/particles exchanges can be found for the other parts of the size spectrum (the Aitken and super micron modes) in the case of the rural site. In summer, the changes are more drastic with, according to the case, a dominant droplet or accumulation mode. Particularly at the rural site, the large extent of processing of the aerosol due to gas/particles exchanges is evident for the Aitken and super micron modes, with increasing of the OC mass fractions in these size ranges. All of these observations give indications on the degree of internal vs. external mixing of the species investigated in the different modes.
Seasonal variations of the Water Soluble Organic Carbon mass fraction of aerosol in two valleys of the French Alps
Authors: Jaffrezo J.-L. , Aymoz G. , Delaval C. , Cozic J.
Published: April 2010

Abstract. Concentrations of Water Soluble Organic Carbon and WSOC fraction to OC were measured at two urban sites in valleys of the French Alps during a period of two and a half years. Concentrations were as high as 10–15 µg/m3 in winter, but there is a clear seasonal cycle of the WSOC fraction, with minima occurring during winter. This reflects a marked dependency on temperature, with the average WSOC fraction being stable at 54.8±7.7% and 75.9±6.3% for temperatures in the ranges −10 to +3°C and 12 to 24°C, respectively. Several points are noteworthy in this evolution. First, there are limiting factors that prevent lower mass fractions in the low temperature range and higher mass fractions in the high temperature range. Second, the mass fraction at the lower temperature is rather high, in apparent contradiction with OC being mainly insoluble close to the emission sources. Third, the range of 20% for the change of the WSOC fraction between these extreme conditions is indeed rather narrow when compared to evaluations of the secondary (and supposedly water soluble) OC fraction proposed in the literature, with most of the published values being in the range 40 to 70%. A comparison of the evolution of WSOC concentrations with that of dicarboxylic acids (DCA) clearly indicates the influence of two regimes in the formation of WSOC: one at higher temperatures classically linked with the increase of DCA concentrations and associated with oxidation processes, and another at lower temperatures involving a much lower increase of DCA concentrations. We proposed several hypotheses involving processes that could be responsible for the large concentrations of WSOC in the particulate phase at our sites during winter.
Global distribution of Earth’s surface shortwave radiation budget
Authors: Hatzianastassiou N. , Matsoukas C. , Fotiadi A. , Pavlakis K. G. , Drakakis E. , Hatzidimitriou D. , Vardavas I.
Published: April 2010

Abstract. The monthly mean shortwave (SW) radiation budget at the Earth's surface (SRB) was computed on 2.5-degree longitude-latitude resolution for the 17-year period from 1984 to 2000, using a radiative transfer model accounting for the key physical parameters that determine the surface SRB, and long-term climatological data from the International Satellite Cloud Climatology Project (ISCCP-D2). The model input data were supplemented by data from the National Centers for Environmental Prediction – National Center for Atmospheric Research (NCEP-NCAR) and European Center for Medium Range Weather Forecasts (ECMWF) Global Reanalysis projects, and other global data bases such as TIROS Operational Vertical Sounder (TOVS) and Global Aerosol Data Set (GADS). The model surface radiative fluxes were validated against surface measurements from 22 stations of the Baseline Surface Radiation Network (BSRN) covering the years 1992–2000, and from 700 stations of the Global Energy Balance Archive (GEBA), covering the period 1984–2000. The model is in very good agreement with BSRN and GEBA, with a negative bias of 14 and 6.5 Wm-2, respectively. The model is able to reproduce interesting features of the seasonal and geographical variation of the surface SW fluxes at global scale, which is not possible with surface measurements. Based on the 17-year average model results, the global mean SW downward surface radiation (DSR) is equal to 171.6 Wm−2, whereas the net downward (or absorbed) surface SW radiation is equal to 149.4 Wm−2, values that correspond to 50.2 and 43.7% of the incoming SW radiation at the top of the Earth's atmosphere. These values involve a long-term surface albedo equal to 12.9%. Significant increasing trends in DSR and net DSR fluxes were found, equal to 4.1 and 3.7 Wm−2, respectively, over the 1984–2000 period (equivalent to 2.4 and 2.2 Wm−2 per decade), indicating an increasing surface solar radiative heating. This surface SW radiative heating is primarily attributed to clouds, especially low-level, and secondarily to other parameters such as total precipitable water. The surface solar heating occurs mainly in the period starting from the early 1990s, in contrast to the commonly reported decreasing trend in DSR through the late 1980s, found also in our study. The computed global mean DSR and net DSR flux anomalies were found to range within ±8 and ±6 Wm−2, respectively, with signals from El Niño and La Niña events, and the Pinatubo eruption, whereas significant positive anomalies have occurred in the period 1992–2000.
Geophysical validation of SCIAMACHY Limb Ozone Profiles
Authors: Brinksma E. J. , Bracher A. , Lolkema D. E. , Segers A. J. , Boyd I. S. , Bramstedt K. , Claude H. , Godin-Beekmann S. , Hansen G. , Kopp G. , Leblanc T. , McDermid I. S. , Meijer Y. J. , Nakane H. , Parrish A. , von Savigny C. , Stebel K. , Swart D. P. J. , Taha G. , Piters A. J. M.
Published: April 2010

Abstract. We discuss the quality of the two available SCIAMACHY limb ozone profile products. They were retrieved with the University of Bremen IFE's algorithm version 1.61 (hereafter IFE), and the official ESA offline algorithm (hereafter OL) versions 2.4 and 2.5. The ozone profiles were compared to a suite of correlative measurements from ground-based lidar and microwave, sondes, SAGE II and SAGE III (Stratospheric Aerosol and Gas Experiment). To correct for the expected Envisat pointing errors, which have not been corrected implicitly in either of the algorithms, we applied a constant altitude shift of −1.5 km to the SCIAMACHY ozone profiles. The IFE ozone profile data between 16 and 40 km are biased low by 3–6%. The average difference profiles show a characteristic zigzag shape with a wavelength of approximately 8 km. The standard deviation of the differences is typically 10% between 20 and 35 km. We show that more than 20% of the SCIAMACHY official ESA offline (OL) ozone profiles version 2.4 and 2.5 have unrealistic ozone values, most of these are north of 15° S. The remaining OL profiles compare well to correlative instruments above 24 km. Between 20 and 24 km, they underestimate ozone by 15±5%.
Size-resolved source apportionment of ambient particles by positive matrix factorization
Authors: Han J. S. , Moon K. J. , Lee S. J. , Kim Y. J. , Ryu S. Y. , Cliff S. S. , Yi S. M.
Published: April 2010

Abstract. Size- and time-resolved aerosol samples were collected using an eight-stage DRUM sampler from 29 March to 29 May in 2002 at Gosan, Jeju Island, Korea, which is one of the representative background sites in East Asia. These samples were analyzed using synchrotron X-ray fluorescence for 3-h average concentrations of 19 elements consisting of S, Si, Al, Fe, Ca, Cl, Cu, Zn, Ti, K, Mn, Pb, Ni, V, Se, As, Rb, Cr, Br. The size-resolved data sets were then analyzed using the positive matrix factorization (PMF) technique in order to identify possible sources and estimate their contribution to particulate matter mass. PMF analysis uses the uncertainty of the measured data to provide an optimal weighting. Fifteen sources were resolved in eight size ranges (0.07–12 µm) and included Chinese aerosol, soil dust, sea salt, biomass burning, coal combustion, oil heating furnace, residual oil-fired boiler, municipal incineration, nonferrous metal source, ferrous metal source, gasoline vehicle, diesel vehicle, copper smelter, and volcano emission. PMF analysis of size-resolved source contributions showed that natural sources represented by soil dust, sea salt and Chinese aerosol contributed about 79% to the predicted primary PM mass in the coarse size range (1.15–12 µm). On the other hand, anthropogenic sources such as coal combustion and biomass burning contributed about 60% in the fine size range (0.56–2.5 µm). The diesel vehicle source contributed the most in the ultra-fine size range (0.07–0.56 µm) and was responsible for about 52% of the primary PM mass.
Validation of ENVISAT/SCIAMACHY columnar CO by FTIR profile retrievals at the Ground-Truthing Station Zugspitze
Authors: Sussmann R. , Buchwitz M.
Published: April 2010

Abstract. Carbon monoxide vertical profile retrievals from ground-based solar FTIR measurements at the Permanent Ground-Truthing Station Zugspitze (47.42° N, 10.98° E, 2964 m a.s.l.), Germany are used to validate columnar CO retrieved from ENVISAT/SCIAMACHY spectra (WFM-DOAS version 0.4). The WFM-DOAS retrievals of CO include an empirical column scaling factor of 0.5. Therefore, not absolute column levels are validated, but the proper response of the SCIAMACHY retrievals to the atmospheric inter-annual variability is quantitatively assessed in comparison to the Zugspitze FTIR results. Although CO WFM-DOAS data for only 33 days are available up to now (data covering January–October 2003), it is possible to retrieve information on the CO annual cycle (≈10% amplitude) in a statistically significant fit out of the scatter of the SCIAMACHY WFM-DOAS data. To obtain this, all pixels within a minimum radius of 2000 km around Zugspitze had to be averaged for each day.
Kinetics and mechanism of the uptake of N2O5 on mineral dust at 298 K
Authors: Seisel S. , Börensen C. , Vogt R. , Zellner R.
Published: April 2010

Abstract. The heterogeneous reaction of N2O5 with mineral (Saharan) dust has been studied at T=298 K using a combination of Knudsen and DRIFTS cell for kinetic and product investigations, respectively. The initial uptake coefficient has been determined to be γ=(8.0±0.3)·10−2. This uptake slowly saturates into a steady state uptake of γ=(1.3±0.3)10−2 suggesting that reaction of N2O5 with the mineral dust surface and hydrolysis of N2O5 on the surface take place simultaneously. Moreover, the product investigations suggest that N2O5 is irreversibly taken up forming nitrate on the surface. The uptake rates of N2O5 on Saharan dust are large enough to influence the photo-oxidant budget of the atmosphere.
Atmospheric bromoform at Mace Head, Ireland: Evidence for a peatland source
Authors: Carpenter L. J. , Wevill D. J. , O’Doherty S. , Spain G. , Simmonds P. G.
Published: April 2010

Abstract. In situ atmospheric observations of bromoform (CHBr3) made over a 2.5 year period at Mace Head, Ireland from May 2001–December 2003, including during the NAMBLEX (North Atlantic Marine Boundary Layer Experiment) campaign, show broad maxima from spring until autumn and winter minima, with mixing ratios of 5.3+1.0 pptv (mid March–mid October) and 1.8+0.8 pptv (December–February). This indicates that, unlike CHCl3, which has a summer minimum and winter maximum at Mace Head, local biological sources of CHBr3 have a greater influence on the atmospheric data than photochemical decay during long-range transport. The emission sources are predominantly macroalgal, but we find evidence for a small terrestrial flux from peatland ecosystems, which so far has not been accounted for in the CHBr3 budget. Sharp increases in CHCl3 and CHBr3 concentrations and decreases in O3 concentrations occurred at night when the wind direction switched from an ocean- to a land-based sector (land breeze) and the wind speed dropped to below 5 ms−1. These observations infer a shallow atmospheric boundary layer with increased O3 deposition and concentration of local emissions of both CHCl3 and CHBr3. The ratio of ΔCHCl3/ΔCHBr3 varied strongly according to the prevailing wind direction; from 0.6+0.1 in south-easterly (100–170°) air to 1.9+0.8 in north-easterly (40–70°) air. Of these land-sectors, the south-easterly air masses are likely to be strongly influenced by macroalgal beds along the coast and the emission ratios probably reflect those from seaweeds in addition to land sources. The north-easterly airmasses however have a fetch predominantly over land, which locally is comprised of coastal peatland ecosystems (peat bogs and coastal conifer plantations), previously identified as being strong sources of atmospheric CHCl3 under these conditions. Although we cannot entirely rule out other local land or coastal sources, our observations also suggest peatland ecosystem emissions of CHBr3. We use correlations between CHCl3 and CHBr3 during the land breeze events in conjunction with previous estimates of local wetland CHCl3 release to tentatively deduce a global wetland CHBr3 source of 26.9 (0.5–1247) Gg yr−1, which is approximately 10% of the total global source.
Case studies of ozone transport between North America and Europe in summer 2000
Authors: Guerova G. , Bey I. , Attié J.-L. , Martin R. V.
Published: April 2010

Abstract. This paper reports on Long Range Transport (LRT) of ozone and related species over the North Atlantic ocean and its impact on Europe. Measurements of NO2 and O3 columns from the GOME and MOPITT satellite instruments are first used in conjunction with the GEOS-CHEM global model of transport and tropospheric chemistry to identify the major events of LRT that reach Europe over the course of the summer 2000. Model simulations are then used to examine surface O3 observations at a European mountain site and O3 vertical profiles over several European cities to quantify the impact of the LRT events on the European ozone distributions. Over the course of summer 2000, we identified nine major episodes of pollution transport between North America and Europe, which are in majority associated with WCB/post-frontal outflow (7 events) and zonal transport (2 events). We find that on average three episodes occur per month with the strongest ones being in June. The number and frequency of LRT events that reach Europe after leaving North America is strongly driven by the position and strength of the Azores anticyclone. After leaving North America, the plumes can either i) travel in the North American cyclones, mostly in the Warm Conveyor Belt (WCB), tracking poleward and thus reach Europe at high latitudes; ii) be transported zonally between 40° and 55° N directly to Europe; iii) be incorporated into the Azores anticyclone and reach Europe at mid-latitudes. Based on model sensitivity simulation it can be concluded that on average the North American sources of ozone contribute between 2–8 ppb in PBL and 10–13 ppb in FT. During particular episodes the North American sources resulted in O3 enhancement up to 25–28 ppb in the layer between 800–600 hPa and 10–12 ppb in PBL. For some episodes a substantial North American contribution (30% or higher) does not translate into a well marked enhancement of the total O3.