Publications (24)27.15 Total impact
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Article: Contrasting winter and summer VOC mixing ratios at a forest site in the Western Mediterranean Basin: the effect of local biogenic emissions
Atmospheric Chemistry and Physics Discussions. 01/2011; 11(7):20389-20431. -
Article: Fossil versus contemporary sources of fine elemental and organic carbonaceous particulate matter during the DAURE campaign in Northeast Spain
Atmospheric Chemistry and Physics Discussions. 01/2011; 11(8):23573-23618. -
Article: Analysis of high mass resolution PTR-TOF mass spectra from 1,3,5-trimethylbenzene (TMB) environmental chamber experiments
Atmospheric Chemistry and Physics Discussions. 01/2011; 11(9):25871-25907. -
Article: Relating hygroscopicity and composition of organic aerosol particulate matter
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ABSTRACT: A hygroscopicity tandem differential mobility analyzer (HTDMA) was used to measure the water uptake (hygroscopicity) of secondary organic aerosol (SOA) formed during the chemical and photochemical oxidation of several organic precursors in a smog chamber. Electron ionization mass spectra of the non-refractory submicron aerosol were simultaneously determined with an aerosol mass spectrometer (AMS), and correlations between the two different signals were investigated. SOA hygroscopicity was found to strongly correlate with the relative abundance of the ion signal m/z 44 expressed as a fraction of total organic signal (f44). m/z 44 is due mostly to the ion fragment CO2+ for all types of SOA systems studied, and has been previously shown to strongly correlate with organic O/C for ambient and chamber OA. The analysis was also performed on ambient OA from two field experiments at the remote site Jungfraujoch, and the megacity Mexico City, where similar results were found. A simple empirical linear relation between the hygroscopicity of OA at subsaturated RH, as given by the hygroscopic growth factor (GF) or "ϰorg" parameter, and f44 was determined and is given by ϰorg = 2.2 × f44 − 0.13. This approximation can be further verified and refined as the database for AMS and HTDMA measurements is constantly being expanded around the world. The use of this approximation could introduce an important simplification in the parameterization of hygroscopicity of OA in atmospheric models, since f44 is correlated with the photochemical age of an air mass.ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2011; 11(3):1155–1165. · 5.52 Impact Factor -
Article: Widening the gap between measurement and modelling of secondary organic aerosol properties?
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ABSTRACT: The link between measured sub-saturated hygroscopicity and cloud activation potential of secondary organic aerosol particles produced by the chamber photo-oxidation of α-pinene in the presence or absence of ammonium sulphate seed aerosol was investigated using two models of varying complexity. A simple single hygroscopicity parameter model and a more complex model (incorporating surface effects) were used to assess the detail required to predict the cloud condensation nucleus (CCN) activity from the sub-saturated water uptake. Sub-saturated water uptake measured by three hygroscopicity tandem differential mobility analyser (HTDMA) instruments was used to determine the water activity for use in the models. The predicted CCN activity was compared to the measured CCN activation potential using a continuous flow CCN counter. Reconciliation using the more complex model formulation with measured cloud activation could be achieved widely different assumed surface tension behavior of the growing droplet; this was entirely determined by the instrument used as the source of water activity data. This unreliable derivation of the water activity as a function of solute concentration from sub-saturated hygroscopicity data indicates a limitation in the use of such data in predicting cloud condensation nucleus behavior of particles with a significant organic fraction. Similarly, the ability of the simpler single parameter model to predict cloud activation behaviour was dependent on the instrument used to measure sub-saturated hygroscopicity and the relative humidity used to provide the model input. However, agreement was observed for inorganic salt solution particles, which were measured by all instruments in agreement with theory. The difference in HTDMA data from validated and extensively used instruments means that it cannot be stated with certainty the detail required to predict the CCN activity from sub-saturated hygroscopicity. In order to narrow the gap between measurements of hygroscopic growth and CCN activity the processes involved must be understood and the instrumentation extensively quality assured. It is impossible to say from the results presented here due to the differences in HTDMA data whether: i) Surface tension suppression occurs ii) Bulk to surface partitioning is important iii) The water activity coefficient changes significantly as a function of the solute concentration.Atmospheric Chemistry and Physics. 03/2010; 10(6):2577-2593. -
Article: Intercomparison study of six HTDMAs: results and recommendations
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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 have never been 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 instruments 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.Atmospheric Measurement Techniques 07/2009; 2(2):363-378. · 3.34 Impact Factor -
Article: Analysis of the hygroscopic and volatile properties of ammonium sulphate seeded and unseeded SOA particles
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ABSTRACT: The volatile and hygroscopic properties of ammonium sulphate seeded and unseeded secondary organic aerosol (SOA) derived from the photo-oxidation of atmospherically relevant concentrations of _-pinene were studied. The seed particles were electrospray generated ammonium sulphate ((NH4)2SO4) having diameters of approximately 33 nm with a quasi-mono-disperse size distribution (geometric standard deviation sg=1.3). The volatile and hygroscopic properties of both seeded and unseeded SOA were simultaneously measured with a VH-TDMA (volatility – hygroscopicity tandem differential mobility analyzer). VH-TDMA measurements of unseeded SOA show a decrease in the hygroscopic growth (HGF) factor for increased volatilisation temperatures such that the more volatile compounds appear to be more hygroscopic. This is opposite to the expected preferential evaporation of more volatile but less hygroscopic material, but could also be due to enhanced oligomerisation occurring at the higher temperature in the thermodenuder. In addition, HGF measurements of seeded SOA were measured as a function of time at two relative humidities, below (RH 75%) and above (RH 85%) the deliquescence relative humidity (DRH) of the pure ammonium sulphate seeds. As these measurements were conducted during the onset phase of photo-oxidation, during particle growth, they enabled us to find the dependence of the HGF as a function of the volume fraction of the SOA coating. HGF’s measured at RH of 85% showed a continuous decrease as the SOA coating thickness increased. The measured growth factors show good agreements with ZSR predictions indicating that, at these RH values, there are only minor solute-solute interactions. At 75% RH, as the SOA fraction increased, a rapid increase in the HGF was observed indicating that an increasing fraction of the (NH4)2SO4 is subject to a phase transition, going into solution, with an increasing volume fraction of SOA. To our knowledge this is the first time that SOA derived from photooxidised _-pinene has been shown to affect the equilibrium water content of inorganic aerosols below their DRH. For SOA volume fractions above _0.3 the measured growth factor followed roughly parallel to the ZSR prediction based on fully dissolved (NH4)2SO4 although with a small difference that was just larger than the error estimate. Both incomplete dissolution and negative solute-solute interactions could be responsible for the lower HGF observed compared to the ZSR predictions.Atmospheric Chemistry and Physics. 01/2009; 9(2):721-732. -
Article: Atmospheric composition change – global and regional air quality
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ABSTRACT: Air quality transcends all scales with in the atmosphere from the local to the global with handovers and feedbacks at each scale interaction. Air quality has manifold effects on health, ecosystems, heritage and climate. In this review the state of scientific understanding in relation to global and regional air quality is outlined. The review discusses air quality, in terms of emissions, processing and transport of trace gases and aerosols. New insights into the characterization of both natural and anthropogenic emissions are reviewed looking at both natural (e.g. dust and lightning) as well as plant emissions. Trends in anthropogenic emissions both by region and globally are discussed as well as biomass burning emissions. In terms of chemical processing the major air quality elements of ozone, non-methane hydrocarbons, nitrogen oxides and aerosols are covered. A number of topics are presented as a way of integrating the process view into the atmospheric context; these include the atmospheric oxidation efficiency, halogen and HOx chemistry, night time chemistry, tropical chemistry, heat waves, megacities, biomass burning and the regional hot spot of the Mediterranean. New findings with respect to the transport of pollutants across the scales are discussed, in particular the move to quantify the impact of long-range transport on regional air quality. Gaps and research questions that remain intractable are identified. The review concludes with a focus of research and policy questions for the coming decade. In particular, the policy challenges for concerted air quality and climate change policy (co-benefit) are discussed. doi:10.1016/j.atmosenv.2009.08.021.Atmospheric Environment 01/2009; 43(43):5268-5350. · 3.46 Impact Factor -
Article: Atmospheric Chemistry and Physics Gas/particle partitioning of carbonyls in the photooxidation of isoprene and 1,3,5-trimethylbenzene
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ABSTRACT: A new denuder-filter sampling technique has been used to investigate the gas/particle partitioning behaviour of the carbonyl products from the photooxidation of isoprene and 1,3,5-trimethylbenzene. A series of experiments was performed in two atmospheric simulation chambers at atmo-spheric pressure and ambient temperature in the presence of NO x and at a relative humidity of approximately 50%. The denuder and filter were both coated with the derivatizing agent O-(2,3,4,5,6-pentafluorobenzyl)-hydroxylamine (PF-BHA) to enable the efficient collection of gas-and particle-phase carbonyls respectively. The tubes and filters were ex-tracted and carbonyls identified as their oxime derivatives by GC-MS. The carbonyl products identified in the experiments accounted for around 5% and 10% of the mass of secondary organic aerosol formed from the photooxidation of isoprene and 1,3,5-trimethylbenzene respectively. Experimental gas/particle partitioning coefficients were determined for a wide range of carbonyl products formed from the photooxidation of isoprene and 1,3,5-trimethylbenzene and compared with the theoretical values based on standard absorptive partitioning theory. Photooxi-dation products with a single carbonyl moiety were not ob-served in the particle phase, but dicarbonyls, and in particu-lar, glyoxal and methylglyoxal, exhibited gas/particle parti-tioning coefficients several orders of magnitude higher than expected theoretically. These findings support the impor-tance of heterogeneous and particle-phase chemical reactions for SOA formation and growth during the atmospheric degra-dation of anthropogenic and biogenic hydrocarbons.ATMOSPHERIC CHEMISTRY AND PHYSICS 07/2008; 8:3215-3230. · 5.52 Impact Factor -
Article: Cloud forming potential of secondary organic aerosol under near atmospheric conditions
Geophysical Research Letters 01/2008; 35:L03818. · 3.79 Impact Factor -
Conference Proceeding: DC/RF and Statistic Modeling of Four Terminal InGap/GaAs Bifet for wireless application
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ABSTRACT: InGaP-GaAs based BIFET is a novel technology that integrates HBT and FET onto a single wafer. The technique expands functionality of circuits and reduces the cost. A novel four-terminal large-signal model was developed for accurate DC and RF applications. The device has a p-layer as backgate that has significant impact on the DC/RF characteristics and therefore, the drain current, gate current, leakage current and all charges/capacitances are 3-dimensional functions, which increases the complexity of the model. The model predicts very well IV/leakage curves for all configurations, including the cases when backgate is connected to source or to gate in that the device reduces to three-terminal. For the three terminal cases, the model also predicts RF performances. Statistic model is also presented to predict the variation of Idss/Vp as well as the corner models that define the extremes of characteristics in terms of epi-layer structureEuropean Microwave Integrated Circuits Conference, 2006. The 1st; 10/2006 -
Conference Proceeding: Software Product Line Variability Management
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ABSTRACT: Software product line engineering (SPLE) is the approach for creating a diversity of similar products at low cost, in short time, and with high quality. Explicitly documenting product line variability is essential for variability management as it significantly supports the following activities: Defining the commonality and the variability of the product line during domain engineering; Realizing reusable artifacts (the domain artifacts) with variability; Defining the binding of variability during application engineering; Deriving individual applications by exploiting the variability in the domain artifacts. This tutorial is based on our text book on software product line engineering [1]. The tutorial is structured along an SPLE framework, which has been defined based on our experiences and the results of the European software product line research projects ESAPS, CAFÉ, and FAMILIES [2].Software Product Line Conference, 2006 10th International; 09/2006 -
Conference Proceeding: Digital generation of RF signals for wireless communications with band-pass delta-sigma modulation
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ABSTRACT: This paper demonstrates a high speed digital technique to produce binary (digital) signals that encode representative RF signals (with time varying envelope) as needed for wireless communications. Specifically, it shows that IS-95 format CDMA signals can be generated with a single bit digital data stream at 3.6 Gb/S. The technique uses band-pass delta-sigma modulation so that the quantization noise is shaped out of the frequency band of interest. This approach points the way to single-chip, DSP-based transmitters, used in conjunction with switching mode power amplifiers and simple analog filters, to implement all the functions of a wireless transmitterMicrowave Symposium Digest, 2001 IEEE MTT-S International; 02/2001 -
Conference Proceeding: 40 Gb/s WDM cross-connect with an electronic switching core: preliminary results from the WEST Consortium
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ABSTRACT: The WEST cross-connect switch is a 3×3 (3 fibers, 4 channels/fiber, 10 Gbs/channel) WDM network switch based on electronic switching (OC-48 and/or OC-192 compatible) with an aggregate data throughput of 120 Gb/s. This WEST switch features full data regeneration and retiming, arbitrary reassignment of wavelengths, and broadcastingLasers and Electro-Optics Society Annual Meeting, 1997. LEOS '97 10th Annual Meeting. Conference Proceedings., IEEE; 12/1997 -
Article: Gas phase precursors to anthropogenic secondary organic aerosol: Using the Master Chemical Mechanism to probe detailed observations of 1, 3, 5-trimethylbenzene …
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ABSTRACT: a b s t r a c t A detailed gas-phase photochemical chamber box model, incorporating the Master Chemical Mechanism (MCMv3.1) degradation scheme for the model anthropogenic aromatic compound 1,3,5-trimethylbenzene, has been used to simulate data measured during a series of aerosol chamber experiments in order to evaluate the mechanism under a variety of VOC/NO x conditions. The chamber model was used in the interpretation of comprehensive high (mass and time) resolution measurements of 1,3,5-trimethylbenzene and its photo-oxidation products recorded by a Chemical Ionisation Reaction Time-of-Flight Mass Spectrometer (CIR-TOF-MS). Supporting gas and aerosol measurements have also enabled us to explore the 'missing link' between the gas and aerosol phases. Model-measurement comparisons have been used to gain insight into the complex array of oxygenated products formed, including the peroxide bicyclic ring opening products (a,b-unsaturated-g-dicarbonyls and furanones) and the O 2 -bridged peroxide bicyclic ring-retaining products. To our knowledge this is the first time such high molecular weight species, corresponding to various peroxide bicyclic products represented in the MCMv3.1, have been observed in the gas-phase. The model was also used to give insight into which gas-phase species were participating in SOA formation, with the primary and secondary peroxide products, formed primarily under low NO x conditions, identified as likely candidates. -
Article: Atmospheric nucleation: highlights of the EUCAARI project and future directions
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ABSTRACT: Within the project EUCAARI (European Integrated project on Aerosol CloudATMOSPHERIC CHEMISTRY AND PHYSICS. 10(22):-10848. -
Article: Atmospheric composition change - global and regional air quality
[show abstract] [hide abstract]
ABSTRACT: Air quality transcends all scales with in the atmosphere from the local to the global with handovers and feedbacks at each scale interaction. Air quality has manifold effects on health, ecosystems, heritage and climate. In this review the state of scientific understanding in relation to global and regional air quality is outlined. The review discusses air quality, in terms of emissions, processing and transport of trace gases and aerosols. New insights into the characterization of both natural and anthropogenic emissions are reviewed looking at both natural (e.g. dust and lightning) as well as plant emissions. Trends in anthropogenic emissions both by region and globally are discussed as well as biomass burning emissions. In terms of chemical processing the major air quality elements of ozone, non-methane hydrocarbons, nitrogen oxides and aerosols are covered. A number of topics are presented as a way of integrating the process view into the atmospheric context; these include the atmospheric oxidation efficiency, halogen and HOx chemistry, nighttime chemistry, tropical chemistry, heat waves, megacities, biomass burning and the regional hot spot of the Mediterranean. New findings with respect to the transport of pollutants across the scales are discussed, in particular the move to quantify the impact of long-range transport on regional air quality. Gaps and research questions that remain intractable are identified. The review concludes with a focus of research and policy questions for the coming decade. In particular, the policy challenges for concerted air quality and climate change policy (co-benefit) are discussed.Atmospheric Environment. -
Article: Evaluation of 1,3,5 trimethylbenzene degradation in the detailed tropospheric chemistry mechanism, MCMv3.1, using environmental chamber data
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ABSTRACT: The degradation mechanism of 1,3,5-trimethylbenzene (TMB) as implemented in the Master Chemical Mechanism version 3.1 (MCM) was evaluated using data from the environmental chamber at the Paul Scherrer Institute. The results show that the MCM provides a consistent description of the photo-oxidation of TMB/NO<sub>x</sub> mixtures for a range of conditions. In all cases the agreement between the measurement and the simulation decreases with decreasing VOC-NO<sub>x</sub> ratio and in addition with increasing precursor concentration. A significant underestimation of the decay rate of TMB and thus underestimation of reactivity in the system, consistent with results from previous appraisals of the MCM, was observed. Much higher nitrous acid (HONO) concentrations compared to simulations and expected from chamber characterization experiments were measured during these smog chamber experiments. A light induced NO<sub>2</sub> to HONO conversion at the chamber walls is suggested to occur. This photo-enhanced NO<sub>2</sub> to HONO conversion with subsequent HONO photolysis enhances the reactivity of the system. After the implementation of this reaction in the model it describes the decay of TMB properly. Nevertheless, the model still over-predicts ozone at a later stage of the experiment. This can be attributed to a too slow removal of NO<sub>2</sub>. It is also shown that this photo-enhanced HONO formation is not restricted to TMB photo-oxidation but also occurs in other chemical systems (e.g. ?-pinene). However, the influence of HONO as a source of OH radicals is less important in these more reactive systems and therefore the importance of the HONO chemistry is less obvious. -
Article: Atmospheric nucleation: highlights of the EUCAARI project and future directions
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ABSTRACT: Within the project EUCAARI (European Integrated project on Aerosol Cloud Climate and Air Quality interactions), atmospheric nucleation was studied by (i) developing and testing new air ion and cluster spectrometers, (ii) conducting homogeneous nucleation experiments for sulphate and organic systems in the laboratory, (iii) investigating atmospheric nucleation mechanism under field conditions, and (iv) applying new theoretical and modelling tools for data interpretation and development of parameterisations. The current paper provides a synthesis of the obtained results and identifies the remaining major knowledge gaps related to atmospheric nucleation. The most important technical achievement of the project was the development of new instruments for measuring sub-3 nm particle populations, along with the extensive application of these instruments in both the laboratory and the field. All the results obtained during EUCAARI indicate that sulphuric acid plays a central role in atmospheric nucleation. However, also vapours other than sulphuric acid are needed to explain the nucleation and the subsequent growth processes, at least in continental boundary layers. Candidate vapours in this respect are some organic compounds, ammonia, and especially amines. Both our field and laboratory data demonstrate that the nucleation rate scales to the first or second power of the nucleating vapour concentration(s). This agrees with the few earlier field observations, but is in stark contrast with classical thermodynamic nucleation theories. The average formation rates of 2-nm particles were found to vary by almost two orders of magnitude between the different EUCAARI sites, whereas the formation rates of charged 2-nm particles varied very little between the sites. Overall, our observations are indicative of frequent, yet moderate, ion-induced nucleation usually outweighed by much stronger neutral nucleation events in the continental lower troposphere. The most concrete outcome of the EUCAARI nucleation studies are the new semi-empirical nucleation rate parameterizations based on field observations, along with updated aerosol formation parameterizations.ATMOSPHERIC CHEMISTRY AND PHYSICS 10(2010):10829-10848. · 5.52 Impact Factor -
Article: Atmospheric nucleation: highlights of the EUCAARI project and future directions
10:10829-10848.
