Auflistung nach Autor:in "Metzger, Axel"

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Analysis of the hygroscopic and volatile properties of ammonium sulphate seeded and unseeded SOA particles
(Copernicus, 28.01.2009) Meyer, Nic K.; Duplissy, Jonathan; Gysel, Martin; Metzger, Axel; Dommen, Josef; Weingartner, Ernest; Alfarra, Rami; Prévôt, André S.H.; Fletcher, C; Good, Nicholas; McFiggans, Gordan; Jonsson, Åsa M.; Hallquist, Mattias; Baltensperger, Urs; Ristovski, Zoran D.
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 α-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 σg=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 photo-oxidised α-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.
01A - Beitrag in wissenschaftlicher Zeitschrift
Cloud forming potential of secondary organic aerosol under near atmospheric conditions
(Wiley, 2008) Duplissy, Jonathan; Gysel, Martin; Alfarra, M. Rami; Dommen, Josef; Metzger, Axel; Prévôt, André S.H.; Weingartner, Ernest; Laaksonen, Ari; Raatikainen, Tomi; Good, Nicholas; Turner, S. Fiona; McFiggans, Gordon; Baltensperger, Urs
Cloud droplets form by nucleation on atmospheric aerosol particles. Populations of such particles invariably contain organic material, a major source of which is thought to be condensation of photo‐oxidation products of biogenic volatile organic compounds (VOCs). We demonstrate that smog chamber studies of the formation of such biogenic secondary organic aerosol (SOA) formed during photo‐oxidation must be conducted at near atmospheric concentrations to yield atmospherically representative particle composition, hygroscopicity and cloud‐forming potential. Under these conditions, the hygroscopicity measured at 95% relative humidity can be used reliably to predict the CCN activity of the SOA particles by assuming droplet surface tension of pure water. We also show that the supersaturation required to activate a given size of particle decreases with age.
01A - Beitrag in wissenschaftlicher Zeitschrift
Evidence for the role of organics in aerosol particle formation under atmospheric conditions
(National Academy of Sciences, 19.01.2010) Metzger, Axel; Verheggen, Bart; Dommen, Josef; Duplissy, Jonathan; Prévôt, André S.H.; Weingartner, Ernest; Riipinen, Ilona; Kulmala, Markku; Spracklen, Dominick V.; Carslaw, Kenneth S.; Baltensperger, Urs
New particle formation in the atmosphere is an important parameter in governing the radiative forcing of atmospheric aerosols. However, detailed nucleation mechanisms remain ambiguous, as laboratory data have so far not been successful in explaining atmospheric nucleation. We investigated the formation of new particles in a smog chamber simulating the photochemical formation of H2SO4 and organic condensable species. Nucleation occurs at H2SO4 concentrations similar to those found in the ambient atmosphere during nucleation events. The measured particle formation rates are proportional to the product of the concentrations of H2SO4 and an organic molecule. This suggests that only one H2SO4 molecule and one organic molecule are involved in the rate-limiting step of the observed nucleation process. Parameterizing this process in a global aerosol model results in substantially better agreement with ambient observations compared to control runs.
01A - Beitrag in wissenschaftlicher Zeitschrift
Intercomparison study of six HTDMAs. results and recommendations
(Copernicus, 24.07.2009) Duplissy, Jonathan; Gysel, Martin; Sjogren, S.; Meyer, Nickolas; Good, Nicholas; Kammermann, Lukas; Michaud, Vincent; Weigel, Ralf; Martins dos Santos, Sebastiao; Gruening, Carsten; Villani, P.; Laj, Paolo; Sellegri, Karine; Metzger, Axel; McFiggans, Gordon B.; Wehrle, Günther; Richter, René; Dommen, Josef; Ristovski, Zoran; Baltensperger, Urs; Weingartner, Ernest
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.
01A - Beitrag in wissenschaftlicher Zeitschrift
Laboratory observation of oligomers in the aerosol from isoprene/NOₓ photooxidation
(Wiley, 2006) Dommen, Josef; Metzger, Axel; Duplissy, Jonathan; Kalberer, Markus; Alfarra, M. Rami; Gascho, Astrid; Weingartner, Ernest; Prévôt, André S.H.; Verheggen, Bart; Baltensperger, Urs
Compounds assigned to be oxidation products of isoprene (2-methyl-1,3-butadiene) have recently been observed in ambient aerosols, suggesting that isoprene might play an important role in secondary organic aerosol (SOA) formation due to its large global source strength. SOA yields from photooxidation of isoprene and NOₓ in a chamber agree fairly well with previous data. Matrix assisted laser desorption/ionization mass spectrometry showed the formation of high molecular weight compounds over the course of 15-hour experiments. Concurrently, the volatility of the SOA decreased markedly as observed by a tandem differential mobility analyzer. The volume fraction remaining of SOA at 150°C increased steadily from 5 to 25% during the same experiments. These observations are attributed to oligomerization reactions occurring in the aerosol phase. Under dry conditions a lower volatility was observed.
01A - Beitrag in wissenschaftlicher Zeitschrift
Relating hygroscopicity and composition of organic aerosol particulate matter
(Copernicus, 10.02.2011) Duplissy, Jonathan; DeCarlo, Peter F.; Dommen, Josef; Alfarra, M. Rami; Metzger, Axel; Barmpadimos, Iakovos; Prevot, Andre S.H.; Weingartner, Ernest; Tritscher, Torsten; Gysel, Martin; Aiken, Allison C.; Jimenez, Jose L; Canagaratna, Manjula R.; Worsnop, Douglas R.; Collins, Don R.; Tomlinson, Jason; Baltensperger, Urs
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.
01A - Beitrag in wissenschaftlicher Zeitschrift
Role of sulphuric acid, ammonia and galactic cosmic rays in atmospheric aerosol nucleation
(Springer, 24.08.2011) Kirkby, Jasper; Curtius, Joachim; Almeida, João; Dunne, Eimear; Duplissy, Jonathan; Ehrhart, Sebastian; Franchin, Alessandro; Gagné, Stéphanie; Ickes, Luisa; Kürten, Andreas; Kupc, Agnieszka; Metzger, Axel; Riccobono, Francesco; Rondo, Linda; Schobesberger, Siegfried; Tsagkogeorgas, Georgios; Wimmer, Daniela; Amorim, Antonio; Bianchi, Federico; Breitenlechner, Martin; David, André; Dommen, Josef; Downard, Andrew; Ehn, Mikael; Flagan, Richard C.; Haider, Stefan; Hansel, Armin; Hauser, Daniel; Jud, Werner; Junninen, Heikki; Kreissl, Fabian; Kvashin, Alexander; Laaksonen, Ari; Lehtipalo, Katrianne; Lima, Jorge; Lovejoy, Edward R.; Makhmutov, Vladimir; Mathot, Serge; Mikkilä, Jyri; Minginette, Pierre; Mogo, Sandra; Nieminen, Tuomo; Onnela, Antti; Pereira, Paulo; Petäjä, Tuukka; Schnitzhofer, Ralf; Seinfeld, John H.; Sipilä, Mikko; Stozhkov, Yuri; Stratmann, Frank; Tomé, Antonio; Vanhanen, Joonas; Viisanen, Yrjo; Vrtala, Aron; Wagner, Paul E.; Walther, Hansueli; Weingartner, Ernest; Wex, Heike; Winkler, Paul M.; Carslaw, Kenneth S.; Worsnop, Douglas R.; Baltensperger, Urs; Kulmala, Markku
Atmospheric aerosols exert an important influence on climate through their effects on stratiform cloud albedo and lifetime and the invigoration of convective storms. Model calculations suggest that almost half of the global cloud condensation nuclei in the atmospheric boundary layer may originate from the nucleation of aerosols from trace condensable vapours, although the sensitivity of the number of cloud condensation nuclei to changes of nucleation rate may be small. Despite extensive research, fundamental questions remain about the nucleation rate of sulphuric acid particles and the mechanisms responsible, including the roles of galactic cosmic rays and other chemical species such as ammonia. Here we present the first results from the CLOUD experiment at CERN. We find that atmospherically relevant ammonia mixing ratios of 100 parts per trillion by volume, or less, increase the nucleation rate of sulphuric acid particles more than 100–1,000-fold. Time-resolved molecular measurements reveal that nucleation proceeds by a base-stabilization mechanism involving the stepwise accretion of ammonia molecules. Ions increase the nucleation rate by an additional factor of between two and more than ten at ground-level galactic-cosmic-ray intensities, provided that the nucleation rate lies below the limiting ion-pair production rate. We find that ion-induced binary nucleation of H2SO4–H2O can occur in the mid-troposphere but is negligible in the boundary layer. However, even with the large enhancements in rate due to ammonia and ions, atmospheric concentrations of ammonia and sulphuric acid are insufficient to account for observed boundary-layer nucleation.
01A - Beitrag in wissenschaftlicher Zeitschrift
Widening the gap between measurement and modelling of secondary organic aerosol properties?
(Copernicus, 2010) Good, Nicholas; Topping, D. O.; Duplissy, Jonathan; Gysel, Martin; Meyer, Nic K.; Metzger, Axel; Turner, S. F.; Baltensperger, Urs; Ristovski, Zoran; Weingartner, Ernest; Coe, Hugh; McFiggans, Gordan
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.
01A - Beitrag in wissenschaftlicher Zeitschrift