lnstitut für Sensorik und Elektronik
Dauerhafte URI für die Sammlunghttps://irf.fhnw.ch/handle/11654/28068
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Ergebnisse nach Hochschule und Institut
Publikation Heterogeneous chemical processing of 13NO2 by monodisperse carbon aerosols at very low concentrations(American Chemical Society, 19.09.1996) Kalberer, Markus; Tabor, K.; Ammann, Markus; Parrat, Yves; Weingartner, Ernest; Piguet, D.; Rössler, E.; Jost, Dieter T.; Türler, Andreas; Gäggeler, Heinz W.; Baltensperger, UrsThe heterogeneous reaction of NO2 with different carbon aerosol particles was investigated in situ. The NO2 was labeled with the β+-emitter 13N (half-life 10.0 min) which allowed application of NO2 at very low concentrations. The carbon aerosol was either produced by a spark discharge generator using graphite electrodes or by a brush generator resuspending commercial soot material. Monodisperse size cuts between 50- and 490-nm diameter were selected and mixed with the 13NO2. After a defined reaction time, the different reaction products were separated by means of selective traps and detected on-line by γ-spectrometry. A sticking coefficient for chemisorption of NO2 between 0.3 × 10ˉ⁴ and 4.0 × 10ˉ⁴ and a rate constant for the reduction of adsorbed NO2 to NO(g) between 4.0 × 10 ˉ⁴ and 9.4 × 10 ˉ⁴ /s were determined for both aerosols. The sticking coefficient obtained in this study in situ with aerosol particles is 2 orders of magnitudes smaller than the uptake coefficient recently reported with bulk carbon material.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Summertime NOy speciation at the Jungfraujoch, 3580 m above sea level, Switzerland(Wiley, 16.03.2000) Zellweger, Christoph; Ammann, Markus; Buchmann, Brigitte; Hofer, Patrick; Lugauer, Matthias; Rüttimann, Ralph; Streit, Niklaus; Weingartner, Ernest; Baltensperger, UrsDuring summer 1997, speciated reactive nitrogen (NO, NO2, peroxyacetyl nitrate (PAN), HNO3, and particulate nitrate) was measured in conjunction with total reactive nitrogen (NOy) at the high-alpine research station Jungfraujoch (JFJ), 3580 m above sea level (asl). The individually measured NOy components averaged to 82% of total NOy. PAN was the most abundant reactive nitrogen compound and composed on average 36% of NOy, followed by NOx, (22%), particulate nitrate (17%), and HNO3 (7%). The NOx/NOy ratio averaged 0.25, but significantly lower values (0.15–0.20) were observed in the presence of high NOy mixing ratios. A classification of the data by synoptic weather conditions indicated that thermally driven vertical transport has a strong impact on the mixing ratios measured at the JFJ during summer. A strong diurnal cycle with maximum mixing ratios in the late afternoon was observed for convective days with north-westerly advection at 500 hPa. In contrast, during a period of convective days with a wind speed below 7.5 m/s at 500 hPa, no obvious diurnal cycle was observed. Under these meteorological conditions the convective boundary layer can be significantly higher over the Alps (i.e., around 4 km asl) than over the surrounding lowlands. Subsequent advection may finally result in the export of reactive nitrogen reservoir compounds to the free troposphere and hence influence global atmospheric chemistry.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Partitioning of reactive nitrogen (NOy) and dependence on meteorological conditions in the lower free troposphere(Copernicus, 19.06.2003) Zellweger, Christoph; Forrer, Jann; Hofer, Peter; Nyeki, Stephan; Schwarzenbach, Beat; Weingartner, Ernest; Ammann, Markus; Baltensperger, UrsResults of continuous nitrogen oxide (NO), nitrogen dioxide (NO2), peroxyacetyl nitrate (PAN) and total reactive nitrogen (NOy) measurements along with seasonal field campaigns of nitric acid (HNO3) and particulate nitrate (NO3-) measurements are presented for a two-year period at the high-alpine research station Jungfraujoch (JFJ), 3580 m asl. The NOy mixing ratio and partitioning is shown to strongly depend on meteorological conditions. Knowledge of these meteorological transport processes allows discrimination between undisturbed (i.e. clean) and disturbed (i.e. influenced by regional pollution sources) free tropospheric (FT) conditions at the JFJ. Median NOy concentrations during undisturbed FT periods ranged from 350 pptv (winter, December to February) to 581 pptv (spring, March to May). PAN was found to be the dominant NOy species during spring and summer, whereas NO2 was most abundant during autumn and winter. Particulate nitrate was found to contribute significantly to total NOy during thermally induced vertical transport. Föhn events, synoptical lifting (e.g. fronts) and thermally induced vertical transport resulted in mixing ratios up to 10 times higher at the JFJ compared to undisturbed FT conditions. Furthermore, this meteorological variability of the NOy concentration and partitioning often dominated the seasonal variability. As a consequence the use of filters at the JFJ (and other mountainous sites) is crucial for the interpretation of data from such measurement sites. This study presents a further development of meteorological filters for the high-alpine site Jungfraujoch, which also could be modified and adapted to other mountainous measurement sites.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Effect of humidity on nitric acid uptake to mineral dust aerosol particles(Copernicus, 20.06.2006) Vlasenko, Alexander; Sjögren, Staffan; Weingartner, Ernest; Stemmler, Konrad; Gäggeler, Heinz W.; Ammann, MarkusThis study presents the first laboratory observation of HNO3 uptake by airborne mineral dust particles. The model aerosols were generated by dry dispersion of Arizona Test Dust (ATD), SiO2, and by nebulizing a saturated solution of calcium carbonate. The uptake of 13N-labeled gaseous nitric acid was observed in a flow reactor on the 0.2–2 s reaction time scale at room temperature and atmospheric pressure. The amount of nitric acid appearing in the aerosol phase at the end of the flow tube was found to be a linear function of the aerosol surface area. SiO2 particles did not show any significant uptake, while the CaCO3 aerosol was found to be more reactive than ATD. Due to the smaller uncertainty associated with the reactive surface area in the case of suspended particles as compared to bulk powder samples, we believe that we provide an improved estimate of the rate of uptake of HNO3 to mineral dust. The fact that the rate of uptake was smaller at a concentration of 10^12 than at 10^11 was indicative of a complex uptake mechanism. The uptake coefficient averaged over the first 2 s of reaction time at a concentration of 10^12 molecules cm³ was found to increase with increasing relative humidity, from 0.022±0.007 at 12% RH to 0.113±0.017 at 73% RH , which was attributed to an increasing degree of solvation of the more basic minerals. The extended processing of the dust by higher concentrations of HNO3 at 85% RH led to a water soluble coating on the particles and enhanced their hygroscopicity.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Changes of fatty acid aerosol hygroscopicity induced by ozonolysis under humid conditions(Copernicus, 18.08.2008) Vesna, O.; Sjögren, Staffan; Weingartner, Ernest; Samburova, Vera; Kalberer, Markus; Gäggeler, Heinz W.; Ammann, MarkusUnsaturated fatty acids are important constituents of the organic fraction of atmospheric aerosols originating from biogenic or combustion sources. Oxidative processing of these may change their interaction with water and thus affect their effect on climate. The ozonolysis of oleic and arachidonic acid aerosol particles was studied under humid conditions in a flow reactor at ozone exposures close to atmospheric levels, at concentrations between 0.5 and 2 ppm. While oleic acid is a widely used proxy for such studies, arachidonic acid represents polyunsaturated fatty acids, which may decompose into hygroscopic products. The hygroscopic (diameter) growth factor at 93% relative humidity (RH) of the oxidized arachidonic particles increased up to 1.09 with increasing RH during the ozonolysis. In contrast, the growth factor of oleic acid was very low (1.03 at 93% RH) and was almost invariant to the ozonolysis conditions, so that oleic acid is not a good model to observe oxidation induced changes of hygroscopicity under atmospheric conditions. We show for arachidonic acid particles that the hygroscopic changes induced by humidity during ozonolysis are accompanied by about a doubling of the ratio of carboxylic acid protons to aliphatic protons. We suggest that, under humid conditions, the reaction of water with the Criegee intermediates might open a pathway for the formation of smaller acids that lead to more significant changes in hygroscopicity. Thus the effect of water to provide a competing pathway during ozonolysis observed in this study should be motivation to include water, which is ubiquitously present in and around atmospheric particles, in future studies related to aerosol particle aging.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Generation of submicron Arizona test dust aerosol. Chemical and hygroscopic properties(Taylor & Francis, 20.10.2005) Vlasenko, Alexander; Sjögren, Staffan; Weingartner, Ernest; Gäggeler, Heinz W.; Ammann, MarkusThis article describes a submicron dust aerosol generation system based on a commercially available dust disperser intended for use in laboratory studies of heterogeneous gas–aerosol interactions. Mineral dust particles are resuspended from Arizona Test Dust (ATD) powder as a case study. The system output in terms of number and surface area is adjustable and stable enough for aerosol flow reactor studies. Particles produced are in the 30–1000 nm size range with a lognormal shape of the number size distribution. The particles are characterized with respect to morphology, electrical properties, hygroscopic properties, and chemical composition. Submicron particle elemental composition is found to be similar for the particle surface and bulk as revealed by X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma optical emission spectroscopy (ICP-OES), respectively. A significant difference in chemical composition is found between the submicron aerosol and the ATD bulk powder from which it was generated. The anionic composition of the water-soluble fraction of this dust sample is dominated by sulfate. Resuspended dust particles show, as expected, nonhygroscopic behavior in a humid environment. Small hygroscopic growth of about 1% (relative change in mobility diameter) was observed for 100 nm particles when the relative humidity (RH) was changed from 12 to 94%. Particles larger than 100–200 nm shrank about 1% once exposed to RH > 90%. This was interpreted as a restructuring of the larger agglomerates of dust to particles of smaller mobility diameter, under the influence of water vapor.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Aging induced changes on NEXAFS fingerprints in individual combustion particles(Copernicus, 24.11.2011) Zelenay, Veronika; Mooser, René; Tritscher, Torsten; Křepelová, Adela; Heringa, Maarten F.; Chirico, Roberto; Prévôt, André SH.; Weingartner, Ernest; Baltensperger, Urs; Dommen, Josef; Watts, B.; Raabe, Jörg; Huthwelker, Thomas; Ammann, MarkusAbstract. Soot particles can significantly influence the Earth's climate by absorbing and scattering solar radiation as well as by acting as cloud condensation nuclei. However, despite their environmental (as well as economic and political) importance, the way these properties are affected by atmospheric processing of the combustion exhaust gases is still a subject of discussion. In this work, individual soot particles emitted from two different vehicles, a EURO 2 transporter, a EURO 3 passenger car, and a wood stove were investigated on a single-particle basis. The emitted exhaust, including the particulate and the gas phase, was processed in a smog chamber with artificial solar radiation. Single particle specimens of both unprocessed and aged soot were characterized using near edge X-ray absorption fine structure spectroscopy (NEXAFS) and scanning electron microscopy. Comparison of NEXAFS spectra from the unprocessed particles and those resulting from exhaust photooxidation in the chamber revealed changes in the carbon functional group content. For the wood stove emissions, these changes were minor, related to the relatively mild oxidation conditions. For the EURO 2 transporter emissions, the most apparent change was that of carboxylic carbon from oxidized organic compounds condensing on the primary soot particles. For the EURO 3 car emissions oxidation of primary soot particles upon photochemical aging has likely contributed as well. Overall, the changes in the NEXAFS fingerprints were in qualitative agreement with data from an aerosol mass spectrometer. Furthermore, by taking full advantage of our in situ microreactor concept, we show that the soot particles from all three combustion sources changed their ability to take up water under humid conditions upon photochemical aging of the exhaust. Due to the selectivity and sensitivity of the NEXAFS technique for the water mass, also small amounts of water taken up into the internal voids of agglomerated particles could be detected. Because such small amounts of water uptake do not lead to measurable changes in particle diameter, it may remain beyond the limits of volume growth measurements, especially for larger agglomerated particles.01A - Beitrag in wissenschaftlicher Zeitschrift