B. Umann

Max Planck Institute for Nuclear Physics, Heidelburg, Baden-Württemberg, Germany

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Publications (14)46.26 Total impact

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    ABSTRACT: Aerosol physical and chemical properties and trace gas concentrations were measured during the QUEST field campaign in March–April 2003, in Hyytiälä, Finland. Our aim was to understand the role of oxidation products of VOC's such as mono-and sesquiterpenes in atmospheric nu-cleation events. Particle chemical compositions were mea-sured using the Aerodyne Aerosol Mass Spectrometer, and chemical compositions of aerosol samples collected with low-pressure impactors and a high volume sampler were analysed using a number of techniques. The results indi-cate that during and after new particle formation, all parti-Correspondence to: A. Laaksonen (ari.laaksonen@uku.fi) cles larger than 50 nm in diameter contained similar organic substances that are likely to be mono-and sesquiterpene ox-idation products. The oxidation products identified in the high volume samples were shown to be mostly aldehydes. In order to study the composition of particles in the 10–50 nm range, we made use of Tandem Differential Mobility Ana-lyzer results. We found that during nucleation events, both 10 and 50 nm particle growth factors due to uptake of ethanol vapour correlate strongly with gas-phase monoterpene oxi-dation product (MTOP) concentrations, indicating that the organic constituents of particles smaller than 50 nm in di-ameter are at least partly similar to those of larger particles. We furthermore showed that particle growth rates during the nucleation events are correlated with the gas-phase MTOP Published by Copernicus Publications on behalf of the European Geosciences Union. 2658 A. Laaksonen et al.: VOC oxidation products and new particle formation concentrations. This indicates that VOC oxidation products may have a key role in determining the spatial and temporal features of the nucleation events. This conclusion was sup-ported by our aircraft measurements of new 3–10 nm particle concentrations, which showed that the nucleation event on 28 March 2003, started at the ground layer, i.e. near the VOC source, and evolved together with the mixed layer. Further-more, no new particle formation was detected upwind away from the forest, above the frozen Gulf of Bothnia.
    Atmospheric Chemistry and Physics 07/2008; 8:2657-2665. · 5.51 Impact Factor
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    ABSTRACT: Atmospheric new particle formation is generally thought to occur due to homogeneous or ion-induced nucleation of sulphuric acid. We compare ambient nucleation rates with laboratory data from nucleation experiments involving either sulphuric acid or oxidized SO2. Atmospheric nucleation occurs at H2SO4 concentrations 2-4 orders of magnitude lower than binary or ternary nucleation rates of H2SO4 produced from a liquid reservoir, and atmospheric H2SO4 concentrations are very well replicated in the SO2 oxidation experiments. We hypothesize these features to be due to the formation of free HSO5 radicals in pace with H2SO4 during the SO2 oxidation. We suggest that at temperatures above ~250 K these radicals produce nuclei of new aerosols much more efficiently than H2SO4. These nuclei are activated to further growth by H2SO4 and possibly other trace species. However, at lower temperatures the atmospheric relative acidity is high enough for the H2SO4-H2O nucleation to dominate.
    ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2008; · 5.51 Impact Factor
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    ABSTRACT: Atmospheric new particle formation is generally thought to occur due to homogeneous or ion-induced nucleation of sulphuric acid. We compare ambient nucleation rates with laboratory data from nucleation experiments involving either sulphuric acid or oxidized SO<sub>2</sub>. Atmospheric nucleation occurs at H<sub>2</sub>SO<sub>4</sub> concentrations 2?4 orders of magnitude lower than binary or ternary H<sub>2</sub>SO<sub>4</sub> nucleation. In contrast, the atmospheric nucleation rates and H<sub>2</sub>SO<sub>4</sub> concentrations are very well replicated in the SO<sub>2</sub> oxidation experiments. We explain these features by the formation of free HSO<sub>5</sub> radicals in pace with H<sub>2</sub>SO<sub>4</sub> during the SO<sub>2</sub> oxidation. We suggest that at temperatures above ~250 K these radicals produce nuclei of new aerosols much more efficiently than H<sub>2</sub>SO<sub>4</sub>. These nuclei are activated to further growth by H<sub>2</sub>SO<sub>4</sub> and possibly other trace species. However, at lower temperatures the atmospheric relative acidity is high enough for the H<sub>2</sub>SO<sub>4</sub>?H<sub>2</sub>O nucleation to dominate.
    Atmospheric Chemistry and Physics 01/2008; · 4.88 Impact Factor
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    ABSTRACT: Aerosol physical and chemical properties and trace gas concentrations were measured during the QUEST field campaign in March–April, 2003, in Hyytiälä, Finland. Our aim was to understand the role of oxidation products of VOC&apos;s such as mono- and sesquiterpenes in atmospheric nucleation events. Particle chemical compositions were measured using the Aerodyne Aerosol Mass Spectrometer, and chemical compositions of aerosol samples collected with low-pressure impactors and a high volume sampler were analysed using a number of techniques. The results indicate that during and after new particle formation, all particles larger than 50 nm in diameter contained similar organic substances that are likely to be mono- and sesquiterpene oxidation products. The oxidation products identified in the high volume samples were shown to be mostly aldehydes. In order to study the composition of particles in the 10–50 nm range, we made use of Tandem Differential Mobility Analyzer results. We found that during nucleation events, both 10 and 50 nm particle growth factors due to uptake of ethanol vapour correlate strongly with gas-phase monoterpene oxidation product (MTOP) concentrations, indicating that the organic constituents of particles smaller than 50 nm in diameter are at least partly similar to those of larger particles. We furthermore showed that particle growth rates during the nucleation events are correlated with the gas-phase MTOP concentrations. This indicates that VOC oxidation products may have a key role in determining the spatial and temporal features of the nucleation events. This conclusion was supported by our aircraft measurements of new 3–10 nm particle concentrations, which showed that the nucleation event on 28 March 2003, started at the ground layer, i.e. near the VOC source, and evolved together with the mixed layer. Furthermore, no new particle formation was detected upwind away from the forest, above the frozen Gulf of Bothnia.
    Atmospheric Chemistry and Physics 01/2007; · 4.88 Impact Factor
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    ABSTRACT: Measurements of atmospheric volatile organic compounds were performed in the Finnish Boreal forest atmosphere during spring 2003, as part of the project QUEST (Quantification of Aerosol Nucleation in the European Boundary Layer), using a ground-based Chemical Ionization Mass Spectrometer (CIMS) instrument. Based on the study of their hydrate distribution, methanol, acetonitrile, acetaldehyde, dimethyl amine (DMA), ethanol/formic acid, acetone, trimethyl amine (TMA), propanol/acetic acid, isoprene, methyl vinyl ketone (MVK) and metacrolein (MaCR), monoterpenes and monoterpene oxidation product (MTOP) are proposed as candidates for masses 32, 41, 44, 45, 46, 58, 59, 60, 68, 70, 136, and 168amu, respectively. It would be, to our knowledge, the first time DMA, TMA and MTOP are measured with this method. Most compounds show a clear diurnal variation with a maximum in the early night, corresponding to the onset of the noctural inversion and in agreement with independant measurements of CO. Biogenic compounds are highly correlated with each other and the ratio monoterpene/oxidation product shows a typical daily pattern of nightime maxima. However, because isoprene mixing ratios are also maximum during the early night, it is likely that it suffers of the interference from another unidentified biogenic compound. Hence mass 68amu is identified as isoprene+compound X.
    ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2005; · 5.51 Impact Factor
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    ABSTRACT: Biogenic VOCs are important in the growth and possibly also in the early stages of formation of atmospheric aerosol particles. In this work, we present 10 min-time resolution measurements of organic trace gases at Hyytiälä, Finland during March 2002. The measurements were part of the project QUEST (Quantification of Aerosol Nucleation in the European Boundary Layer) and took place during a two-week period when nucleation events occurred with various intensities nearly every day. Using a ground-based Chemical Ionization Mass Spectrometer (CIMS) instrument, the following trace gases were detected: acetone, TMA, DMA, mass 68amu (candidate=isoprene), monoterpenes, methyl vinyl ketone (MVK) and methacrolein (MaCR) and monoterpene oxidation products (MTOP). For all of them except for the amines, we present daily variations during different classes of nucleation events, and non-event days. BVOC oxidation products (MVK, MaCR and MTOP) show a higher ratio to the CS on event days compared to non-event days, indicating that their abundance relative to the surface of aerosol available is higher on nucleation days. Moreover, BVOC oxidation products are found to show significant correlations with the condensational sink (CS) on nucleation event days, which indicates that they are representative of less volatile organic compounds that contribute to the growth of the nucleated particles and generally secondary organic aerosol formation. Behaviors of BVOC on event and non event days are compared to the behavior of CO.
    ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2005; · 5.51 Impact Factor
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    ABSTRACT: Mineral dust, one of the most abundant aerosols by mass in the atmosphere, may have a lasting but to date almost unexplored effect on the trace gases nitric acid (HNO3) and sulfur dioxide (SO2). These gases have an important influence on, for example, the tropospheric ozone cycle, aerosol formation or acid rain. Within the second part of the MINATROC project (Mineral Dust and Tropospheric Chemistry) we investigated the interaction of mineral dust with gaseous HNO3 and SO2. The measurements were performed on a high mountain plateau (Izaña, Tenerife, 2367 m asl) using the highly sensitive CIMS (Chemical Ionization Mass Spectrometry) technique. During five periods of medium and one period of high atmospheric dust load, the HNO3 concentration decreased with increasing dust concentrations, and in all cases the HNO3 detection limit was reached. From the HNO3 decrease the uptake coefficient gammaHNO3 was calculated for the first time on the basis of in situ measurements. For the observed events, gammaHNO3 varied between 0.017 and 0.054. Moreover, during the dust events a significant decrease of ozone (O3) of the order of 30% was detected. The measurements and the analyses made in this paper show that the direct uptake of O3 on dust is a minor pathway for O3 depletion compared to the indirect effect, i.e., HNO3 depletion on dust which takes away a source of the O3 precursors nitrogen oxides. In contrast, a general interaction between SO2 and mineral dust was not observed. Positive as well as negative and no correlations between SO2 and mineral dust were detected.
    Journal of Geophysical Research Atmospheres 01/2005; 110. · 3.44 Impact Factor
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    ABSTRACT: The EU-project MINATROC (MINeral dust And TROpospheric Chemistry) aims at enabling an estimation of the influence of mineral dust, a major, but to date largely ignored component of tropospheric aerosol, on tropospheric oxidant cycles. Within the scope of this project continuous atmospheric measurements of gas-phase HNO 3 and SO 2 were conducted in June and July 2000 at the CNR WMO station, situated on Monte Cimone (MTC) (44 # 11 # N -- 10 # 42 # E, 2165 m asl), Italy. African air transporting dust is occasionally advected over the Mediterranean Sea to the site, thus mineral aerosol emitted from Africa will encounter polluted air masses and provide ideal conditions to study their interactions. HNO 3 and SO 2 were measured with an improved CIMS (chemical ionization mass spectrometry) system for ground-based measurements that was developed and built at MPI-K Heidelberg. Since HNO 3 is a very sticky compound special care was paid for the air-sampling and backgroundmeasurement system. Complete data sets could be obtained before, during and after major dust intrusions. For the first time these measurements might provide a strong observational indication of efficient uptake of gas-phase HNO 3 by atmospheric mineral-dust aerosol particles.
    05/2003;
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    ABSTRACT: The EU-project MINATROC (MINeral dust And TROpospheric Chemistry) aims at enabling an estimation of the influence of mineral dust, a major, but to date largely ignored component of tropospheric aerosol, on tropospheric oxidant cycles. Within the scope of this project continuous atmospheric measurements of gas-phase HNO3 and SO2 were conducted in June and July 2000 at the CNR WMO station, situated on Monte Cimone (MTC) (44°11' N --10°42' E, 2165 m asl), Italy. African air transporting dust is occasionally advected over the Mediterranean Sea to the site, thus mineral aerosol emitted from Africa will encounter polluted air masses and provide ideal conditions to study their interactions. HNO3 and SO2 were measured with an improved CIMS (chemical ionization mass spectrometry) system for ground-based measurements that was developed and built at MPI-K Heidelberg. Since HNO3 is a very sticky compound special care was paid for the air-sampling and background-measurement system. Complete data sets could be obtained before, during and after major dust intrusions. For the first time these measurements might provide a strong observational indication of efficient uptake of gas-phase HNO3 by atmospheric mineral-dust aerosol particles.
    ATMOSPHERIC CHEMISTRY AND PHYSICS 04/2003; 3(2):417-436. · 5.51 Impact Factor
  • Atmospheric Chemistry and Physics 01/2003; 3(2):417-436. · 5.51 Impact Factor
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    ABSTRACT: Gas-phase sulfuric acid and OH have been measured by the novel MPI-K ULTRA- CIMS (ultra-trace gas detection by CIMS technique) at the Schneefernerhaus( 2750 m asl; below the summit of Mount Zugspitze, Germany) in October 2001. These mea- surements were accompanied by measurements of SO2 with another MPI-K CIMS instrument and aerosol size distribution measurements by DMPS (differential mobil- ity particle sizer) operated by the Institut fuer Wasserchemie (Technische Universitaet Muenchen). In that way a data set was obtained which allows investigating major sources and sinks of sulfuric acid under relative clean conditions. H2SO4 and espe- cially OH concentrations are relatively well correlated to solar flux. Noon maximum concentrations of OH and H2SO4 of 6.5·106 and 2·106 cm-3, respectively, were ob- served. The average SO2 concentrations were below 20 ppt. The aerosol size distribu- tion was obtained in 39 size ranges from 10 to 1056 nm. Typical aerosol concentrations are in the range of 400 to 1800 cm-3 during the discussed period of time. An estima- tion of the production rate of H2SO4 was inferred building on the reaction of SO2 and OH, while the loss rate was calculated by considering the condensation of H2SO4 on aerosol particles (Fuchs and Sutugin approach). Results of the measurements and calculations will be discussed.
    01/2002;
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    ABSTRACT: The EU-project MINATROC (MINeral dust and TROpospheric Chemistry) aims at enabling an estimation of the influence of mineral dust on tropospheric oxidant cycles. of particular interest is a possible interaction of certain trace gases with mineral dust. Such trace gases include also HNO3 and SO2. Within the scope of this project continu- ous atmospheric measurements of gas-phase HNO3 and SO2 were conducted between May and July 2000 at the CNR WMO station, situated on Monte Cimone (MTC), the highest peak of the Northern Apennines (2165 m a.s.l.) in Italy. The site was chosen because African air transporting dust is occasionally advected over the Mediterranean Sea to the site. Thus mineral aerosol emitted from Africa will encounter polluted air masses and provide ideal conditions to study their interactions. HNO3 and SO2 were measured with an improved CIMS (chemical ionization mass spectrometry) system that was developed and built at MPI-K Heidelberg. Complete data sets could be ob- tained before, during and after major dust intrusions. For the first time these measure- ments might provide a strong observational indication of efficient gas-phase HNO3 uptake by atmospheric mineral dust aerosol particles.
    01/2002;
  • Hjorth, Jens: A changing atmosphere : proceedings / 8th European Symposium on Physico-Chemical Behaviour of Atmospheric Pollutants, 17 - 20 September 2001, Torino (IT) (2002).
  • Transport and chemical transformation in the troposphere : proceedings of EUROTRAC Symposium 2002, Garmisch-Partenkirchen, Germany, 11 - 15 March 2002, Margraf Verlag (2002).