A. Laaksonen

Publications (77)116.63 Total impact

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  Available from: Petri Vaattovaara

  Article: Hygroscopic and chemical characterisation of Po Valley aerosol

  J. Bialek, M. Dall'Osto, P. Vaattovaara, J. Ovadnevaite, S. Decesari, A. Laaksonen, C. O'Dowd
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  ABSTRACT: Continental summer-time aerosol in the Italian Po Valley was characterized in terms of hygroscopic properties and the influence of chemical composition therein. The campaign-average minima in hygroscopic growth factors (HGFs) occurred just before and during sunrise from 03:00–06:00, but more generally, the whole night shows very low hygroscopicity, particularly in the smaller particle sizes. The average HGFs increased from 1.18 for the smallest sized particles (35 nm) to 1.38 for the largest sizes (165 nm) for the lowest HGF period while during the day, the HGF gradually increased to achieve maximum values in the early afternoon hours from 12:00–15:00, reaching 1.32 for 35 nm particles and 1.46 for 165 nm particles. Two contrasting case scenarios were encountered during the measurement period: Case 1 was associated with westerly air flow moving at a moderate pace and Case 2 was associated with more stagnant, slower moving air from the north-easterly sector. Case 1 exhibited low diurnal temporal patterns and was associated with moderate non-refractory aerosol mass concentrations (for 50% size cut at 1 μm) of the order of 4.5 μg m−3. For Case 1, organics contributed typically to 50% of the mass. Case 2 was characterized by > 9.5 μg m−3 total mass (< 1 μm) in the early morning hours (04:00), decreasing to ∼ 3 μg m−3 by late morning (10:00) and exhibited strong diurnal changes in chemical composition, particularly in nitrate mass but also in total organic mass concentrations. Organic growth factors (OGFs) exhibited a minimum around 15:00, 1–2 h after the peak in HGF. Particles sized 165 nm exhibited moderate diurnal variability in HGF, ranging from 80% at night to 95% of "more hygroscopic" growth factors (i.e. GF = 1.35–1.9) around noon. The diurnal changes in HGF progressively became enhanced with decreasing particle size, decreasing from 95% "more hygroscopic" growth factor fraction at noon to 10% fraction at midnight, while the "less hygroscopic" growth factor fraction (1.13–1.34) increased from 5% at noon to > 60% and the "barely hygroscopic" growth factor fraction (1.1–1.2) increased from less than 2% at noon to 30% at midnight. OGFs were generally anti-correlated to HGF and also total organic mass as measured by the aerosol mass spectrometer due to a high sulphate/organics ratio. Surprisingly, the lowest HGFs occurred for periods when nitrate mass reached peak concentrations. This may suggest formation of organonitrates and organosulphates, which significantly decreased the OGF. Coincident with the peak in nitrate was a peak in Hydrocarbon-like Organic Aerosol (HOA) and Semi-Volatile Oxygenated Organic Aerosol (SV-OOA) and analysis of the HGF probability distribution function (PDF) reveals a transformation of a predominant "More Hygroscopic" (MH) mode with HGF of 1.5 around noon, into two modes, one with a "less hygroscopic" (LH) HGF of 1.26, and another with a "barely hygroscopic" (BH) mode of 1.05. The analysis points to an internal mixture of larger size inorganic species, mainly nitrates, coated with a hydrophobic organic layer which suppresses water uptake. In addition, a new, externally mixed BH ultrafine mode appears and persists through the night.
  Atmos. Chem. Phys. Discuss. 01/2013;
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  Available from: Annele Virtanen

  Dataset: acp-11-8759-2011

  A. Virtanen, J. Kannosto, A. Arffman, J. Joutsensaari, H. Kuuluvainen, E. Saukko, L. Hao, P. Yli-Pirilä, P. Tiitta, J.K. Holopainen, J. Keskinen, D.R. Worsnop, J.N. Smith, A. Laaksonen
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  Available from: Petri Tiitta

  Article: Atmospheric Chemistry and Physics Determination of the biogenic secondary organic aerosol fraction in the boreal forest by NMR spectroscopy

  E Finessi, S Decesari, M Paglione, L Giulianelli, C Carbone, S Gilardoni, S Fuzzi, S Saarikoski, T Raatikainen, R Hillamo, J Allan, Th F Mentel, P Tiitta, A Laaksonen, T Petäjä, M Kulmala, D R Worsnop, M C Facchini
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  ABSTRACT: The study investigates the sources of fine organic aerosol (OA) in the boreal forest, based on measurements in-cluding both filter sampling (PM 1) and online methods and carried out during a one-month campaign held in Hyytiälä, Finland, in spring 2007. Two aerosol mass spectrometers (Q-AMS, ToF-AMS) were employed to measure on-line con-centrations of major non-refractory aerosol species, while the water extracts of the filter samples were analyzed by nuclear magnetic resonance (NMR) spectroscopy for organic func-tional group characterization of the polar organic fraction of the aerosol. AMS and NMR spectra were processed sepa-rately by non-negative factorization algorithms, in order to apportion the main components underlying the submicrome-ter organic aerosol composition and depict them in terms of both mass fragmentation patterns and functional group com-positions. The NMR results supported the AMS speciation of oxi-dized organic aerosol (OOA) into two main fractions, which could be generally labelled as more and less oxidized organ-ics. The more oxidized component was characterized by a mass spectrum dominated by the m/z 44 peak, and in parallel by a NMR spectrum showing aromatic and aliphatic back-bones highly substituted with oxygenated functional groups (carbonyls/carboxyls and hydroxyls). Such component, con-tributing on average 50 % of the OA mass throughout the observing period, was associated with pollution outbreaks from the Central Europe. The less oxidized component was enhanced in concomitance with air masses originating from the North-to-West sector, in agreement with previous investi-gations conducted at this site. NMR factor analysis was able to separate two distinct components under the less oxidized fraction of OA. One of these NMR-factors was associated with the formation of terrestrial biogenic secondary organic aerosol (BSOA), based on the comparison with spectral pro-files obtained from laboratory experiments of terpenes photo-oxidation. The second NMR factor associated with western air masses was linked to biogenic marine sources, and was enriched in low-molecular weight aliphatic amines. Such findings provide evidence of at least two independent sources originating biogenic organic aerosols in Hyytiälä by oxida-tion and condensation mechanisms: reactive terpenes emit-ted by the boreal forest and compounds of marine origin, with the latter relatively more important when predominantly polar air masses reach the site. This study is an example of how spectroscopic techniques, such as proton NMR, can add functional group specificity for certain chemical features (like aromatics) of OA with respect to AMS. They can therefore be profitably exploited to com-plement aerosol mass spectrometric measurements in organic source apportionment studies.
  Atmospheric Chemistry and Physics 02/2012; 12:941-959.
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  Available from: Zbigniew Klimont

  Article: General overview: European Integrated project on Aerosol Cloud Climate and Air Quality interactions (EUCAARI) – integrating aerosol research from nano to global scales

  M. Kulmala, A. Asmi, H.K. Lappalainen, U. Baltensperger, J.-L. Brenguier, M.C. Facchini, H.-C. Hansson, Ø. Hov, C.D. O'Dowd, U. Pöschl, [......], J. Wildt, S. Woodward, D.R. Worsnop, G.-J- van Zadelhoff, A.A. Zardini, K. Zhang, P.G. van Zyl, V.-M. Kerminen, K.S. Carslaw, S.N. Pandis
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  ABSTRACT: In this paper we describe and summarize the main achievements of the European Aerosol Cloud Climate and Air Quality Interactions project (EUCAARI). EUCAARI started on 1 January 2007 and ended on 31 December 2010 leaving a rich legacy including: (a) a comprehensive database with a year of observations of the physical, chemical and optical properties of aerosol particles over Europe, (b) comprehensive aerosol measurements in four developing countries, (c) a database of airborne measurements of aerosols and clouds over Europe during May 2008, (d) comprehensive modeling tools to study aerosol processes fron nano to global scale and their effects on climate and air quality. In addition a new Pan-European aerosol emissions inventory was developed and evaluated, a new cluster spectrometer was built and tested in the field and several new aerosol parameterizations and computations modules for chemical transport and global climate models were developed and evaluated. These achievements and related studies have substantially improved our understanding and reduced the uncertainties of aerosol radiative forcing and air quality-climate interactions. The EUCAARI results can be utilized in European and global environmental policy to assess the aerosol impacts and the corresponding abatement strategies.
  Atmospheric Chemistry and Physics 01/2012; 11:13061-13143. · 4.88 Impact Factor
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  Available from: Petri Tiitta

  Article: Atmospheric Chemistry and Physics Aerosol hygroscopicity and CCN activation kinetics in a boreal forest environment during the 2007 EUCAARI campaign

  K M Cerully, T Raatikainen, S Lance, D Tkacik, P Tiitta, T Petäjä, M Ehn, M Kulmala, D R Worsnop, A Laaksonen, J N Smith, A Nenes
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  ABSTRACT: Measurements of size-resolved cloud condensa-tion nuclei (CCN) concentrations, subsaturated hygroscopic growth, size distribution, and chemical composition were collected from March through May, 2007, in the remote Bo-real forests of Hyytiälä, Finland, as part of the European In-tegrated project on Aerosol Cloud Climate and Air Quality Interactions (EUCAARI) campaign. Hygroscopicity param-eter, κ, distributions were derived independently from Con-tinuous Flow-Streamwise Thermal Gradient CCN Chamber (CFSTGC) and Hygroscopicity Tandem Differential Mobil-ity Analyzer (HTDMA) measurements. CFSTGC-derived κ values for 40, 60, and 80 nm particles range mostly between 0.10 and 0.40 with an average characteristic of highly oxi-dized organics of 0.20 ± 0.10, indicating that organics play a dominant role for this environment. HTDMA-derived κ were generally 30 % lower. Diurnal trends of κ show a min-imum at sunrise and a maximum in the late afternoon; this trend covaries with inorganic mass fraction and the m/z 44 organic mass fraction given by a quadrupole aerosol mass spectrometer, further illustrating the importance of organ-Correspondence to: A. Nenes (athanasios.nenes@gatech.edu) ics in aerosol hygroscopicity. The chemical dispersion in-ferred from the observed κ distributions indicates that while 60 and 80 nm dispersion increases around midday, 40 nm dis-persion remains constant. Additionally, 80 nm particles show a markedly higher level of chemical dispersion than both 40 and 60 nm particles. An analysis of droplet activation kinet-ics for the sizes considered indicates that most of the CCN activate as rapidly as (NH 4) 2 SO 4 calibration aerosol.
  Atmospheric Chemistry and Physics 01/2012; 11:12369-12386.
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  Available from: Ismael K. Ortega

  Article: On the formation of sulphuric acid-amine clusters in varying atmospheric conditions and its influence on atmospheric new particle formation

  P Paasonen, T Olenius, O Kupiainen, T Kur En, T Pe, W Birmili, A Hamed, M Hu, L G Huey, C Plass-Duelmer, J N Smith, V Loukonen, M J Mcgrath, I K Ortega, A Laaksonen, V.-M Kerminen, M Kulmala, H. Vehkamäki
  Atmospheric Chemistry and Physics Discussions. 01/2012; 12:11485-11537.
• Article: Effect of aerosol size distribution changes on AOD, CCN and cloud droplet concentration: Case studies from Erfurt and Melpitz, Germany

  S Romakkaniemi, A Arola, H Kokkola, W Birmili, T Tuch, V -M Kerminen, P Raisanen, J N Smith, H Korhonen, A Laaksonen
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  ABSTRACT: For the period of 1990 to 2000, atmospheric particulate mass concentrations have decreased in Central Europe. Simultaneously, the amount of shortwave radiation reaching the ground increased during clear sky conditions. The aerosol indirect effect has not been seen as clearly, as the radiation reaching the ground during overcast conditions has not increased as much as might be expected. Here we show that this may be caused by the condensation kinetics of water during cloud droplet formation. The decrease in the particulate mass led to a clear decrease in the number concentration of cloud condensation nuclei (CCN). However, in urban areas a relatively larger decrease in the number of particles in the upper end of the accumulation mode has led to slower condensation of water. As a result, a higher maximum supersaturation is reached during the cloud droplet formation. This compensates for the effect of decreased CCN concentrations. For example in Erfurt between 1991 and 1996, the aerosol properties changed so that aerosol optical depth decreased by 58% and CCN concentration decreased by 25 to 50%. These led to a 4 to 12% reduction in cloud droplet number concentration (CDNC) and less than a 2 Wm(-2) increase in shortwave radiation during overcast conditions. These results demonstrate that locally the aerosol direct effect can be much larger than the aerosol indirect effect. Furthermore, even though AOD appears to be a valid proxy for CCN, the correlation between AOD and CDNC is not straightforward and thus AOD cannot be used as a proxy for CDNC.
  Journal of Geophysical Research 01/2012; 117. · 3.02 Impact Factor
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  Available from: atmos-chem-phys-discuss.net

  Article: A statistical proxy for sulphuric acid concentration

  S Mikkonen, S Romakkaniemi, J N Smith, H Korhonen, T Petaja, C Plass-Duelmer, M Boy, P H McMurry, K E J Lehtinen, J Joutsensaari, A Hamed, R L Mauldin III, W Birmili, G Spindler, F Arnold, M Kulmala, A Laaksonen
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  ABSTRACT: Gaseous sulphuric acid is a key precursor for new particle formation in the atmosphere. Previous experimental studies have confirmed a strong correlation between the number concentrations of freshly formed particles and the ambient concentrations of sulphuric acid. This study evaluates a body of experimental gas phase sulphuric acid concentrations, as measured by Chemical Ionization Mass Spectrometry (CIMS) during six intensive measurement campaigns and one long-term observational period. The campaign datasets were measured in Hyytiala, Finland, in 2003 and 2007, in San Pietro Capofiume, Italy, in 2009, in Melpitz, Germany, in 2008, in Atlanta, Georgia, USA, in 2002, and in Niwot Ridge, Colorado, USA, in 2007. The long term data were obtained in Hohenpeissenberg, Germany, during 1998 to 2000. The measured time series were used to construct proximity measures ("proxies") for sulphuric acid concentration by using statistical analysis methods. The objective of this study is to find a proxy for sulfuric acid that is valid in as many different atmospheric environments as possible. Our most accurate and universal formulation of the sulphuric acid concentration proxy uses global solar radiation, SO2 concentration, condensation sink and relative humidity as predictor variables, yielding a correlation measure (R) of 0.87 between observed concentration and the proxy predictions. Interestingly, the role of the condensation sink in the proxy was only minor, since similarly accurate proxies could be constructed with global solar radiation and SO2 concentration alone. This could be attributed to SO2 being an indicator for anthropogenic pollution, including particulate and gaseous emissions which represent sinks for the OH radical that, in turn, is needed for the formation of sulphuric acid.
  ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2011; 11(21):11319-11334. · 5.52 Impact Factor
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  Available from: Petri Tiitta

  Article: . Bounce behavior of freshly nucleates secondary organic aerosol

  A. Virtanen, J. Kannosto, A. Arffman, J. Joutsensaari, H. Kuuluvainen, E. Saukko, L. Hao, P. Yli-Pirilä, P. Tiitta, J.K. Holopainen, J. Keskinen, D.R. Worsnop, J.N. Smith, A. Laaksonen
  ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2011; 11:8759-8766. · 5.52 Impact Factor
• Article: EUCAARI ion spectrometer measurements at 12 European sites – analysis of new particle formation events

  H.E. Manninen, T. Nieminen, E. Asmi, S. Gagné, S. Häkkinen, K. Lehtipalo, P. Aalto, M. Vana, A. Mirme, S. Mirme, [......], M. Gysel, N. Bukowiecki, E. Weingartner, G. Wehrle, A. Laaksonen, A. Hamed, J. Joutsensaari, T. Petäjä, V.-M. Kerminen, M. Kulmala
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  ABSTRACT: We present comprehensive results on continuous atmospheric cluster and particle measurements in the size range ~1–42 nm within the European Integrated project on Aerosol Cloud Climate and Air Quality interactions (EUCAARI) project. We focused on characterizing the spatial and temporal variation of new particle formation events and relevant particle formation parameters across Europe. Different types of air ion and cluster mobility spectrometers were deployed at 12 field sites across Europe from March 2008 to May 2009. The measurements were conducted in a wide variety of environments, including coastal and continental locations as well as sites at different altitudes (both in the boundary layer and the free troposphere). New particle formation events were detected at all of the 12 field sites during the year-long measurement period. From the data, nucleation and growth rates of newly formed particles were determined for each environment. In a case of parallel ion and neutral cluster measurements, we could also estimate the relative contribution of ion-induced and neutral nucleation to the total particle formation. The formation rates of charged particles at 2 nm accounted for 1–30% of the corresponding total particle formation rates. As a significant new result, we found out that the total particle formation rate varied much more between the different sites than the formation rate of charged particles. This work presents, so far, the most comprehensive effort to experimentally characterize nucleation and growth of atmospheric molecular clusters and nanoparticles at ground-based observation sites on a continental scale.
  Atmospheric Chemistry and Physics 01/2010; 10(16):7907-7927.
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  Available from: Petri Vaattovaara

  Article: Evolution of organic aerosols in the atmosphere.

  J L Jimenez, M R Canagaratna, N M Donahue, A S H Prevot, Q Zhang, J H Kroll, P F DeCarlo, J D Allan, H Coe, N L Ng, [......], D Sueper, J T Jayne, S C Herndon, A M Trimborn, L R Williams, E C Wood, A M Middlebrook, C E Kolb, U Baltensperger, D R Worsnop
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  ABSTRACT: Organic aerosol (OA) particles affect climate forcing and human health, but their sources and evolution remain poorly characterized. We present a unifying model framework describing the atmospheric evolution of OA that is constrained by high-time-resolution measurements of its composition, volatility, and oxidation state. OA and OA precursor gases evolve by becoming increasingly oxidized, less volatile, and more hygroscopic, leading to the formation of oxygenated organic aerosol (OOA), with concentrations comparable to those of sulfate aerosol throughout the Northern Hemisphere. Our model framework captures the dynamic aging behavior observed in both the atmosphere and laboratory: It can serve as a basis for improving parameterizations in regional and global models.
  Science 12/2009; 326(5959):1525-9. · 31.20 Impact Factor
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  Available from: Petri Vaattovaara

  Article: Atmospheric Chemistry and Physics The role of VOC oxidation products in continental new particle formation

  A Laaksonen, M Kulmala, C D O 'dowd, J Joutsensaari, P Vaattovaara, S Mikkonen, K E J Lehtinen, L Sogacheva, M Dal Maso, P Aalto, [......], K Sellegri, B Umann, W Junkermann, H Coe, J D Allan, M R Alfarra, D R Worsnop, M.-L Riekkola, T Hyötyläinen, Y Viisanen
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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.
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  Available from: Josef Dommen

  Article: Cloud forming potential of secondary organic aerosol under near atmospheric conditions

  J. Duplissy, M. Gysel, M. R. Alfarra, J. Dommen, A. Metzger, A. S. H. Prevot, E. Weingartner, A. Laaksonen, T. Raatikainen, N. Good, F. Turner, G. McFiggans, U. Baltensperger
  Geophysical Research Letters 01/2008; 35:L03818. · 3.79 Impact Factor
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  Available from: bnl.gov

  Article: Thermodynamics, gas-liquid nucleation, and size-dependent surface tension

  A. Laaksonen, R. McGraw
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  ABSTRACT: Phenomenological nucleation theories are considered from the viewpoint of Gibbs' surface thermodynamics. We point out, in defining the critical nucleus, that it is important to make a distinction between the number of molecules enclosed by the surface of tension and the excess number of molecules over the uniform vapor phase. We show that the Kelvin equation should be employed in determining the size of the critical nucleus even if the nucleus free energy contains a size-dependent surface energy term. Furthermore, we make use of the fact that the classical form of Kelvin equation (containing the surface tension of a flat interface) predicts the equimolar radius of the critical nucleus well down to nuclei of about 40 molecules, and derive a new equation for the size-dependent surface tension that differs from the Tolman relation. Density functional calculations support the new formula.
  EPL (Europhysics Letters) 01/2007; 35(5):367. · 2.17 Impact Factor
• Article: The effect of physical and chemical aerosol properties on warm cloud droplet activation

  G. McFiggans, P. Artaxo, U. Baltensperger, H. Coe, M. Facchini, G. Feingold, S. Fuzzi, M. Gysel, A. Laaksonen, U. Lohmann, T.F. Mentel, D.M. Murphy, C.D. O'Dowd, J.R. Snider, E. Weingartner
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  ABSTRACT: The effects of atmospheric aerosol on climate forcing may be very substantial but are quantified poorly at present; in particular, the effects of aerosols on cloud radiative properties, or the "indirect effects" are credited with the greatest range of uncertainty amongst the known causes of radiative forcing. This manuscript explores the effects that the composition and properties of atmospheric aerosol can have on the activation of droplets in warm clouds, so potentially influencing the magnitude of the indirect effect. The effects of size, composition, mixing state and various derived properties are assessed and a range of these properties provided by atmospheric measurements in a variety of locations is briefly reviewed. The suitability of a range of process-level descriptions to capture these aerosol effects is investigated by assessment of their sensitivities to uncertainties in aerosol properties and by their performance in closure studies. The treatment of these effects within global models is reviewed and suggestions for future investigations are made.
  Atmospheric Chemistry and Physics. 07/2006; 6(9):2593-2649.
• Article: Surface tensions and densities of H2SO4+NH3 plus water solutions

  AP Hyvarinen, T Raatikainen, A Laaksonen, Y Viisanen, H Lihavainen
  Geophysical Research Letters 01/2005; 32(16). · 3.79 Impact Factor
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  Available from: Jarmo K Holopainen

  Article: Nanoparticle formation by ozonolysis of inducible plant volatiles

  J. Joutsensaari, M. Loivamaki, T. Vuorinen, P. Miettinen, A. M. Nerg, J. K. Holopainen, A. Laaksonen
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  ABSTRACT: We present the first laboratory experiments of aerosol formation from oxidation of volatile organic species emitted by living plants, a process which for half a century has been known to take place in the atmosphere. We have treated white cabbage plants with methyl jasmonate in order to induce the production of monoterpenes and certain less-volatile sesqui- and homoterpenes. Ozone was introduced into the growth chamber in which the plants were placed, and the subsequent aerosol formation and growth of aerosols were monitored by measuring the particle size distributions continuously during the experiments. Our observations show similar particle formation rates as in the atmosphere but much higher growth rates. The results indicate that the concentrations of nonvolatile oxidation products of plant released precursors needed to induce the nucleation are roughly an order-of-magnitude higher than their concentrations during atmospheric nucleation events. Our results therefore suggest that if oxidized organi
  01/2005; 5:1489-1495.
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  Available from: Miikka Dal Maso

  Article: Overview of the field measurement campaign in Hyytiala, August 2001 in the framework of the EU project OSOA

  M. Boy, T. Petaja, M. Dal Maso, U. Rannik, J. Rinne, P. Aalto, A. Laaksonen, P. Vaattovaara, J. Joutsensaari, T. Hoffmann, [......], A. Kouvarakis, C. Pio, A. Carvalho, A. Rompp, G. Moortgat, C. Spirig, A. Guenther, J. Greenberg, P. Ciccioli, M. Kulmala
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  ABSTRACT: As part of the OSOA (Origin and formation of Secondary Organic Aerosols) project, two intensive field campaigns were conducted in Melpitz, Germany and Hyytiala, Finland. This paper gives an overview of the measurements made during the Hyytiala campaign, which was held between 1 and 16 August 2001. Various instrumental techniques were used to achieve physical and chemical characterisation of aerosols and to investigate possible precursor gases. During the OSOA campaign in Hyytiala, particle formation was observed on three consecutive days at the beginning of the campaign (1 to 3 August 2001) and on three days later on. The investigation of the meteorological situation divided the campaign into two parts. During the first three days of August, relatively cold and clean air masses from northwest passed over the station (condensation sink-CS: <0.002 s(-1), NOx: <0.5 ppb). Daily particle bursts of one fraction of the nucleation mode aerosols (3-10 nm) with number concentrations between 600-1200 particles cm(-3) were observed. After this period, warmer and more polluted air from south-west to south-east arrived at the station (CS: 0.002-0.01 s(-1), NOx: 0.5-4 ppb) and during these 13 days only three events were observed. These events were not as apparent as those that occurred during the earlier period of the campaign. The chemical analyses from different institutes of PM2, PM2.5 and PM10 particles confirmed the assumption that organic matter from the oxidation of various terpenes contributed to the formation of secondary organic aerosols (SOA). Concerning these conclusions among others, the ratio between formic (oxidation product of isoprene and monoterpenes by ozone) and acetic acid (increased by anthropogenic emissions) (ratio=1 to 1.5) and concentration of different carboxylic acids (up to 62 ng m(-3)) were investigated. Gas/particle partitioning of five photo-oxidation products from alpha- and beta-pinene resulted in higher concentrations of pinonic, nor pinonic and pinic acids in the particle phase than in the gas phase, which indicates a preference to the particle phase for these compounds. The average growth factors (GF) from 100 nm particles in water vapour gave a diurnal pattern with a maximum during daytime and values between 1.2 and 1.7. On average, the amount of secondary organic carbon reached values around 19% of the sampled aerosols and we speculate that formation of SOA with the influence of photo-oxidation products from terpenes was the reason for the observed particle bursts during the campaign. However, correlations between the precursor gases or the favourable condensing species with the monitored nucleation mode particles were not found. For the investigated time period other factors like the condensation sink of newly formed particles to the pre-existing aerosols, temperature and solar irradiance seem to be more important steering parameters for the production of new aerosols. Another open question concerns the vertical distribution of the formation of SOA. For this reason measurements were conducted at different altitudes using a tethered balloon platform with particle sampling and particle counting equipment. They were incorporated with eddy covariance (EC) flux measurements made at 23 m above ground level. The results give first indications that production of new aerosols happens throughout the planetary boundary layer (PBL), whereby different parameters e.g. temperature, CS, solar irradiance or concentration of monoterpenes are responsible for the location of the vertical maximum.
  Atmospheric Chemistry and Physics. 01/2004; 4:657-678.
• Article: Evaporation and Condensational Growth of Liquid Droplets in Nonisothermal Gas Mixtures

  A. B. Nadykto, E. R. Shchukin, M. Kulmala, K. E. J. Lehtinen, A. Laaksonen
  Aerosol Science and Technology 04/2003; 37(4):315-324. · 2.67 Impact Factor
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  Available from: E. DOUGLAS Nilsson

  Article: Overview of the international project on biogenic aerosol formation in the boreal forest (BIOFOR)

  M. KULMALA, K. HÄMERI, P. P. AALTO, J. M. MÄKELÄ, L. PIRJOLA, E. DOUGLAS NILSSON, G. BUZORIUS, Ü. RANNIK, M. DAL MASO, W. SEIDL, T. HOFFMAN, R. JANSON, H.-C. HANSSON, Y. VIISANEN, A. LAAKSONEN, C. D. O'DOWD
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  ABSTRACT: Aerosol formation and subsequent particle growth in ambient air have been frequently observed at a boreal forest site (SMEAR II station) in Southern Finland. The EU funded project BIOFOR (Biogenic aerosol formation in the boreal forest) has focused on: (a) determination of formation mechanisms of aerosol particles in the boreal forest site; (b) verification of emissions of secondary organic aerosols from the boreal forest site; and (c) quantification of the amount of condensable vapours produced in photochemical reactions of biogenic volatile organic compounds (BVOC) leading to aerosol formation. The approach of the project was to combine the continuous measurements with a number of intensive field studies. These field studies were organised in three periods, two of which were during the most intense particle production season and one during a non-event season. Although the exact formation route for 3 nm particles remains unclear, the results can be summarised as follows: Nucleation was always connected to Arctic or Polar air advecting over the site, giving conditions for a stable nocturnal boundary layer followed by a rapid formation and growth of a turbulent convective mixed layer closely followed by formation of new particles. The nucleation seems to occur in the mixed layer or entrainment zone. However two more prerequisites seem to be necessary. A certain threshold of high enough sulphuric acid and ammonia concentrations is probably needed as the number of newly formed particles was correlated with the product of the sulphuric acid production and the ammonia concentrations. No such correlation was found with the oxidation products of terpenes. The condensation sink, i.e., effective particle area, is probably of importance as no nucleation was observed at high values of the condensation sink. From measurement of the hygroscopic properties of the nucleation particles it was found that inorganic compounds and hygroscopic organic compounds contributed both to the particle growth during daytime while at night time organic compounds dominated. Emissions rates for several gaseous compounds was determined. Using four independent ways to estimate the amount of the condensable vapour needed for observed growth of aerosol particles we get an estimate of 2–10×107 vapour molecules cm−3. The estimations for source rate give 7.5–11×104 cm−3 s−1. These results lead to the following conclusions: The most probable formation mechanism is ternary nucleation (water-sulphuric acid-ammonia). After nucleation, growth into observable sizes (∼3 nm) is required before new particles appear. The major part of this growth is probably due to condensation of organic vapours. However, there is lack of direct proof of this phenomenon because the composition of 1–5 nm size particles is extremely difficult to determine using the present state-of-art instrumentation
  Tellus B 03/2003; 53(4):324 - 343. · 4.38 Impact Factor