I. Riipinen

Stockholm University, Tukholma, Stockholm, Sweden

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Publications (123)496.51 Total impact

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    ABSTRACT: Formation of new particles through clustering of molecules from condensable vapors is a significant source for atmospheric aerosols. The smallest clusters formed in the very first steps of the condensation process are, however, not directly observable by experimental means. We present here a comprehensive series of electronic structure calculations on the hydrates of clusters formed by up to four molecules of sulfuric acid, and up to two molecules of ammonia or dimethylamine. Though clusters containing ammonia, and certainly dimethylamine, generally exhibit lower average hydration than the pure acid clusters, populations of individual hydrates vary widely. Furthermore, we explore the predictions obtained using a thermodynamic model for the description of these hydrates. The similar magnitude and trends of hydrate formation predicted by both methods illustrate the potential of combining them to obtain more comprehensive models. The stabilization of some clusters relative to others due to their hydration is highly likely to have significant effects on the overall processes that lead to formation of new particles in the atmosphere.
    The Journal of Physical Chemistry A 03/2014; · 2.77 Impact Factor
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    ABSTRACT: The Volatility-Hygroscopicity Tandem Differential Mobility Analyzer (VH-TDMA) was applied to study the hygroscopicity and volatility properties of submicron atmospheric aerosol in a boreal forest environment in Hyytiälä, Finland during the summer of 2010. Aitken and accumulation mode particles (50 nm, 75 nm and 110 nm) were investigated. The results suggest that the particles were internally mixed at all sizes. Hygroscopicity was found to increase with size. The relative mass fraction of organics and SO42- is probably the major contributor to the fluctuation of the hygroscopicity for all particle sizes. The Cloud Condensation Nuclei counter (CCNc)-derived hygroscopicity parameter κ was slightly higher than κ calculated from VH-TDMA data under sub-saturated conditions, which can be explained by the fact that particulate organics have a different degree of dissolution in sub- and supersaturated conditions. Also, the size-resolved volatility properties of particles were investigated. Upon heating, small particles evaporated more compared to large particles. There was a significant amount of aerosol volume (non-volatile material) left even at heating temperatures above 280 °C. Using size resolved volatility-hygroscopicity analysis, we concluded that there was always hygroscopic material remaining in the particles of different sizes at all different heating temperatures, even above 280 °C. This indicates that the observed non-volatile aerosol material was not consisting solely of black carbon.
    Atmospheric Chemistry and Physics 11/2013; 13(11):29097-29136. · 4.88 Impact Factor
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    ABSTRACT: The smelter industry in Kola Peninsula is the largest source of anthropogenic SO2 in the Arctic part of Eurasia and one of the largest within the Arctic domain. Due to socio-economic changes in Russia the emissions have been decreasing especially since the late 1990s resulting in decreased SO2 concentrations close to Kola in Eastern Lapland, Finland. At the same time, the frequency of new particle formation days has been decreasing distinctively at SMEAR I station in Eastern Lapland, especially during spring and autumn. We show that sulphur species, namely sulphur dioxide and sulphuric acid, have an important role in both new particle formation and subsequent growth and that the decrease in new particle formation days is a result of the reduction of sulphur emissions originating from Kola Peninsula. In addition to sulphur species, there are many other quantities, such as formation rate or aerosol particles, condensation sink and nucleation mode particle number concentration, which are related to the number of observed new particle formation (NPF) days and need to be addressed when linking sulphur emissions and NPF. We show that while most of these quantities exhibit statistically significant trends, the reduction in Kola sulphur emissions is the most obvious reason for the rapid decline in NPF days. Sulphuric acid explains approximately 20-50% of the aerosol condensational growth observed at SMEAR I and there is a large seasonal variation with highest values obtained during spring and autumn. We found that (i) particles form earlier after sunrise during late winter and early spring due to high concentrations of SO2 and H2SO4, (ii) several events occurred during the absence of light and they were connected to higher than average concentrations of SO2 and (iii) high SO2 concentrations could advance the onset of nucleation by several hours. Moreover, air masses coming over Kola Peninsula seemed to favour new particle formation.
    Atmospheric Chemistry and Physics 11/2013; 13(11):30721-30763. · 4.88 Impact Factor
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    ABSTRACT: [1] Atmospheric organic aerosol concentrations depend in part on the gas-particle partitioning of primary organic aerosol (POA) emissions. Consequently, heating and dilution were used to investigate the volatility of biomass-burning smoke particles from combustion of common North American trees/shrubs/grasses during the third Fire Lab at Missoula Experiment. Fifty to eighty percent of the mass of biomass-burning POA evaporated when isothermally diluted from plume- (~1000 µg m−3) to ambient-like concentrations (~10 µg m−3), while roughly 80% of the POA evaporated upon heating to 100°C in a thermodenuder with a residence time of ~14 sec. Therefore, the majority of the POA emissions were semivolatile. Thermodenuder measurements performed at three different residence times indicated that there were not substantial mass transfer limitations to evaporation (i.e., the mass accommodation coefficient appears to be between 0.1 and 1). An evaporation kinetics model was used to derive volatility distributions and enthalpies of vaporization from the thermodenuder data. A single volatility distribution can be used to represent the measured gas-particle partitioning from the entire set of experiments, including different fuels, organic aerosol concentrations, and thermodenuder residence times. This distribution, derived from the thermodenuder measurements, also predicts the dilution-driven changes in gas-particle partitioning. This volatility distribution and associated emission factors for each fuel studied can be used to update emission inventories and to simulate the gas-particle partitioning of biomass-burning POA emissions in chemical transport models.
    Journal of Geophysical Research: Atmospheres. 10/2013; 118(19).
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    ABSTRACT: Condensation and evaporation modify the properties and effects of atmospheric aerosol particles. We studied the evaporation of aqueous succinic acid and succinic acid/ammonium sulfate droplets to obtain insights on the effect of ammonium sulfate on the gas/particle partitioning of atmospheric organic acids. Droplet evaporation in a laminar flow tube was measured in a Tandem Differential Mobility Analyzer setup. A wide range of droplet compositions was investigated, and for some of the experiments the composition was tracked using an Aerosol Mass Spectrometer. The measured evaporation was compared to model predictions where the ammonium sulfate was assumed not to directly affect succinic acid evaporation. The model captured the evaporation rates for droplets with large organic content but overestimated the droplet size change when the molar concentration of succinic acid was similar to or lower than that of ammonium sulfate, suggesting that ammonium sulfate enhances the partitioning of dicarboxylic acids to aqueous particles more than currently expected from simple mixture thermodynamics. If extrapolated to the real atmosphere, these results imply enhanced partitioning of secondary organic compounds to particulate phase in environments dominated by inorganic aerosol.
    Environmental Science & Technology 10/2013; · 5.26 Impact Factor
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    ABSTRACT: Nucleation of aerosol particles from trace atmospheric vapours is thought to provide up to half of global cloud condensation nuclei. Aerosols can cause a net cooling of climate by scattering sunlight and by leading to smaller but more numerous cloud droplets, which makes clouds brighter and extends their lifetimes. Atmospheric aerosols derived from human activities are thought to have compensated for a large fraction of the warming caused by greenhouse gases. However, despite its importance for climate, atmospheric nucleation is poorly understood. Recently, it has been shown that sulphuric acid and ammonia cannot explain particle formation rates observed in the lower atmosphere. It is thought that amines may enhance nucleation, but until now there has been no direct evidence for amine ternary nucleation under atmospheric conditions. Here we use the CLOUD (Cosmics Leaving OUtdoor Droplets) chamber at CERN and find that dimethylamine above three parts per trillion by volume can enhance particle formation rates more than 1,000-fold compared with ammonia, sufficient to account for the particle formation rates observed in the atmosphere. Molecular analysis of the clusters reveals that the faster nucleation is explained by a base-stabilization mechanism involving acid-amine pairs, which strongly decrease evaporation. The ion-induced contribution is generally small, reflecting the high stability of sulphuric acid-dimethylamine clusters and indicating that galactic cosmic rays exert only a small influence on their formation, except at low overall formation rates. Our experimental measurements are well reproduced by a dynamical model based on quantum chemical calculations of binding energies of molecular clusters, without any fitted parameters. These results show that, in regions of the atmosphere near amine sources, both amines and sulphur dioxide should be considered when assessing the impact of anthropogenic activities on particle formation.
    Nature 10/2013; · 38.60 Impact Factor
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    ABSTRACT: Sulphuric acid, ammonia, amines, and oxidised organics play a crucial role in nanoparticle formation in the atmosphere. In this study, we investigate the composition of nucleated nanoparticles formed from these compounds in the CLOUD chamber experiments at CERN. The investigation is carried out via analysis of the particle hygroscopicity, ethanol affinity, oxidation state, and ion composition. Hygroscopicity was studied by a hygroscopic tandem differential mobility analyser and a cloud condensation nuclei counter, ethanol affinity by an organic differential mobility analyser and particle oxidation level by a high resolution time-of-flight aerosol mass spectrometer. The ion composition was studied by an atmospheric pressure interface time-of-flight mass spectrometer. The volume fraction of the organics in the particles during their growth from sizes of a few nanometers to tens of nanometers was derived from measured hygroscopicity assuming the Zdanovski-Stokes-Robinson relationship, and compared to values gained from the spectrometers. The ZSR-relationship was also applied to obtain the measured ethanol affinities during the particle growth, which were used to derive the volume fractions of sulphuric acid and the other inorganics (e.g. ammonium salts). In the presence of sulphuric acid and ammonia, particles with a mobility diameter of 150 nm were chemically neutralised to ammonium sulphate. In the presence of oxidation products of pinanediol, the organic volume fraction of freshly nucleated particles increased from 0.4 to ~0.9, with an increase in diameter from 2 to 63 nm. Conversely, the sulphuric acid volume fraction decreased from 0.6 to 0.1 when the particle diameter increased from 2 to 50 nm. The results provide information on the composition of nucleated aerosol particles during their growth in the presence of various combinations of sulphuric acid, ammonia, dimethylamine and organic oxidation products.
    Atmospheric Chemistry and Physics 06/2013; 13:5587. · 4.88 Impact Factor
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    ABSTRACT: Sulfur emissions from the Kola Peninsula smelter industry have been decreasing over the past two decades. We investigated the effect of this to new particle formation at SMEAR I station in Eastern Lapland, Finland, using long-term measurements of trace gases and aerosol size distributions. We show that the number of events per year has decreased and can be linked with the decreasing sulfur emissions from Kola.
    05/2013;
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    ABSTRACT: Freshly formed atmospheric nanoparticles have been observed to contain also such organic compounds which have too high saturation vapor pressure to condense on nanoparticles reversibly. The condensation of these compounds on the particles may be facilitated by particle phase processes that transform the compounds into less-volatile form. Here we use particle growth model MABNAG to study the effect of particle phase acid-base chemistry on the condensation of organic acids and bases.
    05/2013;
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    ABSTRACT: Water uptake or hygroscopicity is one of the most fundamental properties of atmospheric aerosols. Aerosol particles containing soluble materials can grow in size by absorbing water in ambient atmosphere. This property is measured by a parameter known as growth factor (GF), which is defined as the ratio of the wet diameter to the dry diameter. Hygroscopicity controls the size of an aerosol particle and therefore its optical properties in the atmosphere. Hygroscopic growth depends on the dry size of the particle, its chemical composition and the relative humidity in the ambient air (Fitzgerald, 1975; Pilinis et al., 1995). One of the typical problems in aerosol studies is the lack of measurements of aerosol size distributions and optical properties in ambient conditions. The gap between dry measurements and the real humid atmosphere is filled in this study by utilizing a hygroscopic model which calculates the hygroscopic growth of aerosol particles at Mt Zeppelin station, Ny A˚lesund, Svalbard during 2008.
    05/2013;
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    ABSTRACT: A two-compartment binary mass transport model with group contribution methods parametrizations for the physical properties of the organic acids (UNIFAC Dortmund method for activity coefficients, GCVOL-OL-60 method for the pure liquid acid density, GC-MG method for the pure acid surface tension at room temperature, Fuller et al. method for the diffusion coefficients) was used to interpret the evaporation experiments of 100 nm sized ketodicarboxylic acid aqueous solutions droplets at ambient temperature. The determined values for the saturation vapour pressure of liquid 2-keto-glutaric acid are in the order of 10-5 Pa.
    05/2013;
  • Jan Julin, Ilona Riipinen
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    ABSTRACT: The mass accommodation of condensable gaseous species on to the surfaces of atmospheric aerosols controls the growth of submicron-sized particles to atmospherically relevant sizes. In this work we present results from molecular dynamics simulations of mass accommodation of water and organic molecules on surfaces consisting of the same molecular species.
    05/2013;
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    ABSTRACT: Recent research has shown that secondary organic aerosols (SOA) are major contributors to ultrafine particle growth to climatically relevant sizes, increasing global cloud condensation nuclei (CCN) concentrations within the continental boundary layer. Many models treat SOA solely as semivolatile, which leads to condensation of SOA proportional to the aerosol mass distribution; however, recent closure studies with field measurements show that a significant fraction of SOA condenses proportional to the aerosol surface area, which suggests a very low volatility. Additionally, while many global models contain only biogenic sources of SOA (with emissions generally 10-30 Tg yr-1), recent studies have shown a need for an additional source of SOA around 100 Tg yr-1 correlated with anthropogenic carbon monoxide (CO) emissions is required to match measurements. Here, we explore the significance of these two findings using the GEOS-Chem-TOMAS global aerosol microphysics model. The percent change in the number of particles of size Dp > 40 nm (N40) within the continental boundary layer between the surface-area-and massdistribution condensation schemes, both with the base biogenic SOA only, yielded a global increase of 8% but exceeds 100% in biogenically active regions. The percent change in N40 within the continental boundary layer between the base simulation (19 Tg yr-1) and the additional SOA (100 Tg yr-1) both using the surface area condensation scheme (very low volatility) yielded a global increase of 14%, and a global decrease in the number of particles of size Dp > 10 nm (N10) of 32%. These model simulations were compared to measured data from Hyytiälä, Finland and other global locations and confirmed a decrease in the model-measurement bias. Thus, treating SOA as very low volatile as well as including additional SOA correlated with anthropogenic CO emissions causes a significant global increase in the number of climatically relevant sized particles, and therefore we must continue to refine our SOA treatments in aerosol microphysics models.
    05/2013;
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    ABSTRACT: The aerosol particle number concentration is a key parameter when estimating impacts of aerosol particles on climate and human health. We use a three-dimensional chemical transport model with detailed microphysics, PMCAMx-UF, to simulate particle number concentrations over Europe in the year 2030, by applying emission scenarios for trace gases and primary aerosols. The scenarios are based on expected changes in anthropogenic emissions of sulphur dioxide, ammonia, nitrogen oxides, and primary aerosol particles with a diameter less than 2.5 μm (PM2.5) focusing on a photochemically active period. For the baseline scenario, which represents a best estimate of the evolution of anthropogenic emissions in Europe, PMCAMx-UF predicts that the total particle number concentration (Ntot) will decrease by 30-70% between 2008 and 2030. The number concentration of particles larger than 100 nm (N100), a proxy for cloud condensation nuclei (CCN) concentration, is predicted to decrease by 40-70% during the same period. The predicted decrease in Ntot is mainly a result of reduced new particle formation due to the expected reduction in SO2 emissions, whereas the predicted decrease in N100 is a result of both decreasing condensational growth and reduced primary aerosol emissions. For larger emission reductions, PMCAMx-UF predicts reductions of 60-80% in both Ntot and N100 over Europe. Sensitivity tests reveal that a reduction in SO2 emissions is far more efficient than any other emission reduction investigated, in reducing Ntot. For N100, emission reductions of both SO2 and PM2.5 contribute significantly to the reduced concentration, even though SO2 plays the dominant role once more. The impact of SO2 for both new particle formation and growth over Europe may be expected to be somewhat higher during the simulated period with high photochemical activity than during times of the year with less incoming solar radiation. The predicted reductions in both Ntot and N100 between 2008 and 2030 in this study will likely reduce both the aerosol direct and indirect effects, and limit the damaging effects of aerosol particles on human health in Europe.
    Atmospheric Chemistry and Physics 04/2013; 13(4):8769-8803. · 4.88 Impact Factor
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    ABSTRACT: Climatic effects of newly-formed atmospheric secondary aerosol particles are to a large extent determined by their condensational growth rates. However, all the vapors condensing on atmospheric nanoparticles and growing them to climatically relevant sizes are not identified yet and the effects of particle phase processes on particle growth rates are poorly known. Besides sulfuric acid, organic compounds are known to contribute significantly to atmospheric nanoparticle growth. In this study a particle growth model MABNAG (Model for Acid-Base chemistry in NAnoparticle Growth) was developed to study the effect of salt formation on nanoparticle growth, which has been proposed as a potential mechanism lowering the equilibrium vapor pressures of organic compounds through dissociation in the particle phase and thus preventing their evaporation. MABNAG is a model for monodisperse aqueous particles and it couples dynamics of condensation to particle phase chemistry. Non-zero equilibrium vapor pressures, with both size and composition dependence, are considered for condensation. The model was applied for atmospherically relevant systems with sulfuric acid, one organic acid, ammonia, one amine and water in the gas phase allowed to condense on 3-20 nm particles. The effect of dissociation of the organic acid was found to be small under ambient conditions typical for a boreal forest site, but considerable for base-rich environments (gas phase concentrations of about 1010 cm-3 for the sum of the bases). The contribution of the bases to particle mass decreased as particle size increased, except at very high gas phase concentrations of the bases. The relative importance of amine versus ammonia did not change significantly as a function of particle size. While our results give a reasonable first estimate on the maximum contribution of salt formation to nanoparticle growth, further studies on, e.g. the thermodynamic properties of the atmospheric organics, concentrations of low-volatility organic acids and amines, along with studies investigating the applicability of thermodynamics for the smallest nanoparticles are needed to truly understand the acid-base chemistry of atmospheric nanoparticles.
    Atmospheric Chemistry and Physics 03/2013; 13(3):7175-7222. · 4.88 Impact Factor
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    ABSTRACT: Aerosol nucleation occurs frequently in the atmosphere and is an important source of particle number. Observations suggest that nucleated particles are capable of growing to sufficiently large sizes that they act as cloud condensation nuclei (CCN), but some global models have reported that CCN concentrations are only modestly sensitive to large changes in nucleation rates. Here we present a novel approach for using long-term size distribution observations to evaluate a global aerosol model's ability to predict formation rates of CCN from nucleation and growth events. We derive from observations at five locations nucleation-relevant metrics such as nucleation rate of particles at diameter of 3 nm (J3), diameter growth rate (GR), particle survival probability (SP), condensation and coagulation sinks, and CCN formation rate (J100). These quantities are also derived for a global microphysical model, GEOS-Chem-TOMAS, and compared to the observations on a daily basis. Using GEOS-Chem-TOMAS, we simulate nucleation events predicted by ternary (with a 10-5 tuning factor) or activation nucleation over one year and find that the model slightly understates the observed annual-average CCN formation, but by no more than 50% in the ternary simulations. At the two locations expected to be most impacted by large-scale regional nucleation, Hyytiälä and San Pietro Capofiume, predicted annual-average CCN formation rates are within 34% and 2% of the observations, respectively. Model-predicted annual-average growth rates are within 25% across all sites but also show a slight tendency to underestimate the observations, at least in the ternary nucleation simulations. On days that the growing nucleation mode reaches 100 nm, median single-day survival probabilities to 100 nm for the model and measurements range from less than 1% to 6% across the five locations we considered; however, this does not include particles that may eventually grow to 100 nm after the first day. This detailed exploration of new particle formation and growth dynamics adds support to the use of global models as tools for assessing the contribution of microphysical processes such as nucleation to the total number and CCN budget.
    Atmospheric Chemistry and Physics 03/2013; 13(3):8333-8386. · 4.88 Impact Factor
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    ABSTRACT: The capability to accurately yet efficiently represent atmospheric nanoparticle growth by biogenic and anthropogenic secondary organics is a challenge for current atmospheric large-scale models. It is, however, crucial to predict nanoparticle growth accurately in order to reliably estimate the atmospheric cloud condensation nuclei (CCN) concentrations. In this work we introduce a~simple semi-empirical parameterization for sub-20 nm particle growth that distributes secondary organics to the nanoparticles according to their size and is therefore able to reproduce particle growth observed in the atmosphere. The parameterization includes particle growth by sulfuric acid, secondary organics from monoterpene oxidation (SORGMT) and an additional condensable non-monoterpene organics ("background"). The performance of the proposed parameterization was investigated using ambient data on particle growth rates in three size ranges (1.5-3 nm, 3-7 nm and 7-20 nm). The growth rate data was acquired from particle/air ion number size distribution measurements at six continental sites over Europe. The longest time series of 7 yr (2003 to 2009) was obtained from a boreal forest site in Hyytiälä, Finland, while about one year of data (2008-2009) was used for the other stations. The extensive ambient measurements made it possible to test how well the parameterization captures the seasonal cycle observed in sub-20 nm particle growth and to determine the weighing factors for distributing the SORGMT for different sized particles as well as the background mass flux (/concentration). Besides the monoterpene oxidation products, background organics with a concentration comparable to SORGMT, around 6 × 107 cm-3 (consistent with an additional global SOA yield of 100 Tg yr-1) was needed to reproduce the observed nanoparticle growth. Simulations with global models suggest that the "background" could be linked to secondary biogenic organics that are formed in the presence of anthropogenic pollution.
    Atmospheric Chemistry and Physics 03/2013; 13(3):8489-8535. · 4.88 Impact Factor
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    ABSTRACT: Atmospheric nucleation is the dominant source of aerosol particles in the global atmosphere and an important player in aerosol climatic effects. The key steps of this process occur in the sub-2-nanometer (nm) size range, in which direct size-segregated observations have not been possible until very recently. Here, we present detailed observations of atmospheric nanoparticles and clusters down to 1-nm mobility diameter. We identified three separate size regimes below 2-nm diameter that build up a physically, chemically, and dynamically consistent framework on atmospheric nucleation--more specifically, aerosol formation via neutral pathways. Our findings emphasize the important role of organic compounds in atmospheric aerosol formation, subsequent aerosol growth, radiative forcing and associated feedbacks between biogenic emissions, clouds, and climate.
    Science 02/2013; 339(6122):943-6. · 31.20 Impact Factor
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    ABSTRACT: Finland experienced extraordinary smoke episodes in 2006. The smoke was measured at the three SMEAR measurement network stations in Finland after it had been transported several hundreds of kilometers from burning areas in Eastern Europe. A trajectory method combining MODIS fire detections and HYSPLIT trajectories enabled us to separate the effect of biomass burning smoke from the measured concentrations and also study the changes in the smoke during its transport. The long-range transported smoke included at least NOx, SO2, CO2, CO, black carbon and fine aerosol particles, peaking at 100 to 200 nm size. The most reliable smoke markers were CO and SO2, especially when combined with particle data, for which black carbon or the condensation sink are very effective parameters separating the smoke episodes from no-smoke episodes. Signs of fresh secondary particles was observed based on the particle number size distribution data. While transported from south to north, particles grew in size, even after transport of tens of hours and several hundreds of kilometres. No new aerosol particle formation events were observed at the measurement sites during the smoke periods.
    Atmospheric Chemistry and Physics 02/2013; 13(2):4289-4330. · 4.88 Impact Factor
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    ABSTRACT: Highly oxidised organic vapors can effectively stabilize sulphuric acid in heteronuclear clusters and drive new-particle formation. We present quantum chemical calculations of cluster stability, showing that multifunctional species can stabilize sulphuric acid and also present additional polar functional groups for subsequent cluster growth. We also model the multi-generation oxidation of vapors associated with secondary organic aerosol formation using a two-dimensional volatility basis set. The steady-state saturation ratios and absolute concentrations of extremely low volatility products are sufficient to drive new-particle formation with sulphuric acid at atmospherically relevant rates.
    Faraday Discussions 01/2013; 165:91-104. · 3.82 Impact Factor

Publication Stats

898 Citations
496.51 Total Impact Points

Institutions

  • 2012–2013
    • Stockholm University
      Tukholma, Stockholm, Sweden
    • University of Patras
      • Department of Chemical Engineering
      Rhion, West Greece, Greece
  • 2010–2013
    • Carnegie Mellon University
      • Center for Atmospheric Particle Studies (CAPS)
      Pittsburgh, Pennsylvania, United States
  • 2005–2012
    • University of Helsinki
      • • Department of Physics
      • • Department of Physical Sciences
      Helsinki, Province of Southern Finland, Finland
  • 2008
    • Leibniz Institute for Tropospheric Research
      Leipzig, Saxony, Germany
  • 2007
    • IT University of Copenhagen
      København, Capital Region, Denmark
  • 2006
    • Finnish Meteorological Institute
      • Air Quality Research
      Helsinki, Southern Finland Province, Finland