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ABSTRACT: Nucleation of new particles is observed frequently in the atmospheric boundary layer and can substantially increase the total
concentration of particles. The importance of nucleation events for cloud condensation nuclei (CCN) concentrations is poorly
understood, although some observations suggest that, at least locally, CCN can be greatly enhanced. We have used a global
aerosol microphysics model to quantify the impact of boundary layer nucleation events on CCN. Results show that nucleation
events can increase mean summertime boundary layer CCN concentrations by 25–60% over remote continental regions and by 10–30%
over more polluted regions. Observations show that the nucleation rate varies from region to region by several orders of magnitude.
This uncertainty has a substantial impact on model-predicted total particle concentrations but a relatively small impact on
predicted CCN: the predicted CCN enhancement over central Europe changes from 12% to 17% for a two order of magnitude increase
in the rate. These results demonstrate that boundary layer nucleation is a significant global source of CCN.
Keywords Nucleation, boundary layer, CCN, global model
12/2006: pages 911-915;
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ABSTRACT: ABSTRACTA theoretical framework was constructed by which one can estimate the relative role of different processes in the dynamics of atmospheric nucleation mode particles. The framework relies on 14 timescales that describe (1) changes in the total nuclei number concentration, (2) changes in the mean diameter of the nucleation mode and (3) concentrations of low-volatile vapours responsible for the growth of nuclei. The magnitude of the derived timescales can be calculated relatively easily from the available measurement or modelling data. Application to the lower-troposphere revealed that under most conditions removal of nuclei is dominated by their coagulation with larger background particles and that this process competes very strongly with growth of nuclei to sizes relevant to atmospheric chemistry and physics. With some exceptions, self-coagulation of nuclei was shown to be of marginal importance compared with their growth by condensation and their removal by coagulation. Finally, by comparing predictions based on relevant timescales with those obtained from detailed numerical simulations, quantitative criteria were derived concerning (1) when one may neglect self-coagulation of nuclei when looking at nucleation mode dynamics and (2) when the whole nucleation mode can be neglected because of its eventual removal. These criteria are extremely useful for atmospheric modellers who need to simplify their models as much as possible. From the modelling point of view, other processes requiring further attention are the introduction of new nuclei into the system and decrease in nuclei number concentration due to dilution of the air.
Tellus B 03/2004; 56(2):135 - 146. · 4.38 Impact Factor
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Veli-Matti Kerminen,
Liisa Pirjola,
Michael Boy,
Arkke Eskola,
Kimmo Teinilä,
Lauri Laakso,
Ari Asmi,
Jukka Hienola,
Antti Lauri,
Veera Vainio,
Kari Lehtinen,
Markku Kulmala
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ABSTRACT: In the atmosphere, oxidation of sulfur dioxide (SO2) to sulfate may occur in the gas phase, in cloud or fog droplets, or in the aerosol phase on the surface or inside aerosol particles. While aerosol phase reactions have been studied in the case of supermicron sea-salt and crustal particles, very few investigations regarding submicron particles are available. In this paper, the importance of aerosol phase sulfate production to the dynamics of submicron particle populations was examined. The investigation was based on model simulations and theoretical evaluations regarding potential SO2 oxidation reactions. None of the relatively well-quantified aqueous phase reactions was rapid enough to make small nuclei grow to cloud condensation nuclei (CCN) size within the particle lifetime in the lower troposphere. This is consistent with the few observations showing that the smallest atmospheric particles are enriched in organics rather than sulfate. The amount of submicron particulate matter could be enhanced significantly by certain aerosol phase reactions, but this is likely to require a particle population having a pH close to 7. Aerosol phase reactions could partly explain the apparently too low SO2-to-sulfate conversion rates predicted by several chemical transport models over polluted regions. In addition to the bulk aerosol phase, SO2-to-sulfate conversion might involve physical adsorption of SO2 or a compound reacting with it by the particle surface, or it could take place in a liquid surface layer that usually covers atmospheric particles. Reactions involving physical adsorption seem to have negligible influence on the dynamics of submicron atmospheric particle populations. Aerosol phase reactions worth future investigation are those occurring in particle surface layers and those occurring in cloud interstitial particles.
Atmospheric Research.
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ABSTRACT: The ability of organic compounds to grow small atmospheric nuclei via condensation was investigated. The investigation was based on theoretical considerations and model simulations. The results indicate that the condensational growth of atmospheric nuclei having diameters requires the presence of compounds that are able to move irreversibly from the gas phase into these nuclei. The required saturation vapour pressure to make a compound to behave this way is dependent on the nucleus diameter, as well as on the nucleus composition and the physico-chemical properties of the condensing compound. The estimates are applied to identify which organic vapours might induce the growth of small nuclei in the atmosphere. Furthermore, various implications of the obtained results are discussed.
Journal of Aerosol Science.
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ABSTRACT: The chemistry of sea-salt particles was investigated in summer Antarctica at a site about 150 km from the open ocean. Aerosol samples were collected using a low-pressure impactor which divides particles into 12 size fractions over the aerodynamic particle diameter range 0.045–15 μm. Measured sea-salt particle concentrations were clearly lower than concentrations typically observed at coastal Antarctica. The mass size distribution of sea salt was tri-modal with a submicron mode centering at 0.5–1 μm and two supermicron modes centering slightly below 2 μm and somewhere between 2 and 10 μm, respectively. On average more than 70% of sea salt was found in the supermicron size range, the lower supermicron mode being usually the dominant. Sea-salt particles displayed a large chloride loss with respect to the bulk sea water. The average loss percentage was more than 90% for submicron particles and decreased to about 50% for particles larger than 3 μm in diameter. The primary ions causing the chloride loss were sulfate, nitrate, and methanesulfonate (MSA). The aerosol MSA to non-sea-salt sulfate weight ratio seemed to have been increased by the presence of sea-salt particles. Particulate nitrate was associated strongly with sea salt, the most likely formation pathway being the interaction of nitric acid or some other gaseous nitrogen compounds with these particles in the Antarctic atmosphere.
Atmospheric Environment.
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ABSTRACT: New particle formation in boreal forest environment in Hyytiälä, Finland, was studied in an aerosol dynamical model. Basing on the concepts of activation or kinetic collision of two pre-existing clusters at 1.5 nm, several semi-empirical nucleation rate formulae were parameterized. The mechanisms had linear or squared dependence on the concentration of sulphuric acid, or a low volatile organic vapor, or both, and they all showed good agreement with field measurements. A new method for examining the power dependence of apparent formation rate (at 2 nm or 3 nm) on sulphuric acid concentration was developed. The new method produced exponents 1.6–2.1 for cluster activation, and exponents 2.4–3.1 for kinetic collision, which suggests that the activation scenarios are in better agreement with experimental observations that imply exponents around 1–2. However, it was found that if low volatile organic vapors with concentrations exceeding that of sulphuric acid are present, they have a major role in shaping the temporal behavior of the apparent formation rates, causing error in the exponent analyses. Finally, a sensitivity study showed that the analyzed exponents grew even further, if the size of the critical cluster was assumed smaller that 1.5 nm.
Atmospheric Research.
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ABSTRACT: A simple yet relatively accurate analytical formula has been derived between the “real” atmospheric nucleation rate and the rate at which the resulting clusters, or nuclei, appear at some larger size (the “apparent” nucleation rate) as a result of their growth by condensation. In addition, another analytical formula was derived that connects the nucleation rate and the total nuclei concentration in a desired size range. The derived formulae are applicable to situations in which there are no major fluctuations in the pre-existing particle size distribution or in the concentration of vapours responsible for the nuclei growth, and in which the total nuclei number concentration remains sufficiently low (<105–106 nuclei cm−3) to prevent effective self-coagulation between the nuclei. With the help of these formulae, an explicit nucleation scheme can be included into an atmospheric model without the requirement that the modelled particle diameter range must be extended down to one nanometer. In field measurements only the “apparent” nucleation rate can currently be determined. The derived formulae provide a means to convert this rate to a “real” nucleation rate, making it possible to test more rigorously the viability of different nucleation theories under atmospheric conditions.
Journal of Aerosol Science.
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ABSTRACT: The study is based on the work of Lehtinen et al. (2007) [Lehtinen, K. E. J., Dal Maso, M., Kulmala, M., & Kerminen, V.-M. (2007). Estimating nucleation rates from apparent particle formation rates and vice versa: Revised formulation of the Kerminen–Kulmala equation. Journal of Aerosol Science, 38, 988–994] who derived formulae connecting “real” and “apparent” nucleation rates. The parameterization neglected self-coagulation of newly formed particles and clusters, however, and here we have extended the previous work to include the effects of the self-coagulation. Our main focus was on calculating the “apparent” nucleation rate, i.e. the rate at which particles appear at sizes larger than the critical cluster size, as a function of the “real” nucleation rate. The revised parameterization was comprehensively tested against an explicit aerosol dynamic model at diverse atmospheric conditions. It was found out that nuclei self-coagulation has importance to new particle formation when Jnuc/Q>10−2 where Jnuc is the nucleation rate and Q is the production rate of condensable vapours. This corresponds to the nucleation rates ranging from >10 cm−3 s−1 (free troposphere) to >104 cm−3 s−1 (polluted boundary layer) depending on the atmospheric conditions. In terms of the particle number concentration, the calculations performed with the explicit model and the predictions of revised parameterization were generally within an order of magnitude. Several issues related to applications in large-scale models were also discussed.
Journal of Aerosol Science.
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ABSTRACT: Depletion of chloride in sea-salt particles was studied at a site near the Arctic Ocean. The investigation was based on size-segregated particle sampling using a Berner low-pressure impactor. According to the impactor measurements, average chloride losses were close to 100% for submicron particles. However, this is successively less for increasing particle size in the supermicron size range. The main constituents replacing chloride from supermicron sea-salt particles were sulfate and nitrate followed by MSA- and oxalate, and with malonate and succinate giving a minor contribution. Anions of organic dicarboxylic acids became more important for air spending a longer time over the continent. Our analysis suggests that principal mechanisms accumulating sulfate into sea-salt particles are cloud processing and, to a lesser degree, heterogeneous reactions taking place in deliquescent sea-salt particles. Mechanisms for the chloride replacement by nitrate are less clear. The distributions of MSA- and oxalate over the sea-salt particle size range were similar to each other, whereas other organic anions analyzed here had a peak concentration at a somewhat larger particle size. Better understanding on the chemistry associated with sea-salt particles requires investigating not only reactions in deliquescent sea-salt particles, but also the interactions between these particles and clouds.
Journal of Aerosol Science.
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ABSTRACT: Chemistry of oxalic, malonic, and succinic acid was studied at the two sites representing the urban and rural conditions, and at a site intermediate between these two. The investigation was based on the particle collection with a virtual impactor and a Berner low-pressure impactor. Concentrations of the three diacids displayed large seasonal amplitudes with low values in winter. Suggestive of common sources or atmospheric formation processes, the correlation between oxalic and malonic acid concentrations was high. Both the local traffic and secondary production in the long-range transported air masses seemed to be the important sources for these two acids. Contrary to oxalic and malonic acid, no enrichment at the urban site compared with the rural site was observed for succinic acid. The seasonal cycle of this acid resembled that of methanesulfonic acid. The most likely sources for succinic acid in our samples was the secondary production in the long-range transported air, with potentially significant contribution coming from biogenic sources. The three diacids had quite different distributions over the particulate phase. Oxalic acid had a dominant accumulation mode, a clear Aitken mode at sizes below about 0.15 μm of particle diameter, and modes corresponding to the sea-salt and crustal particle size ranges. Most of the malonic acid was associated with sea-salt particles, even though in a few samples an accumulation mode was also present. Succinic acid was distributed between the accumulation and the sea-salt particle modes, in addition to which it frequently had quite a pronounced Aitken mode. Oxalic and succinic acids are among the organics that may contribute to the atmospheric cloud condensation nuclei production. Oxalic and malonic acid, and to a smaller extent succinic acid, participate in reactions occurring in sea-salt particles.
Journal of Aerosol Science 31(3):349-362. · 2.45 Impact Factor
