| 1. |
- Kulmala, Markku, et al.
(författare)
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Overview of the biosphere-aerosol-cloud-climate interactions (BACCI) studies
- 2008
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Ingår i: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 60:3, s. 300-317
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Forskningsöversikt (refereegranskat)abstract
- Here we present research methods and results obtained by the Nordic Centre of Excellence Biosphere-Aerosol-Cloud-Climate Interactions (BACCI) between 1 January 2003 and 31 December 2007. The centre formed an integrated attempt to understand multiple, but interlinked, biosphere-atmosphere interactions applying inter and multidisciplinary approaches in a coherent manner. The main objective was to study the life cycle of aerosol particles and their importance on climate change. The foundation in BACCI was a thorough understanding of physical, meteorological, chemical and ecophysiological processes, providing a unique possibility to study biosphere-aerosol-cloud-climate interactions. Continuous measurements of atmospheric concentrations and fluxes of aerosol particles and precursors and, CO2/aerosol trace gas interactions in different field stations (e.g. SMEAR) were supported by models of particle thermodynamics, transport and dynamics, atmospheric chemistry, boundary layer meteorology and forest growth. The main progress was related to atmospheric new particle formation, existence of clusters, composition of nucleation mode aerosol particles, chemical precursors of fresh aerosol particles, the contribution of biogenic aerosol particles on the global aerosol load, transport, transformation and deposition of aerosol particles, thermodynamics related to aerosol particles and cloud droplets, and the microphysics and chemistry of cloud droplet formation.
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| 2. |
- Rissler, Jenny, et al.
(författare)
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An evaluation and comparison of cloud condensation nucleus activity models: Predicting particle critical saturation from growth at subsaturation
- 2010
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Ingår i: Journal of Geophysical Research. - 2156-2202. ; 115
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Tidskriftsartikel (refereegranskat)abstract
- The ability of particles to activate and form cloud droplets influences the functioning of the Earth's hydrological cycle. This work links the particle water uptake at subsaturation to the critical supersaturation ratio needed for particles to become cloud condensation nuclei (CCN). Five models using the particle hygroscopic growth at subsaturation for predicting the critical supersaturation needed for droplet activation were applied to a laboratory data set of inorganic and organic compounds and mixtures of them. The data set consisted of hygroscopicity tandem differential mobility analyzer measurements and CCN counter measurements. No chemical composition information was used when applying the models. All models tested were based on modifications of Kohler theory and gave similar results. The agreement between predicted and measured critical supersaturations was good, considering the relatively simple models used. A trend of overestimating the critical supersaturations was observed, typically by similar to 15%. The best performing model gave on average only a 4% offset from experimental values; the model with the largest deviation was offset by 20%. A comparison was made between the number of soluble entities (ions or nondissociating molecules) estimated from the particle hygroscopic growth at 90% relative humidity (RH) and the number estimated from the particle critical supersaturation; a similar to 35% increase was observed in the effective number of entities in solution when going from 90% RH to activation. For many types of aerosols, differences in the model approaches tested do not induce large differences in the predicted critical supersaturation. However, it is most important to follow the recommendations published with the respective models and not use them indiscriminately.
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| 3. |
- Svenningsson, Birgitta, et al.
(författare)
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Relaxed step functions for evaluation of CCN counter data on size-separated aerosol particles
- 2008
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Ingår i: Journal of Aerosol Science. - : Elsevier BV. - 0021-8502. ; 39:7, s. 592-608
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Tidskriftsartikel (refereegranskat)abstract
- tmospherically important data are gained from cloud condensation nucleus counter (CCNC) analysis of aerosols that are particle mobility separated using differential mobility analysers (I)MA). We present relaxed step functions that can be fitted to these data to obtain critical diameters or critical supersaturations. The step functions are based on the DMA transfer function. We treat the case with fixed supersaturation and varied particle diameter as well as fixed particle size and varied supersaturation. Comparison with experimental data shows that the width of the DMA transfer function controls the steepness of the relaxed step function. The less steep slope in the activation curve caused by the presence of a slightly soluble compound in the particle is discussed. Also in this case, the DMA transfer function width influences the steepness of the activation curve. Finally we demonstrate the errors made if doubly charged particles are not accounted for and a wide DMA transfer function is used.
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| 4. |
- Yli-Juuti, Taina, et al.
(författare)
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Volatility of Organic Aerosol : Evaporation of Ammonium Sulfate/Succinic Acid Aqueous Solution Droplets
- 2013
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 47:21, s. 12123-12130
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Tidskriftsartikel (refereegranskat)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.
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