Browsing by Subject "VAPOR"

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  • Doulgeris, Konstantinos M.; Brus, David; Raatikainen, Tomi; Kerminen, Veli-Matti (2018)
    The Finnish Meteorological Institute-Aerosol Cloud Interaction Tube (FMI-ACIT) is a multi-purpose instrument for investigating atmospherically relevant interactions between aerosol particles and water vapor under defined laboratory conditions. This work introduces an experimental setup of FMI-ACIT for investigation of the aerosol activation and the droplet growth under supersaturated conditions. Several simulations and experimental tests were conducted to find out what the proper operational parameters are. To verify the ability of FMI-ACIT to perform as a cloud condensation nuclei (CCN) counter, activation experiments were executed using size selected ammonium sulfate [(NH4)(2)SO4] particles in the size range of 10-300 nm. Supersaturations from 0.18% to 1.25% were tested by experiments with different temperature gradients. Those showed that FMI-ACIT can effectively measure CCN in this range. Measured droplet size distributions at supersaturations 0.18% and 1.25% are in good agreement with those determined by a droplet growth model. Published by AIP Publishing.
  • Tuure, Juuso; Korpela, Antti; Hautala, Mikko; Rautkoski, Hille; Hakojarvi, Mikko; Mikkola, Hannu; Duplissy, Jonathan; Pellikka, Petri; Petaja, Tuukka; Kulmala, Markku; Alakukku, Laura (2020)
    Passive dew collection could be a viable option as a source of irrigation water in arid areas. The plastic foil acting as a condensing surface plays a key role in the passive dew collection regime. A laboratory method for comparing various plastic foils for dew collection was prepared and tested. The focus was on creating a method for measuring the attributes affecting dew condensation and the flow of dew droplets on the measured surface. A low-density polyethylene foil designed for dew collection, white polyethylene plastic, black polyethylene plastic, and white polyvinyl chloride plastic were used as the test plastics. The laboratory dew yields were compared with model calculations. In addition, field trials were conducted in arid conditions in Maktau, Kenya, to compare with the laboratory measurement. Results from the hardware model tests were not reflected in the results obtained from the field conditions. The laboratory tests showed that the dew-harvesting quality of plastic foils is difficult to evaluate using the laboratory test rig. A more comprehensive evaluation regime requires tests performed in field conditions or further development of the test rig used here. (C) 2020 IAgrE. Published by Elsevier Ltd. All rights reserved.
  • Kontkanen, Jenni; Olenius, Tinja; Lehtipalo, Katrianne; Vehkamäki, Hanna; Kulmala, Markku; Lehtinen, Kari E. J. (2016)
    We simulated the time evolution of atmospheric cluster concentrations in a one-component system where not only do clusters grow by condensation of monomers, but cluster-cluster collisions also significantly contribute to the growth of the clusters. Our aim was to investigate the consistency of the growth rates of sub-3aEuro-nm clusters determined with different methods and the validity of the common approach to use them to estimate particle formation rates. We compared the growth rate corresponding to particle fluxes (FGR), the growth rate derived from the appearance times of clusters (AGR), and the growth rate calculated based on irreversible vapor condensation (CGR). We found that the relation between the different growth rates depends strongly on the external conditions and the properties of the model substance. The difference between the different growth rates was typically highest at the smallest, sub-2aEuro-nm sizes. FGR was generally lower than AGR and CGR; at the smallest sizes the difference was often very large, while at sizes larger than 2aEuro-nm the growth rates were closer to each other. AGR and CGR were in most cases close to each other at all sizes. The difference between the growth rates was generally lower in conditions where cluster concentrations were high, and evaporation and other losses were thus less significant. Furthermore, our results show that the conventional method used to determine particle formation rates from growth rates may give estimates far from the true values. Thus, care must be taken not only in how the growth rate is determined but also in how it is applied.
  • Wang, Yajun; Tang, Yu; Xu, Yan; Yu, Hongwei; Cao, Xiaofeng; Duan, Gaoqi; Bi, Lijiao; Peng, Jianfeng (2021)
    Shrinkage of plateau lakes under climate strength has drawn growing attention. Because of its intricate implication to hydro-meteorological condition and climate system, stable isotopes in precipitation (e.g. delta H-2(p) and delta O-18(p)) provide us a powerful tool to understand the climate-hydrologic dynamics in shrinking lakes. However, how the regional atmospheric circulation, moisture sources and local fractionation processes drive isotopic variability from temporal to spatial scale has rarely been reported for remote plateau lakes. Hence, we collected a total of 98 rainfall samples at the south and the north shores of Chenghai lake, Yunnan-Guizhou Plateau to study the potential driving forces of precipitation isotope variability during the wet season of 2019. Based on backward trajectories of air masses obtained from HYSPLIT model, 68% of moisture came from delta O-18 depleted ocean (Indian Ocean, Bay of Bengal, South China Sea and Pacific Ocean), and the rainout process promoted the isotopic depletion when moisture arrived at the study basin. Evapotranspiration increased the heavy isotope ratios in precipitation originated from continents (northern China inland and western continents). The temporal dynamics of delta O-18(p) and delta H-2(p) were in phase with the convection activities intensity underlined the influence from large-scale atmospheric circulation. Local meteorological factors played a secondary role in isotope variability. Precipitation amount-effect strongly affected isotope ratios while mild anti-temperature effect was observed at daily scale. Interestingly, the rainfall isotope ratios showed different mechanisms in govern at lake south shore and north shore, with a distance of 19 km in between. This south-to-north difference can be explained by either lower 1.03% sub-evaporation in the south shore or 7% of recycled moisture contributing to precipitation in the north shore. Our findings discover the driving forces for delta O-18(p) variation and provide solid interpretations for hydro-climate change in Southwest China. (C) 2020 Elsevier B.V. All rights reserved.
  • Pääkkönen, Timo; Spiliopoulos, Panagiotis; Nonappa, Dr.; Kontturi, Katri S.; Penttilä, Paavo; Viljanen, Mira; Svedström, Kirsi; Kontturi, Eero (2019)
    HCl gas hydrolysis of a bacterial cellulose (BC) aerogel followed by 2,2,6,6-tetramethylpiperidine-1-oxyl radical-mediated oxidation was used to produce hydrolyzed BC with carboxylate groups, which subsequently disintegrated into a stable dispersion of cellulose nanocrystals (CNCs). The degree of polymerization was successfully reduced from 2160 to 220 with a CNC yield of >80%.
  • Fang, Jiaxi; Wang, Yang; Kangasluoma, Juha; Attoui, Michel; Junninen, Heikki; Kulmala, Markku; Petäjä, Tuukka; Biswas, Pratim (2018)
    The ability to properly scale the synthesis of advanced materials through combustion synthesis routes is limited by our lack of knowledge regarding the initial stages of particle formation. In flame aerosol reactors, the high temperatures, fast reaction rates, and flame chemistry can all play a critical role in determining the properties of the resulting nanomaterials. In particular, multicomponent systems pose a unique challenge as most studies rely on empirical approaches toward designing advanced composite materials. The lack of predictive capabilities can be attributed to a lack of data on particle inception and growth below 2nm. Measurements for the initial stages of particle formation during the combustion synthesis of SiO2 and composite SiO2/TiO2 using an atmospheric pressure inlet time-of-flight mass spectrometer are presented. Both positively and negatively charged clusters can be measured and results show the presence of silicic acid species which grow through dehydration, hydrogen abstraction, and interactions with hydroxyl radicals. In the case of composite SiO2/TiO2 particle formation, new molecular species containing Ti atoms emerge. Tandem differential mobility analysis-mass spectrometry (DMA-MS) provided further insight into the size-resolved chemistry of particle formation to reveal that at each cluster size, further hydroxyl-driven reactions take place. From this we can conclude that previous assumptions on collisional growth from simple monomer species of SiO2 and TiO2 do not sufficiently describe the collisional growth mechanisms for particle growth below 2nm.Copyright (c) 2018 American Association for Aerosol Research