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Träfflista för sökning "WFRF:(Zhou Jingchuan) "

Sökning: WFRF:(Zhou Jingchuan)

  • Resultat 1-10 av 21
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1.
  • Kristensson, Adam, et al. (författare)
  • Characterization of New Particle Formation Events at a Background Site in Southern Sweden: Relation to Air Mass History
  • 2008
  • Ingår i: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 60:3, s. 330-344
  • Tidskriftsartikel (refereegranskat)abstract
    • Particle formation events were analysed from aerosol number size distribution data collected at a background station in southern Sweden between February 2001 and May 2004. Events occurred on about 36% of all days and were favoured by high global radiation values. The clearest events (class I, 20% of all days) were observed when the formation rate of activated hypothetical clusters around 1 nm diameter, J(1) was higher than 10((180*CondS-0.60)), where CondS is the condensation sink (in s(-1)). The median condensable vapour concentration, observed formation rate at 3 nm, and growth rate during class I events were 3.0 x 10(7) cm(-3), 1.1 cm(-3) s(-1) and 2.1 nm h(-1), respectively. On 7% of all days, it was possible to observe growth of the newly formed particles exceeding 30 nm geometric mean diameter during event days in the evening, which is important for the regional particle population, and thereby the climate. A trajectory analysis revealed that cleaner air masses were relatively more important for the contribution of Aitken mode particles than polluted ones. Class I events were registered on 36% of all days when trajectories had passed over the open sea, indicating that ship traffic can contribute to particle formation and growth.
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  • Löndahl, Jakob, et al. (författare)
  • A set-up for field studies of respiratory tract deposition of fine and ultrafine particles in humans
  • 2006
  • Ingår i: Journal of Aerosol Science. - : Elsevier BV. - 0021-8502. ; 37:9, s. 1152-1163
  • Tidskriftsartikel (refereegranskat)abstract
    • Respiratory tract deposition data of ultrafine aerosol particles, hygroscopic particles and ambient particles in general are scarce. Measurements are associated with several difficulties. The objective of this work was to design a method for fast determination of highly size-resolved fine and ultrafine particle deposition, to be used on larger groups of human subjects in exposure studies and in typical ambient and indoor environments. The particle size distributions in dried samples of the inhaled and exhaled air are characterised with an electrical mobility spectrometer. A particle counter desmearing procedure reduces the spectrometer scan time. The precision and sensitivity of the method was tested for hygroscopic sodium chloride (NaCl) and hydrophobic Di-Ethyl-Hexyl-Sebacate (DEHS) aerosols in repeated identical experiments and experiments with different breathing frequencies on a single subject. The accuracy of the method was estimated by comparing results from three subjects with previous data obtained with monodisperse particles and with the well-established International Commission on Radiological Protection model (1994). Potential errors due to size shifts between the inhaled and exhaled samples and coagulation were simulated. The system has low losses in the studied particle size range (10-475 nm), typically 10% or less of the fraction deposited in the respiratory tract. Coagulation is noticeable at 10(5) cm(-3) but can be corrected for up to 5 x 10(5) cm(-3). The precision in the determined deposited fraction is 0.02-0.08. The method is sensitive enough to quantify differences between breathing patterns and differences between hygroscopic and hydrophobic aerosols. Our results for NaCl and DEHS are in agreement with the ICRP 66 model [International Commission on Radiological Protection. (1994). Human respiratory tract model for radiological protection (ICRP Publication 66). Oxford, UK: Elsevier Science], and also suggest that the relative humidity in the respiratory tract is close to 99.5%. A respiratory tract deposition measurement can be done in 15-30 min. Recommendations are given for field applications of the method. (C) 2005 Elsevier Ltd. All rights reserved.
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  • Martinsson, Bengt G., et al. (författare)
  • Droplet nucleation and growth in orographic clouds in relation to the aerosol population
  • 1999
  • Ingår i: Atmospheric Research. - 0169-8095. ; 50:3-4, s. 289-315
  • Tidskriftsartikel (refereegranskat)abstract
    • The formation and development of orographic clouds was studied in a field experiment comprising several measurement sites at a mountain ridge. The influence of the aerosol population present on the cloud microstructure was studied in relation to the dynamics in the cloud formation. Droplet nucleation scavenging was investigated by the introduction of a non-dimensional particle diameter related to the process, and it was found that the scavenging rose rapidly in a relatively narrow particle size interval. The size dependency of the scavenging could partly be explained by external mixture of the aerosol. The large particles in the cloud interstitial aerosol was found to be of a chemical nature which allows for only a very weak uptake of water, implying that the chemical composition of these particles rather than entrainment of dry air prevented the droplet nucleation. The aerosol particle number concentration was found to strongly influence the cloud microstructure. Droplet number concentrations up to approximately 2000 cm-3 were observed together with a substantially reduced effective droplet diameter. The observed effect of elevated particle number concentrations in orographic clouds was generalised to the climatologically more important stratiform clouds by the use of a cloud model. It was found that the microstructure of stratiform clouds was strongly dependent on the aerosol population present as well on the dynamics in the cloud formation.
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8.
  • Martinsson, Bengt G., et al. (författare)
  • Validation of very high cloud droplet number concentrations in air masses transported thousands of kilometres over the ocean
  • 2000
  • Ingår i: Tellus. Series B: Chemical and Physical Meteorology. - 0280-6509. ; 52:2, s. 801-814
  • Tidskriftsartikel (refereegranskat)abstract
    • The microstructure of orographic clouds related to the aerosol present was studied during the second Aerosol Characterisation Experiment (ACE-2). Very high cloud droplet number concentrations (almost 3000 cm -3 ) were observed. These high concentrations occurred when clouds formed on a hill slope at Tenerife in polluted air masses originating in Europe that had transported the order of 1000 km over the Atlantic Ocean. The validity of the measured droplet number concentrations was investigated by comparing with measurements of the aerosol upstream of the cloud and cloud interstitial aerosol. Guided by distributions of the ratios between the measurements, three criteria of typically 30% in maximum deviation were applied to the measurements to test their validity. Agreement was found for 88% of the cases. The validated data set spans droplet number concentrations of 150-3000 cm -3 . The updraught velocity during the cloud formation was estimated to 2.2 m s -1 by model calculations, which is typical of cumuliform clouds. The results of the present study are discussed in relation to cloud droplet number concentrations previously reported in the literature. The importance of promoting the mechanistic understanding of the aerosol/cloud interaction and the use of validation procedures of cloud microphysical parameters is stressed in relation to the assessment of the indirect climatic effect of aerosols.
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  • Resultat 1-10 av 21

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