| 1. |
- Jonsson, Åsa M., 1976, et al.
(författare)
-
Volatility of secondary organic aerosols from the ozone initiated oxidation of alpha-pinene and limonene
- 2007
-
Ingår i: Journal of Aerosol Science. - : Elsevier BV. - 0021-8502. ; 38:8, s. 843-852
-
Tidskriftsartikel (refereegranskat)abstract
- The volatility of secondary organic aerosol (SOA) from the ozone initiated oxidation of a-pinene and limonene has been investigated in a large aerosol chamber facility, the AIDA chamber of Research Centre Karlsruhe, by using a volatility tandem-DMA system (VTDMA). The volatility of particles has been classified by monitoring the change in particle peak diameter at temperatures between 298 and 583 K. Specifically, the volatility of SOA was determined depending on organic precursor molecule, temperature at which the SOA was formed (243-303 K), relative humidity (0.2-72% RH), size of the particles (20-300 nm), and the presence of an OH-scavenger. Depending on experimental conditions the normalised mode particle diameter e.g. at an evaporative temperature of 423 K ranged from 0.32 to 0.65, i.e. remaining volume fraction 0.04-0.27. The thermal characteristics of SOA are influenced the most by reaction temperature and organic precursor. In this paper the benefits of using a VTDMA for mechanistic studies of SOA formation is demonstrated. (c) 2007 Elsevier Ltd. All rights reserved.
|
|
| 2. |
- 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.
|
|
| 3. |
|
|
| 4. |
- Pagels, Joakim, et al.
(författare)
-
Chemical composition and mass emission factors of candle smoke particles
- 2009
-
Ingår i: Journal of Aerosol Science. - : Elsevier BV. - 0021-8502. ; 40:3, s. 193-208
-
Tidskriftsartikel (refereegranskat)abstract
- The aim of this study is to investigate the physical and chemical properties of particle emissions from candle burning in indoor air. Two representative types of tapered candies were studied during steady burn, sooting burn and smouldering (upon extinction) under controlled conditions in a walk-in stainless steel chamber. Steady burn emits relatively high number emissions of ultrafine particles dominated by either phosphates or alkali nitrates. The likely source of these particles is flame retardant additives to the wick. Sooting burn in addition emits larger particles mainly consisting of agglomerated elemental carbon. This burning mode is associated with the highest mass emission factors. Particles emitted during smouldering upon extinction are dominated by organic matter. A mass closure was illustrated for the total mass concentration, the summed mass concentration from chemical analysis and the size-integrated mass concentration assessed from number distribution measurements using empirically determined effective densities for the three particle types. (C) 2008 Published by Elsevier Ltd.
|
|
| 5. |
- Svenningsson, Birgitta, et al.
(författare)
-
Relaxed step functions for evaluation of CCN counter data on size-separated aerosol particles
- 2008
-
Ingår i: Journal of Aerosol Science. - : Elsevier BV. - 0021-8502. ; 39:7, s. 592-608
-
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.
|
|
| 6. |
- Bast, R., et al.
(författare)
-
Role of noncollinear magnetization for the first-order electric-dipole hyperpolarizability at the four-component Kohn-Sham density functional theory level
- 2009
-
Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 130:2
-
Tidskriftsartikel (refereegranskat)abstract
- The quadratic response function has been derived and implemented at the adiabatic four-component Kohn-Sham density functional theory level with inclusion of noncollinear spin magnetization and gradient corrections in the exchange-correlation functional-a work that is an extension of our previous report where magnetization dependencies in the exchange-correlation functional were ignored [J. Henriksson, T. Saue, and P. Norman, J. Chem. Phys. 128, 024105 (2008)]. The electric-field induced second-harmonic generation experiments on CF3 Cl and CF3 Br are addressed by a determination of Β- (-2ω;ω,ω) for a wavelength of 694.3 nm, and the same property is also determined for CF3 I. The relativistic effects on the static hyperpolarizability for the series of molecules amount to 1%, 5%, and 9%, respectively. At the experimental wavelength, the contributions to Β due to the magnetization dependence in the exchange-correlation functional are negligible for CF3 Cl and CF3 Br and small for CF 3 I. The noticeable effect of magnetization in the latter case is attributed to a near two-photon resonance with the excited state 1 E3 (nonrelativistic notation). It is emphasized, however, that the effect of magnetization on Β for CF3 I is negligible both in comparison to the total relativistic correction as well as to the effects of electron correlation. It is concluded that, in calculations of hyperpolarizabilities under nonresonant conditions, the magnetization dependence in the exchange-correlation functional may be ignored. © 2009 American Institute of Physics.
|
|
