Application of bag sampling technique for particle size distribution measurements

Bag sampling techniques can be used to temporarily store an aerosol and therefore provide sufficient time to utilize sensitive but slow instrumental techniques for recording detailed particle size distributions. Laboratory based assessment of the method were conducted to examine size dependant deposition loss coefficients for aerosols held in VelostatTM bags conforming to a horizontal cylindrical geometry. Deposition losses of NaCl particles in the range of 10 nm to 160 nm were analysed in relation to the bag size, storage time, and sampling flow rate. Results of this study suggest that the bag sampling method is most useful for moderately short sampling periods of about 5 minutes

Prompt deliquescence and efflorescence of aerosol nanoparticles

International audienceLiterature reports have differed on the possibilities of discontinuous and continuous (i.e., prompt and nonprompt) deliquescence and efflorescence of aerosol particles in the nanosize regime. Experiments reported herein using a hygroscopic tandem nano-differential mobility analyzer demonstrate prompt deliquescence and efflorescence of ammonium sulfate particles having diameters from 6 to 60 nm. Apparent nonpromptness can be induced both by operation of the experimental apparatus and by interpretation of the measurements, even though the underlying phase transitions of individual particles remain prompt. No nanosize effect on the relative humidity values of deliquescence or efflorescence is observed for the studied size range. Smaller hygroscopic growth factors are, however, observed for the nanoparticles, in agreement with thermodynamic calculations that include the Kelvin effect. A slightly nonspherical shape for dry ammonium sulfate particles is inferred from their hygroscopically induced reconstruction between 5 and 30% relative humidity. Our results provide a further understanding of nanoparticle behavior, especially relevant to the growth rates of atmospheric nanoparticles

A tunable high-pass filter for simple and inexpensive size-segregation of sub-10-nm nanoparticles

© The Author(s) 2017. Recent advanced in the fields of nanotechnology and atmospheric sciences underline the increasing need for sizing sub-10-nm aerosol particles in a simple yet efficient way. In this article, we develop, experimentally test and model the performance of a High-Pass Electrical Mobility Filter (HP-EMF) that can be used for sizing nanoparticles suspended in gaseous media. Experimental measurements of the penetration of nanoparticles having diameters down to ca 1nm through the HP-EMF are compared with predictions by an analytic, a semi-empirical and a numerical model. The results show that the HPEMF effectively filters nanoparticles below a threshold diameter with an extremely high level of sizing performance, while it is easier to use compared to existing nanoparticle sizing techniques through design simplifications. What is more, the HP-EMF is an inexpensive and compact tool, making it an enabling technology for a variety of applications ranging from nanomaterial synthesis to distributed monitoring of atmospheric nanoparticles

Long-term observations of the background aerosol at Cabauw, The Netherlands

Long-term measurements of PM2.5 mass concentrations and aerosol particle size distributions from 2008 to 2015, as well as hygroscopicity measurements conducted over one year (2008-2009) at Cabauw, The Netherlands, are compiled here in order to provide a comprehensive dataset for understanding the trends and annual variabilities of the atmospheric aerosol in the region. PM2.5 concentrations have a mean value of 14.4 mu g m(-3) with standard deviation 2.1 mu g m(-3), and exhibit an overall decreasing trend of -0.74 mu g m(-3) year(-1). The highest values are observed in winter and spring and are associated with a shallower boundary layer and lower precipitation, respectively, compared to the rest of the seasons. Number concentrations of particles smaller than 500 nm have a mean of 9.2 x 10(3) particles cm(-3) and standard deviation 4.9x10(3) particles cm(-3), exhibiting an increasing trend between 2008 and 2011 and a decreasing trend from 2013 to 2015. The particle number concentrations exhibit highest values in spring and summer (despite the increased precipitation) due to the high occurrence of nucleation-mode particles, which most likely are formed elsewhere and are transported to the observation station. Particle hygroscopicity measurements show that, independently of the air mass origin, the particles are mostly externally mixed with the more hydrophobic mode having a mean hygroscopic parameter kappa of 0.1 while for the more hydrophilic mode kappa is 0.35. The hygroscopicity of the smaller particles investigated in this work (i.e., particles having diameters of 35 nm) appears to increase during the course of the nucleation events, reflecting a change in the chemical composition of the particles. (C) 2017 Elsevier B.V. All rights reserved.Peer reviewe

Cloud droplet activation of mixed organic-sulfate particles produced by the photooxidation of isoprene

The cloud condensation nuclei (CCN) properties of ammonium sulfate particles mixed with organic material condensed during the hydroxyl-radical-initiated photooxidation of isoprene (C<sub>5</sub>H<sub>8</sub>) were investigated in the continuous-flow Harvard Environmental Chamber. CCN activation curves were measured for organic particle mass concentrations of 0.5 to 10.0 μg m<sup>−3</sup>, NO<sub>x</sub> concentrations from under 0.4 ppbv up to 38 ppbv, particle mobility diameters from 70 to 150 nm, and thermodenuder temperatures from 25 to 100 °C. At 25 °C, the observed CCN activation curves were accurately described by a Köhler model having two internally mixed components, namely ammonium sulfate and secondary organic material. The modeled physicochemical parameters of the organic material were equivalent to an effective hygroscopicity parameter κ<sub>ORG</sub> of 0.10±0.03, regardless of the C<sub>5</sub>H<sub>8</sub>:NO<sub>x</sub> concentration ratio for the span of >200:0.4 to 50:38 (ppbv:ppbv). The volatilization curves (i.e., plots of the residual organic volume fraction against temperature) were also similar for the span of investigated C<sub>5</sub>H<sub>8</sub>:NO<sub>x</sub> ratios, suggesting a broad similarity of particle chemical composition. This suggestion was supported by limited variance at 25 °C among the particle mass spectra. For example, the signal intensity at <i>m/z</i> 44 (which can result from the fragmentation of oxidized molecules believed to affect hygroscopicity and CCN properties) varied weakly from 6 to 9% across the range of investigated conditions. In contradistinction to the results for 25 °C, conditioning up to 100 °C in the thermodenuder significantly reduced CCN activity. The altered CCN activity might be explained by chemical reactions (e.g., decomposition or oligomerization) of the secondary organic material at elevated temperatures. The study's results at 25 °C, in conjunction with the results of other chamber and field studies for a diverse range of conditions, suggest that a value of 0.10±0.05 for κ<sub>ORG</sub> is representative of both anthropogenic and biogenic secondary organic material. This finding supports the use of κ<sub>ORG</sub> as a simplified yet accurate general parameter to represent the CCN activation of secondary organic material in large-scale atmospheric and climate models

Enhancing the absorption of 1-chloro-1,2,2,2-tetrafluoroethane on carbon nanotubes: an ab initio study

We have investigated the possibility of utilizing various single-walled pristine and doped carbon nanotubes as adsorbents for the 1-chloro-1,2,2,2-tetrafluoroethane (HCFC-124) gaseous molecule. Three candidates, including pristine carbon nanotube (CNT), silicon carbide nanotube (SiCNT) and germanium-doped SiCNT (SiCGeNT) are identified and evaluated theoretically. The quantum simulations have been performed at the density functional theory (DFT) level with four different functionals (i.e., M06-2X, xB97XD, CAM-B3LYP and B3LYP-D3) with a split-valence triple-zeta basis set (6-311G(d)). We found that adsorption on the SiCGeNT is most favourable, while that on the pristine CNT yields the lowest adsorption energy. Adsorption on these nanotubes is not accompanied by an active charge-transfer phenomenon; instead, it is driven by weak van der Waals forces. The HOMO–LUMO energy gaps drastically change when the dopant atom is added to the SiCNT, thereby improving their overall adsorption capability. Among all of the adsorbents inves�tigated here, SiCGeNT shows the most favourable for designing effective HCFC-124 nanosensor

Thin film and nanostructured Pd-based materials for optical H₂ sensors: A review

In this review paper, we provide an overview of state-of-the-art Pd-based materials for optical H2 sensors. The first part of the manuscript introduces the operating principles, providing background information on the thermodynamics and the primary mechanisms of optical detection. Optical H2 sensors using thin films (i.e., films without any nanostructuring) are discussed first, followed by those employing nanostructured materials based on aggregated or isolated nanoparticles (ANPs and INPs, respectively), as well as complex nanostructured (CN) architectures. The different material types are discussed on the basis of the properties they can attribute to the resulting sensors, including their limit of detection, sensitivity, and response time. Limitations induced by cracking and the hysteresis effect, which reduce the repeatability and reliability of the sensors, as well as by CO poisoning that deteriorates their performance in the long run, are also discussed together with an overview of manufacturing approaches (e.g., tailoring the composition and/or applying functionalizing coatings) for addressing these issues.Atmospheric Remote Sensin