129 research outputs found
The monitoring of dirty electricity in A secondary school in kazan, republic of tatarstan, Russia
No full textElectromagnetic fields from electronic equipment are detrimental environmental factors. Recently, a new type of electromagnetic pollution referred to as "dirty electricity" was discovered to affect human health. The current research measures levels of dirty electricity in one secondary school in Kazan, Republic of Tatarstan, Russia. A Microsurge II meter that measures high frequency transients and harmonics between 4 to 100 kHz (expressed as Graham-Stetzer units) was used in this study. Levels of dirty electricity were elevated in all areas of the school and the installation of Graham-Stetzer filters significantly reduced these levels. Taking into account the detrimental effects of the dirty electricity on human health, plugging one Graham-Stetzer filter into each classroom is highly recommended. © PSP Volume 18 - No 6. 2009
The monitoring of dirty electricity in A secondary school in kazan, republic of tatarstan, Russia
No full textElectromagnetic fields from electronic equipment are detrimental environmental factors. Recently, a new type of electromagnetic pollution referred to as "dirty electricity" was discovered to affect human health. The current research measures levels of dirty electricity in one secondary school in Kazan, Republic of Tatarstan, Russia. A Microsurge II meter that measures high frequency transients and harmonics between 4 to 100 kHz (expressed as Graham-Stetzer units) was used in this study. Levels of dirty electricity were elevated in all areas of the school and the installation of Graham-Stetzer filters significantly reduced these levels. Taking into account the detrimental effects of the dirty electricity on human health, plugging one Graham-Stetzer filter into each classroom is highly recommended. © PSP Volume 18 - No 6. 2009
Homogeneous nucleation rates of nitric acid dihydrate (NAD) at simulated stratospheric conditions – Part II: Modelling
No full textActivation energies ΔGact for the nucleation of nitric acid dihydrate (NAD) in supercooled binary HNO3/H2O solution droplets were calculated from volume-based nucleation rate measurements using the AIDA (Aerosol, Interactions, and Dynamics in the Atmosphere) aerosol chamber of Forschungszentrum Karlsruhe. The experimental conditions covered temperatures T between 192 and 197 K, NAD saturation ratios SNAD between 7 and 10, and nitric acid molar fractions of the nucleating sub-micron sized droplets between 0.26 and 0.28. Based on classical nucleation theory, a new parameterisation for ΔGact=A×(T ln SNAD)−2+B is fitted to the experimental data with A=2.5×106 kcal K2 mol−1 and B=11.2−0.1(T−192) kcal mol−1. A and B were chosen to also achieve good agreement with literature data of ΔGact. The parameter A implies, for the temperature and composition range of our analysis, a mean interface tension σsl=51 cal mol−1 cm−2 between the growing NAD germ and the supercooled solution. A slight temperature dependence of the diffusion activation energy is represented by the parameter B. Investigations with a detailed microphysical process model showed that literature formulations of volume-based (Salcedo et al., 2001) and surface-based (Tabazadeh et al., 2002) nucleation rates significantly overestimate NAD formation rates when applied to the conditions of our experiments
Homogeneous nucleation rates of nitric acid dihydrate (NAD) at simulated stratospheric conditions - Part II: Modelling
No full textHomogeneous nucleation rates of nitric acid dihydrate (NAD) at simulated stratospheric conditions ? Part II: Modelling
No full textInternational audienceActivation energies ?Gact for the nucleation of nitric acid dihydrate (NAD) in supercooled binary HNO3/H2O solution droplets were calculated from volume-based nucleation rate measurements using the AIDA (Aerosol Interactions and Dynamics in the Atmosphere) aerosol chamber of Forschungszentrum Karlsruhe. The experimental conditions covered temperatures T between 192 K and 197 K, NAD saturation ratios SNAD between 7 and 10, and nitric acid molar fractions of the nucleating sub-micron sized droplets between 0.26 and 0.28. Based on classical nucleation theory, a new parameterisation ?Gact=A×(T lnSNAD)-2+B is fitted to our experimetnal data with A=2.5×106 kcal K2 mol-1 and B=11.2?0.1(T?192) kcal mol-1. A and B were chosen to also achieve good agreement with literature data of ?Gact. The parameter A implies a constant interfacial tension ?sl=51 cal mol-1 cm-2 between the growing NAD germ and the supercooled solution. A slight temperature dependence of the diffusion activation energy is represented by the parameter B. Investigations with a detailed microphysical process model showed that literature formulations of volume-based (Salcedo et al., 2001) and surface-based (Tabazadeh et al., 2002) nucleation rates significantly overestimate NAD formation rates when applied to the conditions of our experiments
Homogeneous nucleation rates of nitric acid dihydrate (NAD) at simulated stratospheric conditions – Part II: Modelling
No full textCircular depolarization ratios of single water droplets and finite ice circular cylinders: a modeling study
No full textAbstract. Computations of the phase matrix elements for single water droplets and ice crystals in fixed orientations are presented to determine if circular depolarization δ&amp;pm;C is more accurate than linear depolarization for phase discrimination. T-matrix simulations were performed to calculate right-handed and left-handed circular depolarization ratios δ&amp;plus;C, respectively δ−C and to compare them with linear ones. Ice crystals are assumed to have a circular cylindrical shape where their surface-equivalent diameters range up to 5 μm. The circular depolarization ratios of ice particles were generally higher than linear depolarization and depended mostly on the particle orientation as well as their sizes. The fraction of non-detectable ice crystals (δ < 0.05) was smaller considering a circular polarized light source, reaching 4.5%. However, water droplets also depolarized light circularly for scattering angles smaller than 179° and size parameters smaller than 6 at side- and backscattering regions. Differentiation between ice crystals and water droplets might be difficult for experiments performing at backscattering angles which deviate from 180° unlike lidar applications. If the absence of the liquid phase is confirmed, the use of circular depolarization in single particle detection is more sensitive and less affected by particle orientation.
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Homogeneous nucleation rates of nitric acid dihydrate (NAD) at simulated stratospheric conditions ? Part I: Experimental results
No full textInternational audienceThe low temperature aerosol chamber AIDA was used to study the nucleation of nitric acid dihydrate (NAD) in super-cooled nitric acid aerosols under simulated stratospheric conditions in the temperature range 192 K?197 K. The nucleating solution droplets had median diameters between 225 and 290 nm and molar fractions of nitric acid between 0.26 and 0.28. Nucleation of solid particles was unambiguously observed in two out of three experiments during time periods of up to five hours. The newly formed crystals could be clearly distinguished from the remaining liquid droplets by their increasing size with an optical particle spectrometer. The solid particles could be unequivocally identified as strongly aspherical nitric acid dihydrate crystals (?-NAD) by in-situ FTIR-spectroscopy. From our experimental data set there is no indication of direct nucleation of NAT or a conversion of NAD into NAT while having saturation ratios with resprect to NAT of about 20?26. The temporal evolutions of the NAD particle concentrations were used to derive individual nucleation rates for NAD. The measured volume nucleation rates ranged from 3.9·105 cm-3s-1 at 195.8 K and XNA=0.27 to 1.9·107 cm-3s-1 at 192.1 K and XNA=0.28. The corresponding hypothetical surface nucleation rates of 2·100 to 1·102 cm-2s-1 are smaller than the parameterisation of Tabazadeh et al. (2002) by factors between 25 and >103
Comparison of measured and calculated collision efficiencies at low temperatures
No full textInteractions of atmospheric aerosols with clouds influence cloud properties
and modify the aerosol life cycle. Aerosol particles act as cloud
condensation nuclei and ice nucleating particles or become incorporated into
cloud droplets by scavenging. For an accurate description of aerosol
scavenging and ice nucleation in contact mode, collision efficiency between
droplets and aerosol particles needs to be known. This study derives the
collision rate from experimental contact freezing data obtained with the ETH
CoLlision Ice Nucleation CHamber (CLINCH). Freely falling 80 μm diameter water droplets are exposed to an
aerosol consisting of 200 and 400 nm diameter silver iodide particles of
concentrations from 500 to 5000 and 500 to 2000 cm−3, respectively,
which act as ice nucleating particles in contact mode. The experimental data
used to derive collision efficiency are in a temperature range of
238–245 K, where each collision of silver iodide particles with droplets
can be assumed to result in the freezing of the droplet. An upper and lower
limit of collision efficiency is also estimated for 800 nm diameter
kaolinite particles. The chamber is kept at ice saturation at a temperature
range of 236 to 261 K, leading to the slow evaporation of water droplets
giving rise to thermophoresis and diffusiophoresis. Droplets and particles
bear charges inducing electrophoresis. The experimentally derived collision
efficiency values of 0.13, 0.07 and 0.047–0.11 for 200, 400 and 800 nm
particles are around 1 order of magnitude higher than theoretical
formulations which include Brownian diffusion, impaction, interception,
thermophoretic, diffusiophoretic and electric forces. This discrepancy is
most probably due to uncertainties and inaccuracies in the description of
thermophoretic and diffusiophoretic processes acting together. This is, to
the authors' knowledge, the first data set of collision efficiencies acquired
below 273 K. More such experiments with different droplet and particle
diameters are needed to improve our understanding of collision processes
acting together
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