Comparison of dust release from epoxy and paint nanocomposites and conventional products during sanding and sawing.

A 3 week measurement campaign was undertaken to study the effect of local weather parameters, transportation from an urban area, structure of boundary layer, and precipitation on submicron (8–450 nm in mobility diameter) aerosol particles in urban background area in Finland. Also, the concentrations of NOx, O3, and SO2 were monitored. The most important meteorological factor affecting aerosol particles was shown to be local wind direction. It was also seen that the diurnal behavior of boundary layer plays an important role for aerosol particle concentration and size distribution and gas phase chemistry at the ground level. Even the few occurrences of new particle formation that were observed seem to be connected with changes in the boundary layer. Clear indications of the possible effect of precipitation (rain or snow) on aerosol size distributions could not be detected in this study. The effect is obviously small compared to the influences of other meteorological processes.

Abstract. Particle number concentration and size distribution are important variables needed to constrain the role of atmospheric particles in the Earth radiation budget, both directly and indirectly through CCN activation. They are also linked to regulated variables such as particle mass (PM) and therefore of interest to air quality studies. However, data on their long-term variability are scarce, in particular at high altitudes. In this paper, we investigate the diurnal and seasonal variability of the aerosol total number concentration and size distribution at the puy de Dôme research station (France, 1465 m a.s.l.). We report a variability of aerosol particle total number concentration measured over a five-year (2003–2007) period for particles larger than 10 nm and aerosol size distributions between 10 and 500 nm over a two-year period (January 2006 to December 2007). Concentrations show a strong seasonality with maxima during summer and minima during winter. A diurnal variation is also observed with maxima between 12:00 and 18:00 UTC. At night (00:00–06:00 UTC), the median hourly total concentration varies from 600 to 800 cm−3 during winter and from 1700 to 2200 cm−3 during summer. During the day (08:00–18:00 UTC), the concentration is in the range of 700 to 1400 cm−3 during winter and of 2500 to 3500 cm−3 during summer. An averaged size distribution of particles (10–500 nm) was calculated for each season. The total aerosol number concentrations are dominated by the Aitken mode integral concentrations, which drive most of the winter to summer total concentrations increase. The night to day increase in dominated by the nucleation mode integral number concentration. Because the site is located in the free troposphere only a fraction of the time, in particular at night and during the winter season, we have subsequently analyzed the variability for nighttime and free tropospheric (FT)/residual layer (RL) conditions only. We show that a seasonal variability is still observed for these FT/RL conditions. The FT/RL seasonal variation is due to both seasonal changes in the air mass origin from winter to summer and enhanced concentrations of particles in the residual layer/free troposphere in summer. The later observation can be explained by higher emissions intensity in the boundary layer, stronger exchanges between the boundary layer and the free troposphere as well as enhanced photochemical processes. Finally, aerosols mean size distributions are calculated for a given air mass type (marine/continental/regional) according to the season for the specific conditions of the residual layer/free troposphere. The seasonal variability in aerosol sources seems to be predominant over the continent compared to the seasonal variation of marine aerosol sources. These results are of regional relevance and can be used to constrain chemical-transport models over Western Europe.

Evaluation of microwave and magnetic properties of substituted SrFe12O19 and substituted SrFe12O19/multi-walled carbon nanotubes nanocomposites

Prediction of complex modulus in phase-separated poly (lactic acid)/poly (ethylene oxide)/carbon nanotubes nanocomposites

The interphase thickness in polymer carbon nanotube (CNT) nanocomposites (PCNT) is expressed by CNT characteristics and interfacial conductivity between CNT and polymer matrix. Also, the effective length and concentration of CNT are defined supposing interfacial conductivity to suggest the percolation threshold and the fraction of networked CNT. Furthermore, a simple model is developed to predict the conductivity of PCNT assuming tunneling effect, interphase region and interfacial conductivity. The influences of all parameters on the interphase thickness, percolation threshold, the fraction of networked CNT and the conductivity of PCNT are studied. In addition, some experimental results are provided to compare the predictions of developed model to the experimental measurements. The high levels of CNT radius, CNT length, CNT conductivity, interfacial conductivity and conductivity transferring can produce a thick interphase, but the waviness cannot change it. Moreover, the developed model can properly calculate the conductivity of studied samples. A desirable conductivity is obtained by thin and long CNT, medium CNT conductivity, poor waviness, high interfacial conductivity and good conductivity transferring, because they provide high effective CNT concentration and low percolation threshold in nanocomposites.

A coupled aerosol–cloud model is essential for investigating the formation of haze and fog and the interaction of aerosols with clouds and precipitation. One of the key tasks of such a model is to produce correct mass and number size distributions of aerosols. In this paper, a parameterization scheme for aerosol size distribution in initial emission, which took into account the measured mass and number size distributions of aerosols, was developed in the GRAPES–CUACE [Global/Regional Assimilation and PrEdiction System–China Meteorological Administration (CMA) Unified Atmospheric Chemistry Environment model]—an online chemical weather forecast system that contains microphysical processes and emission, transport, and chemical conversion of sectional multi-component aerosols. In addition, the competitive mechanism between nucleation and condensation for secondary aerosol formation was improved, and the dry deposition was also modified to be in consistent with the real depositing length. Based on the above improvements, the GRAPES–CUACE simulations were verified against observational data during 1–31 January 2013, when a series of heavy regional haze–fog events occurred in eastern China. The results show that the aerosol number size distribution from the improved experiment was much closer to the observation, whereas in the old experiment the number concentration was higher in the nucleation mode and lower in the accumulation mode. Meanwhile, the errors in aerosol number size distribution as diagnosed by its sectional mass size distribution were also reduced. Moreover, simulations of organic carbon, sulfate, and other aerosol components were improved and the overestimation as well as underestimation of PM2.5 concentration in eastern China was significantly reduced, leading to increased correlation coefficient between simulated and observed PM2.5 by more than 70%. In the remote areas where bad simulation results were produced previously, the correlation coefficient grew from 0.35 to 0.61, and the mean mass concentration went up from 43% to 87.5% of the observed value. Thus, the simulation of particulate matters in these areas has been improved considerably.

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In this paper, an analytical model of a receiver operating characteristic (ROC) curve for digital fluorescence lidar sensing of an aerosol biowarfare agent (BWA) simulant in the presence of a single aerosol interferent is presented. The BWA simulant and interferent are characterized by their concentrations, particle size distributions, fluorescence cross sections, and complex refractive indexes. The ROC curve calculation is performed for simulant and interferent lidar signals that are plotted in a biodiscrimination plane defined by normalized particle size ratio <formula formulatype="inline"><tex Notation="TeX">$X$</tex></formula> and particle fluorescence ratio <formula formulatype="inline"><tex Notation="TeX">$Y$</tex></formula> . Probability density functions (PDFs) of BWA simulant and interferent in the biodiscrimination plane are due to finite signal-to-noise lidar measurements. These functions are modeled with a joint distribution density function of <formula formulatype="inline"><tex Notation="TeX">$X$</tex></formula> and <formula formulatype="inline"> <tex Notation="TeX">$Y$</tex></formula> as correlated variables. The <formula formulatype="inline"><tex Notation="TeX">$X$</tex> </formula> and <formula formulatype="inline"><tex Notation="TeX">$Y$</tex></formula> variables are calculated from the corresponding lidar equations that compute signal and noise from elastic backscatter and fluorescence cross sections, the concentration of aerosol particles, and lidar optical system parameters. Elastic backscatter is calculated from Mie scattering theory using a particle size distribution approximated by a log-normal distribution. Fluorescence cross sections of BWA simulant or interferent aerosols given in the literature are approximated as being independent/dependent from particle size distribution in the model. Each point of the ROC curve of BWA simulant in the presence of an interferent is defined as the integral of the interferent PDF over the elliptical contour projection of BWA simulant PDF in the biodiscrimination plane for a fixed threshold of aerosol cloud detection, and thus, a fixed probability of aerosol cloud detection. Presented ROC curve method can be generalized to the case of the simultaneous presence of several interferents to the discrimination of one BWA simulant. Calculated elliptical contour projections of the bioaerosol PDF in the biodiscrimination plane, and corresponding ROC curves are computed and presented for the parameters of an experimental lidar that was tested during BWA simulant and interferent aerosol cloud releases, where aerosol cloud particle concentrations and size distributions were also measured. When the number and identity of interferents and their corresponding concentrations are unknown, the ROC curve can be estimated by assuming a constant bioaerosol PDF in the biodiscrimination plane. </para>

Abstract. We took aerosol measurements at Syowa Station, Antarctica, to characterize the aerosol number–size distribution and other aerosol physicochemical properties in 2004–2006. Four modal structures (i.e., mono-, bi-, tri-, and quad-modal) were identified in aerosol size distributions during measurements. Particularly, tri-modal and quad-modal structures were associated closely with new particle formation (NPF). To elucidate where NPF proceeds in the Antarctic, we compared the aerosol size distributions and modal structures to air mass origins computed using backward trajectory analysis. Results of this comparison imply that aerosol size distributions involved with fresh NPF (quad-modal distributions) were observed in coastal and continental free troposphere (FT; 12 % of days) areas and marine and coastal boundary layers (1 %) during September–October and March and in coastal and continental FT (3 %) areas and marine and coastal boundary layers (8 %) during December–February. Photochemical gaseous products, coupled with ultraviolet (UV) radiation, play an important role in NPF, even in the Antarctic troposphere. With the existence of the ozone hole in the Antarctic stratosphere, more UV radiation can enhance atmospheric chemistry, even near the surface in the Antarctic. However, linkage among tropospheric aerosols in the Antarctic, ozone hole, and UV enhancement is unknown. Results demonstrated that NPF started in the Antarctic FT already at the end of August–early September by UV enhancement resulting from the ozone hole. Then, aerosol particles supplied from NPF during periods when the ozone hole appeared to grow gradually by vapor condensation, suggesting modification of aerosol properties such as number concentrations and size distributions in the Antarctic troposphere during summer. Here, we assess the hypothesis that UV enhancement in the upper troposphere by the Antarctic ozone hole modifies the aerosol population, aerosol size distribution, cloud condensation nuclei capabilities, and cloud properties in Antarctic regions during summer.

Machine vision based particle size and size distribution determination of airborne dust particles of wood and bark pellets

In the present work, chitosan (CS)‐grafted multiwalled carbon nanotube (MWCNT) nanocomposites were prepared via covalently bonded CS onto MWCNTs that had weight fractions of MWCNTs ranging from 0.1 to 3.0 wt % by a simple method of solution casting. The structure, morphology, and mechanical properties of the films were investigated by Fourier transform infrared spectroscopy, field emission scanning electron microscopy, optical microscopy, wide‐angle X‐ray diffraction, contact angle, and tensile testing. The results indicated that the CS chains were attached onto the MWCNTs successfully via covalent linkages. More interestingly, the MWCNTs provided a matrix that facilitated the crystallization of CS. Compared with the pure CS, the tensile strength and Young's modulus of the nanocomposites were enhanced significantly from 39.6 to 105.6 MPa and from 2.01 to 4.22 GPa with an increase in the MWCNT loading level from 0 to 3.0 wt %, respectively. The improvement in the tensile strength and modulus were ascribed to the uniform dispersion of MWCNTs covalently linked to the CS matrix. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

This paper expresses a simple equation for conductivity of polymer carbon nanotubes (CNT) nanocomposites (PCNT) based on Halpin-Tsai model supposing the volume fraction of networked CNT, CNT conductivity, CNT size and tunneling dimensions between adjacent CNT. The experimental results of several samples and the effects of all parameters on the conductivity examine the predictions of developed model. Long CNT, thick interphase, thin CNT, high percentage of networked CNT, short tunneling distance, poor waviness and large tunneling diameter advantageously improve the conductivity. The suitable agreements between experimental data and calculations as well as the sensible roles of all parameters in the conductivity justify the developed model. The developed model can provide the optimized levels of parameters introducing the most desirable conductivity.

The effective conductivity of polymer carbon nanotubes (CNT) nanocomposites

Stratospheric aerosols play a crucial role in the climate system, but uncertainties persist in understanding the chemical, dynamical, and microphysical processes governing their distribution and variability. The chemical and radiative impacts of stratospheric aerosols hinge on particle size distribution. However, models exhibit significant variations in how they parameterize aerosol microphysical processes and simulate size distributions, leading to divergent predictions of the time evolution of radiative impacts from stratospheric aerosol perturbation events. To refine models for assessing the effects of potential climate intervention strategies, systematic measurements are crucial.&amp;#160;In pursuit of this understanding, the Baseline Balloon Stratospheric Aerosol Profiles (B2SAP) project utilizes compact, lightweight payloads carried by meteorological balloons. These payloads measure aerosol number density and size distributions, along with water vapor, ozone, and meteorological data from the surface to the middle stratosphere. The long-term goal of the B2SAP project is to generate climatologies of aerosol number and size distributions up to the middle stratosphere at latitudinally distributed measurement sites. Since March 2019, B2SAP payloads have been launched from Boulder, CO, USA (40&amp;#176;N) once to twice per month and four to six times per year from Lauder, NZ (45&amp;#176;S). Starting in 2022, two tropical sites were added to this evanescent network with quarterly launches: Hilo, HI, USA (20&amp;#176;N) and Reunion Island, FR (20&amp;#176;S). These measurements provide a new record of in situ observations allowing to characterize the natural stratospheric aerosol burden, its variability, and responses to perturbations, providing essential data for refining models and aiding in the validation of satellite-based estimates.&amp;#160;In this context, we will present a subset of this growing database, emphasizing the discussion on the stratospheric aerosol layers in the North hemisphere and South hemisphere (SH) mid-latitudes. Perturbations recorded in the SH after the Australian New Year super pyroCb outbreak in 2020 will also be investigated.

Carboxyl-modified multi-walled carbon nanotubes (MWCNT-COOHs) as nanofillers were incorporated into diglycidyl ether of bisphenol A (DGEBA) toughened with carboxyl-terminated butadiene-acrylonitrile (CTBN). The carboxyl functional carbon nanotubes were characterized by Fourier-transform infrared spectroscopy and thermogravimetric analysis. Furthermore, cure kinetics, glass transition temperature (T g ), mechanical properties, thermal stability and morphology of DGEBA/CTBN/MWCNT-COOHs nanocomposites were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), universal test machine, thermogravimetric analysis and scanning electron microscopy (SEM). DSC kinetic studies showed that the addition of MWCNT-COOHs accelerated the curing reaction of the rubber-toughened epoxy resin. DMA results revealed that T g of rubber-toughened epoxy nanocomposites lowered with MWCNT-COOH contents. The tensile strength, elongation at break, flexural strength and flexural modulus of DGEBA/ CTBN/MWCNT-COOHs nanocomposites were increased at lower MWCNT-COOH concentration. A homogenous dispersion of nanocomposites at lower MWCNT-COOH concentration was observed by SEM.

IntroductionThere are fundamental differences between electronic cigarettes (e-cigarettes) and conventional cigarette product categories with regards to potential environmental exposures, notably that e-cigarettes do not contain tobacco or generate side-stream emissions. Here we assess the spatial and temporal patterns of exhaled e-cigarette aerosol at a bystander’s position, and compare it with conventional cigarette smoke emissions.MethodsSmokers were asked to use e-cigarettes or smoke conventional cigarettes in a room-simulating chamber. Volunteers used the products at different distances from a heated mannequin, representing a bystander, and under different room ventilation rates. Aerosol particle concentrations and size distributions at the bystander’s position were measured.ResultsFor both product categories, the particle concentrations registered following each puff were in the same order of magnitude. However, for e-cigarettes the particle concentration returned rapidly to background values within seconds; for conventional cigarettes it increased with successive puffs, returning to background levels after 30–45 minutes. Unlike for the e-cigarette devices tested, such temporal variation was dependent on the room ventilation rate. Particle size measurements showed that exhaled e-cigarette particles were smaller than those emitted during smoking conventional cigarettes and evaporated almost immediately after exhalation, thus affecting the removal of particles through evaporation rather than displacement by ventilation.ConclusionsSignificant differences between emissions from the tested e- and conventional cigarettes are reported. Exhaled e-cigarette particles are liquid droplets evaporating rapidly; conventional cigarette smoke particles are far more stable and linger.Implications• Several factors potentially influencing particle behavior after exhalation of e-cigarette aerosols or emitted during smoking conventional cigarettes were studied.• Differences in particle size between those exhaled following use of e-cigarettes and those emitted during smoking of conventional cigarettes were observed.• E-cigarette particle concentrations decreased rapidly following exhalation due to evaporation.• The removal of particles following smoking conventional cigarettes was much slower and was dependent on the room ventilation rate.