Transport Of Aerosol Particles Research Articles

An experimental approach to measure particle deposition in large circular ventilation ducts.

The topic of this study is related to airborne particle dynamics in indoor environments. Lab-scale experiments have been performed to investigate particle deposition velocity to six different surfaces orientations (with respect to gravity) for fully developed turbulent flow in horizontal large circular ventilation ducts. Monodispersed aerosol particles (1-6μm) were used in the deposition experiments. A very low particle mass (40ng) was measured reliably above background level on duct surfaces by a means of a nondestructive stencil technique associated with fluorescence analysis. For 2-6μm particles (diffusion and impaction regime), deposition rates to floors were much greater than rates to the ceiling and greater than rates to the wall. For 1-μm particles, the effect of surface orientation to particle deposition was not significant. Results were compared to the very few similar and published studies. This work was conducted in the frame of the CleanAirNet project which aimed at producing new knowledge, models, and techniques to help controlling the safety food stuffs, through a better control of aerosol particle (bioaerosols) transport and deposition in the ventilation networks of the food industry.

Evaluating the impact of multisensor data assimilation on a global aerosol particle transport model

AbstractBy evaluating quality‐assured Moderate Resolution Imaging Spectroradiometer (MODIS) Dark Target (DT), MODIS Deep Blue (DB), Multiangle Imaging Spectroradiometer (MISR), and Cloud‐Aerosol Lidar with Orthogonal Polarization (CALIOP) aerosol products assimilated into the U. S. Navy Aerosol Analysis and Prediction System (NAAPS), the impact of single‐sensor and multisensor data assimilation on aerosol optical depth (AOD) analysis and forecast skill is characterized using ground‐based Level 2 Aerosol Robotic Network (AERONET) data sets during the 2007 boreal summer (June–August 2007). The single‐sensor assimilation experiment suggests that all products tested can improve NAAPS performance on a regional or a global scale. The multisensor assimilation experiment suggests that model improvement is greatest with the combined use of Terra and Aqua MODIS DT products, largely due to data density. Incremental improvements are identified, as a function of data density, over regions such as the Saharan desert when adding MISR and MODIS DB products. The inclusion of CALIOP data is mass‐neutral by definition and has an insignificant impact on the NAAPS 00 h analysis. CALIOP assimilation does improve the 48 h forecast from NAAPS due to more accurate 00 h vertical distribution and hence forecasted advection. Root‐mean‐square errors exceeding 0.1 are found over East Asia and North Africa for both the NAAPS analysis and satellite AOD data, indicating that satellite aerosol products in these two regions need improvement. Similarly, low correlation is found between NAAPS and AERONET over Australia, even with the use of all available satellite aerosol products, suggesting that more detailed examination of some critical regions is necessary.

Optical exploration of biomass burning aerosols over a high-altitude station by combining ground-based and satellite data

Biomass burning activity captured the attention of the scientific community because of its significant impact on global climate change. In this paper, we present the results of a study of variations in aerosol optical, microphysical and radiative properties during biomass burning at an high-altitude rural station, Sinhagad (18°21׳N, 73°45׳E, 1450m AMSL), employing ground-based observations of MICROTOPS-II and short-wave (SW) Pyranometer, as well as satellite (MODIS) measurements of AOD during 28 April 2011–06 May 2011. Vertically resolved feature mask images from CALIPSO during night-time on available days are utilized as an additional tool to monitor the smoke/dust vertical distributions. A prominent smoke/dust layer is observed between 2 and 4km altitude, whereas the CALIPSO observations of the vertical profile of aerosols are in qualitative agreement with the values of MODIS-AOD550nm. During the smoke/dust event, a drastic increase (~0.9) in Terra/Aqua MODIS AOD550nm is observed. Satellite data indicate a long-range transport of aerosol particles from Indo-Gangetic Plains (IGP) over large regions. The observed short-wave solar flux at the bottom of the atmosphere (BOA) is found to decrease due to aerosol extinction and was found to be −25 and −16Wm−2 for the aerosol-laden days and normal days, respectively. In addition, the transport of a widespread forest fire plume is observed across the country as evidenced by the MODIS imagery and HYSPLIT back trajectories. The observed features are also explained on the basis of the results from the NCEP/NCAR and ECMWF re-analysis data.

Calculating Efficiency of Separation of Aerosol Particles from Gases in Packed Apparatuses

A mathematical model for the process of removal of aerosols from gases in channels filled with packing is considered. Equations for transport of aerosol particles and results of their numerical solution are given. Influence of operating conditions and of design characteristics of the packed apparatus on gas purification efficiency is analyzed.

Effect of thermophoresis on the motion of aerosol particles in natural convective flow on horizontal plates

The present work investigates the effects of thermophoresis and transverse magnetic field on aerosol particle transport and deposition onto a horizontal plate in the presence of a natural convective flow. Micro to nano sized particles (particle diameter in the range 1nm–1μm) are considered. A similarity solution for the fluid flow field is formulated for natural convection with and without magnetohydrodynamic (MHD) effects above a heated horizontal plate as well as beneath a cold horizontal plate. The mechanisms of particle deposition include the effects of free convection, Brownian diffusion and thermophoresis. Numerical results for the velocity and temperature fields of the fluid, and, the concentration profile and the deposition velocity of the particles are obtained and presented graphically as a function of pertinent parameters. The importance of Cunningham correction on the concentration profile and deposition velocity of ultrafine (sub-micron to nanometer) particles is demonstrated. It is found that the thicknesses of both the hydrodynamic boundary layer and thermal boundary layer increase with an increase in magnetic field parameter. The deposition velocity decreases with an increase in particle diameter dp (i.e an increase in particle Schmidt number Sc), usually decreases with an increase in magnetic field parameter ζ, and increases with an increase in the value of the coefficient of diffusion due to temperature gradient DT. It is shown that for the cold plate facing downward, the thermal drift of particles assists Brownian diffusion. For the heated plate facing upward, the thermal drift away from the surface decreases the overall deposition velocity which decreases drastically above a certain particle size.

AEROSOL VARIABILITY OBSERVED WITH RPAS

Abstract. To observe the origin, vertical and horizontal distribution and variability of aerosol particles, and especially ultrafine particles recently formed, we plan to employ the remotely piloted aircraft system (RPAS) Carolo-P360 "ALADINA" of TU Braunschweig. The goal of the presented project is to investigate the vertical and horizontal distribution, transport and small-scale variability of aerosol particles in the atmospheric boundary layer using RPAS. Two additional RPAS of type MASC of Tübingen University equipped with turbulence instrumentation add the opportunity to study the interaction of the aerosol concentration with turbulent transport and exchange processes of the surface and the atmosphere. The combination of different flight patterns of the three RPAS allows new insights in atmospheric boundary layer processes. Currently, the different aerosol sensors are miniaturized at the Leibniz Institute for Tropospheric Research, Leipzig and together with the TU Braunschweig adapted to fit into the RPAS. Moreover, an additional meteorological payload for measuring temperature, humidity and turbulence properties is constructed by Tübingen University. Two condensation particle counters determine the total aerosol number with a different lower detection threshold in order to investigate the horizontal and vertical aerosol variability and new particle formation (aerosol particles of some nm diameter). Further the aerosol size distribution in the range from about 0.300 to ~5 μm is given by an optical particle counter.

Estimating bacteria emissions from inversion of atmospheric transport: sensitivity to modelled particle characteristics

Abstract. Model-simulated transport of atmospheric trace components can be combined with observed concentrations to obtain estimates of ground-based sources using various inversion techniques. These approaches have been applied in the past primarily to obtain source estimates for long-lived trace gases such as CO2. We consider the application of similar techniques to source estimation for atmospheric aerosols, using as a case study the estimation of bacteria emissions from different ecosystem regions in the global atmospheric chemistry and climate model ECHAM5/MESSy-Atmospheric Chemistry (EMAC). Source estimation via Markov Chain Monte Carlo is applied to a suite of sensitivity simulations, and the global mean emissions are estimated for the example problem of bacteria-containing aerosol particles. We present an analysis of the uncertainties in the global mean emissions, and a partitioning of the uncertainties that are attributable to particle size, activity as cloud condensation nuclei (CCN), the ice nucleation scavenging ratios for mixed-phase and cold clouds, and measurement error. For this example, uncertainty due to CCN activity or to a 1 μm error in particle size is typically between 10% and 40% of the uncertainty due to observation uncertainty, as measured by the 5–95th percentile range of the Monte Carlo ensemble. Uncertainty attributable to the ice nucleation scavenging ratio in mixed-phase clouds is as high as 10–20% of that attributable to observation uncertainty. Taken together, the four model parameters examined contribute about half as much to the uncertainty in the estimated emissions as do the observations. This was a surprisingly large contribution from model uncertainty in light of the substantial observation uncertainty, which ranges from 81–870% of the mean for each of ten ecosystems for this case study. The effects of these and other model parameters in contributing to the uncertainties in the transport of atmospheric aerosol particles should be treated explicitly and systematically in both forward and inverse modelling studies.

A model for the atmospheric transport of sea-salt particles in coastal areas

A model for the aerosol transport in the lower atmosphere is of great interest for studies on air and water quality. One of the difficulties of such a model is to provide the accurate source terms. In particular, for maritime environment, the production of particles generated at the air–sea interface by breaking waves largely varies in time and space (Piazzola et al., 2009). More particularly, near the coastal zone, the sea-spray aerosol fluxes depend on the development of the wave field. The present paper proposes some improvement of the model MACMod, published by Tedeschi and Piazzola (2011), which is dedicated to the transport of aerosol particles in the marine atmospheric boundary layer (MABL). Taking benefit of the experimental campaign MIRAMER conducted in the French Mediterranean in 2008, a new sea-spray source function has been introduced in the latter version of the model MACMod. This consists in a revisited version of the whitecap dependant formulation established by Monahan et al. (1986). The simulations were then validated using aerosol size distributions recorded on board the ship “Atalante” for different wind speeds. Error calculations show a good performance of the model since it predicts the aerosol concentration to within a maximum factor of 3 for particle radii between 0.5 to 5μm.

Trajectory analysis of atmospheric transport of fine particles, SO<sub>2</sub>, NO<sub>x</sub> and O<sub>3</sub> to the SMEAR II station in Finland in 1996–2008

Abstract. Trajectory statistical methods that combine in situ measurements of trace gas or particle concentrations and back trajectories calculated for corresponding times have proven to be a valuable approach in atmospheric research; especially in investigating air pollution episodes, but also in e.g. tracing the air mass history related to high vs. low concentrations of aerosol particles of different sizes at the receptor site. A concentration field method was fine-tuned to take the presumable horizontal error in calculated trajectories into account, tested with SO2 and validated by comparison against EMEP (European Monitoring and Evaluation Programme) emission data. In this work we apply the improved method for characterizing the transport of atmospheric SO2, NOx, O3 and aerosol particles of different size modes to a Finnish measurement station located in Hyytiälä (61°51' N, 24°17' E). Our method did not reproduce the EMEP emission soures, but proved useful for qualitative analysis on where the measured compounds come from, from one measurement station point of view. We applied it to study trends and seasonal variation in atmospheric pollutant transport during 13 yr at the SMEAR II (Station for Measuring Ecosystem-Atmosphere Interactions) station.

Velocity profiles in idealized model of human respiratory tract

This article deals with numerical simulation focused on velocity profiles in idealized model of human upper airways during steady inspiration. Three r gimes of breathing were investigated: Resting condition, Deep breathing and Light activity which correspond to most common regimes used for experiments and simulations. Calculation was validated with experimental data given by Phase Doppler Anemometry performed on the model with same geometry. This comparison was made in multiple points which form one cross-section in trachea near first bifurcation of bronchial tree. Development of velocity profile in trachea during steady inspiration was discussed with respect for common phenomenon formed in trachea and for future research of transport of aerosol particles in human respiratory tract.

Coupling of fog and marine microbial content in the near-shore coastal environment

Abstract. Microbes in the atmosphere (microbial aerosols) play an important role in climate and provide an ecological and biogeochemical connection between oceanic, atmospheric, and terrestrial environments. However, the sources and environmental factors controlling the concentration, diversity, transport, and viability of microbial aerosols are poorly understood. This study examined culturable microbial aerosols from a coastal environment in Maine (USA) and determined the effect of onshore wind speed and fog presence on deposition rate, source, and community composition. During fog events with low onshore winds (<2 m s−1) the near-shore deposition of microbial aerosols (microbial fallout) decreased with increasing wind speeds, whereas microbial fallout rates under clear conditions and comparable low wind speeds showed no wind speed dependence. Mean aerosol particle size also increased with onshore wind speed when fog was present, indicating increased shoreward transport of larger aerosol particles. 16S rRNA sequencing of culturable ocean surface bacteria and microbial aerosols deposited onshore resulted in the detection of 31 bacterial genera, with 5 dominant genera (Vibrio, Bacillus, Pseudoalteromonas, Psychrobacter, Salinibacterium) making up 66 % of all sequences. The sequence library from microbial aerosol isolates, as with libraries found in other coastal/marine aerosol studies, was dominated at the phylum level by Proteobacteria, with additional representation from Firmicutes, Actinobacteria and Bacteroidetes. Seventy-five percent of the culturable microbial aerosols falling out under foggy conditions were most similar to GenBank-published sequences detected in marine environments. Using a 97 % similarity cut-off, sequence libraries from ocean surface and fog isolates shared eight operational taxonomic units (OTU's) in total, three of which were the most dominant OTU's in the library, representing large fractions of the ocean (28 %) and fog (21 %) libraries. The fog and ocean surface libraries were significantly more similar in microbial community composition than clear (non-foggy) and ocean surface libraries, according to both Jaccard and Sorenson indices. These findings provide the first evidence of a difference in community composition and microbial culturability of aerosols associated with fog compared to clear conditions. The data support a dual role for fog in enhancing the fallout of viable microbial aerosols via increased gravitational settling rates and decreased aerosolization stress on the organisms, which may include relief from UV inactivation, desiccation, and oligotrophic microconditions. This study provides a strong case for ocean to terrestrial transport of microbes and a potential connection between water quality and air quality at coastal sites.

Predictions and detection of the “accommodation” forces on Janus particles subjected to directed radiation in a rarefied gas

The results of theoretical and experimental study of so-called “accommodation” forces acting on particles with artificial asymmetry of surface properties in rarefied gas in the directed radiation field are presented. The gas-kinetic theory of phenomenon in the free-molecular regime for some different types of boundary conditions of gas-surface interactions is developed. The theory predicts appearance of the unusual force caused by the difference of the normal momentum accommodation coefficients on hemispheres of considered model Janus particle. The measurements conducted by the experimental technique with macroparticles have confirmed the existence of the accommodation forces affecting a particle together with the forces of radiometric photophoresis. The experimental results for the system “steel particle–helium” are in good agreement with theoretical predictions, and the ratio of the “accommodation” forces to the photophoretic force does not exceed 3%. The estimations show that the “accommodation” forces can be comparable in some cases with the radiometric photophoretic forces for micron-sized particles in stratosphere, but do not exceed the gravity force. The action of “accommodation” forces, in our opinion, is not capable to provide effective vertical transport of aerosol particles against gravity at stratospheric altitudes.

Characterization of Atmospheric Organic and Elemental Carbon of PM2.5 in a Typical Semi-Arid Area of Northeastern China

ABSTRACTIn the spring of 2006, daily particulate matter (PM2.5) aerosol samples were collected in Tongyu, a semi-arid area in northeastern China. The concentrations of organic carbon (OC) and elemental carbon (EC) were determined with a thermal/optical carbon analyzer in the filter samples. The average concentrations of OC and EC in PM2.5 were 14.1 ± 8.7 and 2.0 ± 1.3 μg/m3, respectively. A good correlation between OC and EC was observed during the spring season, suggesting that they might be derived from similar sources. The correlation between OC and K+ was high (R = 0.74), and the K+/OC ratio, as determined from their linear regression slope, reached 2.57. The good correlation and high K+/OC ratio indicated that biomass-burning was probably one of the major sources of OC in this region. The concentrations of estimated secondary organic carbon (SOC) in PM2.5 in Tongyu ranged from below the detection limit to 26.1 μg/m3 (mean, 5.9 μg/m3). The percentages of SOC in OC and in PM2.5 mass were 42.0% and 2.1%, respectively. The SOC concentrations during dust storm (DS) periods were higher than those during non-dust storm (NDS) ones, suggesting that chemical reaction processes involving gas-particle conversion occurred during the long-distance transport of aerosol particles.

A novel approach for the characterization of transport and optical properties of aerosol particles near sources – Part I: Measurement of particle backscatter coefficient maps with a scanning UV lidar

The physical and chemical properties of aerosols emitted from a livestock farm were determined by a novel approach which combines high-resolution lidar measurements (0.33 s, 30 m) with simulations of a microphysics–chemistry–transport model. This first of two companion papers describes the scanning lidar measurements of optical particle properties. The lidar system employed laser radiation at a wavelength of 355 nm with a power of 9 W and a pulse repetition rate of 30 Hz. The laser beam was expanded before transmission to the atmosphere so that it became eye-safe at distances >270 m to the lidar. The elastic backscatter signal was detected with a resolution of 0.033 s and 3 m. A receiving telescope with a primary-mirror diameter of 40 cm was used. For this system, we developed a novel method for two-dimensional retrievals of the particle backscatter coefficient. With this set up and approach, the lidar was able to identify the aerosol plume up to a range of ∼2.5 km from the source, a farm in northern Germany, in daytime. The measurements confirm that the optical particle properties of the emission plume vary largely with distance from the source and that the maximum particle backscatter coefficient is found away from the source. Within a close-to-horizontal scan (elevation angle of 2.3°), we found a mean particle backscatter coefficient of 1.5·10 −5 m −1 sr −1 inside the plume between 1.5 and 2.0 km distance from the source. Subtraction of the mean particle backscatter coefficient of the background aerosol present in this case (4.1·10 −6 m −1 sr −1 ) yields a particle backscatter coefficient of the livestock aerosols of 1.1·10 −5 m −1 sr −1 . The limited extend of the plume is revealed with the scanning lidar: Scans with a slightly higher elevation angle of 4.8° did not pick up the plume.

A novel approach for the characterisation of transport and optical properties of aerosol particles near sources – Part II: Microphysics–chemistry-transport model development and application

Abstract A new high-resolution microphysics–chemistry-transport model (LES-AOP) was developed and applied for the investigation of aerosol transformation and transport in the vicinity of a livestock facility in northern Germany (PLUS1 field campaign). The model is an extension of a Large-Eddy Simulation (LES) model. The PLUS1 field campaign included the first deployment of the new eye-safe scanning aerosol lidar system of the University of Hohenheim. In a combined approach, model and lidar results were used to characterise a faint aerosol source. The farm plume structure was investigated and the absolute value of its particle backscatter coefficient was determined. Aerosol optical properties were predicted on spatial and temporal resolutions below 100 m and 1 min, upon initialisation by measured meteorological and size-resolved particulate matter mass concentration and composition data. Faint aerosol plumes corresponding to a particle backscatter coefficient down to 10−6 sr−1 m−1 were measured and realistically simulated. Budget-related quantities such as the emission flux and change of the particulate matter mass, were estimated from model results and ground measurements.

Effects of LES sub‐grid flow structure on particle deposition in a plane channel with a ribbed wall

AbstractTransport and deposition of aerosol particles in a plane channel with a ribbed wall are studied in order to investigate the effects of the turbulent flow structure on particle deposition. In this paper, kinematic simulation (KS) has been adapted to be a sub‐grid model for particles, in conjunction with large eddy simulation (LES) in real space with boundaries. KS is a Lagrangian model of turbulent dispersion that takes into account the effects of spatio‐temporal flow structure on particle dispersion. It is a unified Lagrangian model of one‐, two‐ and indeed multi‐particle turbulent dispersion and can easily be used as a Lagrangian sub‐grid model for LES codes, thus enabling complex geometry to be taken into account. To study the effect of small‐scale flow structures on particle deposition in the ribbed channel flow, we use a validated LES code to simulate the flow field, and KS to model the sub‐grid flow structures. Thus, the large scales are resolved by the simulation and the small scales are modelled using various sub‐grid models. As none of the existing sub‐grid models is known to have taken into account the effects of small‐scale turbulent flow structures on particle deposition, it is important to use KS's ability to remodel the sub‐grid velocity field and thereby incorporate its effect on particle deposition. The parameters of our simulations for LES are the Reynolds number, width of the channel, height of the rib and sub‐gridmodel parameters. For KS, the parameters are the energy dissipation rate obtained from LES, the energy spectra, ratio of the largest and smallest sub‐grid scales and the total number of modes for the sub‐grid velocity field. The turbulent flow features thus obtained are compared with published experimental data in a ribbed channel. Our results suggest that while the small‐scale (sub‐grid) turbulent flow structures have negligible effects on particles with large relaxation times (compared with the Kolmogorov dissipation time scale), deposition of the particles with small relaxation times in the ribbed channel can be affected by these sub‐grids. Copyright © 2008 John Wiley & Sons, Ltd.

Particle Loss Calculator – a new software tool for the assessment of the performance of aerosol inlet systems

Abstract. Most aerosol measurements require an inlet system to transport aerosols from a select sampling location to a suitable measurement device through some length of tubing. Such inlet systems must be optimized to minimize aerosol sampling artifacts and maximize sampling efficiency. In this study we introduce a new multifunctional software tool (Particle Loss Calculator, PLC) that can be used to quickly determine aerosol sampling efficiency and particle transport losses due to passage through arbitrary tubing systems. The software employs relevant empirical and theoretical relationships found in established literature and accounts for the most important sampling and transport effects that might be encountered during deployment of typical, ground-based ambient aerosol measurements through a constant-diameter sampling probe. The software treats non-isoaxial and non-isokinetic aerosol sampling, aerosol diffusion and sedimentation as well as turbulent inertial deposition and inertial deposition in bends and contractions of tubing. This software was validated through comparison with experimentally determined particle losses for several tubing systems bent to create various diffusion, sedimentation and inertial deposition properties. As long as the tube geometries are not "too extreme", agreement is satisfactory. We discuss the conclusions of these experiments, the limitations of the software and present three examples of the use of the Particle Loss Calculator in the field.

Critical Review of Aerosol Particle Transport Models for Building HVAC Ducts

Literature on aerosol behavior in conventional heating ventilating and air conditioning duct systems that is directly applicable to modeling and simulation of deposition and resuspension of particulate matter is reviewed. Open literature discussing particle resuspension from duct surfaces is rare and most studies investigating particle deposition consider only clean duct surfaces. There is a similar lack of studies on particle deposition and resuspension in mechanical components found in air distribution systems (e.g., heat exchangers, fans, dampers, etc.) and in duct flows where the turbulent velocity profile is not fully developed. An example calculation of penetration through a simple duct system illustrates the characteristics of results produced by the identified modeling methods.

Modeling the process of methane-air plume extinguishing by a solid-propellant pulse aerosol generator

Operation of a pulse aerosol system of fire fighting designed for effective extinguishing of fires in gas wells is modeled by an example of quenching a methane-air subsonic plume escaping from a nozzle. The system consists of two separate parts: a charge of a unitary solid propellant (gas generator) and a container with fine-grain powder of a flame retardant. The combustion of the mixture is described by a one-step global reaction; the effect of the concentration of flame-retardant vapors on the combustion process is taken into account through reduction of the pre-exponent in the Arrhenius law and is described by an empirical dependence. A computational experiment shows that the use of the pulse aerosol system of fire fighting ensures effective transport of fine aerosol particles of the flame retardant and its vapors to the combustion zone in amounts sufficient to suppress the ignition spot.

Mathematical Modeling of Transport of Aerosol Particles in a Shredded Porous Medium

A new mathematical method is proposed to model the transport of polydisperse submicron aerosol particles in a heterogeneous porous media, and as an example, it is applied to study the transport of mainstream smoke aerosol particles in the cigarette tobacco column. The tobacco column is composed of randomly distributed pores and the aerosol particle transport is modeled utilizing a pore sub-model and taking into account aerosol particle coagulation and deposition.