Deposition Velocity Research Articles

Two-phase modelling for sediment water mixtures above the limit deposit velocity in horizontal pipelines

Abstract In dredging applications, deep sea mining and land reclamation projects typically large amounts of sediments are transported through pipes in the form of hyper concentrated (40% sediment or more) sediment-water mixtures or slurries. In this paper it is investigated how well a generic Euler-Euler CFD-model is capable to model velocity, concentration profiles and the pressure gradient of sediment above deposition limit velocity in a pipeline. This Euler-Euler solver treats both phases as a continuum with its own momentum and continuity equations. The full kinetic theory for granular flows is accounted for (no algebraic form is used) and is combined with a buoyant k-ε turbulence model for the fluid phase. The influence of the mesh size has been checked and grid convergence is achieved. All numerical schemes used are of second-order accuracy in space. The pressure gradient was calibrated by adjusting the specularity coefficient in one calibration case and kept constant afterwards. Simulations were carried out in a wide range of slurry flow parameters, in situ volume concentration (9–42%), pipe diameter (0.05–0.90 m), particle diameter (90–440 μm) and flow velocity of (3–7 m/s). The model shows satisfactory agreement to experimental data from existing literature.

Atmospheric Hydrogen Peroxide (H2O2) at the Foot and Summit of Mt. Tai: Variations, Sources and Sinks, and Implications for Ozone Formation Chemistry

AbstractHydrogen peroxide (H2O2) acts as a terminal sink for atmospheric HOx radicals (OH and HO2), playing a key role in tropospheric O3 formation. However, there are few field measurements of atmospheric H2O2 to assess its role in O3 formation, especially for the seriously polluted region of the North China Plain. In this study, H2O2 concentrations were measured at the foot of Mt. Tai from May to July 2018 and the summit of Mt. Tai from May to June 2019, with average values of 0.93 ± 1.01 and 2.05 ± 1.20 ppb, respectively. H2O2 exhibited a pronounced diurnal variation with a noon‐peak at the foot of Mt. Tai, which could be well reproduced by a gas‐phase box model with H2O2 dry deposition velocity of 3 cm s−1 included, indicating H2O2 was mainly photochemically produced. Modeling analysis showed H2O2 production at the foot was most sensitive to alkenes and aromatics, while the source and sink for H2O2 were dominated by HO2 recombination and dry deposition, respectively. Compared with the summer‐measurement in 2007, the remarkable elevation of H2O2 at the summit might be ascribed to volatile organic compounds (VOCs) increase and SO2 decline. Both H2O2‐O3 correlation and H2O2/NOz ratio suggested O3 formation at the foot of Mt. Tai was mainly VOC‐sensitive in the early morning and shifted to NOx‐sensitive thereafter. Therefore, reduction of VOCs emission especially for the reactive species of alkenes and aromatics in the morning as well as NOx emission around noontime will be effective for mitigating the serious O3 (as well as H2O2) pollution in Tai'an city.

Relation between Spherulitic Growth, Molecular Organization, and Charge Carrier Transport in Meniscus‐Guided Coated Organic Semiconducting Films (Adv. Electron. Mater. 8/2021)

Meniscus-Guided Coating Tomasz Marszalek, Wojciech Pisula, and colleagues show how the size and orientation of spherulitic domains of a molecular semiconductor are controlled by the deposition velocity during meniscus-guided coating in article number 2100397. By tuning the thin film morphology into large domains, the charge carrier transport in field-effect transistors is improved.

Hybrid TSA‐RBFNN based approach for MPPT of the solar PV panel under the effects of tilt angles variations and environmental effects

This paper proposes a hybrid approach to improve the performance of photovoltaic (PV) system and track the maximum system power. The proposed hybrid approach is the combination of Tunicate Swarm algorithm (TSA) and Radial Basis Function Neural Network (RBFNN), hence it is called TSA-RBFNN. The main contribution of this paper is to “achieve the best output from solar system by tilt angles variations and environmental effects, like dust accumulation, water drops, partial shading, and maximum power point tracking (MPPT) of the solar PV panel. Here, tilt angle and orientation angles are important factor for obtaining the maximal power of the photovoltaic system with consequently the power fed to load in the PV system. The voltage, current, and PV system power are used to analyze the effect of any particle size and any weight of coal for the performance of PV modules. TSA is used to measure the PV module voltage, current, and power, then it generates a possible dataset in the offline way. The dataset has electrical parameters that are used to create a model by using RBFNN in the online way. In addition, the determination of cleaning frequency is also developed for dirty PV modules depending upon the dust deposition velocity, then the correlation among deposited dust density including power performance of photovoltaic module. The proposed method is activated in MATLAB/Simulink site under four different test cases and the efficiency is compared with other existing methods. Furthermore, optimum solutions for proposed technique, the current, voltage, power are also analyzed. In 100 iterations, the first order statistic evaluation for all the cases is obtained using proposed and existing techniques such as ANN, GBDT, SSA, and SSA-GBDT technique. In addition, the dependability, sensitivity, and accuracy of the proposed technique are also obtained. Computation time using various number of trails of proposed and existing techniques is analyzed for 100, 150, 200, 250, and 500 trails. The proposed technique achieves the trail number of 100, 150, 200, 250, and 500 trails is 48.1740 seconds, 51.2133 seconds, 71.0483 seconds, 60.00126 seconds, and 57.80132 seconds.

Towards improved models for indoor air chemistry: A Monte Carlo simulation study

Model predictions are sensitive to a number of complex and often coupled input parameters. Some of these parameters have a wide range of acceptable values from literature and therefore choosing the appropriate value is non-trivial. In this paper, we use the INdoor Detailed Chemical Model (INDCM) to perform a Monte Carlo analysis, in which a wide but realistic range of model input parameter values is stochastically varied over 1000 model runs. The model output defines the likely range of the model performance, and directly correlates input parameter values with predicted indoor air species concentrations. The air exchange rate or the ozone deposition velocity onto internal materials such as painted walls, control the predicted concentrations of ozone, hydroxyl and peroxy radicals and peroxyacetyl nitrate species for our study conditions. The transmission of UV light from outdoors showed the strongest Spearman's rank positive correlation coefficients with predicted hydroxyl radical (0.92), and organic nitrate (0.95) concentrations. The deposition rate of ozone onto painted walls shows the strongest negative correlations with 4-oxopentanal (−0.86) and acetic acid (−0.83). Reducing the uncertainty around transmission of UV light indoors and ozone deposition rates onto surfaces reduces the model uncertainty by up to 70–80% for ozone and hydroxyl radical concentrations. Some species concentrations showed complex relationships with the various input parameters. For instance, maximum isoprene concentrations decreased with air exchange rate, but minimum isoprene concentrations were largely invariant. Emissions from human breath ensured that isoprene was always present in our model runs. However, its removal rate varied with the air exchange rate, which affected the concentrations of ozone and hydroxyl radicals (which can both chemically remove isoprene), and the direct removal rate by ventilation. Finally, we used our results to understand the 95% confidence bounds around our median predicted concentrations. For hydroxyl radicals, these were ±60% of the median value.

Role of oceanic ozone deposition in explaining temporal variability in surface ozone at High Arctic sites

Abstract. Dry deposition is an important removal mechanism for tropospheric ozone (O3). Currently, O3 deposition to oceans in atmospheric chemistry and transport models (ACTMs) is generally represented using constant surface uptake resistances. This occurs despite the role of solubility, waterside turbulence and O3 reacting with ocean water reactants such as iodide resulting in substantial spatiotemporal variability in O3 deposition and concentrations in marine boundary layers. We hypothesize that O3 deposition to the Arctic Ocean, having a relatively low reactivity, is overestimated in current models with consequences for the tropospheric concentrations, lifetime and long-range transport of O3. We investigate the impact of the representation of oceanic O3 deposition to the simulated magnitude and spatiotemporal variability in Arctic surface O3. We have integrated the Coupled Ocean-Atmosphere Response Experiment Gas transfer algorithm (COAREG) into the mesoscale meteorology and atmospheric chemistry model Polar-WRF-Chem (WRF) which introduces a dependence of O3 deposition on physical and biogeochemical drivers of oceanic O3 deposition. Also, we reduced the O3 deposition to sea ice and snow. Here, we evaluate WRF and CAMS reanalysis data against hourly averaged surface O3 observations at 25 sites (latitudes > 60∘ N). This is the first time such a coupled modeling system has been evaluated against hourly observations at pan-Arctic sites to study the sensitivity of the magnitude and temporal variability in Arctic surface O3 on the deposition scheme. We find that it is important to nudge WRF to the ECMWF ERA5 reanalysis data to ensure adequate meteorological conditions to evaluate surface O3. We show that the mechanistic representation of O3 deposition over oceans and reduced snow/ice deposition improves simulated Arctic O3 mixing ratios both in magnitude and temporal variability compared to the constant resistance approach. Using COAREG, O3 deposition velocities are in the order of 0.01 cm s−1 compared to ∼ 0.05 cm s−1 in the constant resistance approach. The simulated monthly mean spatial variability in the mechanistic approach (0.01 to 0.018 cm s−1) expresses the sensitivity to chemical enhancement with dissolved iodide, whereas the temporal variability (up to ±20 % around the mean) expresses mainly differences in waterside turbulent transport. The mean bias for six sites above 70∘ N reduced from −3.8 to 0.3 ppb with the revision to ocean and snow/ice deposition. Our study confirms that O3 deposition to high-latitude oceans and snow/ice is generally overestimated in ACTMs. We recommend that a mechanistic representation of oceanic O3 deposition is preferred in ACTMs to improve the modeled Arctic surface O3 concentrations in terms of magnitude and temporal variability.

Deposition Process and Equivalent Markov Motion of High-Inertia Particles in a Long Straight Pipeline

Abstract Two methods are used to study the process of particle deposition in a turbulent pipe flow. The Monte Carlo method tracks 10,000 particles in the turbulent pipe flow to reproduce the deposition process of the particles. The deposition velocity of the particles is determined by calculating the proportion of particles passing through the test section. The simplified deposition model uses an equivalent Markov motion instead of the radial movement of the particle in the turbulent core. The probability that a particle leaves the turbulent core depends on the radial particle position and the probability density distribution of the random vortex. The probability that a particle penetrates the boundary layer can be solved by integrating the probability density distribution of radial particle velocity. The deposition velocity of particles can be obtained by calculating the probability of an individual particle leaving the turbulent core and penetrating the boundary layer. Five experimental data series from the literature are applied to examine the predictive abilities of the two methods. The results demonstrate that the Monte Carlo method can be properly used to track the particle deposition process in the diffusion–impaction and inertia-moderated regimes. The simplified model is suitable for high-inertia particles.

Evaluating the Impact of a Wall-Type Green Infrastructure on PM10 and NOx Concentrations in an Urban Street Environment

Nature-based solutions can represent beneficial tools in the field of urban transformation for their contribution to important environmental services such as air quality improvement. To evaluate the impact on urban air pollution of a CityTree (CT), an innovative wall-type green infrastructure in passive (deposition) and active (filtration) modes of operation, a study was conducted in a real urban setting in Modena (Italy) during 2017 and 2018, combining experimental measurements with modelling system evaluations. In this work, relying on the computational resources of CRESCO (Computational Centre for Research on Complex Systems)/ENEAGRID High Performance Computing infrastructure, we used the air pollution microscale model PMSS (Parallel Micro-SWIFT-Micro SPRAY) to simulate air quality during the experimental campaigns. The spatial characteristics of the impact of the CT on local air pollutants concentrations, specifically nitrogen oxides (NOx) and particulate matter (PM10), were assessed. In particular, we used prescribed bulk deposition velocities provided by the experimental campaigns, which tested the CT both in passive (deposition) and in active (filtration) mode of operation. Our results showed that the PM10 and NOx concentration reductions reach from more than 0.1% up to about 0.8% within an area of 10 × 20 m2 around the infrastructure, when the green infrastructure operates in passive mode. In filtration mode the CT exhibited higher performances in the abatement of PM10 concentrations (between 1.5% and 15%), within approximately the same area. We conclude that CTs may find an application in air quality hotspots within specific urban settings (i.e., urban street canyons) where a very localized reduction of pollutants concentration during rush hours might be of interest to limit population exposure. The optimization of the spatial arrangement of CT modules to increment the “clean air zone” is a factor to be investigated in the ongoing development of the CT technology.

Effects of salinity on solid particle settling velocity in non-Newtonian Herschel\u2013Bulkley fluids

Settling velocity or depositional velocity is considered a key parameter to account for in the drilling technology of oil and gas wells as well as hydrocarbon processing since an accurate estimation of this parameter allows the transport of cuttings efficiently, avoids non-productive time, and helps avoid costly problems. Understanding the settling velocity in fluid with high salinity will help for the better separation of oil and natural gas streams in processing facilities. Although a great amount of effort was given to rheology and settling velocity measurements for power-law fluid and Bingham fluids, there are limited studies available in the literature for Herschel–Bulkley (H–B) fluid with salinity. The present study analyzes the fluid rheology of non-Newtonian fluids with, and without, salinity. Moreover, experiments have been conducted to measure the settling velocity of different diameters of solid particles through Herschel–Bulkley fluids with various salinity conditions. For the rheology analysis, it is found that higher weight percentages of NaCl lead to low values of shear stresses. As well, higher weight percentages of CaCl2 concentration result in a slight increase in shear stresses per a given shear rate. On the other hand, higher percentages of salt concentration cause an increase in the terminal velocity.

Thermophoretic particle deposition in the flow of dual stratified Casson fluid with magnetic dipole and generalized Fourier's and Fick's laws

Thermophoretic particle deposition is one of the most rudimentary processes for transferring small particles over a temperature gradient, and it is vital in aero-solution and electronic engineering. In the proposed model, it is intended to explore heat and mass transfer on double-diffusive electrically non-conducting Casson fluid in the two-dimensional flow past a stretching surface with thermophoretic particle deposition. An external magnetic field is subjected to a magnetic dipole. The analysis of Casson fluid along magnetic dipole represents the ferromagnetic fluid. As a consequence of the presence of ferrite particles, the fluid has magnetic properties and is thus a non-Newtonian Casson ferrofluid. Moreover, to enclose heat and mass transfer characteristics, thermal and solutal stratifications are also employed. An eminent bvp4c technique in MATLAB is incorporated to compute these ODEs numerically. Graphical representations of important parameters and their physical behavior are extensively analyzed. The Nusselt number, thermophoretic particle deposition velocity, and drag force coefficient are also addressed graphically. The findings demonstrate that as the values of thermophoretic coefficient and thermophoretic parameter increase, the mass transfer rate diminishes. Further, with the escalating values of the ferromagnetic interaction parameter, the velocity field is reduced but the opposite trend is seen for the thermal field.

Eddy covariance measurements of ozone flux above and below a southern subtropical forest canopy

While extensive eddy covariance (EC) measurements of ozone (O3) flux have been reported in American and European forests, such measurements in Asian forests are scarce. Here, we presented the first EC measurements of O3 flux at two levels (above and below the canopy) in a Chinese forest. Above the canopy, O3 always moved downward, with a maximum O3 flux intensity of −15 ~ −10 nmol m−2 s−1 occurring at 9:00–14:00 LT and a maximum O3 deposition velocity of 1.23 cm s−1 occurring at 9:00 LT; both of these values fell to nearly 0 at night. The O3 deposition flux and O3 deposition velocity below the canopy were both lower than those above the canopy. This discrepancy reached the maximum at 9:00–15:00 local time (LT), with the O3 deposition flux and O3 deposition velocity below the canopy being approximately 35 and 42% of those above the canopy, respectively. The O3 flux was well correlated with the CO2 flux and the latent heat flux, suggesting the important role of stomatal uptake in O3 deposition. The O3 deposition velocity increased with the increase in the air temperature, relative humidity, photosynthetically active radiation and friction velocity, but when these meteorological factors exceeded their optimum values, the increase in the O3 deposition velocity tended to be flat. These findings advanced our understanding of the interactions between forests and the atmosphere. This unique dataset is also of great significance for the validation of relevant models concerned with the various impacts of the rapid increase in global O3 concentrations.

Dosimetry of radon progeny deposited on skin in air and thermal water.

It is held that the skin dose from radon progeny is not negligibly small and that introducing cancer is a possible consequence under normal circumstances as there are a number of uncertainties in terms of related parameters such as activity concentrations in air and water, target cells in skin, skin covering materials, and deposition velocities. An interesting proposal has emerged in that skin exposure to natural radon-rich thermal water as part of balneotherapy can produce an immune response to induce beneficial health effects. The goal of this study was to obtain generic dose coefficients with a focus on the radon progeny deposited on the skin in air or water in relation to risk or treatment assessments. We thus first estimated the skin deposition velocities of radon progeny in air and thermal water based on data from the latest human studies. Skin dosimetry was then performed under different assumptions regarding alpha-emitting source position and target cell (i.e. basal cells or Langerhans cells). Furthermore, the impact of the radon progeny deposition on effective doses from all exposure pathways relating to ‘radon exposure’ was assessed using various possible scenarios. It was found that in both exposure media, effective doses from radon progeny inhalation are one to four orders of magnitude higher than those from the other pathways. In addition, absorbed doses on the skin can be the highest among all pathways when the radon activity concentrations in water are two or more orders of magnitude higher than those in air.

Cooling in Poor Air Quality Environments—Impact of Fan Operation on Particle Deposition

Environmental pollutants are a source for reliability issues across data center and telecommunications equipment. A primary driver of this is the transport and deposition of particle matter (PM$_{2.5}$, PM$_{10}$) on printed circuit boards, electronic components and heat exchange surfaces. This process is enhanced by turbulent air flows generated from cooling fans. Particle pollutants can persist after contemporary filtering, highlighting the importance of elucidating particle transport mechanisms and utilising this information to design robust equipment. This study investigates particle transport behaviour arising from axial fans operating under varied aerodynamic conditions. Transient, multi-phase numerical simulations were performed to model the flow of millions of microscale particles in air and determine their fate. Across a comprehensive range of fan operation conditions, from aerodynamic stall to free delivery, non-dimensional deposition velocities spanned an order of magnitude. Deposition profiles vary from monotonic to non-monotonic behaviour, influenced by local flow impingement, blade tip vortices, and shear velocity. A simple flow control solution that mitigates the factors influencing deposition has been demonstrated for equipment already deployed. The findings and numerical methods can be applied for the optimization of fan-cooled equipment intended for indoor and outdoor environments where air quality is poor, or pollution levels are high.

Impact of magnetic dipole on thermophoretic particle deposition in the flow of Maxwell fluid over a stretching sheet

The current analysis explores the impact of thermophoretic particle deposition and magnetic dipole in the flow of Maxwell liquid over a stretching sheet. Using suitable transformations, the modelling equations are changed into a system of ordinary differential equations (ODEs). Finally, the Runge Kutta Fehlberg 45 (RKF 45) process with shooting technique is then utilized to solve these equations numerically. The impact of relevant parameters on flow fields, heat and mass transfer along with skin friction, Sherwood number, thermophoretic diffusive deposition velocity and Nusselt number are studied and discussed in detail using graphical representations. Results reveal that, the improvement in ferromagnetic interaction parameter value deteriorates the velocity gradient but improves heat and mass transfer. Also, when compared to Maxwell fluid, the heat transfer characteristics of Newtonian liquid is sturdily affected and decays faster for boost up values of both thermophoretic parameter and thermophoretic coefficient. The escalating values of Schmidt number and Maxwell parameter progresses the thermophoretic diffusive deposition velocity but, converse trend is depicted for escalation values of thermophoretic parameter.

Determination of Limit Deposition Velocity and Viscosity in Waste Brines Transported in Pipelines

AbstractThe wastewater generated in the potash mines of the Bages region in Catalonia (Spain) was experimentally tested at the Paterson & Cooke slurry test facility in Cape Town, South Africa, to d...

Nitric acid dry deposition associated with equilibrium shift of ammonium nitrate above a forest by long-term measurement using relaxed eddy accumulation

The dry deposition process of nitrogen compounds still has considerable uncertainty due to the complex compound behavior in the atmosphere. To enhance understanding of the nitric acid (HNO3) dry deposition process that largely contributes to the total nitrogen deposition, we associate this process with the equilibrium shift of ammonium nitrate (NH4NO3) to HNO3 and ammonia (NH3) near the surface. We obtained the flux of HNO3 and PM2.5 components above a forest in suburban Tokyo using a relaxed eddy accumulation (REA) system incorporating the denuder/filter-pack sampling technique. We conducted continuous samplings on a weekly basis over a long-term period, from October 14, 2016 to October 3, 2018, including leafy and leafless conditions. The measured deposition velocities of fine NO3− particles were significantly (p < 0.05) larger than those of fine SO42− particles and similar to those of HNO3, regardless of the leafy and leafless periods. The larger deposition velocities of fine NO3− particles caused by the equilibrium shift of NH4NO3 were found to be similar to previous measurements at the same site. The measured deposition velocities of HNO3 were low and included many emission cases compared to those of fine NO3− particles. The lower HNO3 deposition velocities were associated with the equilibrium shift of NH4NO3 to the gas phase, causing the suppressed deposition and apparent emission of HNO3, particularly during the leafless period. The emission of HNO3 is possibly due to high HNO3 concentration near the surface, which is attributed to a small removal of the leafless canopy. The turbulence enhanced both the upward and downward fluxes of HNO3. These results will contribute to the better understanding for the dynamics of the nitrogen compounds in the atmosphere and the accurate assessment for the nitrogen deposition.

Impact of thermophoretic particle deposition on heat and mass transfer across the dynamics of Casson fluid flow over a moving thin needle

In this current study, the steady, two-dimensional flow of an incompressible Casson fluid along a horizontal thin moving needle is investigated. Influence of Soret/Dufour effect and thermophoretic particle deposition is considered to examine the heat and mass transport analysis. This model finds application in designing of new medical equipment’s for cell delivery to the central nervous system. The efficient Runge–Kutta Fehlberg fourth fifth order method by adopting shooting technique is employed to solve the reduced non-dimensional form of equations. The impact of several non-dimensional parameters on concentration, velocity and thermal fields are discussed with the help of suitable graphs. Also, friction factor, heat passage rate and thermophoretic particle deposition velocity are analyzed graphically. Results reveal that, increase in Dufour number declines heat transfer but opposite behaviour is depicted in mass transfer. The increasing values of thermophoretic parameter improves the mass transfer. Thermophoretic diffusive deposition velocity increases for rising values of thermophoretic parameter.

Comparing i-Tree Eco Estimates of Particulate Matter Deposition with Leaf and Canopy Measurements in an Urban Mediterranean Holm Oak Forest.

Trees and urban forests remove particulate matter (PM) from the air through the deposition of particles on the leaf surface, thus helping to improve air quality and reduce respiratory problems in urban areas. Leaf deposited PM, in turn, is either resuspended back into the atmosphere, washed off during rain events or transported to the ground with litterfall. The net amount of PM removed depends on crown and leaf characteristics, air pollution concentration, and weather conditions, such as wind speed and precipitation. Many existing deposition models, such as i-Tree Eco, calculate PM2.5 removal using a uniform deposition velocity function and resuspension rate for all tree species, which vary based on leaf area and wind speed. However, model results are seldom validated with experimental data. In this study, we compared i-Tree Eco calculations of PM2.5 deposition with fluxes determined by eddy covariance assessments (canopy scale) and particulate matter accumulated on leaves derived from measurements of vacuum/filtration technique as well as scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (leaf scale). These investigations were carried out at the Capodimonte Royal Forest in Naples. Modeled and measured fluxes showed good overall agreement, demonstrating that net deposition mostly happened in the first part of the day when atmospheric PM concentration is higher, followed by high resuspension rates in the second part of the day, corresponding with increased wind speeds. The sensitivity analysis of the model parameters showed that a better representation of PM deposition fluxes could be achieved with adjusted deposition velocities. It is also likely that the standard assumption of a complete removal of particulate matter, after precipitation events that exceed the water storage capacity of the canopy (Ps), should be reconsidered to better account for specific leaf traits. These results represent the first validation of i-Tree Eco PM removal with experimental data and are a starting point for improving the model parametrization and the estimate of particulate matter removed by urban trees.

Aerosol acidity and liquid water content regulate the dry deposition of inorganic reactive nitrogen

Abstract. Ecosystem productivity is strongly modulated by the atmospheric deposition of inorganic reactive nitrogen (the sum of ammonium and nitrate). The individual contributions of ammonium and nitrate vary considerably over space and time, giving rise to complex patterns of nitrogen deposition. In the absence of rain, much of this complexity is driven by the large difference between the dry deposition velocity of nitrogen-containing molecules in the gas or condensed phase. Here we quantify how aerosol liquid water and acidity, through their impact on gas–particle partitioning, modulate the deposition velocity of total NH3 and total HNO3 individually while simultaneously affecting the dry deposition of inorganic reactive nitrogen. Four regimes of deposition velocity emerge: (i) HNO3 – fast, NH3 – slow, (ii) HNO3 – slow, NH3 – fast, (iii) HNO3 – fast, NH3 – fast, and (iv) HNO3 – slow, NH3 – slow. Conditions that favor partitioning of species to the aerosol phase strongly reduce the local deposition of reactive nitrogen species and promote their accumulation in the boundary layer and potential for long-range transport. Application of this framework to select locations around the world reveals fundamentally important insights: the dry deposition of total ammonia displays little sensitivity to pH and liquid water variations, except under conditions of extreme acidity and/or low aerosol liquid water content. The dry deposition of total nitric acid, on the other hand, is quite variable, with maximum deposition velocities (close to gas deposition rates) found in the eastern United States and minimum velocities in northern Europe and China. In the latter case, the low deposition velocity leads to up to 10-fold increases in PM2.5 nitrate aerosol, thus contributing to the high PM2.5 levels observed during haze episodes. In this light, aerosol pH and associated liquid water content can be considered to be control parameters that drive dry deposition flux and can accelerate the accumulation of aerosol contributing to intense haze events throughout the globe.

Experimental study of particle deposition on patterned microstructured surfaces in a chamber environment

Indoor respirable suspended particles may accumulate on textured surfaces such as sofa surfaces and office partitions via particle deposition. Previous studies mainly focus on particle deposition on non-patterned rough surfaces or patterned surfaces with texture scale larger than millimeters, and it is generally concluded that deposition rate increases due to the roughness. However, many indoor surfaces are patterned textures with scale in the order of 100 μm and there is a lack of study of particle deposition behavior in this regime. This study investigates the effect of patterned microstructured surfaces on particle deposition in a turbulent chamber. Different shapes (triangular, rectangular, semi-circular convex and semi-circular concave ribbed structures) and pitch-to-height ratios (i.e. ratio of spacing to height) of patterned structures were studied. Particle sizes ranging from 0.3 μm to 5 μm in diameter were tested. It is found that for submicron particles, deposition velocity was increased by the patterned microstructures, and triangular-ribbed surfaces achieved the highest deposition velocity, which was 10 times higher than that on a non-patterned surface. For micron particles, it is found that deposition velocity was lower than that of a non-patterned surface. Our results show that particle deposition is not always enhanced by roughness and it is possible to be reduced by a suitable length scale of patterned structures.