Size and mineral composition of airborne particles generated by an ultrasonic humidifier

This study describes the size distribution and concentration of particles expelled by a portable, 3‐L ultrasonic humidifier. The ultrasonic humidifier was filled with waters of varying mineral content and hardness. Aerosol size distributions were measured during 8 hours of humidifier operation in a typical bedroom. Humidifiers produced approximately 1.22 × 10¹⁰‐2.50 × 10¹⁰ airborne particles per milliliter of water consumed, resulting in airborne particle concentrations of 3.01‐5.91 × 10⁴ #/cm³, with modes ranging between 109 and 322 nm in diameter. The emission rate of particles varied by water type from 1.02 × 10⁹ to 2.27 × 10⁹ #/s. Lower mineral waters produced fewer, smaller particles when compared to higher mineral waters. Chemical analyses of particles collected with a cascade impactor indicated that the minerals in emitted particles had the same relative mineral concentrations as the fill water. Our results demonstrate that ultrasonic humidifiers should be considered a source of inhalation exposure to minerals dissolved in water, and that the magnitude of exposure to inhalable particles will vary with water quality.     

HEPA filtration improves asthma control in children exposed to traffic-related airborne particles

Traffic-related airborne particles are associated with asthma morbidity. The aim of this study was to assess the impact of a high-efficiency particulate air (HEPA) filtration on the concentrations of traffic particles and the resultant effect on children with asthma. Forty-three children with asthma were enrolled in this double-blind, placebo-controlled crossover design. A HEPA air cleaner or a placebo “dummy” was placed in participants’ homes for four weeks, interrupted by a one-month washout period, before crossing over to the other treatment arm for four weeks. Air sampling and health outcomes, including asthma control (ACQ) and quality of life (AQLQ) measures, were completed prior to and at the end of each treatment arm. Indoor concentrations of traffic particles were significantly reduced with the HEPA treatment but not with the “dummy” treatment. In participants with poorly controlled asthma and lower quality of life at baseline, ACQ and AQLQ scores were significantly improved (1.3 to 0.9, P = .003 and 4.9 to 5.5, P = .02, respectively) following the HEPA treatment. In this study, HEPA filtration is associated with improved clinical outcomes and quality of life measures in children with uncontrolled asthma.     

Transport of airborne particles within a room

The objective of this study is to test a technique used to analyze contaminant transport in the wake of a bluff body under controlled experimental conditions for application to aerosol transport in a complex furnished room. Specifically, the hypothesis tested by our work is that the dispersion of contaminants in a room is related to the turbulence kinetic energy and length scale. This turbulence is, in turn, determined by the size and shape of furnishings within the room and by the ventilation characteristics. This approach was tested for indoor dispersion through computational fluid dynamics simulations and laboratory experiments. In each, 3 mum aerosols were released in a furnished room with varied contaminant release locations (at the inlet vent or under a desk). The realizable k approximately epsilon model was employed in the simulations, followed by a Lagrangian particle trajectory simulation used as input for an in-house FORTRAN code to compute aerosol concentration. For the experiments, concentrations were measured simultaneously at seven locations by laser photometry, and air velocity was measured using laser Doppler velocimetry. The results suggest that turbulent diffusion is a significant factor in contaminant residence time in a furnished room. This procedure was then expanded to develop a simplified correlation between contaminant residence time and the number of enclosing surfaces around a point containing the contaminant. Practical Implications The work presented here provides a methodology for relating local aerosol residence time to properties of room ventilation and furniture arrangement. This technique may be used to assess probable locations of high concentration by knowing only the particle release location, furniture configuration, inlet and outlet locations, and air speeds, which are all observable features. Applications of this method include development of 'rules of thumb' for first responders entering a room where an agent has been released and selection of sampler locations to monitor conditions in sensitive areas.     

Opposite effects of inhaled cadmium microparticles on mouse susceptibility to an airborne bacterial and an airborne viral infection

An experimental study on 489 mice is reported. The test animals were submitted to a single 15-mn exposure to atmosphere containing about 10 mg of cadmium microparticles (CdO) per m³ of air and the controls to an equivalent amount of aluminium microparticles (Al₂O₃). At the 48^th hour after exposures, the test and control mice were submitted to a bacterial (Pasteurella multocida) or to a viral (Orthomyxovirus influenzae A) challenge, via the respiratory route. The exposure to cadmium significantly increased the death-rate of mice submitted to the bacterial challenge, but it significantly decreased the death-rate following the viral challenge.     

多孔介质中沉积颗粒脱离特性试验研究

开展沉积颗粒在多孔介质中脱离过程试验对研究地下水源热泵回灌堵塞过程有重要意义。利用自主研发的砂层沉积–脱离模拟试验系统,研究增加渗流速度和改变渗流方向对多孔介质中已沉积颗粒脱离特性的影响。结果表明:在改变渗流速度大小条件下,渗流速度越大,已沉积的颗粒越容易发生脱离,到达悬浮颗粒相对浓度第二次峰值所需的时间越短,而达到二次峰值时所注入的水量接近;与改变渗流速度大小相比,用改变渗流方向的方式进行沉积颗粒脱离效果更为明显,到达二次峰值所需时间更短、水量更少,但随着时间增加,多孔介质中又会出现类似渗流方向改变前的堵塞现象;渗流条件变化后的初始阶段是已沉积颗粒脱离的主要时期。研究结果为水源热泵回灌过程中悬浮颗粒在地层中的沉积-脱离特性进一步研究奠定了基础。     

Size distribution of airborne particles controls outcome of epidemiological studies

Epidemiological studies typically using wide size range mass metrics (e.g. PM₁₀) have demonstrated associations between airborne particulate matter and several adverse health outcomes. This approach ignores the fact that mass concentration may not correlate with regional lung dose, unlike the case of trace gases. When using measured particle size distributions as the basis for calculating regional lung dose, PM₁₀ mass concentration is found to be a good predictor of the mass dose in all regions of the lung, but is far less predictive of the surface area and particle number dose. On the other hand, measurements of particle number do not well predict mass dose, indicating that the chosen particle metric is likely to determine the health outcomes detectable by an epidemiological study. Consequently, epidemiological studies using mass metrics (PM_2.5 and PM₁₀) may fail to recognise important health consequences of particulate matter exposure, leading to an underestimate of the public health consequences of particle exposure.     

Study on dielectrophoretic deposition of airborne particles in a vertical micro channel

Airborne particles significantly contribute to the toxicity of environmental pollution. A mathematical model is developed and analyzed to study the dielectrophoretic deposition of airborne particles in a vertical micro channel. Finite element programs are utilized to calculate the air flow and potential distribution in the vertical micro channel. The electric field in the numerical solution space is obtained by employing a potential gradient in the x and y directions. The dielectrophoretic force and sedimentation motion of a spherical particle are achieved. The simulated results show that the dielectrophoretic force is maximal at the tips of the shorter electrode. The initial position of the particle, initial direction of the particle, radius of the particle, electrode dimension, applied voltage and air flow velocity are the main factors affecting the trajectories of airborne particles in a micro channel. Modification of the particle size distribution using the technology as a dielectrophoretic filter is more feasible in practice. Sedimentation micro channels in series with the shorter electrode on an alternating side will be beneficial to improve particle sedimentation efficiency.     

Influence of human movement on the transport of airborne infectious particles in hospital

The impacts of human movement on the distribution of airborne infectious particles in hospital environment are investigated numerically. In the case of airborne infection isolation room, the influence of different walking speeds on the distribution of respiratory droplets is investigated by adopting the Lagrangian method for tracing the motion of droplets, the dynamic mesh model for describing human walking and the Eulerian unsteady Reynolds-averaged Navier–Stokes model for solving the airflow. In the case of operating theatre, the impact of surgeon bending movement on the distribution of bacteria-carrying particles (BCPs) is investigated by using a similar approach, except that the drift-flux model is used for modelling BCPs distribution. The adopted models are successfully validated against reported experimental data. The results show that both walking speed and bending posture change considerably the suspended droplets concentration in a room. The key factors regarding the simulation techniques are discussed.     

Characterisation of indoor airborne particles by using real-time aerosol mass spectrometry

An Aerosol Time-of-Flight Mass Spectrometer (ATOFMS; TSI 3800) was deployed to Athens (Greece) during August 2003. The instrument provides information on a polydisperse aerosol, acquiring precise aerodynamic diameter (+/-1%) within the range 0.3 to 3 mum and individual particle positive and negative mass spectral data in real time. Sampling was carried out indoors and outdoors at an office in a building on a minor road in the city centre and various outdoor and indoor sources were identified. Specific outdoor particles such as dust and carbon particles were detected in indoor air. The generation of particles from indoor sources was studied and several different types of particle were found to be present in environmental tobacco smoke (ETS): three were potassium-rich (with differing proportions of carbon) emitted directly in the exhaled mainstream smoke. Two other types arose mainly when the cigarette was left smouldering on an ash-tray. Another particle type exhibited a strong signal at m/z 84, most likely due to a nicotine fragment. The temporal trend of this specific particle type showed likely condensation of semi-volatile constituents on existing potassium-rich particles. A release of insect repellent in the room was also successfully monitored.     

航空伽玛能谱数据在突泉地区铀成矿预测中的应用

受森林分布广、覆盖厚及矿体隐伏等因素制约,大兴安岭成矿带突泉地区铀找矿进展缓慢。航空伽玛能谱数据蕴含有丰富的铀矿化信息,除地表矿化信息外,亦含有部分深部铀矿化弱信息。在典型铀矿点地质特征及伽玛能谱特征分析的基础上,利用K、U、Th元素含量之间的地球化学特征差异,构建了3个航放参数模型(U高场、△U高值晕、N高值晕),增强航放微弱异常信息。在航放异常信息提取、优选的基础上,结合地质、化探等找矿有利信息,预测铀成矿远景区9处。其中4处远景区成矿地质条件优越,异常线索丰富,尚属铀矿空白区,在进一步工作中应引起重视。     

Histopathology of the digestive gland of an Antarctic limpet exposed to cadmium

Histopathological alterations induced experimentally with cadmium (Cd) in Antarctic limpets (Nacella concinna), exposed for different times and concentrations were compared to controls. At the light microscope level, samples exposed to the contaminant for short periods (6, 12 and 24 h) at two different concentrations (0.25 and 0.5 mg l(-1)) showed no alterations compared to controls. After 48 h of exposure at a 0.5 mg l(-1) Cd concentration, vacuolisation of the basophilic cells was observed. After 72 h exposure, there was a marked loss of all the digestive gland structure, with cell autolysis and loss of basophilia.     

Characterization of winter airborne particles at Emperor Qin's Terra-cotta Museum, China

Daytime and nighttime total suspended particulate matters (TSP) were collected inside and outside Emperor Qin's Terra-cotta Museum, the most popular on-site museum in China, in winter 2008. The purpose of this study was to investigate the contribution of visitors to indoor airborne particles in two display halls with different architectural and ventilating conditions, including Exhibition Hall and Pit No.1. Morphological and elemental analyses of 7-day individual particle samples were performed with scanning electron microscopy and energy dispersive X-ray spectrometer (SEM-EDX). Particle mass concentrations in Exhibition Hall and Pit No.1 were in a range of 54.7–291.7 μg m^− 3 and 95.3–285.4 μg m^− 3 with maximum diameters of 17.5 μm and 26.0 μm, respectively. In most sampling days, daytime/nighttime particle mass ratios in Exhibition Hall (1.30–3.12) were higher than those in Pit No.1 (0.96–2.59), indicating more contribution of the tourist flow in Exhibition Hall than in Pit No. 1. The maximum of particle size distributions were in a range of 0.5–1.0 μm, with the highest abundance (43.4%) occurred in Exhibition Hall at night. The majority of airborne particles at the Museum was composed of soil dust, S-containing particles, and low-Z particles like soot aggregate and biogenic particles. Both size distributions and particle types were found to be associated with visitor numbers in Exhibition Hall and with natural ventilation in Pit No.1. No significant influence of visitors on indoor temperature and relative humidity (RH) was found in either display halls. Those baseline data on the nature of the airborne particles inside the Museum can be incorporated into the maintenance criteria, display management, and ventilation strategy by conservators of the museum.     

A study to characterize the suspended particulate matter in an indoor environment in Delhi,India

To investigate potential particulate matter (PM) exposure, and the possible effective measures for interventions and assessment of sources in indoor environments, a pilot study was conducted at Jawaharlal Nehru University (JNU), New Delhi. The indoor particles were collected from 5th April to 26th June 2000, using a tapered element oscillating microbalance (TEOM). The particles were analyzed by gravimetry, atomic absorption spectrometry (AAS) and scanning electron microscopy (SEM) in order to investigate the mass concentration, physico-chemical properties and morphology of the particles. The gravimetric and AAS results confirmed that the suspended particulate matter (SPM) and metal concentrations were higher than the National Ambient Air Quality Standards (NAAQS) for Delhi. The maximum contributions of SPM were observed to be due to wind-blown crustal dust and vehicular pollution. The SEM analysis of particles showed the presence of a variety of particles, but confirmed the dominance of silicon and soot particles.     

Numerical simulation on a horizontal airflow for airborne particles control in hospital operating room

Provision of downward unidirectional clean air has been prevalent for decades in modern hospital operating rooms (ORs) to protect patients and surgeons from infectious airborne particles and has been found to be effective in reducing Surgical Site Infection (SSI), however, its shortcomings are inevitable. In this study we investigated an alternative of horizontal airflow pattern and the airflow performance in an OR with a dimension of 300 cm long, 296 cm wide and 240 cm high. We also evaluated the effectiveness of the horizontal unidirectional airflow to control infectious airborne particles through onsite test and computational fluid dynamics (CFD) simulation method. The investigation was focused mainly on the influence of the medical lamps and the thermal plume with different airflow patterns around the critical zone under the horizontal air supply system. Ultraclean air was supplied from a fan-filter unit. The patient and surgeon were assumed to be releasing 200 and 400 particles per minute, respectively. The results show that when the air supply and return facilities are installed on the same lateral wall to keep a state of horizontal flow ventilation in the OR, medical lamps and the thermal plume have no obvious influence on the horizontal airflow patterns around the critical zone in the OR, and performance of the air supply system is highly related to the relative position of the source to the wound.     

Mutagenicity and polycyclic aromatic hydrocarbons analysis of ambient airborne particles collected in Athens, Greece

Samples of airborne particulates from the Athens atmosphere were examined for mutagenicity and various polycyclic aromatic hydrocarbons (PAH). Extracts induced linear, dose-related increases in TA98 His+ revertants in the Ames/Salmonella assay and contained average benzo[a]pyrene (BaP) levels of 3.9 ng/m3 of air. The levels of revertants/m3 of the samples showed a linear relation to their BaP and benzo[b]-(BbF) + benzo[k]-fluoranthene (BkF) concentrations and were higher in areas with dense traffic than in industrial areas. It is suggested that the atmosphere of Athens favours the formation of secondary direct-acting mutagens due to the oxidation and nitration of PAH by ozone and nitrogen oxides, which are more abundant in the late spring months.     

Subway tunnel design using a ground surface settlement profile to characterize an acceptable configuration

Tunneling induced settlement is often a controlling factor in the design of a subway or underground facility due to the impact on adjacent or overhead infrastructure. A method is proposed that uses an acceptable ground surface settlement profile to generate a tunnel system configuration that reproduces the acceptable/tolerable settlement profile. A brief discussion of existing methods of tunnel settlement analysis and two (2) case studies illustrating the proposed method are presented. The chosen case studies are urban subgrade rail tunnels (subways) constructed in Istanbul, Turkey and Bangkok, Thailand. Each case study is used to illustrate the use of the bifurcated static back calculation – iterative finite element model prediction/solution method.The initial settlement profiles used for both case histories were measured settlement profiles obtained from the literature (Ercelbi et al., 2005, Suwansawat, 2002). These settlement profiles were assumed to be the tolerable settlement profiles for the subway systems. For each case history, the iterative static back calculation – finite element model ingested the individual literature obtained design settlement profile to identify an optimum tunnel configuration (depth and size) that will reproduce the design settlement profile. Comparisons were made between the as-built tunnel configuration and the tunnel configuration predicted using the proposed method.     

机载测量系统在大比例尺地形图测绘中的应用——以雄安新区为例

针对传统大范围基础测绘地形图更新工作资金投入多、安全隐患大、外业工作周期较长等问题,本文将机载测量系统应用到大范围地形图测绘中,详细介绍了机载激光雷达和航空摄影测量的系统检校、外业数据采集、内业处理等方法。通过工程应用实例表明,采用机载测量系统可以满足1∶2000地形图测绘工作的要求,有效减少外业测量工作量,是大范围基础地形图测绘工作的有效手段。     

基于机载LIDAR树木提取应用

随着3S技术的发展,机载LIDAR测量技术是一种新兴的对地探测和定位模式,逐渐广泛应用于铁路勘察设计、数字城市三维建模、航测等领域,尤其是数字化电力巡线,引起电网运营单位高度重视。基于此背景,利用机载LIDAR技术对实验区梅州市平原县焦富甲乙线路进行树障隐患检测,对激光点云从几何空间分布特征进行分析,以规则格网区域增长算法为基础,通过冠层高度模型CHM和拉普拉斯算子方法研究树木提取,最后实现树障在架空输电线路中安全性分析。