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.     

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.     

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.     

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.     

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.     

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.     

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.     

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。     

LED在南极科学考察站室外照明的应用

本文通过对我国南极科学考察站室外照明系统的需求调研分析,介绍了LED在科考站室夕h照明的应用,并在环境适应性、能耗、光环境、维护、照明控制等方面与其他光源进行了比较,探讨了LED在特定领域中的优势。     

The physicochemical characterisation of microscopic airborne particles in south Wales: a review of the locations and methodologies

As part of the NERC-URGENT thematic programme, research was undertaken into the physicochemistry and bioreactivity of microscopic airborne particulate matter in south Wales. This paper reviews the collecting and characterisation methods used in the research; some of the results obtained are shown as examples. Four main collecting locations were chosen: Cardiff (urban); Port Talbot (urban/industrial); Park Slip West coal opencast pit (industrial/rural); the Black Mountains (rural/background). Collections initially used a 30-l/min Negretti PM10 filter collection system, however in the later stages of the project increased use was made of a 1100-l/min impaction system (nicknamed the super-sucker). This latter device was developed at Harvard University USA, however was adapted and optimised at Cardiff University. Methods for the extraction of PM10 off polycarbonate filters and polyurethane substrates were developed, with particular attention being paid to minimise physical or chemical changes during the extraction, and the extracts being in an appropriate state for bioreactivity assessment. Physicochemical characterisation of the PM10 included the empirical measurement of shape and size using electron microscopy and semi-automated image analysis. The determinations of the water-soluble and -insoluble chemical components were undertaken by ion chromatography and inductive coupled plasma-mass spectrometry. The bioreactivity of south Wales airborne particles is not covered by this review.     

Application of thermal analysis to the characterization of organic aerosol particles

A number of Los Angeles aerosol samples, collected on quartz filters, were analyzed by thermal (effluent gas) analysis. The method involves heating the sample at a predetermined termperature rate in oxygen. The evolved gases are passed over a copper oxide catalyst to assure their complete conversion to carbon dioxide, which is detected by a nondispersive infrared carbon dioxide analyzer. The output of the analysis is a thermogram, i.e., a CO₂ versus temperature plot. The thermograms of ambient samples show distinctive peaks that correspond to the volatilization, decomposition and combustion of different carbonaceous materials, such as volatile organics, higher molecular weight organic species, elemental carbon, and carbonates. The features of the thermograms are distinctly different for aged aerosols than for fresh source-dominated particles. Also, at the receptor site there are substantial differences between daytime and nighttime samples. Based on these results, aided by results on solvent treated samples, an empirical approach to differentiate primary and secondary organics will be described.     

Size-resolved emission rates of airborne bacteria and fungi in an occupied classroom

The role of human occupancy as a source of indoor biological aerosols is poorly understood. Size-resolved concentrations of total and biological particles in indoor air were quantified in a classroom under occupied and vacant conditions. Per-occupant emission rates were estimated through a mass-balance modeling approach, and the microbial diversity of indoor and outdoor air during occupancy was determined via rDNA gene sequence analysis. Significant increases of total particle mass and bacterial genome concentrations were observed during the occupied period compared to the vacant case. These increases varied in magnitude with the particle size and ranged from 3 to 68 times for total mass, 12-2700 times for bacterial genomes, and 1.5-5.2 times for fungal genomes. Emission rates per person-hour because of occupancy were 31 mg, 37 × 10(6) genome copies, and 7.3 × 10(6) genome copies for total particle mass, bacteria, and fungi, respectively. Of the bacterial emissions, ～18% are from taxa that are closely associated with the human skin microbiome. This analysis provides size-resolved, per person-hour emission rates for these biological particles and illustrates the extent to which being in an occupied room results in exposure to bacteria that are associated with previous or current human occupants. PRACTICAL IMPLICATIONS: Presented here are the first size-resolved, per person emission rate estimates of bacterial and fungal genomes for a common occupied indoor space. The marked differences observed between total particle and bacterial size distributions suggest that size-dependent aerosol models that use total particles as a surrogate for microbial particles incorrectly assess the fate of and human exposure to airborne bacteria. The strong signal of human microbiota in airborne particulate matter in an occupied setting demonstrates that the aerosol route can be a source of exposure to microorganisms emitted from the skin, hair, nostrils, and mouths of other occupants.     

Tolerance of Antarctic soil fungi to hydrocarbons

Little is known about the effects of hydrocarbons and fuel oil on Antarctic filamentous fungi in the terrestrial Antarctic environment. Growth of fungi and bacteria from soils around Rothera Research Station (Adelaide Island, Antarctic Peninsula) was assessed in the presence of ten separate aromatic and aliphatic hydrocarbons [marine gas oil (MGO), dodecane, hexadecane, benzoic acid, p-hydroxybenzoic acid, toluene, phenol, biphenyl, naphthalene and m- and p-xylenes with ethylbenzene]. Aromatic hydrocarbons inhibited soil microbial growth more than aliphatic hydrocarbons. Soil microorganisms from a moss patch, where little previous impact or hydrocarbon contamination had occurred, were less tolerant of hydrocarbons than those from high impact sites. Fungal growth rates of Mollisia sp., Penicillium commune, Mortierella sp., Trichoderma koningii, Trichoderma sp. and Phoma herbarum were assessed in the presence of hydrocarbons. Generally, aromatic hydrocarbons inhibited or stopped hyphal extension, though growth rates increased with some aliphatic hydrocarbons. Hyphal dry weight measurements suggested that Mortierella sp. may be able to use dodecane as sole carbon and energy source. Hydrocarbon-degrading Antarctic fungi may have use in future hydrocarbon spill bioremediation.     

Traffic-generated airborne particles in naturally ventilated multi-storey residential buildings of Singapore: Vertical distribution and potential health risks

The main objective of the study is to quantify the mass concentration exposure levels of fine traffic-generated particles (PM_2.5) at various heights of typical multi-storey public housing buildings located in close proximity, i.e. within 30 m and along a busy major expressway in Singapore. The secondary objective is to compare the potential health risks of occupants in the buildings, associated with inhalation exposure of fine traffic-generated particulate matter, based on estimated dose rates and the lowest observed adverse effect levels (loael) at the various floors of these buildings. Two typical public housing buildings, both naturally ventilated residential apartment blocks, of point block configuration (22-storey) and slab block configuration (16-storey) were selected for the study. Particulate samples were collected for both mass and chemical analysis (OC/EC ratio) at three representative floors: the lower, the mid, and upper floors of the buildings. Key meteorological parameters such as wind speed, wind direction, ambient temperature, and relative humidity were also concurrently measured at the sampling locations. For the potential health risk analysis, the occupants have been divided into four age categories namely, infants, children (1 year), children (8–10 years) and adults. The analysis takes into account age-specific breathing rates, body weights for different age categories. Experimental results explicitly showed that PM_2.5 mean particle mass concentration was highest at the midfloors of both buildings when compared to those measured at upper and lower floors during a typical day. Although the lower floors were closest to traffic emissions, the mean particle mass concentration was lower there than that at the midfloors, which could presumably be due to the interception of PM_2.5 particles by tree leaves or the inflow of clean and drier air from higher altitude with lower aerosol burden mixing with the traffic-polluted air at the lower levels thus lowering the concentration at the lower floors similar to induced chimney effect or both. The upper floors had the least fine particulate matter mass concentration due to dilution following pronounced mixing of traffic-polluted air with ambient air. The only difference between both blocks is that at corresponding floors, the mass concentration levels for slab block is much higher than that of point block. This could be attributed to the configuration of the blocks. Observational data show the slab block tends to slow down the approaching wind thus allowing the accumulation of the fine traffic-generated particulate matter in front of the building. For point block, the HR values at the mid and lower floors suggest that occupants living in these floors experience 1.81 and 1.34 times more health risk, respectively, in contracting respiratory diseases when compared to those living at the upper floors for all age categories. Similarly, for the slab block, occupants living in the mid and lower floors had 1.62 and 1.28 times more risk, respectively, in contracting respiratory diseases when compared to those living at the upper floors for all age categories.     

Size distribution and chemical composition of airborne particles in south-eastern Finland during different seasons and wildfire episodes in 2006

The inorganic main elements, trace elements and PAHs were determined from selected PM₁, PM_2.5 and PM₁₀ samples collected at the Nordic background station in Virolahti during different seasons and during the wildfire episodes in 2006. Submicron particles are those most harmful to human beings, as they are able to penetrate deep into the human respiratory system and may cause severe health effects. About 70-80%, of the toxic trace elements, like lead, cadmium, arsenic and nickel, as well as PAH compounds, were found in particles smaller than 1 µm. Furthermore, the main part of the copper, zinc, and vanadium was associated with submicron particles. In practice, all the PAHs found in PM₁₀ were actually in PM_2.5. For PAHs and trace elements, it is more beneficial to analyse the PM_2.5 or even the PM₁ fraction instead of PM₁₀, because exclusion of the large particles reduces the need for sample cleaning to minimize the matrix effects during the analysis. During the wildfire episodes, the concentrations of particles smaller than 2.5 µm, as well as those of submicron particles, increased, and also the ratio PM₁/PM₁₀ increased to about 50%. On the fire days, the mean potassium concentration was higher in all particle fractions, but ammonium and nitrate concentrations rose only in particles smaller than 1.0 µm. PAH concentrations rose even to the same level as in winter.     

有粘结预应力在252m地下室顶板中的应用

在总长度 2 5 2m的超长不设缝地下室顶板中 ,采用了预应力、设置后浇带等综合抗裂技术 ,并对有粘结预应力平板的设计理论、施工工艺、锚固体系及超长结构预应力损失控制和抗裂控制作了深入研究。