Ultrafine particle concentrations and exposures in six elementary school classrooms in northern California

Potential health risks may result from environmental exposure to ultrafine particles (UFP), i.e., those smaller than 0.1 μm in diameter. One important exposure setting that has received relatively little attention is school classrooms. We made time-resolved, continuous measurements of particle number (PN) concentrations for 2-4 school days per site (18 days total) inside and outside of six classrooms in northern California during normal occupancy and use. Additional time-resolved information was gathered on ventilation conditions, occupancy, and classroom activity. Across the six classrooms, average indoor PN concentrations when students were present were 5200-16,500/cm(3) (overall average 10,800/cm(3)); corresponding outdoor concentrations were 9000-26,000/cm(3) (overall average 18,100/cm(3)). Average indoor levels were higher when classrooms were occupied than when they were unoccupied because of higher outdoor concentrations and higher ventilation rates during occupancy. In these classrooms, PN exposures appear to be primarily attributable to outdoor sources. Indoor emission sources (candle use, cooking on an electric griddle, use of a heater, use of terpene-containing cleaning products) were seen to affect indoor PN concentrations only in a few instances. The daily-integrated exposure of students in these six classrooms averaged 52,000/cm(3) h/day for the 18 days monitored. PRACTICAL IMPLICATIONS: This study provides data and insight concerning the UFP exposure levels children may encounter within classrooms and the factors that most significantly affect these levels in an urban area in northern California. This information can serve as a basis to guide further study of children's UFP exposure and the potential associated health risks.     

Comparison of short-term exposure to particle number, PM10 and soot concentrations on three (sub) urban locations

Recent interest has focused on the health effects of ultrafine particles because of the documented toxicity and the larger concentration contrast near motorways of UFP than for PM10 or PM2.5. There are only few studies that have measured UFP at inner-city streets simultaneously with other PM components.The aim of this study was to compare the contrast of UFP, PM₁₀ and soot measured simultaneously at 3 inner-city locations, namely a moderately busy street (15,000 vehicles/day), a city and a suburban background location.Simultaneously, measurements of particle number concentrations (PNC), PM₁₀ and soot have been conducted on three locations in and around Utrecht, a medium-sized city in the Netherlands for 20 weekdays in autumn 2008. Measurements were done for 6-h during afternoon and early evening.The mean PNC at the street location was more than 3 times higher than at the two background locations. The contrast was similar for soot concentrations. In PM₁₀ concentrations less contrast was found, namely 1.8 times. Mean PNC concentrations were poorly correlated with PM₁₀ and soot. At the street location, high temporal variation of PNC concentrations occurred within each sampling day, probably related to variations in traffic volumes, high-emission individual vehicles and wind direction. Temporal variation was smaller at the two background locations. Occasional unexplained short-term peaks occurred at the suburban background location. A relatively high correlation between PNC minute values at the two background locations was found, pointing to similar area-wide sources. Typically low correlations were found with the street locations, consistent with the dominant impact of local traffic.A large contrast between two background locations and a moderately busy urban street location was found for PNC and soot, comparable to previous studies of much busier motorways. Temporal variation of PNC was higher at the street location and uncorrelated with background variations.     

Variation in indoor particle number and PM2.5 concentrations in a radio station surrounded by busy roads before and after an upgrade of the HVAC system

Indoor particle number and PM_2.5 concentrations were investigated in a radio station surrounded by busy roads. Two extensive field measurement campaigns were conducted to determine the critical parameters affecting indoor air quality. The results indicated that indoor particle number and PM_2.5 concentrations were governed by outdoor air, and were significantly affected by the location of air intake and design of HVAC system. Prior to the upgrade of the HVAC system and relocation of the air intake, the indoor median particle number concentration was 7.4×10³ particles/cm³ and the median PM_2.5 concentration was 7 μg/m³. After the relocation of air intake and the redesign of the HVAC system, the indoor particle number concentration was between 2.3×10³ and 3.4×10³ particles/cm³, with a median value of 2.7×10³ particles/cm³, and the indoor PM_2.5 concentration was in the range of 3–5 μg/m³, with a median value of 4 μg/m³. By relocating the air intake of the HVAC, the outdoor particle number and PM_2.5 concentrations near the air intake were reduced by 35% and 55%, respectively. In addition, with the relocation of air intake and the redesign of the HVAC system, the particle number penetration rate was reduced from 42% to 14%, and the overall filtration efficiency of the HVAC system (relocation of air intake, pre-filter, AHU and particle losses in the air duct) increased from 58% to 86%. For PM_2.5, the penetration rate after the upgrade was approximately 18% and the overall filtration efficiency was 82%. This study demonstrates that by using a comprehensive approach, including the assessment of outdoor conditions and characterisation of ventilation and filtration parameters, satisfactory indoor air quality can be achieved, even for those indoor environments facing challenging outdoor air conditions.     

Characterization of indoor sources of fine and ultrafine particles: a study conducted in a full-scale chamber

Humans and their activities are known to generate considerable amounts of particulate matter indoors. Some of the activities are cooking, smoking and cleaning. In this study 13 different particle sources were for the first time examined in a 32 m3 full-scale chamber with an air change rate of 1.7 +/- 0.1/h. Two different instruments, a condensation particle counter (CPC) and an optical particle counter (OPC) were used to quantitatively determine ultrafine and fine particle emissions, respectively. The CPC measures particles from 0.02 microm to larger than 1.0 microm. The OPC was adjusted to measure particle concentrations in eight fractions between 0.3 and 1.0 microm. The sources were cigarette side-stream smoke, pure wax candles, scented candles, a vacuum cleaner, an air-freshener spray, a flat iron (with and without steam) on a cotton sheet, electric radiators, an electric stove, a gas stove, and frying meat. The cigarette burning, frying meat, air freshener spray and gas stove showed a particle size distribution that changed over time towards larger particles. In most of the experiments the maximum concentration was reached within a few minutes. Typically, the increase of the particle concentration immediately after activation of the source was more rapid than the decay of the concentration observed after deactivation of the source. The highest observed concentration of ultrafine particles was approximately 241,000 particles/cm3 and originated from the combustion of pure wax candles. The weakest generation of ultrafine particles (1.17 x 10(7) particles per second) was observed when ironing without steam on a cotton sheet, which resulted in a concentration of 550 particles/cm3 in the chamber air. The highest generation rate (1.47 x 10(10) particles per second) was observed in the radiator test. PRACTICAL IMPLICATIONS: Humans and their activities are known to generate substantial amounts of particulate matter indoors and potentially they can have a strong influence on short-term exposure. In this study a quantitative determination of the emissions of fine and ultrafine particles from different indoor sources was performed. The aim is a better understanding of the origin and fate of indoor particles. The results may be useful for Indoor Air Quality models.     

调谐质量阻尼器和调谐型颗粒阻尼器减震性能对比研究

基于5层钢框架模型,通过试验对比了在地震激励下调谐质量阻尼器和调谐型颗粒阻尼器的减震性能,并探究了频率失调等因素的影响。通过数值模拟实现了两种阻尼器的优化设计,以考察充分发挥其性能的工况下,两种阻尼器的减震效果以及阻尼器相对位移行程的对比。研究表明：在频率调谐时,调谐质量阻尼器和调谐型颗粒阻尼器均能显著降低主体结构位移和加速度响应,调谐型颗粒阻尼器的减震效果更好,具有一定的减震优势,并且调谐型颗粒阻尼器的相对位移行程更小、减震频带更宽;当两者均为最优设计时,减震效果相当,但是最优化调谐型颗粒阻尼器系统的阻尼器与主体结构之间的相对位移更小,可降低相对位移幅值24.5%,并且具有更好的鲁棒性。     

三种室内颗粒运动分布模拟方法的比较

用拉格朗日模型和滑移通量模型及将颗粒当作被动运输标量处理的方法对三维通风小室内颗粒的扩散分布进行了数值模拟,并将模拟结果与相关文献中的实验数据进行了对比。结果表明,用拉格朗日模型模拟的结果除了天花板和入口处附近外与实验数据吻合得都较好;用滑移通量模型模拟的结果在靠近天花板附近与实验数据吻合得较好,其他地方的模拟结果比实验数据稍小;将颗粒当作被动运输标量处理的模拟结果在0.3m以下位置与实验数据吻合得较好,而在靠近天花板附近与实验数据差别较大。     

Measurements of Smoke Characteristics in HVAC Ducts

The characteristics of smoke traveling in an HVAC duct have been observed along with the response of selected duct smoke detectors. The simulated HVAC system consists of a 9 m long duct, 0.45 m in diameter. An exhaust fan is placed at one end of the duct and is capable of inducing airflow rates that range from 0 to 1.5 m ³/s. The flow is controlled by means of a manual damper. On the upstream end of the duct there is a square exhaust hood approximately 2.2 m at the bottom and 0.3 m at the top. The bottom of the hood is approximately 2.5 m above the floor a shroud extends down to approximately 1.5 m above the floor. The test section, placed immediately downstream of the hood, is 3.5 m long duct with a square cross section of 0.4 m on a side. The instrumentation includes oxygen, carbon monoxide and carbon dioxide gas analyzers and a load cell to determine the energy release rate of the fires tested. The smoke within the duct is characterized by means of a laser light sheet and charge coupled device (CCD) camera, two white light source and photocell ensembles, a Pitot tube and an array of eight thermocouples placed on the vertical plane of symmetry. A smoke detector was placed at the downstream end of the test section. Two types of detectors were tested, ionization and photoelectric, with a single sampling probe geometry. The fires tested cover a wide range of fuels (propane, heptane, toluene, toluene/heptane mixture, shredded paper, polyurethane foam, wood cribs) with the peak energy release rates up to 800 kW. The smoke detector performance, temperature, flow field, smoke particle size and particle distributions are dependent on the fire characteristics and airflow through the duct. The different measurements could be scaled by means of the fire size and airflow rate but left a strong dependency on the fuel and burning characteristics (i.e., smoldering, flaming). The optical density and mass optical density are analyzed as metrics for characterizing smoke and smoke detector response. Detailed comparisons between the different metrics used are presented throughout this work. Clear evidence of stratification and aging of the smoke along the duct are also presented. The limitations of the present configuration and the need for a larger scale study are also discussed.     

Electrostatic dust collectors compared to inhalable samplers for measuring endotoxin concentrations in farm homes

Paired electrostatic dust collectors (EDCs) and daily, inhalable button samplers (BS) were used concurrently to sample endotoxin in 10 farm homes during 7‐day periods in summer and winter. Winter sampling included an optical particle counter (OPC) to measure PM_2.5 and PM_2.5–10. Electrostatic dust collectors and BS filters were analyzed for endotoxin using the kinetic chromogenic Limulus amebocyte lysate assay. Optical particle counter particulate matter (PM) data were divided into two PM categories. In summer, geometric mean (geometric standard deviation) endotoxin concentrations were 0.82 EU/m³ (2.7) measured with the BS and 737 EU/m² (1.9) measured with the EDC. Winter values were 0.52 EU/m³ (3.1) for BS and 538 EU/m² (3.0) for EDCs. Seven‐day endotoxin values of EDCs were highly correlated with the 7‐day BS sampling averages (r = 0.70; P < 0.001). Analysis of variance indicated a 2.4‐fold increase in EDC endotoxin concentrations for each unit increase of the ratio of PM_2.5 to PM_2.5–10. There was also a significant correlation between BS and EDCs endotoxin concentrations for winter (r = 0.67; P < 0.05) and summer (r = 0.75; P < 0.05). Thus, EDCs sample comparable endotoxin concentrations to BS, making EDCs a feasible, easy to use alternative to BS for endotoxin sampling.     

基于颗粒流程序的仿真节理岩体模型及其应用

为实现采矿巷道周边节理网络的仿真模拟以及节理岩体中巷道的稳定性分析,构建了包含颗粒流块体模型、原生节理网络和次生节理网络的仿真节理岩体模型。针对岩体内部次生节理产状和面积不可准确测量的难题,提出了卸荷作用下次生节理产状和面积的计算方法:根据开挖前后应力张量变化计算卸荷方向,利用Fisher分布函数生成围绕在卸荷方向附近的随机节理产状;监测卸荷前后颗粒中储存能量的变化,计算节理面积和半径。通过布置测线方式获得巷道中原生节理密度和产状信息,利用Monte-Carlo方法实现对原生节理的重建;利用次生节理计算方法实现次生节理网络的建立,从而建立仿真节理网络以及仿真节理岩体模型。计算结果显示:无节理模型中顶板和底板先破坏,以张拉破坏为主;而在仿真节理岩体模型中节理部位最先破坏,原生节理以剪切破坏为主,次生节理以张拉破坏为主,在高应力作用下巷道周边基本全部破坏,需整体支护且重点在左右两帮。该计算方法可为节理岩体中巷道的稳定性计算提供参考及建议。     

采用颗粒调谐质量阻尼器的钢框架结构振动台试验研究

通过附加和不附加颗粒调谐质量阻尼器的5层钢框架振动台试验,研究其在实际地震波以及上海人工波激励下的减震效果。通过调整不同悬挂长度（频率比）、质量比、颗粒到阻尼器壁净距等参数,分析阻尼器参数对其减震效果的影响。试验结果表明：不同地震作用下该类阻尼器均能达到较好的减震效果,其中上海人工波的减震效果最好;对于多层钢框架结构,阻尼器能够有效控制第1振型的振动,但是对于高阶振型的控制作用无法保证;当阻尼器频率与主体结构基频相同时,能够达到最优减震效果,而当二者频率不同时,依然有一定的减震效果,说明其具有一定的鲁棒性;在合适的质量比（0.66%）下,阻尼器能够达到最佳减震效果;当颗粒到容器内壁净距为1.6D~3.6D时,可使阻尼器响应最小,且减震效果较好。     

Vertical variations of particle number concentration and size distribution in a street canyon in Shanghai, China

Measurements of particle number size distribution in the range of 10-487 nm were made at four heights on one side of an asymmetric street canyon on Beijing East Road in Shanghai, China. The result showed that the number size distributions were bimodal or trimodal and lognormal in form. Within a certain height from 1.5 to 20 m, the particle size distributions significantly changed with increasing height. The particle number concentrations in the nucleation mode and in the Aitken mode significantly dropped, and the peaking diameter in the Aitken mode shifted to larger sizes. The variations of the particle number size distributions in the accumulation mode were less significant than those in the nucleation and Aitken modes. The particle number size distributions slightly changed with increasing height ranging from 20 to 38 m. The particle number concentrations in the street canyon showed a stronger association with the pre-existing particle concentrations and the intensity of the solar radiation when the traffic flow was stable. The particle number concentrations were observed higher in Test I than in Test II, probably because the small pre-existing particle concentrations and the intense solar radiation promoted the formation of new particles. The pollutant concentrations in the street canyon showed a stronger association with wind speed and direction. For example, the concentrations of total particle surface area, total particle volume, PM2.5 and CO were lower in Test I (high wind speed and step-up canyon) than in Test II (low wind speed and wind blowing parallel to the canyon). The equations for the normalized concentration curves of the total particle number, CO and PM2.5 in Test I and Test II were derived. A power functions was found to be a good estimator for predicting the concentrations of total particle number, CO and PM2.5 at different heights. The decay rates of PM2.5 and CO concentrations were lower in Test I than in Test II. However, the decay rate of the total particle number concentration in Test I was similar to that in Test II. No matter how the wind direction changed, for example, in the step-up case or wind blowing parallel to the canyon, the decay rates of the total particle number concentration were larger than those of PM2.5 and CO concentrations. For example, CO concentrations decreased by 0.33 and 0.69 at the heights ranging from 1.5 to 38 m in Test I and Test II, while the total particle number concentrations decreased by 0.72 and 0.85 within the same height ranges in Test I and Test II. It is concluded that the coagulation process, besides the dilution process, affected the total particle number concentration.     

A recurrent neural network using historical data to predict time series indoor PM2.5 concentrations for residential buildings

Due to the severe outdoor PM2.5 pollution in China, many people have installed air-cleaning systems in homes. To make the systems run automatically and intelligently, we developed a recurrent neural network (RNN) that uses historical data to predict the future indoor PM2.5 concentration. The RNN architecture includes an autoencoder and a recurrent part. We used data measured in an apartment over the course of an entire year to train and test the RNN. The data include indoor/outdoor PM2.5 concentration, environmental parameters and time of day. By comparing three different input strategies, we found that a strategy employing historical PM2.5 and time of day as inputs performed best. With this strategy, the model can be applied to predict the relatively stable trend of indoor PM2.5 concentration in advance. When the input length is 2 h and the prediction horizon is 30 min, the median prediction error is 8.3 µg/m³ for the whole test set. For times with indoor PM2.5 concentrations between (20,50] µg/m³ and (50,100] µg/m³, the median prediction error is 8.3 and 9.2 µg/m³, respectively. The low prediction error between the ground-truth and predicted values shows that the RNN can predict indoor PM2.5 concentrations with satisfactory performance.     

Particle number emission rates of aerosol sources in 40 German households and their contributions to ultrafine and fine particle exposure

More representative data on source-specific particle number emission rates and associated exposure in European households are needed. In this study, indoor and outdoor particle number size distributions (10–800 nm) were measured in 40 German households under real-use conditions in over 500 days. Particle number emission rates were derived for around 800 reported indoor source events. The highest emission rate was caused by burning candles (5.3 × 10¹³ h⁻¹). Data were analyzed by the single-parameter approach (SPA) and the indoor aerosol dynamics model approach (IAM). Due to the consideration of particle deposition, coagulation, and time-dependent ventilation rates, the emission rates of the IAM approach were about twice as high as those of the SPA. Correction factors are proposed to convert the emission rates obtained from the SPA approach into more realistic values. Overall, indoor sources contributed ~ 56% of the daily-integrated particle number exposure in households under study. Burning candles and opening the window leads to seasonal differences in the contributions of indoor sources to residential exposure (70% and 40% in the cold and warm season, respectively). Application of the IAM approach allowed to attribute the contributions of outdoor particles to the penetration through building shell and entry through open windows (26% and 15%, respectively).     

Performance evaluation of air quality models for predicting PM10 and PM2.5 concentrations at urban traffic intersection during winter period

There are several models that can be used to evaluate roadside air quality. The comparison of the operational performance of different models pertinent to local conditions is desirable so that the model that performs best can be identified. Three air quality models, namely the 'modified General Finite Line Source Model' (M-GFLSM) of particulates, the 'California Line Source' (CALINE3) model, and the 'California Line Source for Queuing & Hot Spot Calculations' (CAL3QHC) model have been identified for evaluating the air quality at one of the busiest traffic intersections in the city of Guwahati. These models have been evaluated statistically with the vehicle-derived airborne particulate mass emissions in two sizes, i.e. PM10 and PM2.5, the prevailing meteorology and the temporal distribution of the measured daily average PM10 and PM2.5 concentrations in wintertime. The study has shown that the CAL3QHC model would make better predictions compared to other models for varied meteorology and traffic conditions. The detailed study reveals that the agreements between the measured and the modeled PM10 and PM2.5 concentrations have been reasonably good for CALINE3 and CAL3QHC models. Further detailed analysis shows that the CAL3QHC model performed well compared to the CALINE3. The monthly performance measures have also led to the similar results. These two models have also outperformed for a class of wind speed velocities except for low winds (<1 m s(-1)), for which, the M-GFLSM model has shown the tendency of better performance for PM10. Nevertheless, the CAL3QHC model has outperformed for both the particulate sizes and for all the wind classes, which therefore can be optional for air quality assessment at urban traffic intersections.     

大气颗粒污染物源解析技术方法研究进展

介绍了大气颗粒污染物源解析技术的发展历程及现阶段主要的源解析技术方法,通过对各种方法的基本原理和实际应用情况的阐述,分析了各种方法的侧重点及适用范围,并对颗粒物源解析技术的下一步发展趋势和研究热点进行了评述。     

Comparison of next-generation portable pollution monitors to measure exposure to PM2.5 from household air pollution in Puno,Peru

Assessment of personal exposure to PM_2.5 is critical for understanding intervention effectiveness and exposure-response relationships in household air pollution studies. In this pilot study, we compared PM_2.5 concentrations obtained from two next-generation personal exposure monitors (the Enhanced Children MicroPEM or ECM; and the Ultrasonic Personal Air Sampler or UPAS) to those obtained with a traditional Triplex Cyclone and SKC Air Pump (a gravimetric cyclone/pump sampler). We co-located cyclone/pumps with an ECM and UPAS to obtain 24-hour kitchen concentrations and personal exposure measurements. We measured Spearmen correlations and evaluated agreement using the Bland-Altman method. We obtained 215 filters from 72 ECM and 71 UPAS co-locations. Overall, the ECM and the UPAS had similar correlation (ECM ρ = 0.91 vs UPAS ρ = 0.88) and agreement (ECM mean difference of 121.7 µg/m³ vs UPAS mean difference of 93.9 µg/m³) with overlapping confidence intervals when compared against the cyclone/pump. When adjusted for the limit of detection, agreement between the devices and the cyclone/pump was also similar for all samples (ECM mean difference of 68.8 µg/m³ vs UPAS mean difference of 65.4 µg/m³) and personal exposure samples (ECM mean difference of −3.8 µg/m³ vs UPAS mean difference of −12.9 µg/m³). Both the ECM and UPAS produced comparable measurements when compared against a cyclone/pump setup.     

基坑内降水井封堵数量计算方法

针对广泛应用的筏形基础和桩基础,提出一个适用于基础工程施工完毕后的封井数量计算公式,并结合工程实例阐述了该计算公式的应用方法,同时对后浇带的抗浮效果进行了研究探讨。     

附加PTMD风力发电机结构减振控制试验研究

通过开展附加颗粒调谐质量阻尼器(particle tuned mass damper, PTMD)风力发电机结构模型的自由振动试验和振动台试验,研究PTMD自身参数对其减振性能的影响规律,检验PTMD用于降低风力发电机结构不利振动的合理性与有效性,揭示随机激励下耦合系统的工作机理。借助自由振动试验研究了设计参数对PTMD减振性能的影响规律,初步确定了系统的参数配置。同时,通过地震波激励工况、风荷载激励工况和风-地震耦合荷载激励工况对风力发电机结构使用PTMD进行振动控制的合理性与有效性进行了检验,进一步揭示随机激励下耦合系统的减振机理。试验结果表明：颗粒-腔体质量比和频率比参数分别取值0.27和0.97时PTMD表现出较好的减振性能;3种随机激励下PTMD能够有效抑制风力发电机结构的动力响应,其中,El Centro波作用下,PTMD对结构顶部加速度和位移峰值响应的控制效果分别为5.52%和7.73%,而对均方根响应的控制效果则高达33.3%和32.08%。由此可见,PTMD对均方根响应的控制效果优于峰值响应。对比传统调谐质量阻尼器(TMD)结果可知,经合理设计的PTMD具有更佳的减振...     

复振型叠加方法合理振型数量的确定

针对适用于非经典阻尼体系的复振型叠加方法,基于理论推导,得到了评价振型贡献程度的复振型质量参与系数,并给出了两种等效的表达形式,可作为评估非经典阻尼系统所需振型数量的一种方法。同时,根据复振型退化为实振型的条件(即实部与虚部成比例关系),论证了实、复振型质量参与系数法的统一性。实、复振型质量参与系数基于相同的原理和假定,具有相同的物理意义,易于工程设计人员掌握和使用。采用典型的减隔震系统数值算例和安装黏滞阻尼器的9层钢结构Benchmark模型对复振型质量参与系数方法进行了验证,结果表明该方法能够有效估计所需振型数量。但是由于实、复振型质量参与系数法是基于基底剪力推导而得到,当用于评估加速度响应所需振型时,其数量往往偏小。     

Experimental parametric study on wind‐induced vibration control of particle tuned mass damper on a benchmark high‐rise building

A particle tuned mass damper system is an integration of tuned mass damper and particle damper. The damping performance of such device is investigated by an aero‐elastic wind tunnel test on a benchmark high‐rise building. The robustness of the system is studied by comparing the damping performance to that of a traditional tuned mass damper, and the results show that the damper has excellent and steady wind‐induced vibration control effects. Meanwhile, the parameters (filling ratio, mass ratio, and mass ratio of the container to particles), which have great influence on the vibration reduction performance of the system, are also analyzed, and it is found that the particles filling ratio plays the most important role in deciding the damping effects of the dampers. There exists an optimum filling ratio and mass ratios in which the damper can reach the best damping state. Proper parameter selections can greatly improve the damping performance.