Automated Measurement of the Size and Concentration of Airborne Particulate Nitrate

A three-stage, cascaded integrated collection and vaporization system has been developed to provide automated, 10 min resolution monitoring of the size and concentration of fine particulate nitrate in the atmosphere. Particles are collected (7 min) by a humidified impaction process, and analyzed in place (3 min) by flash vaporization and chemiluminescent detection of the evolved nitrogen oxides. The three size fractions, < 0.45 w m, 0.45-1.0 w m, and 1.0-2.5 w m, are chosen to distinguish the condensation, droplet, and coarse components of PM 2.5 . The size precut at 2.5 w m is done at ambient conditions, while the size fractionation at 1.0 w m and 0.45 w m is done at a constant relative humidity of 65%. The system is calibrated with laboratory aerosols, including comparison of sizing for hygroscopic salt and hydrophobic organic aerosols. The complete system is tested with monodisperse ammonium nitrate aerosol generated with a high-flow differential mobility analyzer coupled with an impactor precut and yields results consistent with the calibration of the individual stages.     

新竹地区大气环境纳米微粒粒径分布及数目浓度变化研究

监测了新竹地区不同区域的纳米微粒粒径分布及数目浓度变化,分别针对光复国宅(住宅区)、食品路及西大路口(道路)、湖口工业区(工业区)及宝山水库(水源集水区)等区域进行纳米微粒背景值测量.在粒径分布方面,《100 nm以下微粒以食品路及西大路口浓度最高,其次为湖口工业区,各占当日总浓度90%以上.而光复国宅及宝山水库则分别占有80%以上及60%以上比例.其中《15 nm以下微粒分别为食品路及西大路口占26%,湖口工业区占18%,光复国宅占有14%及宝山水库则占了5%.在数目浓度方面,以粒径6～225 nm的日平均值来看,这四个采样点中,以食品路及西大路交叉口所测量到总数目浓度最高(5.58×105 cm-3),其次为湖口工业区的3.64×104 cm-3,第三为光复国宅总浓度1.27×104 cm-3,总浓度最低者为宝山水库只有1.07×104 cm-3.以粒径15～661 nm的日平均值来看,仍以食品路及西大路交叉口所测量到总数目浓度最高,约7.31×104 cm-3,其次为湖口工业区的3.05×104 cm-3,第三为宝山水库总浓度为1.254×104 cm-3,总浓度最低者为光复国宅1.25×104 cm-3.     

北京市大气颗粒物中多环芳烃的分布特征

用撞击式分级采样器同步采集了北京市城乡结合部、郊区的2003年4个季节的不同粒径大气颗粒物样品,用气相色谱-质谱分析了其中的多环芳烃,并对两个地区大气颗粒物中的多环片烃含量、分布及季节性变化特征进行了探讨。     

Use of an Andersen Bioaerosol Sampler to Simultaneously Provide Culturable Particle and Culturable Organism Size Distributions

A method is provided for estimating size distributions in terms of both culturable particles (CP) and culturable organisms (CO) from a single sample collected with an Andersen bioaerosol impactor. Half of the agar surface of each Petri dish is covered with a polycarbonate filter substrate through which liquid from the agar can wick and thereby form a flat wetted collection surface, and the other half of the agar surface is uncovered. Quantification of CO distribution results involves washing the collected particles from the filter surfaces and plating suitable dilutions of de-agglomerated particles, followed by incubating the organisms, and counting the resulting colonies; whereas, quantification of CP results is based on direct culturing of the agar media. Experiments were conducted with near-monodisperse clusters of Bacillus atrophaeus (aka BG) aerosols covering APS-determined geometric number mean sizes from 1.83 to 8.7 μm aerodynamic diameter (AD). There is little difference between the Andersen-determined median sizes of the CO and CP distributions of the near-monodisperse clusters, which supports the utility of the CO method. The method was applied to sampling bioaerosol in a previously occupied classroom and the results showed median sizes of 1.7 and 3.1 μm AD for the CP and CO distributions, respectively. Total bioaerosol concentrations were 0.53 and 3.4 CO/L, respectively, so the average CP contained 6.4 CO.

Copyright 2012 American Association for Aerosol Research     

Dominant Mechanisms that Shape the Airborne Particle Size and Composition Distribution in Central California

The size and composition of ambient airborne particulate matter is reported for winter conditions at five locations in (or near) the San Joaquin Valley in central California. Two distinct types of airborne particles were identified based on diurnal patterns and size distribution similarity: hygroscopic sulfate/ammonium/nitrate particles and less hygroscopic particles composed of mostly organic carbon with smaller amounts of elemental carbon. Daytime PM₁₀ concentrations for sulfate/ammonium/nitrate particles were measured to be 10.1 μ g m^?3, 28.3 μ g m^?3, and 52.8 μ g m^?3 at Sacramento, Modesto and Bakersfield, California, respectively. Nighttime concentrations were 10–30% lower, suggesting that these particles are dominated by secondary production. Simulation of the data with a box model suggests that these particles were formed by the condensation of ammonia and nitric acid onto background or primary sulfate particles. These hygroscopic particles had a mass distribution peak in the accumulation mode (0.56–1.0 μ m) at all times. Daytime PM₁₀ carbon particle concentrations were measured to be 9.5 μ g m^?3, 15.1 μ g m^?3, and 16.2 μ g m^?3 at Sacramento, Modesto, and Bakersfield, respectively. Corresponding nighttime concentrations were 200–300% higher, suggesting that these particles are dominated by primary emissions. The peak in the carbon particle mass distribution varied between 0.2–1.0 μ m. Carbon particles emitted directly from combustion sources typically have a mass distribution peak diameter between 0.1–0.32 μ m. Box model calculations suggest that the formation of secondary organic aerosol is negligible under cool winter conditions, and that the observed shift in the carbon particle mass distribution results from coagulation in the heavily polluted concentrations experienced during the current study. The analysis suggests that carbon particles and sulfate/ammonium/nitrate particles exist separately in the atmosphere of the San Joaquin Valley until coagulation mixes them in the accumulation mode.     

上海吴淞地区气溶胶粒径分布和元素浓度研究

为了有效降低颗粒物浓度和提高吴淞工业区大气环境质量,重要的任务是测定大气颗粒物的粒径分布和化学组分.本研究使用DYLEC-120型冲击式9级采样仪,选择该地区有代表性的4个采样点,在冬季(2004年1月)采集不同粒径大气颗粒物(分别为》11,11～7,7～4.7,4.7～3.3,3.3～2.1,2.1～1.1,1.1～0.65,0.65～0.43,《0.43μm).使用质子激发X荧光发射技术测定不同粒径颗粒物中S,K,Ca,Ti,Cr,Mn,Fe,Ni,Cu,Zn,Br和Pfb 12种无机元素浓度.结果发现,吴淞工业区气溶胶质量浓度呈现双峰分布,峰值分别位于1.1～2.1和4.7～7.0 μm两个粒径范围.富集因子分析结果表明,4个监测点无机元素浓度和污染状况与监测点所在地及周边工矿企业排放紧密相关.应当引起重视的是S,Cr,Ni,Cu,Zn,Br和Pb等元素已严重地受到人为污染源的影响,而且这些元素更趋于富集在直径小于2.1 μm的细颗粒物中,呈现粒径变小而污染加剧的特征.     

北京市火电厂排放颗粒物的粒径分布

本文重点研究了北京市燃煤、燃油电厂锅炉的颗粒物排放及其粒径分布,静电除尘器的分级效率.文中对所采用的WY-Ⅱ型冲击式尘粒分级仪进行简要介绍,指出存在的问题,并提出建议.     

大气颗粒物中多环芳烃的粒径分布

用GC/MS法测定了北京市北部的城乡结合部和远郊区的大气颗粒物中的16种优控多环芳烃(PAHs)的浓度。采样时间从2003年1月到11月,分季节采样。采样器采集的大气颗粒物粒径分为5段,粒径范围从小于等于1.1μm到100μm。对颗粒物中的总优控PAHs和检测出的单一优控PAHs在不同地区、不同时期的粒径分布进行了比较和讨论。总优控PAHs和单一优控PAHs化合物均趋向于吸附在小粒径颗粒物中,占总量47%~65%的总优控PAHs分布在粒径小于1.1μm的颗粒物中,只有不到10%的总优控PAHs分布在粒径大于7.0μm的粗颗粒物上。     

聚氨酯分散体粒径及粒径分布与粒径控制

介绍了聚氨酯分散体粒径与粒径分布概念、测定粒径的方法,分析探讨了分散体内在因素和外部因素对粒径的影响以及聚氨酯分散体的粒径控制。     

Contributions of Foot Traffic and Outdoor Concentrations to Indoor Airborne Aspergillus

Aspergillus is a mold genus that can cause allergies, asthma, and pulmonary infections in sensitive people; its particles are common in indoor air. Two potential contributors to indoor Aspergillus particles were examined in this field study: human activity (walking over carpet), and outdoor Aspergillus concentrations. Filtered air samples were collected outdoors and inside two carpeted hallways in public buildings, while measuring indoor foot traffic. Aspergillus concentrations were analyzed using quantitative Polymerase Chain Reaction (qPCR). A bivariate model was used to predict indoor Aspergillus concentrations based on foot traffic and outdoor Aspergillus concentrations. For 3 of 4 scenarios, most of the variation in indoor Aspergillus could be explained by the combined effect of outdoor Aspergillus concentrations and foot traffic, with particularly strong correlations during peak traffic times. In addition, indoor Aspergillus was significantly associated with outdoor Aspergillus in 2 of 4 scenarios, and with foot traffic in 2 of 4 scenarios. For 2 of 3 sampling campaigns, Aspergillus did not have a significant association either with gravimetric particulate matter ≤5 μm (PM₅), or with optically measured PM of 0.75–1 μm, 1–2 μm, 2–3.5 μm, or 3.5–5 μm. Controlled experiments, examining whether the foot traffic contribution was due to resuspension from carpeting or to shedding from clothing and/or human bodies, saw a significant increase in Aspergillus levels from resuspension. Although an increase was also seen for clothing over Tyvek suits, it was not statistically significant.     

钛白粉粒度分布与颜料体积浓度对颜料性能的影响

通过实验研究钛白粉粒度分布与颜料体积浓度在丙烯酸体系下对色调L*、b*、白度、遮盖力、涂膜的光泽度等颜料性能的影响。理解钛白粉应用特性,对金红石型钛白生产企业开展钛白粉应用研究、改进企业的产品质量和开发金红石型新品种都是大有助益的。     

Particle Size, Particle Size Distribution, and Related Measurements of Supported Metal Catalysts

It should be apparent from the contents of this review that no single method provides a full characterization of particle size and/or particle size distribution in supported metal catalysts without some inherent theoretical shortcoming, experimental difficulty, or ambiguities in interpretation of results. The message is clearly to use more than one technique whenever possible in order to obtain intercomparisons both of size/size distribution number themselves and internal consistency of the data. However, to be avoided are incorrect comparisons, such as sizes obtained from the Scherrer formula and chemisorption experiments, for example, which measure different things. We believe that high-resolution TEM has a bright future in catalyst characterization, but perhaps the most accessible and convenient combination at present is that of Fourier line profile x-ray analysis and chemisorption, albeit at the expense of some analysis in the former case.     

Size Distribution and Sources of Trace Metals in Ultrafine/Fine/Coarse Airborne Particles in the Atmosphere of Shanghai

Airborne particulate matter (PM) samples in 13 different size-fractions from 0.0283 to 9.92 μm were collected in winter of 2007 at three sites in Shanghai, China. The PM exhibited a bimodal distribution with a major mode in the fine particle size range (D_p = 0.2–1 μm) and a minor mode in the coarse range (D_p = 1–10 μm), suggesting that fine particle pollution is dominant in the Shanghai atmosphere. Trace metals in PM exhibited the following distribution patterns: (1) unimodal distribution in the fine fraction (Pb, Cd, Se, Sn, Bi, and Zn), (2) unimodal distribution in the coarse fraction (Mg, Al, Fe, Ca, Ba, Sr, Ge, Zr, U, and rare earth elements), (3) bimodal distribution, with one mode in the fine fraction and one in the coarse fraction (Cu, Mn, K, Ga, V, Rb, and Cs), and (4) multimodal distribution (Na, Ti, Cr, Co, As, Ni, Mo, Ag, W, Pt, Au, S, and Cl) throughout the entire aerosol size spectrum. In addition to these size distributions, Aitken modes due to local origins were also evident for Se, Sn, Cu, V, Ti, Cr, Co, As, Ag, Mo, and Pt, whose respective mass in the ultrafine particles (<0.1 μm) was 10, 23, 13, 19, 23, 14, 67, 32, 79, 40, and 21%, with submicron mass median aerodynamic diameters (MMADs) in PM_0.02-9.92 (except Pt). In particular, the MMADs for Co and Ag were <0.1 μm, which increase potential health issues. The measured distributions are believed to result from a combination of processes including local anthropogenic and natural sources, such as traffic, coal combustion, and the steel industry.     

The Annual Bacterial Particle Concentration and Size Distribution in the Ambient Atmosphere in a Rural Area of the Willamette Valley,Oregon

Airborne bacterial samples were collected using wet cyclone and cascade impact samplers 2 to 3 times a week at 2 agricultural sites in the mid-Willamette River valley, near Corvallis, OR during 1997. The concentrations of total (TB), culturable (CB), and particulate-associated culturable (PACB) bacteria in the ambient atmosphere were measured using epifluorescence microscopic and culture methods. All three categories of airborne bacteria were found to have major concentration peaks in the summer (e.g., from June to September), especially in July and August. This may reflect the greater summer flux of bacteria from agricultural sources and activities and dry/dusty soil conditions. The PACB had several smaller peaks scattered in the winter and autumn. Size analysis of the PACB showed that the summer PACB peak was composed primarily of larger bacterial particles, whereas the smaller peaks in other seasons were composed primarily of smaller bacterial particles that occur during rainfall or storms events. The concentrations of TB and CB were positively correlated with temperature and solar radiation, but negatively with relative humidity. This is thought to reflect the contributions of agricultural activities and solar ground-heating effects outweighing the biologically damaging/lethal effects of solar radiation, high temperature, and dry conditions. It was shown that the count median diameter (CMD) of the PACB varied during the year with no obvious seasonal pattern. The ratios of CB to PACB and CB to TB concentrations in the atmosphere were greater in the summer than in the other seasons, while the TB to PACB ratio was the greatest in the spring. These observations could be interpreted as follows: more culturable bacteria, compared with the total, were aggregated in clumps or rafted on plant/soil debris in the summer, while single or relatively fewer culturable bacteria were associated with the particles in other seasons. This may be caused by the newly exposed bacterial particles with a high proportion of culturable bacteria, short transport time interval from aerosolization to deposition in the sampler, and/or more resistant bacterial populations in/on the summer-time sources. Spring airborne bacterial populations may be more sensitive to, and/or extensively exposed to, environmental stresses (starvation, sunlight, etc.) and aerosolization, thus fewer culturable bacteria per particle might be expected. A seasonal microstructure illustration of airborne bacteria particles is proposed that may be useful for the interpretation of aerobiological data, the investigation of health or ecological effect, and the detection of the 3 categories of airborne bacteria defined herein.     

Diurnal Distribution of Total and Culturable Atmospheric Bacteria at a Rural Site

During the summer and fall of 1996 ambient air samples were collected using a high-volume wet cyclone sampler positioned 2 m above ground level in an agricultural area near Corvallis, OR. Samples were collected for approximately 2-hr periods from 0500 to 2100 hr on 11 days. Total and culturable atmospheric bacterial (TAB and CAB) concentrations in the samples were determined using epifluorescence microscopy and filtration-culture methods. It was found that the CAB concentration in the atmosphere was the lowest at dawn, gradually increased from sunrise to reach a maximum in the afternoon, and finally decreased in the evening. The TAB load had a similar but much less pronounced trend. The geometric mean of TAB concentration was about 27 to 222 times greater than that of CAB concentration in the atmosphere. A much higher TAB determination suggests that atmospheric bacteria might play a greater role than expected when the culturable determination is used as an investigation method in allergic disease and ecological research. This finding also indicates the necessity for using nonculturable airborne pathogen detection methods such as those targeted on nucleic acid or other macromolecules, rather than the classical culturable methods currently used in airborne epidemiological investigation. The CAB to TAB ratio in the atmosphere was highest in the afternoon, coincident with the maximum CAB concentration. This could be explained by either or both of the following reasons: (1) the maximum live bacterial flux from the ground at that time does not have sufficient time to be rendered nonculturable before reaching the sampler's position; and (2) the prevalence of large, protected bacterial particles in the afternoon and a high collection efficiency of the cyclone sampler for these particles.     

Evaluation of a Method for Measurement of the Concentration and Size Distribution of Black Carbon Particles Suspended in Rainwater

We make detailed evaluations of a method of measuring the mass concentration and size distribution of black carbon (BC) particles suspended in water for the purpose of application to rainwater samples. Water samples were aerosolized with an ultrasonic nebulizer. Generated water droplets were dried in order to extract airborne BC particles. The mass of each BC particle was then measured by a Single Particle Soot Photometer (SP2), based on the laser-induced incandescence technique. Under the optimized operating conditions of our measurement system, the overall efficiency of the extraction of BC particles from rainwater was determined to be 11.4% ± 0.83% by mass, resulting in a total uncertainty of about ±20% for the measurement of the BC concentration in rainwater. The change in efficiency due to water-soluble species was found to be negligibly small for rainwater samples analyzed in this study. The determination of the efficiency by using standard BC solutions was necessary at an appropriate frequency because changes in the overall conditions of the system lead to changes in the efficiency in the long term. The size of BC particles in rainwater can be overestimated because of the coagulation of BC particles in the process of extraction by the nebulizer. This effect increased with the increase in BC concentration in rainwater. The effect can be minimized by dilution of rainwater samples by pure water. The volume of a rainwater sample required for BC measurement was less than 5 mL, enabling measurement for weak rain or highly time-resolved measurements during each rain event.     

Application of the Volatility-TDMA Technique to Determine the Number Size Distribution and Mass Concentration of Less Volatile Particles

A Volatility-Tandem-Differential-Mobility-Analyzer (VTDMA) and a Differential Mobility Particle Sizer (DMPS) were used to determine the number and mass concentration of externally mixed aerosol particles in urban background air. In the VTDMA the less-volatile (LV) particle fraction was measured at 300°C for particles in the size range 20–250 nm. The LV particle fraction was converted to the number concentration of LV particles (N_LV) and the mass concentration (M_LV). M_LV was compared with the mass concentration of black carbon (M_BC) measured by a Multi-Angle Absorption Photometer (MAAP). The DMPS and VTDMA data were used for calculating scattering and absorption coefficients (σ_SP and σ _AP) with a Mie model and compared with σ _SP and σ _AP measured with a TSI nephelometer and the MAAP. The model was run by assuming external and internal mixing of absorbing and scattering aerosol. The best fit of measured and modeled σ _SP and σ _AP was sought by varying the refractive index. During periods dominated by local emissions LV particle fraction ??_LV ? was high ( >0.2). In these cases, the M_LV and the modeled σ _AP assuming external mixing agreed well with the measured M_BC and σ _AP, respectively. For the long-range transported aerosol ??_LV ? was small ( <0.1) and M_BC was higher than M_LV. For the whole period the average (± std) refractive index was 1.55 (± 0.09) – 0.04 (±0.02)i when internal mixing was assumed. When ??_LV ? was >0.2 the average refractive index of LV particles was 1.96 – 0.8 (±0.18)i when σ _AP was modeled assuming external mixing.     

多晶硅中杂质含量、分布及其检测方法的探讨

多晶硅中杂质的组成及含量是衡量多晶硅产品质量的重要指标之一,由于其杂质组成复杂、含量低于常规检测方法检出限,这就使对多晶硅中杂质含量、分布及检测方法的研究具有重要意义。概述了目前用于检测分析多晶硅中杂质含量、分布的方法及其优缺点;总结了近年来国内外在多晶硅杂质检测方法研究中的进展以及多晶硅中杂质的含量和分布数据,为多晶硅的检测提供了参考。     

悬浮法聚苯乙烯的粒径和粒径分布

通过苯乙烯悬浮聚合,研究了搅拌转速、分散剂浓度、相比、釜径和桨型对聚苯乙烯粒径和粒径分布的影响,并确定了相应的关联式,为选择最佳操作条件和聚合反应器的设计提供依据.