Particle Size Distributions for an Office Aerosol

As attention has focused on indoor air quality, it has become important to obtain basic information on the effects of heating, ventilating, and air-conditioning system operating parameters on office aerosols. In addition, it is important to know the particle size distributions (PSDs) in a typical office environment in order to address mitigation strategies. Therefore, this study was undertaken to evaluate the effect of percent outdoor air supplied and occupation level on the PSDs and mass concentrations for a typical office building. The outdoor, return, and supply air streams, as well as hallway air, were sampled using measuring equipment covering particle diameters from below 0.1 to above 3.5 μm. The mass concentrations, when the building was occupled, increased by a factor of approximately 2 when return air was recycled over ventilating with maximum outdoor air. The concentrations when unoccupied were at least as low using minimum outdoor air as those when occupied using maximum outdoor air. As expected, the outdoor air was cleaner than the other streams. The next lowest concentrations were obtained for supply air, then return air, with hallway air showing the highest concentrations. The normalized number distributions were found to have a single mode consistently near 0.13 μm; the volumetric distributions show a peak at 0.3 μm. The influence of the damper setting and occupancy level shows up only in the magnitude of the peaks. The distributions found in the hall and for the air streams showed the same general shapes, but the differences in instrumentation preclude other conclusions.     

Size Distributions of Organonitrates in Ambient Aerosol Collected in Houston,Texas

The size distributions of organonitrate functional groups in ambient Houston, TX aerosol were determined at 3 sites during an air quality field study conducted during August and September 2000. Samples were collected using a Hering low-pressure impactor and were analyzed, in transmission mode, using Fourier transform infrared spectroscopy. The size distributions of organonitrate groups generally fell into 4 categories. In approximately 25% of the samples, the majority of the organonitrate group mass was found in aerosol of approximately 0.1 w m aerodynamic diameter. In approximately 26% and 12% of the samples, the majority of the mass was found in aerosol of approximately 0.25 and 1 w m diameter, respectively; 21% of the samples displayed both 0.1 and 1 w m size modes. The remainder of the samples had relatively low organonitrate mass or other size distributions. Total organonitrate group absorbances, per m 3 of air sampled, were generally similar to measurements from samples collected in Los Angeles in previous studies, however,some samples had organonitrate absorbances that were an order of magnitude more intense than observed at urban sites in Los Angeles. The events with high organonitrate concentrations were observed at source-dominated (industrial) sites and were not correlated with either high NO x or high ozone concentrations, suggesting that the high concentrations are due to primary sources. The high organonitrate concentrations were generally accompanied by evidence of high acidity and high organic concentrations.     

Development and Evaluation of a Compact,Highly Efficient Coarse Particle Concentrator for Toxicological Studies

A high-efficiency coarse-mode particle concentrator (CPC) has been developed and evaluated in the laboratory as well as validated in the field experiments at the University of Southern California, in Los Angeles, CA, and in Bilthoven, the Netherlands. The CPC operates with a total intake flow of 1000 LPM. The minor flow rate, containing the concentrated coarse-mode particles (2.5-10 w m), can be adjusted from 33 to 120 LPM in order to enrich ambient coarse PM concentrations by a factor of 8-30, depending on the desirable exposure level and flow rate needed. The laboratory evaluation of the virtual impactors at 3 minor flow rates (3.3, 7, and 10 LPM, respectively) indicated that extremely efficient concentration enrichment was obtained for 2.5-10 w m particles. In the field tests, the CPC operated at a minor flow rate of 33 LPM and the mass obtained was compared to the mass collected by a reference sampler, a (rotating) micro-orifice uniform deposit impactor (MOUDI), which sampled at 30 LPM. Concentration enrichment factors in the range of 26 to 30 were achieved based on particle mass, sulfate, and nitrate as well as selected trace element and metal concentrations (Al, Si, Ca, Fe, K, Mn, Cu, Zn, Ti). CPC and MOUDI concentrations were highly correlated for all species, with R 2 in the range of 0.74 to 0.89. The use of round (compared to rectangular geometry) nozzle virtual impactors in the CPC results in a high concentration efficiency, which reduces the CPC size as well as the power requirement that is required for its operation. The compact size of the CPC makes it readily transportable to desired locations for exposure to coarse-mode particles derived from different sources and thus of a varying chemical composition.     

Characterization of Indoor-Outdoor Aerosol Concentration Relationships during the Fresno PM Exposure Studies

Particle size distributions were measured indoors and outdoors of a single, detached residence during the Fresno particulate matter exposure studies in winter (February 1-28, 1999) and spring (April 18-May 16, 1999). Data was collected for particle sizes ranging from about 0.01 to 2.5     

Measurement of Atlanta Aerosol Size Distributions: Observations of Ultrafine Particle Events

As part of EPRI's Aerosol Research Inhalation Epidemiology Study (ARIES), measurements of aerosol size distributions in the 3 nm to 2     

Physical Characterization of the University of Toronto Coarse,Fine, and Ultrafine High-Volume Particle Concentrator Systems

Particle concentrators allow exposure to controlled levels of concentrated ambient particulate matter (PM) over a broad range of concentrations. The performance of these systems can be influenced by the physicochemical characteristics of PM and so it is vital to characterize the concentrators at a given site. The quasi-ultrafine PM (<0.2 μm), fine PM (0.15–2.5 μm), and coarse PM (2.5–10 μm) concentrators at the Southern Ontario Center for Atmospheric Aerosol Research (SOCAAR), University of Toronto, were characterized as a part of the “Health Effects of Aerosols in Toronto (HEAT)” campaign held during February–March, 2010. The full size distributions of ambient and concentrated particles were simultaneously measured in terms of number, surface area, and volume using high time-resolution instruments. Examination of the complete size distribution, including the unconcentrated particles beyond the cutpoints of the concentrator systems, revealed that particles in the unconcentrated size ranges made significant contributions to the particle number and surface area present in the concentrated airstreams of fine and coarse concentrators. Further transients in the ambient ultrafine particle concentrations were evident as dampened signals in these concentrated airstreams. The ultrafine concentrator exhibited a significant size shift when the ambient particle size distribution had a mode ≤30 nm. Overall the fine and coarse concentrators provided a reasonable concentrated reproduction of the ambient PM mass while questions remain regarding the representativeness of the ultrafine concentrator.

Copyright 2012 American Association for Aerosol Research     

Comparison and Combination of Aerosol Size Distributions Measured with a Low Pressure Impactor,Differential Mobility Particle Sizer,Electrical Aerosol Analyzer,and Aerodynamic Particle Sizer

Data from a different mobility particle sizer (DMPS) or an electrical aerosol analyzer (EAA) has been combined with data from an aerodynamic particle sizer (APS) and converted to obtain aerosol mass distribution parameters on a near real-time basis. A low pressure impactor (LPI), a direct and independent measure of this mass distribution, provided information for comparison.

The number distribution of particles within the electrical measurement range was obtained with the DMPS and EAA. Data from the APS for particles greater than that size were used to complete the number distribution. Two methods of obtaining mass distribution parameters from this number data were attempted. The first was to convert the number data, channel by channel, to mass data and then fit a log-normal function to this new mass distribution. The second method was to fit a log-normal function to the combined number distribution and then use the Hatch-Choate equations to obtain mass parameters.

Both the DMPS / APS and the EAA / APS systems were shown to successfully measure aerosol mass distribution as a function of aerodynamic diameter. Careful operation of the measurement equipment and proper data manipulation are necessary to achieve reliable results. A channel-by-channel conversion from number to mass distribution provided the best comparison to the LPI measurement. The DMPS / APS combination furnishes higher-size resolution and accuracy than the EAA / APS system. A small gap was observed in the EAA / APS combined data; however, this did not seem to adversely affect the determination of mass distribution parameters.     

Deposition Uniformity and Particle Size Distribution of Ambient Aerosol Collected with a Rotating Drum Impactor

Rotating drum impactors (RDI) are cascade type impactors used for size and time resolved aerosol sampling, mostly followed by spectrometric analysis of the deposited material. They are characterized by one rectangular nozzle per stage and are equipped with an automated stepping mechanism for the impaction wheels. An existing three-stage rotating drum impactor was modified, to obtain new midpoint cutoff diameters at 2.5 μm, 1 μm, and 0.1 μm, respectively. For RDI samples collected under ambient air conditions, information on the size-segregation and the spatial uniformity of the deposited particles are key factors for a reliable spectrometric analysis of the RDI deposits. Two aerodynamic particle sizers (APS) were used for the determination of the RDI size fractionation characteristics, using polydisperse laboratory room air as quasi-stable proxy for urban ambient air. This experimental approach was suitable for the scope of this study, but was subject to numerous boundary conditions that limit a general use. Aerodynamic stage penetration midpoint diameters were estimated to be 2.4 and 1.0 μm for the first two RDI stages. Additionally, the spatial uniformity and geometrical size distribution of the deposited aerosol were investigated using micro-focus synchrotron radiation X-ray fluorescence spectrometry (micro-SR-XRF) and transmission electron microscopy (TEM), respectively. The size distribution of the particles found on the TEM samples agreed well with the results from the APS experiments. The RDI deposits showed sufficient uniformity for subsequent spectrometric analysis, but in the 2.5–10 μm size range the particle area density was very low. All of the applied methods confirmed the theoretical cutoff values of the modified RDI and showed that compared to other cascade impactors, the determined stage penetration sharpness was rather broad for the individual impactor stages.     

An Aerosol Chemical Speciation Monitor (ACSM) for Routine Monitoring of the Composition and Mass Concentrations of Ambient Aerosol

We present a new instrument, the Aerosol Chemical Speciation Monitor (ACSM), which routinely characterizes and monitors the mass and chemical composition of non-refractory submicron particulate matter in real time. Under ambient conditions, mass concentrations of particulate organics, sulfate, nitrate, ammonium, and chloride are obtained with a detection limit <0.2 μg/m³ for 30 min of signal averaging. The ACSM is built upon the same technology as the widely used Aerodyne Aerosol Mass Spectrometer (AMS), in which an aerodynamic particle focusing lens is combined with high vacuum thermal particle vaporization, electron impact ionization, and mass spectrometry. Modifications in the ACSM design, however, allow it to be smaller, lower cost, and simpler to operate than the AMS. The ACSM is also capable of routine stable operation for long periods of time (months). Results from a field measurement campaign in Queens, NY where the ACSM operated unattended and continuously for 8 weeks, are presented. ACSM data is analyzed with the same well-developed techniques that are used for the AMS. Trends in the ACSM mass concentrations observed during the Queens, NY study compare well with those from co-located instruments. Positive Matrix Factorization (PMF) of the ACSM organic aerosol spectra extracts two components: hydrocarbon-like organic aerosol (HOA) and oxygenated organic aerosol (OOA). The mass spectra and time trends of both components correlate well with PMF results obtained from a co-located high resolution time-of-flight AMS instrument.     

Aerosol Concentrations During the 1999 Fresno Exposure Studies as Functions of Size,Season, and Meterology

Two 1999 Fresno exposure studies took place in February (winter season) and April/May (spring season) for periods of four weeks each. During that time, nearly continuous measurements of outdoor aerosol concentrations were made with a TSI Scanning Mobility Particle Sizer (SMPS) and a PMS optical particle counter (LASX). These instruments provide particle size distribution information from about 0.01 to 3     

Development of an Aerosol Mass Spectrometer for Size and Composition Analysis of Submicron Particles

The importance of atmospheric aerosols in regulating the Earth's climate and their potential detrimental impact on air quality and human health has stimulated the need for instrumentation which can provide real-time analysis of size resolved aerosol, mass, and chemical composition. We describe here an aerosol mass spectrometer (AMS) which has been developed in response to these aerosol sampling needs and present results which demonstrate quantitative mea surement capability for a laboratory-generated pure component NH₄ NO₃ aerosol. The instrument combines standard vacuum and mass spectrometric technologies with recently developed aerosol sampling techniques. A unique aerodynamic aerosol inlet (developed at the University of Minnesota) focuses particles into a narrow beam and efficiently transports them into vacuum where aerodynamic particle size is determined via a particle time-of-flight (TOF) measurement. Time-resolved particle mass detection is performed mass spectrometrically following particle flash vaporization on a resistively heated surface. Calibration data are presented for aerodynamic particle velocity and particle collection efficiency measurements. The capability to measure aerosol size and mass distributions is compared to simultaneous measurements using a differential mobility analyzer (DMA) and condensation particle counter (CPC). Quantitative size classification is demonstrated for pure component NH₄ NO₃ aerosols having mass concentrations 0.25_mu g m -3. Results of fluid dynamics calculations illustrating the performance of the aerodynamic lens are also presented and compared to the measured performance. The utility of this AMS as both a laboratory and field portable instrument is discussed.     

颗粒分布、比表面积、化学组成对水泥强度的影响

水泥的化学组成、细度决定着水泥的力学性能.根据已有的关于水泥颗粒的粒度分布和比表面积的数学模型,对4个不同水泥厂的水泥数据进行了分析,发现这些数据与模型之间没有很好的对应.利用120组数据建立了水泥颗粒的粒度分布与比表面积新的数学模型及28 d抗压强度与4种矿物组成的数学关系式,并把水泥的抗压强度用水泥颗粒大小、比表面积和化学组成表示出来了.     

Particle Size and Temporal Characteristics of Aerosol Composition near Coal-Fired Electric Power Plants of the Eastern Transvaal

Mine-mouth power plants near the rich coal deposits of the eastern Transvaal supply most of the electricity used in the Republic of South Africa. Their emissions of particulate matter are a significant fraction of the total from all sources in the region and may be partly the cause of visibility degradation, especially in the dry winter months. A study in the vicinity of seven plants was conducted during November and December 1980 in order to demonstrate the usefulness of cascade impactors, time sequence streaker filter samplers, and elemental analysis by particle-induced x-ray emission (PIXE) for characterizing coal combustion aerosol at a nonurban site where relatively few nearby industrial or natural aerosol sources were present. Particle size analysis indicated a distribution of elements on the particles from principally coarse to principally fine (submicrometer diameter) in the sequence Ti, Al, Ca, Fe, Mn, Cr, Zn, K, Si, and S, apparently reflecting a progression of element volatility during combustion. S and Si each contributed nearly half the total fine aerosol mass (< 2 μm aerodynamic diameter) of the elements determined. The identification of a distinct fine-mode Si aerosol is a reflection of the high initial ash content of the fuel and the lower efficiency of the particulate control devices in the submicrometer range. Time sequence analysis of aerosol composition with 2-hr resolution indicated associations of concentrations with wind direction and of elements with each other that permitted distinction of individual plumes in the complex source area.     

Toward the Determination of Joint Volatility-Hygroscopicity Distributions: Development and Response Characterization for Single-Component Aerosol

This work presents the development and characterization of a thermodenuder for the study and interpretation of aerosol volatility. Thermodenuder measurements are further combined with a continuous-flow streamwise thermal gradient CCN counter to obtain the corresponding aerosol hygroscopicity. The thermodenuder response function is characterized with monodisperse aerosol of variable volatility and hygroscopicity. The measurements are then interpreted with a comprehensive instrument model embedded within an optimization framework to retrieve aerosol properties with constrained uncertainty. Special attention is given to the interpretation of the size distribution of the thermodenuded aerosol, deconvoluting the effects of impurities and multiple charging, and to simplifications on the treatment of thermodenuder geometry, temperature, the cooling section, and the effects of curvature and accommodation coefficient on inferred particle volatility. Retrieved vapor pressures are consistent with published literature and shown to be most sensitive to uncertainty in the accommodation coefficient.

Copyright 2014 American Association for Aerosol Research     

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.     

Development and Evaluation of a Prototype System for Collecting Sub-Hourly Ambient Aerosol for Chemical Analysis

Aerosol growth technology is used as a means of collecting ambient aerosol particles for subsequent chemical analyses. Condensational growth has previously been used in Condensation Nucleus Counters and in ultrafine particle concentrators at flow rates up to 110 L ^. min^-1. Here, air is sampled at a flow rate of 170 L ^.min^-1     

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     

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.     

Ferroelectrics of Ultrafine Particle Size: II, Grain Growth Inhibition Studies

Inhibition of grain growth in pure, fine-particle-size barium titanate bodies by coating the surfaces of the barium titanate particles with tantalum oxide was so effective that doping with a sintering aid was necessary for densification of the bulk material at temperatures below the melting point. A correlation, which was independent of starting particle size, was established between inhibitor concentration and final grain size of the fired bodies. Barium titanate bodies of predetermined grain size not larger than 2000 A were obtained even with extended firing schedules. In the smallest grain sizes, the Curie point was shifted below the measured temperature range, and hysteresis losses were reduced markedly. The dielectric constant had a smooth variation from approximately 3000 at room temperature to 800 at 180°C.     

Characterization of Fine Particle Material in Ambient Air and Personal Samples from an Underground Mine

Personal samplers representing 4 job classifications and stationary samplers at 2 locations in an underground mine were deployed to measure fine particle carbon (organic/elemental), ions (sulfate plus nitrate), elements (metals and others), and speciated organic compounds including polycyclic aromatic hydrocarbons (PAH), oxygenated PAH, and hopanes/steranes. Chemically segregated size distribution was investigated after collection with a multistage impactor placed at 1 sampling site. All samples exceeded the currently proposed mine air standard of 160 w g/m 3 total carbon, and most exceeded the interim standard of 400 w g/m 3 . Carbon accounted for about 70% of the fine particle mass (described as a reconstructed mass of all measured chemical species); sulfate and ore/waste rock-derived metals constituted most of the remainder. Most of the personal samples were more concentrated than the ambient samples; 1 sample exceeded 2.5 mg/m 3 total mass. The PAH consisted mostly of gas-phase/semivolatile compounds and minor amounts of the particle-phase species, which is consistent with the composition of diesel exhaust, the major source of fine particle material in the mine. Size-segregated chemistry showed that the majority of the material below 1 w m of aerodynamic diameter was carbon, with the largest amount at approximately 0.2 w m. Metals, derived primarily from resuspended ore/waste rock, comprised the majority of the material above 1 w m. Results are placed in context of current mine-monitoring techniques that aim to regulate diesel particulate material.