Showing papers in "Aerosol Science and Technology in 2008"
TL;DR: In this article, the authors investigated the effect of particulate phase on AMS collection efficiency for ammonium nitrate, ammonium sulfate, mixed ammonium ionate/ammonium sulfates, and particles coated with an organic liquid, and found that the higher CEs for liquid particles compared with solid particles tended to stick upon impact with the AMS vaporizer.
Abstract: The Aerodyne Aerosol Mass Spectrometer (AMS) is a useful tool to study ambient particles. To be quantitative, the mass or (number) of particles detected by the AMS relative to the mass (or number) of particles sampled by the AMS, or the AMS collection efficiency (CE), must be known. Here we investigated the effect of particulate phase on AMS CE for ammonium nitrate, ammonium sulfate, mixed ammonium nitrate/ammonium sulfate, and ammonium sulfate particles coated with an organic liquid. Dry, solid ammonium sulfate particles were sampled with a CE of 24 ± 3%. Liquid droplets and solid particles that were thickly coated with a liquid organic were collected with a CE of 100%. Mixed phase particles, solid particles thinly coated with liquid organic, and metastable aqueous ammonium sulfate droplets had intermediate CEs. The higher CEs for liquid particles compared with solid particles were attributed to wet or coated particles tending to stick upon impact with the AMS vaporizer, while a significant fraction of s...
317 citations
TL;DR: In this article, light absorption by soot or nigrosin dye aerosol particles were measured in the laboratory using a particle soot absorption photometer (PSAP) and a photo-acoustic spectrometer (PAS) to assess the influence of nonabsorbing organic aerosol (OA) on the PSAP measurements.
Abstract: Light absorption by soot or nigrosin dye aerosol particles were measured in the laboratory using a particle soot absorption photometer (PSAP) and a photo-acoustic spectrometer (PAS) to assess the influence of non-absorbing organic aerosol (OA) on the PSAP measurements. For the PSAP, particle light absorption is measured after collection on a filter, whereas for the PAS light absorption is measured while the particles remain suspended in the gas phase. OA was generated from the reaction of α -pinene with ozone. It was observed that the presence of this OA in an external mixture of absorbing aerosol and OA can cause an increase in the light absorption measured by the PSAP, relative to that measured by the PAS, by more than a factor of two. This enhancement in the PSAP absorption was found to increase as the amount of OA increased relative to the absorbing compound. Additionally, experiments where absorbing aerosol was deposited on a PSAP filter prior to addition of OA demonstrated that the non-absorbing OA ...
228 citations
TL;DR: In this article, the basic equations governing the responses of single and tandem differential mobility analyzer (DMA) systems are summarized, and a new lognormal approximation to the DMA transfer function is introduced leading to a simple Lognormal form for the TDMA response function.
Abstract: The basic equations governing the responses of single and tandem differential mobility analyzer (DMA) systems are summarized. Particle diffusion within the DMA resulting in broadening of the transfer function is included in this analysis. For tandem DMA (TDMA) work, a given particle diameter exiting the first DMA is modeled in the following conditioner as growing into a multi-modal lognormal distribution before entering the second DMA. Approximations and solution techniques for both single and tandem DMA systems are discussed. A new lognormal approximation to the DMA transfer function is introduced leading to a simple lognormal form for the TDMA response function. The maximum absolute error of the transfer function is 0.10 at 200 nm in the range plus or minus one and a half standard deviations of the lognormal fit. It is 0.035 at 3 nm in the range plus or minus two standard deviations of the lognormal fit. The maximum fractional error in the calculated TDMA response is no more than 0.08 at 200 nm and 3 nm...
205 citations
TL;DR: In this article, a new numerical approach for solving coagulation equation, TEMOM model, is presented, where the closure of the moment equations is approached using the Taylor-series expansion technique.
Abstract: A new numerical approach for solving coagulation equation, TEMOM model, is first presented. In this model, the closure of the moment equations is approached using the Taylor-series expansion technique. Through constructing a system of three first-order ordinary differential equations, the most important indexes for describing aerosol dynamics, including particle number density, particle mass and geometric standard deviation, are easily obtained. This approach has no prior requirement for particle size spectrum, and the limitation existing in the log-normal distribution theory automatically disappears. This new approach is tested by comparing it with known accurate solutions both in the free molecular and the continuum regime. The results show that this new approach can be used to solve the particle general dynamic equation undergoing Brownian coagulation with sufficient accuracy, while less computational cost is needed.
202 citations
TL;DR: Wehner et al. as discussed by the authors designed and constructed a thermodenuder based on the design of Wehner et. al. (2002), which consists of a heated tube held at a constant temperature by a 3-zone controller, followed by a cooling zone with a diffusion tube lined with activated charcoal for adsorption of evaporated gases.
Abstract: A thermodenuder (TD) system, based on the design of Wehner et al. (2002), was designed, constructed, and characterized in the laboratory. The TD consists of a heated tube (2.5 cm ID, 55 cm long) held at a constant temperature by a 3-zone controller, followed by a cooling zone with a diffusion tube lined with activated charcoal for adsorption of evaporated gases. An important improvement over previous designs is the ability to step through TD temperatures in ∼ 10 min. per step by the reduction of thermal inertia, and the addition of two cooling fans. The TD was characterized in the laboratory, showing that temperature profiles inside are relatively uniform and for response to standard generated particle species. Losses at ambient temperature are close to diffusion losses estimated with literature techniques and to those experimentally measured by Wehner et al. Particle number losses are observed to increase for volatile species upon heating due to particles shrinking to sizes where diffusion and thermophor...
196 citations
TL;DR: In this paper, the authors investigated particle resuspension from human activities in a full-scale experimental chamber and found that heavy and fast walking was associated with higher particle ressuspension rates than less active walking.
Abstract: Experiments investigating particle resuspension from human activities were conducted in a full-scale experimental chamber. The experiments tested three types of flooring (vinyl tiles, new and old level-loop carpets) and two ventilation configurations (ceiling and side wall supply systems). The floorings were seeded with 0.1–10 μ m test particles. The airborne particle concentration was measured by an array of optical particle counters (OPCs) in the chamber. Resuspension rates were estimated in size ranges of 0.8–1, 1.0–2.0, 2.0–5.0, and 5.0–10 μm ranging from 10−5–10−2 hr−1, with higher resuspension rates associated with larger particles. Resuspension via walking activity varied from experiment to experiment. “Heavy and fast” walking was associated with higher resuspension rates than less active walking, most likely due to a combination of increased pace, increased air swirl velocity, and electrostatic field effects established by the walking. The type of floorings also influenced the particle resuspensio...
164 citations
TL;DR: In this article, a rapid, inexpensive, method that can be employed to assess the potential of sub-mg masses of PM to generate oxidative stress in alveolar macrophage cells is presented.
Abstract: Both short- and long-term exposure to particulate matter (PM) air pollution have been demonstrated to cause increases in cardiovascular disease, cancer, and respiratory disorders. Although the specific mechanisms by which exposure to PM cause these affects are unclear, significant evidence has accumulated to suggest that PM exposure leads to increased inflammation as the result of excessive production of reactive oxygen species (ROS) in critical cell types. In order to better understand how real-world PM exposure causes adverse health effects, there is a need to efficiently integrate metrics of PM toxicity into large scale air monitoring and health effects/epidemiology studies. Here we describe a rapid, inexpensive, method that can be employed to assess the potential of sub-mg masses of PM to generate oxidative stress in alveolar macrophage cells. Importantly, the approach is compatible with routine daily PM sampling programs such as those administered by EPA (Speciation trends network (STN), IMPROVE netw...
151 citations
Journal Article•
TL;DR: In this paper, the sizing accuracies of two widely used yet hitherto unevaluated optical particle counters (OPCs) as well as one high-resolution, non-commercial OPC were evaluated.
Abstract: The sizing accuracies of two widely used yet hitherto unevaluated optical particle counters (OPCs—Grimm Model 1.109 and Palas Model WELAS 2100) as well as one high-resolution, non-commercial OPC were evaluated. The measured data were compared to scattering intensity calculations based on Mie theory. Additionally, the counting efficiency for all three counters was measured, as was the influence of coincidence effects for the OPC with the lowest (manufacturer specified) upper concentration limit. Beside the traditional polystyrene latex calibration, a little-known, very fast and precise “multimodal” calibration method was used, which is based on the simultaneous generation of up to eight sharp multiple-charge modes from polydisperse di-ethyl-hexyl-sebacate (DEHS) particles by electrical mobility classification.
130 citations
TL;DR: The Zurich Ice Nucleation chamber (ZINC) as mentioned in this paper is a continuous flow diffusion chamber with a flat parallel plate geometry that can operate at temperatures as low as 236 K with the current setup with ice supersaturations of up to 50%.
Abstract: A new instrument to study ice nucleation, the Zurich Ice Nucleation Chamber (ZINC), has been constructed. It is a continuous flow diffusion chamber following the design by Rogers (1988) but has a flat parallel plate geometry. The instrument can operate at temperatures as low as 236 K with the current setup with ice supersaturations of up to 50%. The typical sample flow is 1 lpm with a total flow of 10 lpm using twice 4.5 lpm for sheath flows. FLUENT simulations were performed and are presented to discuss the flow, temperature, and humidity profiles within the main chamber. Activation experiments with silver iodide particles were used to validate the instrument against literature data. We report the onset of freezing for an activated fraction of 2% of all particles. The data exhibit an almost linear trend between 257 K (111.5% RHi) and 237 K (119% RHi) with very good agreement with literature data.
122 citations
TL;DR: Two pressure-controlled inlets have been designed and integrated into the Aerodyne Aerosol Mass Spectrometer (AMS) inlet system containing an aerodynamic aerosol lens system for use in airborne measurements as mentioned in this paper.
Abstract: Two pressure-controlled inlets (PCI) have been designed and integrated into the Aerodyne Aerosol Mass Spectrometer (AMS) inlet system containing an aerodynamic aerosol lens system for use in airborne measurements. Laboratory experiments show that size calibration and mass flow rate into the AMS are not affected by changes in upstream pressure (P 0 ) of the PCI as long as the pressure within the PCI chamber (P PCI ) is controlled to values lower than P 0 . Numerous experiments were conducted at different P PCI , P 0 , and AMS lens pressures (P Lens ) to determine particle transmission efficiency into the AMS. Based on the results, optimum operating conditions were selected which allow for constant pressure sampling with close to 100% transmission efficiency of particles in the size range of ∼ 100–700 nm vacuum aerodynamic diameter (d va ) at altitudes up to ∼ 6.5 km. Data from an airborne field study are presented for illustration.
116 citations
TL;DR: In this article, the authors evaluated the effect of condensation particle growth on the transport and deposition of concentrated cigarette smoke particles in the upper respiratory tract under various relative humidity and temperature conditions.
Abstract: Previous experimental studies have shown that concentrated cigarette smoke particles (CSPs) deposit in the upper airways like much larger 6 to 7 μ m aerosols. Based on the frequent assumption that relative humidity (RH) in the lungs does not exceed approximately 99.5%, the hygroscopic growth of initially submicrometer CSPs is expected to be a relatively minor factor. However, the inhalation of mainstream smoke may result in humidity values ranging from sub-saturated through supersaturated conditions. The objective of this study is to evaluate the effect of condensation particle growth on the transport and deposition of CSPs in the upper respiratory tract under various RH and temperature conditions. To achieve this objective, a computational model of transport in the continuous phase surrounding a CSP was developed for a multicomponent aerosol consisting of water soluble and insoluble species. To evaluate the transport and deposition of dilute hygroscopic CSPs in the upper airways, a model of the human mou...
TL;DR: In this paper, an Aerodyne quadrupole-based Aerosol Mass Spectrometer (Q-AMS) is used to measure speciated aerosol fluxes by the direct eddy covariance technique.
Abstract: Until now, micrometeorological measurements of surface/ atmosphere exchange fluxes of submicron aerosol chemical components such as nitrate, sulfate or organics could only be made with gradient techniques. This article describes a novel setup to measure speciated aerosol fluxes by the more direct eddy covariance technique. The system is based on the Aerodyne quadrupole-based Aerosol Mass Spectrometer (Q-AMS), providing a quantitative measurement of aerosol constituents of environmental concern at a time resolution sufficient for eddy-covariance. The Q-AMS control software was modified to maximize duty cycle and statistics and enable fast data acquisition, synchronized with that of an ultrasonic anemometer. The detection limit of the Q-AMS based system for flux measurements ranges from 0.2 for NO3 − to 15 ng m−2 s−1 for hydrocarbon-like organic aerosol (HOA), with an estimated precision of around 6 ng m−2 s−1, depending on aerosol loading. At common ambient concentrations the system is capable of resolving...
TL;DR: A polarity-based extraction/fractionation method validated with standard compounds was used to characterize organic aerosol samples collected during the Pittsburgh Air Quality Study (PAQS) as discussed by the authors.
Abstract: A polarity-based extraction/fractionation method validated with standard compounds was used to characterize organic aerosol samples collected during the Pittsburgh Air Quality Study (PAQS). Organic extracts were separated into 5 polarity classes by sequential elution with hexane, dichloromethane, ethyl acetate, acetone, and methanol. Organic mass (OM) and carbon mass (OC) were measured in samples, their extracts, and their corresponding fractions yielding OM/OC ratios and the contribution of each polarity fraction to total OM. The study average OM/OC ratio for each fraction [(OM/OC)fraction] varied from 1.37 for the hexane fraction to 2.25 for the methanol fraction. OM/OC ratios for “non-extractable” organics ((OM/OC)N-E) were also predicted; the study average (OM/OC)N - E was 2.54, consistent with ratios of 2.1–3.2 for water-soluble organic aerosol species. Annual average ratios with and without the contributions of the “non-extractable” material [(OM/OC)total and (OM/OC)extract, respectively] were 2.05 ...
TL;DR: In this article, the quality of composite filters composed of micrometer and nanometer fibers is evaluated using the figure of merit, also known as the quality factor, and analytical expressions for the pressure drop and filtration efficiency are used to compute the figure.
Abstract: We investigate the filtration performance of composite filters composed of micrometer and nanometer fibers. The filter quality is evaluated using the figure of merit, also known as the quality factor. We use analytical expressions for the pressure drop and filtration efficiency to compute the figure of merit. The effects on the figure of merit by fiber diameter, solidity, and thickness of nanometer and micrometer fibers and face velocity are investigated. Experimental data obtained using conventional filter media and nanofiber composite filters are then used to verify the calculated results. We find that for large particles (approximately 0.1 μm and above), nanofibers can improve the figure of merit compared to conventional filters. Smaller fiber size, larger solidity, and thickness of the nanofiber layer lead to better filtration performance in this size range. For small particles (approximately below 0.1 μm), nanofibers do not improve the figure of merit compared to conventional filter media. Larger fib...
TL;DR: A Euro 4 Light-Duty Diesel vehicle equipped with a diesel particulate filter (DPF) was circulated to 9 labs where repetitions of the current regulatory New European Drive Cycle (NEDC) were conducte...
Abstract: A Euro 4 Light-Duty Diesel vehicle equipped with a diesel particulate filter (DPF) was circulated to 9 labs where repetitions of the current regulatory New European Drive Cycle (NEDC) were conducte...
TL;DR: Wang et al. as discussed by the authors conducted a one-year study of airborne microbial concentration and size distribution at three selected sampling sites in Beijing and found that the concentration of total culturable microorganisms ranged from 4.8 × 10 2 colony forming units (CFU)/m 3 to 2.4 × 10 4 CFU/m 3, with an arithmetic mean of 3.7 × 10 3 ± 2.
Abstract: A one-year (from June 2003 to May 2004) study of airborne microbial concentration and size distribution was conducted systematically at three selected sampling sites in Beijing. Microbial samples were collected in triplicate for 3 min, 3 times per day, for 3 consecutive days of each month using FA-I sampler (imitated Andersen sampler, made by Applied Technical Institute of Liaoyang, China). Results showed that the concentration of total culturable microorganisms ranged from 4.8 × 10 2 colony forming units (CFU)/m 3 to 2.4 × 10 4 CFU/m 3 , with an arithmetic mean of 3.7 × 10 3 ± 2.1 × 10 2 (standard deviation) CFU/m 3 . As a whole, the percentage of airborne bacteria, accounting for 59.0% of the total culturable microorganisms, was significantly higher than those of airborne fungi (35.2%) and actinomycetes (5.8%). At RCEES (Research Center for Eco-Environmental Sciences—a culture and education area) and XZM (Xizhimen—a main traffic line), significantly higher percentages of airborne bacteria were found as ...
TL;DR: In this article, an atmospheric measurement campaign took place in the spring of 2006 to characterize the emission of particles from an integrated iron and steelmaking site, where the PM 10 daily limit value of 50 μ g m − 3 was not exceeded during any day.
Abstract: An atmospheric measurement campaign took place in the spring of 2006 to characterize the emission of particles from an integrated iron and steelmaking site. During the measurement campaign, the PM 10 daily limit value of 50 μ g m − 3 was not exceeded during any day. However, excursions in PM 10 concentrations occurred over periods of a few hours which were associated with wind passing over the steelworks' site. Measurements with an Aerosol Time-of-Flight Mass Spectrometer (ATOFMS) showed six particle classes associated with emissions from steelmaking processes. Two of these were iron-rich, one showing internal mixing with nitrate, the other internally mixed with phosphate, which subsequent analysis identified as arising from the ironmaking sector and the hot and cold mills as the dominant sources, respectively. Other ATOFMS classes were rich in lead, zinc, and nickel, which were also associated with steelmaking sources. A Micro Orifice Uniform Deposit Impactor (MOUDI), used to measure particle size distri...
TL;DR: In this paper, the authors investigated the resuspension and subsequent translocation of particulate matter (PM) from carpeted flooring surfaces due to walking and the effect of HVAC systems and ceiling fans on mixing and/or translocating of resuspended PM.
Abstract: This work investigated the resuspension and subsequent translocation of particulate matter (PM) from carpeted flooring surfaces due to walking. In addition, the effect of HVAC systems and ceiling fans on mixing and/or translocation of resuspended PM was studied. Testing took place both in a residence with a well-worn, soiled carpet and in an environmental test chamber. Prescribed walking occurred with PM measurements taken at multiple sampling heights. Scanning electron microscopy (SEM) of carpet fibers was used to determine the fraction of dust available for resuspension. These data, in conjunction with resuspended mass concentrations from this study, were used to generate emission factors by particle size for walking on both new and worn carpet. Carpet loading does not affect the emission factor, indicating that the amount of resuspended PM is directly proportional to the available PM in the carpet. While relative humidity (RH) plays an important role in resuspension from new carpets, with high RH enhan...
TL;DR: The Aerosol Parameter Estimation (APE) model as discussed by the authors is an inverse model that solves the aerosol general dynamic equation to determine best estimates for the size-dependent wall-loss rate.
Abstract: A goal of secondary organic aerosol (SOA) experiments performed in smog chambers is to determine the condensation of SOA onto suspended particles. Complicating the calculation of the condensation rate are uncertainties in particle wall-loss rates. Wall-loss rates generally depend on particle size, turbulence in the bag, the size and shape of the bag, and particle charge. In analyzing smog-chamber data, some or all of the following assumptions are commonly made regarding the first-order wall-loss rate constant: (a) that it is constant during an experiment; (b) that it is constant between experiments; and (c) that it is not a strong function of particle size for the relatively narrow size distributions in smog chamber experiments. Each of these assumptions may not be justified in some circumstances. We present the development and evaluation of the Aerosol Parameter Estimation (APE) model. APE is an inverse model that solves the aerosol general dynamic equation to determine best estimates for the size-depend...
TL;DR: In this paper, a Lagrangian-based particle tracking model with near-wall correction functions for turbulence was employed to simulate the fate of expiratory droplets in a three-bed hospital ward setting.
Abstract: The transport and removal characteristics of expiratory droplets at different supply airflow rates and “coughing” orientations were investigated both numerically and experimentally in a three-bed hospital ward setting. A Lagrangian-based particle-tracking model with near-wall correction functions for turbulence was employed to simulate the fate of the expiratory droplets. The model was tested against experimental droplet dispersion data obtained in an experimental hospital ward using Interferometric Mie Imaging and a light-scattering aerosol spectrometer. The change in airflow supply rate had insignificant effect on the transport and deposition of very large droplets (initial sizes ≥ 87.5 μm) due to the dominance of gravitational settling on these behaviors. Smaller droplets (initial sizes ≤ 45 μm) exhibited certain airborne behaviors. The effect of thermal plumes from heat sources was observed only when the supply airflow was low and when the droplet size was small, as observed in the vertical mixing pat...
TL;DR: In this article, the authors discuss the use of tandem measurements to measure various transport properties (e.g., dynamic shape factor, sedimentation speed, diffusion coefficient) and physicochemical properties such as mixing state, shape, fractal dimension, density, vapor pressure, equilibrium water content, composition).
Abstract: When multiple instruments are used in tandem it is possible to obtain more complete information on particle transport and physicochemical properties than can be obtained with a single instrument. This article discusses tandem measurements in which submicrometer particles classified according to electrical mobility are then characterized with one or more additional methods. Measurement combinations that are summarized here include mobility plus mass, aerodynamic (or vacuum aerodynamic) diameter, integrated or multiangle light scattering, composition by single particle mass spectrometry, electron microscopy, and so on. Such measurements enable intercomparisons of different measures of size including mobility diameter, optical size, aerodynamic diameter, volume (for agglomerates and nanowires), length (for nanowires), and mass, even for particles that are morphologically and chemically complex. In addition, the article summarizes the use of tandem techniques to measure various transport properties (e.g., dynamic shape factor, sedimentation speed, diffusion coefficient) and physicochemical properties (e.g., mixing state, shape, fractal dimension, density, vapor pressure, equilibrium water content, composition). In addition to providing an overview of such tandem measurements we describe previously unreported results from several novel tandem measurement methods.
TL;DR: In this paper, the lattice Boltzmann method was used for the calculation of deposition efficiency on nanosized particles for the system consisting of two nano- and micro-sized fibers.
Abstract: Filtration of aerosol particles using composites of nano- and microsized fibrous structures is a promising method of effective separation of nanoparticles from gases. The multiscale physical system describing the flow pattern and particles deposition in it requires other than a continuous approach for the process analysis. The lattice-Boltzmann method was used for the calculation of deposition efficiency on nanosized particles for the system consisting of two nano- and microsized fibers. The proposed method allows to calculate the deposition efficiency of nanoparticles on both fibers for a very wide range of Knudsen numbers in the case of each nanofiber considering molecular, slip, and continuous flow patterns. The nanofiber is a significant attractor for collecting particles as an element of multiscale fibers of the filtration composite. The results of particle deposition efficiency calculated for the microfiber, using proposed method, are similar to those obtained from the classical continuum approach (...
TL;DR: Using an environmental transmission electron microscope (ETEM), this paper showed that a significant amount of water, far exceeding the multilayers caused by surface adsorption, is associated prior to deliquescence with substrate-supported NaCl particles.
Abstract: Using an environmental transmission electron microscope (ETEM), we show that a significant amount of water, far exceeding the multilayers caused by surface adsorption, is reversibly associated prior to deliquescence with substrate-supported NaCl particles (dry diameters of ∼ 40 nm to 1.5 μ m; ∼ 18°C). We hypothesize that the water is present as an aqueous solution containing dissolved Na and Cl ions. Water uptake occurs at relative humidities (RH) as low as 70%, and the resulting liquid layer coating the particles is stable over extended times if the RH is held constant. We exposed CaSO 4 and CaSO 4 · 2H 2 O particles to elevated RH values in the ETEM to show that chemically nonspecific condensation of gas-phase water on the TEM substrate does not explain our observations. Furthermore, damage to the NaCl surface induced by the electron beam and small fluctuations in RH do not seem to contribute to or otherwise affect water uptake. We have similar observations of water association for other alkali halide p...
TL;DR: In this article, the performance characteristics of an ultrafine water condensation particle counter (UWCPC, TSI3786) were examined using different temperature differences between saturator and growth tube.
Abstract: In this study we examined performance characteristics of an ultrafine water condensation particle counter (UWCPC, TSI3786). The detection efficiency was investigated using different temperature differences between saturator and growth tube. The cut-sizes D90, D50, D10, and D0 were determined by fitting a two-free-parameter equation to the experimental data. The determined cut-sizes were comparable (± 8%) with other two widely used fitting equations. The cut-sizes were studied changing the growth tube temperature from 65 to 78°C and varying the saturator temperature from 8 to 20°C. For silver particles the smallest detected cut-size D50 was 2.9 nm, and the largest one –4.5 nm, and in default operation conditions it was 3.9 nm. Additionally, the effect of particle chemical composition on the detection efficiency was studied. The cut-sizes D50 were 2 2.9, 2.3, and 1.8 nm for silver, ammonium sulfate, and sodium chloride particles, respectively. A concentration calibration was performed with high particle num...
TL;DR: In this paper, the performance of the Artium Flight PDI, an instrument specifically designed for airborne cloud measurements, is studied Drop size distributions, liquid water content, and velocity distributions are compared with those measured by other airborne instruments.
Abstract: Conducting accurate cloud microphysical measurements from airborne platforms poses a number of challenges The technique of phase Doppler interferometry (PDI) confers numerous advantages relative to traditional light-scattering techniques for measurement of the cloud drop size distribution, and, in addition, yields drop velocity information Here, we describe PDI for the purposes of aiding atmospheric scientists in understanding the technique fundamentals, advantages, and limitations in measuring cloud microphysical properties The performance of the Artium Flight PDI, an instrument specifically designed for airborne cloud measurements, is studied Drop size distributions, liquid water content, and velocity distributions are compared with those measured by other airborne instruments
TL;DR: In this paper, an automated monitor for the continuous sampling of ambient aerosol and the measurement of concentrations of ROS on the sampled aerosol was developed, and the dichlorofluorescein (DCFH) fluorescence method was found to be the most non-specific, general indicator of particle-bound oxidants.
Abstract: Previous studies have found significant quantities of oxidative species associated with airborne particulate matter. Although oxidative stress is thought to be an important part of the mechanism by which particles produce adverse health effects, the lack of a suitable method to measure ROS on a routine basis has resulted in no work being undertaken to assess the effects of particle-bound ROS on health. In order to fill this need, an automated monitor for the continuous sampling of ambient aerosol and the measurement of concentrations of ROS on the sampled aerosol was developed. Potential methods to quantify ROS were compared in order to arrive at a suitable method to automate. The dichlorofluorescein (DCFH) fluorescence method was found to be the most non-specific, general indicator of particle-bound oxidants. Hence it was deemed the best suited method for the automated monitor. An integrated sampling-analysis system was designed and constructed based on collection of atmospheric particles in an aqueous s...
TL;DR: The DASH-SP as mentioned in this paper is a new instrument developed to perform rapid, size-resolved aerosol hygroscopicity measurements, with time resolution as short as a few seconds.
Abstract: We report on a new instrument developed to perform rapid, size-resolved aerosol hygroscopicity measurements. The differential aerosol sizing and hygroscopicity spectrometer probe (DASH-SP) employs differential mobility analysis in-concert with multiple humidification and optical sizing steps to determine dry optical size and hygroscopic growth factors for size-selected aerosols simultaneously at three elevated relative humidities. The DASH-SP has been designed especially for aircraft-based measurements, with time resolution as short as a few seconds. The minimum particle diameter detected with 50% efficiency in the optical particle counters (OPCs) is 135 ± 8 nm, while the maximum detectable particle diameter is in excess of 1 μm. An iterative data processing algorithm quantifies growth factors and “effective” refractive indices for humidified particles using an empirically derived three-dimensional surface (OPC pulse height–refractive index–particle size), based on a calculated value of the “effective” dry particle refractive index. Excellent agreement is obtained between DASH-SP laboratory data and thermodynamic model predictions for growth factor dependence on relative humidity for various inorganic salts. Growth factor data are also presented for several organic acids. Oxalic, malonic, glutaric, and glyoxylic acids grow gradually with increasing relative humidity up to 94%, while succinic and adipic acids show no growth. Airborne measurements of hygroscopic growth factors of ship exhaust aerosol during the 2007 Marine Stratus/Stratocumulus Experiment (MASE II) field campaign off the central coast of California are presented as the first report of the aircraft integration of the DASH-SP.
TL;DR: In this article, a simple and novel unipolar charger using carbon fiber ionizers was developed to effectively charge fine and ultra-fine aerosol particles without the generation of ozone, and particle penetration in the charger was investigated for non-charged, neutralized, and singly charged particles in the size range of 20-200 nm.
Abstract: A simple and novel unipolar charger using carbon fiber ionizers was developed to effectively charge fine and ultra-fine aerosol particles without the generation of ozone. The particle penetration in the charger was investigated for non-charged, neutralized, and singly charged particles in the size range of 20–200 nm. Particle loss and the intrinsic, exit and extrinsic charging efficiencies of fine and ultra-fine particles were also investigated for non-charged particles at different applied voltages to the charger. Particle penetrations in the charger were nearly 100% for particles larger than 20 nm, irrespective of the initial particle charging state. Particle losses in the charger could be decreased by decreasing the applied voltage to the charger from 4.0 kV to 2.3 kV. The intrinsic charging efficiencies were proportionally increased with the applied voltage, whereas the exit charging efficiencies were almost independent of the applied voltage. Therefore, the extrinsic charging efficiency of the charge...
Abstract: Quinones are reactive organic compounds known to initiate reactions associated with a host of toxicological events. Their presence in different atmospheres has been demonstrated although their sources remain uncertain. As a result of their reactivity and instability during chemical analysis, only a limited number of studies have reported on atmospheric concentrations of quinones in ambient air. Furthermore, besides the limited information on quinones associated with particulate matter, no previous studies have quantified vapor-phase quinones. We report vapor- and particle-phase concentrations of 1,2- and 1,4-naphthoquinones (1,2-NQ, 1,4-NQ), 9,10-phenanthraquinone (9,10-PQ), and 9,10-anthraquinone (9,10-AQ), measured over a 5-year period in Southern California. The results showed that vapor-phase concentrations of the target quinones were in general higher than those in the particle-phase. Vapor-phase concentrations ranged from 80 pg/m 3 for the AQ to 1747 pg/m 3 for the 1,4-NQ, and the particle-phase con...
TL;DR: In this paper, a new development combining thermo-desorption and humidification aerosol conditioning in series is presented that allows to measure changes in the hygroscopic behavior of aerosol at 90% relative humidity.
Abstract: The nature of atmospheric aerosols is extremely complex and often requires advanced analytical tools for the determination of its physical and chemical properties. In particular, the interaction of particles with atmospheric water is a complex function of both particle size and composition. The ability of a particle to grow in a humid environment can be measured by humidity tandem differential mobility analyzing techniques (H-TDMA). In this article, we present a new development combining thermo-desorption and humidification aerosol conditioning in series that allows to measure changes in the hygroscopic behavior of aerosol at 90% relative humidity (RH) after conditioning of the particle by thermo-desorption to a temperature between 25°C and 300°C. The main feature of this system, named Volatility Hygroscopic—Tandem Differential Mobility Analyzer (VH-TDMA), is to allow for rapid (10 minutes) series of scans to control particle response to 1-thermal conditioning, 2- RH increase to 90% and 3—a combination of...