Showing papers in "Aerosol Science and Technology in 2012"
TL;DR: In this article, the authors evaluated the AMS collection efficiency using independent measurements of fine particle volume or particle-into-liquid sampler (PILS) ion chromatography measurements for three field campaigns with different dominant aerosol mixtures: acidic sulfate particles, ammonium nitrate, and biomass burning emissions.
Abstract: In recent years, Aerodyne aerosol mass spectrometers (AMS) have been used in many locations around the world to study the size-resolved, nonrefractory chemical composition of ambient particles. In order to obtain quantitative data, the mass or (number) of particles detected by the AMS relative to the mass (or number) of particles sampled by the AMS, i.e., the AMS collection efficiency (CE) must be known. Previous studies have proposed and used parameterizations of the AMS CE based on the aerosol composition and sampling line relative humidity. Here, we evaluate these parameterizations by comparing AMS mass concentrations with independent measurements of fine particle volume or particle-into-liquid sampler (PILS) ion chromatography measurements for 3 field campaigns with different dominant aerosol mixtures: (1) acidic sulfate particles, (2) aerosol containing a high mass fraction of ammonium nitrate, and (3) aerosol composed of primarily biomass burning emissions. The use of the default CE of 0.5 for all c...
681 citations
TL;DR: The Soot Particle Aerosol Mass Spectrometer (SP-AMS) as discussed by the authors was developed to measure the chemical and physical properties of particles containing refractory black carbon (rBC).
Abstract: The Soot Particle Aerosol Mass Spectrometer (SP-AMS) was developed to measure the chemical and physical properties of particles containing refractory black carbon (rBC). The SP-AMS is an Aerodyne Aerosol Mass Spectrometer (AMS) equipped with an intracavity laser vaporizer (1064 nm) based on the Single Particle Soot Photometer (SP2) design, in addition to the resistively heated, tungsten vaporizer used in a standard AMS. The SP-AMS can be operated with the laser vaporizer alone, with both the laser and tungsten vaporizers, or with the tungsten vaporizer alone. When operating with only the laser vaporizer, the SP-AMS is selectively sensitive to laser-light absorbing particles, such as ambient rBC-containing particles as well as metal nanoparticles, and measures both the refractory and nonrefractory components. When operated with both vaporizers and modulating the laser on and off, the instrument measures the refractory components of absorbing particles and the nonrefractory particulate matter of all sampled...
354 citations
AVL1
TL;DR: In 2011, the European Commission introduced a limit for nonvolatile particle number (PN) emissions >23 nm from light duty (LD) vehicles and the stated intent is to implement similar legislation for on-road heavy-duty (HD) engines at the next legislative stage as discussed by the authors.
Abstract: In 2011, the European Commission introduced a limit for nonvolatile particle number (PN) emissions >23 nm from light-duty (LD) vehicles and the stated intent is to implement similar legislation for on-road heavy-duty (HD) engines at the next legislative stage. This paper reviews the recent literature regarding the operation-dependent emission of PN from LD vehicles and HD engines, and the measurement procedure used for regulatory purposes. The repeatability of the PN method is of the order of 5% and higher scatter of the results can easily be explained by the effect of the vehicles or the aftertreatment devices on the PN emissions (e.g., the fill state of the diesel particulate filters). Reproducibility remains an issue since it may exceed 30%. These high-variability levels are mainly associated with calibration uncertainties of the PN instruments. Correlation measurements between the full-flow dilution tunnels (constant-volume samplers, CVS) and the proportional partial-flow dilution systems (PFDS) showe...
193 citations
TL;DR: In this article, the influence of ethanol on particulate matter (PM) emissions from gasoline direct injection (GDI) vehicles was explored and two engine calibrations were examined to gauge the robustness of the results.
Abstract: This study explores the influence of ethanol on particulate matter (PM) emissions from gasoline direct injection (GDI) vehicles, a technology introduced to improve fuel economy and lower CO2 emissions, but facing challenges to meet next-generation emissions standards. Because PM formation in GDI engines is sensitive to a number of operating parameters, two engine calibrations are examined to gauge the robustness of the results. As the ethanol level in gasoline increases from 0% to 20%, there is possibly a small ( 30%, there is a statistically significant 30%–45% reduction in PM mass and number emissions observed for both engine calibrations. Particle size is unaffected by ethanol level. PM composition is primarily elemental carbon; the organic fraction increases from ∼5% for E0 to 15% for E45 fuel. Engine-out hydrocarbon and NOx emissions exhibit 10–20% decreases, consistent w...
155 citations
TL;DR: In this article, the authors provided the first evidence for particle-phase hydrolysis of ON groups, a process that could substantially reduce the amount of ozone in the atmosphere, and showed that secondary nitrogen-containing molecules absorb light, with greater absorption under dry and high-NOx conditions.
Abstract: Organonitrate (ON) groups are thought to be important substituents in secondary organic aerosols (SOAs). Model simulations and laboratory studies indicate a large fraction of ON groups in aerosol particles, but much lower quantities are observed in the atmosphere. Hydrolysis of ON groups in aerosol particles has been proposed recently to account for this discrepancy. To test this hypothesis, we simulated formation of ON molecules in a reaction chamber under a wide range of relative humidity (RH) (0 to 90%). The mass fraction of ON groups (5 to 20% for high-NOx experiments) consistently decreased with increasing RH, which was best explained by hydrolysis of ON groups at a rate of 4 day−1 (lifetime of 6 h) for reactions under RH greater than 20%. In addition, we found that secondary nitrogen-containing molecules absorb light, with greater absorption under dry and high-NOx conditions. This work provides the first evidence for particle-phase hydrolysis of ON groups, a process that could substantially reduce O...
143 citations
TL;DR: A photo-acoustic aerosol absorption spectrometer (PAS) built for operation on a research aircraft platform is described in this paper, which is capable of measuring dry absorption at 659 nm, 532 nm, and 404 nm.
Abstract: This paper describes the design and performance of a photo-acoustic aerosol absorption spectrometer (PAS) built for operation on a research aircraft platform. The PAS instrument is capable of measuring dry absorption at 659 nm, 532 nm, and 404 nm, and absorption enhancement due to coatings at 532 nm and 404 nm. The measurement accuracy for all channels is < = 10% and in flight 1 Hz sensitivities lie within the range of 0.5–1.5 Mm−1. PAS measurements of calibrated absorbing aerosol samples are shown to be consistent with measurements made by a previous generation single channel photo-acoustic instrument. Aircraft data collected during a recent field campaign in California are used to demonstrate the capabilities of the PAS. In combination with an aircraft cavity ring down aerosol extinction spectrometer described in a companion paper, the new PAS instrument provides a sensitive airborne in-situ characterization of aerosol optics. Copyright 2012 American Association for Aerosol Research
137 citations
TL;DR: In this article, the authors present measurements of traffic-related pollutants made near the Long Island Expressway (LIE, I-495), in Queens, New York, and observe that pollutant levels build up during the early morning hours under stable boundary layer conditions yet fall off quickly within 150m downwind of the highway.
Abstract: We present measurements of traffic-related pollutants made near the Long Island Expressway (LIE, I-495), in Queens, New York. The Aerodyne Research Inc. (ARI) mobile laboratory (AML) was deployed to map spatial and temporal gradients of gas-phase species and particulate matter (PM) associated with vehicular exhaust in the residential areas near the LIE. We observe that pollutant levels build up during the early morning hours under stable boundary layer conditions yet fall off quickly within 150 m downwind of the highway. An ARI soot particle aerosol mass spectrometer (SP-AMS) provided measurements of the size-resolved chemical composition of refractory black carbon (rBC) and the associated coating species. The average size distribution of the traffic related PM is characterized by a rBC mode centered at ∼100 nm in vacuum aerodynamic diameter, D va (rBC mass fraction ∼50%). A second rBC mode (rBC mass fraction ∼5%) more heavily coated with organic material is also observed at D va ∼500 nm. Positive matrix ...
105 citations
TL;DR: The spark discharge generator (SDG) is a versatile device for the production of nanoparticle aerosols as mentioned in this paper, which can produce aerosol nanoparticles in the entire nanometer range (1-100nm).
Abstract: In the growing field of nanotechnology there is an increasing need to develop production methods for nanoparticles, especially methods that provide control and reproducibility. The spark discharge generator (SDG) is a versatile device for the production of nanoparticle aerosols. It can produce aerosol nanoparticles in the entire nanometer range (1–100 nm), and beyond. Depending on requirements, and the system used, these nanoparticles can be completely contamination free and composed of one or more materials. This provides a unique opportunity to create new materials on the nanoscale. Already in use in semiconductor, materials, health and environmental research, the SDG shows promise for yet more applications. If needed, particle production by the SDG could be scaled up using parallel generators facilitating continuous high-volume production of aerosol nanoparticles. Still, there is a surprisingly low knowledge of fundamental processes in the SDG. In this article we present a thorough review of the most c...
104 citations
TL;DR: In this article, the authors use direct simulation Monte Carlo (DSMC) to evaluate an algebraic expression for the transition regime friction factor that is intended for application to arbitrarily shaped particles.
Abstract: The friction factor of an aerosol particle depends upon the Knudsen number (Kn), as gas molecule–particle momentum transfer occurs in the transition regime. For spheres, the friction factor can be calculated using the Stokes–Millikan equation (with the slip correction factor). However, a suitable friction factor relationship remains sought-after for nonspherical particles. We use direct simulation Monte Carlo (DSMC) to evaluate an algebraic expression for the transition regime friction factor that is intended for application to arbitrarily shaped particles. The tested friction factor expression is derived from dimensional analysis and is analogous to Dahneke's adjusted sphere expression. In applying this expression to nonspherical objects, we argue for the use of two previously developed drag approximations in the continuum (Kn → 0) and free molecular (Kn → ∞) regimes: the Hubbard–Douglas approximation and the projected area (PA) approximation, respectively. These approximations lead to two calculable geo...
95 citations
TL;DR: The MOVI-HRToF-CIMS instrument as discussed by the authors provides quantifiable molecular-level information for both gas and particle-phase organic species on timescales ranging from ≤ 1-s for gases to 10-60 min for particle phase compounds that can be used to efficiently probe secondary organic aerosol (SOA) formation mechanisms.
Abstract: We describe a new instrument, chemical ionization (CI) high-resolution time-of-flight mass spectrometer (ToFMS) coupled to a micro-orifice volatilization impactor (MOVI-HRToF-CIMS). The MOVI-HRToF-CIMS instrument is unique in that, within a compact field-deployable package, it provides (1) quantifiable molecular-level information for both gas and particle-phase organic species on timescales ranging from ≤1 s for gases to 10–60 min for particle-phase compounds that can be used to efficiently probe oxidation and secondary organic aerosol (SOA) formation mechanisms, and (2) relative volatility information of the detected compounds simultaneously estimated using the programmed thermal desorption information obtained from the MOVI. We demonstrate the capabilities of a prototype instrument using known test compounds and complex mixtures generated from the oxidation of biogenic and anthropogenic hydrocarbons. We present spectra obtained using both negative and positive ion CI with acetate (CH3C(O)O−) and protona...
91 citations
TL;DR: In this paper, the effect of PP polydispersity on the fractal dimension, Df, and preexponential factor, kn, of simulated agglomerates of monodisperse primary particles (PP) for ballistic or diffusion-limited particle-cluster and cluster-clusters collision mechanisms was investigated with agglomers consisting of 16 - 1024 PP with closely controlled size distribution (geometric standard deviation, σ g = 1-3).
Abstract: Agglomeration is encountered in many natural or industrial processes, like growth of aerosol particles in the atmosphere and during material synthesis or even flocculation of suspensions, granulation, crystallization and with colloidal particle processing These particles collide by different mechanisms and stick together forming irregular or fractal-like agglomerates Typically, the structure of these agglomerates is characterized with the fractal dimension, Df , and pre-exponential factor, kn , of simulated agglomerates of monodisperse primary particles (PP) for ballistic or diffusion-limited particle-cluster and cluster-cluster collision mechanisms Here, the effect of PP polydispersity on Df and kn is investigated with agglomerates consisting of 16 - 1024 PP with closely controlled size distribution (geometric standard deviation, σ g = 1-3) These simulations are in excellent agreement with the classic structure (Df and kn ) of agglomerates consisting of monodisperse PPs made by four different collision mechanisms as well as with agglomerates of bi-, tri-disperse and normally distributed PPs Broadening the PP size distribution of agglomerates decreases monotonically their Df and for sufficiently broad PP distributions (σ g > 25) the Df reaches about 15 and kn about 1 regardless of collision mechanism Furthermore with increasing PP polydispersity, the corresponding projected area exponent, Dα , and pre-exponential factor, ka , decrease monotonically from their standard values for agglomerates with monodisperse PPs So Df as well as Dα and ka can be an indication for PP polydispersity in mass-mobility and light scattering measurements, if the dominant agglomeration mechanism is known, like diffusion-limited and/or ballistic cluster-cluster coagulation in aerosols
TL;DR: In this article, a strategy for examining the dynamic hygroscopic response of single aerosol particles is reported, allowing a direct investigation of the interplay of thermodynamic and kinetic factors regulating the time dependence of particle size.
Abstract: A strategy for examining the dynamic hygroscopic response of single aerosol particles is reported, allowing a direct investigation of the interplay of thermodynamic and kinetic factors regulating the time dependence of particle size. In particular, we investigate the rapid evaporation of water from water–glycerol droplets, measuring the evolving size with a time resolution of 2 s. The time-dependent measurements of evolving droplet size are compared with an analytical treatment of the evaporation process. Excellent agreement between measurements and simulations is found over a wide range of starting droplet compositions. The benefits of using this a...
TL;DR: In this paper, the authors examined theoretically and numerically collisions of arbitrarily shaped particles in the mass transfer transition regime, where ambiguities remain regarding the collision rate coefficient (collision kernel).
Abstract: We examine theoretically and numerically collisions of arbitrarily shaped particles in the mass transfer transition regime, where ambiguities remain regarding the collision rate coefficient (collision kernel). Specifically, we show that the dimensionless collision kernel for arbitrarily shaped particles, H, depends solely on a correctly defined diffusive Knudsen number (KnD , in contrast with the traditional Knudsen number), and to determine the diffusive Knudsen number, it is necessary to calculate two combined size parameters for the colliding particles: the Smoluchowski radius, which defines the collision rate in the continuum (KnD →0) regime, and the projected area, which defines the collision rate in the free molecular (KnD →∞) regime. Algorithms are provided to compute these parameters. Using mean first passage time calculations with computationally generated quasifractal (statistically fractal) aggregates, we find that with correct definitions of H and KnD , the H(KnD) relationship found valid for ...
TL;DR: In this article, different thermal-optical methods used to measure OC/EC and EC/TC ratios in atmospheric aerosols often produce significantly different results due to variations within the temperature programming and optical techniques of each method.
Abstract: Different thermal-optical methods used to measure OC/EC and EC/TC ratios in atmospheric aerosols often produce significantly different results due to variations within the temperature programming and optical techniques of each method. To quantify the thermal and optical effects on these ratios, various source (residential cookstoves and diesel exhaust) and atmospheric (rural and urban) aerosols were analyzed using 3 thermal protocols: (1) two modified versions of the Birch and Cary (1996, Elemental Carbon-Based Method for Monitoring Occupational Exposures to Particulate Diesel Exhaust. Aerosol Sci. Technol., 25:221–241) National Institute of Occupational Safety and Health (NIOSH 5040) protocol—designated in this paper as NIOSH and NIST-EPA protocols, and (2) the IMPROVE (the Interagency Monitoring of Protected Visual Environments) protocol outlined by Chow et al. 1993 (The DRI Thermal/Optical Reflectance Carbon Analysis System: Description, Evaluation, and Applications in U.S. Air Quality Studies. Atmos. ...
TL;DR: In this article, a nonlinear solution to the mass balance equation for the whole building was used to predict the coagulation rate for two different conditions: central fan on versus central fan off.
Abstract: Indoor ultrafine particles (UFP, 24 nm. The model was parameterized using different values of the Hamaker constant for predicting the coagulation rate. Deposition was determined for two different conditions: central fan on versus central fan off. For the case of a central fan running, deposition rates were measured by using a nonlinear solution to the mass balance equation for the whole building. For the centra...
TL;DR: In this paper, simple modifications to thermally diffusive laminar flow ultrafine condensation particle counters (UCPCs) are described, which allow detection of ∼1 nm condensation nuclei with much higher efficiencies than have been previously reported.
Abstract: This paper describes simple modifications to thermally diffusive laminar flow ultrafine condensation particle counters (UCPCs) that allow detection of ∼1 nm condensation nuclei with much higher efficiencies than have been previously reported. These non-destructive modifications were applied to a commercial butanol-based UCPC (TSI 3025A) and to a diethylene glycol-based UCPC (UMN DEG-UCPC). Size and charge dependent detection efficiencies using the modified UCPCs (BNL 3025A and BNL DEG-UCPC) were measured with high resolution mobility classified aerosols composed of NaCl, W, molecular ion standards of tetra-alkyl ammonium bromide, and neutralizer-generated ions. With negatively charged NaCl aerosol, the BNL 3025A and BNL DEG-UCPC achieved detection efficiencies of 37% (90× increase over TSI 3025A) at 1.68 nm mobility diameter (1.39 nm geometric diameter) and 23% (8× increase over UMN DEG-UCPC) at 1.19 nm mobility diameter (0.89 nm geometric diameter), respectively. Operating conditions for both UCPCs were ...
TL;DR: In this paper, 6 Humic-like substances (HULIS) were isolated from atmospheric total suspended particle (TSP) samples collected at 3 locations in Guangzhou of China, 1 each in summer and winter.
Abstract: Humic-like substances (HULIS) constitute a class of organic compounds identified in atmospheric samples that influence many properties of aerosols in the atmosphere. In this study, 6 HULIS samples were isolated from atmospheric total suspended particle (TSP) samples collected at 3 locations in Guangzhou of China, 1 each in summer and winter. On the basis of analyses by elemental analyzer, more detailed chemical species of elements were explored by proton nuclear magnetic resonance (1H NMR) spectroscopy for hydrogen and X-ray photoelectron spectroscopy (XPS) for carbon, oxygen, nitrogen, and sulfur. The sources of HULIS were identified by carbon isotopic techniques. The results show that HULIS made up an important component of water-soluble organic carbon (WSOC). Carbon and oxygen were the predominant components in the HULIS. The 1H NMR spectra indicated that H functional groups consisted of aliphatic C‒H, aromatic C‒H, H‒C‒C˭, and H‒C‒O groups. They were all characterized by the highest contents of alipha...
TL;DR: In this article, a whole-house method for in situ testing of HVAC filters for size-resolved particle removal in buildings is compared with standard laboratory test results as measured by an independent laboratory and as reported by the manufacturer.
Abstract: Central heating, ventilating, and air-conditioning (HVAC) filters are often the dominant mechanism for particle removal in buildings. However, little is known about filter performance in real environments, particularly in residential and light-commercial buildings where particle concentrations and compositions can be very different from laboratory test conditions. This article explores differences in HVAC filter test protocols and refines a whole-house method for in situ testing of filters for size-resolved particle removal efficiencies. Results from the in situ method are compared with those from a simple upstream–downstream method for three types of commercially available filters in an unoccupied test house. Results from both field methods are compared with standardized laboratory test results as measured by an independent laboratory and as reported by the manufacturer. In general, comparisons between filter efficiency as measured by the refined whole-house method and as measured by the upstream–downstr...
TL;DR: In this article, aqueous hydroxyl radical (∼10−12 M) oxidation of glycolaldehyde, followed by droplet evaporation, forms secondary organic aerosol (SOA) that exhibits an effective liquid vapor pressure and enthalpy of vaporization of ∼10−7 atm and ∼70 kJ/mol, respectively, similar to the mix of organic acids identified in reaction samples.
Abstract: Aqueous hydroxyl radical (∼10−12 M) oxidation of glycolaldehyde (1 mM), followed by droplet evaporation, forms secondary organic aerosol (SOA) that exhibits an effective liquid vapor pressure and enthalpy of vaporization of ∼10−7 atm and ∼70 kJ/mol, respectively, similar to the mix of organic acids identified in reaction samples. Salts of these acids have vapor pressures about three orders of magnitude lower (e.g., ammonium succinate ∼10−11 atm), suggesting that the gas–particle partitioning behavior of glycolaldehyde SOA depends strongly on whether products are present in the atmosphere as acids or salts. Several reaction samples were used to simulate cloud droplet evaporation using a vibrating orifice aerosol generator. Samples were also analyzed by ion chromatography (IC), electrospray ionization mass spectrometry (ESI-MS), IC-ESI-MS, and for total carbon. Glycolaldehyde SOA mass yields were 50–120%, somewhat higher than yields reported previously (40–60%). Possible reasons are discussed: (1) formation...
TL;DR: In this paper, size-dependent removal of UFP by two conifer species: pine and juniper was investigated by placing freshly cut branches into a wind tunnel and measuring UFP size distributions upstream and downstream of the branches.
Abstract: Vegetation is an important sink for atmospheric ultrafine particles (UFP). Prediction of UFP deposition to vegetation, however, is still problematic. In this study, we have investigated size-dependent removal of UFP by two conifer species: pine and juniper. The experiments were performed by placing freshly cut branches into a wind tunnel and measuring UFP size distributions upstream and downstream of the branches. Five air velocities ranging from 0.3 to 1.5 m/s, two packing densities (volume fraction occupied by the branches) and two branch orientations were tested to assess their effect on particle removal. The UFP removal efficiency was found to decrease with increasing particle size, increasing wind speed, and decreasing packing density. The branch orientation did not affect the removal efficiency within the uncertainty of the measurements. To facilitate extrapolation of the measurement results to real-life conditions, we have tested the applicability of filtration theory to particle removal by vegetat...
TL;DR: In this paper, the change of composition, structure, and oxidation reactivity of laboratory-produced soot aerosol with varying iron content was studied, where electron microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDX) was combined with cluster analysis to separate individual particles into definable groups of similar chemical composition representing the particle types in dependence of the iron content in soot.
Abstract: Soot aerosol, which is a major pollutant in the atmosphere of urban areas, often contains not only carbonaceous matter but also inorganic material. These species, for example, iron compounds, originated from impurities in fuel or lubricating oil, additives or engine wear may change the physico-chemical characteristics of soot and hence its environmental impact. We studied the change of composition, structure, and oxidation reactivity of laboratory-produced soot aerosol with varying iron content. Soot types of various iron contents were generated in a propane/air diffusion flame by adjusting the doping amount of iron pentacarbonyl Fe(CO)5 to the flame. Scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDX) was combined with cluster analysis (CA) to separate individual particles into definable groups of similar chemical composition representing the particle types in dependence of the iron content in soot. Raman microspectroscopy (RM) and infrared spectroscopy were applied for the char...
TL;DR: In this article, the effects of dust on black carbon analysis and to optimize filtration methods were evaluated and a correction procedure was suggested and used to revise the elemental carbon and organic carbon measurements of filters with a thermal/optical method.
Abstract: Accurate measurements of black carbon concentrations in snow and ice are essential to quantify its impact on glacial melting and sequential climate forcing via snow albedo However, snow and ice contain dust that may severely bias the precision of the elemental carbon (EC) and organic carbon (OC) measurements of filters with a thermal/optical method To evaluate the effects of dust on black carbon analysis and to optimize filtration methods, meltwater from ice core and surface snow samples with variable dust content were filtered with different methods, including filtration of the entire material (including settling) and supernatant liquid, mechanical stirring and sonication, as well as utilization of single and double quartz filters In this research, it is shown that dust can induce an extra decrease in optical reflectance during the 250°C heating stage in the thermal/optical method and an improper OC and EC split To address this problem, a correction procedure was suggested and used to revise the OC a
TL;DR: In this paper, an analytical solution for the evolution of an organic aerosol size distribution undergoing quasi-equilibrium growth and irreversible diffusion-limited growth is obtained for open and closed systems.
Abstract: Condensation of gas-phase material onto particulate matter
is the predominant route by which atmospheric aerosols evolve. The traditional approach to representing formation of secondary organic aerosols (SOAs) is to assume instantaneous partitioning equilibrium of semivolatile organic compounds between gas and particle phases. Growth occurs as the vapor concentration of the species increases owing to gas-phase chemistry. The fundamental mathematical basis of such a condensation growth mechanism (quasi-equilibrium growth) has been lacking. Analytical solutions
for the evolution of an organic aerosol size distribution undergoing quasi-equilibrium growth and irreversible diffusion-limited growth are obtained for open and closed systems. The quasi-equilibrium growth emerges as a limiting case for semivolatile species condensation when the rate of change of the ambient vapor concentration is slow compared with the rate of establishment of local gas-aerosol equilibrium. The results suggest that the growth mechanism in a particular situation might be inferred from the
characteristics of the evolving size distribution. In certain conditions, a bimodal size distribution can occur during the condensation of a single species on an initially unimodal distribution.
TL;DR: Analysis of OC and EC in about 100 ambient samples collected in the Pearl River Delta in China by implementing the IMPROVE protocol and a NIOSH-derived (ACE-Asia) protocol reveals that the cause of the EC difference could be quantitatively attributed to temperature protocol and optical pyrolysis correction method.
Abstract: Organic carbon (OC) and elemental carbon (EC) are operationally defined due to the lack of definitive standards. Consequently, their quantification is protocol dependent. IMPROVE and NIOSH are the two widely used thermal/optical protocols for OCEC analysis, differing in temperature programs and in the optical method for charring correction. The IMPROVE protocol is often implemented on a DRI analyzer while the NIOSH protocol is often implemented on a Sunset Laboratory Analyzer. Evaluation of the implementation of the IMPROVE protocol on the Sunset Laboratory analyzer or implementation of the NIOSH or NIOSH-derived protocols on the DRI analyzer has rarely been reported. We analyzed OC and EC in about 100 ambient samples collected in the Pearl River Delta in China by implementing the IMPROVE protocol and a NIOSH-derived (ACE-Asia) protocol on both a DRI Model 2001 analyzer and a Sunset Laboratory analyzer. The total carbon (TC) and EC filter loading as determined by the ACE-Asia protocol on the Sunset analyz...
TL;DR: In this paper, the authors introduce a new physical approach to account for the influence of surface roughness on the dry deposition velocity, which relies on a hybrid parameter that combines the roughness height and the peak-to-peak distance between roughness elements.
Abstract: Dry deposition is a primary mechanism by which suspended particles are transported from gas onto surfaces. Prediction of this transport rate is needed in a vast range of applications, including environmental, industrial, and engineering, and in studying the impacts of aerosols. Besides air flow characteristics and properties of aerosol particles, the dry deposition velocity depends greatly on surface properties. However, existing models describe rough surfaces with only one parameter, the surface roughness height, and are therefore of limited accuracy. Here, we introduce a new, and yet simple, physical approach to account for the influence of surface roughness on the dry deposition velocity. The approach relies on a hybrid parameter that combines the surface roughness height and the peak-to-peak distance between roughness elements. Our new approach is able to predict the deposition velocity accurately, being superior to many of the earlier models, which overpredict deposition velocities by a factor as hig...
TL;DR: In this article, the authors investigated the antiviral activity of two natural disinfectants, i.e., TTO and eucalyptus oil (EUO), against the influenza virus captured onto the filter surface.
Abstract: Our previous studies demonstrated that precoating of filter fibers with biologically active tea tree oil (TTO) enhances physical collection efficiency of conventional heating, ventilation, and air conditioning (HVAC) filters, and provides cost effective and rapid inactivation of captured bacterial and fungal particles on the filter surface. The main aim of this study was to investigate the antiviral activity of two natural disinfectants, i.e., TTO and eucalyptus oil (EUO), against the influenza virus captured onto the filter surface. It was found that both tested oils possess strong antiviral properties when used as fiber coating materials, capable of inactivating captured microorganisms within 5–10 min of contact on the fiber surface. The antiviral activity of TTO was also successfully challenged in aerosol form by mixing viable airborne viral particles with oil droplets in the rotational aerosol chamber. The results look very promising for further development of virus inactivating procedures and technol...
TL;DR: In this article, a new computational fluid dynamics (CFD) modeling approach for pharmaceutical aerosols is further developed by evaluating the effects of turbulence, polydisperse aerosol size distribution, and multiple lung lobes on deposition in the mouth-throat and entire tracheobronchial (TB) airways.
Abstract: In this study, a new computational fluid dynamics (CFD) modeling approach for pharmaceutical aerosols is further developed by evaluating the effects of turbulence, polydisperse aerosol size distribution, and multiple lung lobes on deposition in the mouth–throat (MT) and entire tracheobronchial (TB) airways. To evaluate a range of respiratory drug delivery conditions, a model dry powder inhaler (DPI; NovolizerTM) and a model spray soft-mist inhaler (SMI; RespimatTM) were considered. The respiratory geometry consisted of a previously developed characteristic MT and complete upper TB geometry through the third bifurcation (B3). More distal TB airways were simulated using stochastic individual path (SIP) models extending into each of the five lung lobes through bifurcation B15. Based on comparisons with new in vitro deposition data, results indicated that the low Reynolds number (LRN) k–ω turbulence model with near-wall corrections for anisotropic turbulence and velocity conditions accurately predicted deposi...
TL;DR: In this article, an evaluation of the nature of sub-23-nm particles downstream of the European Particulate Measurement Programme (PMP) methodology, with prescribed cycles and on-road flow-of-traffic driving conditions, was provided.
Abstract: This study provides an evaluation of the nature of sub-23-nm particles downstream of the European Particulate Measurement Programme (PMP) methodology, with prescribed cycles and on-road flow-of-traffic driving conditions. Particle number concentrations and size distributions were measured using two PMP measurement systems running simultaneously. For this analysis, the focus is on the real-time results from multiple instruments. The results revealed that a significant fraction of particles downstream of both PMP systems for all tested cycles were below 11 nm. The fraction of sub-11-nm particles observed downstream of the PMP system decreased when the overall dilution ratio of one PMP system was increased from 300 to 1500, suggesting those sub-11-nm particles were formed through re-nucleation of semivolatile precursors. When the evaporation tube temperature was increased from 300°C to 500°C, no difference in particle number concentrations was observed, suggesting that incomplete evaporation of semivolatile ...
TL;DR: In this study, the amounts of gas-phase and particle-bound ROS in tobacco smoke were determined using 2′,7′-dichlorodihydrofluorescin diacetate as the fluorescent probe with hydrogen peroxide as the standard.
Abstract: Reactive oxygen species (ROS) have been related to adverse health effects in recent years. Previous studies have reported ROS concentrations in mainstream smoke, but the reports have shown considerable variability and conclusions. There have been no prior measurements on sidestream smoke. In this study, the amounts of gas-phase and particle-bound ROS in tobacco smoke were determined using 2′,7′-dichlorodihydrofluorescin diacetate (DCFH-DA) as the fluorescent probe with hydrogen peroxide as the standard. Both research and commercially available cigarettes were tested using mainstream and sidestream smoke generated by a Single Cigarette Smoking Machine. For mainstream smoke from regular and light cigarettes, the total quantities of ROS were 120–150 nmol and 90–110 nmol, respectively. For sidestream smoke, the values were 60–90 nmol and 30–70 nmol for regular and light cigarettes, respectively. The effects of the cigarette filter on the emissions were to reduce the particle mass and particle-phase ROS in the...
TL;DR: In this article, a new technique for measuring the primary organic aerosol (POA) emissions from internal combustion engines is presented, which combines thermal-optical OC/EC analysis and thermal desorption gas chromatography mass spectrometry (TD-GC-MS) of quartz filter samples collected using a dilution sampler to quantify the total emissions of low-volatility organics and to distribute them across the volatility basis set.
Abstract: A new technique for measuring the primary organic aerosol (POA) emissions from internal combustion engines is presented. The method combines thermal-optical OC/EC analysis and thermal desorption gas chromatography mass spectrometry (TD-GC-MS) of quartz filter samples collected using a dilution sampler to quantify the total emissions of low-volatility organics and to distribute them across the volatility basis set. These data can be used in conjunction with partitioning theory to predict the gas-particle partitioning and thus the total amount of POA over the entire range of atmospheric conditions. The approach is evaluated using POA emissions data from two gas-turbine engines and one diesel generator. To evaluate the new method, we directly measured the effects of temperature and concentration on gas-particle partitioning of the emissions from each. Predictions based on the volatility distributions derived from the filter analyses are consistent with the direct partitioning measurements. The new approach r...