Development of polydisperse aerosol generation and measurement
procedures for wind tunnel evaluation of size-selective aerosol samplers
Andrew Darta, Jonathan D. Krugb , Carlton L. Witherspoonc, Jerome Gilberrya,c, Quentin Malloya,
Surender Kaushikb, and Robert W. Vanderpoolb
aRTI International, Research Triangle Park, North Carolina, USA; bU.S. EPA, Research Triangle Park, North Carolina, USA; cJacobs Technology Inc., Research Triangle Park, North Carolina, USA
ABSTRACT
Accurate development and evaluation of inlets for representatively collecting ambient particulate matter typically involves the use of monodisperse particles in aerosol wind tunnels. However, the resource requirements of using monodisperse aerosols for inlet evaluation creates the need for more rapid and less-expensive techniques to enable determination of size-selective performance in aerosol wind tunnels. The goal of recent wind tunnel research at the U.S. EPA was to develop and validate the use of polydisperse aerosols, which provide more rapid, less resource-intensive test results, which still meet data quality requirements necessary for developing and evaluating ambient aerosol inlets. This goal was successfully achieved through comprehensive efforts regarding polydisperse aerosol generation, dispersion, collection, extraction, and analysis over a wide range of aerodynamic particle sizes.
Using proper experimental techniques, a sampler’s complete size-selective efficiency curve can be estimated with polydisperse aerosols in a single test, as opposed to the use of monodisperse aerosols, which require conducting multiple tests using several different particle sizes. While this polydisperse aerosol technique is not proposed as a regulatory substitute for use of monodisperse aerosols, the use of polydisperse aerosols is advantageous during an inlet’s development where variables of sampling flow rate and inlet geometry are often iteratively evaluated before a final inlet design can be successfully achieved. Complete Standard Operating Procedures for the generation, collection, and analysis of polydisperse calibration aerosols are available from EPA as downloadable files. The described experimental methods will be of value to other researchers during the development of ambient sampling inlets and size-selective evaluation of the inlets in aerosol wind tunnels.
Hygroscopicity of dimethylaminium-, sulfate-, and ammonium-containing
nanoparticles
Olli-Pekka Tikkanena, , Olli V€ais€anena, , Liqing Haoa, Eemeli Holopainena, Hao Wanga,b,c,
Kari E. J. Lehtinena,d, Annele Virtanena, and Taina Yli-Juutia
aDepartment of Applied Physics, University of Eastern Finland, Kuopio, Finland; bInstitute for Environmental and Climate Research, Jinan University, Guangzhou, China; cJNU-QUT Joint Laboratory for Air Quality Science and Management, Jinan University, Guangzhou, China; dAtmospheric Research Centre of Eastern Finland, Finnish Meteorological Institute, Kuopio, Finland
ABSTRACT
Dimethylamine (DMA) and sulfuric acid (SA) are the important constituents of atmospheric aerosols. To accurately predict the behavior of DMA-containing aerosol systems, exact thermodynamic models are needed. The applicability of these models needs to be tested carefully in different experimental settings to continuously validate and improve their performance. In this work, the Extended Aerosol Inorganics Model (E-AIM) was used to simulate the hygroscopicity of aerosol particles generated from five different aqueous DMA-SA solutions. The applicability of the model was tested in the 10–200 nm size range and from DMASA molar ratios ranging from 1:3 to 2:1. The aerosol hygroscopic growth at 0–80% RH was determined with two tandem differential mobility analyzers, and the composition of the generated particles was measured with the Aerosol Mass Spectrometer (AMS), which revealed that the particles contained also ammonium. The model accurately captured the hygroscopicity for particles larger than 80 nm. With particles smaller than 80 nm, the model underestimated the hygroscopicity in all the studied experimental conditions. An increase in hygroscopicity parameter j with decreasing particle size implied a plausible base evaporation
in the experimental setup, which in turn may have affected the modeled hygroscopicity as the composition of the smallest particles may have differed from the AMS measurements. Coupling E-AIM to a dynamic evaporation model, however, could not produce compositions whose modeled hygroscopic behavior would match the measured hygroscopic growth at smaller sizes. Our results, therefore, suggest that DMA thermodynamics are not modeled correctly in E-AIM or there exists uncertainty in the physicochemical parameters.
Copper– zinc particles with zinc-enriched surfaces generated
via spray pyrolysis
Ryan Felixa , Joseph Repaca , Yujia Lianga , Afshan Urooja, Howard Glicksmanb , and
Sheryl Ehrmana,c
aDepartment of Chemical and Biomolecular Engineering, University of Maryland, College Park, Maryland, USA; bDuPont Electronic Technologies, Research Triangle Park, North Carolina, USA; cCharles W. Davidson College of Engineering, San Jose State University, San Jose, California, USA
ABSTRACT
Copper is an inexpensive replacement for silver in electronic applications such as solar cell metallization, electromagnetic interference packaging, and printable electronics. However, copper has a characteristically low reduction potential under ambient conditions, favoring formation of non-conducting copper oxides. Here, a spray pyrolysis method of producing oxidation resistant copper particles with surfaces rich in zinc, without need for post-fabrication modifications is described. The effects of precursor and reactor parameters on the particle surface composition with respect to the bulk composition are explored. At reactor temperature conditions of 1000 C with a precursor containing 90 at% copper–10 at% zinc, the formation of desired morphologies was achieved, smooth dense particles with surfaces enriched in zinc. Increasing the concentration of zinc in the precursor did not improve enrichment, and instead led to the formation of a zinc diamine chloride [Zn(NH3)2Cl2] byproduct.
Trends in the oxidation and relative volatility of chamber-generated
secondary organic aerosol
Kenneth S. Dochertya, Eric W. Corsea, Mohammed Jaouib, John H. Offenbergb, Tadeusz E. Kleindienstb,
Jonathan D. Krugb , Theran P. Riedelb, and Michael Lewandowskib
aJacobs Technology, Inc., Research Triangle Park, Durham, North Carolina, USA; bUnited States Environmental Protection Agency, Office of Research and Development, Research Triangle Park, Durham, North Carolina, USA
ABSTRACT
The relationship between the oxidation state and relative volatility of secondary organic aerosol (SOA) from the oxidation of a wide range of hydrocarbons is investigated using a fast-stepping, scanning thermodenuder interfaced with a high-resolution time-of-flight aerosol mass spectrometer (AMS). SOA oxidation state varied widely across the investigated range of parent hydrocarbons but was relatively stable for replicate experiments using a single hydrocarbon precursor. On average, unit mass resolution indicators of SOA oxidation (e.g., AMS f43 and f44) are consistent with previously reported values. Linear regression of H:C vs. O:C obtained from parameterization of f43 and f44 and elemental analysis of high-resolution spectra in Van Krevelen space both yield a slope of 0.5 across different SOA types. A similar slope was obtained for a distinct subset of toluene/NOx reactions in which the integrated oxidant exposure was varied to alter oxidation. The relative volatility of different SOA types displays similar variability and is strongly correlated with SOA oxidation state (OSC). On average, relatively low oxidation and volatility were observed for aliphatic alkene (including terpenes) and n-alkane SOA while the opposite is true for mono- and polycyclic aromatic hydrocarbon SOA. Effective enthalpy for total chamber aerosol obtained from volatility differential mobility analysis is also highly correlated with OSC indicating a primary role for oxidation levels in determining the volatility of chamber SOA. Effective enthalpies for chamber SOA are substantially lower than those of neat organic standards but are on the order of those obtained for partially oligomerized glyoxal and methyl glyoxal.
Reducing the risk of particulate matter containing asbestos using a highefficiency, low-differential pressure system
Sung Ho Hwanga, Jaehoon Rohb,c,d,e, Chanjung Parkf, Jongcheol Kimf, Byong Hyoek Leef, and
Wha Me Parkb,c
aNational Cancer Control Institute, National Cancer Center, Goyang-si, Gyeonggi-do, South Korea; bGraduate School of Public Health, Yonsei University, Seoul, South Korea; cThe institute for Occupational Health, Yonsei University College of Medicine, Seoul, South Korea; dDepartment of Preventive Medicine, College of Medicine, Yonsei University, Seoul, Korea; eIncheon Worker’s Health Center, Incheon, Korea; fThe Environment Technology Institute Coway Co Ltd., Seoul, South Korea
ABSTRACT
The purpose of this study was to improve the efficiency of filters used in asbestos control systems, such as those used at asbestos removal sites. We evaluated the melt-blown (MB) filter media for their asbestos removal efficiencies. The filter grades were based on the ISO and European standards (EN 1822) of E12 ( 99.5% collection efficiency) and H13 ( 99.95% collection efficiency) with a size of <0.2 lm asbestos diameter. Based on test chamber experiments, the asbestos removal efficiency of the grade H13 MB filter (99.974%) was higher than that of the E12 grade MB filter (97.120%). In addition, the lowest level of pressure drop was observed in the case with a 3.8 mm pitch interval. The concentrations of airborne asbestos based on phase contrast microscopy in the sites with asbestos concentrations presenting high risks before turning on the asbestos control system was 0.038 fiber cm 3 at demolition site A and 0.027 fiber cm 3 at demolition site B. Chrysotile asbestos was detected at both demolition sites A and B before turning on the system, but were not detected after using the system. Therefore, MB filters present an efficient alternative to current commercial filters and should be considered for use in asbestos removal applications.
An intercomparison of aerosol absorption measurements conducted during
the SEAC4RS campaign
B. Masona,b, , N. L. Wagnera,b , G. Adlera,b , E. Andrewsa,b , C. A. Brocka , T. D. Gordona,b, , D. A. Lacka,b, A. E. Perringa,b, , M. S. Richardsona,b , J. P. Schwarza,b , M. A. Shookc, K. L. Thornhillc, L. D. Ziembad , and D. M. Murphya
aNOAA Earth System Research Laboratory, Boulder, Colorado, USA; bCooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA; cScience Systems and Applications, Inc., Hampton, Virginia, USA; dNASA Langley Research Center, Hampton, Virginia, USA
ABSTRACT
During the SEAC4RS campaign in 2013, inflight measurements of light-absorption by aerosol in biomass burning and agriculture fire plumes were collected along with concomitant measurements of aerosol extinction, scattering, and black carbon mass concentration. Here, we compare three measurements of aerosol absorption coefficients: from a photoacoustic spectrometer (PAS), a particle soot absorption photometer (PSAP), and a continuous light absorption photometer (CLAP). Each of these
absorption measurements was collected in three visible spectral regions: red, green, and blue (although the precise wavelength and bandwidth vary with each instrument). The absorption measurements were compared during the plumes, in the boundary layer, and in the free troposphere. The slopes from the comparison ranged from 0.6 to 1.24. For biomass burning plumes, the uncertainty in the absorption measurements translates into a range in single scattering albedos of 0.93–0.94 at a wavelength of 660 nm, 0.94–0.95 at 532 nm and 0.92–0.95 at 405 nm. Overall, the aerosol absorption instruments agreed within their stated accuracies. Comparisons with simultaneous measurements of refractive black carbon mass concentration (collected by a single particle soot photometer), were used to derive the mass absorption coefficients (MAC). For all wavelengths, the MAC was high by greater than a factor of three compared to the expected MAC for black carbon.
Thermophoresis at small but finite Peclet numbers
Yu Chen Chang and Huan J. Keh
Department of Chemical Engineering, National Taiwan University, Taipei, Taiwan, ROC
ABSTRACT
The thermophoretic motion of a spherical particle suspended in a gaseous medium possessing a uniform temperature gradient is analytically studied for a small but nonzero P eclet number Pe. The Knudsen number is small for the gas motion in the slip-flow regime, and the thermal creep, temperature jump, frictional slip, and thermal stress slip are allowed over the particle surface. Through the use of a method of matched asymptotic expansions, the energy and momentum equations governing the problem are solved and an expansion formula for the thermophoretic velocity of the particle good to O ðPe3 Þ is obtained in closed form. This singular perturbation analysis shows that the perturbed temperature and velocity fields are of O ðPe Þ, but the first correction to the particle velocity is of O ðPe2 Þ. This correction can be either negative or positive depending on several thermal and interfacial parameters, indicating that the effect of heat convection is complex and can retard or enhance the thermophoresis of the particle. The convection effect is generally negligible as Pe 0:1 but significant as Pe equals about unity
Performance evaluation of the HR-ELPI þ inversion
Sampo Saaria,b, Anssi Arffmana, Juha Harraa , Topi Ronkk€ o€ a , and Jorma Keskinena
aAerosol Physics Lab, Tampere University of Technology, Tampere, Finland; bClean Air and Acoustic Solutions, VTT Technical Research Centre of Finland, Tampere, Finland
ABSTRACT
Data inversion methods used in aerosol measurement instruments have significant influence on the resolution and quality of the result. A freshly launched new electrical low pressure impactor (ELPI) instrument version, high resolution ELPI þ (HR-ELPI þ, Dekati Ltd.), uses an iterative inversion calculation method to improve particle size resolution, concentration, and data analysis quality. In this article, the performance of the HR-ELPI þ is critically analyzed by simulations and experiments in laboratory and field conditions, and the results are compared with a conventional inversion data analysis method (cut-point diameter concept) and with common reference instruments (e.g., SMPS and EEPS). The results showed that the HRELPI þ inversion has limited performance at the lower and upper limits of the instrument’s size range, and can suffer if the raw currents have signal dependent noise more than 50% or electric noise more than 1%. However, the HR-ELPI þ clearly provide remarkably better resolution and quality with low oscillation risk compared to the conventional cut-point diameter concept of the ELPI. The HR-ELPI þ also showed generally very similar size distributions and number concentrations compared to the reference instruments. Abbreviations: DEHS: dioctyl sebacate; DMA: differential mobility analyzer; EEPS: engine exhaust particle sizer spectrometer; ELPI þ: electrical low pressure impactor (Dekati Ltd.); GMD: geometric median diameter; GSD: geometric standard deviation; HR-ELPI þ: high resolution low pressure impactor (Dekati Ltd.); HRLPI: high-resolution low-pressure cascade impactor (Arffman et al. 2014); RMSE: root-mean-square error; SMPS: scanning mobility particle spectrometer
Thermal/optical reflectance equivalent organic and elemental carbon
determined from federal reference and equivalent method fine particulate
matter samples using Fourier transform infrared spectrometry
Andrew T. Weakleya, Satoshi Takahamab, and Ann M. Dillnera
aAir Quality Research Center, University of California Davis, Davis, California, USA; bENAC/IIE Swiss Federal Institute of Technology Lausanne (EPFL), Lausanne, Switzerland
ABSTRACT
A fine particulate matter (PM2.5) monitoring network of filter-based federal reference methods and federal equivalent methods (FRM/FEMs) is used to assess local ambient air quality by comparison to National Ambient Air Quality Standards (NAAQS) at about 750 sites across the continental United States. Currently, FRM samplers utilize polytetrafluoroethylene (PTFE) filters to gravimetrically determine PM2.5 mass concentrations. At most of these sites, sample composition is unavailable. In this study, we present the proof-of-principle estimation of the carbonaceous fraction of fine aerosols on FRM filters using a nondestructive Fourier transform infrared (FT-IR) method. Previously, a quantitative FT-IR method accurately determined thermal/optical reflectance equivalent organic and elemental carbon (a.k.a., FT-IR organic carbon [OC] and elemental carbon [EC]) on filters collected from the chemical speciation network (CSN). Given the similar configuration of FRM and CSN aerosol samplers,
OC and EC were directly determined on FRM filters on a mass-per-filter-area basis using CSN calibrations developed from nine sites during 2013 that have collocated CSN and FRM samplers. FRM OC and EC predictions were found to be comparable to those of the CSN on most figures of merit (e.g.,R2) when the type of PTFE filter used for aerosol collection was the same in both networks. Although prediction accuracy remained unaffected, FT-IR OC and EC determined on filters produced by a different manufacturer show marginally increased prediction errors suggesting that PTFE filter type influences extending CSN calibrations to FRM samples. Overall, these findings suggest that quantifying FT-IR OC and EC on FRM samples appears feasible.
Detection of RDX traces at the surface with sonic aerosol flow desorption
Viktor V. Pervukhin and Yuri N. Kolomiets
Nikolaev Institute of Inorganic Chemistry of SB RAS, Novosibirsk, Russia
ABSTRACT
The use of a high-speed aerosol flow is proposed for sampling RDX from the surface followed by chromatographic analysis. The aerosol is generated from different solvents by means of a coaxial nebulizer. The effect of the aerosol flow parameters (solvent flowrate, an angle of the nebulizer inclination with respect to the surface) and various solvents (water, acetone, and hexane) on the efficiency of the RDX desorption was investigated. The optimal angle of the nebulizer was found to be 30 , under these conditions, the desorption of RDX from the surfaces of different structure (metal, glass, leather, cotton fabric, and paper) has
also been studied. It is shown that under the action of an aerosol created using water and acetone, desorption from a smooth surface occurs most efficiently (1.5 times higher than with hexane). In this case, the sample removes almost completely (about 80%) by the aerosol flow in a few seconds. A relationship between the desorption efficiency and the amount of the solvent sprayed (that is the amount of aerosol particles in desorbing flow) has a characteristic maximum which location depends on the properties of the solvent spray. This effect is associated with a rate of solvent evaporation. Under optimal conditions for desorption of RDX from a smooth surface using an aqueous aerosol, an LOD of 10 ng can be achieved. For porous and rough surfaces, the efficiency of the analyte desorption decreases (three times for leather and cotton fabric). The results of the experiments conducted allow one to conclude that the RDX solubility in the solvent used does not affect considerably the
efficiency of the RDX desorption. It is assumed that small aerosol drops are very active and can capture the particles of the target analyte. This promotes the desorption of RDX molecules from the surface.
Growth rate and oscillation frequency of electrified jet and droplet: Effects
of charge and electric field
Boo-Hyoung Banga,b , Min-Woo Kima , Yong-Il Kima, and Sam S. Yoona
aSchool of Mechanical Engineering, Korea University, Seoul, Korea; bTechnology Development Team, Daewoo Institute of Construction Technology, Jangan-gu, Suwon, Korea
ABSTRACT
Electrified jets are applied industrially in agriculture, automobiles, targeted drug delivery systems, spacecraft propulsion units, liquid metal sprayers, ion sources, emulsifiers, dust scavenging systems, and ink-jet printers. Electrified columnar jets experience instability caused by electrohydrodynamic interactions of the charged liquid surfaces with electric fields. Electrostatic and surface tension forces competing along the liquid surface create surface pressure differences. The temporal rise and fall of the surface pressure induce oscillations of jets and droplet. A linear theory was derived to yield a dispersion equation determining the most dominant wavelength of oscillation for a given charge level and electric field; this enabled the estimation of the diameter of an atomized droplet. In addition, the frequency of oscillation was derived for a cylindrical jet and spherical droplet. Parametric studies were performed for various charging levels and electric field strengths.
