The Experts below are selected from a list of 249 Experts worldwide ranked by ideXlab platform
Myoseon Jang - One of the best experts on this subject based on the ideXlab platform.
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Aerosol acidity measurement using colorimetry coupled with a reflectance UV-visible spectrometer
Aerosol Science and Technology, 2012Co-Authors: Jiaying Li, Myoseon JangAbstract:In this study, aerosol acidity was measured using colorimetry integrated with a Reflectance UV-Visible spectrometer (C-RUV). An inorganic aerosol comprising NH4+-H+-SO42--H2O was generated using an atomizer and introduced into a 2-m(3) indoor Teflon Film chamber. The produced aerosol was collected on the Teflon-coated glass fiber filter dyed with metanil yellow (MY) as an indicator for measuring proton concentrations in aerosol. A calibration curve for measuring aerosol acidity using the C-RUV technique was obtained through the relationship between the absorbance of the UV-Visible spectrum of the filter sample vs. theoretically calculated proton concentrations using the E-AIM Model II. To develop the C-RUV method under various humidities, the aerosol filter sample was mounted inside a small optical flow chamber controlled for humidity in situ. The humidity effect on the equilibrium thermodynamics of the indicator was theoretically described by inclusion of excess acidity (X) into the calibration curve. The calibration curve obtained from relatively highly acidic aerosols (e.g., H2SO4, NH4H3(SO4)(2), and(NH4)(7)H-13(SO4)(10)) was extrapolated to estimate proton concentrations for weakly acidic aerosols (e.g., NH4HSO4 and (NH4)(3)H(SO4)(2)), which is more relevant to the ambient aerosol acidity but has been poorly predicted with typical inorganic thermodynamic models due to the limited experimental data. The C-RUV technique of this study permits one to estimate aerosol acidity for a variety of compositions of the NH4+-H+-SO42--H(2)Osystem including both ammonia-poor and ammonia-rich sulfate aerosols.
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Colorimetric Particle Acidity Analysis of Secondary Organic Aerosol Coating on Submicron Acidic Aerosols
Aerosol Science and Technology, 2008Co-Authors: Myoseon Jang, Jared J. PaulAbstract:The particle acidity of secondary organic aerosol (SOA) created from ozonolysis of α-pinene in the presence of acidic inorganic seed aerosols was investigated using an indoor Teflon Film chamber. Colorimetry integrated with a reflectance UV-Visible spectrometer was used for the first time to dynamically measure the aerosol acidity over time. An external calibration curve was produced based on the correlation between the proton mass (ng) collected on the filter, which was impregnated with metanil yellow, and the absorbance of the reflectance UV-Visible spectra for the protonated and the unprotonated metanil yellow on the filter. Using this calibration curve, the particle acidity of the submicron acidic sulfate aerosol coated with SOA was measured from the reflectance UV-Visible spectra of filter samples. The colorimetric analysis requires a short sampling time (less than 2 m) for SOA studies using the laboratory Teflon Film chamber and eliminates extraction of the filter sample with water. Results show tha...
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Colorimetric particle acidity analysis of secondary organic aerosol coating on submicron acidic aerosols
Aerosol Science and Technology, 2008Co-Authors: Myoseon Jang, Gang Cao, Jared PaulAbstract:The particle acidity of secondary organic aerosol (SOA) created from ozonolysis of α-pinene in the presence of acidic inorganic seed aerosols was investigated using an indoor Teflon Film chamber. Colorimetry integrated with a reflectance UV-Visible spectrometer was used for the first time to dynamically measure the aerosol acidity over time. An external calibration curve was produced based on the correlation between the proton mass (ng) collected on the filter, which was impregnated with metanil yellow, and the absorbance of the reflectance UV-Visible spectra for the protonated and the unprotonated metanil yellow on the filter. Using this calibration curve, the particle acidity of the submicron acidic sulfate aerosol coated with SOA was measured from the reflectance UV-Visible spectra of filter samples. The colorimetric analysis requires a short sampling time (less than 2 m) for SOA studies using the laboratory Teflon Film chamber and eliminates extraction of the filter sample with water. Results show that the particle acidity of the aerosol decreased over time due to the formation of organic sulfate through the interaction of sulfuric acid with SOA products. The feasibility of this method is also demonstrated for the measurement of the acidity of ambient particles.
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Atmospheric secondary aerosol formation by heterogeneous reactions of aldehydes in the presence of a sulfuric acid aerosol catalyst
Environmental Science and Technology, 2001Co-Authors: Myoseon Jang, Richard M. KamensAbstract:Particle growth by the heterogeneous reaction of aldehydes was evaluated in 0.5 m3 Teflon Film bags under darkness in the presence of background seed aerosols. The aldehydes used were as follows: glyoxal, butanal, hexanal, octanal, and decanal. To study acid catalyst effects on aldehyde heterogeneous reactions, one of the Teflon bags was initially filled with seed aerosols composed of ammonium sulfate-aerosol acidified with sulfuric acid. These results were compared to particle growth reactions that contained only ammonium sulfate as a background seed aerosol. The gas-phase aldehydes were then added to the Teflon bags. In selected experiments, 1-decanol was also added to the Teflon bags with aldehydes to clarify particle growth via a heterogeneous hemiacetal/acetal formation in the presence/absence of an acid catalyst. The particle size distribution and growth were measured using a scanning mobility particle sizer (TSI-SMPS), and the results were applied to predicting aerosol growth and size distribution changes by condensation and heterogeneous reactions. Aerosols created from the heterogeneous reactions of aldehydes were collected directly on an ungreased zinc selenide (ZnSe) FTIR disk (25 mm in diameter) by impaction. The ZnSe disks were directly analyzed for product functional groups inthe aerosol phase using a Fourier transform infrared (FTIR) spectrometer with a deuterated triglycine sulfate (DTGS) detector. Aerosol growth by heterogeneous aldehyde reactions proceeds via a hydration, polymerization process, and hemiacetal/acetal formation from the reaction of aldehydes with alcohols. These aldehyde heterogeneous reactions were accelerated in the presence of an acid catalyst, H2SO4, and led to higher aerosol yields than when H2SO4 was not present in the seed aerosol. The FTIR spectra obtained from the growing aerosol, also illustrated aldehyde group transformation in the particle phase as a function of the heterogeneous reaction. It was concluded that aldehydes, which can be produced by atmospheric photochemical reactions, can significantly contribute on secondary aerosol formation through heterogeneous reactions in the presence of an acid catalyst.
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Partitioning of Semivolatile Organic Compounds in the Presence of a Secondary Organic Aerosol in a Controlled Atmosphere
Journal of Atmospheric Chemistry, 1999Co-Authors: Keri B. Leach, Richard M. Kamens, Michael R. Strommen, Myoseon JangAbstract:The gas-particle partitioning of select semivolatile organic compounds (SOCs) was studied by injecting the SOCs into a 190 m3 Teflon Film chamber containing a secondary organic aerosol (SOA) generated by volatilizing liquid α-pinene into an ozone-concentrated atmosphere. The concentration of total suspended particulates (TSP) and gas and particle-phase SOCs was measured over the course of three experiments spanning a temperature range of 268–297 K and a relative humidity range of 55–100%. An equilibrium partition coefficient, Kp, was calculated for each sampling event. Empirical relationships were then developed to predict the partitioning of the SOCs on the SOA particle source as a function of temperature. Partitioning in this SOA system was compared to that of a SOA generated by the photochemical reaction of NOx with m-xylene. The results indicate that partitioning is similar between the two SOA systems. The effects of multiple particle sources on partitioning was also examined, revealing that a weighted average of predicted Kp values for individual sources can be used to predict partitioning in aerosol mixtures.
Jared Paul - One of the best experts on this subject based on the ideXlab platform.
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Colorimetric particle acidity analysis of secondary organic aerosol coating on submicron acidic aerosols
Aerosol Science and Technology, 2008Co-Authors: Myoseon Jang, Gang Cao, Jared PaulAbstract:The particle acidity of secondary organic aerosol (SOA) created from ozonolysis of α-pinene in the presence of acidic inorganic seed aerosols was investigated using an indoor Teflon Film chamber. Colorimetry integrated with a reflectance UV-Visible spectrometer was used for the first time to dynamically measure the aerosol acidity over time. An external calibration curve was produced based on the correlation between the proton mass (ng) collected on the filter, which was impregnated with metanil yellow, and the absorbance of the reflectance UV-Visible spectra for the protonated and the unprotonated metanil yellow on the filter. Using this calibration curve, the particle acidity of the submicron acidic sulfate aerosol coated with SOA was measured from the reflectance UV-Visible spectra of filter samples. The colorimetric analysis requires a short sampling time (less than 2 m) for SOA studies using the laboratory Teflon Film chamber and eliminates extraction of the filter sample with water. Results show that the particle acidity of the aerosol decreased over time due to the formation of organic sulfate through the interaction of sulfuric acid with SOA products. The feasibility of this method is also demonstrated for the measurement of the acidity of ambient particles.
E E Fesenko - One of the best experts on this subject based on the ideXlab platform.
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Selective Heating of Membrane-forming Holes in Teflon Film Exposed to Decimeter Waves
Biofizika, 2020Co-Authors: S I Alekseev, E E FesenkoAbstract:Calculations of heating of membrane-forming holes in Teflon Film exposed to decimeter waves were performed. The dependence of the temperature increment in holes on the geometry of holes, electrolyte concentration, and decimeter wave frequency was studied. The kinetics of heating depending on the hole diameter was also obtained. It was concluded that the observed in the experiment effects of the decimeter wave on bilayer lipid membranes resulted from the elevated concentration of decimeter electromagnetic waves in membrane-forming hole that led to selective heating of electrolyte in hole and bilayer lipid membranes.
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selective heating of membrane forming holes in Teflon Film exposed to decimeter waves
Biophysics, 2015Co-Authors: S I Alekseev, E E FesenkoAbstract:The heating of a membrane-forming hole in a Teflon Film upon irradiation with decimeter waves was calculated. The dependence of the temperature increase in the membrane-forming hole on its geometry, the concentration of electrolyte solution, and the frequency of decimeter radiation were studied. The heating kinetics of the hole depending on its diameter were obtained. It is concluded that the effects of decimeter waves on bilayer lipid membranes that were observed in experiments are caused by the concentration of the electromagnetic field of decimeter waves at the membrane-forming hole, which lead to the selective heating of the electrolyte in the hole with the bilayer lipid membranes.
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enhanced absorption of microwaves within cylindrical holes in Teflon Film
IEEE Transactions on Biomedical Engineering, 2010Co-Authors: S I Alekseev, E E Fesenko, M S ZiskinAbstract:Earlier publications demonstrated that 0.9 GHz microwave exposure induced notable changes of the conductivity of modified bilayer lipid membranes (BLM) formed in holes in thin Teflon Film (TF). The aims of this study were: 1) to perform detailed calculations of the microwave field distributions in holes formed in TF, using the finite-difference time-domain technique and 2) to model microwave heating of the hole under the conditions used in the BLM experiments but in the absence of BLM in the hole. We found that with the E -field oriented perpendicular to the TF plane the local-specific absorption rate in holes increased significantly. The increase became larger with increasing electrolyte concentration and with decreasing diameter of the hole and frequency. The calculated temperature elevations in the hole were in good agreement with those determined experimentally. These findings allowed us to conclude that the microwave effects on BLM conductivity reported previously resulted mostly from the enhanced absorption of microwave energy by the membrane-forming holes and subsequent local temperature elevation in the holes.
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on the mechanism of microwave action on bilayer lipid membranes the role of the membrane forming hole in Teflon Film
Biophysics, 2009Co-Authors: S I Alekseev, M S Ziskin, E E FesenkoAbstract:The distributions of specific absorption rate (SAR) and E-field in the membrane-forming hole of Teflon Film and the surrounding electrolyte were calculated for 0.9 GHz microwave exposure. It was found that SAR in the hole increased greatly with increasing thickness of the Teflon Film, increasing electrolyte concentration, and decreasing diameter of the hole. The previously demonstrated significant changes in the conductivity of modified bilayer lipid membranes induced by microwave exposure can be explained by a local increase in SAR and subsequent elevation of temperature in the membrane-forming hole.
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effect of microwaves on bilayer lipid membranes role of a membrane forming hole in the Teflon Film
Biofizika, 2009Co-Authors: S I Alekseev, M S Ziskin, E E FesenkoAbstract:The distributions of specific abcorption rate (SAR) and E-field in a membrane-forming hole of Teflon Film and surrounding electrolyte were calculated for 0.9 GHz exposure. It was found that the specific absorption rate in the membrane-forming hole increased greatly with increasing thickness of the Teflon Film, and electrolyte concentration and decreasing diameter of the hole. The previously demonstrated significant changes in the conductivity of modified bilayer lipid membranes induced by microwave exposure can be explained by a local increase in specific absorption rate and subsequent elevation of temperature in the membrane-forming hole of the Teflon Film.
S I Alekseev - One of the best experts on this subject based on the ideXlab platform.
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Selective Heating of Membrane-forming Holes in Teflon Film Exposed to Decimeter Waves
Biofizika, 2020Co-Authors: S I Alekseev, E E FesenkoAbstract:Calculations of heating of membrane-forming holes in Teflon Film exposed to decimeter waves were performed. The dependence of the temperature increment in holes on the geometry of holes, electrolyte concentration, and decimeter wave frequency was studied. The kinetics of heating depending on the hole diameter was also obtained. It was concluded that the observed in the experiment effects of the decimeter wave on bilayer lipid membranes resulted from the elevated concentration of decimeter electromagnetic waves in membrane-forming hole that led to selective heating of electrolyte in hole and bilayer lipid membranes.
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selective heating of membrane forming holes in Teflon Film exposed to decimeter waves
Biophysics, 2015Co-Authors: S I Alekseev, E E FesenkoAbstract:The heating of a membrane-forming hole in a Teflon Film upon irradiation with decimeter waves was calculated. The dependence of the temperature increase in the membrane-forming hole on its geometry, the concentration of electrolyte solution, and the frequency of decimeter radiation were studied. The heating kinetics of the hole depending on its diameter were obtained. It is concluded that the effects of decimeter waves on bilayer lipid membranes that were observed in experiments are caused by the concentration of the electromagnetic field of decimeter waves at the membrane-forming hole, which lead to the selective heating of the electrolyte in the hole with the bilayer lipid membranes.
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enhanced absorption of microwaves within cylindrical holes in Teflon Film
IEEE Transactions on Biomedical Engineering, 2010Co-Authors: S I Alekseev, E E Fesenko, M S ZiskinAbstract:Earlier publications demonstrated that 0.9 GHz microwave exposure induced notable changes of the conductivity of modified bilayer lipid membranes (BLM) formed in holes in thin Teflon Film (TF). The aims of this study were: 1) to perform detailed calculations of the microwave field distributions in holes formed in TF, using the finite-difference time-domain technique and 2) to model microwave heating of the hole under the conditions used in the BLM experiments but in the absence of BLM in the hole. We found that with the E -field oriented perpendicular to the TF plane the local-specific absorption rate in holes increased significantly. The increase became larger with increasing electrolyte concentration and with decreasing diameter of the hole and frequency. The calculated temperature elevations in the hole were in good agreement with those determined experimentally. These findings allowed us to conclude that the microwave effects on BLM conductivity reported previously resulted mostly from the enhanced absorption of microwave energy by the membrane-forming holes and subsequent local temperature elevation in the holes.
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on the mechanism of microwave action on bilayer lipid membranes the role of the membrane forming hole in Teflon Film
Biophysics, 2009Co-Authors: S I Alekseev, M S Ziskin, E E FesenkoAbstract:The distributions of specific absorption rate (SAR) and E-field in the membrane-forming hole of Teflon Film and the surrounding electrolyte were calculated for 0.9 GHz microwave exposure. It was found that SAR in the hole increased greatly with increasing thickness of the Teflon Film, increasing electrolyte concentration, and decreasing diameter of the hole. The previously demonstrated significant changes in the conductivity of modified bilayer lipid membranes induced by microwave exposure can be explained by a local increase in SAR and subsequent elevation of temperature in the membrane-forming hole.
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effect of microwaves on bilayer lipid membranes role of a membrane forming hole in the Teflon Film
Biofizika, 2009Co-Authors: S I Alekseev, M S Ziskin, E E FesenkoAbstract:The distributions of specific abcorption rate (SAR) and E-field in a membrane-forming hole of Teflon Film and surrounding electrolyte were calculated for 0.9 GHz exposure. It was found that the specific absorption rate in the membrane-forming hole increased greatly with increasing thickness of the Teflon Film, and electrolyte concentration and decreasing diameter of the hole. The previously demonstrated significant changes in the conductivity of modified bilayer lipid membranes induced by microwave exposure can be explained by a local increase in specific absorption rate and subsequent elevation of temperature in the membrane-forming hole of the Teflon Film.
Richard M. Kamens - One of the best experts on this subject based on the ideXlab platform.
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Atmospheric secondary aerosol formation by heterogeneous reactions of aldehydes in the presence of a sulfuric acid aerosol catalyst
Environmental Science and Technology, 2001Co-Authors: Myoseon Jang, Richard M. KamensAbstract:Particle growth by the heterogeneous reaction of aldehydes was evaluated in 0.5 m3 Teflon Film bags under darkness in the presence of background seed aerosols. The aldehydes used were as follows: glyoxal, butanal, hexanal, octanal, and decanal. To study acid catalyst effects on aldehyde heterogeneous reactions, one of the Teflon bags was initially filled with seed aerosols composed of ammonium sulfate-aerosol acidified with sulfuric acid. These results were compared to particle growth reactions that contained only ammonium sulfate as a background seed aerosol. The gas-phase aldehydes were then added to the Teflon bags. In selected experiments, 1-decanol was also added to the Teflon bags with aldehydes to clarify particle growth via a heterogeneous hemiacetal/acetal formation in the presence/absence of an acid catalyst. The particle size distribution and growth were measured using a scanning mobility particle sizer (TSI-SMPS), and the results were applied to predicting aerosol growth and size distribution changes by condensation and heterogeneous reactions. Aerosols created from the heterogeneous reactions of aldehydes were collected directly on an ungreased zinc selenide (ZnSe) FTIR disk (25 mm in diameter) by impaction. The ZnSe disks were directly analyzed for product functional groups inthe aerosol phase using a Fourier transform infrared (FTIR) spectrometer with a deuterated triglycine sulfate (DTGS) detector. Aerosol growth by heterogeneous aldehyde reactions proceeds via a hydration, polymerization process, and hemiacetal/acetal formation from the reaction of aldehydes with alcohols. These aldehyde heterogeneous reactions were accelerated in the presence of an acid catalyst, H2SO4, and led to higher aerosol yields than when H2SO4 was not present in the seed aerosol. The FTIR spectra obtained from the growing aerosol, also illustrated aldehyde group transformation in the particle phase as a function of the heterogeneous reaction. It was concluded that aldehydes, which can be produced by atmospheric photochemical reactions, can significantly contribute on secondary aerosol formation through heterogeneous reactions in the presence of an acid catalyst.
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Partitioning of Semivolatile Organic Compounds in the Presence of a Secondary Organic Aerosol in a Controlled Atmosphere
Journal of Atmospheric Chemistry, 1999Co-Authors: Keri B. Leach, Richard M. Kamens, Michael R. Strommen, Myoseon JangAbstract:The gas-particle partitioning of select semivolatile organic compounds (SOCs) was studied by injecting the SOCs into a 190 m3 Teflon Film chamber containing a secondary organic aerosol (SOA) generated by volatilizing liquid α-pinene into an ozone-concentrated atmosphere. The concentration of total suspended particulates (TSP) and gas and particle-phase SOCs was measured over the course of three experiments spanning a temperature range of 268–297 K and a relative humidity range of 55–100%. An equilibrium partition coefficient, Kp, was calculated for each sampling event. Empirical relationships were then developed to predict the partitioning of the SOCs on the SOA particle source as a function of temperature. Partitioning in this SOA system was compared to that of a SOA generated by the photochemical reaction of NOx with m-xylene. The results indicate that partitioning is similar between the two SOA systems. The effects of multiple particle sources on partitioning was also examined, revealing that a weighted average of predicted Kp values for individual sources can be used to predict partitioning in aerosol mixtures.
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A Predictive Model for Adsorptive Gas Partitioning of SOCs on Fine Atmospheric Inorganic Dust Particles
Environmental Science & Technology, 1999Co-Authors: Myoseon Jang, Richard M. KamensAbstract:The adsorptive gas/particle (G/P) partitioning of semivolatile organic compounds (SOCs) on inorganic Arizona road dust was studied using outdoor Teflon Film chambers. Physicochemical parameters from SOC molecular structural information were implemented to describe nonspecific and specific interactions relating to G/P adsorption. Experimental partitioning data were successfully interpreted using physicochemical parameters such as vapor pressure, molecular polarizability, and solute solvation. To evaluate the effect of surface functional groups on the adsorptive G/P partitioning of SOCs, untreated and baked Arizona road dust particles were used. The partitioning coefficients, Kp, for a range of different SOCs on baked dust particles and on untreated dust particles were measured from simultaneous experiments in two outdoor Teflon Film chambers that were operated at the same temperature and humidity conditions. Kp values for the two different surface properties of untreated and baked particles were better pre...
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The atmospheric stability of polybrominated dibenzo-p-dioxins and dibenzofurans
Chemosphere, 1992Co-Authors: Christopher C. Lutes, M. Judith Charles, Richard M. KamensAbstract:Abstract In order to study the photochemistry of polybrominated dibenzo- p -dioxins (PBDDs) and dibenzofurans (PBDFs) dilute emissions from the combustion of polyurethane foam containing polybrominated diphenyl ethers (PBDPEs) were introduced into 25 m 3 outdoor Teflon Film chambers and aged in the presence of sunlight. PBDDs and PBDFs were found primarily in the particulate phase where they were stable or degraded slowly over a period of hours. The half life of the reaction on actual soot particles agreed better with the predictions of laboratory solid phase then laboratory solution phase experiments.
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Chamber aging studies on the atmospheric stability of polybrominated dibenzo-p-dioxins and dibenzofurans
Environmental Science & Technology, 1992Co-Authors: Christopher C. Lutes, M. Judith Charles, Jay R. Odum, Richard M. KamensAbstract:In this study dilute emissions from the combustion of polyurethane foam containing polybrominated diphenyl ethers (PBDPEs) were introduced into 25-m 3 outdoor Teflon Film chambers and aged in the presence of sunlight. Concentrations of tetra- and pentabrominated dibenzo-p-diorins and dibenzofurans were monitored over time by collecting and analyzing particulate- and vapor-phase samples. The results demonstrated that polybrominated dibenzo-p-dioxins (PBDDs) and polybrominated dibenzofurans (PBDFs) are stable or slowly degrade over periods of hours
