The Experts below are selected from a list of 231 Experts worldwide ranked by ideXlab platform
John H Seinfeld - One of the best experts on this subject based on the ideXlab platform.
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Science of the Environmental Chamber
2020Co-Authors: Rebecca H. Schwantes, Richard C Flagan, Xuan Zhang, Renee C. Mcvay, Matthew M. Coggon, Hanna Idamaria Lignell, Paul O. Wennberg, John H SeinfeldAbstract:Atmospheric chemistry is simulated in the laboratory using several types of Environmental Chambers; these include the batch chamber, the continuously mixed flow reactor, and the flow tube reactor. These reactors are used to study gas-phase oxidation of volatile organic compounds (VOCs) as well as the formation of secondary organic aerosol (SOA), the process by which VOCs undergo oxidation to form low-volatility products that condense onto particles. This chapter focuses on the design and characterization of Environmental Chambers, including: (1) radiation conditions; (2) chamber mixing state; (3) chemical blank experiments; (4) free radical generation (principally the hydroxyl (OH) radical); (5) high-versus-low-NO conditions that govern the nature of VOC oxidation chemistry; (6) deposition of particles onto chamber walls; (7) deposition of organic vapors onto chamber walls; and (8) determination of the yield of SOA. Comparison of the design and behavior of the different types of reactor is addressed in detail. The performance of the differential mobility analyzer (DMA), the prime instrument for measuring aerosol size distributions in Chambers, is addressed.
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effect of particle charge on aerosol dynamics in teflon Environmental Chambers
Aerosol Science and Technology, 2018Co-Authors: Sophia M Charan, Weimeng Kong, Richard C Flagan, John H SeinfeldAbstract:AbstractThe contribution of particle charge to the rate of particle wall deposition has been a persistent source of uncertainty for experiments performed in Environmental Chambers. By tracking the preferential deposition of positively charged particles; by comparing experiments carried out under standard, humid, and highly statically charged conditions; and by performing two-parameter optimizations for the chamber eddy-diffusion coefficient (ke) and the average magnitude of the electric field (), the effect of charge on the rate of particle-wall deposition is isolated. A combined experimental and computational method is also developed for determining values for ke and within a FEP Teflon chamber. To fully account for the effects of charge on particle dynamics in Environmental Chambers, studies of the effect of air ion concentration on the rate of particle coagulation over a typical 20 h experiment are performed and demonstrated, in general, that particle charge is negligible for characteristic chamber ion...
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unified theory of vapor wall mass transport in teflon walled Environmental Chambers
Environmental Science & Technology, 2018Co-Authors: Yuanlong Huang, Sophia M Charan, R Zhao, Christopher M Kenseth, Xuan Zhang, John H SeinfeldAbstract:Secondary organic aerosol (SOA) formation is studied in laboratory Chambers, in which volatile organic compounds (VOCs) are oxidized to produce low-volatility compounds that condense into the aerosol phase. It has been established that such oxidized low-volatility compounds can partition into the chamber walls, which traditionally consist of Teflon film. Several studies exist in which the rates of uptake of individual vapor compounds to the chamber walls have been measured, but a unified theory capable of describing the range of experimental measurements has been lacking. Here, a two-layer model of observed short and long vapor–wall interaction time scales in Teflon-walled Environmental Chambers is presented and shown to be consistent with experimental data on the rate of wall deposition of more than 90 compounds. Semiempirical relationships between key parameters in the model and vapor molecular properties are derived, which can be used to predict the fate of gas-phase vapor in the chamber under dry cond...
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Unified Theory of Vapor–Wall Mass Transport in Teflon-Walled Environmental Chambers
Environmental Science & Technology, 2018Co-Authors: Yuanlong Huang, Sophia M Charan, R Zhao, Christopher M Kenseth, Xuan Zhang, John H SeinfeldAbstract:Secondary organic aerosol (SOA) formation is studied in laboratory Chambers, in which volatile organic compounds (VOCs) are oxidized to produce low-volatility compounds that condense into the aerosol phase. It has been established that such oxidized low-volatility compounds can partition into the chamber walls, which traditionally consist of Teflon film. Several studies exist in which the rates of uptake of individual vapor compounds to the chamber walls have been measured, but a unified theory capable of describing the range of experimental measurements has been lacking. Here, a two-layer model of observed short and long vapor–wall interaction time scales in Teflon-walled Environmental Chambers is presented and shown to be consistent with experimental data on the rate of wall deposition of more than 90 compounds. Semiempirical relationships between key parameters in the model and vapor molecular properties are derived, which can be used to predict the fate of gas-phase vapor in the chamber under dry cond...
Sophia M Charan - One of the best experts on this subject based on the ideXlab platform.
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effect of particle charge on aerosol dynamics in teflon Environmental Chambers
Aerosol Science and Technology, 2018Co-Authors: Sophia M Charan, Weimeng Kong, Richard C Flagan, John H SeinfeldAbstract:AbstractThe contribution of particle charge to the rate of particle wall deposition has been a persistent source of uncertainty for experiments performed in Environmental Chambers. By tracking the preferential deposition of positively charged particles; by comparing experiments carried out under standard, humid, and highly statically charged conditions; and by performing two-parameter optimizations for the chamber eddy-diffusion coefficient (ke) and the average magnitude of the electric field (), the effect of charge on the rate of particle-wall deposition is isolated. A combined experimental and computational method is also developed for determining values for ke and within a FEP Teflon chamber. To fully account for the effects of charge on particle dynamics in Environmental Chambers, studies of the effect of air ion concentration on the rate of particle coagulation over a typical 20 h experiment are performed and demonstrated, in general, that particle charge is negligible for characteristic chamber ion...
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unified theory of vapor wall mass transport in teflon walled Environmental Chambers
Environmental Science & Technology, 2018Co-Authors: Yuanlong Huang, Sophia M Charan, R Zhao, Christopher M Kenseth, Xuan Zhang, John H SeinfeldAbstract:Secondary organic aerosol (SOA) formation is studied in laboratory Chambers, in which volatile organic compounds (VOCs) are oxidized to produce low-volatility compounds that condense into the aerosol phase. It has been established that such oxidized low-volatility compounds can partition into the chamber walls, which traditionally consist of Teflon film. Several studies exist in which the rates of uptake of individual vapor compounds to the chamber walls have been measured, but a unified theory capable of describing the range of experimental measurements has been lacking. Here, a two-layer model of observed short and long vapor–wall interaction time scales in Teflon-walled Environmental Chambers is presented and shown to be consistent with experimental data on the rate of wall deposition of more than 90 compounds. Semiempirical relationships between key parameters in the model and vapor molecular properties are derived, which can be used to predict the fate of gas-phase vapor in the chamber under dry cond...
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Unified Theory of Vapor–Wall Mass Transport in Teflon-Walled Environmental Chambers
Environmental Science & Technology, 2018Co-Authors: Yuanlong Huang, Sophia M Charan, R Zhao, Christopher M Kenseth, Xuan Zhang, John H SeinfeldAbstract:Secondary organic aerosol (SOA) formation is studied in laboratory Chambers, in which volatile organic compounds (VOCs) are oxidized to produce low-volatility compounds that condense into the aerosol phase. It has been established that such oxidized low-volatility compounds can partition into the chamber walls, which traditionally consist of Teflon film. Several studies exist in which the rates of uptake of individual vapor compounds to the chamber walls have been measured, but a unified theory capable of describing the range of experimental measurements has been lacking. Here, a two-layer model of observed short and long vapor–wall interaction time scales in Teflon-walled Environmental Chambers is presented and shown to be consistent with experimental data on the rate of wall deposition of more than 90 compounds. Semiempirical relationships between key parameters in the model and vapor molecular properties are derived, which can be used to predict the fate of gas-phase vapor in the chamber under dry cond...
Jose L Jimenez - One of the best experts on this subject based on the ideXlab platform.
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organic peroxy radical chemistry in oxidation flow reactors and Environmental Chambers and their atmospheric relevance
Atmospheric Chemistry and Physics, 2019Co-Authors: Zhe Peng, J Leetaylor, John J Orlando, Geoffrey S Tyndall, Jose L JimenezAbstract:Abstract. Oxidation flow reactors (OFRs) are a promising complement to Environmental Chambers for investigating atmospheric oxidation processes and secondary aerosol formation. However, questions have been raised about how representative the chemistry within OFRs is of that in the troposphere. We investigate the fates of organic peroxy radicals ( RO2 ), which play a central role in atmospheric organic chemistry, in OFRs and Environmental Chambers by chemical kinetic modeling and compare to a variety of ambient conditions to help define a range of atmospherically relevant OFR operating conditions. For most types of RO2 , their bimolecular fates in OFRs are mainly RO2+HO2 and RO2+NO , similar to Chambers and atmospheric studies. For substituted primary RO2 and acyl RO2 , RO2+RO2 can make a significant contribution to the fate of RO2 in OFRs, Chambers and the atmosphere, but RO2+RO2 in OFRs is in general somewhat less important than in the atmosphere. At high NO, RO2+NO dominates RO2 fate in OFRs, as in the atmosphere. At a high UV lamp setting in OFRs, RO2+OH can be a major RO2 fate and RO2 isomerization can be negligible for common multifunctional RO2 , both of which deviate from common atmospheric conditions. In the OFR254 operation mode (for which OH is generated only from the photolysis of added O3 ), we cannot identify any conditions that can simultaneously avoid significant organic photolysis at 254 nm and lead to RO2 lifetimes long enough ( ∼ 10 s) to allow atmospherically relevant RO2 isomerization. In the OFR185 mode (for which OH is generated from reactions initiated by 185 nm photons), high relative humidity, low UV intensity and low precursor concentrations are recommended for the atmospherically relevant gas-phase chemistry of both stable species and RO2 . These conditions ensure minor or negligible RO2+OH and a relative importance of RO2 isomerization in RO2 fate in OFRs within ∼ × 2 of that in the atmosphere. Under these conditions, the photochemical age within OFR185 systems can reach a few equivalent days at most, encompassing the typical ages for maximum secondary organic aerosol (SOA) production. A small increase in OFR temperature may allow the relative importance of RO2 isomerization to approach the ambient values. To study the heterogeneous oxidation of SOA formed under atmospherically relevant OFR conditions, a different UV source with higher intensity is needed after the SOA formation stage, which can be done with another reactor in series. Finally, we recommend evaluating the atmospheric relevance of RO2 chemistry by always reporting measured and/or estimated OH, HO2 , NO, NO2 and OH reactivity (or at least precursor composition and concentration) in all chamber and flow reactor experiments. An easy-to-use RO2 fate estimator program is included with this paper to facilitate the investigation of this topic in future studies.
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direct measurements of gas particle partitioning and mass accommodation coefficients in Environmental Chambers
Environmental Science & Technology, 2017Co-Authors: Jordan E Krechmer, P Ziemann, Jose L JimenezAbstract:Secondary organic aerosols (SOA) are a major contributor to fine particulate mass and wield substantial influences on the Earth’s climate and human health. Despite extensive research in recent years, many of the fundamental processes of SOA formation and evolution remain poorly understood. Most atmospheric aerosol models use gas/particle equilibrium partitioning theory as a default treatment of gas-aerosol transfer, despite questions about potentially large kinetic effects. We have conducted fundamental SOA formation experiments in a Teflon Environmental chamber using a novel method. A simple chemical system produces a very fast burst of low-volatility gas-phase products, which are competitively taken up by liquid organic seed particles and Teflon chamber walls. Clear changes in the species time evolution with differing amounts of seed allow us to quantify the particle uptake processes. We reproduce gas- and aerosol-phase observations using a kinetic box model, from which we quantify the aerosol mass acco...
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Direct measurements of gas/particle partitioning and mass accommodation coefficients in Environmental Chambers
Environmental Science & Technology, 2017Co-Authors: Jordan E Krechmer, Paul J. Ziemann, Jose L JimenezAbstract:Secondary organic aerosols (SOA) are a major contributor to fine particulate mass and wield substantial influences on the Earth’s climate and human health. Despite extensive research in recent years, many of the fundamental processes of SOA formation and evolution remain poorly understood. Most atmospheric aerosol models use gas/particle equilibrium partitioning theory as a default treatment of gas-aerosol transfer, despite questions about potentially large kinetic effects. We have conducted fundamental SOA formation experiments in a Teflon Environmental chamber using a novel method. A simple chemical system produces a very fast burst of low-volatility gas-phase products, which are competitively taken up by liquid organic seed particles and Teflon chamber walls. Clear changes in the species time evolution with differing amounts of seed allow us to quantify the particle uptake processes. We reproduce gas- and aerosol-phase observations using a kinetic box model, from which we quantify the aerosol mass acco...
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quantification of gas wall partitioning in teflon Environmental Chambers using rapid bursts of low volatility oxidized species generated in situ
Environmental Science & Technology, 2016Co-Authors: Jordan E Krechmer, Demetrios Pagonis, P Ziemann, Jose L JimenezAbstract:Partitioning of gas-phase organic compounds to the walls of Teflon Environmental Chambers is a recently reported phenomenon than can affect the yields of reaction products and secondary organic aerosol (SOA) measured in laboratory experiments. Reported time scales for reaching gas-wall partitioning (GWP) equilibrium (τGWE) differ by up to 3 orders of magnitude, however, leading to predicted effects that vary from substantial to negligible. A new technique is demonstrated here in which semi- and low-volatility oxidized organic compounds (saturation concentration c* < 100 μg m–3) were photochemically generated in rapid bursts in situ in an 8 m3 Environmental chamber, and then their decay in the absence of aerosol was measured using a high-resolution chemical ionization mass spectrometer (CIMS) equipped with an “inlet-less” NO3– ion source. Measured τGWE were 7–13 min (rel. std. dev. 33%) for all compounds. The fraction of each compound that partitioned to the walls at equilibrium follows absorptive partitio...
Yuanlong Huang - One of the best experts on this subject based on the ideXlab platform.
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unified theory of vapor wall mass transport in teflon walled Environmental Chambers
Environmental Science & Technology, 2018Co-Authors: Yuanlong Huang, Sophia M Charan, R Zhao, Christopher M Kenseth, Xuan Zhang, John H SeinfeldAbstract:Secondary organic aerosol (SOA) formation is studied in laboratory Chambers, in which volatile organic compounds (VOCs) are oxidized to produce low-volatility compounds that condense into the aerosol phase. It has been established that such oxidized low-volatility compounds can partition into the chamber walls, which traditionally consist of Teflon film. Several studies exist in which the rates of uptake of individual vapor compounds to the chamber walls have been measured, but a unified theory capable of describing the range of experimental measurements has been lacking. Here, a two-layer model of observed short and long vapor–wall interaction time scales in Teflon-walled Environmental Chambers is presented and shown to be consistent with experimental data on the rate of wall deposition of more than 90 compounds. Semiempirical relationships between key parameters in the model and vapor molecular properties are derived, which can be used to predict the fate of gas-phase vapor in the chamber under dry cond...
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Unified Theory of Vapor–Wall Mass Transport in Teflon-Walled Environmental Chambers
Environmental Science & Technology, 2018Co-Authors: Yuanlong Huang, Sophia M Charan, R Zhao, Christopher M Kenseth, Xuan Zhang, John H SeinfeldAbstract:Secondary organic aerosol (SOA) formation is studied in laboratory Chambers, in which volatile organic compounds (VOCs) are oxidized to produce low-volatility compounds that condense into the aerosol phase. It has been established that such oxidized low-volatility compounds can partition into the chamber walls, which traditionally consist of Teflon film. Several studies exist in which the rates of uptake of individual vapor compounds to the chamber walls have been measured, but a unified theory capable of describing the range of experimental measurements has been lacking. Here, a two-layer model of observed short and long vapor–wall interaction time scales in Teflon-walled Environmental Chambers is presented and shown to be consistent with experimental data on the rate of wall deposition of more than 90 compounds. Semiempirical relationships between key parameters in the model and vapor molecular properties are derived, which can be used to predict the fate of gas-phase vapor in the chamber under dry cond...
Xuan Zhang - One of the best experts on this subject based on the ideXlab platform.
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Science of the Environmental Chamber
2020Co-Authors: Rebecca H. Schwantes, Richard C Flagan, Xuan Zhang, Renee C. Mcvay, Matthew M. Coggon, Hanna Idamaria Lignell, Paul O. Wennberg, John H SeinfeldAbstract:Atmospheric chemistry is simulated in the laboratory using several types of Environmental Chambers; these include the batch chamber, the continuously mixed flow reactor, and the flow tube reactor. These reactors are used to study gas-phase oxidation of volatile organic compounds (VOCs) as well as the formation of secondary organic aerosol (SOA), the process by which VOCs undergo oxidation to form low-volatility products that condense onto particles. This chapter focuses on the design and characterization of Environmental Chambers, including: (1) radiation conditions; (2) chamber mixing state; (3) chemical blank experiments; (4) free radical generation (principally the hydroxyl (OH) radical); (5) high-versus-low-NO conditions that govern the nature of VOC oxidation chemistry; (6) deposition of particles onto chamber walls; (7) deposition of organic vapors onto chamber walls; and (8) determination of the yield of SOA. Comparison of the design and behavior of the different types of reactor is addressed in detail. The performance of the differential mobility analyzer (DMA), the prime instrument for measuring aerosol size distributions in Chambers, is addressed.
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unified theory of vapor wall mass transport in teflon walled Environmental Chambers
Environmental Science & Technology, 2018Co-Authors: Yuanlong Huang, Sophia M Charan, R Zhao, Christopher M Kenseth, Xuan Zhang, John H SeinfeldAbstract:Secondary organic aerosol (SOA) formation is studied in laboratory Chambers, in which volatile organic compounds (VOCs) are oxidized to produce low-volatility compounds that condense into the aerosol phase. It has been established that such oxidized low-volatility compounds can partition into the chamber walls, which traditionally consist of Teflon film. Several studies exist in which the rates of uptake of individual vapor compounds to the chamber walls have been measured, but a unified theory capable of describing the range of experimental measurements has been lacking. Here, a two-layer model of observed short and long vapor–wall interaction time scales in Teflon-walled Environmental Chambers is presented and shown to be consistent with experimental data on the rate of wall deposition of more than 90 compounds. Semiempirical relationships between key parameters in the model and vapor molecular properties are derived, which can be used to predict the fate of gas-phase vapor in the chamber under dry cond...
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Unified Theory of Vapor–Wall Mass Transport in Teflon-Walled Environmental Chambers
Environmental Science & Technology, 2018Co-Authors: Yuanlong Huang, Sophia M Charan, R Zhao, Christopher M Kenseth, Xuan Zhang, John H SeinfeldAbstract:Secondary organic aerosol (SOA) formation is studied in laboratory Chambers, in which volatile organic compounds (VOCs) are oxidized to produce low-volatility compounds that condense into the aerosol phase. It has been established that such oxidized low-volatility compounds can partition into the chamber walls, which traditionally consist of Teflon film. Several studies exist in which the rates of uptake of individual vapor compounds to the chamber walls have been measured, but a unified theory capable of describing the range of experimental measurements has been lacking. Here, a two-layer model of observed short and long vapor–wall interaction time scales in Teflon-walled Environmental Chambers is presented and shown to be consistent with experimental data on the rate of wall deposition of more than 90 compounds. Semiempirical relationships between key parameters in the model and vapor molecular properties are derived, which can be used to predict the fate of gas-phase vapor in the chamber under dry cond...