Gas and aerosol wall losses in Teflon film smog chambers

1985 ◽  
Vol 19 (12) ◽  
pp. 1176-1182 ◽  
Author(s):  
Peter H. McMurry ◽  
Daniel. Grosjean
Keyword(s):  
Wall Losses ◽  
Smog Chambers ◽  
Teflon Film

scholarly journals Investigation of particle and vapor wall-loss effects on controlled wood-smoke smog-chamber experiments

2015 ◽  
Vol 15 (11) ◽  
pp. 15243-15288
Author(s):  
Q. Bian ◽  
A. A. May ◽  
S. M. Kreidenweis ◽  
J. R. Pierce
Keyword(s):  
Mass Loss ◽  
Gas Phase ◽  
Basis Set ◽  
Wood Smoke ◽  
Smog Chamber ◽  
Organic Mass ◽  
Final Particle ◽  
Wall Losses ◽  
Wall Loss ◽  
Smog Chambers

Abstract. Smog chambers are extensively used to study processes that drive gas and particle evolution in the atmosphere. A limitation of these experiments is that particles and gas-phase species may be lost to chamber walls on shorter timescales than the timescales of the atmospheric processes being studied in the chamber experiments. These particle and vapor wall losses have been investigated in recent studies of secondary organic aerosol (SOA) formation, but they have not been systematically investigated in experiments of primary emissions from combustion. The semi-volatile nature of combustion emissions (e.g. from wood smoke) may complicate the behavior of particle and vapor wall deposition in the chamber over the course of the experiments due to the competition between gas/particle and gas/wall partitioning. Losses of vapors to the walls may impact particle evaporation in these experiments, and potential precursors for SOA formation from combustion may be lost to the walls, causing underestimates of aerosol yields. Here, we conduct simulations to determine how particle and gas-phase wall losses contributed to the observed evolution of the aerosol during experiments in the third Fire Lab At Missoula Experiment (FLAME III). We use the TwO-Moment Aerosol Sectional (TOMAS) microphysics algorithm coupled with the organic volatility basis set (VBS) and wall-loss formulations to examine the predicted extent of particle and vapor wall losses. We limit the scope of our study to the dark periods in the chamber before photo-oxidation to simplify the aerosol system for this initial study. Our model simulations suggest that over one third of the initial particle-phase organic mass (36%) was lost during the experiments, and roughly half of this particle organic mass loss was from direct particle wall loss (56% of the loss) with the remainder from evaporation of the particles driven by vapor losses to the walls (44% of the loss). We perform a series of sensitivity tests to understand uncertainties in our simulations. Uncertainty in the initial wood-smoke volatility distribution contributes 23% uncertainty to the final particle organic mass remaining in the chamber (relative to base-assumptions simulation). We show that the total mass loss may depend on the effective saturation concentration of vapor with respect to the walls as these values currently vary widely in the literature. The details of smoke dilution during the filling of smog chambers may influence the mass loss to the walls, and a dilution of ~ 25:1 during the experiments increased particle organic mass loss by 64% compared to a simulation where we assume the particles and vapors are initially in equilibrium in the chamber. Finally, we discuss how our findings may influence interpretations of emission factors and SOA production in wood-smoke smog-chamber experiments.

Molecule and aerosol particle wall losses in SMOG chambers made of glass

1989 ◽  
Vol 20 (1) ◽  
pp. 113-122 ◽  
Author(s):  
R. Van Dingenen ◽  
F. Raes ◽  
H. Vanmarcke
Keyword(s):  
Aerosol Particle ◽  
Wall Losses ◽  
Smog Chambers

scholarly journals Investigation of particle and vapor wall-loss effects on controlled wood-smoke smog-chamber experiments

2015 ◽  
Vol 15 (19) ◽  
pp. 11027-11045 ◽  
Author(s):  
Q. Bian ◽  
A. A. May ◽  
S. M. Kreidenweis ◽  
J. R. Pierce
Keyword(s):  
Mass Loss ◽  
Gas Phase ◽  
Basis Set ◽  
Wood Smoke ◽  
Smog Chamber ◽  
Organic Mass ◽  
Final Particle ◽  
Wall Losses ◽  
Wall Loss ◽  
Smog Chambers

Abstract. Smog chambers are extensively used to study processes that drive gas and particle evolution in the atmosphere. A limitation of these experiments is that particles and gas-phase species may be lost to chamber walls on shorter timescales than the timescales of the atmospheric processes being studied in the chamber experiments. These particle and vapor wall losses have been investigated in recent studies of secondary organic aerosol (SOA) formation, but they have not been systematically investigated in experiments of primary emissions from combustion. The semi-volatile nature of combustion emissions (e.g. from wood smoke) may complicate the behavior of particle and vapor wall deposition in the chamber over the course of the experiments due to the competition between gas/particle and gas/wall partitioning. Losses of vapors to the walls may impact particle evaporation in these experiments, and potential precursors for SOA formation from combustion may be lost to the walls, causing underestimations of aerosol yields. Here, we conduct simulations to determine how particle and gas-phase wall losses contributed to the observed evolution of the aerosol during experiments in the third Fire Lab At Missoula Experiment (FLAME III). We use the TwO-Moment Aerosol Sectional (TOMAS) microphysics algorithm coupled with the organic volatility basis set (VBS) and wall-loss formulations to examine the predicted extent of particle and vapor wall losses. We limit the scope of our study to the dark periods in the chamber before photo-oxidation to simplify the aerosol system for this initial study. Our model simulations suggest that over one-third of the initial particle-phase organic mass (41 %) was lost during the experiments, and over half of this particle-organic mass loss was from direct particle wall loss (65 % of the loss) with the remainder from evaporation of the particles driven by vapor losses to the walls (35 % of the loss). We perform a series of sensitivity tests to understand uncertainties in our simulations. Uncertainty in the initial wood-smoke volatility distribution contributes 18 % uncertainty to the final particle-organic mass remaining in the chamber (relative to base-assumption simulation). We show that the total mass loss may depend on the effective saturation concentration of vapor with respect to the walls as these values currently vary widely in the literature. The details of smoke dilution during the filling of smog chambers may influence the mass loss to the walls, and a dilution of ~ 25:1 during the experiments increased particle-organic mass loss by 33 % compared to a simulation where we assume the particles and vapors are initially in equilibrium in the chamber. Finally, we discuss how our findings may influence interpretations of emission factors and SOA production in wood-smoke smog-chamber experiments.

scholarly journals Use of a heated graphite scrubber as a means of reducing interferences in UV-absorbance measurements of atmospheric ozone

2017 ◽  
Vol 10 (6) ◽  
pp. 2253-2269 ◽  
Author(s):  
Andrew A. Turnipseed ◽  
Peter C. Andersen ◽  
Craig J. Williford ◽  
Christine A. Ennis ◽  
John W. Birks
Keyword(s):  
Water Vapor ◽  
Solid Phase ◽  
Mercury Vapor ◽  
Packed Bed ◽  
The United States ◽  
Voc Adsorption ◽  
Clean Air ◽  
Smog Chambers ◽  
Equivalent Method ◽  
Ambient Measurements

Abstract. A new solid-phase scrubber for use in conventional ozone (O3) photometers was investigated as a means of reducing interferences from other UV-absorbing species and water vapor. It was found that when heated to 100–130 °C, a tubular graphite scrubber efficiently removed up to 500 ppb ozone and ozone monitors using the heated graphite scrubber were found to be less susceptible to interferences from water vapor, mercury vapor, and aromatic volatile organic compounds (VOCs) compared to conventional metal oxide scrubbers. Ambient measurements from a graphite scrubber-equipped photometer and a co-located Federal equivalent method (FEM) ozone analyzer showed excellent agreement over 38 days of measurements and indicated no loss in the scrubber's ability to remove ozone when operated at 130 °C. The use of a heated graphite scrubber was found to reduce the interference from mercury vapor to ≤ 3 % of that obtained using a packed-bed Hopcalite scrubber. For a series of substituted aromatic compounds (ranging in volatility and absorption cross section at 253.7 nm), the graphite scrubber was observed to consistently exhibit reduced levels of interference, typically by factors of 2.5 to 20 less than with Hopcalite. Conventional solid-phase scrubbers also exhibited complex VOC adsorption and desorption characteristics that were dependent upon the relative humidity (RH), volatility of the VOC, and the available surface area of the scrubber. This complex behavior involving humidity is avoided by use of a heated graphite scrubber. These results suggest that heated graphite scrubbers could be substituted in most ozone photometers as a means of reducing interferences from other UV-absorbing species found in the atmosphere. This could be particularly important in ozone monitoring for compliance with the United States (U.S.) Clean Air Act or for use in VOC-rich environments such as in smog chambers and monitoring indoor air quality.

Computer simulations of Hall thrusters without wall losses designed using two permanent magnetic rings

2016 ◽  
Vol 49 (46) ◽  
pp. 465001 ◽  
Author(s):  
Ding Yongjie ◽  
Peng Wuji ◽  
Wei Liqiu ◽  
Sun Guoshun ◽  
Li Hong ◽  
...  
Keyword(s):  
Computer Simulations ◽  
Hall Thrusters ◽  
Wall Losses ◽  
Magnetic Rings

scholarly journals Measurement of Ozone Production Sensor

2010 ◽  
Vol 3 (3) ◽  
pp. 545-555 ◽  
Author(s):  
M. Cazorla ◽  
W. H. Brune
Keyword(s):  
Production Rate ◽  
High Efficiency ◽  
Ambient Air ◽  
Ozone Production ◽  
State University ◽  
Photostationary State ◽  
Sample Chamber ◽  
Efficiency Conversion ◽  
The Difference ◽  
Teflon Film

Abstract. A new ambient air monitor, the Measurement of Ozone Production Sensor (MOPS), measures directly the rate of ozone production in the atmosphere. The sensor consists of two 11.3 L environmental chambers made of UV-transmitting Teflon film, a unit to convert NO2 to O3, and a modified ozone monitor. In the sample chamber, flowing ambient air is exposed to the sunlight so that ozone is produced just as it is in the atmosphere. In the second chamber, called the reference chamber, a UV-blocking film over the Teflon film prevents ozone formation but allows other processes to occur as they do in the sample chamber. The air flows that exit the two chambers are sampled by an ozone monitor operating in differential mode so that the difference between the two ozone signals, divided by the exposure time in the chambers, gives the ozone production rate. High-efficiency conversion of NO2 to O3 prior to detection in the ozone monitor accounts for differences in the NOx photostationary state that can occur in the two chambers. The MOPS measures the ozone production rate, but with the addition of NO to the sampled air flow, the MOPS can be used to study the sensitivity of ozone production to NO. Preliminary studies with the MOPS on the campus of the Pennsylvania State University show the potential of this new technique.

NUMERICAL SIMULATION AND TESTING OF A COMPOSITE-STIFFENED STRUCTURE UNDER COMBINED BUCKLING LOADS

2010 ◽  
Vol 10 (04) ◽  
pp. 871-884 ◽  
Author(s):  
E. KARACHALIOS ◽  
C. VRETTOS ◽  
Z. MARIOLI-RIGA ◽  
C. BISAGNI ◽  
P. CORDISCO ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Fe Model ◽  
Release Rates ◽  
Actual Structure ◽  
Physical Test ◽  
Buckling Behavior ◽  
Energy Release Rates ◽  
Experimental Findings ◽  
Teflon Film ◽  
Level Of Agreement

Prediction of the buckling behavior of structures is of great interest in the aerospace industry, and extensive research is taking place worldwide in that area. The current work concerns numerical simulation of the collapse test of a closed stiffened composite box subjected to compression followed by torsion. Numerical simulation is performed and the results are correlated with experimental findings. The objective is to validate the numerical model and detect any deficiencies of the modeling procedure. For this purpose, a series of quantities numerically predicted are directly compared with experimental ones: strains, displacements, deformation plots and load–displacement curves. The physical test article also contains artificial stringer–skin debondings realized via Teflon film inserts. The energy release rates are calculated at the debonding front using the virtual crack closure technique. The FE model is slightly stiffer than the actual structure but the numerical results are at a reasonable level of agreement with the experimental data.

scholarly journals Technical Note: Effect of varying the <i>λ</i> = 185 and 254 nm photon flux ratio on radical generation in oxidation flow reactors

2020 ◽  
Vol 20 (21) ◽  
pp. 13417-13424
Author(s):  
Jake P. Rowe ◽  
Andrew T. Lambe ◽  
William H. Brune
Keyword(s):  
Residence Time ◽  
Low Cost ◽  
Flux Ratio ◽  
Technical Note ◽  
Photon Flux ◽  
Oh Radicals ◽  
Flow Reactors ◽  
Series Of Experiments ◽  
Radical Generation ◽  
Smog Chambers

Abstract. Oxidation flow reactors (OFRs) complement environmental smog chambers as a portable, low-cost technique for exposing atmospheric compounds to oxidants such as ozone (O3), nitrate (NO3) radicals, and hydroxyl (OH) radicals. OH is most commonly generated in OFRs via photolysis of externally added O3 at λ=254 nm (OFR254) or combined photolysis of O2 and H2O at λ=185 nm plus photolysis of O3 at λ=254 nm (OFR185) using low-pressure mercury (Hg) lamps. Whereas OFR254 radical generation is influenced by [O3], [H2O], and photon flux at λ=254 nm (I254), OFR185 radical generation is influenced by [O2], [H2O], I185, and I254. Because the ratio of photon fluxes, I185:I254, is OFR-specific, OFR185 performance varies between different systems even when constant [H2O] and I254 are maintained. Thus, calibrations and models developed for one OFR185 system may not be applicable to another. To investigate these issues, we conducted a series of experiments in which I185:I254 emitted by Hg lamps installed in an OFR was systematically varied by fusing multiple segments of lamp quartz together that either transmitted or blocked λ=185 nm radiation. Integrated OH exposure (OHexp) values achieved for each lamp type were obtained using the tracer decay method as a function of UV intensity, humidity, residence time, and external OH reactivity (OHRext). Following previous related studies, a photochemical box model was used to develop a generalized OHexp estimation equation as a function of [H2O], [O3], and OHRext that is applicable for I185:I254≈0.001 to 0.1.

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