W. P. L. Carter 10/1/04 UCR EPA Environmental Chamber 1
THE UCR-EPA ENVIRONMENTAL CHAMBER
By
William P. L. Carter
CE-CERT, University of CaliforniaRiverside, California, USA
Outline• Background and Objectives• Facility Descriptions• Characterization Results• Representative Gas-Phase Results• Current and Anticipated Projects
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IMPORTANCE OF ENVIRONMENTAL CHAMBERS TO AIR POLLUTION MODELS
• Chemical mechanisms are critical components of models for predictions of secondary pollutants such as O3 and PM
• Mechanisms in current pollution models have many uncertain estimates, simplifications and approximations
• Environmental chambers, simulating atmospheric reactions under controlled conditions, are essential to:• Developing predictive mechanisms when basic mechanistic
data insufficient, e.g., for aromatics• Testing approximations and estimates for almost all VOCs
under simulated atmospheric conditions• Testing entire mechanisms under varied conditions
• Results of experiments are influenced by chamber effects, so developing an appropriate chamber effects model is important
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NEED FOR IMPROVED CHAMBER FACILITY FOR REDUCING CHEMICAL MECHANISM UNCERTAINTY
• Chamber effects and analytical limitations make most previous chambers unsuitable for simulating low ambient pollutant levels
• Large volume chambers are needed to reduce chamber effects, for studies of low volatility VOCs and PM, and to permit use of equipment with high sampling rates
• Largest current chambers are outdoors. But outdoor chambers are difficult to control and characterize for model testing
• Need to test predictions on how temperature affects O3 and PM formation. Current chambers not suitable for this.
• Most U.S. chambers lack the analytical instrumentation needed to monitor many important trace species
• The new UCR U.S. EPA Chamber was funded and constructed to address these needs
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DESIGN CHARACTERISTICS OF NEW CHAMBER FACILITY
• Indoor chamber design used for maximum control and characterization of conditions
• Dual reactor design for experimental productivity and to simplify reactivity assessment
• Largest practical volume for indoors (two ~100,000-L reactors)
• 200 KW filtered argon arc solar simulator
• Replaceable Teflon reactors in “clean room” to minimize background
• Positive pressure reactor volume control to minimize dilution and minimize contamination
• Temperature controlled to ±1oC in ~5oC to ~50oC range.
• Improved array of analytical instrumentation and provision for additional instrumentation in the future
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DIAGRAM OF UCR EPA CHAMBER
20 ft. 20 ft.
20 ft.
This volume kept clear to maintain light
uniformity
Temperature controlled room flushed with purified air and with reflective
material on all inner surfaces
Dual Teflon Reactors
Two air Handlers are located in the corners on each side of the light
(not shown).
Gas sample lines to laboratory below Access
Door
200 KW Arc Light
2 Banks of Blacklights
SEMS (PM) Instrument
Floor Frame
Movable top frame allows reactors to collapse
under pressure control
Mixing SystemUnder floor of reactors
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DIAGRAM OF REACTOR AND FRAMEWORK(One of Two)
CableCeiling
UpperFrame
Pulleys
Takeup Drum
MotorShaft Supports Shaft
LowerFrame
Teflon Film
Supports
Access Hatch and Sampling Port Holder
Ports for Mixing, Low Volatility Injection and Exchange System
Enclosure Floor
~ 90,000Liters
MaximumVolume
WallLightSource
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PHOTOGRAPHS OF CHAMBER AND LIGHTSLooking Towards Reactors (from light) Looking Towards Lights and Air Inlet
Arc Light
Partially Filled Reactors
Black Lights
Reflective walls
Air Intake
Reflective walls and
Ceiling
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LIGHT SOURCE AND SPECTRUM
0
1
2
3
300 400 500 600 700Wavelength (nm)
Nor
mal
ized
Pow
er(a
rbitr
ary
units
)
Solar Blacklights New Chamber
0.6 M
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SUMMARY OF CHARACTERIZATION RESULTS
• Contamination or dilution by enclosure air is negligible when run on positive pressure control. (Volume decreases as sample is withdrawn)
• Light intensity with Argon arc lamp at 80% recommended maximum power gives NO2 photolysis rate of 0.26 min-1
• Characterization results indicate chamber effects are comparable or lower than in other Teflon film chambers
• Both chamber radical source and NO2 offgasing can be represented by HONO offgasing at rates comparable to those observed in the SAPHIR chamber
• Good side equivalency in gas-phase results obtained when the same experiment is simultaneously run in the two reactors (except for some NOx offgasing-sensitive runs)
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DERIVATION AND VALUES OF MAJOR CHAMBER CHARACTERIZATION PARAMETERS
Model pure air and CO – air runs
NOx Offgasing(Also Represented as HONO offgasing)
Loss = 1.1% /hourO3 dark decay runsO3 Decay
0 - 0.05 ppbModel char. runs sensitive to initial HONOInitial HONO
SHCHO / JNO2 = 10 pptModel HCHO in runs without HCHO source
Formaldehyde offgasing
SHONO / JNO2 =
Runs 55-80: 5 pptRuns 81-168:•Side A: 8.5 ppt•Side B: 12.5 ppt
Model CO – NOx and n−butane – NOx runs
Continuous Radical source (Represented as HONO offgasing)
ValuesDerivationParameter
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HONO OFFGASING PARAMETER VS. RUN NO.
1
10
100
50 100 150 200 250 300 350EPA Run Number
HO
NO
Inpu
t Rat
e / k
1 (p
pt)
Rad. Source [A]Rad. Source [B]NOx Source [A]NOx Source [B]
Assigned [A]Assigned [B]
MaintenanceNew Reactors
`
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COMPARISONS OF RADICAL SOURCE PARAMETER VALUES FOR VARIOUS CHAMBERS
1
10
100
1000
280 290 300 310 320 330
Average Temperature (K)
NO
x of
fgas
ing
or R
adic
al S
ourc
e R
ate
/ NO
2 ph
otol
ysis
rate
ratio
(ppt
)
Previous UCR IndoorPrevious UCR OutdoorPrevious UCR Default Model
Used for Modeling UNC OutdoorTVA Indoor (NOx offgasing)
UCR EPA Chamber
SAPHIR HONO offgasing (dry)
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SUMMARY OF CHAMBER PROJECTS TO DATE
• Funded by U.S. EPA
• Funded chamber construction and initial characterization
• Initial exploratory experiments:• Low NOx experiments with selected VOCs• Reactive organic gas (ROG) surrogate – NOx experiments at
varying ROG and NOx levels• Incremental reactivity of m-xylene and n-octane at varying
ROG and NOx levels
• Status: complete. Report in preparation
“Development of a Next-Generation Environmental Chamber Facility …”
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SUMMARY OF CHAMBER PROJECTS TO DATE
• Funded by the California Air Resources Board
• Primary objective is to evaluate the SAPRC-99 mechanism using previous and new low NOx environmental chamber data
• A limited number of low NOx ROG surrogate runs carried out for this project
• Data from the CSIRO and TVA chambers also used in this evaluation
• Project completed. Reporte available at http://www.cert.ucr.edu/~carter/absts.htm#lnoxrpt
“Development and Evaluation of a Gas-Phase Atmospheric Reaction Mechanism for Low NOx Conditions”
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SUMMARY OF CHAMBER PROJECTS TO DATE(continued)
• Funded by U.S. EPA
• Objective is to provide data to evaluate OBMs using well-characterized chamber data
• ROG Surrogate – NOx experiments at varying ROG and NOxwith measurements of key radical and “indicator” species
• Collaborated with Bill Brune of Penn State University to provideOH, HO2, and “OH reactivity” measurements using LIF
• Successfully completed 20 dual-chamber surrogate experiments with radical measurements; 40 separate ROG/NOx irradiations
• Report and journal articles in preparation
“Experimental Evaluation of Observational Based Methods for Evaluating the Sensitivity of O3 to VOCs and NOx”
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SUMMARY OF INITIAL EVALUATION EXPERIMENTS
0.2 – 4.2 ppmC
Toluene: 0.6 – 0.16Xylene: 0.18CO: 25 - 50
0.4 – 0.5
~0.6
HCHO: 0.4 – 0.5CO: 15 - 80
0.35 – 0.50
Varied
VOC Range (ppm)
15-202Formaldehyde - CO - NOx
~0.2 - 31564*Ambient Surrogate - NOx
5 - 306Aromatic - NOx + CO
5 - 254Toluene or m-Xylene - NOx
5 - 252Propene - NOx
10 - 252Ethene - NOx
8 - 252Formaldehyde - NOX
0 - 20032Characterization
NOx Range (ppb)RunsRun Type
* Includes later experiments carried out for the EPA OBM study
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FITS TO ∆([O3]-[NO]) FOR SAPRC-99 MECHANISM FOR THE INITIAL EVALUATION EXPERIMENTS
All CharacterizationHCHO - NOx
HCHO - CO - NOx
Ethene - NOx
Propene - NOx
Toluene - NOx
Toluene - CO - NOx
m-Xylene - NOx
m-Xylene - CO - NOx
Surrogate - NOx
-50% -25% 0% 25% 50%
(Calculated - Experimental) / Experimental
Single Run Average
← Model Biased Low Model Biased High →
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LOW NOx SURROGATE EXPERIMENT(ROG SURROGATE = 300 PPBC, NOx = 2 PPB)
Concentration (ppm) vs Time (minutes)
O3
0.00
0.02
0.04
0.06
0 120 240 360
NO
0.000
0.001
0.002
0 120 240 360
NO2
0.0000
0.0004
0.0008
0.0012
0.0016
0 120 240 360
M-XYLENE
0.000
0.002
0.004
0.006
0.008
0 120 240 360
PAN
0.0000
0.0002
0.0004
0.0006
0.0008
0 120 240 360
NOy - HNO3
0.000
0.001
0.002
0.003
0.004
0 120 240 360
Experimental Standard ModelNo HONO Offgasing Maximum HONO Offgasing
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EXAMPLE DATA FROM AN OBM EXPERIMENT
0.0
0.1
0.2
0.3
0 120 240 360
OH
(ppt
)
LIF DataDerived from m-Xylene
Lights Off
0
20
40
60
80
0 120 240 360Time (minutes)
HO
2 (pp
t)
0
50
100
150
0 120 240 360
O3 (
ppb)
ExperimentalSAPRC-99 Calc.
Lights Off
EPA 189AROG = 1 ppmCNOx = 20 ppb
0
1
2
3
4
5
0 120 240 360Time (minutes)
H2O
2 (pp
b)
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SUMMARY OF CHAMBER PROJECTS TO DATE(continued)
• Funded by the California Air Resources Board
• Objective is to reduce uncertainties in O3 impact estimates of major types of coatings VOCs where reactivity data needed
• Environmental chamber incremental reactivity experiments being carried out for various types of petroleum distillates, and Texanol®, an important component in water-based coatings
• Experiments carried out at two ROG and NOx conditions and evaluated using SAPRC-99 mechanism
• Most experiments completed, data now being analyzed
“Evaluation of Atmospheric Impacts of Selected Coatings VOC Emissions”
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SUMMARY OF CHAMBER PROJECTS TO DATE(continued)
• Funded by the South Coast Air Quality Management District
• Primarily supplements CARB architectural coatings reactivity project to allow for additional work:• PM measurements during reactivity experiments• Incremental reactivity experiments with ethylene and
propylene glycols, benzyl alcohol, and butyl carbitol
• Limited experiments to investigate interactions between glycols and aerosols for availability assessment
• Experiments near completion and being analyzed
“Environmental Chamber Studies of VOC Species in Architectural Coatings And Mobile Source Emissions”
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SUMMARY OF CHAMBER PROJECTS TO DATE(continued)
• Funded by the California Air Resources Board
• Major effort is updating and improving the SAPRC mechanism:• Updating to be consistent with current literature• Improving performance for aromatics and low ROG/NOx
• Developing condensed version for models to replace CB4
• Includes limited funding to support mechanism update effort (primarily for aromatics) (~10 runs)
• Project is now underway
“Updated Chemical Mechanisms for Airshed Model Applications”
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SUMMARY OF CHAMBER PROJECTS TO DATE(continued)
• To be funded by the U.S. EPA
• Primary objective is to support research utilizing chamber for O3and secondary PM mechanism evaluations
• Experiments to be conducted include:• Studies of temperature and humidity effects on O3 and SOA• PM and SOA formation characterization experiments• Study effects of variable ROG and NOx on and SOA
• Approved for funding. Waiting for contract paperwork
“Utilization of a Next Generation Environmental Chamber Facility ...”
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SUMMARY OF CHAMBER PROJECTS TO DATE(continued)
• Carried out in collaboration with Dr. David Cocker of CE-CERT
• Funded in part by the SCAQMD and EPA projects and in part by other CE-CERT programs
• Experiments include• PM characterization and background experiments, and
experiments for comparison with data from other chambers• Studies of SOA formation from aromatics and the ROG
surrogate mixture under various conditions
• Work is underway. Some manuscripts submitted for publication
PM Characterization and Secondary PM Formation Assessment Studies
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FUTURE RESEARCH DIRECTIONS
• Continue O3 reactivity and mechanism evaluation experiments as currently underway
• Utilize the capabilities of chamber for well-characterized SOA studies needed for SOA model development and evaluation
• Investigate temperature and humidity effects on O3 and SOA
• Obtain instrumentation needed for NO3, N2O5, HOx, and other trace species to improve capabilities and utility of this facility
• Serve as a resource for collaborative studies where environmental chamber measurements under highly controlled and characterized conditions would be useful
• Serve as test bed for instrumentation for ambient monitoring