Secondary Organic Aerosol and Ozone Formation from Photo- oxidation of Select Low Vapor Pressure-Volatile Organic Compounds, hydrocarbon Solvents, and Generic Consumer Products in a Surrogate Atmospheric Environment Weihua Li 1,2 , Lijie Li 3 , Chia-Li Chen 4 , Mary Kacarab 5 , Weihan Peng 1,2 , David Cocker 1,2 1. Department of Chemical and Environmental Engineering in University of California, Riverside 2. College of Engineering-Center for Environmental Research and Technology 3. Environmental Science and Engineering, California Institute of Technology 4. Scripps Institution of Oceanography, University of California, San Diego 5. Earth & Atmospheric Science, Georgia Institute of Technology
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Secondary Organic Aerosol and Ozone Formation from Photo-oxidation of Select Low Vapor
Pressure-Volatile Organic Compounds, hydrocarbon Solvents, and Generic Consumer Products in
a Surrogate Atmospheric Environment
Weihua Li1,2, Lijie Li3, Chia-Li Chen4, Mary Kacarab5, Weihan Peng1,2, David Cocker1,2
1. Department of Chemical and Environmental Engineering in University of California, Riverside
2. College of Engineering-Center for Environmental Research and Technology 3. Environmental Science and Engineering, California Institute of Technology
4. Scripps Institution of Oceanography, University of California, San Diego 5. Earth & Atmospheric Science, Georgia Institute of Technology
Objectives Evaluate the evaporation rate, of specific Low Vapor Pressure-Volatile Organic Compounds (LVP-VOCs) in pure form and as part of mixtures as they are used in consumer products. Study ozone and SOA formation of select LVP-VOCs under low NOx conditions in a surrogate mixture. Apply experimental data from series LVP-VOCs oxidation experiments to the SAPRC-2011 mechanism to evaluate ozone formation. Compare ozone and SOA formation from consumer products with that from their LVP-VOCs components under the same conditions. Explore ozone and SOA formation of hydrocarbon solvents under low NOx conditions in a surrogate mixture.
2
Motivation
VOC + NOx + sunlight Ozone
*Preliminary data, may change in validation process
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Num
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asin
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s E
xcee
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Number of Basin-Days Exceeding 2015 Federal Ozone Health Standard Levels (>0.070 ppm) in SoCAB
132*
Chart created from data on AQMD website
Ozone
Gas Phase Oxidation Products
Fuel/Industry Open fires Vegetation Fuel/Industry Open fires Animal Consumer feedlots products
isoprene terpenes oxygenatesβ¦
alkanes alkenes aromaticsβ¦
VOC EMISSION
PRIMARY EMISSION
Primary Organic Aerosol
(POA)
Aerosol Formation
Volatile Organic Compounds (VOC)
Nucleation Condensation
Coagulation
Evaporation Secondary Organic Aerosol
(SOA) Gas-phase Oxidation
Β·OH, O3, Β·NO3
Paul J. Ziemann*z and Roger Atkinsonz, 2012
Human Health
PM Enters trough mouth and nose
>PM10 eliminated through coughing, sneezing, and swallowing
<PM5 travel deep into lungs, causing lung and heart problems
Isopar M Low-aromatic mixture of alkanes, C11-C16 iso-alkanes, and
cycloalkanes.
Conosol C200 Low-aromatic mixture of cycloparaffinic and isoparaffinic hydrocarbons
(C5-C20 ).
Conosol-200* A custom mixture of Conosol-70* and Conosol-400* blended to create
Conosol-200* with appropriate viscosity and used prior to obtaining Conosol-200 (labelled in report as C-200**) from a major vendor.
Aromatics 200 Predominantly aromatic compounds.
Volatility Study of Select LVP-VOCs
Vent
Schematic for LVP-VOC volatilization measurement. (Exchange air per hour=3.5)
Evaporation Chamber
Volatility and the extent of oxidation. Volatility ranges are identified with colored bands. ELVOC refers to extremely low volatility organic compounds (gray shading); LVOC refers to low volatility organic compounds (light red shading); SVOC
refers to semi-volatile organic compounds (light green shading); IVOC refers to intermediate volatility organic compounds (light blue shading); VOC refers to volatile organic compounds (no shading); (Donahue VBS 2012).
Weight Loss of select IVOCs in Evaporation chambers
Select LVP-VOCs can enter earthβs atmosphere and contribute to SOA and ozone formation at
ambient conditions.
Volatility and the extent of oxidation. Volatility ranges are identified with colored bands. ELVOC refers to extremely low volatility organic compounds (gray shading); LVOC refers to low volatility organic compounds (light red shading); SVOC
refers to semi-volatile organic compounds (light green shading); IVOC refers to intermediate volatility organic compounds (light blue shading); VOC refers to volatile organic compounds (no shading); (Donahue VBS 2012).
All of the chemical compounds studied fall into IVOC range.
Evaporation Rate (calculated from weight loss results). All had the same starting volume.
Semi-empirical Prediction Equation
The relation of initial liquid LVP-VOC and final gas concentration in equilibrium zone
πππΌπΌ β Ξ¦πΌπΌ = π₯π₯πΌπΌ β πΎπΎπΌπΌ β πππΌπΌπ π π π π π Φα: Gas phase activity, 1 for high dilution system; xΞ±: Mole fraction of Ξ± component in mixture, 1 for pure compound; Ξ³Ξ±: Aqueous phase activity, 1 for pure compound; πππΌπΌπ π π π π π : Saturation pressure of component Ξ± in air. PΞ±: Partial pressure of component Ξ± in air.
Kinetics
How about mixtures?
Evaporation of a LVP-VOC from a Consumer Product
Air in Air out
Selected Ion Flow Tube Mass Spectrometry
200 ul mixture
Evaporation results of three pure LVP-VOCs
A linear increase is observed with increasing volume of LVP-VOC placed into the evaporation
chamber.
Evaporation Results of Pure LVP-VOC
The relation of initial liquid LVP-VOC and final gas concentration in equilibrium zone
The relation of initial liquid LVP-VOC and final gas concentration
πππΌπΌ β Ξ¦πΌπΌ = π₯π₯πΌπΌ β πΎπΎπΌπΌ β πππΌπΌπ π π π π π Φα: Gas phase activity, 1 for high dilution system; xΞ±: Mole fraction of Ξ± component in mixture, 1 for pure compound; Ξ³Ξ±: Aqueous phase activity, 1 for pure compound; πππΌπΌπ π π π π π : Saturation pressure of component Ξ± in air. PΞ±: Partial pressure of component Ξ± in air.
Kinetics
Evaporation results of three pure LVP-VOCs
Mass transfer limited.
Evaporation Results of Pure LVP-VOC
Why Viscosity is not important? Stokes-Einstein relationship
ΞΊB: Boltzmann constant, 1.38*10-23 m2*kg*s-2*K-1; T: Temperature of the evaporation system, 298K; Ξ·: Viscosity of liquid LVP-VOC; d: Diffusive length. ππ : Characteristic time of mass transfer L: Relevant length in vertical direction. D: Molecular diffusivity
Koop et al., 2011
The co-relation of viscosity, diffusivity, mixing time and evaporation particle scale. Spherical particles with microscopic length dimensions (1 nm to 10 mm).
ππ = πΏπΏ2
π·π·
Water Honey Propylene Glycol Diffusivity (cm2/s) 2.4e-1 NA 1.06e-1 Viscosity (Pa*s) 8.9e-4 6.3 4.2e-2
Assumption: The thickness of liquid LVP-VOC on aluminum dish L = 1 mm. Diffusive length d = 10 um, or 1% of L If viscosity Ξ· <10 Pa*s, ππ through the upper layer of the mixture < 1 minute, which is considerably shorter than the time scale of the evaporation study
π·π· = πππ΅π΅ππ
6ππππ β ππ
Diffusion to the boundary layer.
Evaporation Results of Pure LVP-VOC and its Mixture
Volume of LVP equals volume of LVP in the consumer product.
Volume of LVP equals volume of consumer product.
Trends varies. For some consumer products, LVP ingredients cross-linked to other materials.
UCR CE-CERT Chamber Facility
β’ 90 m3 each β’ Insulated
enclosure (purified air flushed) Movable top frame
(272 115W)
β’ Humidity Control
β’ Temperature control (5-45ΒΊC)
1ppm H2O2 as needed
+ 25 ppb NOx + 1.1ppmC Surrogate
LVP-VOCs/Mixture
NO/NO2
N2
Liquid Hydrocarbons /H2O2(wt 50%)
Instrumentation Gas-phase Analysis GC-FID β Hydrocarbon decay SIFT-MS β Gas phase concentration (Selected Ion Flow Tube β Mass Spectrometer) Gas Analyzer β O3,NO,NOX
Particle-phase Analysis HR-ToF-AMS β bulk chemical composition (High Resolution Time-of-Flight Mass Spectrometer) SMPS β volume concentration and size distribution (Scanning Mobility Particle Sizer) APM-SMPS β density (Aerosol Particle Mass Analyzer β SMPS) VTDMA β volatility (Volatility Tandem Differential Mobility Analyzer) HTDMA β hygroscopicity (Hygroscopicity Tandem Differential Mobility Analyzer)
Surrogate
A simplified ROG surrogate was used for this work to mimic total urban atmospheric reactivity. Seven representative compounds used were n-butane, n-Octane, ethylene, propylene, trans-2-butene, toluene, and m-xylene.
Volatility Tandem Differential Mobility Analyzer
Volume Fraction Remaining (VFR) = (Df/Di)3
+
+
+
+
-
-
-
-
+ +
+
Electrical force
Drag force
DMA
Thermodenuder
DMA
Df
Di
Condensation Particle Counter
SMPS
Courtesy of Ping Tang
Aerosol Particle Mass Analyzer β SMPS
(Malloy et al.,2009)
SMPS
www.kanomax.com
High-Resolution-Time-of-Flight Aerosol Mass Spectrometer
V-mode: higher sensitivity W-mode: higher mass resolution Particle size range : 35 nm ~ 1.5 Β΅m
(DeCarlo, et al. 2006)
Stability Runs
Stability test for LVP-VOCs in chamber.
All LVP-VOCs maintained a constant concentration within measurement error.
Ozone Formation from Select Individual LVP-VOCs
O3 Formation from LVP-VOCs with Surrogate and NOx
O3 formation was suppressed?
O3 Formation from LVP-VOCs with Surrogate and NOx
Larger changes in radical concentrations, NOx loadings, etc. than expected to occur within the
more complex ambient atmosphere with its more significant reservoir.
Ozone formation from individual LVP-VOCs with surrogate, NOx, and H2O2
O3 Formation from LVP-VOCs with Surrogate, NOx, H2O2
Ozone formation comparison between runs with or without H2O2
Ozone formation for solvent mixtures. Two Conosol C200 mixtures were investigated for ozone formation (local vendor (*) and large vendor (**)). Aromatic-200 is not shown due to
interferences of the Aromatic 200 with the UV absorption of the ozone analyzer.
SOA formation was the highest for conditions that favored greater consumption of the LVP-
VOC.
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0.1
0.15
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0.25
0 50 100 150 200 250 300 350 400 450
Y
Mo (Β΅g/m3)
ββi
iomio KMY ,Ξ±
At small Mo
ββββ
ii
o
YM
Ξ±
More organic aerosol present, more aerosol will form
Ξ±i : mass-based stoichiometric coefficient Kom,i :gas-particle partitioning coefficient Mo: mass of aerosol formed
oMYHC
β=β
(Odum, et al. 1996; Odum, et al. 1997 a,b;)
ββ +==
i oiom
iomio
ii MK
KMYY
,
,
1Ξ±
Aerosol Yield
Chamber data-> Yield-> Model
Run # Compound ΞHC(Β΅g/m3) ΞM(Β΅g/m3) Yield
EPA1883 Diethylene Glycol 140.00 3.40 0.02
EPA1886 DEGEE 338.18 23.00 0.07
EPA1887 Diethylene Glycol 309.95 2.58 0.01
EPA1888 Propylene Glycol 84.93 0.16 0.00
EPA1891 DEGBE 293.13 47.80 0.16
EPA1892 n-Tridecane 183.76 14.69 0.08
EPA1910 n-Heptadecane 199.86 103.60 0.52
EPA1911 DBE-5 158.00 9.73 0.06
EPA1987 Benzyl Alcohol 186.91 43.20 0.23
EPA2023 DPGMEA 255.06 6.00 0.02
EPA2024 Texanol 151.29 1.10 0.01
Yield (Select LVP-VOC + Surrogate + NOx)
Typical Aerosol Yield for Aromatics
Yield curves for C6-C9 aromatics.
Comparison of SOA formation with and without H2O2 for select LVP-VOCs in the presence of NOx and surrogate.
More aerosols formed after injecting H2O2 for LVP-VOCs that formed measurable SOA.
H2O2 Effects
Comparison of SOA formation with and without H2O2 for select LVP-VOCs.
H2O2 Effects
SOA Formation from Select Consumer Products
SOA formation from LVP-VOCs containing consumer products with surrogate and NOx.
SOA Formation from Select Consumer Products + Surrogate + NOx
SOA formation from LVP-VOCs containing consumer products with surrogate, NOx, and H2O2
SOA Formation from Select Consumer Products + Surrogate + NOx + H2O2
Comparison of SOA formation from single LVP-VOCs with that from mixtures in the presence of surrogate and NOx. Colored individual LVP matched with corresponding consumer products.
Consumer products formed more SOA than LVP-VOCs alone.
Comparison of SOA formation from single LVP-VOCs with that from mixtures in the presence of surrogate and NOx. Colored individual LVP matched with corresponding consumer products.
The presence of other chemicals in the consumer product influences the reactivity and
aerosol formation routes.
SOA Formation from Select Hydrocarbon Solvents
SOA Formation (Hydrocarbon Solvents + Surrogate + NOx)
SOA Formation (Hydrocarbon Solvents + Surrogate + NOx + H2O2)
Relationship of SOA to chemical structures glycol ether case study
Molecular Structure of Ethers Investigated
SOA yield from glycol ethers and related ethers in absence of NOx.(Colored by the amount of ether (precursor) reacted to aid in visual comparison of which ethers on a per ether reacted
basis is producing the greatest relative amount of SOA)
β’ SOA formation from the photo-oxidation of selected ethers is associated with the presence and location of βOH.
β’ Dominating SOA precursor: Ethers with β(OCH2CH2)2 β OH structure.
β’ The SOA fractional yields of ether depend on the amount of ether precursor reacted.
Summary β’ The UCR CE-CERT environmental chambers were suitable to meet the
goals of the study of ozone and SOA formation from LVP-VOCs. β’ Most LVP-VOCs studied evaporated (>95%) in less than 6 months. β’ SAPRC-11 as evaluated for the LVP-VOCs studied and was found to
predict well the gas-phase chemistry and ozone formation from the compounds.
β’ The hypothesis that LVP-VOCs begin with lower vapor pressure than VOCs and therefore will form more secondary aerosol was proven to be generally not true for the compounds studied. Half LVP-VOCs did not form SOA. However, several selected LVP-VOCs formed appreciable SOA.
β’ Chemical structure was found to be a significant driver of SOA formation (e.g., glycol ether case study).
β’ Lab created generic consumer products had a weak influence on ozone formation from the surrogate mixture but strongly affected SOA formation, which can not be explained solely by the results of the pure LVP-VOC experiments.
β’ Hydrocarbon solvents formed appreciable SOA.
Future Work β’ SOA and ozone formation from photo-oxidation of other
classes of LVP-VOCs. β’ Evaporation study about mass transfer kinetic limitations. β’ Predict the influence of hydroperoxy levels on SOA
generation as a function of HO2/NO. β’ A detailed study on their SOA formation as a function of
chain length and branching is necessary to provide experimental parameters needed to predict overall ambient impacts of alkanes on SOA formation. (e.g., relationship seen for glycol ethers)
β’ Vapor and particle wall loss.
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