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Final Report: Partitioning of Semivolatile Organic Compounds in Organic and Inorganic Aerosols: A Unified Approach
EPA Grant Number: R826771Title: Partitioning of Semivolatile Organic Compounds in Organic and Inorganic Aerosols: A Unified Approach
Investigators: Kamens, Richard M. , Chandramouli, Bharadwaj , Jang, Myoseon
Institution: University of North Carolina at Chapel Hill
EPA Project Officer: Shapiro, Paul
Project Period: October 1, 1998 through September 30, 2001
Project Amount: $562,536
RFA: Air Pollution Chemistry and Physics (1998)
Research Category: Engineering and Environmental Chemistry
Description:
Objective:The objective of this research project was to provide a unified model to predict the equilibrium gas-particle partitioning (G/P) of semivolatile organic compounds (SOCs) on both organic and inorganic aerosols. To do this, it was necessary to: (1) implement new models for both SOC gas-liquid (absorptive) and gas-solid (adsorptive) behavior; (2) provide an experimental database to test these models; and (3) demonstrate that these models can be used and applied to a variety of different situations.
Summary/Accomplishments (Outputs/Outcomes):In this work, the G/P of mixtures of aerosols from two and three sources, organic and inorganic, primary and secondary in origin, was studied using outdoor smog-chamber experiments to generate partitioning coefficient data for a set of diverse SOCs. The system was then modeled using thermodynamic G/P models. The models were successful in predicting G/P using a knowledge of the physical makeup, and chemical composition of the aerosol in the chamber. The calculations are sensitive to the mixing state of the aerosol, which has important ramifications in predicting G/P in the ambient atmosphere. Some single-aerosol source experiments also were conducted and the partitioning model's sensitivity to input parameter choices was tested using the generated experimental data in conjunction with preexisting smog chamber data. The calculation of partitioning coefficient required the use of parameter estimation methods for various model inputs and a software toolkit incorporating many of these methods also is presented as part of this work.
The parameter estimation methods and calculation routines used in this work
were codified into a toolkit called semiVolatile, and a description of this
toolkit was provided along with a user manual. The toolkit features a modular
structure separating the data needed by the methods from the methods themselves.
Graphical user interfaces (GUIs) also are provided to facilitate easy input
of parameters. The toolkit is easily extensible, given its modular structure
and will be made available on the Web at http://airsite.unc.edu/~kamens 
.
We also further expanded an 
-pinene aerosol kinetic prediction model and can
now successfully predict daytime particle formation in the presence of NOx under
various sunlight conditions and concentration regimes. A kinetic mechanism was
used to describe the gas- and aerosol-phase reactions of -pinene in the presence
of sunlight, ozone (O3), and oxides of nitrogen (NOx). Reaction products and
aerosol formation from the kinetic model were compared to outdoor smog-chamber
experiments conducted under natural sunlight in the presence of NOx, and in
the dark in the presence of O3.
G/P of SOCs on Organic Aerosols Using a Predictive Activity Coefficient
Model: Analysis of the Effects of Parameter Choices on Model Performance.
The partitioning of a diverse set of SOCs on a variety of organic aerosols was
studied using smog-chamber experimental data. Existing data on the partitioning
of SOCs on aerosols from wood combustion, diesel combustion, and the -pinene-O3
reaction was augmented by conducting smog-chamber partitioning experiments on
aerosols from meat cooking, and by catalyzing and uncatalyzing gasoline engine
exhaust. Model compositions for aerosols from meat cooking and gasoline combustion
emissions were used to calculate activity coefficients for the SOCs in the organic
aerosols and the Pankow absorptive G/P model was used to calculate the partitioning
coefficient Kp and quantitate the predictive improvements
of using the activity coefficient. The slope of the logKp
versus log p0L correlation for partitioning
on aerosols from meat cooking (see Figure 1) improved from -0.81 to -0.94 after
incorporation of activity coefficients i
om.
Figure 1. Results of Correcting Kp With
for Meat Cooking Aerosol During a May 18, 2000, Experiment. (a) shows logKp-logp0L
and (b) shows log Kp-log
p0L (UNIFAC). C23 refers to d48-tricosane.
A stepwise regression analysis of the partitioning model revealed that for
the data set used in this study, partitioning predictions on -pinene-O3
secondary aerosol and wood-combustion aerosol showed statistically significant
improvement after incorporation of iom,
which can be attributed to their overall polarity. The partitioning model was
sensitive to changes in aerosol composition when updated compositions for -pinene-O3
aerosol and wood-combustion aerosol were used. The octanol-air partitioning
coefficient's (KOA) effectiveness as a partitioning correlator over a
variety of aerosol types was evaluated. The slope of the logKp-logKOA
correlation was not constant over the aerosol types and SOCs used in the study
and the use of KOA for partitioning correlations can potentially lead
to significant deviations, especially for nonpolar aerosols.
G/P of SOCs on Mixtures of Aerosols in a Smog Chamber. The partitioning behavior of a set of diverse SOCs on two- and three-component mixtures of aerosols from different sources was studied using smog chamber experimental data. A "cocktail" of SOCs of different compound types was introduced into a system containing a mixture of aerosols from two or more sources. Gas and particle samples were taken using a filter-filter-denuder sampling system and a partitioning coefficient Kp was estimated using Kp = Cp/(Cg .TSP). Particle-size distributions were measured using a differential mobility analyzer and a light-scattering detector. Gas and particle samples were analyzed using gas chromatography-mass spectrometry (GCMS). The aerosol composition in the chamber was tracked chemically using a combination of signature compounds and the organic matter mass fraction (fom) of the individual aerosol sources. The physical nature of the aerosol mixture in the chamber was determined using particle-size distributions and an aggregate Kp was estimated from theoretically calculated Kp on the individual sources. Model fits for Kp showed that when the mixture involved primary sources of aerosol, the aggregate Kp of the mixture could be successfully modeled as an external mixture of the Kp on the individual aerosols. There were significant differences observed for some SOCs between modeling the system as an external and an internal mixture. However, when one of the aerosols sources was secondary (see Figure 2), the aggregate model Kp required incorporation of the secondary aerosol products on the preexisting aerosol for adequate model fits. Modeling such a system as an external mixture grossly overpredicted the Kp of alkanes in the mixture. Indirect evidence of heterogeneous, acid-catalyzed reactions in the particle phase also was seen, leading to a significant increase in the polarity of the resulting aerosol mix and a resulting decrease in the observed Kp of alkanes in the chamber. The model partly tracked this decrease, but could not completely explain the reduction in Kp because of insufficient knowledge of the secondary organic aerosol composition.
Figure 2. Comparison of Measured and Model Kp
for: (a) d40-nonadecane; (b) d42-eicosane;
(c) d10-phenanthrene; and (d) 4-biphenylcarboxaldehyde,
During the June 4, 2002, Wood Soot + Diesel Soot + -pinene-O3
SOA Partitioning Experiment. The comparison with a partitioning calculation
using an external mixture also is shown.
Modeling Aerosol Formation From a-pinene + NOx in the Presence of Natural
Sunlight Using Gas-Phase Kinetics and G/P Theory. A kinetic mechanism was
used to link and model the gas-phase reactions and aerosol accumulation resulting
from -pinene
reactions in the presence of sunlight, O3, and NOx.
Reaction products and aerosol formation from the kinetic model were compared
to outdoor smog chamber experiments conducted under natural sunlight in the
presence of NOx, and in the dark in the presence of O3.
The G/P of semivolatile organics generated in the gas phase was treated as an
equilibrium process between particle absorption and desorption. Models versus
experimental aerosol yields illustrate that reasonable predictions of secondary
aerosol formation are possible from both dark ozone and light-NOx--pinene
systems over a variety of different outdoor conditions. On average, measured
gas- and particle-phase products accounted for approximately 54-72 percent of
the reacted -pinene
carbon. Model predictions suggest that organic nitrates account for another
approximately 25 percent of the reacted carbon, and most of this is in the gas
phase. Measured particle-phase products accounted for 60-100 percent of the
particle filter mass, with pinic acid and pinonic acid being the primary aerosol
phase products. In the gas phase, pinonaldehyde and pinonic acid are major products.
Model simulations (see Figure 3) of these and other products show generally
reasonable fits to the experimental data from the perspective of timing and
concentrations. These results are very encouraging for a compound such as pinonaldehyde,
because it is formed from OH attack on a-pinene, and also is simultaneously
photolyzed and reacted with OH. We feel that the framework for this model can
be used in current airshed models and this will be the subject of future investigations.
Figure 3. Simulation of UNC Outdoor Chamber Data Without Acid Seed (Symbols)
and Model (Lines) of SOA Formation (Right) and Gas-Phase Pinonaldehyde (Middle)
From Gas-Phase Reactions of -pinene
and NOx in Early June, Under Clear Sunlight in North
Carolina Starting at 295 and Increasing to 315K (left).
Journal Articles on this Report: 6 Displayed | Download in RIS Format
| Other project views: | All 8 publications | 8 publications in selected types | All 8 journal articles |
| Type | Citation | ||
|---|---|---|---|
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Chandramouli B, Jang M, Kamens RM. Gas-particle partitioning of semi-volatile organics on organic aerosols using a predictive activity coefficient model: analysis of the effects of parameter choices on model performance. Atmospheric Environment 2003;37(6):853-864. |
R826771 (Final) |
not available |
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|
Chandramouli B, Jang M, Kamens RM. Gas-particle partitioning of semivolatile organic compounds (SOCs) on mixtures of aerosols in a smog chamber. Environmental Science & Technology 2003;37(18):4113-4121. |
R826771 (Final) R828176 (Final) |
|
|
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Jaoui M, Kamens RM. Mass balance of gaseous and particulate products analysis from a-pinene + NOx in the presence of natural sunlight. Journal of Geophysical Research - Atmospheres 2001;106(D12):12,541-12,558. |
R826771 (2000) R826771 (Final) |
not available |
|
|
Jaoui M, Kamens RM. Gas phase photolysis of pinonaldehyde in the presence of sunlight. Atmospheric Environment 2003;37(13):1835-1851. |
R826771 (1999) R826771 (Final) R828176 (Final) |
not available |
|
|
Kamens RM, Jaoui M. Modeling aerosol formation from alpha-pinene plus NOx in the presence of natural sunlight using gas-phase kinetics and gas-particle partitioning theory. Environmental Science & Technology 2001;35(7):1394-1405. |
R826771 (2000) R826771 (Final) R828176 (2002) R828176 (Final) |
not available |
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Lee S, Kamens RM. Particle nucleation from the reaction of α-pinene and O3. Atmospheric Environment 2005;39(36):6822-6832. |
R826771 (1999) R826771 (Final) R831084 (2005) R831084 (2006) R831084 (2007) |
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semivolatile organic aerosols, gas-particle partitioning, G/P activity coefficients, adsorption, absorption, atmospheric chemistry. , Toxics, Air, Scientific Discipline, RFA, Engineering, Chemistry, & Physics, Ecological Risk Assessment, air toxics, particulate matter, Environmental Chemistry, National Recommended Water Quality, VOCs, aerosol partitioning, aerosols, chemical mixtures, vapor phase, exposure and effects, semivolatile organic compounds, aerosol particles, combustion, monitoring, particulates, PM 2.5, air modeling, PAH, linear solution energy realtionships, gas/particle partitioning
Relevant Websites:
http://airsite.unc.edu/~kamens
Progress and Final Reports:
1999 Progress Report
2000 Progress Report
Original Abstract