Grantee Research Project Results
2006 Progress Report: Secondary Aerosol Formation from Gas and Particle Phase Reactions of Aromatic Hydrocarbons
EPA Grant Number: R831084Title: Secondary Aerosol Formation from Gas and Particle Phase Reactions of Aromatic Hydrocarbons
Investigators: Kamens, Richard M.
Institution: University of North Carolina at Chapel Hill
EPA Project Officer: Chung, Serena
Project Period: July 28, 2003 through July 27, 2006 (Extended to July 27, 2008)
Project Period Covered by this Report: July 28, 2005 through July 27,2006
Project Amount: $400,000
RFA: Measurement, Modeling, and Analysis Methods for Airborne Carbonaceous Fine Particulate Matter (PM2.5) (2003) RFA Text | Recipients Lists
Research Category: Air , Air Quality and Air Toxics , Particulate Matter
Objective:
This project focuses on the elucidation of the fundamental chemistry that brings about the secondary organic aerosol formation (SOA) from aromatic reactions in the atmosphere. The overall goal is to develop a “new generation” aromatic chemical mechanism that can integrate newly discovered particle phase heterogeneous processes with the known gas phase chemistry, as a unified, multiphase, chemical reaction mechanism, which will ultimately permit the prediction of SOA formation in the aromatic system.
Progress Summary:
During this reporting period, we have finalized a chemical mechanism for toluene that reasonably predicts the gas phase chemistry and also predicts the SOA formation from toluene oxidation (Figure 1). Three new papers have been submitted for publication on this mechanism. Our model includes aerosol phase chemistry that includes nucleation, gas-particle partitioning, and particle phase reactions; the gas-phase chemistry of toluene and its degradation products also are represented. A series of experiments that cover a wide range of temperature, solar conditions, and initial reactant concentrations were carried out in the University of North Carolina (UNC) 270 m3 dual outdoor aerosol smog chambers. Data obtained from these experiments were used to develop and test the mechanism. The model adequately simulates the decay of toluene, the NO to NO2 conversion, and ozone formation. Although it provides a reasonable prediction of SOA production under different conditions that range from 15 to 300 μg m-3, the model tends to underestimate the initial particle burst for almost all high toluene concentration experiments.
Figure 1. Model Simulation (Lines) of Toluene + Oxides of Nitrogen Reacting in Natural Sunlight in the Presence of NOx in One Side of the UNC 270 m3 Outdoor Smog Chamber
The main contribution that this study makes to science is that it describes an atmospheric aromatic mechanism that: (1) simultaneously considers gas phase reactions, trace gas phase-particle phase partitioning, and subsequent particle phase reactions; (2) proposes a simple chemical mechanism for particle phase nucleation; (3) permits one to distinguish between gas-particle partitioning of SOA and heterogeneous SOA formation; (4) demonstrates the relative importance of organic nitrate formation at high and low toluene concentrations; and (5) successfully simulates gas phase toluene oxidation in smog chamber systems. To date, this has not been accomplished by any of the existing aromatic mechanisms.
The dominant particle phase species predicted by the mechanism are glyoxal oligomers (organic nitrates), methyl nitro-phenol analogues, C7 organic peroxides, acylperoxy nitrates, and, for the low concentration experiments, unsaturated hydroxyl nitro-acids. The relative amounts of these products vary depending on initial experimental conditions. In general, with decreasing toluene/NO ratios, the relative amount of total organic nitrates and acylperoxy nitrates in the particle phase increases and the mass fraction of total oligomers and organic peroxides decreases. It also is important to note that the relative amount of different SOA species dramatically changes with time. The model also predicts well the SOA mass concentrations observed from the European Photoreactor and smog chambers at the California Institute of Technology (Caltech). To implement the developed mechanism into the regional airshed model, however, it would be desirable to reduce the reaction steps and number of represented species.
It is recommended that future studies should focus on: (1) reaction mechanisms that contribute the rapid particle formation in the toluene/NOx system; (2) identification of particle phase oligomers; (3) measurement of organic nitrates and acylperoxy nitrates; (4) chamber experiments with reactant concentrations at ambient levels; and (5) the combination of aromatics and monoterpenes mechanisms into one unified mechanism.
Future Activities:
We already have requested a no-cost extension and will continue with our modeling of p-xylene and trimethyl benzene systems. If it is possible, we will also try to integrate these compounds into one combined model.
Journal Articles on this Report : 3 Displayed | Download in RIS Format
Other project views: | All 8 publications | 6 publications in selected types | All 6 journal articles |
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Type | Citation | ||
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Hu D, Tolocka M, Li Q, Kamens RM. A kinetic mechanism for predicting secondary organic aerosol formation from toluene oxidation in the presence of NOx and natural sunlight. Atmospheric Environment 2007;41(31):6478-6496. |
R831084 (2006) R831084 (2007) R831084 (Final) |
Exit Exit Exit |
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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. |
R831084 (2005) R831084 (2006) R831084 (2007) R831084 (Final) |
Exit Exit Exit |
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Leungsakul S, Jeffries HE, Kamens RM. A kinetic mechanism for predicting secondary aerosol formation from the reactions of d-limonene in the presence of oxides of nitrogen and natural sunlight. Atmospheric Environment 2005;39(37):7063-7082. |
R831084 (2005) R831084 (2006) R831084 (2007) R831084 (Final) R828176 (Final) |
Exit Exit Exit |
Supplemental Keywords:
secondary organic aerosol formation, aromatics, modeling, organic particle formation,, RFA, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Environmental Chemistry, Monitoring/Modeling, Environmental Monitoring, Atmospheric Sciences, environmental measurement, Toluene, gas phase chemistry, particle phase reactions, organic chemistry, secondary organic aerosol, aromatic compounds, aerosol analyzersProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.