Final Report: Engineering Environmentally Benign Solvent Systems

EPA Grant Number: R828169
Title: Engineering Environmentally Benign Solvent Systems
Investigators: Broadbelt, Linda J. , Khan, Shumaila , Zhang, Qizhi
Institution: Northwestern University
EPA Project Officer: Shapiro, Paul
Project Period: September 1, 2000 through August 31, 2002
Project Amount: $223,199
RFA: Exploratory Research - Engineering, Chemistry, and Physics) (1999) RFA Text |  Recipients Lists
Research Category: Engineering and Environmental Chemistry , Water , Land and Waste Management , Air

Objective:

The objective of this research project was to develop a mechanistic model that can accurately predict ozone formation in the atmosphere. Photochemical smog is an atmospheric condition that can be harmful to all forms of life. The major constituent of photochemical smog is ozone, which results from the reactions that take place between volatile organic compounds (VOCs) and nitrogen oxides (NOx). Thus, accurate prediction of ozone formation in the atmosphere from VOCs has raised great interest. A detailed mechanistic model is a valuable tool that can be used to predict the effects of various atmospheric conditions on the production of ozone.

Summary/Accomplishments (Outputs/Outcomes):

Two aspects of developing detailed models of atmospheric chemistry impose particular challenges: (1) the sheer size of the models implied, and (2) the lack of experimental information for rate coefficients for all reactions of interest. The challenges presented in modeling atmospheric chemistry can be overcome by automated mechanism generation. Categorization of reactions into reaction families and determination of structure/reactivity correlations for each reaction family are important steps toward understanding and developing mechanisms of atmospheric chemistry that eventually will lead to accurate determinations of ozone concentrations in the atmosphere. Using our knowledge of predictable reaction types in the atmosphere, we classified ozone formation chemistry into 15 thermal reaction families and 5 photolysis reaction families. These reaction families then were implemented into the automatic mechanism generation software we have developed. One main focal point for the work conducted during the project period was the development of relationships for estimating rate coefficients for reactions relevant to atmospheric chemistry. Correlations relating existing experimental data to properties of reactions and molecules were developed for 15 thermal reaction families. Strategies also were developed for predicting rate coefficients of photochemical processes. Methods for estimating thermodynamic data used in reactivity correlations were refined and augmented. These last two efforts are described in more detail below.

The presence of sunlight causes photochemical reactions to take place; therefore, relevant photochemical reactions were incorporated. Photolysis is an important loss process of carbonyl, peroxy, and nitrate species in the atmosphere. In general, photolysis rate coefficients depend on the intensity of radiation, wavelength, temperature, and the specific molecule reacting. One key source of differences in rate coefficients between different molecules is the absorption cross-section, which is specific to the reactive molecule under consideration. To calculate rate coefficients for photolytic processes, a value of absorption cross-section must be specified or estimated. To this end, a group additivity approach was developed that can be used to estimate the values of absorption cross-section of species that photolyze primarily in the 290-370 nm wavelength range. We have demonstrated that this approach can be used to predict unknown values of absorption cross-section of species for which experimental data are not available.

For the reactivity correlations developed to quantify the rate coefficients of thermal reaction families, thermodynamic properties were the chief reactivity index used. Thus, an estimate of the thermodynamic properties of all molecules in a given reaction must be known. Thermochemistry of radicals is not as well known as that of stable molecular species, even when group additivity schemes are applied. When these radicals contain oxygen or nitrogen atoms, the availability of radical groups is further reduced. Many oxygen- and nitrogen-substituted radicals are present in the atmosphere, and thus, knowledge of their thermochemistry was critical. Quantum chemical calculations using G3//B3LYP were performed to obtain the thermochemistry of radicals from which group values missing from present group additivity databases were obtained. Values based on atomization energies, bond separation reactions, and isodesmic reactions agreed well. Enthalpies of formation, entropies, and heat capacities using the regressed group values were in very good agreement with the values obtained from quantum chemical calculations. Furthermore, the group values obtained showed little sensitivity to the molecules not used in optimization as evidenced by only small changes in the calculated enthalpies of formation for the removed molecules. The group additivity values obtained in this work substantially augment the current database of groups for estimating thermodynamic properties.

Finally, preliminary mechanism generation results indicate a need for mechanism reduction techniques such as using rates of reaction to prune the mechanism as it is being built. This technique has been shown to control mechanism growth for silicon nanoparticle formation chemistry and hydrocarbon pyrolysis and will likely apply to atmospheric chemistry as well. However, application of the approach hinges on having the properties and rate coefficients for all reactions generated, and thus, will be used once the group additivity database is complete.


Journal Articles on this Report : 3 Displayed | Download in RIS Format

Other project views: All 11 publications 3 publications in selected types All 3 journal articles
Type Citation Project Document Sources
Journal Article Khan SS, Broadbelt LJ. A group additivity approach for the prediction of wavelength-dependent absorption cross-sections. Atmospheric Environment 2004;38(7):1015-1022. R828169 (Final)
  • Full-text: ScienceDirect - Full Text PDF
    Exit
  • Abstract: ScienceDirect-Abstract & Full Text HTML
    Exit
  • Other: ResearchGate - Abstract
    Exit
  • Journal Article Khan SS, Yu X, Wade JR, Malmgren D, Broadbelt LJ. Thermochemistry of radicals and molecules relevant to atmospheric chemistry: determination of group additivity values using G3//B3LYP theory. Journal of Physical Chemistry A 2009;113(17):5176-5194. R828169 (Final)
  • Abstract from PubMed
  • Full-text: ResearchGate - Abstract & Full Text PDF
    Exit
  • Abstract: ACS-Abstract
    Exit
  • Journal Article Khan SS, Zhang Q, Broadbelt LJ. Automated mechanism generation. Part 1: Mechanism development and rate constant estimation for VOC chemistry in the atmosphere. Journal of Atmospheric Chemistry 2009;63(2):125-156. R828169 (Final)
  • Abstract: Springer-Abstract
    Exit
  • Supplemental Keywords:

    volatile organic compounds, VOCs, photochemical smog, ozone, photochemical reactions, radiation,, RFA, Scientific Discipline, Air, Toxics, INTERNATIONAL COOPERATION, Sustainable Industry/Business, air toxics, Environmental Chemistry, cleaner production/pollution prevention, VOCs, tropospheric ozone, Engineering, Chemistry, & Physics, Chemicals Management, air quality standards, urban air, exposure and effects, stratospheric ozone, atmospheric particles, environmentally conscious manufacturing, ozone, chemical composition, chemical kinetics, quantum chemistry, mathematical formulations, pollution dispersion models, urban air , pollution prevention, green chemistry, solvents

    Progress and Final Reports:

    Original Abstract
  • 2001 Progress Report