Atmospheric Degradation of Organic Compounds

Recipient Organization
STATE UNIV OF NEW YORK
(N/A)
SYRACUSE,NY 13210

Performing Department
Chemistry

Non Technical Summary
The degradation of the compound isoprene strongly affects global atmospheric chemistry, yet we are ignorant of critical factors controlling its reaction pathways in the atmosphere. This laboratory project collects key information about the reactions of unstable molecules produced in the degradation of isoprene.Co-Project Director Chhuji Wang Pysics Department, Mississippi State University

Animal Health Component

(N/A)

Research Effort Categories

Basic

100%

Applied

(N/A)

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
133	0499	2000	100%

Knowledge Area
133 - Pollution Prevention and Mitigation;

Subject Of Investigation
0499 - Atmosphere, general/other;

Field Of Science
2000 - Chemistry;

Goals / Objectives
Our goal is to determine the rate constants and branching ratios for the reactions that control the fates of isoprene-OH peroxy radicals under low-NOx conditions. The proposed quantum chemical studies of the mechanism of RO2 + HO2 and RO2 + RO2 reactions will be the first on this subject, and will yield significant insights into peroxy radical chemistry, generally. Statistical rate theory will be used to predict branching ratios for different product channels, and theoretical results will be tested against experiment. No theory has even been proposed to explain, at the molecular level, how structure controls the yields of different product channels; therefore, these computational studies will be critical for developing sorely-needed structure-activity relationships (SARs) for product yields from these reactions. The computational studies of mechanism will support the experimental determinations of product branching ratios for peroxy radical reactions. The proposed work will catalyze additional advances in our understanding of isoprene chemistry: (1) experimentalists will use both the kinetic and computational results to better understand the product yields from their chamber studies of isoprene chemistry; (2) kinetic and mechanistic results will constrain analyses of chamber studies (such as at EUPHORE) that are coupled to real-time monitoring of radicals; (3) the selective source chemistry will enable more direct studies of the kinetics and mechanism of other reactions, such as RO2 + NO3, (an important sink for isoprene-OH peroxy radicals in the evening). The ultimate motivation for this research is to validate and improve chemical mechanisms used in atmospheric modeling in order to help improve our understanding of the atmosphere. To render our research results readily available for incorporation into chemical mechanisms, we will recommend refinements to representations of isoprene chemistry. Currently, gaps in our knowledge of kinetics and mechanism may confound the ability of modelers to understand atmospheric chemistry in areas heavily influenced by isoprene. Although comprehensive mechanisms are too cumbersome for use except in 0-D box models, the results of the proposed research will allow modelers to make informed choices when condensing chemical mechanisms.

Project Methods
To accomplish our goals we will exploit the sensitivity of cavity ringdown spectroscopy (CRDS) and the isomeric specificity of the near-infrared (NIR) absorption features of peroxy radical spectra. The latest techniques of CRDS will be employed to minimize the noise and maximize the reproducibility of the kinetic data. Selective photochemistry will be used to reduce the complexity of the reacting system. Additional insights will be gained by studying analogues of selected isoprene-OH peroxy radicals. Computational chemistry will be used to complement experiment, by providing insight into the competing product channels of individual reactions. The isomer-specific information generated by the proposed research will lead to significant advances in our understanding of tropospheric chemistry on local and global scales.

Progress 07/01/03 to 06/30/13

Outputs
Target Audience: Nothing Reported Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Two postdocs received training. One was trained in quantum chemistry and theoretical kinetics, and applications of these tools to problems in atmospheric chemistry. The other postdoc received training in solid-state lasers, laser spectroscopy, and applications of these tools to problems in atmospheric chemistry. One post-doc is now a professor, and the other is on the technical staff at a major university. How have the results been disseminated to communities of interest?Results have been disseminated through publication of three scientific papers in peer-reviewed journals. In addition, talks and posters have been presented at national or international scientific meetings incorporating the results of this project. What do you plan to do during the next reporting period to accomplish the goals?N/A (the project is completed)

Impacts
What was accomplished under these goals? We obtained quantitative spectra of isoprene and related compounds in the near-infrared that may be useful for monitoring these compounds with high temporal resolution (as for eddy-flux covariance measurements). We determined the transition energies and molecular structures of the electronic excited states formed by near-infrared excitation of peroxy radicals from isoprene. We determined the structures and stability of the peroxy radicals formed from methylbutenol, a compound closely related to isoprene.

Publications

Progress 10/01/05 to 09/30/06

Outputs
We considered some new reaction pathways in the atmospheric degradation of ethylene, a plant hormone. Computational chemistry was used to determine the rate of the proposed reactions over a range of temperature. These pathways appear not to be important in the lower atmosphere.

Impacts
This will help scientists better model atmospheric chemistry.

Publications

Exploration of the Potential Energy Surface and Prediction of the Atmospheric Abundance and Vibrational Spectra of the HO2-(H2O)n (n=1-2) Hydrogen-Bonded Complexes, K. S. Alongi, T. S. Dibble, G. C. Shields, and K. N. Kirschner, J. Phys. Chem. A, 110, 3686-3691 (2006).