Using Cavity Ringdown Spectroscopy for Direct Laboratory Studies of the Oxidation Reaction of Alkenes by Tropospheric OzoneEPA Grant Number: F07B10428
Title: Using Cavity Ringdown Spectroscopy for Direct Laboratory Studies of the Oxidation Reaction of Alkenes by Tropospheric Ozone
Investigators: Takematsu, Kana
Institution: California Institute of Technology
EPA Project Officer: Cobbs-Green, Gladys M.
Project Period: October 1, 2007 through September 30, 2010
RFA: STAR Graduate Fellowships (2007) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Academic Fellowships , Fellowship - Atmospheric Chemistry
The project goal is to study the reaction of alkenes (a major class of hydrocarbon emission) with ozone by directly detecting the intermediate of the reaction, the Criegee intermediate. The intermediate, which has previously never been detected in the gas phase, can be used as a tracer to better measure the rates and product yields of the reaction. It is crucial that we quantify these parameters accurately, as the reaction plays an important role in smog and aerosol formation in the atmosphere.
We propose to directly detect the Criegee intermediate in the gas phase using the high sensitivity analytical laser method cavity ringdown spectroscopy (CRDS). CRDS is a spectroscopic method utilizing an optical cavity, a cell with two highly reflective mirrors (R > 99.9%) on each end, to substantially increase the effective pathlength (>km). Sensitivities of 10-6~10-8 fractional absorption per pass are achieved, magnitudes higher than traditional absorption methods (10-4). This project utilizes the fast response time, high sensitivity, and large scanning range of CRDS to directly detect the Criegee intermediate. Calculations are now being run to provide an estimate of the initial scanning range, while modifications to the flow system and chemistry are being made to increase the effective concentration of the intermediate.
Direct detection of the Criegee intermediate will enable us to measure the rates and product yields of the reaction for a variety of alkene species. The data gained from this project will be used in atmospheric models to provide better predictions for air quality control and air pollutant regulation.