David W. T. Griffith

Atmospheric trace gas analysis using matrix isolation-fourier transform infrared spectroscopy

A novel cryogenic sampling method combining the matrix isolation technique with FTIR spectroscopy has been developed for atmospheric trace gas analysis. It is applicable to a wide range of molecules with detection limits typically in the 10–50 ppt range. The method is described along with some measurements of N2O, CFCl3, CF2Cl2, OCS, CS2, SO2 and PAN from samples collected at ground level and from an aircraft between 9 and 14 km.

Cryogenic Sampling Techniques

Most long-lived atmospheric trace gases originate at the earth’s surface. Because of their long chemical lifetimes, they mix rather well in the troposphere where they interact in the photochemical system and act as so-called “source gases”. This group of gases includes CH4, H2, CO2, CO, N2O, and some man-made halogenated hydrocarbons such as CFC13, CF2C12, CH3C1, CH3CC13, CC14, etc.. For more than two decades increasing efforts have been made to investigate the vertical distribution of these trace gases in the stratosphere. These measurements provide distinct information on their (photo)chemical fate in the stratosphere. Combined data sets for several compounds obtained at the same time and location also offer the possibility to study photochemical reaction mechanisms to achieve some insight into dynamic processes in the stratosphere. To date, most of the available data on the distribution of long lived-trace gases have been obtained from analyses of air samples collected during balloon flights employing grab and cryogenic sampling techniques.

Atmospheric Trace Gas Measurements Using Matrix Isolation - FTIR Spectroscopy

The technique of matrix isolation combined with Fourier transform infrared spectroscopy has been developed as a sensitive method for atmospheric trace gas analysis. Matrices of solid CO2 are grown at 77K using natural CO2 as the matrix material, in which the atmospheric trace gases are embedded. Analysis of the matrix by FTIR absorption spectroscopy yields simultaneous measurements of a wide range of atmospheric trace gas species, including unstable and reactive ones, with detection limits typically around 101i molecules or 10-11 mixing ratio from a 20-40 litre air sample.