Multi-Gas analysis of ambient air using FTIR spectroscopy over Mexico City

Abstract

A Fourier Transform Infrared (FTIR) spectrometer was used to analyze the composition of ambient air at a specific site in the Mexico City metropolitan area. A continuous flow of air was passed through a multi-pass gas cell and the absorption spectra were collected over a period of two weeks Quantitative analysis was performed by means of the classical-least square (CLS) method using synthetically generated spectra as references and calibration sources. Ambient levels of CO, CO₂, CH₄ and N₂O are reported with a time resolution of five minutes for September 2001, showing interesting results in their diurnal patterns Comments on the precision, detection limits and signal-to-noise of the instrument are included for the evaluation of this technique. Water concentrations were estimated and compared with those obtained with a relative-humidity sensor. The technique of extractive FTIR for ambient trace-gas monitoring was utilized in Mexico for the first time and some potential applications are given.