CO₂ Laser Photoacoustic Spectroscopy Applied to Environmental Analysis in the Metropolitan Area of Mexico City

Abstract

Measurements of atmospheric ethene were performed in the Metropolitan Area of Mexico City by means of a ¹²C¹⁶O₂ laser‐based photoacoustic spectrometer. Two types of experimental campaigns were conducted. In the first type, performed in November 1999 and March 2000, air samples were simultaneously collected in canisters during the morning (06:00 to 09:00 h) in Xalostoc (industrial site), La Merced (commercial site), and Pedregal (residential site). The highest ethene levels were usually detected in Xalostoc, followed by those in La Merced and Pedregal. In the second type of campaign, carried out in March 2002, real‐time ethene measurements were performed at the facilities of our institute (CINVESTAV) by continuously drawing ambient air to the photoacoustic spectrometer. Typically, the ethene concentration exhibited two broad bands daily, reaching up to 104 ppbV at around 07:10 h. Ethene levels were also studied as a function of nitrogen oxide data obtained from a government network for atmospheric monitoring, and a linear correlation between ethene and NO_x concentrations was found. Finally, the ethene levels in Mexico City were compared with those measured in other cities worldwide.

Keywords:

• CO₂ laser
• Photoacoustic spectroscopy
• Environmental analysis

Acknowledgments

This work was partially supported by the Instituto Mexicano del Petróleo through project IMP‐FIES‐97‐07‐VI and by CONACyT through project 33126‐E. The authors thank the RAMA authorities for allowing the use of their database.