CARBON-MONOXIDE TREND, METEOROLOGY, AND 3-WAY CATALYSTS IN MEXICO-CITY

From the analysis of data of the Inspection/Maintenance (I/M) program, and of the long-term trend of ambient CO concentrations in Mexico Cit y, it is inferred that three-way catalysts (TWCs) have a 45% efficienc y, well below the expected 90% value. The most probable causes are sul fur poisoning, lead contamination, and ceramic breakage due to bumps a nd potholes on the streets. Also, we have found a ratio between the av erage daily peak value of atmospheric CO and gasoline consumption: (11 +/- 1) ppbCO/MLm (million liters of gasoline per month) in 1988 decay ing to (10 +/- 1) in 1991 for Mexico City before the introduction of T WCs. In addition, we found a correlation between the monthly averages of CO daily peak and meteorological variables, explaining most of the seasonal changes using only the intensity of the inversion layer and s urface wind speed.