WORLD METEOROLOGICAL ORGANIZATION

UNITED NATIONS ENVIRONMENT PROGRAMME

MEXICO

Most of research on stratospheric ozone that has been or is being carried out in Mexico deals with measurements of ozone column, on impact of a reduction on the ozone layer in Mexico on several system (i.e. UV penetration, photolysis rate constants of atmospheric oxidants on surface and photochemical smog reactivity).

OZONE COLUMN

A long standing Gobson spectrophotometer has been in operation (with some interruptions) for many years in the Solar Radiation Laboratory at campus of the National University placed in the southwest of Mexico City. Since 1994 daily observations of ozone columns are being carried out and reported to the World Data Center on Ozone in Canada. Umkeher observations are being. carried out in winter months. Measurements in an unpolluted place north of Mexico City have been made to estimate the effect of urban ozone.

From these measurements Juarez et. al, [1] examine observations total ozone column between 1986 and 1989 in Mexico City. Considering different depths of the mixing layer depending on the season, and comparing their results with those reported for Mauna Loa in Hawaii and Poona in India, at the same latitude as Mexico City, they are able to estimate the growing effect of urban ozone on the total column above Mexico City.

A research project to parallely observe the ozone column outside Mexico City with a Brewer spectrophotometer will be funded by UNAM and the National Council for Science and Technology.

PHOTOLYSIS RATES

Photolysis of key species such as nitrogen dioxide, ozone and aldehydes, are the elementary reactions leading to the formation of photochemical smog. Calculations and experimental measurements (in particular, nitrogen dioxide) of these key reactions are reported. Sensitivity analysis of them to the ozone column has been carried out [2,3] using a radiation transfer model (RTM), based on the delta-Eddington approximation [4]. Measurements of UV radiation are being carried out. Measurements of ozone photolysis rate constants are due to start soon at the Center for Atmospheric Sciences of the National University (CCA-UNAM)

PHOTOCHEMICAL SMOG REACTIVITY

Sensitivity analysis of a fully detailed chemical mechanism of 8 surrogate hydrocarbons is being carried out at CCA and full air quality models are due to be run under different scenarios of ozone depletion and global warming.

REFERENCES

1. Juarez A., C. Gay and J.L. Bravo "Influence of urban ozone in the measurements of the total ozone column in Mexico City". Atmosfera, Vol. 8, No. 1, 1995

2. Castro T., L.G. Ruiz-Suárez, C. Gay, M. Helguera and J.C. Ruiz-Suárez. "Direct measurements of NO₂ photolysis rates for Mexico City". Atmosfera, Vol. 8, 1995.

3. Castro T., L.G. Ruiz-Suárez, M. Molina, J.C. Ruiz-Suárez and M. Montero "Sensitivity Analysis of a UV Radiation Transfer Model and Experimental Photolysis Rates of NO₂ in the Atmosphere of Mexico City". Submitted to Atmospheric Environment, 1995

4. Ruiz-Suárez J.C, L.G. Ruiz-Suárez, C. Gay, T. Castro, M. Montero, S. Eidels-Dubovoi and A Muhlia. "Photolytic rate for NO₂, O₃ and HCHO in the atmosphere of Mexico City". Atmospheric Environment, Vol. 27A, No. 3, 427 430, 1993