Time and space variations of sulfur dioxide concentrations in the metropolitan area of Mexico City

Abstract

S02 concentration measurements in the Metropolitan Zone of Mexico City (MZMC) over the period from 1986 through 1989 are analyzed. Mean hourly measurements recorded by the governmental monitoring network (SEDUE) and by the Centro de Ciencias de la Atmosfera monitoring station were used. The survey covers annual, seasonal, monthly, weekly and diurnal variations. An analysis and discussion of the trend of S02 in the south of the MZMC for 1986-1989 is also included. The highest S02 concentrations occur in the northern area of the Mexico City where the industrial zone is located. Concentrations decrease toward the South of the city following the prevailing wind direction. The EPA air quality standard of 30 ppb annual average is exceeded for most of the MZMC. During the winter months the S02 problem is worse. The week~y cycle shows that normal weekday concentrations are significantly higher than weekends and holidays near the industrial zone. The diurnal cycle of S02 concentration is strong. The morning peak varies in time with distance from the main industrial area. The winter trend of S02 since 1986 in a suburban area (University Campus) shows that the S02 problem is large and growing, despite soothing official statements.