SEASONAL BEHAVIOR OF TROPOSPHERIC OZONE IN THE SAO-PAULO (BRAZIL) METROPOLITAN-AREA

This paper presents a study of the seasonal behavior of tropospheric ozone and its precursors in the Sao Paulo Metropolitan Area as observed during 1987. The O3, NO, NO2, NMHC, and meteorological data were collected at an air quality station in downtown Sao Paulo by the State Environmental Protection Agency (CETESB). The air pollutant measurements were related to both daily total insolation and the number of hours of insolation measured at the Sao Paulo University Climatological Station. Correlations between both radiation parameters and total daily integrated ozone amounts were performed. The total number of sunshine hours was highly correlated to mean hourly ozone concentration values during each month of 1987. The seasonal behavior of NO, NO2, and NMHC was also studied. Two diurnal peaks in average NO concentration were observed, i.e. one in early morning and one in early evening; both were due to emissions from urban mobile sources. The magnitude of these peaks doubled in value during the winter months. Its diurnal concentration variation was inverse to that of the O3; similar behavior was found for NO2 and for NMHC. The data presented herein show the influence of solar radiation and of ozone precursors on photochemical smog formation in this tropical region.