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

This paper presents a study of the seasonal behavior of tropospheric o zone and its precursors in the Sao Paulo Metropolitan Area as observed during 1987. The O3, NO, NO2, NMHC, and meteorological data were coll ected at an air quality station in downtown Sao Paulo by the State Env ironmental 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 Statio n. Correlations between both radiation parameters and total daily inte grated ozone amounts were performed. The total number of sunshine hour s was highly correlated to mean hourly ozone concentration values duri ng each month of 1987. The seasonal behavior of NO, NO2, and NMHC was also studied. Two diurnal peaks in average NO concentration were obser ved, 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 v ariation was inverse to that of the O3; similar behavior was found for NO2 and for NMHC. The data presented herein show the influence of sol ar radiation and of ozone precursors on photochemical smog formation i n this tropical region.