Measurement of surface ozone and its precursors in an urban area in South Brazil

Weekly and seasonal variations of surface ozone and their precursors – nitrogen oxides, carbon monoxide-associated with meteorological parameters (wind direction, temperature, solar radiation) – are reported. Measurements were performed continuously during 2006 at two sampling stations located in the metropolitan area of Porto Alegre, Brazil. Results have shown that O 3 concentrations remained almost constant between weekdays. Levels of NO x precursors decreased especially on Sundays, due to lighter traffic. The seasonal variation has shown a maximum O 3 concentration during summer and spring while NO x and NO 2 have maxima at the colder months. The daily cycle of highest ozone concentrations reveals a lower nightly level and an inverse relation between O 3 and NO x , evidencing the photochemical formation of O 3. There are seasonal variation and source heterogeneity.