RESUMO
In the city of Rio de Janeiro (Brazil), the districts located in the northern area are considered the most critical regarding ozone levels year-round. In this study, the potential factors that contribute to high levels of ozone in the district of Irajá were investigated. The obtained results clearly showed that, in spite of the high correlation of ozone concentrations with wind speed and temperature, ozone episodes depend on the ratios of volatile organic compounds (VOCs) to nitrogen oxides (NOx) rather than on the individual VOC and NOx levels, as expected for the VOC-controlled condition typical of the urban area of Rio de Janeiro. Moreover, high VOCs/NOx ratios are highly dependent on the transport of air masses. When pollutants are transported from urban areas with heavy vehicular flux and high NOx concentrations, ozone levels are reduced. When air masses are transported from the industrial petrochemical area, NOx levels are relatively low, and ozone episodes are frequent.