In different cities around the world, higher ozone concentrations are observed during weekends for various reasons. This study aims to determine the causes of this effect in the city of Rio de Janeiro based on measurements obtained at three automatic air quality monitoring stations in the Bangu, Campo Grande and Irajá neighborhoods between 2012 and 2013. Variations in the solar radiation and hourly carbon monoxide, nitrogen oxides, non-methane hydrocarbons, ozone and particulate matter concentrations were determined. The Bangu station showed the lowest ozone concentration differences between the weekdays and weekends (8.9%) and recorded the highest ozone concentrations and largest number of exceedances. The low ozone consumption by nitrogen oxide resulted in the high ozone concentrations at the Bangu station. In addition, the volatile organic compounds (VOC)/nitrogen oxides (NOx) ratio for this station was evaluated for each day of the week between 6 and 9 AM, and the observed VOC/NOx ratios were higher at the Campo Grande and Irajá stations. We concluded that the weekend effect occurred at all three of the evaluated stations, with greater intensity at the Campo Grande and Irajá stations. The main cause of this weekend effect is the greater reductions in NO emissions over the weekends, which increase the VOC/NOx ratio.

Neste trabalho, dados de poluentes legislados e não legislados foram obtidos em uma região industrial-residencial no Rio de Janeiro, no período de abril a novembro de 2002. As concentrações de formaldeído e acetaldeído encontradas estavam na faixa de 25,25-231,73 ppb e 9,48-75,74 ppb respectivamente. Estas altas concentrações podem ser atribuídas a diversas fontes: emissões veiculares e industriais, a presença de incineradores de lixo, efluentes e rejeitos despejados no rio Faria Timbó e emissões de uma industria de metanol. As concentrações médias de BTEX foram: 1,92, 9,02, 6,37, 21,65 e 5,99 µg m-3 para benzeno, tolueno, etilbenzeno, m,p-xileno e o-xileno, respectivamente. As concentrações médias de PM10 mostram valores máximos para o mês de outubro, abril e junho. As concentrações obtidas nas simulações foram para o mês de agosto usando um modelo de trajetórias. A concentração máxima de ozônio calculada foi de 39,8 ppb, as 15:00 horas, obtendo uma boa concordância com os dados experimentais (38,5 ppb). A isopleta de ozônio mostra que o local está em uma região alta de VOC/NOx, típica de áreas suburbanas e a favor do vento.

In this work, data for criteria and non-criteria pollutants were obtained in a suburban industrial-residential area in Rio de Janeiro, from April to November 2002. Formaldehyde and acetaldehyde concentrations were found in the ranges 25.25-231.73 ppb and 9.48-75.74 ppb, respectively. These high concentrations may be attributed to several sources: vehicular and industrial emissions, the presence of several trash incinerators, effluents and waste rejected in the Faria Timbó river and emissions from a methanol industry. Average BTEX concentrations were: 1.92, 9.02, 6.37, 21.65 and 5.99 µg m-3 for benzene, toluene, ethylbenzene, m,p-xylene and o-xylene, respectively. PM10 concentrations showed maximum mean values in October, April and June. Simulated concentrations were obtained for August 2002 using a trajectory model. The maximum calculated ozone concentration was 39.8 ppb, at 3:00 pm, in good agreement with experimental data (38.5 ppb). The ozone isopleths show that the local is in the high VOC/NOx region, typical of suburban and downwind areas.

As concentrações de ozônio para um área urbana, com alto fluxo veicular, no centro da cidade, foram simuladas usando um modelo cinético empírico. Foi desenhado um caso base usando dados experimentais, do mês de dezembro de 1999, para a Avenida Presidente Vargas, Rio de Janeiro. O acordo entre os resultados calculados e os dados experimentais é satisfatório. O pico de ozônio calculado acontece às 15:15 horas (23,0 ppb). Foi realizada uma análise de sensibilidade e incertezas e desenhados alguns cenários hipotéticos para ilustrar a capacidade preditiva do modelo.

An empirical kinetic modeling approach is used in order to simulate ozone concentrations for an urban downtown area with high vehicular traffic. A base case was designed using experimental data for December 1999 in Presidente Vargas Avenue, Rio de Janeiro. The agreement between experimental and simulated results was quite good. The simulated ozone peak was obtained at 3:15 PM (23.0 ppb). A sensitivity-uncertainty analysis was performed and hypothetical scenarios were designed to illustrate the predictive potential of Air Quality Models.