Why did ozone levels remain high in Rio de Janeiro during the Brazilian truck driver strike?

On May 21st, 2018, Brazilian truck drivers began a 10-day strike to protest high diesel prices. This was Brazil's longest trucker strike, and within a few days, gas stations ran out of fuel, drivers waited in line for hours to fuel their cars, transport was severely affected, and airports began cancelling flights. In Rio de Janeiro, the second largest city in Brazil, Air Quality Indexes (AQI) during the strike showed that the high ozone concentrations, determined in three monitoring stations (Iraja, Bangu and Campo Grande), led to "Moderate" and "Unhealthy" AQI in spite of reduced primary pollutant concentrations: nitrogen oxides (NOx = NO + NO2), particulate matter with a diameter < 10 mu m carbon monoxide (CO) and non-methane hydrocarbons (NMHC). In this work, the causes of the high ozone concentrations were analyzed. Criteria pollutant concentrations, as well as meteorological parameters, were compiled for the interval of May 14th to June 6th, 2018. The NMHC/NOx and NO2/NO ratios indicated that the most likely cause of the high ozone levels was the reduced NOx concentrations under VOC-limited conditions (where VOC stands for volatile organic compounds). VOC speciation also showed that the vehicular fleet composition was altered during the strike. Considering that the legislation regarding emissions and air quality standards is being revised in Brazil and other countries, these results show that the control and speciation of VOC emissions is a desirable strategy, while NOx-focused strategies to reduce O-3 in VOC-limited areas should be evaluated carefully.