Kinetic and mechanistic reactivity. Isoprene impact on ozone levels in an urban area near Tijuca Forest, Rio de Janeiro

Preliminary Study of Ambiente Levels and Exposure to BTEX in the Rio de Janeiro Olympic Metropolitan Region, Brazil

This study aims to determine BTEX concentrations in the Metropolitan Region of Rio de Janeiro (MRRJ, Brazil) and evaluate potential health risks of benzene and ethylbenzene exposure based on the collected data, in 2015, the year before the Rio 2016 Olympic Games. Samples were collected and analyzed following method TO-15 (U.S.EPA). Toluene was the most abundant compound in all samples (mean concentration 16.72 ± 15.70 µg m^-3). The average benzene concentration in ambient air (3.44 ± 3.14 µg m^-3) was slightly lower than the yearly average "upper assessment threshold", 3.5 µg m^-3, established by EU Directive 2008/50/EC. The calculated cancer risk values were > 1 × 10^-6 for all samples, clearly indicating a potential cancer risk and the importance of fixed measurements by the monitoring stations to assess ambient air quality in the urban areas of the MRRJ. Calculated ratios for the BTEX species indicate that these compounds are predominantly emitted from vehicular sources with a contribution from industrial sources.

Impact of the Petrochemical Complex on the Air Quality of an Urban Area in the City of Rio de Janeiro, Brazil

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 (NO_x) rather than on the individual VOC and NO_x levels, as expected for the VOC-controlled condition typical of the urban area of Rio de Janeiro. Moreover, high VOCs/NO_x ratios are highly dependent on the transport of air masses. When pollutants are transported from urban areas with heavy vehicular flux and high NO_x concentrations, ozone levels are reduced. When air masses are transported from the industrial petrochemical area, NO_x levels are relatively low, and ozone episodes are frequent.

Levels of Volatile Carbonyl Compounds in the Atlantic Rainforest, in the City of Rio de Janeiro

When Europeans arrived in America, the Brazilian Atlantic rainforest covered approximately 1,290,000 km². Now, only 8% of the biome's original vegetation remains. One of the largest areas is Tijuca Forest National Park. In this work, the concentrations of 13 carbonyl compounds in an isolated area inside Tijuca Forest, in an urban park with primary and secondary vegetation (Gericinó Natural Park) and in two typical urban areas (Tijuca District and the city of Nilópolis) were determined. The main compounds were formaldehyde and acetaldehyde. The formaldehyde mean concentrations were 0.98 ± 1.00, 1.27 ± 1.67, 3.09 ± 1.60 and 2.33 ± 2.17 μg m^-3 for Tijuca Forest, Gericinó Natural Park, Tijuca District and the city of Nilópolis, respectively. The mean acetaldehyde concentrations were, for the same locations, 0.93 ± 1.05, 2.94 ± 2.54, 2.78 ± 0.91 and 5.48 ± 1.90 μg m^-3. The results indicate that the compounds measured within the forest are transported from the city and that the trees play an important role in removing air pollutants. In contrast, the Gericinó protected area is heavily affected by urban emissions, and its capacity to dilute or absorb pollutants is low because of the sparse vegetation.

Isoprene Emissions and Ozone Formation in Urban Conditions: A Case Study in the City of Rio de Janeiro

The potential role of isoprene oxidative processes, as well as the possible impact of air pollution on isoprene emissions, are more important in tropical cities, surrounded by rainforests. In this study, the contribution of isoprene to ozone formation was determined considering different scenarios, mainly volatile organic compounds/NO _x (VOC/NO _x ) ratios, and typical atmospheric conditions for the city of Rio de Janeiro, where more than 36% of the urbanized area is covered by vegetation. Ozone isopleths and incremental reactivity coefficients (IR) were evaluated to understand the direct contribution of isoprene to ground-level ozone formation and the negative impact of anthropogenic NO _x emissions on the natural atmospheric balance. Although isoprene accounted for only 2.7% of the total VOC mass, excluding the isoprene concentration from the model reduced the maximum ozone value by 14.1%. The calculated IR coefficient (grams of O₃ formed per gram of added isoprene) was 2.2 for a VOC/NO _x ratio of 8.86.

An Analytical Investigation of Ozone Episodes in Bangu, Rio de Janeiro

This study investigated the potential factors that contribute to frequent high levels of ozone as well as ozone episodes in Bangu, one of the most critical areas in the city of Rio de Janeiro regarding ozone levels. For 74 days in a two-year period (10.3%), the national air quality standard was exceeded. For the same period, a total of 378 days (51.8%) had ozone concentrations that were between 80 and 160 µg m^-3. A statistical analysis of pollutant concentrations and meteorological data as well as a kinetic and mechanistic analysis of VOC reactivity showed that the high ozone concentrations did not seem to be closely related to local emissions but, rather, were related to pollutant transport and triggered by photochemical activity. The mountains in the southern and northern part of the district contribute to the increase of surface temperatures and the accumulation of pollutants. The VOC/NO_x ratios corresponded to a VOC-limited process.