Cleyton Martins da Silva

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

Volatile organic compounds (VOCs) play a central role in atmospheric chemistry. In this work, the kinetic and mechanistic reactivities of VOCs are analyzed, and the contribution of the organic compounds emitted by anthropogenic and natural sources is estimated. VOCs react with hydroxyl radicals and other photochemical oxidants, such as ozone and nitrate radicals, which cause the conversion of NO to NO2 in various potential reaction paths, including photolysis, to form oxygen atoms, which generate ozone. The kinetic reactivity was evaluated based on the reaction coefficients for hydroxyl radicals with VOCs. The mechanistic reactivity was estimated using a detailed mechanism and the incremental reactivity scale that Carter proposed. Different scenarios were proposed and discussed, and a minimum set of compounds, which may describe the tropospheric reactivity in the studied area, was determined. The role of isoprene was analyzed in terms of its contribution to ozone formation.

Avaliação da eficiência do método TO-15 para determinação de compostos orgânicos voláteis em condições típicas de ambiente urbano

detection limit of ≤0.2 ng for all target compounds, replicate precision for a calibration standard and ambient samples within 20%. The stability of the target compounds during storage of sampled air in canisters was also evaluated at atmospheric pressure and relative humidity of 50%. Results show that, in the sampling conditions, compounds are not stable for more than a week. For validation experiments, samples were collected at the entrance of Tijuca National Park, located at the city of Rio de Janeiro. Isoprene was selected as a marker of biogenic emissions, and aromatic compounds were selected as markers of anthropogenic emissions, primarily vehicular emissions. Then, samples were collected in Saens Pena Square, a central area in the Tijuca District, in the northern part of the city, approximately 10 km from the entrance of Tijuca National Park. Volatile organic compounds were determined and the results were compared with previous data obtained in the same local using other methods.

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/NOx (VOC/NOx) 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 NOx 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/NOx ratio of 8.86.

Análise de Especiação de Compostos Orgânicos Voláteis Precursores de Ozônio nas Bacias Aéreas da Região Metropolitana do Rio de Janeiro

Neste trabalho foram determinadas as concentracoes e especiacao dos compostos orgânicos volateis (COVs) precursores de ozonio, na atmosfera das Bacias Aereas I, II, III e IV e da Microbacia Aerea da Zona Sul, na Regiao Metropolitana de Rio de Janeiro. Os COVs foram determinados segundo o Metodo TO-15 da US EPA, usando canisters (botijoes de aco inox eletropolidos) para a amostragem e cromatografia gasosa acoplada a espectrometria de massas e termodessorcao (CG-EM-DT) para injecao e analise quimica das amostras. Foram determinados 52 COVs, na faixa C3-C12, estando os valores medios para a concentracao total de COVs na faixa de 169,32 µg m-3 para a Bacia Aerea II ate 274,62 µg m-3 para a Microbacia Aerea da Zona Sul. A distribuicao massica dos compostos, classificados por grupos quimicos e reatividade dos mesmos, mostram que existem caracteristicas proprias de cada bacia, relacionadas as fontes de emissao. Assim, mesmo existindo eventual transporte de massas de ar entre as diferentes bacias, os resultados sugerem que as bacias apresentam nao so caracteristicas geograficas diferentes, como, tambem, caracteristicas quimicas (composicao do ar) e fisico-quimicas (reatividade e potencial formador de ozonio) diferentes.

Determinação de Gases do Efeito Estufa em Cinco Capitais de Diferentes Biomas Brasileiros

Em um mundo em constante transformacao, as concentracoes crescentes de gases de efeito estufa (GEE) e os processos que podem levar ao sequestro de CO2 e a mitigacao das concentracoes destes gases para conter o aquecimento global sao relevantes. Neste trabalho foram determinadas as concentracoes de CO2, CH4 e N2O em cinco capitais brasileiras, pertencentes aos tres principais biomas brasileiros: Curitiba, Sao Paulo e Rio de Janeiro na Mata Atlântica, Brasilia no Cerrado e Belem na Amazonia. As coletas e analises quimicas foram realizadas utilizando um metodo de analise de baixo custo recentemente desenvolvido por alguns dos autores deste estudo. As concentracoes de CO2, CH4 e N2O se encontram nos intervalos 391-542 ppmv, 1,74-2,31 ppmv e 263-342 ppbv, respectivamente. Os valores encontrados neste trabalho sao consistentes com os reportados para outras areas urbanas no mundo e nao apresentaram diferencas importantes dentro de uma mesma cidade, ao se comparar a area verde com a area livre de cobertura vegetal, devido provavelmente a rapida mistura das massas de ar e o efeito global das areas verdes como sumidouro de carbono. Contudo, para a cidade do Rio de Janeiro as concentracoes de CO2 foram claramente menores, tanto no inverno quanto no verao, que nas outras cidades, sugerindo a importância das areas compactas de florestas, especialmente de floresta secundaria e outras areas de reflorestamento recente, no processo de sequestro de carbono.

Air Quality Indexes in the City of Rio de Janeiro During the 2016 Olympic and Paralympic Games

In this work, the air quality indexes (AQIs) determined in Rio de Janeiro from July to September 2016, before and during the Summer Olympic and Paralympic Games, in the monitoring stations operated by the Municipal Secretariat of the Environment, were compiled and analyzed. Only four automatic monitoring stations determined all the Brazilian criteria pollutants (smog, total particulate matter, PM10 (particulate matter < 10 mm), NO2, ozone and SO2). NO2 and PM10 levels were generally lower during the Olympic period because of restrictions on vehicular flux. However, ozone concentrations remained high, due to unfavorable meteorological conditions. The worst conditions were observed in Bangu and Irajá Districts, where ozone concentrations frequently exceeded 160 mg m. According to the World Health Organization (WHO), as ozone concentrations increase above this value, health effects became increasingly numerous and more severe. Brazilian air quality allowable standards are clearly higher than WHO guidelines, which, in addition to the combined results of the adopted air quality indexes and the use of a restricted number of criteria pollutants to report the air quality, led to AQIs in the intervals good and moderate, despite concentrations frequently being high in terms of WHO guidelines.