Graciela Arbilla

Kinetics and thermodynamics of limonene ozonolysis.

Using density functional methods, the initial reaction steps of limonene ozonolysis have been investigated with a focus on primary ozonide formation and its decomposition to Criegee intermediates and carbonyl compounds. The ozonide formation is highly exothermic, and the decomposition channels have similar free energies of activation, ΔG(‡), indicating that there is no primary pathway for ozonide decomposition. Assuming that ozonide formation is the rate limiting step, the theoretical rate coefficient, k = 1.6 × 10(-16) molecule(-1) cm(3) s(-1), evaluated at the CCSD(T)/6-31G(d,p)//BHandHLYP/cc-pvdz level and 298.15 K for d-limonene is in good agreement with the experimental value, k(exp) = 3.3 × 10(-16) molecule(-1) cm(3) s(-1). The theoretical Arrhenius expression is also in good agreement with experimental results.

Trace metals in the urban aerosols of Rio de Janeiro city

-3 . Em PM2.5, os metais mais abundantes foram Fe e Ca (307 e 60 ng m-3, respectivamente), enquanto que as concentracoes de Mg, Zn e Cu foram aproximadamente 20 ng m -3 . Para PM 10 e PM 2,5 , correlacoes elevadas foram obtidas para Ca, Mg e Al, enquanto a correlacao de Ca e Mg com Fe mostrou-se pobre, indicando assim que Ca, Mg e Al provavelmente se originam principalmente da resuspensao de poeira, enquanto Fe pode ser tambem proveniente de uma fonte adicional, como o desgaste de freio. Elementos antropogenicos (Zn e Cu) tiveram fatores de correlacao baixos, sugerindo fontes de emissoes diferentes. A presenca de Cu pode estar relacionada com o desgaste dos freios e a de Zn pode ser atribuida ao desgaste do pneu. Em particulas finas, Ca, Mn, Fe, Zn e Cu estavam presentes em razoes mais elevadas do que em material da crosta. Uma vez que estas particulas sao observadas principalmente devido aos processos de combustao, elas podem estar presentes na gasolina, oleo e lubrificantes. Fe foi correlacionado com Mn, enquanto fatores de correlacao entre Ca e Mg foram relativamente baixos.

A two-year monitoring program of aromatic hydrocarbons in Rio de Janeiro downtown area

Benzene, toluene, ethylbenzene, m+p+o-xylene (BTEX) and two trimethylbenzenes (BTEXT) were monitored in Rio de Janeiro downtown area during 2004 and 2005. Some criteria pollutants and meteorological parameters were also determined in order to assess the main data correlations. 94 samples were collected, using activated charcoal cartridges, between 9:00 am and 3:00 pm. The mean concentrations obtained were: 14.5, 22.8, 9.19, 19.3, 8.5, 10.4 and 12.1 µg m-3 for benzene, toluene, ethylbenzene, m+p-xylene, o-xylene, 1,2,3-trimethylbenzene and 1,3,5-trimethylbenzene, respectively. These values are similar to mean concentrations obtained in the Brazilian cities of Porto Alegre, Volta Redonda and Sao Paulo, which use the same type of fuel. Multivariate analyses showed that individual BTEXT are emitted by the same source and are not well correlated with other primary pollutants. These results may be due to the contribution of evaporative losses of the BTEXT and to the formation of secondary volatile organic compounds in the atmosphere.

Ozone Air Quality Modeling. A Case Study: A Heavily Vehicle Impacted Urban Avenue in Rio de Janeiro, Brazil

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.

Unimolecular reactions on formaldehyde S0 PES

Abstract The competitive unimolecular reactions of formaldehyde, H 2 CO→H 2 +CO; H 2 CO→ trans -HCOH and H 2 CO→H+HCO, were comparatively studied under the direct dynamics formalism, using Density functional and ab initio levels of theory. In addition, the geometric isomerization trans -HCOH→ cis -HCOH was evaluated. Calculated reaction path properties were used in the determination of Rice–Ramsperger–Kassel–Marcus microcanonical rate coefficients. The reaction dynamics was evaluated for each individual process based on the nuclear displacements in the reaction path and normal coordinate analysis. Our results found are in very good agreement with experimental barrier heights and quantum yields trends.

Pattern of volatile aldehydes and aromatic hydrocarbons in the largest urban rainforest in the Americas.

Atmospheric concentrations of aldehydes and monoaromatic hydrocarbons were determined in Tijuca Forest, the largest urban tropical forest in the Americas. The forest is a protected area, surrounded by the city of Rio de Janeiro. Data were also obtained in a commercial and a residential area for comparison. A total of 160 aldehyde samples and 60 BTEX (benzene, toluene, ethyl-benzene and xylenes) samples were collected from four locations between January and August of 2008. The aldehydes were collected using C18 resin cartridges coated with 2,4-dinitrophenylhydrazine and analyzed by high performance liquid chromatography (HPLC) with a diode array UV-Vis detector, while the BTEX samples were collected using tubes of coconut charcoal, which were then extracted with dichloromethane and analyzed by gas chromatography (GC). Within Tijuca Forest, formaldehyde and acetaldehyde levels were in the range of <detection limit - 5.09 ppbV and <detection limit - 4.08 ppbV, respectively. Formaldehyde concentrations strongly correlated with temperature and solar radiation. The different ratios for formaldehyde and acetaldehyde concentrations in the forest and in the urban sites clearly suggested that carbonyl levels within the forest might have an important contribution from biogenic sources. BTEX concentrations in the forest were very low, showing that the forest acted as a sink for many pollutants. Toluene/benzene ratios in the forest were also lower than in the city, which may be attributed to the faster photochemical oxidation of toluene. These observations were indicators of the low impact of the urban area on the studied forest.

Otimização de um mecanismo fotoquímico para a simulação da atmosfera urbana brasileira

A photochemical reaction mechanism for the description of air quality in Brazilian urban regions is described and evaluated by comparison with chamber experiments. The mechanism was developed for use in ozone modeling and application of control strategies. The oxidation of ethanol and methyl-ter-butyl-ether is also considered. Using this chemical model, a trajectory simulation of Brazil Avenue, Rio de Janeiro, was performed. The model predicts that ozone should reach a maximum of 22.4 ppb at 14:57 h. This value is in good agreement with the experimental measurements of 22.5 ppb for 14:00 h and 22.3 ppb for 15:00 h.

Simulation of Air Pollution from Mobile Source Emissions in the City of Rio de Janeiro

Foi usado um modelo de trajetorias simples e o modelo quimico SAPRC, com inclusao da quimica do etanol e do metil-terc-butil-eter (MTBE), para simular as concentracoes de ozonio na Avenida Brasil, uma rua muito movimentada na cidade de Rio de Janeiro (Brasil), onde pode considerar-se que a principal fonte de poluicao sao os veiculos. O maximo calculado para ozonio, 22,4 ppb as 14:57 h, esta em bom acordo com os dados experimentais. Foram calculadas as isopletas de ozonio, usando dados meteorologicos e de emissoes apropriados para esse local, mostrando que esses niveis de ozonio na cidade de Rio de Janeiro sao uma consequencia das altas concentracoes de NOx.

Concentration of airbone trace metals in a bus station with a high heavy-duty diesel fraction

Amostras de material particulado total (MPT) e MP10 foram coletadas numa estacao de onibus, no periodo de agosto de 2006 a fevereiro de 2007. Na area, as unicas fontes importantes de emissao de poluentes sao os onibus, ja que os veiculos leves representam apenas 1-2% do fluxo total e nao sao desenvolvidas outras atividades no local. As concentracoes de metais foram determinadas por espectroscopia de emissao por plasma indutivamente acoplado (ICP-OES). Os metais mais abundantes foram Ca, Mg, Fe e Al, que correspondem a 50,1%; 24,2%; 6,5% e 18,7%, respectivamente, do conteudo metalico. O Co, Ni, Cd, Cr e Pb foram encontrados em niveis inferiores ao seu limite de deteccao, exceto para algumas poucas amostras. Os fatores de enriquecimento calculados, mostram que o Zn e o Cu sao devidos provavelmente a composicao do combustivel e do oleo lubrificante. O Ca, Mg e Al podem ser atribuidos a resuspensao de poeira, enquanto que o Fe pode ser devido tanto a ressuspensao de poeira como as emissoes dos veiculos.

Experimental and theorical study of the air quality in a suburban industrial-residential area in Rio de Janeiro, Brazil

Neste trabalho, dados de poluentes legislados e nao legislados foram obtidos em uma regiao industrial-residencial no Rio de Janeiro, no periodo de abril a novembro de 2002. As concentracoes de formaldeido e acetaldeido encontradas estavam na faixa de 25,25-231,73 ppb e 9,48-75,74 ppb respectivamente. Estas altas concentracoes podem ser atribuidas a diversas fontes: emissoes veiculares e industriais, a presenca de incineradores de lixo, efluentes e rejeitos despejados no rio Faria Timbo e emissoes de uma industria de metanol. As concentracoes medias 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 concentracoes medias de PM10 mostram valores maximos para o mes de outubro, abril e junho. As concentracoes obtidas nas simulacoes foram para o mes de agosto usando um modelo de trajetorias. A concentracao maxima de ozonio calculada foi de 39,8 ppb, as 15:00 horas, obtendo uma boa concordância com os dados experimentais (38,5 ppb). A isopleta de ozonio mostra que o local esta em uma regiao alta de VOC/NOx, tipica de areas suburbanas e a favor do vento.