RESUMO
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.
Assuntos
Poluentes Atmosféricos/análise , Poluição do Ar/estatística & dados numéricos , Butadienos/análise , Monitoramento Ambiental , Hemiterpenos/análise , Ozônio/análise , Pentanos/análise , Compostos Orgânicos Voláteis/análise , Brasil , Cidades , ClimaRESUMO
Volatile organic compounds (VOCs) play a central role in atmospheric chemistry. In this work, VOCs in the Botanical Garden of Rio de Janeiro were determined using the TO-15 Method. The park occupies 1,370,000 m2 in the southern area of the city and is next to the Tijuca Forest, which is considered the largest secondary urban forest in the world. The total VOC concentrations ranged from 43.52 to 168.75 µg m-3, depending on the sampling site and dates. In terms of concentration isoprene represented 4 %-14 % of the total VOC masses. The results suggested that the differences in biomass, distance from the street and activities within the park affected the concentrations of VOCs. The ratios of isoprene/aromatic compounds were higher than those determined in other areas of the city, confirming that the atmosphere of this green area has the contribution of other sources. Kinetic and mechanistic reactivities were also evaluated.
Assuntos
Poluentes Atmosféricos/análise , Atmosfera/química , Cidades , Jardins , Compostos Orgânicos Voláteis/análise , Brasil , Butadienos/análise , Monitoramento Ambiental , Hemiterpenos/análise , Pentanos/análiseRESUMO
In addition to oxygen, hydrocarbons are the most reactive chemical compounds produced by plants into the atmosphere. These compounds are part of the family of volatile organic compounds (VOCs) and are discharged in a great variety of forms. Among the VOCs produced by natural sources such as vegetation, the most studied until today are the isoprene and monoterpene. These substances can play an important role in the chemical balance of the atmosphere of a region. In this project, we develop a methodology to estimate the natural (vegetation) emission of isoprene and monoterpenes and applied it to the Monterrey Metropolitan Area, Mexico and its surrounding areas. Landsat-TM data was used to identify the dominant vegetation communities and field work to determine the foliage biomass density of key species. The studied communities were submontane scrub, oak, and pine forests and a combination of both. We carried out the estimation of emissions for isoprene and monoterpenes compounds in the different plant communities, with two different criteria: (1) taking into account the average foliage biomass density obtained from the various sample point in each vegetation community, and (2) using the foliage biomass density obtained for each transect, associated to an individual spectral class within a particular vegetation type. With this information, we obtained emission maps for each case. The results show that the main producers of isoprene are the communities that include species of the genus Quercus, located mainly on the Sierra Madre Oriental and Sierra de Picachos, with average isoprene emissions of 314.6 ton/day and 207.3 ton/day for the two methods utilized. The higher estimates of monoterpenes were found in the submontane scrub areas distributed along the valley of the metropolitan zone, with an estimated average emissions of 47.1 ton/day and 181.4 tons for the two methods respectively.
Assuntos
Butadienos/análise , Monitoramento Ambiental/métodos , Hemiterpenos/análise , Monoterpenos/análise , Pentanos/análise , Quercus/crescimento & desenvolvimento , Tecnologia de Sensoriamento Remoto , Compostos Orgânicos Voláteis/análise , Atmosfera/química , Biomassa , México , Pinus/crescimento & desenvolvimento , Pinus/metabolismo , Quercus/metabolismoRESUMO
Thirteen volatile organic compounds (VOCs) were quantified at three sites in southwestern Mexico City from July 2000 to February 2001. High concentrations of different VOCs were found at a Gasoline refueling station (GS), a Condominium area (CA), and at the University Center for Atmospheric Sciences (CAS). The most abundant VOCs at CA and CAS were propane, n-butane, toluene, acetylene and pentane. In comparison, at GS the most abundant were toluene, pentane, propane, n-butane, and acetylene. Benzene, a known carcinogenic compound had average levels of 28, 35 and 250ppbC at CAS, CA, and GS respectively. The main contributing sources of the measured VOCs at CA and CAS were the handling and management of LP (Liquid Propane) gas, vehicle exhaust, asphalt works, and use of solvents. At GS almost all of the VOCs came from vehicle exhaust and fuel evaporation, although components of LP gas were also present. Based on the overall results possible abatement strategies are discussed.
Assuntos
Poluentes Atmosféricos/análise , Poluição do Ar/análise , Compostos Orgânicos Voláteis/análise , Acetileno/análise , Benzeno/análise , Butanos/análise , Carcinógenos/análise , Cidades , Gasolina , Habitação , Resíduos Industriais , México , Pentanos/análise , Propano/análise , Tolueno/análise , Emissões de Veículos , VolatilizaçãoRESUMO
Emissions of volatile organic compounds (VOC) from vegetation are believed to be a major source of secondary organic aerosol (SOA), which in turn comprises a large fraction of fine particulate matter in many areas. Sesquiterpenes are a class of biogenic VOC with high chemical reactivity and SOA yields. Sesquiterpenes have only recently been quantified in emissions from a wide variety of plants. In this study, a new sesquiterpene emission inventory is used to provide input to the Models-3 Community Multiscale Air Quality (CMAQ) model. CMAQ is used to estimate the contribution of sesquiterpenes and monoterpenes to SOA concentrations over the contiguous United States. The gas-particle partitioning module of CMAQ was modified to include condensable products of sesquiterpene oxidation and to update values of the enthalpy of vaporization. The resulting model predicts July monthly average surface concentrations of total SOA in the eastern U.S. ranging from about 0.2-0.8 microg m(-3). This is roughly double the amount of SOA produced in this region when sesquiterpenes are not included. Even with sesquiterpenes included, however, the model significantly underpredicts surface concentrations of particle-phase organic matter compared to observed values. Treating all SOA as capable of undergoing polymerization increases predicted monthly average surface concentrations in July to 0.4-1.2 microg m(-3), in closer agreement with observations. Using the original enthalpy of vaporization value in CMAQ in place of the values estimated from the recent literature results in predicted SOA concentrations of about 0.3-1.3 microg m(-3).
Assuntos
Aerossóis/análise , Monoterpenos/análise , Sesquiterpenos/análise , Butadienos/análise , Canadá , Geografia , Hemiterpenos/análise , Humanos , México , Modelos Químicos , Pentanos/análise , Padrões de Referência , Propriedades de Superfície , Estados Unidos , VolatilizaçãoRESUMO
In the present study, we have tentatively identified the structures of three oxygenated derivatives of isoprene in Amazonian rain forest aerosols as the C(5) alkene triols, 2-methyl-1,3,4-trihydroxy-1-butene (cis and trans) and 3-methyl-2,3,4-trihydroxy-1-butene. The formation of these oxygenated derivatives of isoprene can be explained by acid-catalyzed ring opening of epoxydiol derivatives of isoprene, namely, 1,2-epoxy-2-methyl-3,4-dihydroxybutane and 1,2-dihydroxy-2-methyl-3,4-epoxybutane. The structural proposals of the C(5) alkene triols were based on chemical derivatization reactions and detailed interpretation of electron and chemical ionization mass spectral data, including data obtained from first-order mass spectra, deuterium labeling of the trimethylsilyl methyl groups, and MS(2) ion trap experiments. The characterization of 2-methyl-1,3,4-trihydroxy-1-butene (cis and trans) and 3-methyl-2,3,4-trihydroxy-1-butene in forest aerosols is important from an atmospheric chemistry viewpoint in that these compounds hint at the formation of intermediate isomeric epoxydiol derivatives of isoprene and as such provide mechanistic insights into the formation of the previously reported 2-methyltetrols through photooxidation of isoprene.
Assuntos
Aerossóis/química , Butadienos/análise , Butadienos/química , Cromatografia Gasosa-Espectrometria de Massas/métodos , Hemiterpenos/análise , Hemiterpenos/química , Oxigênio/química , Pentanos/análise , Pentanos/química , Árvores/metabolismo , Compostos de Trimetilsilil/química , Brasil , Estrutura Molecular , Oxirredução , Chuva , Clima TropicalRESUMO
Lipid peroxidation was measured in 19 very low birth weight infants with respiratory distress syndrome by quantitating ethane and pentane in expired air during the first 5 days postnatally. Despite high levels of inspiratory oxygen, the ethane and pentane output was low within the first 24 hours; thereafter it increased up to 100 and 30 fold, respectively. On days 1 to 3 there was no detectable correlation between lipid peroxidation and fractional inspiratory oxygen. However, on days 4 and 5, lipid peroxidation and fractional inspiratory oxygen showed a significant correlation. Maximal amounts of expired ethane and pentane were significantly higher for patients with a poor outcome (five deaths, six cases of bronchopulmonary dysplasia) than for those with good outcome (eight infants surviving intact) (p less than 0.01). The results imply a role for free oxygen radicals in the pathogenesis of life-threatening complications in the very low birth weight infant.