77 research outputs found
Estudos observacionais das principais fontes de emissão de compostos orgânicos voláteis (COV) em floresta intacta de terra firme na Amazônia Central
Get PDFOn a global scale, the largest emissions of volatile organic compounds (VOCs) biogenic occur in the tropics, and tropical forests are considered to be the largest source of VOCs in the atmosphere. In the Amazon, a significant fraction of carbon that goes into the atmosphere is emitted as COVBs, and knowledge of these issues is important for understanding the Tropical Atmospheric Chemistry and Global and the carbon cycle, which, in turn, to understanding of global climate change. This study is part of the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA) and was developed in Cuieiras Reserve, north of Manaus. Sampling of VOCs were carried out in May and June 2009, samples were collected simultaneously at three different heights within the pefil floesta (1 m, 10 m and 20 m) in the K34 tower and ground (including litter, no litter and mineral soil) for determining the concentration of VOCs and data flows in the soil. The samples were analyzed with a gas chromatograph with Mass Spectrometer. We calculated the average concentrations of the compound isoprene, monoterpenes and sesquiterpenes in three different heights. Isoprene was predominant at all times, with an average concentration of about 4 ppb (parts per billion). The sum of the concentrations of monoterpenes was below 1 ppb and the concentrations of sesquiterpenes accounted for less than 2% of the VOCs identified. The highest concentrations of monoterpenes and sesquiterpenes were found to 10 m high, while for isoprene, its concentrations were directly proportional to height. Chemical species of monotrpenos the most abundant species were α-pinene, limonene and among the sesquiterpenes, the β-selineno stood out. We identified a dependence of the concentrations of terpenoids photosynthetically active radiation, mainly above 10 m, and a correlation between isoprene and the monoterpenes and sesquiterpenes. Flows of terpenes soil were higher in the presence of litter cover and discovered that the most abundant species were camphene, d-carene, o-cymene and α-copaene.Em escala global, as maiores emissões de compostos orgânicos voláteis (COV) biogênicos ocorrem nos trópicos, e as florestas tropicais são consideradas como sendo a maior fonte de COVs na atmosfera. Na Amazônia, uma significante fração de carbono que vai para a atmosfera é emitida na forma de COV biogênico, e o conhecimento destas emissões é importante para o entendimento da Química Atmosférica Tropical e Global e para o ciclo de carbono, e, por sua vez, para o entendimento das mudanças climáticas globais. Este estudo é parte integrante do Experimento de Grande Escala da Biosfera-Atmosfera na Amazônia (LBA) e foi desenvolvido na Reserva do Cuieiras, ao norte de Manaus. As coletas de COVs foram realizadas nos meses de maio e junho de 2009, as amostras foram coletadas simultaneamente em três alturas diferentes dentro do pefil da floesta (1 m, 10 m e 20 m) na torre K34 e no solo (com liteira, sem liteira e solo mineral) para a determinação da concentração de COVs e o fluxo dos mesmos no solo. As amostras foram analisadas com Cromatógrafo a Gas acoplado ao Espectrômetro de Massas. Foram calculadas as concentrações médias dos compostos isopreno, monoterpenos e sesquiterpenos nas três diferentes alturas. Isopreno foi predominante em todas as alturas, com uma concentração média de aproximadamente 4 ppb (partes por bilhão). A soma das concentrações de monoterpenos deu abaixo de 1 ppb e as concentrações de sesquiterpenos representaram menos de 2 % dos COVs identificados. As maiores concentrações médias de monoterpenos e sesquiterpenos foram encontradas a 10 m de altura, enquanto para o isopreno, suas concentrações médias foram diretamente propocionais a altura. Das espécies químicas de monoterpenos as mais abundantes foram α-pineno, limoneno, e dentre os sesquiterpenos, o β-selineno se destacou. Identificou-se uma dependência das concentrações dos terpenóides à radiação fotossintéticamente ativa, principalmente acima de 10 m, e uma correlação entre o isopreno e os monoterpenos e sesquiterpenos. Os fluxos de terpenos do solo foram maiores com a presença da cobertura de liteira do que descoberto e as espécies mais abundantes foram canfeno, d-careno, o-cimeno e α-copaeno
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Short-term air quality forecasts for the Pacific Northwest and long-range global change predictions for the U.S.
Get PDFThis dissertation presents the development and evaluation of a comprehensive numerical air quality modeling system designed to provide daily forecasts in the Pacific Northwest. The system was also applied to predict the impact of global change upon air quality in the future for the US. This system employs the EPA Community Multi-scale Air Quality (CMAQ) model to treat photochemical gas and aerosol formation, transport and deposition. For short-term regional air quality forecasts, CMAQ was coupled with the University of Washington meteorological forecast operations using the MM5 weather model to create a regional system called AIRPACT-3. An important aspect of the development was the use of an automated, dynamic emissions processing system. The detailed evaluation of the system against observational data covering a four month period showed the system performed well. For ozone, it correctly predicted high episodic conditions, but over-predicted lower observed concentrations. For PM2.5, it captured concentration variations between urban and rural regions, and concentrations of nitrate and ammonium PM2.5 components, but under-predicted sulfate PM2.5.; For global change impacts on US regional air quality, the CMAQ model was employed along with MM5 to downscale results from the Parallel Climate Model and the MOZART2 global chemistry model based upon the IPCC A2 'business as usual' scenario. US anthropogenic emissions were projected using the EPA EGAS economic model and biogenic emissions were projected using the MEGAN model with adjusted land use. Evaluation using a decade of ozone measurements showed that the system reproduced episodic conditions (defined as the 98th percentile of daily maximum 8-hr concentration) with a predicted average US concentration of 93 ppbv and a measured concentration of 90 ppbv. Predictions for 2045-2054 indicated poorer air quality for the selected future scenario. The results showed that the future average daily maximum 8-hour ozone concentration will increase 8 ppbv, and larger areas of the US will be impacted at ozone levels greater than 80 ppbv. Additional simulations showed changing future land use and land cover scenarios significantly reduced the magnitude and spatial distributions of future biogenic emissions, which subsequently reduced ozone and secondary organic aerosol levels in the future
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Atmospheric dispersion in the arctic: Winter-time boundary-layer measurements
Get PDFThe winter-time arctic atmospheric boundary layer was investigated with micrometeorological and SF6 tracer measurements collected in Prudhoe Bay, Alaska. The flat, snow-covered tundra surface at this site generates a very small (0.03 cm) surface roughness. The relatively warm maritime air mass originating over the nearby, partially frozen Beaufort Sea is cooled at the tundra surface resulting in strong (4 to 30 °C · (100 m)-1) temperature inversions with light winds and a persistent weak (1 to 2 °C · (100 m)-1) surface inversion with wind speeds up to 17 m s-1. The absence of any diurnal atmospheric stability pattern during the study was due to the very limited solar insolation. Vertical profiles were measured with a multi-level mast from 1 to 17 m and with a Doppler acoustic sounder from 60 to 450 m. With high wind speeds, stable layers below 17 m and above 300 m were typically separated by a layer of neutral stability. Turbulence statistics and spectra calculated at a height of 33 m are similar to measurements reported for non-arctic, open terrain sites and indicate that the production of turbulence is primarily due to wind shear. The distribution of wind direction recorded at 1 Hz was frequently non-Gaussian for 1-hr periods but was always Gaussian for 5-min periods. We also observed non-Gaussian hourly averaged crosswind concentration profiles and assume that they can be modeled by calculating sequential short-term concentrations, using the 5-min standard deviation of horizontal wind direction fluctuations (Σθ) to estimate a horizontal dispersion coefficient (Σy), and constructing hourly concentrations by averaging the short-term results. Non-Gaussian hourly crosswind distributions are not unique to the arctic and can be observed at most field sites. A weak correlation between horizontal (Σv) and vertical (Σw) turbulence observed for both 1-hr and 5-min periods indicates that a single stability classification method is not sufficient to determine both vertical and horizontal dispersion at this site. An estimate of the vertical dispersion coefficient, Σz, could be based on ΣΦ or a stability classification parameter which includes vertical thermal and wind shear effects (e.g., Monin-Obukhov length, L)
Impacts of industrial and biogenic emissions on air quality
Get PDFThesis (Ph.D.), Engineering Science, Washington State UniversityVolatile organic compounds play important roles in atmospheric chemistry, air quality and wellness of human being. This dissertation investigated two air quality problems related to volatile organic compounds and compared two techniques used to measure formaldehyde at ambient levels. The first study addresses formaldehyde sources in a local valley, the Lewiston and Clarkston Valley. Two summer field campaigns in 2016 and 2017 measured formaldehyde and a number of other speciated VOCs at three sites. Average formaldehyde mixing ratios were 2.35 ± 0.95 ppbv in 2016 and 4.20 ± 1.2 ppbv in 2017. Formaldehyde displayed strong correlation with SO2 observed both in morning peak events at around 6:30 am PST, accompanied by peaks in reduced sulfur compounds and in the afternoon with short spikes in SO2 and formaldehyde. Formaldehyde abundance was low in the afternoon when abundances of typical secondary pollutants such as NOz and O3 were high. The influence of traffic emissions, biogenic emissions and secondary photoproduction was not pronounced on the local airshed. Primary emissions from the pulp mill were concluded to be the dominant formaldehyde sources in the valley. The second study characterized monoterpene speciation and emission rates in the air from the marijuana growing and processing facilities in Spokane. Whole air samples collected using SUMMA canisters were analyzed with GC-MS. -myrcene, d-limonene, -pinene and -pinene constitute the main monoterpene species with average relative abundance of 40%, 30%, 12% and 4%. High terpinolene abundance was found in some air samples. Estimated emission rates for one of the facilities sampled were 25g hr-1, equivalent to emissions from about 400 ponderosa pine trees. In addition, two different methods used to measure formaldehyde and acetaldehyde in the Lewiston study were compared. The precision of the method dinitrophenylhydrazine cartridge sampling followed by high performance liquid chromatography is reported to be 20 to 30% for formaldehyde and 10% for acetaldehyde in this study. Agreement between proton-transfer-reaction mass spectrometry and the cartridge sampling method is typically larger than 80%, suggesting viable measurements of formaldehyde can be made with this newer technology.Washington State University, Engineering ScienceBy student request, this dissertation cannot be exposed to search engines and is, therefore, only accessible to Washington State University users
Study of biogenic volatile organic compounds in the Amazon, French Guiana and Mata Atlântica Tropical Forests
No full textA atmosfera terrestre contém nitrogênio e oxigênio, sendo este último, um composto altamente reativo e fundamental ao desenvolvimento e manutenção da vida. Além desses gases, diversos outros compostos em pequenas concentrações, os quais podem atuar como reagentes e/ou catalisadores também a compõe. Os compostos gasosos variados e material particulado (orgânico e inorgânico) de diferentes dimensões lançados constantemente à atmosfera são provenientes de fontes diversas. Tais fontes podem ser de origem natural ou antrópica e ainda, podem ser pontuais, difusas, primárias, secundárias, móveis e/ou estacionárias. Os processos envolvendo transformações químicas na atmosfera são extremamente importantes porque tendem a manter a sua composição em estado estacionário. A vegetação, que constitui uma fonte natural, é responsável pela emissão de grandes quantidades de compostos carbonados para a atmosfera. Dentre os vários compostos orgânicos emitidos da superfície do planeta, destacam-se em particular, alguns gases traços, denominados compostos orgânicos voláteis (COVs). A emissão dos compostos orgânicos voláteis pela vegetação ocorre, em escala global, predominantemente nos trópicos ou nos meses de verão em outras regiões. As reações fotoquímicas dos compostos orgânicos voláteis desempenham um papel diferenciado e importante na química da troposfera, podendo alterar de forma significativa a concentração de ozônio em áreas tanto urbanas quanto rurais. O presente projeto contempla o estudo de alguns dos inúmeros compostos orgânicos voláteis de origem biogênica (COVBs) emitidos pela vegetação constituinte, das regiões da Floresta Amazônica, da Mata Atlântica e da floresta Tropical da Guiana Francesa, comparando-se os dados de saída gerados pelos Modelos MOZART-4 e CAM-Chem. A escolha dos sítios experimentais para realização deste estudo se deu em parte em função da importância dos locais em termos de biodiversidade, extensão territorial, influência na climatologia (local e/ou regional), bem como também em função da acessibilidade, proximidade a centros urbanos e alterações devido à influência humana. O procedimento metodológico adotado para coleta das amostras de COVBs se deu por meio da técnica conhecida como acumulação de vórtices turbulentos (Relaxed Eddy Accumulation - REA), a qual faz uso de um dispositivo coletor denominado acumulador compacto de vórtices turbulentos (Compact Relaxed Eddy Accumulator - CREA). As amostras gasosas de COVBs foram coletadas por meio de cartuchos comerciais apropriados, compostos por diferentes materiais adsorvedores que apresentavam afinidade química também diferenciada para os variados compostos aos quais foram expostos. Estudos primários para determinação da natureza dos cartuchos que foram utilizados neste projeto foram realizados, a fim de se obter dispositivos adequados a este propósito. Os resultados evidenciam, como esperado, que a presença de isopreno é predominante em todos os sítios experimentais, sendo sua concentração média diária máxima de 5,0 ± 0,3 μg/cm3 registrada na Amazônia e de 8,0 ± 0,4 μg/cm3 (concentração diária) na floresta da Guiana Francesa, seguido pelo alfa-pineno cuja concentração máxima obtida foi de aproximadamente 1,6 ± 0,08 μg/cm3 no último sítio experimental, ambos detectados na estação seca. A emissão de isopreno e dos monoterpenos ocorreu de forma mais acentuada na época seca em comparação ao período úmido. Contudo, observou-se em algumas situações uma pequena discrepância. De maneira geral os resultados gerados pelos modelos estão subestimados, como exceção do parâmetro de radiação fotossinteticamente ativa (PAR), o que indica que a defasagem entre os resultados observados e os simulados pode estar relacionada parâmetros de OH-, NOx e em algumas reações químicas fotoquímicas envolvendo o ozônio.The Earth\'s atmosphere contains nitrogen and oxygen, the last one being a highly reactive compound and fundamental to the development and maintenance of life. Besides these gases, many other compounds in small concentrations, which can act as reactants and /or catalysts can be found in the atmosphere. Various gaseous compounds and particulate matter (organic and inorganic) of different dimensions constantly released into the atmosphere come from various sources. Such sources can be natural or anthropogenic and still be punctual, diffuse, primary, secondary, mobile and or stationary. Processes involving chemical transformations in the atmosphere are extremely important because they tend to maintain their steady-state composition. The vegetation, which is a natural source, is responsible for producing large amounts of carbon compounds in the atmosphere. Among the various organic compounds emitted from the planet\'s surface, stand out in particular, some trace gases, called volatile organic compounds (VOCs). The emission of volatile organic compounds by vegetation occurs on a global scale, predominantly in the tropics or in the summer months in other regions. The photochemical reactions of volatile organic compounds play an important and unique role in the chemistry of the troposphere, which can significantly change the concentration of ozone in both urban and rural areas. This project involves the study of some of the numerous biogenic volatile organic compounds (BVOC) emitted by vegetation from the Amazon Forest, the Mata Atlântica forest and the Tropical forest of French Guiana, comparing the output data generated by MOZART -4 and CAM-Chem models. The choice of experimental sites for this study was in part due to the importance of local biodiversity , territorial extent , influence the weather (local and/or regional), and also because of accessibility, proximity to urban centers and changes due to human influence . The methodological procedures for collecting samples of VOCs was through the technique known as eddy accumulation (Relaxed Eddy Accumulation - REA), which uses an equipment known as compact relaxed eddy accumulator (CREA). The gas samples were collected from BVOCs through appropriate commercial cartridges, composed of different materials showed that chemical affinity adsorbents also differentiated for the various compounds which were exposed. Primary studies to determine the nature of cartridges that were used in the field campaigns were conducted in order to obtain devices suitable for this purpose. The results show, as expected, the presence of isoprene as a prevalent compound in all experimental sites, with maximum daily average concentration of 5,0 ± 0,3 μg/cm3 registered on the Amazon basin and 8,0 ± 0,4 μg/cm3 (daily concentration) in the forest of French Guiana, followed by alpha-pinene, whose maximum concentration obtained was approximately 1,6 ± 0,08 μg/cm3 in the last experimental site, both detected in the dry season. The emission of isoprene and monoterpenes occurred sharply in the dry season compared to the wet season. However, it was observed in some situations a small discrepancy. In general, the results generated by the models are underestimated, as an exception of photosynthetically active radiation parameter (PAR), indicating that the gap between the observed and simulated results can be related to OH- and NOx parameters and some chemical reactions involving photochemical ozone
An infrared method for plume rise visualization and measurement
Get PDFAn infrared video camera and recording system were used to record near source plume rise from a low turbine stack at an oil gathering center at Prudhoe Bay, AK. The system provided real-time, continuous visualization of the plume using a color monitor while the images were recorded with a standard video tape recorder. Following the field study, single frame images were digitized using a micro-computer video system. As part of the digitization, the plume centerline was determined as well as an isotherm of the plume outline. In this application, one frame from each 2-min period in the record was digitized. The results were used to calculate the variability in plume centerline during each hour. During strong winds with blowing snow, the mean plume rise for the hour at 15 m downwind was 6±2 m. The observed plume rise from the turbine stack was greater than that calculated using momentum-only or buoyancy-only plume rise models and only slightly larger than that estimated from combined momentum-buoyancy plume rise models
Modeling of Plume Downwash and Enhanced Diffusion near Buildings: Comparison to Wind Tunnel Observations for in Arctic Industrial Site
Get PDFThe ability of a modified Industrial Source Complex model to simulate concentration distributions resulting from high wind speeds (neutral conditions) has been evaluated by comparison to data from a wind tunnel study of a Prudhoe Bay, AK oil-gathering center characterized by short stacks and interconnecting buildings. The model tends to predict correctly the concentrations further downwind (500–1700 m) and underpredict the higher concentrations in the building wake region from 3 to 10 building heights downwind (100–350 m). The model cannot be used to predict concentrations at downwind distances less than 100 m where the maximum concentrations typically occurred. A large variation in the amount of building enhanced diffusion was observed for different wind direction. The Huber-Snyder algorithm could simulate lateral diffusion best when the combined width of all buildings of a height similar to the release height, up to a maximum of 5HB (building height), was considered the dominant length scale. Enhanced lateral dispersion was observed even when the plume reached a height above 1.2HB, estimated with Briggs plume rise equations, at a downwind distance of 2HB
Three-Dimensional Numerical Simulation of Plume Downwash with ak–ϵ Turbulence Model
Get PDFPlume downwash at a large oil-gathering facility in the Prudhoe Bay, Alaska oil-field reservation was simulated in a series of numerical experiments. The purpose of this study was to investigate the potential of the numerical model as a means of assessing the impact of pollutants emitted from buoyant sources influenced by complex aerodynamic wakes. The model is a three-dimensional, Cartesian coordinate, finite difference code that solves the nonhydrostatic, time-averaged equations for the conservation of momentum and energy. The code uses a modified form of the standard first-order, two-equation (k–ϵ) engineering turbulence closure model. Wind tunnel and field investigations of dispersion at this arctic industrial complex indicate that dispersion is significantly influenced by building-generated airflow disturbances. We have used the numerical model to simulate directly the mean features of the flow field and dispersion from a buoyant source at an industrial site. The flow features varied depending on the size, number, and orientation of the buildings. A recirculation cavity was present in all model simulations and varied from 0.8 HB to 2 HB (building height). This agrees closely with results of wind tunnel studies. The model simulates a velocity defect of 0.6, a factor of 3.4 increase (relative to the approach flow) in turbulent kinetic energy (k), a factor of 5 increase in dissipation of k(ϵ), and a 45% increase in turbulent viscosity at a downwind distance of 2 HB from the building. At a downwind distance of 5 HB, the plume rise of the simulated thermal plume decreased by 70% compared to the no-building case while the vertical and horizontal widths of the plume increased by 45% and 30%, respectively. These results generally reproduce the plume downwash and dispersion observed in wind tunnel and field investigations
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Building wake dispersion at an Arctic industrial site: Field tracer observations and plume model evaluations
Get PDFTen multi-hour atmospheric dispersion SF6 tracer experiments were conducted during October and November of 1987 near a large oil gathering facility in the Prudhoe Bay, Alaska, oilfield reservation. The purpose of this study was to investigate dispersion under arctic conditions and in situations where building-generated airflow disturbances dominate downwind distributions of ground level pollutant concentrations. This was accomplished with a network of micrometeorological instruments, portable syringe tracer samplers, continuous tracer analyzers, and infrared visualization of near source plume behavior.Atmospheric stability and wind speed profiles at this arctic site are influenced by the smooth (surface roughness = 0.03 cm), snow covered tundra surface which receives negligible levels of solar isolation in winter. The dispersion of pollutants emitted from sources within the oil gathering facility, however, is dominated by the influence of nearby buildings when high winds generate elevated ground level concentrations. An order of magnitude increase in maximum ground level concentration was observed as wind speeds increased from 5 to 8 m s−1 and another order of magnitude increase was observed as winds increased from 8 to 16 m s−1. Variation in maximum concentrations was also observed with changes in wind direction. Vertical plume diffusion (σz) near the buildings was a factor of 2–3 greater than that observed in open terrain and was dependent on both wind speed and the projected building width and location of nearby buildings. Wind tunnel tracer distributions for east winds agree with field observations but also indicate that a significant increase in plume downwash occurs with other wind directions. Concentration distributions were calculated using several versions of the Industrial Source Complex (ISC) model. Model estimates of ground level concentrations were within a factor of three depending on wind direction. The model predictions are extremely sensitive to the ratio of plume height to vertical plume diffusion which is significantly influenced by a complex aerodynamic wake in the field
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A national inventory of biogenic hydrocarbon emissions
Get PDFEmission rate vs temperature algorithms for different vegetation types, including deciduous, coniferous and agricultural sources, were used with available biomass and land use data for the U.S. to develop a national emission inventory with county spatial and monthly temporal scales. The estimated total NMHC emission rate from the U.S. is 30.7 Mt annually; more than half of these emissions occur in the summer, and approximately half arise in the SE and SW U.S. Total emission rates of isoprene from deciduous forest and α-pinene from deciduous and coniferous forests are 4.9 and 6.6 Mt annually. Emissions from agricultural crops contribute less than 3 % of the annual total. The average flux of biogenic NMHC in the U.S. is estimated to be 450 μgm−2h−1which is 20 times less than reported emissions of anthropogenic NMHC averaged over urban land areas in the U.S. Geochemical NMHC emissions from hydrocarbon rich soils in the U.S. are estimated to be negligible compared to vegetative sources. The uncertainty in the inventory is estimated to be on the order of a factor of three
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