Persistent organic pollutants (POPs) are organic compounds of anthropogenic origin that have been linked to the development of cancer, neurobehavioural impairment, and immune system biochemical alterations. These chemicals have various industrial applications as well as acting as pesticides. Dioxins and furans are some of these compounds that are unintentionally produced in combustion and industrial processes. By definition these compounds have 4 common qualities: they are highly toxic, they are resistant to environmental degradation, they are introduced into the air and water where they travel long distances, and they accumulate in fatty tissues. Photochemical degradation is a method that has been extensively researched in the last few decades. In the aqueous phase it has already been shown to be able to degrade a number of refractory organics, such as dioxins and furans. The ultimate products of this process tend to be carbon dioxide, water, and mineral anions. Air phase work has been also gaining attention in recent decades as a possible alternative to incineration methods in air pollution control. The advantages of photochemical degradation processes are that they can be initiated at low temperatures, are relatively low cost compared to incineration processes, environmentally benign, and have the potential for quick and complete degradation of organic compounds. The main aim of the research is to investigate the photochemical degradation potential of PCDD/ PCDFs in gaseous air streams as a potential air pollution control technology. In order to do this, the photodegradation reaction kinetics were determined for chlorobenzene as a suitable surrogate for PCDD/PCDFs. Three different photodegradation schemes were employed: direct photolysis, UV/O3, and UV/H2O2. In addition, ozonolysis reaction rates were also determined to evaluate the effects of on the overall photodegradation rates for the UV/O3 process. Factors such as humidity levels and temperature were investigated to determine their effects on degradation rates. Temperature and humidity were not greatly influential on the degradation rates of direct photolysis. The degradation rate of chlorobenzene at a temperature of 100°C and high humidity was noticeably reduced, but unchanged at the 10% RH and 60% RH levels for all temperatures. Ozonolysis of chlorobenzene was negligible at 30°C for all humidity levels. Ozonolysis reactions at the 60°C and 100°C levels were higher than direct photolysis rates and in the 100°C case exceeded the UV/O3 degradation rates. Ozone coupled with UV experiments proved to be the most destructive at the low temperature of 30°C and molar ratio of 10:1 ozone to chlorobenzene. There was a clear and positive relationship between the amount of ozone present in the reactor and the degradation rate. At lower ozone to chlorobenzene molar ratios the degradation rates were not much higher than those for direct photolysis of ozone. The 5:1 molar ratio saw a significant increase in degradation rates over the photolysis rates. The fastest degradation rate was achieved for the 10:1 molar ratio and high humidity, which was over 10 times the rate of direct photolysis. In addition, humidity had a noticeably significant positive effect in these reactions. The effect of temperature on the UV/ozone reaction scheme was determined for the 5:1 ozone to chlorobenzene ratio. Temperature had an interesting effect on the degradation rates at higher temperatures. As the reactor temperature increased, the degradation rates from ozonolysis and UV/O3 began to converge at 60°C, ultimately leading to the ozonolysis reaction being faster than the UV/O3. Exploratory experiments for the H2O2 scheme were performed. H2O2 had a positive influence on the degradation rate of chlorobenzene and was about 26% higher than the direct photolysis rates. However for similar conditions, the UV/O3 process had higher degradation rates as was expected from the difference in absorption values between ozone and hydrogen peroxide.

The abatement of ground-level ozone has been a priority of air pollution policy because of its harmful effects on human health, ecosystems, and climate. The responsiveness of ozone to emissions of its principal precursors, nitrogen oxides (NOx) and volatile organic compounds (VOCs), is known to depend nonlinearly on spatially and temporally variable factors. Given this variability, scientific understanding of ozone formation processes can facilitate the development of sensible control policies. This thesis applies a high-order sensitivity analysis technique, the Decoupled Direct Method in Three Dimensions (HDDM-3D), to examine ozone response to precursor emissions during summertime air pollution episodes in the southeastern United States. HDDM-3D is shown to accurately capture ozone response within an underlying air quality model, even over large ranges of emission perturbations. Nonlinearity of response is quantified, and nonlinear terms are applied to examine how estimates of sensitivity and source attribution respond to uncertainty in an emissions inventory. Ozone production regime is assessed using both HDDM-3D and species indicator ratios and found to be primarily NOx-limited outside urban centers. However, ozone response to region-wide emissions does not necessarily correspond to its sensitivity to local controls, hindering the usefulness of bipartite ozone regime classification. Significant heterogeneity of ozone response to NOx is found even over small spatial scales of emission origin, a potential complication often ignored in atmospheric modeling and emissions trading mechanisms. Atmospheric sensitivity analysis is linked with a comprehensive menu of potential control measures to demonstrate potential integration of scientific and economic considerations for control strategy formulation. Cost-optimized strategies are identified for attainment of federal ozone standards in Macon, Georgia, and for minimizing potential population exposure to unhealthful concentrations of ozone.

A photochemical mechanism is a very important component of an air quality model, which simulates the change of pollutant concentrations due to chemical reactions in the air. The accuracy of model prediction is directly impacted by the photochemical mechanism. In this study, two state-of-the-science photochemical mechanisms, SAPRC07 and Master Chemical Mechanism (MCM) v3.1, were implemented in the Community Multi-scale Air Quality Model (CMAQ) version 4.6 developed by the US EPA to study a high ozone (O3) episode during the 2000 Texas Air Quality Study (TexAQS) from August 16, 2000 to September 7, 2000. Predicted O3 concentrations by S07C are lower than those of S99 with a maximum difference as high as 20 percent. The two mechanisms also show significant differences in the predicted OH, PAN, HCHO and HNO3 concentrations. Although the two mechanisms predict different ozone concentrations, the relative response factors (RRFs) of O3 at rural, urban and industrial sites under emission controls of anthropogenic NOx and VOC by factors 0.6 – 1.4 predicted by the two mechanisms are very similar. Predicted O3 concentrations by MCM are similar to those of SAPRC07. The MCM predicted total VOC OH reactivity is similar to the SAPRC07 predictions at a suburban site where biogenic emissions dominate the OH reactivity and is slightly lower than the SAPRC07 predictions at an industrial site where anthropogenic emissions dominate. Besides, the predicted 1-hr and 24-hr average concentrations of major O3 precursor VOCs by MCM show under predictions of alkanes and alkenes by a factor of 2-5, 6 for ethane and 8.5 for propane. Major aromatic compounds generally agree better with observations, although benzene is under-predicted by 80 percent. Species specific emission adjustment factors can be derived from these direct comparisons to improve emission inventories in future studies. At the Clinton Drive site, most of the under-predictions occur in the afternoon when industrial facilities are in the immediate upwind direction and the missing industrial emissions are likely evaporative sources whose emission rates are temperature dependent.

The rapid rising anthropogenic emissions driven by economic growth over China documented by satellite observations and bottom-up inventories have led to severely degraded air quality, and also have been suggested to be linked to the recent upward trends of tropospheric O₃ over the regions downwind of China. Multi-scale modeling analyses facilitated by ground-level, aircraft and satellite observations have been conducted to understand the atmospheric chemistry over China. Analyses using a 1-D photochemical model constrained by measurements at Beijing in August of 2007 suggest that reactive aromatic VOCs are the major source (~75%) of peroxy acetyl nitrate (PAN). Detailed radical budget analyses reveal the very fast ROₓ (OH + HO₂ + RO₂) production, recycling and destruction driven by VOC oxidation and heterogeneous processes. Photoenhanced aerosol surface uptake of NO₂ is found to be the predominant source of nitrous acid (HONO) during daytime (~70%). 3-D regional modeling analyses of tropospheric vertical column densities of glyoxal (CHOCHO) from SCIAMACHY show that anthropogenic emissions of aromatic VOCs are substantially underestimated (by a factor of 5 - 6, regionally varied) over China. Such an underestimation is the main cause of a large missing source of CHOCHO over the region in current global models, and could also partly explain the underestimation of organic aerosols in previous modeling studies.

The increasing food demand as well as the need to predict the impact of warming climate on vegetation makes it critical to find the best tools to assess crop production and carbon dioxide (CO₂) exchange between the land and atmosphere. Photosynthesis is a good indicator of crop production and CO₂ exchange. Chlorophyll fluorescence (ChF) is directly related to photosynthesis. ChF can be measured at leaf-scale using active techniques and at field-scales using passive techniques. The measurement principles of both techniques are different. In this study, three overarching questions about ChF were addressed: Q1) How water, nutrient and ambient light conditions determine the relationships between photosynthesis and ChF? Which is the optimum irradiance level for detecting water and nutrient deficit conditions with ChF?; Q2) which are the limits within which active and passive techniques are comparable?; and Q3) What is the seasonal relationship between photosynthesis and ChF when nitrogen is the limiting factor? To address these questions, two main experiments were conducted: Exp1) Concurrent photosynthesis and ChF light-response curves were measured in camelina and wheat plants growing under (i) intermediate-light and (ii) high-light conditions respectively. Plant stress was induced by (i) withdrawing water, and (ii) applying different nitrogen levels; and Exp2) coincident active and passive ChF measurements were made in a wheat field under different nitrogen treatments. The results indicated ChF has a direct relationship with photosynthesis when water or nitrogen drives the relationship. This study demonstrates that the light level at which plants were grown was optimum for detecting water and nutrient deficit with ChF. Also, the results showed that for leaf-average-values, active measurements can be used to better understand the daily and seasonal behavior of passive ChF. Further, the seasonal relation between photosynthesis and ChF with nitrogen stress was not a simple linear function. Our study showed that at times in the season when nitrogen was sufficient and photosynthesis was highest, ChF decreased because these two processes compete for available energy. These results demonstrated that ChF is a reliable indicator of crop stress and has great potential for better understand the CO₂ exchange between the land and atmosphere.

Persistent organic pollutants (POPs) are organic compounds of anthropogenic origin that have been linked to the development of cancer, neurobehavioural impairment, and immune system biochemical alterations. These chemicals have various industrial applications as well as acting as pesticides. Dioxins and furans are some of these compounds that are unintentionally produced in combustion and industrial processes. By definition these compounds have 4 common qualities: they are highly toxic, they are resistant to environmental degradation, they are introduced into the air and water where they travel long distances, and they accumulate in fatty tissues. Photochemical degradation is a method that has been extensively researched in the last few decades. In the aqueous phase it has already been shown to be able to degrade a number of refractory organics, such as dioxins and furans. The ultimate products of this process tend to be carbon dioxide, water, and mineral anions. Air phase work has been also gaining attention in recent decades as a possible alternative to incineration methods in air pollution control. The advantages of photochemical degradation processes are that they can be initiated at low temperatures, are relatively low cost compared to incineration processes, environmentally benign, and have the potential for quick and complete degradation of organic compounds. The main aim of the research is to investigate the photochemical degradation potential of PCDD/ PCDFs in gaseous air streams as a potential air pollution control technology. In order to do this, the photodegradation reaction kinetics were determined for chlorobenzene as a suitable surrogate for PCDD/PCDFs. Three different photodegradation schemes were employed: direct photolysis, UV/O3, and UV/H2O2. In addition, ozonolysis reaction rates were also determined to evaluate the effects of on the overall photodegradation rates for the UV/O3 process. Factors such as humidity levels and temperature were investigated to determine their effects on degradation rates. Temperature and humidity were not greatly influential on the degradation rates of direct photolysis. The degradation rate of chlorobenzene at a temperature of 100°C and high humidity was noticeably reduced, but unchanged at the 10% RH and 60% RH levels for all temperatures. Ozonolysis of chlorobenzene was negligible at 30°C for all humidity levels. Ozonolysis reactions at the 60°C and 100°C levels were higher than direct photolysis rates and in the 100°C case exceeded the UV/O3 degradation rates. Ozone coupled with UV experiments proved to be the most destructive at the low temperature of 30°C and molar ratio of 10:1 ozone to chlorobenzene. There was a clear and positive relationship between the amount of ozone present in the reactor and the degradation rate. At lower ozone to chlorobenzene molar ratios the degradation rates were not much higher than those for direct photolysis of ozone. The 5:1 molar ratio saw a significant increase in degradation rates over the photolysis rates. The fastest degradation rate was achieved for the 10:1 molar ratio and high humidity, which was over 10 times the rate of direct photolysis. In addition, humidity had a noticeably significant positive effect in these reactions. The effect of temperature on the UV/ozone reaction scheme was determined for the 5:1 ozone to chlorobenzene ratio. Temperature had an interesting effect on the degradation rates at higher temperatures. As the reactor temperature increased, the degradation rates from ozonolysis and UV/O3 began to converge at 60°C, ultimately leading to the ozonolysis reaction being faster than the UV/O3. Exploratory experiments for the H2O2 scheme were performed. H2O2 had a positive influence on the degradation rate of chlorobenzene and was about 26% higher than the direct photolysis rates. However for similar conditions, the UV/O3 process had higher degradation rates as was expected from the difference in absorption values between ozone and hydrogen peroxide.

Thesis (M.S.)--Rochester Institute of Technology, 1989. / Includes bibliographical references (leaves 81-83).

Atrazine photochemical degradation in homogeneous phase using Fe(III)/UV/air system was studied. Two toxicity assessments, a Lemna minor growth inhibition test and a Daphnia magna acute immobilisation test, were employed to test potential toxicity of atrazine and its degradation products. The occurrence of atrazine in rivers from the Vltava River basin was evaluated from the analyses performed by Povodí Vltavy, State Enterprise.

abstract: Non-photochemical quenching (NPQ) is a photoprotective regulatory mechanism essential to the robustness of the photosynthetic apparatus of green plants. Energy flow within the low-light adapted reaction centers is dynamically optimized to match the continuously fluctuating light conditions found in nature. Activated by compartmentalized decreases in pH resulting from photosynthetic activity during periods of elevated photon flux, NPQ induces rapid thermal dissipation of excess excitation energy that would otherwise overwhelm the apparatus’s ability to consume it. Consequently, the frequency of charge separation decreases and the formation of potentially deleterious, high-energy intermediates slows, thereby reducing the threat of photodamage by disallowing their accumulation. Herein is described the synthesis and photophysical analysis of a molecular triad that mimics the effects of NPQ on charge separation within the photosynthetic reaction centers. Steady-state absorption and emission, time-resolved fluorescence, and transient absorption spectroscopies were used to demonstrate reversible quenching of the first singlet excited state affecting the quantum yield of charge separation by approximately one order of magnitude. As in the natural system, the populations of unquenched and quenched states and, therefore, the overall yields of charge separation were found to be dependent upon acid concentration. / Dissertation/Thesis / Doctoral Dissertation Chemistry 2015

Orientador: Luiz Fernando Rolim Almeida / Resumo: A dormência de gemas é um mecanismo metabólico e fisiológico do ciclo de vida de plantas, regulado pelo ambiente e pelos hormônios vegetais. A partir disso, nesse estudo foram investigados dois momentos cruciais no ciclo da dormência de Curcuma zedoaria (Christm.) Roscoe. O primeiro momento se trata da ação dos reguladores vegetais ethephon (ETH) e cinetina (Kt) na superação da dormência de gemas e na alteração do perfil metabólico volátil nos primeiros dias após as gemas superarem a dormência. O segundo momento consiste da ação do défice hídrico na mudança dos padrões metabólicos da planta e na comparação dos ajustes metabólicos durante a perda da parte aérea ocasionada pelo défice hídrico. Diante da primeira etapa da investigação, altas concentrações de ETH (600 mg.L-1) atrasam a brotação das gemas de rizomas e as demais concentrações diminuem o crescimento de raízes. Ethephon aumenta a proporção relativa de sesquiterpenos oxigenados e diminui a proporção de hidrocarbonetos monoterpênicos. Cinetina manteve a brotação de gemas semelhante às condições normais de crescimento. Além disso, Kt promoveu aumento das proporções relativas de monoterpenos e queda de sesquiterpenos. Na segunda etapa da investigação, as plantas que sofreram défice hídrico apresentaram tolerância ao estresse até o 17o dia de experimento. Plantas totalmente irrigadas também entraram em dormência, apresentando perda total da parte aérea após 99 dias de experimento. Além disso, a variação na fluorescência d... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Bud dormancy is a metabolic and physiologic mechanism occurring during the plant life cycle, which is regulate by environment and plant hormones. In this study, we investigated two crucial points of dormancy cycle on Curcuma zedoaria (Christm.) Roscoe. The first one focused on the action of ethephon (ETH) and kinetin (Kt) on bud break and the alterations on volatile metabolic profile during the days after releasing of bud dormancy. The second aspect focused on the action of drought in changes of plant metabolic patterns and comparing the metabolic adjustments during leaf shedding provoked by water deficit. The first investigation showed that high concentrations on ETH (600 mg.L-1 ) delays the rhizome bud flush and the other concentrations of ETH decrease root growth. Ethephon enhances oxygenated sesquiterpenes and decreases monoterpene production. Kinetin maintains bud sprout similarly to control. Further, Kt increases the relative proportions of monoterpenes and decrease the relative proportions of sesquiterpenes. The second step of this investigation showed that plants under water stress presented drought tolerance until the 17th day of experiment. Plants totally irrigated also enter in dormancy, showing total aboveground loss after 99 days of experiment. Furthermore, the variation of chlorophyll a fluorescence of those plants was similar between plants that went through drought. Instead of water stress causes starch degradation, after dormancy entrance and rehydration of C... (Complete abstract click electronic access below) / Mestre