Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 169-184).

The object of the research described in this thesis is to provide, by means of laboratory experiments, data required to understand the atmospheric chemistry of the nitrate radical, from both a mechanistic and kinetic point of view. The low pressure discharge-flow kinetic technique coupled detection of the NO₃ radical by optical absorption was used to measure the temperature-dependent rate coefficients for the reaction of NO₃ with 1-butene, 1-chloro-l-butene, 2-chloro-2-butene, 3-chloro-l-butene, 1-chloro-2-butene, 2-chloro-2-butene, 1-chloromethylpropene, 3-chloromethylpropene, 3-bromo-1-butene, 4-bromo-l-butene and 2-bromo-2-butene. The atmospheric implications for the reaction of NO₃ with these compounds are discussed. In order to understand the patterns of reactivity towards NO₃ exhibited by these compounds, a number of approaches were adopted. First, a non-quantitative approach employing the simple ideas of inductive and mesomeric effects. Secondly the observed reactivity of NO₃ towards these compounds was discussed, quantitatively, in terms of the relative energies of the interacting orbitals. This quantitative analysis required an extensive set of molecular orbital calculations were undertaken at various levels of sophistication. A good correlation was found, for compounds not containing vinylic halogen atoms, between -E(HOMO) and the measured rate constant; the data were used also to calculate "group-reactivity factors". In an extension to this work a new empirical correlation is presented that takes account of the contribution, in terms of the atomic orbital coefficients, of vinylic halogen atoms to the observed rate constant. To provide support for these calculations, work was undertaken using photoelectron spectroscopy to characterise experimentally the individual molecular orbitals. A correlation between the inverse of the molecular polarisability and the activation energy of the reaction is also described. Complementary work was undertaken in a unconventional flash-photolysis system to look at the kinetics of the reaction NO₃ + NO₃ andlongrightarrow; 2 NO₂ + O₂ over a pressure range of 2 to 100 Torr in helium. The measured rate coefficient was found to be pressure independent and to have a value of (2.2±1.0) x 10^-16 cm₃ molecule^-1 s^-1. The experimental work on the nitrate radical was extended to look at the laser-induced fluorescence (LIF) spectrum and at the quenching of the excited state of the nitrate radical.

Thesis (M.Sc.)--York University, 2009. Graduate Programme in Mathematics / Typescript. Includes bibliographical references (leaves 70-73). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:MR51617

This work has focused on showing the differences among four different NMHC oxidation mechanisms: GT Lurmann, CBIV, RACM, and SAPRC mechanisms. This study was carried out to characterize these mechanisms using both specified NOx/NMHC gas mixtures and observational data from NASAs TRACE-P campaign. The differences among these mechanisms were found to be mainly driven by the use of different kinetic data and the specifics of each oxidation scheme. In the test runs, the differences between mechanisms were shown to be dependent on the levels of NOx and NMHC, as well as the reactivity of NMHC species used. Typically, propane had the smallest impact on all product species, whereas propene had the largest. Differences in the predicted levels of OH and HO2 were much smaller compared to those for CH3O2 and CH2O due to the fact that HOx species were generally less sensitive to the presence of NMHCs. During TRACE-P, which involved flights over only marine areas that were slightly polluted by the inflow of pollutants, the alkanes were the dominant NMHC family. Thus, most of the model runs involved relatively low levels of NMHCs and NOx. Therefore, the levels of OH, HO2, CH3O2, and CH2O predicted by the four mechanisms were not dramatically different. A net O3 increase was found only in areas where the NMHC reactivity was high. Because of the similar O3 destruction rates given by all four mechanisms, the difference in O3 tendency among these mechanisms was mainly determined by the O3 formation rate. A significantly higher (e.g., ~30%) O3 formation was found in the Lurmann mechanism than in CBIV due to the stronger contribution from the NO/RO2 channel in this mechanism. This resulted in a difference in the O3 tendency of a factor of 1.5. A major need in terms of future studies will be that of examining these same four mechanisms with a data set that enfolds observations in more polluted regions.

No description available.

Isoprene is the most abundant volatile organic compound (VOC) emitted from vegetation, mainly trees. Because it plays an important role in tropospheric chemistry leading to formation of pollutants and enhancing the lifetime of the greenhouse gas methane, concern about the response of isoprene emissions to the rise in atmospheric CO2 concentration and global climate change has been increasing over the last few years. The consequences of predicted climate change will have complex repercussions on global isoprene emission. The increasing atmospheric CO2 per se will have direct effects on terrestrial vegetation since CO2 is the substrate of photosynthesis. Because photosynthesis is limited by CO2 at current ambient concentrations, an increase in CO2 is expected to increase leaf biomass (i.e. isoprene emitting surface). Predicted warmer climate, extended drought periods, the possible shift in plant species in favour of isoprene emitters and the increase in length of growing season, may cause an increase in global isoprene emissions with profound perturbations of air quality and the global carbon cycle. The aim of this thesis was to investigate the effect of environmental variables such as light, temperature, drought and leaf-to-air vapour pressure deficit (VPD), and the short- and long-term effect of atmospheric [CO2] on isoprene emission from temperate and tropical tree species. Both leaf and whole ecosystem level fluxes were studied. At the leaf scale, a short-term experiment with leaves of potted two-year old trees of Quercus virginiana was carried out, exposing plants to two drying-rewatering cycles. Leaf isoprene emission fell, but the process was considerably less sensitive to water stress than photosynthesis and stomatal conductance. In drought conditions, the large reduction in photosynthesis caused the percentage of fixed carbon lost as isoprene to increase as plants became more stressed, reaching peaks of 50% when photosynthesis was almost zero. Isoprene emissions also showed a strong negative linear relationship with pre-dawn leaf water potential (psi-leaf). In another experiment carried out at the large enclosed facility of Biosphere 2 (B2L, Arizona, USA), studying isoprene emission from leaves of three-year-old plants of Populus deltoides grown at three CO2 atmospheric concentrations (430, 800 and 1200 mu mol mol-1 CO2) in non-stressed conditions, instantaneous increases in atmospheric [CO2] always resulted in a reduction of isoprene emission and a stimulation of photosynthesis. Moreover, in the long-term, the CO2 inhibition effect for isoprene emission became a permanent feature for plants growing under elevated [CO2]. Again, isoprene emission was less responsive to drought than photosynthesis. Both water-stress and high VPD strongly stimulated isoprene emission and depressed photosynthetic rate as a result of stomatal closure and the resulting decreases in intercellular [CO2] (Ci). This also led to a dramatic increase in the proportion of assimilated carbon lost as isoprene. The effect of atmospheric elevated [CO2] and its interaction with high VPD and water stress on ecosystem gross isoprene production (GIP) and net ecosystem exchange of CO2 (NEE) in the Populus deltoides plantations was also studied. Although GIP and NEE showed a similar response to light and temperature, NEE was stimulated by elevated CO2 by 72% and depressed by high VPD, while GIP was inhibited by elevated CO2 by 58% and stimulated by high VPD. Similar to what was observed at leaf level, under water stress conditions GIP was stimulated in the short term and declined only when the stress was severe, whereas NEE started to decrease from the beginning of the experiment. This contrasting response led the percentage of assimilated carbon lost by the ecosystem as isoprene to increase as water stress progressed from 2.5% and 0.6% in well-watered conditions to 60% and 40% for the ambient and the elevated CO2 treatments, respectively. Again, we found water limitation and high VPD off-set the inhibitory effect of elevated CO2, leading to increased isoprene emissions. The effect of a mild water stress on GIP and gross primary production (GPP) was also observed in the model tropical rainforest mesocosm of B2L. Although GPP was reduced by 32% during drought, GIP was not affected and correlated very well with both light and temperature. The percentage of fixed C lost as isoprene tended to increase during drought because of the reduction in GPP. Consumption of isoprene by soil was observed in both systems. The isoprene sink capacity of litter-free soil of the agroforest stands showed no significant response to different CO2 treatments, while isoprene production was strongly depressed by elevated atmospheric [CO2]. In both mesocosms, drought suppressed the sink capacity, but the full sink capacity of dry soil was recovered within a few hours upon rewetting. In summary, elevated CO2 increased biomass production and photosynthesis while depressing isoprene production. However, both drought and VPD may off-set the CO2 effect and lead to enhanced isoprene emission. We conclude that the overall effect of global climate change could be of enhancing global isoprene emissions while depressing the soil sink, and that the soil uptake of atmospheric isoprene is likely to be modest but significant and needs to be taken into account for a comprehensive estimate of the global isoprene budget.

Distributions of air pollutants and their precursors in the troposphere are driven largely by meteorological conditions (e.g., wind, cloud convection, lightning, and precipitation) and emissions such as those of NOx from anthropogenic sources (e.g., fossil fuel combustion) and natural sources (e.g., soils and lightning). As the most polluted regions in the world, North America and East Asia significantly contribute to climate change on both regional and global scales. Therefore, it deserves to investigate the vertical and horizontal distributions of the air pollutants in the troposphere over these two regions to better quantify the interaction between air pollution and climate change, which remains until now largely uninvestigated. Here, a Regional chEmical trAnsport Model (REAM) was developed and applied to examine the uncertainties in modeling the effect of convective transport and lightning NOx production on upper tropospheric chemical tracer distributions over North America, and to identify the features of air pollutions over East Asia.

Thesis (Ph.D)--Civil and Environmental Engineering, Georgia Institute of Technology, 2007. / Committee Chair: Russell, Armistead G.; Committee Member: Bostrom, Ann; Committee Member: Krupnick, Alan J.; Committee Member: Mulholland, James A.; Committee Member: Odman, M. Talat.

Thesis (Ph. D.)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2006. / Wang, Yuhang, Committee Chair ; Black, Robert, Committee Member ; Curry, Judith, Committee Member ; Huey, Greg, Committee Member ; Russell, Armistead G, Committee Member. Includes bibliographical references.

Thesis (Ph. D.)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2007. / Wang Yuhang, Committee Chair ; Cunnold Derek, Committee Member ; Weber Rodney, Committee Member ; Nenes Athanasios, Committee Member ; Guillas Serge, Committee Member.