Vapor Pressure At Different Temperatures. Pahs And Pcdd / Fs Data Evaluation And Quantitative Forecast Model

Polycyclic aromatic hydrocarbons (PAHs) and polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) are typical and ubiquitous persistent organic pollutants. PAHs mainly originate from incomplete combustion of fossil fuels. PCDD/Fs are mainly unwanted by-products of chemical industry, and can also be resulted from municipal waste incineration and industrial processes such as pulp and paper industry. Once they have entered the environment, they tend to bioaccumulate in organism because of their very high lipophilicity and chemical stability. Owing to their toxicity (such as highly mutagenic and carcinogenic features of some PAHs and PCDD/Fs) and widespread distribution in the global environment, PAHs and PCDD/Fs have attracted the attention of environmental chemists, toxicologists and regulatory agencies for decades.Vapor pressures, which can be classified as solid vapor pressure (Ps) and (subcooled) liquid vapor pressure (PL), arc key physicochemical properties governing the environmental fate of organic pollutants. The vapor pressure of each compound is different, and it has strong temperature dependence, thus cost and time consuming will not allow us to measure the data one by one. It is of great importance to develop predictive models of vapor pressures based on molecular structre information. In this paper, quantitative relationships between molecular structures, environmental temperatures and properties (QRSETPs) for vapor pressures were developd. The siganificant modles can be used to predict vapor pressures of PAHs and PCDD/Fs at different temperatures. They may also provide insight into which aspect of the molecular structure influences the property. The main results of the thesis are concluded as follows:(1) PS and PL values for PAHs at different temperatures were derived from various literatures. There are 1113 observations totally in the training set. In this study, partial least squares (PLS) regression together with 15 theoretical molecular structural descriptors computed by PM3 Hamiltonian was used to develop quantitative predictive models for vapor pressures of PAHs at different temperatures. Two procedures were adopted to develop the optimal predictive models by eliminating redundant molecular structural descriptors. The cross-validated Q2 cum values for the obtained models are higher than 0.975, indicating good predictive ability and robustness of the models. Temperature and intermolecular dispersive interactions play a leading role in governing the values of logPL. In addition to temperature and intermolecular dispersive interactions, dipole-dipole interactions also play a secondary role in determining the magnitude of logPS. In view of the scarceness of chemical standards for some PAHs, the difficulty in experimental determinations, and the high cost involved inexperimental determinations, the obtained models should serve as a fast and simple first approximation of the vapor pressure values for PAHs at different environmental temperatures. (2) Based on some quantum chemical descriptors, Connolly desciptors and temperature, by the use of PLS regression, two QRSETP modles for logPL and logPS of PCDD/Fs were developed. The predictive values are consistent with the observed logPL or logPs The cross-validated Q2cum values for the obtained models are 0.994 and 0.966, respectively, greatly higher than 0.5, indicating good predictive ability and robustness of the models. Thus the obtained models can be used to predict vapor pressures of PCDD/Fs at different temperatures. It was found that temperature and dispersive interactions play a leading role in governing the values of logPL and logPs of PCDD/Fs.