~~ Oh With Some Typical Organic Pollutants In The Reaction Rate Constant (k <sub> Oh </ Sub>) Linear Free Energy Relationship Study

Polycyclic aromatic hydrocarbons (PAHs), polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), and polychlorinated biphenyls (PCBs) are typical persistent toxic substances. They can undergo long-range atmospheric transport and partition between air and other environmental phases. Reactions with OH radicals (OH), NO3 radicals and O3 radicals are likely to be dominant atmospheric loss process for the gas-phase PAHs, PCDD/Fs and PCBs. kOH is a key parameter charactering atmospheric behavior of organic pollutants. The aim of this thesis is to develop temperature dependent polyparameter LFERs for kOH of PAHs, PCDD/Fs and PCBs, by using theoretical molecular structural descriptors and PLS regression.Aldehydes are volatile hazardous air pollutants. Aldehydes are present in exhaust gases during incomplete burning of organic compounds and are also formed by photochemical reaction with hydrocarbons in air. Many aldehydes such as formaldehyde and acetaldehyde can irritate the eyes and respiratoty. Reactions with OH are dominant atmospheric loss process for aldehydes, kOH is a key parameter assessing the fate of organic pollutions in the air. The aim of this paper is to develop polyparameter LFERs for kOH of aldehydes, by using theoretical molecular structural descriptors and PLS regression.(1) Polyparameter LFER models on rate constants for the gas-phase reaction of OH with PAHs and PCDD/Fs at different temperature were successfully developed by partial least squares(PLS) regression based on 19 theoretical molecular structural descriptors. The Q2cum value of the model is 0.974, indicating good robustness and predictive power of the model. The main factors affecting kOH values of the PAHs and PCDD/Fs are molecular ability to donate electrons. The PAH and PCDD/F molecules with higher Ehomo and lower qH result high logkOH values. A positive temperature dependence, which was greater, but still slight, can be considered insignificant from an environmental point of view.(2) Based on some theoretical molecular structural descriptors computed by PM3 Hamiltonian, by the use of PLS analysis, polyparameter LFER models for the gas-phase reaction of OH with PCBs at different temperature is developed. The Q2cum value of the model is 0.896, indicating good robustness and predictive power of themodel. The main factors affecting kOH values of the PCBs are molecular size and molecular ability to donate electrons. Increased of bulkness of PCB molecules leads to the decrease of logkOH The more chlorines in the PCB molecules, the greater the logkOH values. The PCB molecules with lower qc-H and lower qcl result high logkOHvalues. All the reactions show positive, but relatively weak, temperature dependences. (3) By the use of partial least squares (PLS) method, a LFER model for rate constants of 24 aldehydes reacting with OH in the gas phase is developed. The LFER results show that it is mainly the energy of the highest occupied molecular orbital (Ehomo), the energy of the lowest unoccupied molecular orbital (Elumo), total energy (TE) and the largest negative net atomic charges on a oxygen atom (qo(min)) that determine the rate constants of aldehydes reacting with OH. Increasing Ehomo ELUMO and TE leads to increase of rate constants. Increasing qo-(min) leads to decrease of the rate constants.