Theoretical Studies On The Interaction Of Glyoxylic Acid With Common Atmospheric Nucleation Precursors

Atmospheric aerosol has a great influence on our environment and human health. The lack of the understanding of the composition of aerosol and the process of aerosol formation results in the discrepancy between atmospheric model predictions in the atmosphere and results of field measurements. Glyoxylic acid, which has a relatively low volatility and a high hydrophily, is the dominant ketocarboxylic acids in the atmosphere. It plays a vital role in the formation of atmospheric aerosol. Recent gas-phase studies of glyoxylic acid performed in laboratory observed the hydration of glyoxylic acid suggesting that this chemistry can occur in water restricted enviroments. But how the glyoxylic acid transforms to the geminal diol and the effects of them on the process of the formation of aerosol are still unknown. In this thesis, the conversion of glyoxylic acid to the geminal diol and the effects of glyoxylic acid and geminal diol on the nucleation process in the presence of water were investigated using density functional M06-2X method in conjunction with the 6-311++G(3df,3pd) basis set. The main results are listed as follows:Our results show that the reactions of glyoxylic acid transformed to its geminal diol couterpart catalyzed by atmospheric common nucleation precursors(H2O, NH3 and H2SO4)are expected to be protential dynamically favorable and sulfuric acid can the most effectively catalyze this conversion process. In the process of the cluster formation, only the carboxyl of glyoxylic acid forms hydrogen bonds and the aldehyde group doesn’t participate and the structures of the hydration clusters of glyoxylic acid are almost linear.Both the carboxyl and the alcohol hydroxyl group of geminal diol form hydrogen bonds in the process of forming aerosol cluster and the structures of the hydration clusters of geminal diol are almost like cages. When forming clusters with two sulfuric acid molecules,glyoxylic acid and geminal diol can enhance the relative hydrate populations of the clusters containing more water molecules. However, when forming clusters with one sulfuric acid molecule and one ammonia molecule, glyoxylic acid can enhance the relative populations of the clusters without water molecules while geminal diol can enhance the relative hydrate populations of the clusters containing more water molecules.The formation rates were considerably enhanced in the presence of glyoxylic acid and geminal diol. The formation rates were first increased and then decreased with the increase of the relative humidity. The formation rates were decreased with the increase of the temperature and were increased with increase of the concentration of glyoxylic acid. It can be seen from the formation path that the formations of most of the clusters containing geminal diol are transformed form the clusters containing glyoxylic acid. Geminal diol is more easier to evaporate from the clusters than glyoxylic acid to generate smaller clusters.