This thesis is motivated by the need to develop a photochemical box model that would be a valuable tool for the analysis of the ICE-HT/FORTH smog chamber results but could be also applied to other chambers around the world.
The Master Chemical Mechanism (MCM) is a detailed gas phase, near-explicit, mechanism for the photooxidation of 143 primary volatile organic compounds (VOCs) in the atmosphere. This work uses as a case study the toluene oxidation focusing on the oxygenated products of toluene degradation. The reactions of toluene are translated to differential equations (ODEs) and they are integrated with a Rosenbrock solver. This solver proved to be effective for stiff systems, which is a major challenge in the numerical simulation of atmospheric transport-chemistry processes.
The toluene model was applied to many different initial conditions. The results show that most of the carbon ends up as CO and CO2 in a matter of hours in typical laboratory experiments. The rest is peroxy acetyl nitrates (PAN), maleic anhydride, glyoxal, and others. The model predictions were evaluated against experimental data found in the literature. Despite some discrepancies, the model seems to be promising if a suitable auxiliary mechanism for each chamber is included. Moreover, the evaluation results confirm that CO and CO2 are indeed major products in these experiments.
Finally, a partitioning model combined with the volatility basis set (VBS) is incorporated in the main model in order to predict the particulate mass in the system. Presence of sufficient initial seeds is assumed in the system so homogeneous nucleation is not simulated. The results show that the current model tends to overestimate particulate mass, especially that of organonitrates. Improvements in the estimation of the vapor pressure of these complex organic molecules are needed. The addition of the partitioning model reduced the predicted production of CO and CO2.
(EL)
University of Patras
