The chemistry of atmospheric smog and aerosols: Critical roles of ammonia

Title : The chemistry of atmospheric smog and aerosols: Critical roles of ammonia

Abstract:

Oxides of nitrogen and sulfur are two major sources of air pollution, commonly known as Los Angeles (LA) smog and London smog, respectively. In this talk, I will briefly review prototype chemical reactions for the production of each type of smog. I will then show how a unique chemical species, ammonia, play a critical role in smog production as well as a possible solution of preventing smog in the atmosphere. Related to LA smog, we present a series of reactions involving three gases, NO2 , H2 O, and NH3 , to form ammonium nitrate (NH4 NO3 ) aerosols and gaseous nitrous acid (HONO). We attribute these reactions to be a significant source of atmospheric HONO responsible for the oxidation of all hydrocarbons and other organic compounds, leading to LA smog and ozone. In these reactions, ammonia is shown to play a critical role in lowering the Gibbs free energy barrier and stabilizing the nitric acid (HNO3 ) product by forming particulate ammonium nitrate. Related to London smog, we present two series of contrasting reactions of SO2 , with and without NH3 . Once released into the atmosphere, SO2 is shown react gradually with water (H2 O), molecular oxygen (O2 ), and other species, converting into sulfate-based aerosols to form London smog. On the other hand, if NH3 is added before SO2 is released into the atmosphere, SO2 reacts more readily to form ammonium bisulfate and ammonium sulfate solids. As a result, NH3 may serve to prevent SO2 from forming London smog. All reactions were studied by high-level quantum mechanical calculations with Dunning’s augmented correlation-consistent basis sets. The M062X hybrid density functional method with the aug-cc-pVDZ basis set was used to determine molecular geometries, electronic energies, harmonic vibrational frequencies, and thermodynamic properties at stationary points of the potential energy surface. Single-point energy calculations were performed using coupled-cluster method with single, double, quadruple, and perturbative triple excitations, CCSD(T), with the aug-cc-pVDZ and aug-cc-pVTZ basis sets.

Biography:

Dr. Fu-Ming Tao studied Chemistry at the University of Science and Technology of China and Suzhou University, and graduated as BS in 1982 and MS in 1985, respectively. He received his PhD degree from Boston College in 1991. After postdoctoral work supervised by Professor Edward Mason at Brown University and by Professor William Klemperer at Harvard University, he started a tenure-track faculty position at California State University Fullerton in 1995. He was promoted to Associate Professor with tenure in 2000 and Full Professor in 2005. He was a Henry Dreyfus Teacher-Scholar in 2000 and received research grants from different agencies including US National Science Foundation. He has published more than 140 research articles in SCI (E) journals. The frequent citations of his papers have made him as the top 2% cited in the world list.