The Chemistry of Atmospheric Smog and Aerosols: Critical Roles of Ammonia
TITLE:
The Chemistry of Atmospheric Smog and Aerosols: Critical Roles of Ammonia
DATE:
Friday, November 9th, 2018
TIME:
4:00 PM
LOCATION:
GMCS-301
SPEAKER:
Fu-Ming Tao, Professor, Physical Chemistry, CSU Fullerton.
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, H2O, and NH3, to form ammonium nitrate (NH4NO3) 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 (H2O), 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.
HOST:
Dr. Andrew Cooksy
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