Development and Evaluation of a Comprehensive Tropospheric Chemistry Model for Regional and Global Applications

Type of Document Dissertation
Author Zaveri, Rahul A.
Author's Email Address zaveri@vtaix.cc.vt.edu
URN etd-7197-18361
Title Development and Evaluation of a Comprehensive Tropospheric Chemistry Model for Regional and Global Applications
Degree Doctor of Philosophy
Department Chemical Engineering
Advisory Committee
Advisor Name Title
Leonard K. Peters Committee Chair
John C. Little none
Rick D. Saylor none
Wayne L. Neu none
William L. Conger none
Keywords

* Air quality model
* monoterpenes
* dimethylsulfide
* aerosol chemistry
* aqueous chemistry

Date of Defense 1997-06-27
Availability unrestricted
Abstract

Accurate simulations of the global radiative impact of anthropogenic

emissions must employ a tropospheric chemistry model that predicts

realistic distributions of aerosols of all types. The need for a such

a comprehensive yet computationally efficient tropospheric chemistry

model is addressed in this research via systematic development of the

various sub-models/mechanisms representing the gas-, aerosol-, and

cloud-phase chemistries.

The gas-phase model encompasses three tropospheric chemical regimes -

background and urban, continental rural, and remote marine.

The background and urban gas-phase mechanism is based on the paradigm

of the Carbon Bond approach, modified for global-scale applications.

The rural gas-phase chemistry includes highly condensed isoprene and

a-pinene reactions. The isoprene photooxidation scheme is adapted for

the present model from an available mechanism in the literature, while

an a-pinene photooxidation mechanism, capable of predicting secondary

organic aerosol formation, is developed for the first time from the

available kinetic and product formation data. The remote marine gas-

phase chemistry includes a highly condensed dimethylsulfide (DMS)

photooxidation mechanism, based on a comprehensive scheme available

in the literature. The proposed DMS mechanism can successfully explain

the observed latitudinal variation in the ratios of methanesulfonic

acid to non-sea-salt sulfate concentrations.

A highly efficient dynamic aerosol growth model is developed for

condensing inorganic gases. Algorithms are presented for calculating

equilibrium surface concentrations over dry and wet multicomponent

aerosols containing sulfate, nitrate, chloride, ammonium, and sodium.

This alternative model is capable of predictions as accurate for

completely dissolved aerosols, and more accurate for completely dry

aerosols than some of the similar models available in the literature.

For cloud processes, gas to liquid mass-transfer limitations to

aqueous-phase reactions within cloud droplets are examined for all

absorbing species by using the two-film model coupled with a

comprehensive gas and aqueous-phase reaction mechanisms. Results

indicate appreciable limitations only for the OH, HO2, and NO3

radicals. Subsequently, an accurate highly condensed aqueous-phase

mechanism is derived for global-scale applications.

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