Pathway Analysis of Selected Atmospheric Selenium and Arsenic Reactions

As the use of coal for power increases, attention turns to the potentially-harmful effects associated with its combustion. When coal combusts, both arsenic and selenium are volatilized and escape the smokestacks either as a gas or enriched in the fly ash (Senior et al., 2000). Both trace elements naturally occur in the earth's crust; however, at high concentrations they can have adverse effects on the environment and human health. By understanding the speciation and lifetime of arsenic and selenium in the atmosphere, technologies can be developed to better deal with these potentially-harmful elements.

Atmospheric chemistry is known to be driven by photochemically produced free radicals as supported by the findings of Molina. The reaction chains occurring in the atmosphere are driven primarily by the OH and HO2 radicals. In this analysis, reactions of selected stable species found from flue gas speciation with the aforementioned radicals were considered, primarily reactions stemming from elemental and oxide combinations with the radicals. Theoretical ab initio kinetic rate constants from the applicable RRKM, TST, and VTST theories have been found using the QCISD method, employing the 6-311G* basis set for selenium containing species, while treating arsenic containing species with relativistic effective core potentials.