On the Gas Phase Reactions Between Volatile Biogenic Mercury Species and the Nitrate Radical

Abstract

Tropospheric mercury is dominated by gas phase species. In this paper, the gas phase reactions between the nitrate radical and volatile biogenic mercury species have been investigated. An upper limit for the gas phase rate coefficient for reaction between elemental mercury and NO3-radicals was determined to 4 × 10−15 cm3 molecule−1 s−1 by using the fast flow-discharge technique. The reaction between dimethyl mercury and NO3, previously shown to be rapid, has also been studied in the laboratory with respect to product distribution using FT-IR. The result from the product study is consistent with a transformation of dimethyl mercury into inorganic, divalent mercury. All carbon delivered as dimethyl mercury was transformed into formaldehyde, methanol and methyl peroxynitrate. Hg was observed as a minor (≈2%) product. By exclusion, HgO is proposed as the mercury-containing product. Thus, the reaction between dimethyl mercury and the nitrate radical is excluded as a source of monomethyl mercury species in the atmosphere.