Modeling the pathways of generation of O-MIF in tropospheric sulfates
Abstract
Volcanic emissions are among the major
natural sources of sulfur and SO2 in the
atmosphere. However, there are still
significant uncertainties pertaining to
atmospheric oxidation pathways of SO2
and its implications on the budget of
atmospheric sulfate particles. Mass-
independent fractionations (MIF) can be
used as quantitative markers to detect
atmospheric pathways of reaction. The
majority of the oxygen isotopic anomalies
observed in sulfates originate from ozone
and it is transferred during tropospheric
oxidation of SO2. An oxygen isotopic
chemistry scheme for sulfate is
implemented into a photochemical box-
model (CiTTyCAT) that contains a detailed
description of tropospheric chemistry. The
chemical scheme has been extended with
heterogeneous chemistry of S(IV) and
S(VI) species. The mass transfer and
oxidation in liquid phases are explicitly
treated with no assumptions regarding
phase equilibria of soluble gases, and the
acid-base equilibrium. The oxygen
isotopes MIF scheme has been
implemented to simulate the evolution of
O-MIF of tropospheric sulfate. The model
is used to determine pathways of sulfate
formation during the oxidation of volcanic
SO2. Comparisons within isotopic
compositions of sulfate from volcanic
deposits and modeled O-MIF suggest that
SO2 is oxidized by O2/TMI in the liquid
phase within the volcanic plume.