Modeling the possible role of iodine oxides in atmospheric new particle formation S. Pechtl1, E. R. Lovejoy2, J. B. Burkholder2, and R. von Glasow1 1Institute for Environmental Physics, University of Heidelberg, Heidelberg, Germany 2Aeronomy Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO, USA
Abstract. We studied the possible role of iodine oxides in atmospheric new particle
formation with the one-dimensional marine boundary layer model MISTRA,
which includes chemistry in the gas and aerosol phase as well as aerosol
microphysics. The chemical reaction set focuses on halogen
(Cl-Br-I) chemistry. We included a two-step nucleation parameterization, where
in the first step, the "real" nucleation process is parameterized,
i.e., the formation of cluster-sized nuclei via homogeneous condensation of gases.
We considered both ternary sulfuric acid-ammonia-water nucleation and
homomolecular homogeneous OIO nucleation.
For the latter, we derived a parameterization based
on combined laboratory-model studies. The second step of the nucleation
parameterization treats the "apparent" nucleation rate, i.e., the growth
of clusters into the model's lowest size bin by condensable vapors such as OIO.
We compared different scenarios for a clean marine versus a polluted continental
background atmosphere. In every scenario, we assumed the air to move,
independent of its origin, first over a coastal region (where it is exposed
to surface fluxes of different reactive iodine precursors) and later over the open ocean.
According to these sensitivity studies, in the clean marine background atmosphere
OIO can be responsible for both
homogeneous nuclei formation and the subsequent growth of the clusters
to detectable sizes. In contrast to this, in the continental case with its higher
levels of pollutants, gas phase OIO mixing ratios, and hence related nucleation rates,
are significantly lower. Compared to ternary H2SO4-NH3-H2O
nucleation, homogeneous OIO nucleation can be neglected
for new particle formation in this case, but OIO can contribute to
early particle growth, i.e., to apparent nucleation rates.
In general, we found OIO to be more important for the growth of newly formed
particles than for the formation of new nuclei.
According to our studies, observations of particle "bursts" can only
be explained by hot spot-like, not by homogeneously distributed emissions.
Citation: Pechtl, S., Lovejoy, E. R., Burkholder, J. B., and von Glasow, R.: Modeling the possible role of iodine oxides in atmospheric new particle formation, Atmos. Chem. Phys., 6, 505-523, doi:10.5194/acp-6-505-2006, 2006.