Do organic surface films on sea salt aerosols influence atmospheric chemistry? – a model study L. Smoydzin and R. von Glasow Institute of Environmental Physics, University of Heidelberg, Im Neuenheimer Feld 229, 69120 Heidelberg, Germany now at: School of Environmental Sciences, University of East Anglia, Norwich, UK
Abstract. Organic material from the ocean's surface can be incorporated into sea salt aerosol
particles often producing a surface film on the aerosol.
Such an organic coating can reduce the
mass transfer between the gas phase and the aerosol phase influencing
sea salt chemistry in the marine atmosphere.
To investigate these effects and their importance for the marine boundary
layer (MBL) we used the one-dimensional numerical model MISTRA.
We considered the uncertainties regarding the
magnitude of uptake reduction, the concentrations of organic compounds in
sea salt aerosols and the oxidation rate of the organics to analyse the possible
influence of organic surfactants on gas and liquid phase chemistry
with a special focus on halogen chemistry.
By assuming destruction rates for the organic coating based on laboratory
measurements we get a rapid destruction of the organic monolayer within the first
meters of the MBL. Larger organic initial concentrations lead to a longer
lifetime of the coating but lead also to an unrealistically strong decrease of
O3 concentrations as the organic film is destroyed by reaction with
O3. The lifetime of the film is increased by assuming
smaller reactive uptake coefficients for O3 or by assuming that
a part of the organic surfactants react with OH.
With regard to tropospheric chemistry we found that gas phase concentrations
for chlorine and bromine species decreased due to the decreased mass transfer
between gas phase and aerosol phase.
Aqueous phase chlorine concentrations also decreased but
aqueous phase bromine concentrations increased.
Differences for gas phase concentrations are in general smaller than for
liquid phase concentrations. The effect on gas phase NO2 or NO is
very small (reduction less than 5%) whereas liquid phase NO2 concentrations
increased in some cases by nearly 100%. We list suggestions for further
laboratory studies which are needed for improved model studies.
Citation: Smoydzin, L. and von Glasow, R.: Do organic surface films on sea salt aerosols influence atmospheric chemistry? – a model study, Atmos. Chem. Phys., 7, 5555-5567, doi:10.5194/acp-7-5555-2007, 2007.