HR: 14:10h
AN: A22E-02 [PDF]
TI: DMS oxidation: effects of halogens and of increased sea salt alkalinity.
AU: * von Glasow, R
EM: roland@fiji.ucsd.edu
AF: Scripps Inst. of Oceanography,
Univ. California, San Diego, 9500 Gilman Drive \#0221, La Jolla, CA 92093-0221 United States
AU: Sievering, H
EM: hsieveri@carbon.cudenver.edu
AF: Global Change and Env. Quality Program,
Univ. Colorado, Denver, Campus Box 172
P.O. Box 173364, Denver, CO 80217-3364 United States
AU: Crutzen, P J
EM: air@mpch-mainz.mpg.de
AF: Scripps Inst. of Oceanography,
Univ. California, San Diego, 9500 Gilman Drive \#0221, La Jolla, CA 92093-0221 United States
AU: Crutzen, P J
EM: air@mpch-mainz.mpg.de
AF: Max-Planck-Institut f\"ur Chemie, P.O. Box 3060, Mainz, 55029
Germany
AB:
The oxidation of DMS is the main source of SO$_2$, MSA, and non-sea-salt
sulfate (nss) in the clean marine boundary layer (MBL). Recently the importance
of BrO - in addition to OH and NO$_3$ - has been suggested as oxidant for DMS.
Furthermore HOCl$_{aq}$ and HOBr$_{aq}$ can increase the oxidation of S(IV) to
S(VI) in aerosol and cloud particles. Chlorine and bromine in the MBL are
derived from seasalt aerosol.
We investigated the importance of these processes for the chemistry of the MBL
and possible climate links with the one-dimensional chemical and microphysical
model MISTRA-MPIC. BrO plays a very significant role as oxidant even under very
low mixing ratios of 0.5 pmol mol$^{-1}$. We found that still significant
uncertainty exists in the kinetics of DMS oxidation especially with regard to
the endproducts of DMS oxidation. Under most conditions that we studied the net
effect of halogens, especially under cloudy conditions, is an increase in
particulate sulfur (MSA plus nss) and decrease of precursors for the formation
of new CCN.
In field experiments at Baring Head, New Zealand, it was found that supermicron
sea salt aerosols were enriched several fold in their alkalinity resulting
from ocean surface layer biogenic sources. Extrapolation of these Baring Head
results to typical open ocean lower MBL conditions indicate that supermicron
sea salt aerosol alkalinity is enriched by a factor of 100 - 150% compared to
deeper ocean water. This would lead to increased alkalinity in the seasalt
aerosol and therefore an enhancement of the importance of the nss production by
O$_{3,aq}$. Our model runs show a non-linear response of the oxidation by
O$_{3,aq}$ with increasing alkalinity due to saturation effects. In the
model runs with increased alkalinity O$_{3,aq}$ dominates the total nss production.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0312 Air/sea constituent fluxes (3339, 4504)
DE: 0320 Cloud physics and chemistry
DE: 0365 Troposphere--composition and chemistry
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting