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@ARTICLE{Berresheim:172737,
author = {Berresheim, H. and Adam, M. and Monahan, C. and O'Dowd, C.
and Plane, J. M. C. and Bohn, B. and Rohrer, F.},
title = {{M}issing {SO}2 oxidant in the coastal atmosphere? -
observations from high-resolution measurements of {OH} and
atmospheric sulfur compounds},
journal = {Atmospheric chemistry and physics},
volume = {14},
number = {22},
issn = {1680-7324},
address = {Katlenburg-Lindau},
publisher = {EGU},
reportid = {FZJ-2014-06181},
pages = {12209 - 12223},
year = {2014},
abstract = {Diurnal and seasonal variations of gaseous sulfuric acid
(H2SO4) and methane sulfonic acid (MSA) were measured in NE
Atlantic air at the Mace Head atmospheric research station
during the years 2010 and 2011. The measurements utilized
selected-ion chemical ionization mass spectrometry (SI/CIMS)
with a detection limit for both compounds of 4.3 × 104
cm−3 at 5 min signal integration. The H2SO4 and MSA
gas-phase concentrations were analyzed in conjunction with
the condensational sink for both compounds derived from 3 nm
to 10 μm (aerodynamic diameter) aerosol size distributions.
Accommodation coefficients of 1.0 for H2SO4 and 0.12 for MSA
were assumed, leading to estimated atmospheric lifetimes on
the order of 7 and 25 min, respectively. With the SI/CIMS
instrument in OH measurement mode alternating between OH
signal and background (non-OH) signal, evidence was obtained
for the presence of one or more unknown oxidants of SO2 in
addition to OH. Depending on the nature of the oxidant(s),
its ambient concentration may be enhanced in the CIMS inlet
system by additional production. The apparent unknown SO2
oxidant was additionally confirmed by direct measurements of
SO2 in conjunction with calculated H2SO4 concentrations. The
calculated H2SO4 concentrations were consistently lower than
the measured concentrations by a factor of 4.7 ± 2.4 when
considering the oxidation of SO2 by OH as the only source of
H2SO4. Both the OH and the background signal were also
observed to increase significantly during daytime aerosol
nucleation events, independent of the ozone photolysis
frequency, J(O1D), and were followed by peaks in both H2SO4
and MSA concentrations. This suggests a strong relation
between the unknown oxidant(s), OH chemistry, and the
atmospheric photolysis and photooxidation of biogenic iodine
compounds. As to the identity of the atmospheric SO2
oxidant(s), we have been able to exclude ClO, BrO, IO, and
OIO as possible candidates based on {ab initio}
calculations. $Never\-theless,$ IO could contribute
significantly to the observed CIMS background signal. A
detailed analysis of this CIMS background signal in context
with recently published kinetic data currently suggests that
Criegee intermediates (CIs) produced from ozonolysis of
alkenes play no significant role for SO2 oxidation in the
marine atmosphere at Mace Head. On the other hand, SO2
oxidation by small CIs such as CH2OO produced photolytically
or possibly in the photochemical degradation of methane is
consistent with our observations. In addition, H2SO4
formation from dimethyl sulfide oxidation via SO3 as an
intermediate instead of SO2 also appears to be a viable
explanation. Both pathways need to be further explored.},
cin = {IEK-8},
ddc = {550},
cid = {I:(DE-Juel1)IEK-8-20101013},
pnm = {233 - Trace gas and aerosol processes in the troposphere
(POF2-233)},
pid = {G:(DE-HGF)POF2-233},
typ = {PUB:(DE-HGF)16},
UT = {WOS:000345290700014},
doi = {10.5194/acp-14-12209-2014},
url = {https://juser.fz-juelich.de/record/172737},
}