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@ARTICLE{Tan:903131,
author = {Tan, Zhaofeng and Hantschke, Luisa and Kaminski, Martin and
Acir, Ismail-Hakki and Bohn, Birger and Cho, Changmin and
Dorn, Hans-Peter and Li, Xin and Novelli, Anna and Nehr,
Sascha and Rohrer, Franz and Tillmann, Ralf and Wegener,
Robert and Hofzumahaus, Andreas and Kiendler-Scharr, Astrid
and Wahner, Andreas and Fuchs, Hendrik},
title = {{A}tmospheric photo-oxidation of myrcene: {OH} reaction
rate constant, gas-phase oxidation products and radical
budgets},
journal = {Atmospheric chemistry and physics},
volume = {21},
number = {20},
issn = {1680-7316},
address = {Katlenburg-Lindau},
publisher = {EGU},
reportid = {FZJ-2021-04855},
pages = {16067 - 16091},
year = {2021},
abstract = {The photo-oxidation of myrcene, a monoterpene species
emitted by plants, was investigated at atmospheric
conditions in the outdoor simulation chamber SAPHIR
(Simulation of Atmospheric PHotochemistry In a Large
Reaction Chamber). The chemical structure of myrcene
consists of one moiety that is a conjugated π system
(similar to isoprene) and another moiety that is a
triple-substituted olefinic unit (similar to
2-methyl-2-butene). Hydrogen shift reactions of organic
peroxy radicals (RO2) formed in the reaction of isoprene
with atmospheric OH radicals are known to be of importance
for the regeneration of OH. Structure–activity
relationships (SARs) suggest that similar hydrogen shift
reactions like in isoprene may apply to the isoprenyl part
of RO2 radicals formed during the OH oxidation of myrcene.
In addition, SAR predicts further isomerization reactions
that would be competitive with bimolecular RO2 reactions for
chemical conditions that are typical for forested
environments with low concentrations of nitric oxide.
Assuming that OH peroxy radicals can rapidly interconvert by
addition and elimination of O2 like in isoprene, bulk
isomerization rate constants of 0.21 and 0.097 s−1
(T=298 K) for the three isomers resulting from the 3′-OH
and 1-OH addition, respectively, can be derived from SAR.
Measurements of radicals and trace gases in the experiments
allowed us to calculate radical production and destruction
rates, which are expected to be balanced. The largest
discrepancies between production and destruction rates were
found for RO2. Additional loss of organic peroxy radicals
due to isomerization reactions could explain the observed
discrepancies. The uncertainty of the total radical
(ROx=OH+HO2+RO2) production rates was high due to the
uncertainty in the yield of radicals from myrcene
ozonolysis. However, results indicate that radical
production can only be balanced if the reaction rate
constant of the reaction between hydroperoxy (HO2) and RO2
radicals derived from myrcene is lower (0.9 to
1.6×10−11 cm3 s−1) than predicted by SAR. Another
explanation of the discrepancies would be that a significant
fraction of products (yield: 0.3 to 0.6) from these
reactions include OH and HO2 radicals instead of
radical-terminating organic peroxides. Experiments also
allowed us to determine the yields of organic oxidation
products acetone (yield: 0.45±0.08) and formaldehyde
(yield: 0.35±0.08). Acetone and formaldehyde are produced
from different oxidation pathways, so that yields of these
compounds reflect the branching ratios of the initial OH
addition to myrcene. Yields determined in the experiments
are consistent with branching ratios expected from SAR. The
yield of organic nitrate was determined from the gas-phase
budget analysis of reactive oxidized nitrogen in the
chamber, giving a value of 0.13±0.03. In addition, the
reaction rate constant for myrcene + OH was determined
from the measured myrcene concentration, yielding a value of
(2.3±0.3)×10−10 cm3 s−1.},
cin = {IEK-8},
ddc = {550},
cid = {I:(DE-Juel1)IEK-8-20101013},
pnm = {2111 - Air Quality (POF4-211)},
pid = {G:(DE-HGF)POF4-2111},
typ = {PUB:(DE-HGF)16},
UT = {WOS:000714359600001},
doi = {10.5194/acp-21-16067-2021},
url = {https://juser.fz-juelich.de/record/903131},
}