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@ARTICLE{Dlugi:866649,
author = {Dlugi, Ralph and Berger, Martina and Mallik, Chinmay and
Tsokankunku, Anywhere and Zelger, Michael and Acevedo,
Otávio C. and Bourtsoukidis, Efstratios and Hofzumahaus,
Andreas and Kesselmeier, Jürgen and Kramm, Gerhard and
Marno, Daniel and Martinez, Monica and Nölscher, Anke C.
and Ouwersloot, Huug and Pfannerstill, Eva Y. and Rohrer,
Franz and Tauer, Sebastian and Williams, Jonathan and
Yáñez-Serrano, Ana-Maria and Andreae, Meinrat O. and
Harder, Hartwig and Sörgel, Matthias},
title = {{S}egregation in the {A}tmospheric {B}oundary {L}ayer:
{T}he {C}ase of {OH} $\–$ {I}soprene},
journal = {Atmospheric chemistry and physics / Discussions Discussions
[...]},
volume = {1325},
issn = {1680-7375},
address = {Katlenburg-Lindau},
publisher = {EGU},
reportid = {FZJ-2019-05728},
pages = {1 - 61},
year = {2019},
abstract = {In the atmospheric boundary layer (ABL), incomplete mixing
(i.e., segregation) results in reduced chemical reaction
rates compared to those expected from mean values and rate
constants derived under well mixed conditions. Recently,
segregation has been suggested as a potential cause of
discrepancies between modelled and measured OH radical
concentrations, especially under high isoprene conditions.
Therefore, the influence of segregation on the reaction of
OH radicals with isoprene has been investigated by modelling
studies and one ground-based and one aircraft campaign.In
this study, we measured isoprene and OH radicals with high
time resolution in order to directly calculate the influence
of segregation in a low-NOx and high-isoprene environment in
the central Amazon basin. The calculated intensities of
segregation (Is) at the Amazon Tall Tower Observatory (ATTO)
above canopy top are in the range of values determined at a
temperate deciduous forest (ECHO-campaign) in a high-NOx
low-isoprene environment, but stay below $10 \%.$ To
establish a more general idea about the causes of
segregation and their potential limits, further analysis was
based on the budget equations of isoprene mixing ratios, the
variance of mixing ratios, and the balance of the intensity
of segregation itself. Furthermore, it was investigated if a
relation of Is to the turbulent isoprene surface flux can be
established theoretically and empirically, as proposed
previously. A direct relation is not given and the amount of
variance in Is explained by the isoprene flux will be higher
the less the influence from other processes (e.g., vertical
advection) is and will therefore be greater near the
surface. Although ground based values of Is from ATTO and
ECHO are in the same range, we could identify different
dominating processes driving Is. For ECHO the normalized
variance of isoprene had the largest contribution, whereas
for ATTO the different transport terms expressed as a
residual were dominating. To get a more general picture of
Is and its potential limits in the ABL, we also compared
these ground based measurements to ABL modelling studies and
results from an aircraft campaign. The ground based
measurements show the lowest values of the degree of
inhomogenous mixing $(< 20 \%,$ mostly below $10 \%).$
These values increase if the contribution of lower
frequencies is added. Values integrated over the whole
boundary layer (modelling studies) are in the range from
$10 \%$ to $30 \%$ and aircraft measurements integrating
over different landscapes are amongst the largest reported.
This presents evidence that larger scale heterogeneities in
land surface properties contribute substantially to Is.},
cin = {IEK-8},
ddc = {550},
cid = {I:(DE-Juel1)IEK-8-20101013},
pnm = {243 - Tropospheric trace substances and their
transformation processes (POF3-243)},
pid = {G:(DE-HGF)POF3-243},
typ = {PUB:(DE-HGF)16},
doi = {10.5194/acp-2018-1325},
url = {https://juser.fz-juelich.de/record/866649},
}