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@ARTICLE{Hens:187193,
author = {Hens, K. and Novelli, A. and Martinez, M. and Auld, J. and
Axinte, R. and Bohn, B. and Fischer, H. and Keronen, P. and
Kubistin, D. and Nölscher, A. C. and Oswald, R. and
Paasonen, P. and Petäjä, T. and Regelin, E. and Sander, R.
and Sinha, V. and Sipilä, M. and Taraborrelli, D. and Tatum
Ernest, C. and Williams, J. and Lelieveld, J. and Harder,
H.},
title = {{O}bservation and modelling of {HO}x radicals in a boreal
forest},
journal = {Atmospheric chemistry and physics},
volume = {14},
number = {16},
issn = {1680-7324},
address = {Katlenburg-Lindau},
publisher = {EGU},
reportid = {FZJ-2015-00867},
pages = {8723 - 8747},
year = {2014},
abstract = {Measurements of OH and HO2 radicals were conducted in a
pine-dominated forest in southern Finland during the
HUMPPA-COPEC-2010 (Hyytiälä United Measurements of
Photochemistry and Particles in Air – Comprehensive
Organic Precursor Emission and Concentration study) field
campaign in summer 2010. Simultaneous side-by-side
measurements of hydroxyl radicals were conducted with two
instruments using chemical ionization mass spectrometry
(CIMS) and laser-induced fluorescence (LIF), indicating
small systematic disagreement, OHLIF / OHCIMS = (1.31 ±
0.14). Subsequently, the LIF instrument was moved to the top
of a 20 m tower, just above the canopy, to investigate the
radical chemistry at the ecosystem–atmosphere interface.
Comprehensive measurements including observations of many
volatile organic compounds (VOCs) and the total OH
reactivity were conducted and analysed using steady-state
calculations as well as an observationally constrained box
model.Production rates of OH calculated from measured OH
precursors are consistent with those derived from the
steady-state assumption and measured total OH loss under
conditions of moderate OH reactivity. The primary photolytic
sources of OH contribute up to one-third to the total OH
production. OH recycling, which occurs mainly by HO2
reacting with NO and O3, dominates the total hydroxyl
radical production in this boreal forest. Box model
simulations agree with measurements for hydroxyl radicals
(OHmod. / OHobs. = 1.00 ± 0.16), while HO2 mixing ratios
are significantly under-predicted (HO2mod. / HO2obs. = 0.3
± 0.2), and simulated OH reactivity does not match the
observed OH reactivity. The simultaneous under-prediction of
HO2 and OH reactivity in periods in which OH concentrations
were simulated realistically suggests that the missing OH
reactivity is an unaccounted-for source of HO2.Detailed
analysis of the HOx production, loss, and recycling pathways
suggests that in periods of high total OH reactivity there
are additional recycling processes forming OH directly, not
via reaction of HO2 with NO or O3, or unaccounted-for
primary HOx sources. Under conditions of moderate observed
OH reactivity and high actinic flux, an additional RO2
source of approximately 1 × 106 molec cm−3 s−1 would be
required to close the radical budget. Nevertheless, a major
fraction of the OH recycling occurs via the reaction of HO2
with NO and O3 in this terpene-dominated environment.},
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:000341991600029},
doi = {10.5194/acp-14-8723-2014},
url = {https://juser.fz-juelich.de/record/187193},
}