Direct measurement of NO 3 radical reactivity in a boreal forest
We present the first direct measurements of NO3 reactivity (or inverse lifetime, s−1) in the Finnish boreal forest. The data were obtained during the IBAIRN campaign (Influence of Biosphere-Atmosphere Interactions on the Reactive Nitrogen budget) which took place in Hyytiälä, Finland during the summ...
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Veröffentlicht in: | Atmospheric chemistry and physics 2018-03, Vol.18 (5), p.3799-3815 |
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Zusammenfassung: | We present the first direct measurements of NO3 reactivity (or
inverse lifetime, s−1) in the Finnish boreal forest. The data were
obtained during the IBAIRN campaign (Influence of Biosphere-Atmosphere
Interactions on the Reactive Nitrogen budget) which took place in
Hyytiälä, Finland during the summer/autumn transition in
September 2016. The NO3 reactivity was generally very high with a
maximum value of 0.94 s−1 and displayed a strong diel variation with a
campaign-averaged nighttime mean value of 0.11 s−1 compared to a
daytime value of 0.04 s−1. The highest nighttime NO3 reactivity
was accompanied by major depletion of canopy level ozone and was associated
with strong temperature inversions and high levels of monoterpenes. The
daytime reactivity was sufficiently large that reactions of NO3 with
organic trace gases could compete with photolysis and reaction with NO. There
was no significant reduction in the measured NO3 reactivity between
the beginning and end of the campaign, indicating that any seasonal reduction
in canopy emissions of reactive biogenic trace gases was offset by emissions
from the forest floor. Observations of biogenic hydrocarbons (BVOCs) suggested
a dominant role for monoterpenes in determining the NO3 reactivity.
Reactivity not accounted for by in situ measurement of NO and BVOCs was
variable across the diel cycle with, on average, ≈ 30 %
“missing” during nighttime and ≈ 60 % missing during the day.
Measurement of the NO3 reactivity at various heights (8.5 to 25 m)
both above and below the canopy, revealed a strong nighttime, vertical
gradient with maximum values closest to the ground. The gradient disappeared
during the daytime due to efficient vertical mixing. |
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ISSN: | 1680-7324 1680-7316 1680-7324 |
DOI: | 10.5194/acp-18-3799-2018 |