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Simultaneous HONO measurements in and above a forest canopy : influence of turbulent exchange on mixing ratio differences

Title data

Sörgel, Matthias ; Trebs, Ivonne ; Serafimovich, Andrei ; Moravek, Alexander ; Held, Andreas ; Zetzsch, Cornelius:
Simultaneous HONO measurements in and above a forest canopy : influence of turbulent exchange on mixing ratio differences.
In: Atmospheric Chemistry and Physics. Vol. 11 (2011) Issue 2 . - pp. 841-855.
ISSN 1680-7324
DOI: https://doi.org/10.5194/acp-11-841-2011

Abstract in another language

We have combined chemical and micrometeorological measurements to investigate the formation and distribution of HONO throughout a forest canopy. HONO was measured simultaneously at two heights, close to the forest floor and just above canopy. The turbulent exchange between the forest and the atmosphere above was studied using vertical profiles of eddy covariance measurements of wind velocity, sonic temperature, water vapour and CO₂. HONO mixing ratios at both heights showed typical diel cycles with low daytime values (~80 ppt) and high nighttime values (up to 500 ppt), but were influenced by various sources and sinks leading to mixing ratio differences (above canopy minus below) of up to +240 ppt at nighttime. In the late afternoon and early night mixing ratios increased at higher rates near the forest floor, indicating a possible ground source. Due to the simultaneous decoupling of the forest from the air layer above the canopy, mixing ratio differences reached about −170 ppt. From the late night until the early morning mixing ratios above the forest were typically higher than close to the forest floor. For some cases, this could be attributed to advection above the forest, which only partly penetrated the canopy. Measured photolysis frequencies above and below the forest canopy differed by a factor of 10–25 resulting in HONO lifetimes of about 10 min above and 100–250 min below the canopy at noontime. However, these differences of the main daytime HONO sink were not evident in the mixing ratio differences, which were close to zero during the morning hours. Effective turbulent exchange due to a complete coupling of the forest to the air layer above the canopy in the morning has offset the differences caused by the daytime photolytic sink and added to the interplay between different HONO production and loss processes.

Further data

Item Type: Article in a journal
Refereed: Yes
Additional notes: BAYCEER92990
Institutions of the University: Faculties > Faculty of Biology, Chemistry and Earth Sciences > Department of Earth Sciences > Professorship Micrometeorology
Research Institutions > Research Centres > Bayreuth Center of Ecology and Environmental Research- BayCEER
Faculties > Faculty of Biology, Chemistry and Earth Sciences > Department of Earth Sciences
Faculties > Faculty of Biology, Chemistry and Earth Sciences > Department of Earth Sciences > Professorship Atmospheric Chemistry
Faculties
Faculties > Faculty of Biology, Chemistry and Earth Sciences
Research Institutions
Research Institutions > Research Centres
Result of work at the UBT: Yes
DDC Subjects: 500 Science
Date Deposited: 13 Aug 2015 06:11
Last Modified: 13 Aug 2015 06:11
URI: https://eref.uni-bayreuth.de/id/eprint/17948