Measurements of nitrogen oxides and ozone fluxes by eddy covariance at a meadow: evidence for an internal leaf resistance to NO<sub>2</sub>
Nitrogen dioxide (NO<sub>2</sub>) plays an important role in atmospheric pollution, in particular for tropospheric ozone production. However, the removal processes involved in NO<sub>2</sub> deposition to terrestrial ecosystems are still the subject of ongoing discussion. Thi...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2013-09-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/10/5997/2013/bg-10-5997-2013.pdf |
| Summary: | Nitrogen dioxide (NO<sub>2</sub>) plays an important role in atmospheric pollution, in particular for tropospheric ozone production. However, the removal processes involved in NO<sub>2</sub> deposition to terrestrial ecosystems are still the subject of ongoing discussion. This study reports NO<sub>2</sub> flux measurements made over a meadow using the eddy covariance method. The measured NO<sub>2</sub> deposition fluxes during daytime were about a factor of two lower than a priori calculated fluxes using the Surfatm model without taking into account an internal (also called mesophyllic or sub-stomatal) resistance. Neither an underestimation of the measured NO<sub>2</sub> deposition flux due to chemical divergence or an in-canopy NO<sub>2</sub> source nor an underestimation of the resistances used to model the NO<sub>2</sub> deposition explained the large difference between measured and modelled NO<sub>2</sub> fluxes. Thus, only the existence of the internal resistance could account for this large discrepancy between model and measurements. The median internal resistance was estimated to be 300 s m<sup>−1</sup> during daytime, but exhibited a large variability (100–800 s m<sup>−1</sup>). In comparison, the stomatal resistance was only around 100 s m<sup>−1</sup> during daytime. Hence, the internal resistance accounted for 50–90% of the total leaf resistance to NO<sub>2</sub>. This study presents the first clear evidence and quantification of the internal resistance using the eddy covariance method; i.e. plant functioning was not affected by changes of microclimatological (turbulent) conditions that typically occur when using enclosure methods. |
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| ISSN: | 1726-4170 1726-4189 |