Derivation of canopy resistance for water vapour fluxes over a spruce forest, using a new technique for the viscous sublayer resistance

We report fluxes and dry deposition velocities for 16 atmospheric compounds above a southeastern United States forest, including: hydrogen peroxide (H 2 O 2 ), nitric acid (HNO 3 ), hydrogen cyanide (HCN), hydroxymethyl hydroperoxide, peroxyacetic acid, organic hydroxy nitrates, and other multifunctional species derived from the oxidation of isoprene and monoterpenes. The data suggest that dry deposition is the dominant daytime sink for small, saturated oxygenates. Greater than 6 wt %C emitted as isoprene by the forest was returned by dry deposition of its oxidized products. Peroxides account for a large fraction of the oxidant flux, possibly eclipsing ozone in more pristine regions. The measured organic nitrates comprise a sizable portion (15%) of the oxidized nitrogen input into the canopy, with HNO 3 making up the balance. We observe that water-soluble compounds (e.g., strong acids and hydroperoxides) deposit with low surface resistance whereas compounds with moderate solubility (e.g., organic nitrates and hydroxycarbonyls) or poor solubility (e.g., HCN) exhibited reduced uptake at the surface of plants. To first order, the relative deposition velocities of water-soluble compounds are constrained by their molecular diffusivity. From resistance modeling, we infer a substantial emission flux of formic acid at the canopy level (∼1 nmol m −2 ·s −1 ). GEOS−Chem, a widely used atmospheric chemical transport model, currently underestimates dry deposition for most molecules studied in this work. Reconciling GEOS−Chem deposition velocities with observations resulted in up to a 45% decrease in the simulated surface concentration of trace gases.biosphere−atmosphere exchange | isoprene | dry deposition | OVOCs | fluxes

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“…We used R a and R b parameterization as suggested (32)(33)(34). R a is dependent only on the atmospheric stability (i.e., turbulence).…”

Section: Resultsmentioning

confidence: 99%

Rapid deposition of oxidized biogenic compounds to a temperate forest

Nguyen

Crounse

Teng

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

246

433

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“…Minimal relative precision requirements ( C max /C in %) assuming a maximum HNO 3 deposition flux (R c =0) for a grassland site (NEU) and a forest site (EGER). For the forest site different parameterizations for R b existing in literature (Businger, 1986;Hummelshoj, 1995, 1997;Meyers et al, 1989) are applied. stable conditions (32% at the forest site) to less than 10% at the grassland (around 5% at the forest site) for labile conditions.…”

Section: Influence Of Atmospheric Stabilitymentioning

confidence: 99%

Aerodynamic gradient measurements of the NH3-HNO3-NH4NO3 triad using a wet chemical instrument: an analysis of precision requirements and flux errors

et al. 2010

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Abstract. The aerodynamic gradient method is widely used for flux measurements of ammonia, nitric acid, particulate ammonium nitrate (the NH 3 -HNO 3 -NH 4 NO 3 triad) and other water-soluble reactive trace compounds. The surface exchange flux is derived from a measured concentration difference and micrometeorological quantities (turbulent exchange coefficient). The significance of the measured concentration difference is crucial for the significant determination of surface exchange fluxes. Additionally, measurements of surface exchange fluxes of ammonia, nitric acid and ammonium nitrate are often strongly affected by phase changes between gaseous and particulate compounds of the triad, which make measurements of the four individual species (NH 3 , HNO 3 , NH + 4 , NO − 3 ) necessary for a correct interpretation of the measured concentration differences.We present here a rigorous analysis of results obtained with a multi-component, wet-chemical instrument, able to simultaneously measure gradients of both gaseous and particulate trace substances. Basis for our analysis are two field experiments, conducted above contrasting ecosystems (grassland, forest). Precision requirements of the instrument as well as errors of concentration differences and micrometeorological exchange parameters have been estimated, which, in turn, allows the establishment of thorough error estimates of the derived fluxes of NH 3 , HNO 3 , NH + 4 , and NO − 3 . Derived median flux errors for the grassland and forest field experiments were: 39% and 50% (NH 3 ), 31% and 38% (HNO 3 ), 62% and 57% (NH + 4 ), and 47% and 68% (NO − 3 ), respectively. Additionally, we provide the basis for using Correspondence to: V. Wolff (veronika.wolff@art.admin.ch) field data to characterize the instrument performance, as well as subsequent quantification of surface exchange fluxes and underlying mechanistic processes under realistic ambient measurement conditions.

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“…These ecosystem-scale light response curves were derived using all available peak wet season daytime data. Canopy conductance exchange with the atmosphere was calculated as proposed by Herbst et al (2002) and Jensen and Hummelshoj (1995). This approach includes the influence of leaf area index (LAI), where only peak season values were used for analysis.…”

Section: Flux Partitioning and Ecosystem-physiological Parametersmentioning

confidence: 99%

Precipitation as driver of carbon fluxes in 11 African ecosystems

et al. 2009

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Abstract. This study reports carbon and water fluxes between the land surface and atmosphere in eleven different ecosystems types in Sub-Saharan Africa, as measured using eddy covariance (EC) technology in the first two years of the CarboAfrica network operation. The ecosystems for which data were available ranged in mean annual rainfall from 320 mm (Sudan) to 1150 mm (Republic of Congo) and include a spectrum of vegetation types (or land cover) (open savannas, woodlands, croplands and grasslands). Given the shortness of the record, the EC data were analysed across the network rather than longitudinally at sites, in order to understand the driving factors for ecosystem respiration and carbon assimilation, and to reveal the different water use strategies in these highly seasonal environments.Correspondence to: L. Merbold (lmerbold@bgc-jena.mpg.de) Values for maximum net carbon assimilation rates (photosynthesis) ranged from −12.5 µmol CO 2 m −2 s −1 in a dry, open Millet cropland (C 4 -plants) up to −48 µmol CO 2 m −2 s −1 for a tropical moist grassland. Maximum carbon assimilation rates were highly correlated with mean annual rainfall (r 2 =0.74). Maximum photosynthetic uptake rates (Fp max ) were positively related to satellite-derived f APAR . Ecosystem respiration was dependent on temperature at all sites, and was additionally dependent on soil water content at sites receiving less than 1000 mm of rain per year. All included ecosystems dominated by C 3 -plants, showed a strong decrease in 30-min assimilation rates with increasing water vapour pressure deficit above 2.0 kPa.

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Derivation of canopy resistance for water vapour fluxes over a spruce forest, using a new technique for the viscous sublayer resistance

Cited by 70 publications

References 12 publications

Rapid deposition of oxidized biogenic compounds to a temperate forest

Rapid deposition of oxidized biogenic compounds to a temperate forest

Aerodynamic gradient measurements of the NH<sub>3</sub>-HNO<sub>3</sub>-NH<sub>4</sub>NO<sub>3</sub> triad using a wet chemical instrument: an analysis of precision requirements and flux errors

Precipitation as driver of carbon fluxes in 11 African ecosystems

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Derivation of canopy resistance for water vapour fluxes over a spruce forest, using a new technique for the viscous sublayer resistance

Cited by 70 publications

References 12 publications

Rapid deposition of oxidized biogenic compounds to a temperate forest

Rapid deposition of oxidized biogenic compounds to a temperate forest

Aerodynamic gradient measurements of the NH&lt;sub&gt;3&lt;/sub&gt;-HNO&lt;sub&gt;3&lt;/sub&gt;-NH&lt;sub&gt;4&lt;/sub&gt;NO&lt;sub&gt;3&lt;/sub&gt; triad using a wet chemical instrument: an analysis of precision requirements and flux errors

Precipitation as driver of carbon fluxes in 11 African ecosystems

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Aerodynamic gradient measurements of the NH<sub>3</sub>-HNO<sub>3</sub>-NH<sub>4</sub>NO<sub>3</sub> triad using a wet chemical instrument: an analysis of precision requirements and flux errors