Bi-directional Exchange of Volatile Organic Compounds

Forkel, R.; Ashworth, Kirsti; Bedos, Carole; Delon, Claire; Lathière, Juliette; Noe, Steffen M.; Potier, Élise; Rinne, Janne; Tchepel, Oxana; Zhang, L.

doi:10.1007/978-94-017-7285-3_8

Cited by 3 publications

(2 citation statements)

References 34 publications

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“…Competing physical and chemical processes that induce biosphere-atmosphere exchange of OVOCs include dry deposition, direct plant emission, in-canopy reactive chemistry, , and heterogeneous or multiphase reactions on the surfaces of leaves, water droplets, and other ecosystem surfaces . The result of these competing processes is that many OVOCs show bidirectional exchange. , This bidirectional exchange influences the fate of OVOCs and ultimately how they impact the production of aerosol and the budgets of oxidants and NO x . ,, While canopy-resolved models have provided insight on in-canopy ozone fluxes, few studies have investigated the in-canopy processes regulating the flux of key reactive OVOCs that contribute to oxidant flux and are produced from oxidation of major precursors, such as isoprene or 3-methyl-3-buten-2-ol (MBO). While isoprene has major biogenic emission sources from broadleaf vegetation and grasses with broad geographical significance, MBO is primarily emitted from coniferous vegetation like Ponderosa or Scots pine with regional significance as a reactive atmospheric VOC in parts of western North America .…”

Section: Introductionmentioning

confidence: 99%

“…24 The result of these competing processes is that many OVOCs show bidirectional exchange. 2,25 This bidirectional exchange influences the fate of OVOCs and ultimately how they impact the production of aerosol 4 and the budgets of oxidants and NO x . 14,15,26 While canopy-resolved models have provided insight on in-canopy ozone fluxes, 27 few studies have investigated the in-canopy processes regulating the flux of key reactive OVOCs that contribute to oxidant flux and are produced from oxidation of major precursors, such as isoprene or 3-methyl-3-buten-2-ol (MBO).…”

Section: ■ Introductionmentioning

confidence: 99%

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In-Canopy Chemistry, Emissions, Deposition, and Surface Reactivity Compete to Drive Bidirectional Forest-Atmosphere Exchange of VOC Oxidation Products

Link,

Pothier,

Vermeuel

et al. 2024

ACS EST Air

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Dry deposition is an important sink of oxygenated volatile organic compounds (OVOCs) in forest ecosystems. In the summer of 2021, we measured concentration gradients and exchange velocities of oxidation products of isoprene and 3methyl-3-buten-2-ol (MBO) from a Colorado Ponderosa pine forest as part of the Flux Closure Study (FluCS). MBO oxidation products exhibited bidirectional exchange over the forest. Vertical gradients of MBO oxidation products reveal in-canopy chemical production as a daytime source, whereas air transported from the urban outflow of the front range creates periods of enhanced deposition. Differences between our observed deposition velocities over the arid, sparse pine forest and those from a previous study over a temperate, dense mixed forest suggest that ecosystem type may impact deposition rates in ways not currently captured by GEOS-Chem. We show that a previously inferred increased OVOC solubility threshold on leaf cuticles is not likely to explain the observed rapid rates of deposition but instead suggest that peroxides/epoxides could undergo reactive uptake to broadleaf vegetation while organic nitrates could undergo reactive uptake to pine needles. We point to the need to understand the role of reactive OVOC uptake and its potential implications for bidirectional ecosystem-atmosphere exchange.

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Section: Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

In-Canopy Chemistry, Emissions, Deposition, and Surface Reactivity Compete to Drive Bidirectional Forest-Atmosphere Exchange of VOC Oxidation Products

Link,

Pothier,

Vermeuel

et al. 2024

ACS EST Air

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Realistic Forests and the Modeling of Forest‐Atmosphere Exchange

Bannister

MacKenzie

Cai

2022

Reviews of Geophysics

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Forests cover nearly a third of the Earth's land area and exchange mass, momentum, and energy with the atmosphere. Most studies of these exchanges, particularly using numerical models, consider forests whose structure has been heavily simplified. In many landscapes, these simplifications are unrealistic. Inhomogeneous landscapes and unsteady weather conditions generate fluid dynamical features that cause observations to be inaccurately interpreted, biased, or over‐generalized. In Part I, we discuss experimental, theoretical, and numerical progress in the understanding of turbulent exchange over realistic forests. Scalar transport does not necessarily follow the flow in realistic settings, meaning scalar quantities are rarely at equilibrium around patchy forests, and significant scalar fluxes may form in the lee of forested hills. Gaps and patchiness generate significant spatial fluxes that current models and observations neglect. Atmospheric instability increases the distance over which fluxes adjust at forest edges. In deciduous forests, the effects of patchiness differ between seasons; counter intuitively, eddies reach further into leafy canopies (because they are rougher aerodynamically). Air parcel residence times are likely much lower in patchy forests than homogeneous ones, especially around edges. In Part II, we set out practical ways to make numerical models of forest‐atmosphere more realistic, including by accounting for reconfiguration and realistic canopy structure and beginning to include more chemical and physical processes in turbulence resolving models. Future challenges include: (a) customizing numerical models to real study sites, (b) connecting space and time scales, and (c) incorporating a greater range of weather conditions in numerical models.

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Residence times of air in a mature forest: observational evidence from a free-air CO₂ enrichment experiment

Bannister

Jesson²,

Harper³

et al. 2023

Atmos. Chem. Phys.

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Abstract. In forests, the residence time of air – the inverse of first-order exchange rates – influences in-canopy chemistry and the exchanges of momentum, energy, and mass with the surrounding atmosphere. Accurate estimates are needed for chemical investigations of reactive trace species, such as volatile organic compounds, some of whose chemical lifetimes are on the order of average residence times. However, very few observational residence-time estimates have been reported. Little is known about even the basic statistics of real-world residence times or how they are influenced by meteorological variables such as turbulence or atmospheric stability. Here, we report opportunistic investigations of residence time of air in a free-air carbon dioxide enrichment (FACE) facility in a mature, broadleaf deciduous forest with canopy height of hc≈25 m. Using nearly 50 million FACE observations, we find that median daytime residence times in the tree crowns range from around 70 s when the trees are in leaf to just over 34 s when they are not. Residence times increase with increasing atmospheric stability, as does the spread around their central value. Residence times scale approximately with the reciprocal of the friction velocity, u∗. During some calm evenings in the growing season, we observe distinctly different behaviour: pooled air being sporadically and unpredictably vented – evidenced by sustained increases in CO2 concentration – when intermittent turbulence penetrates the canopy. In these conditions, the concept of a residence time is less clearly defined. Parameterisations available in the literature underestimate turbulent exchange in the upper half of forest crowns and overestimate the frequency of long residence times. Robust parameterisations of residence times (or, equivalently, fractions of emissions escaping the canopy) may be generated from inverse-gamma distributions, with the parameters 1.4≤α≤1.8 and β=hc/u∗ estimated from widely measured flow variables. In this case, the mean value for τ becomes formally defined as τ‾=β/(α-1). For species released in the canopy during the daytime, chemical transformations are unlikely unless the reaction timescale is on the order of a few minutes or less.

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Bi-directional Exchange of Volatile Organic Compounds

Cited by 3 publications

References 34 publications

In-Canopy Chemistry, Emissions, Deposition, and Surface Reactivity Compete to Drive Bidirectional Forest-Atmosphere Exchange of VOC Oxidation Products

In-Canopy Chemistry, Emissions, Deposition, and Surface Reactivity Compete to Drive Bidirectional Forest-Atmosphere Exchange of VOC Oxidation Products

Realistic Forests and the Modeling of Forest‐Atmosphere Exchange

Residence times of air in a mature forest: observational evidence from a free-air CO₂ enrichment experiment

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Bi-directional Exchange of Volatile Organic Compounds

Cited by 3 publications

References 34 publications

In-Canopy Chemistry, Emissions, Deposition, and Surface Reactivity Compete to Drive Bidirectional Forest-Atmosphere Exchange of VOC Oxidation Products

In-Canopy Chemistry, Emissions, Deposition, and Surface Reactivity Compete to Drive Bidirectional Forest-Atmosphere Exchange of VOC Oxidation Products

Realistic Forests and the Modeling of Forest‐Atmosphere Exchange

Residence times of air in a mature forest: observational evidence from a free-air CO2 enrichment experiment

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Residence times of air in a mature forest: observational evidence from a free-air CO₂ enrichment experiment