posted on 2024-03-14, 14:11authored byMichael
F. Link, Matson A. Pothier, Michael P. Vermeuel, Mj Riches, Dylan B. Millet, Delphine K. Farmer
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 3-methyl-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.