title: Rapid deposition of oxidized biogenic compounds to a temperate forest.
abstract: We report fluxes and dry deposition velocities for 16 atmospheric compounds above a southeastern United States forest, including: hydrogen peroxide (H2O2), nitric acid (HNO3), 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 HNO3 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.
authors.affiliation: Divisions of Geological and Planetary Sciences and wennberg@caltech.edu tbn@caltech.edu.
authors.forename: Tran B
authors.initials: TB
authors.lastname: Nguyen
authors.affiliation: Divisions of Geological and Planetary Sciences and.
authors.forename: John D
authors.initials: JD
authors.lastname: Crounse
authors.affiliation: Divisions of Geological and Planetary Sciences and.
authors.forename: Alex P
authors.initials: AP
authors.lastname: Teng
authors.affiliation: Divisions of Geological and Planetary Sciences and.
authors.forename: Jason M
authors.initials: JM
authors.lastname: St Clair
authors.affiliation: Geophysical Fluid Dynamics Laboratory, National Oceanic and Atmospheric Administration, Princeton, NJ 08540; Atmospheric and Oceanic Sciences, Princeton University, Princeton, NJ 08544;
authors.forename: Fabien
authors.initials: F
authors.lastname: Paulot
authors.affiliation: Atmospheric Chemistry and Dynamics Lab, NASA Goddard Space Flight Center, Greenbelt, MD 20771; and Joint Center for Earth Systems Technology, University of Maryland Baltimore County, Baltimore, MD 21250.
authors.forename: Glenn M
authors.initials: GM
authors.lastname: Wolfe
authors.affiliation: Divisions of Geological and Planetary Sciences and Engineering and Applied Science, California Institute of Technology, Pasadena, CA 91125; wennberg@caltech.edu tbn@caltech.edu.
authors.forename: Paul O
authors.initials: PO
authors.lastname: Wennberg
mesh_terms: D000393:Air Pollutants / Q000737:chemistry; D065928:Forests; D010084:Oxidation-Reduction
chemical_list: D000393:Air Pollutants
keywords: OVOCs; biosphere−atmosphere exchange; dry deposition; fluxes; isoprene