4.7 Article

Simultaneous Measurements of O3 and HCOOH Vertical Fluxes Indicate Rapid In-Canopy Terpene Chemistry Enhances O3 Removal Over Mixed Temperate Forests

Journal

GEOPHYSICAL RESEARCH LETTERS
Volume 48, Issue 3, Pages -

Publisher

AMER GEOPHYSICAL UNION
DOI: 10.1029/2020GL090996

Keywords

deposition; eddy covariance; flux; formic acid; ozone

Funding

  1. National Science Foundation (NSF) [GEO AGS 1822420]
  2. US Department of Energy Ameriflux Network Management Project award
  3. NOAA Carbon Cycle and Greenhouse Gases tall tower program
  4. Student Blugold Commitment Differential Tuition funds through the UW-Eau Claire Summer Research Experiences for Undergraduates program
  5. UW-Madison
  6. Advanced Computing Initiative
  7. Wisconsin Alumni Research Foundation
  8. Wisconsin Institutes for Discovery
  9. National Science Foundation

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The study reveals a significant contribution of nonstomatal pathways in canopy to the dry deposition of O-3, which is not correctly captured in current models. Stomatal uptake and estimated absorption only explain a small portion of O-3 loss.
Dry deposition, the second largest removal process of ozone (O-3) in the troposphere, plays a role in controlling the natural variability of surface O-3 concentrations. Terrestrial ecosystems remove O-3 either through stomatal uptake or nonstomatal processes. In chemical transport models, nonstomatal pathways are roughly constrained and may not correctly capture total O-3 loss. To address this, the first simultaneous eddy covariance measurements of O-3 and formic acid (HCOOH), a tracer of in-canopy oxidation of biogenic terpenes, were made in a mixed temperate forest in Northern Wisconsin. Daytime maximum O-3 deposition velocities, v(d) (O-3), ranged between 0.5 and 1.2 cm s(-1). Comparison of observed v(d) (O-3) with observationally constrained estimates of stomatal uptake and parameterized estimates of cuticular and soil uptake reveal a large (10%-90%) residual nonstomatal contribution to v(d) (O-3). The residual downward flux of O-3 was well correlated with measurements of HCOOH upward flux, suggesting unaccounted for in-canopy gas-phase chemistry.

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