Vertical ozone fluxes and related deposition parameters over agricultural and forested landscapes

Abstract

The spatial variability and temporal behavior of the vertical flux of ozone have been investigated from turbulence measurements collected on aircraft flight legs in the daytime period during two consecutive summer experimental field programs. The data were obtained during horizontal flight legs conducted over agricultural crops and forested land in three different regions of the eastern United States.Results from individual experimental cases and statistics derived from all cases in each region are presented. Ozone flux generally exhibited a significant height dependency. The strongest negative (downward) fluxes in the lowest-level flight legs were primarily attributed to the uptake of ozone by the surface and vegetative cover. Fluxes were near-zero in the middle of the convective boundary layer (CBL) in the afternoon period. As ozone flux was proportional to concentration, slightly stronger fluxes were found in low-level urban plume segments where ozone concentrations were 10-20ppb higher than in the surrounding area. The derived deposition velocity showed no such bias as a function of position across the urban plume. Ozone flux differences were not apparent between the more heavily forested sections and the primarily agricultural cropland areas in these regions. During the afternoon period when no clear temporal trend was evident, means from values obtained below O.lSZ; (Z, being the CBL height) were -0.421 and -0.431 ppb m-* s-r for ozone flux and 0.81 and 0.82 cm s-r for the derived mean deposition velocity in the southeastern Pennsylvania and central Ohio areas, respectively. These experimental results for ozone provide support to a dry deposition parameterization module which computes grid-area averaged deposition velocities for use in regional-scale models.

A novel ozone sensor for direct eddy flux measurements

“…Considering that the two independent micrometeorological techniques are field measurement techniques, the correspondence of both diurnal variations of the dry deposition velocity is fair. The dry deposition velocities range between 0.2 and 1.0 cm s q, which is consistent with previous observations (Wesely, 1983;Neumann and Den Hartog, 1985;Colbeck and Harrison, 1985;Droppo, 1985;Delany et al, 1986, Godowitch, 1990. Thus, the novel rapid-response ozone sensor described here is well suited for direct eddy flux measurements.…”

Dry Deposition of Ozone Over Land: Processes, Measurement, and Modeling

“…Not only is nonstomatal uptake nonnegligible, but it is also highly variable. Observationally based studies illustrate unexpected variations in nonstomatal deposition in diel cycles (Coe et al, ; Rondón et al, ) including over soil and snow (Fumagalli et al, ; Helmig, Cohen, et al, ; Stella, Loubet, et al, ; Stella et al, ), year‐to‐year variability (Clifton et al, ; Rannik et al, ), after rain and dew (Fuentes et al, ; Potier et al, ), and spatially (Clifton et al, ; Godowitch, ; Lenschow et al, ; Mahrt et al, ; Wolfe et al, ). Measurements also show that ambient chemistry with unmeasured biogenic volatile organic compounds (BVOCs) influences ozone flux observations (Goldstein et al, ; Kurpius & Goldstein, ; Wolfe et al, ).…”