Dry deposition of nitrogen dioxide and ozone to coniferous forests

Abstract

The exchange of NO2, NO, and 0 3 between the atmosphere and coniferous forests has been studied by using a dynamic flow-through chamber technique. The measurements were performed during summer at two coniferous forest sites in Sweden, J•idrafis (Scots pine) and Simlfingsdalen (Scots pine and Norway spruce). In Simlfingsdalen, the flux of NO2 was found to be quantitatively determined by the stomatal openings. Generally, the flux of NO 2 was towards the vegetation surface, and only in a few cases a small emission of NO was detected. The average deposition velocities per projected needle area were 1.5 _+ 1.3 mm s -• for Norway spruce and 1.4 m 1.1 mm s -1 for Scots pine. The results from J•idrafis are slightly different; the deposition velocity of NO2, at concentrations lower than 1 ppbv, was always lower than the stomatal conductance and net emissions of NO2 were observed at concentrations below 0.5-0.7 ppbv. The average deposition velocity per projected needle area observed in J•idrafis was 0.8 -+ 0.7 mm s -• . In only a few cases, both for J•idrafis and Simlf. ngsdalen, the uptake of NO 2 was limited by mesophyllic resistance. The difference between Simlfingsdalen and J•idrafis may be attributed to physiological variations or nutrient supply. The exchange rate of NO between the air and vegetation per projected needle area was generally found to be less than the 2 1 detection limit of the method (0.1 ng N m-s-). The deposition velocity per projected needle area for 03 varied typically from 0 to 15.7 mm s -• in J•idra•ts and between 0 and 9.0 mm s -• in Simlfingsdalen, with average values of 3.1 and 2.5 mm s -•, respectively. The ratio between the deposition velocity for 03 and stomatal conductance was in general larger than one, indicating deposition of 03 to the external surfaces of the vegetation. The residual deposition of 03 showed a marked diurnal variation with maximum values around noon. It seems to follow a complex mechanism in which several factors such as light intensity, temperature, humidity and chemical properties of the surface of the cuticle might be important. No significant differences between Norway spruce and Scots pine species were observed in terms of the dry deposition of NO 2 and 03. The dry deposition of NO 2 to the forest floor is of the same magnitude as the deposition to the canopy. The average deposition velocity of NO 2 to the forest floor in Jgdrafis was equal to 4 mm s-1. The maximum contribution from the dry deposition of NO 2 to the total deposition of oxidized nitrogen compounds to the forest was estimated to be about 5% and 30% (as nitrogen) for J•idra•ts and Simlfingsdalen, respectively. The emission flux of NO from the forest soil is at least 4 times smaller than the deposition rate of NO 2 to the floor. 1. Several authors [Hill, 1971; Bennett and Hill, 1973; Eastman et al., 1981; Wesely, 1981; Ennis et al., 1990] have studied the possible pathways for the uptake of NO.,. and 0 3 by vegetation. The generally existing idea is that the uptake of NO,c and 03 by vegetation is mainl...

Leaf uptake of nitrogen dioxide (NO2) in a tropical wet forest: implications for tropospheric chemistry

“…Our observations support past studies that have reported the dependence of NO 2 uptake rate on stomatal conductance (Johansson 1987;Rondon et al 1993;Thoene et al 1991;Weber and Rennenberg 1996). However, we only observed evidence of stomatal control when conductances were below 0.5 mol m -2 s -1 (Fig.…”

“…3), which is consistent with previous studies (Johansson 1987;Rondon et al 1993;Thoene et al 1991; Each data point represents a single measurement tance to NO 2 assimilation or emission exists within the mesophyll tissue. Possible internal resistances include the disproportionation reaction of NO 2 in the apoplast and scavenging of NO 2 in the leaf apoplast by ascorbate or other free-radical scavenging compounds.…”

“…219 and Rennenberg 1996). The range of NO 2 compensation points measured for leaves in this study (0.52-1.60 ppbv) is comparable to the value of 1.15 ppbv reported in a past study of wheat leaves and 1.60-1.90 in beech trees (Gessler et al 2000;Kaplan et al 1988), but is somewhat higher than the range reported for coniferous trees (0.1-0.7 ppbv; Rondon et al 1993;Rondon and Granat 1994). NO 2 compensation points were generally related to leaf N concentration with the highest compensation points corresponding to the highest leaf N concentrations (Table 1).…”

“…1) that NO 2 uptake rates are substantial in tropical forest trees and that there is variation among species in their ability to take up or emit NO 2 . At NO 2 concentrations above the compensation point, the average uptake rate for NO 2 was similar in magnitude to that reported for other plant species (Hanson and Lindberg 1991;Okano et al 1986;Weber and Rennenberg 1996), but the maximum uptake rates we recorded (>1000 pmol m -2 s -1 ) were somewhat higher than those reported for temperate trees (Ammann et al 1995;Rondon et al 1993;Rondon and Granat 1994;Thoene et al 1996).…”

Tropospheric ozone and its precursors from the urban to the global scale from air quality to short-lived climate forcer

“…Given its reactive nature it is not unreasonable to find effects of surface temperature on R ns , and indications of such an effect were first reported by Rondon et al (1993). In their measurements of ozone deposition to a coniferous forest, they found that the surface resistance to ozone was much lower than that predicted by stomatal conductance alone and the residual term (R ns ) varied with air temperature, radiation and stomatal conductance.…”