Seasonal variation of ozone deposition to a tropical rain forest in southwest Amazonia

Abstract

Abstract. Within the project EUropean Studies on Trace gases and Atmospheric CHemistry as a contribution toLarge-scale Biosphere-atmosphere experiment in Amazonia (LBA-EUSTACH), we performed tower-based eddy covariance measurements of O 3 flux above an Amazonian primary rain forest at the end of the wet and dry season. Ozone deposition revealed distinct seasonal differences in the magnitude and diel variation. In the wet season, the rain forest was an effective O 3 sink with a mean daytime (midday) maximum deposition velocity of 2.3 cm s −1 , and a corresponding O 3 flux of −11 nmol m −2 s −1 . At the end of the dry season, the ozone mixing ratio was about four times higher (up to maximum values of 80 ppb) than in the wet season, as a consequence of strong regional biomass burning activity. However, the typical maximum daytime deposition flux was very similar to the wet season. This results from a strong limitation of daytime O 3 deposition due to reduced plant stomatal aperture as a response to large values of the specific humidity deficit. As a result, the average midday deposition velocity in the dry burning season was only 0.5 cm s −1 . The large diel ozone variation caused large canopy storage effects that masked the true diel variation of ozone deposition mechanisms in the measured eddy covariance flux, and for which corrections had to be made. In general, stomatal aperture was sufficient to explain the largest part of daytime ozone deposition. However, during nighttime, chemical reaction with nitrogen monoxide (NO) was found to contribute substantially to the O 3 sink in the rain forest canopy. Further contributions Correspondence to: U. Rummel (udo.rummel@dwd.de) were from non-stomatal plant uptake and other processes that could not be clearly identified.Measurements, made simultaneously on a 22 years old cattle pasture enabled the spatially and temporally direct comparison of O 3 dry deposition values from this site with typical vegetation cover of deforested land in southwest Amazonia to the results from the primary rain forest. The mean ozone deposition to the pasture was found to be systematically lower than that to the forest by 30% in the wet and 18% in the dry season.

Dry deposition of nitrogen compounds (NO<sub>2</sub>, HNO<sub>3</sub>, NH<sub>3</sub>), sulfur dioxide and ozone in west and central African ecosystems using the inferential method

“…The V d of O 3 and SO 2 lie well within the range of values determined for other tropical forests (Matsuda et al, 2006, Rummel et al, 2007Tsai et al, 2010) and grasslands (Takahashi et al, 2001;Sorimachi et al, 2003). The modeled V d of NO 2 and NH 3 are within a reasonable range compared to reference values (Zhang et al, 2005Trebs et al, 2006;Kirkman et al, 2002;Delon et al, 2010;Endo et al, 2011).…”

“…Few observational studies of O 3 deposition fluxes for a long-term period are available over tropical areas, although several studies concerning the diurnal evolution have been conducted in the rainforests (Cros et al, , 2000Andreae et al, 1992;Rummel et al, 2007;Matsuda et al, 2005). The modeled O 3 V d in our study are within the range of values determined in other tropical ecosystems (Table 4).…”

“…The low values of O 3 dry deposition in forests are correlated to low values of O 3 concentrations that were 2 to 3 times lower than those measured in the other ecosystems (Table 2). Several studies have shown that tropical forests appear to be major O 3 sinks, through ground and foliage deposits and loss through chemical reactions with hydrocarbons and nitrogen oxides (Rummel at al., 2007;Jacob and Wofsy, 1990;Bakwin et al, 1990;Kaplan et al, 1988).…”

“…Tropospheric ozone (O 3 ) is known to harm human health, damage vegetation and lead to deterioration of materials. The dry deposition of O 3 is one of the most important sinks in the boundary layer ozone budget (Rummel et al, 2007).…”

A fast and precise chemiluminescence ozone detector for eddy flux and airborne application

“…It will play out its strength in particular for eddy-covariance flux measurements, usually at ground (Rummel et al, 2007) or ship (Bariteau et al, 2010) and aircraft observations (Ulanovsky et al, 2001;Bradshaw et al, 2002;Zahn et al, 2002).…”