Exchange of short‐chain monocarboxylic acids by vegetation at a remote tropical forest site in Amazonia

Abstract

[1] As part of the project LBA-EUSTACH (European Studies on Trace gases and Atmospheric Chemistry as a contribution to the Large-Scale Biosphere-Atmosphere experiment in Amazonia), the exchange of formic acid and acetic acid between vegetation and the atmosphere was investigated in the wet-to-dry season transition and the dry-to-wet season transition periods in 1999 in Rondônia, Brazil. Direct exchange measurements on the branch level mainly exhibited uptake of formic acid and acetic acid for all plant species in both seasons, although diel, seasonal, and interspecies variations were observed. Even though other physiological and physico-chemical parameters may have contributed, the uptake of organic acids was found to be primarily a function of the ambient atmospheric mixing ratios. The linear dependence suggests a bidirectional exchange behavior of the plants and calculated deposition velocities (0.17-0.23 cm s À1 ), compensation point mixing ratios (0.16-0.30 ppb), and potential emission rates under purified air conditions (0.013-0.031 nmol m À2 s À1 ) are discussed. Vertical profile measurements in and above the primary forest canopy further strengthened the assumption that the forest is rather a sink than a source for organic acids. The generally lower mixing ratios observed within the canopy were indicative of an uptake by vegetation and/or the soil surface. Continuous measurements of the ambient atmospheric mixing ratios at the canopy top revealed strong diel variations in both seasons and a marked seasonality with higher mixing ratios during the dry season, both being mirrored in the variation of observed uptake rates of the plants. High atmospheric concentrations during the dry season were attributed to biomass burning. During the wet season, when biomass burning activity was low, indirect emission by the vegetation, i.e., photochemical oxidation of primarily emitted biogenic reactive hydrocarbons, was assumed to dominantly contribute to the atmospheric burden of the organic acids. The high degree of correlation between atmospheric formic acid and acetic acid indicated that similar atmospheric processes were affecting their mixing ratios.

Urban and rural observations of carboxylic acids in rainwater in Southwest of China: the impact of urbanization

“…It was estimated the anthropogenic activity could be insignificant in this area. As a result, the seasonal variations of carboxylic acids indicate the biogenic emissions from vegetation dominated the sources of carboxylic acids in this site which was consistently with previous studies (Talbot et al 1990;Kuhn et al 2002;Peña et al 2002). However, the remarkable opposite seasonal pattern of carboxylic acids were observed in Guiyang (Fig.…”

“…Formic, acetic and oxalic acids were roughly 8, 10 and 2 times higher than that during the non-growing season, respectively. The seasonal variations of carboxylic acids in rainwater point to the importance of vegetation emissions (Kuhn et al 2002). The seasonal study of formic and acetic acids in rainwater was firstly made by Keene and Galloway (1986).…”

OH reactivity in a South East Asian tropical rainforest during the Oxidant and Particle Photochemical Processes (OP3) project

“…However, the solubility of many hydroperoxides and other oxygenated organics is extremely uncertain and known to cover a wide range, with the measured Henry's law constants for methyl hydroperoxide and peroxyacetic acid being 2-3 orders of magnitude lower than that for H2O2 [Lind and Kok, 1986]. Observations of OVOC deposition velocities are sparse, with only a handful reported for forested regions [Hall and Claiborn, 1997;Valverde-Canossa et al, 2006;Hall et al, 1999;Karl et al, 2004;Kuhn et al, 2002]. An observation of the deposition velocity of the sum of MVK and MACR in a Fig.…”

“…2006; Hall et al, 1999;Karl et al, 2004;Kuhn et al, 2002). An observation of the deposition velocity of the sum of MVK and MACR in a tropical rainforest by Karl et al (2004) found velocities of 0.45 ± 0.15 cm s −1 .…”

The effect of flooding on the exchange of the volatile C<sub>2</sub>-compounds ethanol, acetaldehyde and acetic acid between leaves of Amazonian floodplain tree species and the atmosphere

“…Moreover, measurements by conventional techniques showed predominantly a deposition of acetaldehyde and acetic acid at rates which were linearly correlated to the ambient air concentrations. The compensation points were in the range of 0.1 to 1.1 ppb, suggesting that under natural ambient air conditions Amazonian floodplain forests may represent a sink for these oxygenated compounds during the non-flooded terrestrial phase, similar to vegetation from the adjacent terra firme forests Kuhn et al, 2002) or European forests (Kesselmeier 2001). Contrasting these low compensation points, Jardin et al (2008) observed very high compensation points for poplar (>12 ppb) and Holm oak (>22 ppb) in the light and suggested that solar radiation and/or temperature may have a large impact on acetaldehyde exchange patterns, due to a stimulation of acetaldehyde production in leaves.…”