Within-canopy sesquiterpene ozonolysis in Amazonia

Abstract

[1] Through rapid reactions with ozone, which can initiate the formation of secondary organic aerosols, the emission of sesquiterpenes from vegetation in Amazonia may have significant impacts on tropospheric chemistry and climate. Little is known, however, about sesquiterpene emissions, transport, and chemistry within plant canopies owing to analytical difficulties stemming from very low ambient concentrations, high reactivities, and sampling losses. Here, we present ambient sesquiterpene concentration measurements obtained during the 2010 dry season within and above a primary tropical forest canopy in Amazonia. We show that by peaking at night instead of during the day, and near the ground instead of within the canopy, sesquiterpene concentrations followed a pattern different from that of monoterpenes, suggesting that unlike monoterpene emissions, which are mainly light dependent, sesquiterpene emissions are mainly temperature dependent. In addition, we observed that sesquiterpene concentrations were inversely related with ozone (with respect to time of day and vertical concentration), suggesting that ambient concentrations are highly sensitive to ozone. These conclusions are supported by experiments in a tropical rain forest mesocosm, where little atmospheric oxidation occurs and sesquiterpene and monoterpene concentrations followed similar diurnal patterns. We estimate that the daytime dry season ozone flux of −0.6 to −1.5 nmol m −2 s −1 due to in-canopy sesquiterpene reactivity could account for 7%-28% of the net ozone flux. Our study provides experimental evidence that a large fraction of total plant sesquiterpene emissions (46%-61% by mass) undergo within-canopy ozonolysis, which may benefit plants by reducing ozone uptake and its associated oxidative damage.

Rapid deposition of oxidized biogenic compounds to a temperate forest

“…For example, the in-canopy ozonolysis of sesquiterpenes (τ ≈ 1-2 min) has been estimated to consume 0.6-1.5 nmol·m −2 ·s −1 (7-28%) of the downward ozone flux and 46-61% of the sesquiterpenes mass in Amazonia (48). Approximately 6% of the ozone flux at this site is required to account for the entire formic acid flux.…”

Direct measurement of NO<sub>3</sub> reactivity in a boreal forest

“…CC BY 4.0 License. sesquiterpenes concentrations can peak at ground level rather than within the canopy (Jardine et al, 2011), though the applicability of this result to the boreal forest is unclear.…”

Ozone stress as a driving force of sesquiterpene emissions: a suggested parameterisation

“…Filella et al (2007) concluded that algorithms which use only incident irradiance and leaf temperature as drivers to predict VOC emission rates may be inadequate. As the review of Holopainen and Gershenzon (2010) has shown, the interaction of multiples stresses, both biotic and abiotic, provides a great potential to alter VOC emission. It is most likely that other environmental factors such as drought, ozone and CO 2 concentrations can amplify or attenuate such alterations in the emission responses to temperature and light .…”

“…Enclosure approaches "cannot be used to estimate emission rates without the exclusion or corrections of ozone and disturbance effects during the studies" (Jardine et al, 2011). In order to correct for ozone destruction during the sampling process, selected branch emissions were studied by GC-MS technique at the Finnish Meteorological Institute in Helsinki and compared with the chemical analysis performed earlier at Mainz University (Münz, 2010) for the site of interest.…”

“…They have been hypothesized to protect plants from oxidative damage under elevated concentrations of reactive oxygen species (Vickers et al, 2009). Especially SQT, react readily with atmospheric ozone, with a high potential to form secondary organic aerosol (Hoffmann et al, 1997;Jaoui et al, 2003;Bonn et al, 2008). Their vital role on atmospheric chemistry is stressed out by their ability to influence the oxidative capacity of the atmosphere (Fuentes et al, 2000) and their contribution to secondary organic aerosol production (Hoffmann et al, 1997;Andreae and Crutzen, 1997;Bonn et al, 2003;Kulmala et al, 2004).…”