Diel and seasonal changes of biogenic volatile organic compounds within and above an Amazonian rainforest

Abstract

Abstract. The Amazonian rainforest is a large tropical ecosystem, which is one of the last pristine continental terrains. This ecosystem is ideally located for the study of diel and seasonal behaviour of biogenic volatile organic compounds (BVOCs) in the absence of local human interference. In this study, we report the first atmospheric BVOC measurements at the Amazonian Tall Tower Observatory (ATTO) site, located in central Amazonia. A quadrupole proton-transfer-reaction mass spectrometer (PTR-MS), with seven ambient air inlets, positioned from near ground to about 80 m (0.05, 0.5, 4, 24, 38, 53 and 79 m above the forest floor), was deployed for BVOC monitoring. We report diel and seasonal (February-March 2013 as wet season and September 2013 as dry season) ambient mixing ratios for isoprene, monoterpenes, isoprene oxidation products, acetaldehyde, acetone, methyl ethyl ketone (MEK), methanol and acetonitrile. Clear diel and seasonal patterns were observed for all compounds. In general, lower mixing ratios were observed during night, while maximum mixing ratios were observed during the wet season (February-March 2013), with the peak in solar irradiation at 12:00 LT (local time) and during the dry season (September 2013) with the peak in temperature at 16:00 LT. Isoprene and monoterpene mixing ratios were the highest within the canopy with a median of 7.6 and 1 ppb, respectively (interquartile range (IQR) of 6.1 and 0.38 ppb) during the dry season (at 24 m, from 12:00 to 15:00 LT). The increased contribution of oxygenated volatile organic compounds (OVOCs) above the canopy indicated a transition from dominating forest emissions during the wet season (when mixing ratios were higher than within the canopy), to a blend of biogenic emission, photochemical production and advection during the dry season when mixing ratios were higher above the canopy. Our observations suggest strong seasonal interactions between environmental (insolation, temperature) and biological (phenology) drivers of leaf BVOC emissions and atmospheric chemistry. Considerable differences in the magnitude of BVOC mixing ratios, as compared to other reports of Amazonian BVOC, demonstrate the need for long-term observations at different sites and more standardized measurement procedures, in order to better characterize the natural exchange of BVOCs between the Amazonian rainforest and the atmosphere.

Volatile organic compounds (VOCs) in photochemically aged air from the eastern and western Mediterranean

“…This is in contrast to tropical forest regions where typical values of 7.6 ppbv isoprene and 1 ppbv monoterpene have been reported recently (Yañez Serrano et al, 2015) and boreal forest regions where levels of isoprene and monoterpenes are ca. 100 and 300 pptv respectively (Yassaa et al, 2012).…”

Monoterpene chemical speciation in a tropical rainforest:variation with season, height, and time of dayat the Amazon Tall Tower Observatory (ATTO)

“…The limit of detection of the PTR-MS for total monoterpenes was 0.1 and 0.2 ppb for isoprene, determined as 3σ of the background noise. More information about the gradient system and PTR-MS operation at ATTO can be found elsewhere Yáñez-Serrano et al, 2015).…”

“…Considering the overall size of the Amazon rainforest (5.4 million km 2 in 2001; Malhi et al, 2008) and the significant contribution of biogenic volatile organic compound (BVOC) emissions from this vast forest to the global volatile organic compound (VOC) budget (globally 1000 Tg of carbon yr −1 ; Guenther et al, 2012), measurements of total monoterpene emissions and mixing ratios from this ecosystem are scarce (Greenberg and Zimmerman, 1984;Helmig et al, 1998;Jardine et al, 2015Jardine et al, , 2011Jardine et al, , 2017Karl et al, 2007;Rinne et al, 2002;Yáñez-Serrano et al, 2015). Speciated measurements are even more rare (Jardine et al, , 2017Kesselmeier et al, 2002;Kuhn et al, 2004).…”

Long-term observations of cloud condensation nuclei in the Amazon rain forest – Part 2: Variability and characteristic differences under near-pristine, biomass burning, and long-range transport conditions

“…of the Amazonian atmosphere (Martin et al, 2010b;Andreae et al, 2015). During this time of the year, biogenic aerosols from the surrounding rain forest ecosystem, such as secondary organic aerosol (SOA) from the oxidation of biogenic volatile organic compounds (BVOC) as well as primary biological aerosol particles (PBAP), prevail (Pöschl et al, 2010;Huffman et al, 2012;Yanez-Serrano et al, 2015). However, the regionally and biogenically dominated background state of the atmosphere is frequently perturbed by the episodic advection of 5 long-range transport (LRT) aerosols from Africa in air masses that bypass the major rain fields and, therefore, 'survive' the intense scavenging (Moran-Zuloaga et al, 2017).…”