Isoprene and monoterpene fluxes measured above Amazonian rainforest and their dependence on light and temperature

PUBLICATIONS Geophysical Research Letters RESEARCH LETTER 10.1002/2014GL062573 Key Points: • Mixing ratios of 12 Amazon monoterpenes reﬂect vertical forest structure • Light-dependent reactive monoterpene leaf emissions observed in ambient air • Monoterpene ozonolysis rates suggest important local aerosol precursor source Supporting Information: • Readme • Figure S1 • Figure S2 • Figure S3 • Figure S4 • Text S1 Correspondence to: A. B. Jardine, angela.jardine@inpa.gov.br Citation: Jardine, A. B., K. J. Jardine, J. D. Fuentes, S. T. Martin, G. Martins, F. Durgante, V. Carneiro, N. Higuchi, A. O. Manzi, and J. Q. Chambers (2015), Highly reactive light-dependent monoterpenes in the Amazon, Geophys. Res. Lett., 42, 1576–1583, doi:10.1002/2014GL062573. Received 19 NOV 2014 Accepted 1 FEB 2015 Accepted article online 4 FEB 2015 Published online 6 MAR 2015 Corrected 13 APR 2015 This article was corrected on 13 APR 2015. See the end of the full text for details. Highly reactive light-dependent monoterpenes in the Amazon A. B. Jardine 1 , K. J. Jardine 2 , J. D. Fuentes 3 , S. T. Martin 4 , G. Martins 1 , F. Durgante 1 , V. Carneiro 1 , N. Higuchi 1 , A. O. Manzi 1 , and J. Q. Chambers 2,5 Climate and Environment Department, Instituto Nacional de Pesquisas da Amazonia, Manaus, Brazil, 2 Climate Science Department, Earth Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA, 3 Department of Meteorology, College of Earth and Mineral Sciences, Pennsylvania State University, University Park, Pennsylvania, USA, School of Engineering and Applied Sciences and Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA, 5 Department of Geography, University of California, Berkeley, California, USA Abstract Despite orders of magnitude difference in atmospheric reactivity and great diversity in biological functioning, little is known about monoterpene speciation in tropical forests. Here we report vertically resolved ambient air mixing ratios for 12 monoterpenes in a central Amazon rainforest including observations of the highly reactive cis-β-ocimene (160 ppt), trans-β-ocimene (79 ppt), and terpinolene (32 ppt) which accounted for an estimated 21% of total monoterpene composition yet 55% of the upper canopy monoterpene ozonolysis rate. All 12 monoterpenes showed a mixing ratio peak in the upper canopy, with three demonstrating subcanopy peaks in 7 of 11 proﬁles. Leaf level emissions of highly reactive monoterpenes accounted for up to 1.9% of photosynthesis conﬁrming light-dependent emissions across several Amazon tree genera. These results suggest that highly reactive monoterpenes play important antioxidant roles during photosynthesis in plants and serve as near-canopy sources of secondary organic aerosol precursors through atmospheric photooxidation via ozonolysis. 1. Introduction Many tree species produce monoterpenes (C 10 H 16 ), a diverse class of volatile terpenoids, which can be emitted into the atmosphere at high rates [Kesselmeier and Staudt, 1999; Fuentes et al., 2000]. Within ecosystems, monoterpenes mediate plant-microbe [Dorman and Deans, 2000] and plant-insect [Beyaert and Hilker, 2014] interactions and protect photosynthesis during abiotic stress [Penuelas and Llusia, 2002; Vickers et al., 2009]. Fueled by large total monoterpene emissions from forested ecosystems [Karl et al., 2002, 2003, 2004], atmospheric photochemical oxidation of monoterpenes generates low-volatility oxidation products that can partition to the particle phase [Yu et al., 1999; Fuentes et al., 2000; Kurpius and Goldstein, 2003; Mcfrederick et al., 2008; Martin et al., 2010]. These oxidation products, along with the oxidation products of isoprene (C 5 H 8 ), sesquiterpenes (C 15 H 24 ), and possibly higher-order terpenoids (C 20 H 32 and above), play important roles in the formation and growth of secondary organic aerosol (SOA) particles that can activate into cloud condensation nuclei [Claeys et al., 2004; Poschl et al., 2010]. Monoterpene ozonolysis reactions are important for SOA formation [Presto et al., 2005; Zhao et al., 2014] and postnucleation growth processes [Presto et al., 2005; Hao et al., 2009]. Further, the studies of Goldstein et al. [2004] and Fares et al. [2010] demonstrated that O 3 ﬂuxes above a ponderosa pine forest (Pinus ponderosa) were dominated by gas phase chemistry, and their results suggested highly reactive monoterpenes likely contributing to a “missing” within-canopy O 3 sink. Thus, characterization of speciated monoterpenes and their associated ozonolysis reactions in the atmosphere is important for a comprehensive understanding of SOA sources [Chen et al., 2009]. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distri- bution in any medium, provided the original work is properly cited, the use is non-commercial and no modiﬁcations or adaptations are made. JARDINE ET AL. Little is known about monoterpene composition in the tropics—a widely recognized major global source of terpenoids to the atmosphere [Guenther et al., 1995]. To date, only a few ﬁeld observations targeting plant and atmospheric monoterpenes have been reported from the Amazon. Ambient levels of monoterpenes including α-pinene, β-pinene, and p-cymene have been reported [Helmig et al., 1998; Rinne et al., 2002; Kuhn et al., 2007] as well as low levels of highly reactive monoterpenes including myrcene, terpinolene, α-phellandrene and α-terpinene [Kesselmeier et al., 2000]. Other atmospheric monoterpene studies in the Amazon used the online technique of proton transfer reaction-mass spectrometry (PTR-MS), ©2015. The Authors.