Monoterpenes Play Important Antioxidant Roles, Serve as Sources of Secondary Organic Aerosol Precursors
Despite orders of magnitude difference in atmospheric reactivity and great diversity in biological functioning, little is known about monoterpene speciation in tropical forests. In a recent study, researchers 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 parts per trillion (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 seven 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.
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,” Geophysical Research Letters 42(5), 1576–83. DOI: 10.1002/2014GL062573.