Large emissions of sesquiterpenes and methyl chavicol quantified from branch enclosure measurements

Multiple field studies have suggested chemistry within a forest canopy is poorly understood due to inadequate detection and quantification of reactive biogenic emissions, such as terpenes. To measure emission rates of terpenes at Blodgett Forest, a coniferous forest in the Sierra Nevada mountains of California, we placed enclosures over branches of the dominant species at the site – Ponderosa pine, manzanita, and ceanothus – in the summer of 2005. Zero air, with ambient CO2 concentrations, flowed through the chamber system and volatile organic compound (VOC) emission measurements were made by proton transfer reaction mass spectrometry (PTR-MS), solid phase microextraction (SPME) on fibers followed by direct injection into a gas chromatograph with an ion trap mass spectrometer (GC-ITMS), and by in situ GC with a flame ionization detector (GC-FID). We show that previously undetected sesquiterpenes and methyl chavicol significantly contribute to the total reactive biogenic emission profile from this field site.