Measurement report: Age-dependent BVOC emissions in <i>Eucalyptus urophylla</i> : a comparison of leaf cuvette and branch chamber measurements

Abstract. Biogenic volatile organic compound (BVOC) emission factors (Es) underpin air quality and climate models, yet current databases intermingle data from both greenhouse seedlings and field mature trees and from two enclosure techniques, leaf cuvettes and dynamic branch chambers, whose comparability has rarely been rigorously tested. Here we quantified BVOC emissions from Eucalyptus urophylla by pairing the two methods on a statistically representative number of 2-month-old seedlings in the laboratory and 2-year-old in-situ saplings measured at a managed plantations in subtropical China. Leaf-cuvette and branch-chamber determination of isoprene Es matched within 5 % for both age classes, demonstrating method equivalence. In contrast, tree age exerted a significant impact on both the magnitude and speciation of emissions. Seedlings emitted ∼ 50 % more isoprene and were enriched in cyclic monoterpenes like α-pinene and 1,8-cineole, whereas field-grown trees shifted toward highly reactive acyclic monoterpenes, with β-ocimenes accounted for over 85 % of the terpene flux and a double rise in sesquiterpenes. These ontogenetic shifts imply that one-third of the entries in global Es compilations, which are derived from seedling studies, are likely inappropriate as generic surrogates for natural forest emissions. Our results validate the use of either chamber type for measuring isoprene Es, highlight the need for improved analytical sensitivity before extending this equivalence to terpenes, and call for systematic, large-sample, branch-level measurements of adult trees to produce representative Es values. Incorporating age-resolved emission factors into models will refine estimates of ozone and secondary organic aerosol formation in fast-growing subtropical plantations and other managed forests worldwide.