Estimations of isoprenoid emission capacity from enclosure studies: measurements, data processing, quality and standardized measurement protocols

Abstract. The capacity for volatile isoprenoid production under standardized environmental conditions at a certain time (E_S, the emission factor) is a key characteristic in constructing isoprenoid emission inventories. However, there is large variation in published E_S estimates for any given species partly driven by dynamic modifications in E_S due to acclimation and stress responses. Here we review additional sources of variation in E_S estimates that are due to measurement and analytical techniques and calculation and averaging procedures, and demonstrate that estimations of E_S critically depend on applied experimental protocols and on data processing and reporting. A great variety of experimental setups has been used in the past, contributing to study-to-study variations in E_S estimates. We suggest that past experimental data should be distributed into broad quality classes depending on whether the data can or cannot be considered quantitative based on rigorous experimental standards. Apart from analytical issues, the accuracy of E_S values is strongly driven by extrapolation and integration errors introduced during data processing. Additional sources of error, especially in meta-database construction, can further arise from inconsistent use of units and expression bases of E_S. We propose a standardized experimental protocol for BVOC estimations and highlight basic meta-information that we strongly recommend to report with any E_S measurement. We conclude that standardization of experimental and calculation protocols and critical examination of past reports is essential for development of accurate emission factor databases.