Thermal history regulates methylbutenol basal emission rate in Pinus ponderosa

Methylbutenol (MBO) is a 5-carbon alcohol that is emitted by many pines in western North America, which may have important impacts on the tropospheric chemistry of this region. In this study, we document seasonal changes in basal MBO emission rates and test several models predicting these changes based on thermal history. These models represent extensions of the ISO G93 model that add a correction factor Cbasal, allowing MBO basal emission rates to change as a function of thermal history. These models also allow the calculation of a new emission parameter Estandard₃₀, which represents the inherent capacity of a plant to produce MBO, independent of current or past environmental conditions. Most single-component models exhibited large departures in early and late season, and predicted day-to-day changes in basal emission rate with temporal offsets of up to 3 d relative to measured basal emission rates. Adding a second variable describing thermal history at a longer time scale improved early and late season model performance while retaining the day-to-day performance of the parent single-component model. Out of the models tested, the Tamb,Tmax₇ model exhibited the best combination of day-to-day and seasonal predictions of basal MBO emission rates.