UC Irvine

The heatwave and drought stresses induced by rapid climate change can alter the emission of isoprene from terrestrial ecosystems. This, in turn, affects climate and air quality by modifying photochemistry and forming secondary organic aerosols. Understanding the complex interactions and feedback loops between climate and isoprene emissions is a challenging yet urgent task. This study integrates laboratory experiments and in-situ measurements to investigate and model these impacts within the Model of Emissions of Gases and Aerosols from Nature (MEGAN).In the first chapter, an empirical algorithm was developed to simulate drought effects on isoprene emissions, revealing an 11% global decrease in isoprene in 2012 due to drought. This algorithm improved the agreement between model simulations and satellite formaldehyde observations during droughts, as formaldehyde is widely used as a proxy for isoprene. However, its performance was limited by the model's ability to accurately capture drought severity. The second and third chapters focus on Arctic ecosystems, where rapid warming is accelerating isoprene emissions. The second chapter characterizes the temperature response of Arctic willows, finding that their hourly temperature response curve is similar to that of temperate plants. Isoprene emissions increase with rising temperature, reaching an optimal level before declining due to enzyme denaturation. Additionally, the isoprene capacity of willows could increase rapidly with rising ambient temperatures from the previous day. During heatwaves, Arctic willows exhibited a 66% higher isoprene emission when using a modified algorithm based on my measurements. The third chapter investigates sedges, another major Arctic isoprene emitter, and finds that their temperature response is notably stronger compared to other isoprene emitters. Integrating these findings into MEGAN improved the capacity of model to reproduce observations. The omission of these strong temperature responses from both willows and sedges led to a 20% underestimation of isoprene emissions in high-latitude regions between 2000 and 2009, and a 55% underestimation of long-term trends from 1960 to 2009. Therefore, rapid warming in the Arctic could significantly increase isoprene emissions, altering local chemistry and impacting the climate.