Plants emit a diverse range of biogenic volatile organic compounds (BVOCs) into the atmosphere and these emissions are the dominant source of atmospheric VOCs. Many BVOCs have high chemical reactivities and contribute to ozone and secondary organic aerosol (SOA) production, which can influence climate and radiative forcing on a regional to global scale. Therefore, accurate estimations of BVOC emissions are needed to advance predictions of current and future climate scenarios. The magnitude of BVOC emissions is modulated by environmental conditions, principally light and temperature, and by external stresses (e.g., heat, drought, ozone). Current emission models perform well in characterizing the emission behavior of constitutive terpenoids at unstressed temperatures (less than approximately 35°C) but could sometimes underestimate the emission response from heat-stressed plants. In my dissertation, I investigated the effects of short-term (15–20 minutes) and longer-term (1–24 hours) heat stress on the BVOC emissions from different plant species via leaf-, branch-, and plant-scale enclosure measurements. My results indicate that plants with specialized terpenoid storage structures (i.e., glandular trichomes, resin ducts/glands, or secretory cavities) have a greater potential of emitting stress-induced terpenes at elevated temperatures (greater than approximately 37–40°C), which are not accounted for in current emission models. With climate warming and the increasing frequency and severity of heat waves, strong heat-induced BVOC emissions from plants with specialized terpenoid storage structures could potentially represent a large and unanticipated source of hydrocarbon emissions that could have important implications for regional and global atmospheric chemistry.

Biogenic volatile organic compounds (BVOCs) play a crucial role in the formation of tropospheric ozone and secondary organic aerosols (SOAs) due to their high chemical reactivity. Accurate estimation of BVOC emissions is essential for atmospheric chemistry modeling and understanding their impact on air quality and climate. Temperature and solar radiation are the primary environmental factors influencing BVOC emissions, and these factors are incorporated into the Model of Emissions of Gases and Aerosols from Nature (MEGAN) for estimating BVOC fluxes. While MEGAN effectively captures short-term BVOC emission responses to environmental changes, its performance diminishes under extreme conditions such as drought and heatwaves. Additionally, emission factors in MEGAN, defined as BVOC emission potential at 1000 mol m-2 s-1 of solar radiation and 30C temperature, need evaluation for more accurate emission estimates. This study investigates BVOC flux and concentration measurements in various types of forests to assess the impact of environmental factors on short-term (diurnal), intermediate-term (seasonal), and long-term (interannual) emission changes. In the first study, the diurnal emission variations of isoprene and monoterpenes during a growing season in warm temperate forests of Alabama confirmed that isoprene emissions are highly dependent on light and temperature, with MEGAN explaining most of their variation. Conversely, monoterpene emission variations, primarily temperature-dependent, are not fully captured by the model algorithms. Next, ambient BVOC sampling during wet and dry seasons over two years in tropical forests of Northern Thailand was investigated. The results indicate that severe drought could diminish isoprene emissions during the growing season, while monoterpene emissions showed minimal response to drought stress. The final study uses long-term isoprene flux measurements over six years in a hardwood temperate forest of Michigan to demonstrate that lower temperature years, associated with less heat stress, exhibited significantly higher isoprene emission factors compared to higher temperature years. MEGAN also underperformed in the year prone to drought and heat stress. Observations from all campaigns were used to estimate emission factors for MEGAN, enhancing the prediction accuracy. This comprehensive evaluation underscores the necessity of considering extreme environmental conditions and site-specific emission factors to improve BVOC emission modeling and its implications for air quality and climate projections.

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.