UC Irvine

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.