Investigating Variability and Driving Factors for the Ensemble of Volatile Organic Compound Emissions from Pine Trees Using a Comprehensive Suite of Measurements

Plants emit biogenic volatile organic compounds (VOCs) that influence local and global atmospheric composition through complex feedback loops between atmospheric oxidants (e.g., ozone and hydroxyl radicals) and secondary organic aerosol. Factors influencing these emissions are complex and there exist many disagreements between leaf-level and canopy-level measurements of these compounds. To address these knowledge gaps, we conducted the Flux Closure Study (FluCS-2020) in a Ponderosa pine forest near Woodland Park, Colorado in summer and fall of 2020. This study aimed to understand how biogenic VOC emissions from Ponderosa pines varied as a function of environmental parameters including temperature, relative humidity, CO2, and light and how these VOC emissions correlated to plant physiology. We measured needle-level photosynthesis and an extensive range of emitted biogenic VOCs with a comprehensive instrument suite that simultaneously coupled a portable photosynthesis system to two chemical ionization mass spectrometers - one with an iodide reagent ion and one with proton transfer reaction ionization - and thermal desorption cartridges for analysis with gas chromatography-mass spectrometry. Highlights from the work include the importance of humidity as a driving variable for biogenic VOC emissions, the disconnect between plant CO2 assimilation rates and VOC emissions, and strong variability in both emissions and photosynthesis rates between needles of the same tree, branches of the same tree, and different trees.