Variability in the composition of biogenic volatile organic compounds in a southeastern US forest and its role in atmospheric reactivity

Abstract:

Despite their significant contribution to organic aerosol and role in ozone production and loss, there are few long-term year-round measurements of biogenic volatile organic compounds (BVOCs) with molecule-level chemical resolution. These measurements are critical, as BVOC emissions vary widely due to ecosystem composition and environmental factors, and with different BVOCs having widely varying reaction rates with atmospheric oxidants and aerosol yields. To address this gap, hourly measurements of chemically resolved BVOCs are being collected at a research tower outside of Charlottesville, VA in a mixed forest representative of the Southeastern U.S. The measurements are taken using a custom-built, field deployable gas chromatograph (GC) - flame ionization detector (FID) capable of measuring concentrations of individual BVOCs from all major terpenoid classes: isoprene (C₅H₈), monoterpenes (C₁₀H₁₆), and sesquiterpenes (C₁₅H₂₄). Approximately one year of measurements are currently available and are planned to continue over the next two years, alongside measurements of many other ecological and meteorological parameters. Measured gases account for up to 35 s^-1 OH reactivity and 10 х 10^-6 s^-1 O₃ reactivity. High levels of isoprene in the summer are a major contributor to summertime reactivity, while monoterpenes are detected year-round at ppbv-level concentrations. Limonene and α-pinene are consistently major species, but relative contributions of these and other monoterpenes have significant impacts on the reactivity of the monoterpene mixture. We focus in this presentation on the short- and long-term variability in monoterpene composition and its implications for atmospheric reactivity and aerosol yield.