Abstract. Despite the significant contribution of biogenic volatile organic compounds (BVOCs) to organic aerosol formation and ozone production and loss, there are few long-term, year-round, ongoing measurements of their concentrations and their impacts on atmospheric reactivity. To address this gap, we present one year of hourly measurements of chemically resolved BVOCs between September 15, 2019, and September 15, 2020, collected at a research tower in Central Virginia in a mixed forest representative of ecosystems in the Southeastern U.S. Concentrations of isoprene, isoprene reaction products, monoterpenes, and sesquiterpenes are described and examined for their impact on hydroxy radical (OH), ozone, and nitrate reactivity. Concentrations of isoprene range from negligible in the winter to typical summertime 24-hour averages of 4–6 ppb, while monoterpenes have more stable concentrations in the range of tenths of a ppb up to ~ 1 ppb year-round. Sesquiterpenes are typically observed at concentrations of < 10 ppt, but this represents a lower bound in their abundance. In the growing season, isoprene dominates OH reactivity but is less important for ozone and nitrate reactivity. Monoterpenes are the most important BVOCs for ozone and nitrate reactivity throughout the year and for OH reactivity outside of the growing season. To better understand the impact of this compound class on OH, ozone, and nitrate reactivity, the role of individual monoterpenes is examined. Despite the dominant contribution of α-pinene to total monoterpene mass, the average rate constants for reaction of the monoterpene mixture with atmospheric oxidants is between 20% and 30% faster than α-pinene due to the contribution of more-reactive but less abundant compounds. A majority of reactivity comes from α-pinene and limonene (the most significant low-concentration, high-reactivity isomer), highlighting the importance of both concentration and structure in assessing atmospheric impacts of emissions.
Measurement report: Variability in the composition of biogenic volatile organic compounds in a Southeastern US forest and their role in atmospheric reactivity
