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. Despite the significant contribution of biogenic volatileorganic compounds (BVOCs) to organic aerosol formation and ozone productionand loss, there are few long-term, year-round, ongoing measurements oftheir volume mixing ratios and quantification of their impacts onatmospheric reactivity. To address this gap, we present 1 year of hourlymeasurements of chemically resolved BVOCs between 15 September 2019 and15 September 2020, collected at a research tower in Central Virginiain a mixed forest representative of ecosystems in the Southeastern US.Mixing ratios of isoprene, isoprene oxidation products, monoterpenes, andsesquiterpenes are described and examined for their impact on the hydroxyradical (OH), ozone, and nitrate reactivity. Mixing ratios of isoprene rangefrom negligible in the winter to typical summertime 24 h averages of 4–6 ppb, while monoterpenes have more stable mixing ratios in the range of tenths of a part per billion up to ∼2 ppb year-round. Sesquiterpenes aretypically observed at mixing ratios of &lt;10 ppt, but this representsa lower bound in their abundance. In the growing season, isoprene dominatesOH reactivity but is less important for ozone and nitrate reactivity.Monoterpenes are the most important BVOCs for ozone and nitrate reactivitythroughout the year and for OH reactivity outside of the growing season. Tobetter understand the impact of this compound class on OH, ozone, andnitrate reactivity, the role of individual monoterpenes is examined. Despitethe dominant contribution of α-pinene to total monoterpene mass, theaverage reaction rate of the monoterpene mixture with atmospheric oxidantsis between 25 % and 30 % faster than α-pinene due to thecontribution of more reactive but less abundant compounds. A majority ofreactivity comes from α-pinene and limonene (the most significantlow-mixing-ratio, high-reactivity isomer), highlighting the importance ofboth mixing ratio and structure in assessing atmospheric impacts ofemissions.

atmospheric chemistry and physics

Measurement report: Variability in the composition of biogenic volatile organic compounds in a Southeastern US forest and their role in atmospheric reactivity