Abstract
Abstract. Biogenic volatile organic compounds (BVOCs) can react in the atmosphere to form organic nitrates, which serve as NOx (NO + NO2) reservoirs, impacting ozone and secondary organic aerosol production, the oxidative capacity of the atmosphere, and nitrogen availability to ecosystems. To examine the contributions of biogenic emissions and the formation and fate of organic nitrates in a forest environment, we simulated the oxidation of 57 individual BVOCs emitted from a rural mixed forest in northern Michigan. Key BVOC-oxidant reactions were identified for future laboratory and field investigations into reaction rate constants, yields, and speciation of oxidation products. Of the total simulated organic nitrates, monoterpenes contributed ~70% in the early morning at ~12 m above the forest canopy when isoprene emissions were low. In the afternoon, when vertical mixing and isoprene nitrate production were highest, the simulated contribution of isoprene-derived organic nitrates was greater than 90% at all altitudes, with the concentration of secondary isoprene nitrates increasing with altitude. Notably, reaction of isoprene with NO3 leading to isoprene nitrate formation was found to be significant (~8% of primary organic nitrate production) during the daytime, and monoterpene reactions with NO3 were simulated to comprise up to ~83% of primary organic nitrate production at night. Lastly, forest succession, wherein aspen trees are being replaced by pine and maple trees, was predicted to lead to increased afternoon concentrations of monoterpene-derived organic nitrates. This further underscores the need to understand the formation and fate of these species, which have different chemical pathways and oxidation products compared to isoprene-derived organic nitrates and can lead to secondary organic aerosol formation.
Highlights
Biogenic volatile organic compound (BVOC) emissions (∼ 1150 Tg C yr−1) comprise ∼ 90 % of total nonmethane VOC emissions, and isoprene and monoterpenes alone are estimated to account for ∼ 55 % of total nonmethane VOC emissions (Guenther et al, 1995; Goldstein and Galbally, 2007)
The fate of the 57 individual Biogenic volatile organic compounds (BVOCs) locally emitted from the mixed forest in northern Michigan and their role in organic nitrate formation in the lower troposphere was investigated
BVOC emission rates are difficult to determine due to tree-to-tree variability and sampling challenges during branch enclosure BVOC emission measurements (e.g., Ortega et al, 2008), leading to large ranges in estimated production rates, shown here to result in a range of oxidation product concentrations
Summary
Biogenic volatile organic compound (BVOC) emissions (∼ 1150 Tg C yr−1) comprise ∼ 90 % of total nonmethane VOC emissions, and isoprene and monoterpenes alone are estimated to account for ∼ 55 % of total nonmethane VOC emissions (Guenther et al, 1995; Goldstein and Galbally, 2007). These BVOCs typically have atmospheric lifetimes of minutes to hours for reactions with the hydroxyl (OH) radical, ozone (O3), and the nitrate (NO3) radical (Atkinson and Arey, 2003a). Organic nitrates (RONO2) are formed via reactions of VOCs with OH in the presence of NO, as shown in Reactions (1)–(3), which show H-atom abstraction from a C-H bond, followed by O2 addition yielding a peroxy radical that can react with NO to produce RONO2 (Orlando et al, 2003)
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