Leaf Stomatal Uptake of Alkyl Nitrates

Abstract

The relative role of the formation of atmospheric multifunctional and alkyl nitrates (RONO2) is expected to increase as anthropogenic emissions of NO and NO2 continue to decrease. A more complete understanding of the chemistry and fate of RONO2 will therefore be needed in order to describe the composition of our atmosphere. In this study, we investigate the atmospheric loss of three alkyl nitrates via deposition to tree branches. Using a dynamic chamber, we measure deposition fluxes of isopropyl nitrate (IPN), methylbutyl nitrate (MBN), and ethylhexyl nitrate (EHN) to Pinus sabiniana branches. Flux measurements showed a linear relationship between the stomatal uptake of EHN and MBN and their respective ambient chamber concentration and that deposition occurred solely through a leaf stomatal pathway. No significant deposition of IPN to Pinus sabiniana was observed. The measured rates of MBN and EHN deposition were too fast to be described by a dissolution/hydrolysis mechanism, indicating that uptake was likely driven by an alternative process. We compared our measured deposition rates of MBN and EHN with their photochemical losses and conclude that the stomatal uptake of these compounds could be an important loss process for these RONO2 under favorable biological and meteorological conditions.