Laboratory measurements of stomatal NO.sub.2 deposition to native California trees and the role of forests in the NO.sub.x cycle

• Published in: Atmospheric chemistry and physics 2020-11, Vol.20 (22), p.14023
• Main Authors: Delaria, Erin R, Place, Bryan K, Liu, Amy X, Cohen, Ronald C
• Format: Article
• Language: English
• ISSN: 1680-7316; 1680-7324

Both canopy-level field measurements and laboratory studies suggest that uptake of NO.sub.2 through the leaf stomata of vegetation is a significant sink of atmospheric NO.sub.x . However, the mechanisms of this foliar NO.sub.2 uptake and their impact on NO.sub.x lifetimes remain incompletely understood. To understand the leaf-level processes affecting ecosystem-scale atmosphere-biosphere NO.sub.x exchange, we have conducted laboratory experiments of branch-level NO.sub.2 deposition fluxes to six coniferous and four broadleaf native California trees using a branch enclosure system with direct laser-induced fluorescence (LIF) detection of NO.sub.2 . We report NO.sub.2 foliar deposition that demonstrates a large degree of inter-species variability, with maximum observed deposition velocities ranging from 0.15 to 0.51 cm s.sup.-1 during the daytime, as well as significant stomatal opening during the night. We also find that the contribution of mesophyllic processing to the overall deposition rate of NO.sub.2 varies by tree species but has an ultimately inconsequential impact on NO.sub.x budgets and lifetimes. Additionally, we find no evidence of any emission of NO.sub.2 from leaves, suggesting an effective unidirectional exchange of NO.sub.x between the atmosphere and vegetation.