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

Abstract

Abstract. Both canopy-level field measurements and laboratory studies suggest that uptake of NO2 through the leaf stomata of vegetation is a significant sink of atmospheric NOx. However, the mechanisms of this foliar NO2 uptake and their impact on NOx lifetimes remain incompletely understood. To understand the leaf-level processes affecting ecosystem-scale atmosphere–biosphere NOx exchange, we have conducted laboratory experiments of branch-level NO2 deposition fluxes to six coniferous and four broadleaf native California trees using a branch enclosure system with direct laser-induced fluorescence (LIF) detection of NO2. We report NO2 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−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 NO2 varies by tree species but has an ultimately inconsequential impact on NOx budgets and lifetimes. Additionally, we find no evidence of any emission of NO2 from leaves, suggesting an effective unidirectional exchange of NOx between the atmosphere and vegetation.

Impacts of Soil NOx Emission on O3 Air Quality in Rural California

“…However, its default canopy reduction scheme is not mechanistic in nature and may not accurately represent the temporal and spatial variability in canopy effects. We thus stress that future users of the model should implement a more appropriate canopy reduction scheme for their application, which can be achieved by using stomatal uptake to calculate the CRF through analyzing the laboratory measurements of stomatal NO 2 deposition to local vegetation . In addition, the biome emission factors (e.g., grassland, savannas, and needleleaf) based on the work of Steinkamp and Lawrence and the emission factor associated with fertilization (set to 2.5% in BDISNP) are uncertain and may be underestimated.…”

“…We thus stress that future users of the model should implement a more appropriate canopy reduction scheme for their application, which can be achieved by using stomatal uptake to calculate the CRF through analyzing the laboratory measurements of stomatal NO 2 deposition to local vegetation. 63 In addition, the biome emission factors (e.g., grassland, savannas, and needleleaf) based on the work of Steinkamp and Lawrence 26 and the emission factor associated with fertilization (set to 2.5% in BDISNP) are uncertain and may be underestimated. Consequently, a more intensive evaluation of the BDISNP scheme is needed when ground-based measurements of NO x flux are available to improve the parameterization in future studies.…”

Forest–atmosphere exchange of reactive nitrogen in a remote region – Part I: Measuring temporal dynamics

“…The concentration of NH 3 was still lower than of NO 2 , but the v d of NH 3 is significantly higher than of NO 2 for woodland. Deposition velocities of NH 3 range between 1.1 and 2.2 cm s −1 (see Schrader and Brümmer, 2014, and references therein), and values between 0.015 and 0.51 cm s −1 were reported for NO 2 (e.g., Rondon et al, 1993;Horii et al, 2004;Breuninger et al, 2013;Delaria et al, 2018Delaria et al, , 2020. However, variations in the composition of N r may correlate with micrometeorological parameters.…”

Assessment of NO2 Purification by Urban Forests Based on the i-Tree Eco Model: Case Study in Beijing, China

“…Stomatal resistance depends on various factors such as canopy stomatal conductance, photosynthetically active radiation, air temperature, leaf water potential, etc. For simplicity of the calculation, the average stomatal resistance for different forest types was obtained from the published literature [14,15,32]. Leaf mesophyll resistance is related to the diffusion rate of pollutant gas in the mesophyll layer, the resistance value of leaf mesophyll for NO 2 was set to 100 s/m [34].…”

“…Therefore, using green infrastructure in cities can be considered a cost-effective and nature-based approach to improve air quality. Previous studies have measured the uptake capacity of vegetation for NO 2 in indoor experiments based on a dynamic gas chamber method [14,15]. However, the uptake of NO 2 by urban forests in the urban environment is influenced by a combination of factors, including air pollutants concentrations, meteorological conditions, and the physiological features of plants [16].…”