Measurements of NO and NO 2 exchange between the atmosphere and Quercus agrifolia

Delaria, Erin R.; Vieira, Megan; Cremieux, Julie; Cohen, Ronald C.

inline-formulaNO2 foliar deposition through the stomata of leaves has been identified as a significant sink of inline-formulaNOx within a forest canopy. In this study, we investigated inline-formulaNO2 and NO exchange between the atmosphere and the leaves of the native California oak tree Quercus agrifolia using a branch enclosure system. inline-formulaNO2 detection was performed with laser-induced fluorescence (LIF), which excludes biases from other reactive nitrogen compounds and has a low detection limit of 5–50 ppt. We performed both light and dark experiments with concentrations between 0.5 and 10 ppb inline-formulaNO2 and NO under constant ambient conditions. Deposition velocities for inline-formulaNO2 during light and dark experiments were inline-formula0.123±0.009 and inline-formula0.015±0.001 cm sinline-formula−1, respectively. Much slower deposition was seen for NO, with deposition velocities of inline-formula0.012±0.002 and inline-formula0.005±0.002 cm sinline-formula−1 measured during light and dark experiments, respectively. This corresponded to a summed resistance of the stomata and mesophyll of inline-formula6.9±0.9 s cminline-formula−1 for inline-formulaNO2 and inline-formula140±40 s cminline-formula−1 for NO. No significant compensation point was detected for inline-formulaNO2 uptake, but compensation points ranging from 0.74 to 3.8 ppb were observed for NO. inline-formulaNO2 and NO deposition velocities reported here are comparable both with previous leaf-level chamber studies and inferences from canopy-level field measurements. In parallel with these laboratory experiments, we have constructed a detailed 1-D atmospheric model to assess the contribution of leaf-level inline-formulaNOx deposition to the total inline-formulaNOx loss and inline-formulaNOx canopy fluxes. Using the leaf uptake rates measured in the laboratory, these modeling studies suggest that loss of inline-formulaNOx to deposition in a California oak woodland competes with the pathways of inline-formulaHNO3 and ROinline-formulaNO2 formation, with deposition making up 3 %–22 % of the total inline-formulaNOx loss. Additionally, foliar uptake of inline-formulaNOx at these rates could account for inline-formula∼15 %–30 % canopy reduction of soil inline-formulaNOx emissions.

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Delaria, Erin R. / Vieira, Megan / Cremieux, Julie / et al: Measurements of NO and NO2 exchange between the atmosphere and Quercus agrifolia. 2018. Copernicus Publications.

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