New Evidence for the Importance of Non‐Stomatal Pathways in Ozone Deposition During Extreme Heat and Dry Anomalies

Abstract

Dry deposition could partially explain the observed response in ambient ozone to extreme hot and dry episodes. We examine the response of ozone deposition to heat and dry anomalies using three long‐term co‐located ecosystem‐scale carbon dioxide, water vapor and ozone flux measurement records. We find that, as expected, canopy stomatal conductance generally decreases during days with dry air or soil. However, during hot days, concurrent increases in non‐stomatal conductance are inferred at all three sites, which may be related to several temperature‐sensitive processes not represented in the current generation of big‐leaf models. This may offset the reduction in stomatal conductance, leading to smaller net reduction, or even net increase, in total deposition velocity. We find the response of deposition velocity to soil dryness may be related to its impact on photosynthetic activity, though considerable variability exists. Our findings emphasize the need for better understanding and representation of non‐stomatal ozone deposition.

Contrasting the Biophysical and Radiative Effects of Rising CO2 Concentrations on Ozone Dry Deposition Fluxes

“…Despite the limited data for full evaluation, we have sufficient information to point to intriguing relationships consistent with existing work demonstrating the complexity of plant physiological responses, and the importance of non‐stomatal processes in controlling dry deposition responses to changes in the Earth system (Clifton, Fiore, et al., 2020; Clifton, Lombardozzi, et al., 2020; Clifton, Paulot, et al., 2020; Silva & Heald, 2018; Wong et al., 2022).…”

“…Despite the limited data for full evaluation, we have sufficient information to point to intriguing relationships consistent with existing work demonstrating the complexity of plant physiological responses, and the importance of non-stomatal processes in controlling dry deposition responses to changes in the Earth system Clifton, Lombardozzi, et al, 2020;Silva & Heald, 2018;Wong et al, 2022). In E3SM, LAI is used in the dry deposition parameterization as an inverse multiplicative scaling factor for the stomatal resistance (i.e., higher values of LAI will lead to reduced stomatal resistance).…”

The Combined Impact of Canopy Stability and Soil NOx Exchange on Ozone Removal in a Temperate Deciduous Forest

“…Under such conditions, hydrological interactions leading to droughts reduce the stomatal ozone sink (Lin et al., 2020). Whether this results in an overall decrease in dry deposition depends on the behavior of non‐stomatal deposition during droughts, and observational evidence suggests that non‐stomatal deposition may increase under these conditions (Agyei et al., 2020; Wong et al., 2022). The summer of 2012 was characterized by slightly drier meteorological conditions (±1 σ ) compared to the long‐year average around Bosco Fontana, while the area south of the Po Valley experienced dry conditions (Figure 1b, more details can be found in Text S1 in Supporting Information ).…”

The combined impact of canopy stability and soil NOx exchange on ozone removal in a temperate deciduous forest

“…Under such conditions, hydrological interactions leading to droughts reduce the stomatal ozone sink (Lin et al, 2020). Whether this results in an overall decrease in dry deposition depends on the behavior of non-stomatal deposition during droughts, and observational evidence suggests that non-stomatal deposition may increase under these conditions (Agyei et al, 2020;Wong et al, 2022). The summer of 2012 was characterized by slightly drier meteorological conditions (±1σ) compared to the long-year average around Bosco Fontana, while the area south of the Po Valley experienced dry conditions (Figure 1b, more details can be found in Text S1 in Supporting Information S1).…”