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

• Published in: Geophysical research letters 2022-04, Vol.49 (8), p.n/a
• Main Authors: Wong, A. Y. H., Geddes, J. A., Ducker, J. A., Holmes, C. D., Fares, S., Goldstein, A. H., Mammarella, I., Munger, J. W.
• Format: Article
• Language: English
• Subjects: Air pollution; air quality; Anomalies; atmosphere-biosphere flux; Atmospheric models; Carbon dioxide; Conductance; Deposition; Dry air; Dry deposition; Emission measurements; Environmental conditions; ENVIRONMENTAL SCIENCES; extreme condition; Extreme heat; Extreme high temperatures; Herbivores; Ozone; Ozone deposition; Photosynthesis; Photosynthetic activity; Plant cover; Pollutants; Reduction; Soil; Soils; Stomata; Stomatal conductance; Uptake; Velocity; Water vapor; Water vapour
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2021GL095717

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. Plain Language Summary Ozone is an important air pollutant that can threaten both human and plant health. Removal of ozone from the atmosphere may be reduced during extremely hot or dry events due to how plants respond to such environmental conditions (governed by stomatal or non‐stomatal processes separately). Using long‐term observations at three different sites, we find that non‐stomatal uptake generally increases on hot days, which can offset a reduction in stomatal uptake that is expected under the same conditions. The response to soil dryness is more complicated, but potentially related to responses in photosynthetic activity. Current models of on how ozone deposition affects surface ozone concentrations during hot and dry episodes are inaccurate because of their inability to represent non‐stomatal responses. Key Points Responses of total ozone deposition to heat and dry anomalies vary considerably from site to site Non‐stomatal deposition increases significantly during hot days in all three sites considered Current big‐leaf parameterizations largely fail to capture the response mainly because of non‐stomatal deposition