Crop Physiological Control on Tropospheric Ozone Dry Deposition over a Maize Agricultural Field in Central Illinois

Tropospheric ozone (O₃) is a phytotoxic air pollutant known to cause reductions in net photosynthesis and vegetation biomass, which poses a threat to critical carbon sinks and yields of major agricultural crops. The ambient concentrations that plants are exposed to are often used in risk assessments, but it is the uptake through plant stomata which delivers the phytotoxic dose. The cumulative stomatal uptake of O₃ often correlates tightly with O₃ induced losses in net photosynthesis and biomass. Furthermore, stomatal uptake represents a significant portion of dry deposition of O₃ onto the land surface and can directly impact the tropospheric O₃ budget. The dual significance of stomatal O₃ flux as an indicator of the phytotoxic dose to vegetation and as a tropospheric O₃ loss pathway warrants continued monitoring of O₃ fluxes over agricultural fields and natural ecosystems. Here, we present O₃ fluxes and the stomatal and non-stomatal components of O₃ dry deposition over the growing season in a maize (Zea mays) agricultural field in central Illinois. We monitored O₃ fluxes using the eddy covariance technique with 10 Hz measurements of wind velocity and O₃ concentrations from two instruments based on UV-absorption. We partitioned the total O₃ flux into stomatal and non-stomatal components. The stomatal component was estimated using CO₂ and H₂O fluxes with an inversion of the Penman-Monteith equation which describes ecosystem latent heat flux and a separate approach based on partitioning H₂O and CO₂ fluxes into their stomatal and non-stomatal components. We analyze how micrometeorological conditions and crop physiological activity impact diurnal and growing season O₃ dry deposition and the cumulative growing season uptake of O₃ by the maize field. Eddy covariance fluxes of O₃ across tower networks can help monitor the cumulative uptake of O₃ by natural ecosystems and agricultural fields along with providing relevant observations for testing O₃ dry deposition schemes in air quality and chemical transport models.