Supplementary material to "Ozone deposition measurements over wheat fields in the North China Plain: variability and related factors of deposition flux and velocity"

Abstract. Ozone (O3) deposition is closely related to air quality, ecosystem and climate changes. Due to the instrument and method shortage, O3 deposition was less observed and investigated in China, experiencing significantly increasing O3 exposure. Here, we conducted a comprehensive measurement of O3 deposition over the wheat canopy at a typical polluted agricultural site in the North China Plain using a newly developed relaxed eddy accumulation system. For the main wheat growing season in 2023, O3 deposition flux and velocity (Vd) averaged -0.25 ± 0.39 μg m-2 s-1 and 0.29 ± 0.33 cm s-1, respectively. Daytime Vd (0.40 ± 0.38 cm s-1) was obviously higher than in the nighttime (0.17 ± 0.26 cm s-1). The temporal changes of Vd were mainly determined by crop growth, with predominant contribution of stomatal uptake. Both daytime and nighttime Vd exhibited significant increases with decreasing relative humidity, and increasing friction velocity and soil water content, enhanced by higher leaf area index. With rapid increases of soil moisture, simultaneous and following overall increments in Vd were detected, attributed to remarkably strengthening O3 stomatal uptake under increased stomatal conductance and extended opening to the night, and more non-stomatal O3 removal at night resulted from strengthened soil NO emission at moist conditions. This study confirms the leading effects of crop growth on O3 deposition modulated by environmental conditions and the non-negligible influences of nocturnal plant activities, and emphasizes the needs for O3 deposition observation over different surfaces and accurate evaluation of O3 agricultural impacts based on deposition fluxes.