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 the main sink of surface O3, exerting great influences on air quality and ecosystems. Due to instrument limitations and method shortages, O3 deposition was less observed and investigated in China, where O3 has been reported to be continuously and significantly rising. Here, we conducted comprehensive measurements of O3 deposition over a 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 µgm-2s-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 in Vd were mainly determined by crop growth, and Vd significantly increased with decreasing relative humidity and increasing friction velocity and soil water content, enhanced by a higher leaf area index. With rapid increases in 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 into the night, and more non-stomatal O3 removal at night resulted from strengthened soil NO emission in 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 it emphasizes the need for O3 deposition observation over different surfaces and accurate evaluation of O3 agricultural impacts based on deposition fluxes.