Characteristics and partitioning of ozone dry deposition measured by eddy-covariance technology in a winter wheat field

Abstract

Aims Anthropogenic pollutants cause an increase in ground-level ozone concentration, which is a known threat to plant growth and yield and has been extensively observed worldwide. Since ozone is only slightly soluble in water, it is deposited mainly through dry deposition in terrestrial ecosystem. The object of this study was to analyze the characteristics of ozone dry deposition and to estimate the contribution of stomatal and non-stomatal ozone deposition pathways to total ozone deposition in a winter wheat field. Methods The research site was a winter wheat (Triticum aestivum) field located in Yongfeng experimental station of Nanjing University of Information Science & Technology. The data used in this study were collected from March 16, 2016 to May 30, 2016. We observed ozone dry deposition with an eddy-covariance system. This system mainly included a 3D sonic anemometer, an open-path infrared absorption spectrometer, a fast-response ozone chemiluminescent analyzer and a slow-response ozone monitor. We simultaneously measured meteorological data including solar radiation (SR), air temperature (T), air relativity humidity (RH), wind speed, net radiation, and rainfall. All raw data were recorded with data-logger and averaged every 30 min. Important findings Half hourly means of ozone concentrations (CO3), ozone flux (FO3) and ozone dry deposition velocity (Vd) in the winter wheat field were 32.9 nLL.-1, .5.09 nmolm-2s-1, 0.39 cm-1, and the ranges of them were 16.58 nLL.-1,-2.9-11.7 nmolm-2s-1, 0.17.0.63 cm-1, respectively. FO3 and CO3/Vd were found to be mismatched with phase peaks occurring at different time intervals. The ecosystem was more effective on ozone dry deposition, under conditions of moderate to high SR (SR . 400 W-2), moderate T and humility (T = 18 °C and RH < 40%). The relationship between Vdmax and SR was this function (y = 1.06 .exp (-0.0094-x)).Vdmax increased with SR When SR < 400 W-2, and Vdmax reached its maximum when SR =400 W-2. Vdmax maintained its maximum when SR . 400 W-2. The relationship between Vdmax and T was bell curve (y = 1.06-(x-18)2/169). Vdmax reached its maximum when T = 18 °C. Vdmax decreased with RH when RH < 40 % (y = 0.030x-0.106). The variation of Vd might uncertainty when RH was high. There was a liner positive relationship between friction velocity (u∗) and Vd, but this relationship was not significant. The mean day-to-day and daytime contributions of stomatal and non-stomatal ozone deposition pathway to total ozone deposition were 32%, 68% and 42%, 58%, respectively, during the whole experimental period.