[Ozone Deposition and Risk Assessment for a Winter Wheat Field:Partitioning Between Stomatal and Non-stomatal Pathways].

To better understand the ozone deposition and risk assessment over agroecosystems based on the ozone flux indices, an eddy-covariance system was used for measuring the ozone deposition continuously and dynamically in a winter wheat field. We analyzed the variations in ozone concentration, total ozone flux, and stomatal and non-stomatal flux. The relationships between stomatal/non-stomatal ozone deposition velocity and the main meteorological factors were investigated. Finally, the yield losses of winter wheat based on the ozone-dose index (AOT40) and ozone flux index (DFs06) were calculated. Results showed that average daily ozone concentration (cO3) was 32.9 nL·L-1. The daytime (08:00-18:00) and nighttime total ozone flux (FO3) were -7.6 nmol·(m2·s)-1 and -3.1 nmol·(m2·s)-1, respectively, and the mean diurnal FO3 was -5.1 nmol·(m2·s)-1. The mean daily stomatal ozone flux (Fs) and non-stomatal ozone flux (Fns) ranged from 0 to -5.1 nmol·(m2·s)-1 and from -1.43 to -10.31 nmol·(m2·s)-1, respectively. The mean diurnal Fs and Fns were -1.43 nmol·(m2·s)-1 and -3.66 nmol·(m2·s)-1. High solar radiation (SR), high temperature (T), and moderate humidity were used to analyze stomatal ozone deposition; high SR, moderate T, and high humidity were suitable to analyze non-stomatal ozone deposition. The cumulative total ozone flux (DFO3), cumulative stomatal ozone flux (DFs), and cumulative non-stomatal ozone flux (DFns) were 31.58, 9.99, and 21.59 mmol·m-2 during the entire experimental period, and DFs and DFns accounted for 32% and 68% of DFO3. The ranges of yield loss in winter wheat were estimated at 11.58%-20.37% and 20%-23.56% using different assessment models based on the ozone dose index AOT40 and ozone flux index DFs06, respectively.

[O3 dry deposition flux observation and soil resistance modeling over a bare soil in Nanjing area in autumn]. / 南京秋季裸地臭氧干沉降通量观测及土壤阻力模拟.

In this study, the concentration of O3 and its deposition flux over a bare soil in Nanjing in autumn were observed by using an eddy covariance system with rapid ozone analyzer. We analyzed the correlation of ozone concentration, deposition flux, and meteorological conditions in order to explore the characteristics of the variations in ozone deposition flux and deposition velocity. We also compared flux and velocity by using modeled soil resistance with observations. The results showed that the diurnal variation of ozone concentration exhibited a single peak distribution, and it increased due to radiation enhancement from September 25th to October 28th, 2015. Ozone deposition flux over a bare soil in autumn was mainly affected by its concentration, with diurnal average values varying from -31.4 to -156.8 ng·s-1·m-2(the negative sign indicated that the deposition direction was toward the ground). As a result of non-vegetation over a bare soil, the ozone deposition flux was significantly influenced by environmental factors. Diurnal average of deposition velocities varied in the range of 0.09-0.30 cm·s-1. The turbulence exchange played a major role in the atmosphere transportation of ozone, and underlying surface condition was particularly important to O3 dry deposition over the bare soil. Soil resistance (Rs) increased exponentially with air relative humidity (RH), and the equation was Rs=89.981e0.0246RH. The parameterized ozone deposition velocities and fluxes were in good agreement with the measured values.