Observation And Simulation On Ozone Dry Deposition Flux Of Farmland In Nanjing

As one of the major atmospheric pollutants in the near-surface layer,ozone can enter the crop through the pores of the crop,thus affecting the photosynthesis of the crop leaves,changing the morphology of the leaves,inhibiting the normal growth of the crop,and damaging the yield of the crop.In this paper,the ozone-porosity flux of winter wheat was studied by the vortex correlation system,and the WRF-Chem model was used to simulate the ozone concentration,stomatal conductance and ozone stomatal flux of winter wheat in the Yangtze River Delta region.The main findings are as follows:(1)During the observation period,the average values of ozone concentration is 37.40nL·L-1,the average values of ozone deposit flux is-5.58nmol·m-2·s-1(the negative sign represents the descending direction)and the average values of ozone deposit rate is 0.29 cm·s-1.The average values of aerodynamic resistance is 69.25s·m-1,the average values of quasi-laminar boundary layer resistance is 254.64 s·m-1 and the average values of canopy resistance is 262.59 s·m-1.(2)The experimental results show that the daily variation of stomatal conductance of winter wheat shows a trend of increasing at first and then decreasing,between 12:00-14:00 reaching a maximum.Absorption of ozone by crop stomata may be significantly affected by meteorological factors such as temperature,light,and vapor pressure.In addition,the diurnal change of stomatal conductance of winter wheat still has a phenomenon of "midday break".The stomatal conductance of winter wheat showed a single-peak growth pattern of the growth period,and the maximum appeared in the flowering period.During the observation period,the average value of the stomatal conductance was 2.5 cm·s-1.(3)During the observation period,the ratio of the average stomatal ozone settling channel and the non-stomatal ozone settling channel to the total ozone sedimentation volume was 29%and 71%respectively.The stomatal ozone settling flux reached a high value(35.68%)at around 12:00 a.m.and reached a high value(35.16%)at around 14:00 p.m.in the afternoon.The percentage of stomatal ozone settling flux to the total ozone flux reached the maximum(33.86%)at flowering stage.(4)The WRF-Chem model simulates ozone concentration,ozone deposition rate,and ozone deposition flux from March to May,with mean values of 22.84 nL·L-1,0.38 cm·s-1,and-8.41 nmol·m-2·s-1,respectively.In addition to the ozone concentration,the simulated values of ozone deposition rate and ozone deposition flux are slightly higher than the observed values.In addition,the simulation results of stomatal conductance from March to May in the Yangtze River Delta showed that the stomatal conductance in March was less than in April and May.In May,due to the maturity of winter wheat,the stomatal conductance gradually decreased.The simulation results showed that the maximum stomatal conductance in April was 0.49 cm·s-1.The stomatal ozone flux of winter wheat is determined by both stomatal conductance and ozone concentration.What's more,the calculation results show that the winter wheat has the largest stomatal flux in April.Although the ozone concentration was relatively high in May,the stomatal conductance became smaller due to the gradual aging of winter wheat,so the stomatal flux in May was smaller than in April.(5)The ozone concentration simulated by the WRF-Chem model is lower than the measured value,resulting in a slightly lower stomatal flux of the simulated winter wheat than the measured value,which in turn underestimates the damage caused by ozone pollution to the winter wheat.From the observation period,ozone deposition is still dominated by non-stomatal settlement.The average stomatal ozone deposition channel and non-porous ozone deposition channel account for 24%and 76%of total ozone deposition respectively.