Measurements And Modeling The Mechanism Of Ozone Dry Deposition On The Yields Of Winter Wheat

As the process of industrialization becoming faster and faster and the living standard improving, the ozone precursor emission, which is a kind of secondary pollutant, increases a lot, so the ozone concentration elevates constantly. The effect of ozone to human health or plant growth poses national security risks. Ozone deposits to the earth surface or crop canopy by dry deposition. It’s considered that there are three kinds of deposition way which are stoma uptake, surface sink and soil settlement. The ozone that deposits to crop canopy or be taken in by stoma can influence the plant physiology and harvest.In order to explore ozone deposition law and the influence of ozone to plants, this paper gets the ozone settlement data through observation. The observation data come from the winter wheat field in the agricultural meteorology station of Nanjing University of Information Science and Technology. Firstly, the influencing factors are analyzed and the model of ozone precipitation is introduced and revised. The accuracy of the risk assessment index is analyzed. Secondly, in order to measure the wheat crop stoma absorption amount, surface deposition amount and soil settlement, Surfatm-O3deposition model is introduced and revised. At last, the amount of ozone absorbed by winter wheat is evaluated, which can provide basis for research on ozone risk assessment index. The main results are as follows:(1) The mean value of the ozone dry precipitation flux of ozone is-0.35ug·m-2·s-1(negative sign indicates that the precipitation direction is down to the ground). The mean value of its aerodynamic resistance is30.02sm-1. The mean value of viscous sub layer resistance is257.13s·m-1. The mean value of the canopy resistance is162.99s·m-1. The flux and rate of ozone precipitation, the aerodynamic resistance, and the viscous sub layer resistance and the canopy resistance have distinguish diurnal fluctuation.(2) The wheat field deposition flux is affected by the concentration of the ozone and resistance of the ozone deposition. The max value generally appears at13o’clock. That is because the sensible heat and latent heat flux reaches the maximum level which let the photochemical reaction can easily occur. On the other hand, the air temperature is higher which make the air in great friction velocity and vertical atmospheric turbulence very strong and this makes the atmosphere and surface transportation more easily. The smallest ozone deposition resistance appears at the high noon. During the daytime, the non-stomata conductance resistance increases as the solar radiation intensity increases. The reason is the thermal decomposition in high temperature which is caused by strong solar radiation. During nighttime, the canopy resistance is affected by relative humidity, temperature and velocity. As the friction velocity increase, the canopy air flow more quickly which helps ozone deposition. When the relative humidity is50-60%, the canopy resistance increases as the humidity increases. When the relative humidity is higher than60%, the canopy resistance decreases as the relative humidity increase. The bare soil resistance impact factor is surface relative humidity which can increase the soil resistance.(3) In order to refine the resistance of ozone deposition and understand its process, Surfatm-O3model is introduced and revised through regression analysis., this model can further improve the accuracy of ozone risk prediction and assessment by combining with AFst ozone risk assessment which is proposed by UNECE. The ozone absorption flux of the winter wheat during observation period is6.98mmolO3m-2。(4) This study distributes the ozone deposition proportion of different channel. During the ozone deposition observatory period, non-stomata precipitation consists67%, and stomata precipitation consists33%.23.1%of the precipitation is daytime stomata precipitation.30.6%of the precipitation is surface precipitation.46.3%of the precipitation is soil precipitation. The mean value of nighttime precipitations consist46.8%of all the precipitation and the mean value of soil precipitation consists53.2of all the precipitation.