Model Improvement And Application Researching Of Ammonia Volatilization In Paddy Field

Ammonia is an important precursor to secondary aerosols in the atmosphere,which plays an important role in the formation of PM_2.5.In order to correctly evaluate the effect of ammonia volatilization,it is inevitable to analyze quantificationally ammonia volatilization flux and ammonia volatilization loss of farmland.Continuous measurement of ammonia volatilization with high temporal resolution and estimation of ammonia volatilization at the regional scale can be used as a method to predict the process of ammonia volatilization.In this paper,the mid-season rice in Jingzhou,Hubei Province,was selected as the research object.Continuous extraction of air in closed rooms was used to observe high-frequency ammonia volatilization during the growth period.Based on the high-frequency observation data,the deficiency of the ammonia volatilization model in the existing rice fields was analyzed and improved to increase the simulation accuracy of the model.At the same time,high-frequency observation data of ammonia volatilization critical periods in Changshu of Jiangsu,Dali of Yunnan,Guangxi of Nanning,Nanchang of Jiangxi,and Jilin of Siping,which were obtained to verify the model,and the effect of the model was evaluated.To simulate the ammonia volatilization amount and calculate its rate in rice fields in China that could use the modified model（RJM）and the activity data of rice nitrogen application rate.Considering the above mentioned,the following conclusions can be shown:（1）The improved model of ammonium volatilization in paddy fields can simulate the ammonia volatilization process in paddy fields better.As for the six experimental sites selected in this study,except for the two double-season rice locations in Guangxi and Jiangxi Provinces,the correlation coefficient between the model values and the observed values reached over 70%.（2）The RJM model was used to simulate and estimate the rate of Ammonia Volatilization in China‘s paddy fields.In 2013,the ammonia volatilization in paddy fields was 0.49 Tg N yr^-1(nitrogen application rate was 4.38 Tg yr^-1),and the ammonia evaporation rate was 11.3%.The ammonia evaporation rate（16.0-17.7%）estimated by the site data set method and the simulation results of the process model（14.2-28.2%）.（3）Based on the data from the six experimental observation points,the preliminary assessment of ammonia volatilization method in the region was conducted.Compared with the RJM model results,the dynamic chamber method overestimated the ammonia volatilization flux.The reason for the overestimation is that the experimental wind speed was not corrected to the actual wind speed.In addition,the sampling frequency in（twice per day）in the dynamic chamber method also caused an estimation error.The main reason why ammonia volatilization rate be overestimated by the process model is that the difference between the model’s over-sensitivity to the aqueous ammonia（JM model）and the model structure（DNDC model）.