Research On Exhaust Gas Diffusion Of Ships At Sea Based On Gaussian Model

With the increasingly stringent limits for the sulfur content of marine fuel oil in the ship emission control area,the issue of ship exhaust emission supervision has been widely concerned by researchers in the field of transportation.Based on the background requirements of remote telemetry and online law enforcement,this paper focuses on the diffusion characteristics of ship exhaust at small scales,explores the factors influencing the diffusion of exhaust and its influencing mechanism,and considers the actual environment to provide method guidance for the dynamic setting of the exhaust gas threshold.This paper takes Nanjing Dashengguan Yangtze River Bridge（the former Nanjing No.3 Yangtze River Bridge）as the research object,collects the data of ship exhaust gas concentration,AIS data and meteorological data through the monitoring equipment,and makes an overall analysis and evaluation on the situation of local ship exhaust gas pollution in a certain period of time.The results show that the meteorological factors have a significant impact on the concentration of ship exhaust.Based on the Gauss plume basic diffusion model,considering the actual marine environmental factors,this paper analyzes the components of atmospheric stability and its calculation method.At the same time,the key parameters of the model are modified from the effective source height,effective wind speed,heading angle.Considering the characteristics of ship exhaust pollutants,the reflection factor of exhaust gas is introduced to modify the diffusion model.At the same time,an algorithm for calculating the diffusion of multi-source exhaust gas is proposed.Based on the improved Gaussian plume model,this paper uses the control variable method to carry out multiple sets of simulation experiments on the factors affecting the diffusion of ship exhaust.The results show that wind speed,wind direction,heading angle and atmospheric stability are the key factors affecting the diffusion range and concentration of exhaust gas.In addition,this paper explores the diffusion of ship exhaust gas under some typical working conditions,mainly including the characteristics of concentration variation in the vertical direction,the diffusion of exhaust gas under the influence of day and night,and the summation of emissions from multi-source ships.The research shows that multi-source ships have an important impact on the exhaust gas concentration at the monitoring height,and the concentration in the overlapping area of exhaust gas diffusion will increase significantly.The results of model optimization analysis show that the modified model can more effectively simulate the direction of exhaust gas diffusion,and the monitoring value of the off-shore exhaust gas concentration is more realistic.Finally,this paper proposes a method to determine the threshold of ship exhaust in dynamic environment.Based on the preset parameters in this paper,the threshold of the Nanjing No.3 Yangtze River Bridge is recommended to be 56.65μg·m^-3 during the day with C-level stability and 37.89μg·m^-3 at night with E-level stability.It is of great significance to build the diffusion model of ship exhaust gas and study the diffusion mechanism and influencing factors of exhaust gas pollutants for the traceability of exhaust gas emission,marine environmental assessment,engineering design and safety management.The research results can provide useful support for the remote sensing monitoring project of ship exhaust gas in the pilot project of Nanjing No.3 Yangtze River Bridge,thus providing reference for the prevention and management of pollutants in China’s ship emission control area.