## 5 Discussion  
In this paper, the methods for calculating the air pollution emission inventory of ships are investigated, and the advantages and disadvantages of the methods are analyzed and compared with reference to the literature. Finally, the power method with higher calculation accuracy is selected to calculate the regional air pollution emission inventory of ships. Considering the complex and changeable hydrological environment of inland rivers in the region, the generally high age of ships, old diesel engines, untimely maintenance, etc., the representative ship load conditions were measured, and a calculation model of ship air pollutant emissions with regional characteristics was established. The research of this paper mainly focuses on the following three aspects:  
Firstly, using the power method to calculate the air pollution emission inventory of ships. Among them, AIS real-time navigation data help to identify various basic information about the ships, and the ship navigation information database provides us with a convenient data storage platform, which makes the subsequent emission inventory calculation more intuitive. In previous studies, AIS data did not play to the advantage it should have.  
Secondly, with reference to the latest regulations of the Ministry of Transport on the sulfur content of fuel oil for ships entering the Yangtze River, the pollution emission factors of the ship's main and auxiliary engines in the ship's emission inventory model have been updated. For inland ships in the Yangtze River, previous researchers used diesel with a sulfur content of 2.7%. According to the regulations, light diesel oil with a sulfur content of 0.1% was introduced as the fuel correction factor for the emission factor. In this way, the emission inventory calculation model of inland ships can be updated in time.  
Thirdly, real-time tracking and measurement of the tail shaft power of diesel engines were carried out on five representative inland river ships, and the matching of the propellers of the marine diesel engines was studied. The propeller load of ships in the region is generally heavy, and the unreasonable matching of propellers leads to an increase in the load of diesel engines during the sailing process of ships, resulting in an increase in fuel consumption rate, which directly affects the air pollution emissions of ships. In previous studies, the pollution discharge inventory of inland river ships did not take into account the matching of the ship's engine and propeller, resulting in increased uncertainty in the emission inventory. Therefore, after the field test, the load ratio of the marine diesel engine was selected as 1.25. The above shaft power measurement experiment verified the heavy load of the ship according to the actual situation of the inland ship and introduced the engine propeller matching coefficient. This provides a strong basis for the calculation of emission inventory of old ships in inland rivers and improves the universality of the calculation model of ship emission inventory.  
Compared with the research in China in recent years, the advantages of real-time navigation status data carried by AIS in the process of ship emission inventory development have been fully utilized. In this paper, many parameters involved in the compilation of ship emission inventory based on AIS data, including main and auxiliary engine power, main and auxiliary engine load factor, emission factor, fuel correction factor, engine propeller matching coefficient, etc., are analyzed and determined one by one. On the basis of referring to foreign ship emission inventories, it is necessary to combine the actual situation of local ships, and comprehensively select parameters suitable for the ship air pollution emission inventory in the region, so that the established ship air pollution emission inventory can better reflect the actual local ship air pollution emissions.