Study on Air Pollutant Emission Inventory for Offshore Fishery Resources Survey

—With the promotion of reform in various fields and the release of vitality of fishery development, Chinese fishery has achieved sustained and rapid development. Today, China has become one of the largest fishing countries, with abundant offshore and pelagic fishing routes, and a large number of vessels. The result is more and more pollutants emitted by vessels, which seriously affects the air quality of the surrounding environment. In this paper, a survey of offshore fishery resources in the East China Sea in 2020 was selected as the research object. The emission factors were summarized combined with the existing research results. The operation status of the survey was divided, and the calculation flow chart of air pollutant emissions was established, finally the emission inventory was estimated. The sharing rate of main/auxiliary engine and different operation status was discussed. The research data is the basement for the green, energy-saving, low-carbon and sustainable development of fishery in the future.


INTRODUCTION
According to studies, the pollutants are summarized as follows: particulate matter, nitrogen oxides, carbon oxides, hydrocarbons and other harmful gases [1]. Climate warming is one major issue of the world, vessels account for 3% of global greenhouse gas emissions. Without future emission control measures, greenhouse gas emissions are expected to more than double in the next few years. Particulate matter emitted from vessels can cause allergies, asthma, and other disease [2,3]. In addition, marine vessels are critical in global nitrogen oxide (NOx) emissions [4]. Even fifteen years ago, marine vessels accounted for a quarter of global NOx emissions [5]. With the high attention of the international community in recent years, the low-carbon environmental protection requirements and standards have been continuously improved. Reducing the emission of vessels pollutants is one of the keys to achieving green fisheries. The development trend of green fisheries has also become inevitable.
According to the IMO Study, global vessels emissions as pollutants and greenhouse gases increased doubled in two decades [6]. IIASA research gives the total vessels emissions worldwide [7]. Psaraftis, Kontovas [8] and others used fuel consumption method to estimate global vessels emission inventory.
The research on vessels emission in China is in its early stage. Zhang Lijun [9] and others collected data on the activity of non-road mobile sources in the Pearl River Delta and established an emission inventory of non-road mobile sources in the region. Li Zhiheng and He Long [10]analyzed the shipping database in Hong Kong, analyzed the relationship between database statistics and pollutant emissions, and obtained the pollutant emission inventory of ships in the region.
In this study, a survey of offshore fishery resources in the East China Sea in 2020 was selected as the research object, and the data sample collection was completed for a total voyage of 31 days. The emission factors were summarized combined with the existing research results. The operation status of the survey was divided, and the calculation flow chart of air pollutant emissions was established, finally the emission inventory was estimated. The sharing rate of main/auxiliary engine and different operation status was discussed. The research data is the basement for the green, energy-saving, low-carbon and sustainable development of fishery in the future.

Overall algorithm
The estimation of vessels air pollution emissions is divided into two methods [11]: based on power and based on fuel consumption. The first method is to obtain the basic information of the vessel (rated power, voyage time, full load power, fuel consumption rate and others), the corresponding emission factors are selected, then calculate the ship's emission inventory; The second method is to select the corresponding emission factor to calculate the emission according to the real-time navigation information (real time speed, maximum design speed, spatial position, output power and others).The systematic study can combine two calculation methods to establish emission inventory.
The method based on fuel consumption estimation was selected in this study. According to the basic data of the research vessel, combined with the existing research results, the emission factors were analyzed and summarized, and then the operation status were divided, and the fuel consumption of each state was estimated, so as to obtain the emission of air pollutants.
Where I i is the certain pollution emission (t/a), E i is the certain emission factor (g/L), C f is the fuel consumption (10 6 L/a).

Emission factors
According to vessel emission factor research [12,13], the emission factors are summarized in Tab. 1 and Tab. 2. The data in Table 1 is based on the survey data of the main engine model of the large ships, and the emission factors are fine-tuned with reference to the main engine and auxiliary engine power parameters, fuel type, and emission time. Tab. 2 is based on the emission factor data obtained from the investigation of four sets of literature [3][4][5][6], combined with the basic parameters of the scientific survey vessel, the emission factor unit is unified and the emission factor is calculated. In this study, Tab. 1 and Tab. 2 are averaged to obtain the emission factors as shown in Table  3 (the unit of all tables is g.L -1 .

Operation status divided
According to the classification of inland and offshore ship emission characteristics and emission inventory research reports [11], the actual voyage status of ships is divided into: cruising state, deceleration zone navigation, maneuvering operation state and berthing state. According to the actual situation of our survey vessel and the navigation data, we classified the voyage status as follows: larger than 7 knots in this survey as cruising status; Sections 1-7 are the operation status; Less than or equal to 1 knot is berthing status. We analyze the voyage data recorded by observers, and divide the three statuses and corresponding voyage times, the specific data are shown in Tab. 4.

The calculation flow chart of pollutant emissions
According to the calculation method of the inventory above, a flow chart of emission calculation was established as Fig.1.

Fuel consumption estimation
The survey of total 31 days, which the operation time was 202.9 hours, the cruising time was 249.4 hours, and the berthing time was 288.73 hours. Based on the status of the voyage, this study uses the formula for estimating fuel consumption as follows: C f =T*200*(OP/LP)*RP (2) T is the time, OP is the output power, LP is the full load power, and RP is the rated power.The manufactured data of survey vessel in this project are shown in Tab. 5.
The fuel consumption of the cruising and operating status can be calculated by "(2)". When operating state, the fuel consumption of the main engine is 23962.09L and the fuel consumption of the auxiliary engine is 9637.75L; when cruising state, the fuel consumption of the main engine is 39064.84L and the fuel consumption of the auxiliary engine is 4676.25L.
According to the load ratio coefficient of the auxiliary engine summarized in the inland and offshore ship emission characteristics and emission inventory research [11], when berthing state, the load ratio coefficient of the auxiliary engine is 0.22. It can be calculated that when berthed, the fuel consumption of the auxiliary engine is 2743.4L.
The fuel consumption of the main engine is 63062.93L and the fuel consumption of the auxiliary engine is 17057.4L.

Emission inventory calculation
Based on the above parameters, the air pollutant emissions of the scientific survey vessel are calculated, as shown in Tab. 6. The results show that the total air pollutant emissions in this study are 142.48 tons, and among all the air pollutants, CO 2 emissions account for 95% of the total emissions of this study. Global warming is already affecting natural ecosystems in many areas, and controlling CO 2 emissions is a top priority in future emission control.

The sharing rate analysis
From the previous results, it can be seen that: when operation, the fuel consumption of the main engine is 23962.09L and the fuel consumption of the auxiliary engine is 9637.75L; when cruising, the fuel consumption of the main engine is 39064.84L and the fuel consumption of the auxiliary engine is 4676.25L; and when berthed, the fuel consumption of the auxiliary engine is 2743.4L. The total fuel consumption of the main engine is 63026.93L, and the total fuel consumption of the auxiliary engine is 17057.4L. Fig. 2 shows the sharing rate of the voyage status of the vessel pollutant emissions, and it can be seen from the figure that the cruising state is the largest state of emissions, with a sharing rate of about 55%. The operating state sharing rate of 40%, and a berthing state sharing rate was about 5%.
If the emission model is divided, as shown in Figure 3, the main engine sharing rate is about 80%, and the auxiliary engine is only 20%.   The sharing rate of the emission model

DISCUSSION
For the estimation of pollution emissions, divided into two ideas: based on power and based on fuel consumption, this study selects a method based on fuel consumption, because the basic information and fuel consumption rate data of the research vessel are more sufficient. The selection of emission factors is also summarized by a variety of existing analysis results, and the corresponding results are more credible. Another method of calculating base on the navigation information, voyage path, spatial details and others by the vessel automatic identification system. Combined with the design speed, actual speed, output power and other information of the vessel to obtain the emission and the spatial distribution map of air pollutant emissions. The two methods can be compared with each other, and more accurate emission factors can be obtained through analogy verification, which will lay a good foundation for future emission inventory research. The fuel standard based on this study refers to ISO8217-2010, and the selection of emission factors and load factors is based on the emission study of fuel sulfur content of 2.7%. However, in actual operation now, the sulfur content of marine fuel is greatly reduced, and the emission factor should be corrected by the fuel coefficient to be more in line with the actual situation, which is worth more in-depth analysis in future research.