Coupling of island tourism carbon emission and sustainable resource development – taking Hainan Fenjie Island as an example

ABSTRACT

Fenjie Island, as an isolated island, has evolved into a 5A-rated tourist destination. However, in recent years, due to the one-sided pursuit of economic gains, the island has continuously developed its tourism resources, resulting in over-exploitation of resources and significant ecological impacts. This study meticulously scrutinizes tourism-related carbon emissions in comparison to the island's natural capacities. Comprehensive research spans ships, accommodations, dining, and various activities, revealing emissions surpassing nature's limits. The study delves into intricate emission models, emphasizing energy-intensive sectors.Empirical findings underscore a pressing disparity: daily emissions far exceed the island's absorption and purification capacities, underscoring the urgency for intervention. To restore equilibrium, the study proposes recalibrating tourism by aligning it with the island's natural resources. Forest and seawater capacities emerge as vital benchmarks for sustainable tourist numbers. Proposed strategies emphasize rigorous energy conservation and emissions reduction, offering a roadmap for sustainable development.These robust findings provide an essential scientific basis for Fenjie Island's future. They illuminate a path toward balanced growth, crucial for harmonizing economic prosperity and environmental preservation. Informed by this research, policymakers can steer the island's trajectory, ensuring a sustainable, thriving future amidst the challenges of modern tourism..

KEYWORDS:

• Carbon emissions model
• environmental protection
• emission factors
• tourism resources
• visitor capacity

Fenjie Island, located in the southeastern sea of Linghsui Li Autonomous County, Hainan Province, China, with coordinates of longitude 110.20 and latitude 18.57, serves as the Fenjie between the tropical and subtropical zones at the 18th parallel north. It is situated approximately 1.2 nautical miles from the nearest coastline of Hainan Island and has a total area of 4.53 square kilometres. The island boasts breathtaking scenery, featuring towering cliffs on one side and soft sandy beaches on the other, making it an enchanting destination to enjoy the beauty of the turquoise sea and blue sky. Currently, the only means of accessing the island is by boat, with a one-way journey taking approximately 10 min. Fenjie Island holds a unique geographical position as an uninhabited island and has been developed as a 5A-level tourist attraction, showcasing the distinctive characteristics of a pure island environment. Over 20 natural landscapes, including uncanny workmanship, big caves, and vibrant floral displays, have been created on the island. Additionally, there are more than 20 unique maritime entertainment projects available, such as diving expeditions, water-based recreational towing, and aerial flying, providing a variety of exciting sea-based leisure activities.

The massive influx of tourists has injected vitality into the local economy, but it also brings significant challenges in terms of tourism resource allocation and environmental preservation. As tourism offerings continue to innovate and expand, the island's environmental resources face severe issues of footprint pollution. Without proper scientific planning, the consequences of uncontrolled and long-term development would be unsustainable. The impact of open tourism on the environment is widely acknowledged in the industry. Muhammad Mehedi Masud, while discussing the key factors influencing natural resource management in marine protected areas, emphasises the critical importance of sustainable development awareness and attitudes for coastal parks (Masud et al. 2021). However, Lukman, KM, Uchiyama, in their in-depth study on sustainable tourism in the coastal ecosystems of Indonesian small islands, found that when the economy and tourism resources are weighed on the same scale, people often prioritise economic aspects (Lukman et al. 2022). Ara, S., Alif, conducted a comprehensive study on two islands in Bangladesh, Chera Dwip and South Beach, revealing adverse impacts of human activities on the local environment, along with a 38% reduction in coral reef footprint (Ara, Alif, and Islam 2021). Katircioglu, S., supported the hypothesis of an inverted U-shaped Environmental Kuznets Curve (EKC) and demonstrated that the growth of the tourism industry leads to environmental degradation (Katircioglu et al. 2020). The above literature sufficiently illustrates that excessive tourism development can have adverse effects on the environment.

In the face of the need for economic development, how can we ensure the scientific development of tourism resources? Most literature supports the idea of controlling tourist numbers to the maximum extent possible. For example, de Albuquerque, K., conducted a quantitative examination of tourism characteristics and tourist density across 23 Caribbean islands, proposing the ‘destination lifecycle model’ (Mcelroy and Albuquerque 1986). Liu Jing, Liu Yaolong, and others proposed a correlation analysis between the maximum carrying capacity of scenic areas and tourist reception capacity to establish a model based on the carrying capacity and tourist reception capacity of the scenic areas. Yan Huili, Xiong Hao focused on the study of visitor mobility within the scenic area and derived models for the number of visitors allowed entry and the reception capacity. Sun Yuanmin, Zhang Yue studied the ecological tourism environmental capacity of Nanao Island based on the criteria of water supply capacity in the scenic area, and so on. These studies, while considering various factors, overlook the inherent elements of nature, and the conditions of service and guarantee are subject to change, making it difficult to truly achieve harmonious integration between nature and economic development.

In order to mitigate the carbon emissions caused by excessive human activities on FenJie Island, as required by the tourism planning department, the research team conducted a detailed survey on the island based on the maximum tourist flow in the area and the actual situation of the existing tourism resources. Taking a natural perspective and considering carbon neutrality, the sustainability of island tourism was discussed.

This paper, based on on-site surveys and theoretical validation data, analyses the carbon emissions at various stages of tourism activities in this 5A-rated scenic area. Furthermore, it focuses on examining underwater coral, which imposes the highest demands on marine environmental standards. The upper limit for assessing coral growth aligns with the minimum requirements for the marine environment. Combining these findings with a comprehensive review of the literature, we calculate the total daily carbon emissions for the entire island, considering the carbon footprint of tourism activities on the island. Subsequently, we compare these emissions with the natural self-purification capacity of the island, encompassing both its forests and the surrounding marine environment. This assessment allows us to evaluate the potential for carbon neutrality. This method, which we propose, stands out as a more scientifically grounded approach compared to the methodology favoured by many scholars, which primarily relies on the capacity of water supply facilities as the main criterion for limiting tourist capacity. We suggest employing this method for calculating tourism capacity on the island, proposing a maximum fixed capacity for accommodating tourists. This recommendation aims to assist the scenic area in addressing the long-standing conflict between tourism-driven economic growth and environmental preservation.

The main contributions of this paper are:

1. A comprehensive mathematical modelling of carbon emissions in various aspects of island tourism, including accommodation, transportation, shopping, entertainment, and public services.

2. Researching the concept of carbon neutrality to establish reference standards for sustainable development of tourist capacity in island tourism resources.

3. Disproving the existing calculation method for tourism capacity in scenic areas based on the qualitative barrel effect, which relies on ensuring supply capacity.

4. Providing empirical evidence that the comprehensive carbon emissions from island tourism exceed the absorption and self-purification capacity of forests and seawater, indicating that the daily number of visitors has exceeded the island's actual carrying capacity.

5. Proposing measures to address energy-saving and emission reduction in island tourism based on the calculations from the carbon emissions modelling.

1. Basic data

In 2019, before the epidemic, the average annual reception of tourists has amounted to more than 10 million, with a tourism income of nearly 200–300 million yuan. There are 18 large vistor boats, each carrying an average of 150–200 visitors and taking about 30 min for a round trip. In addition, Fenjie Island is equipped with 18 speedboats (3–5 people), a diving pier, office buildings, reception halls, 22 restaurants and stalls of various sizes, hotels and various supporting facilities to provide tourists with safe and comfortable island sightseeing and vacation services. This group of tourists board the ship in the morning and leave the island in the afternoon, so the tourist reception capacity during the day is larger. They mainly focus on travel and sightseeing, sea entertainment, food consumption and shopping, among which the demand for lunch food consumption is larger. Accommodation tourists account for about 20% of the total number of tourists, and Fenjie Island has about 200 hotel rooms and 420 beds, such as sea view rooms on the pier, single wooden houses on the mountain, hotel rooms with unbeatable sea view on the mountain, single wooden houses on the mountain, luxury nautical duplex suites and sea fishing clubs.

The average daily number of visitors to Fenjie Island was 7400 during the peak season (national holidays and December-February each year) until 2019, with a peak of over 15,000 visitors per day, and about 5,400 during the peak season in the last three years due to the epidemic. The first Chinese New Year after the pandemic was released in 2023, the island received more than the historical extreme, reaching more than 21,500 visitors on January 18. In addition, there were more than 410 people in various position of management, sales, service and security on the island.

2. Carbon footprint model of tourism activities

2.1. Estimation model of tourism traffic carbon emissions

2.1.1. Estimation model of carbon emissions of vistor ships between land and island

The research on the carbon emission estimation model of ships was relatively late.in 2012, the Ministry of Transportation and Communications Water Transport Scientific Research Institute, China Classification Society and other units issued the industry standard JT/T 826–2012 ‘Operating Ship Fuel Consumption Limits and Verification Methods’ and JT/T 827–2012 ‘Operating Ship CO2 Emission Limits and Verification Methods’. However, these two documents only give the limit values, but the specific estimation model is not involved, so many literature borrowed the car carbon emissions estimation model to estimate, and the more representative one should be the STEAM (Ship Traffic Exhaust Assessment Model) model proposed by Jalkanen et al. (2009). Chunlin Luo et al. proposed a top-down and bottom-up calculation method for transportation energy consumption In the top-down method, the fuel consumption of a ship is multiplied by the corresponding emission factor (Chunlin 2018); in the bottom-up method, the amount of black carbon emissions of a ship is calculated per unit time according to the different main engine loads of the ship.

However, the sailing conditions of ships and motor vehicles are fundamentally different. Jianlin Luan and Yinwei Feng introduced the Convolutional Long Short-Term Memory (ConvLSTM) model in the field of deep predictive learning to realise the timely identification of the sailing condition of a ship, so that its carbon emissions can be effectively measured Unfortunately (Jianlin et al. 2023), they did not give any specific results. Here, we use the ConvLSTM model to classify the entire ship navigation into the four states in Table 1.

Table 1. Vessel sailing status and output power table.

Sailing status	Sailing speed	Host load	Host output power	One-way time node/h	Oil consumption/kg
Mooring	V < 1		25%	1/4	36.9
Anchoring	1 < v < 3		50%	1/12	49.2
Manipulation	V> = 3	<20%	75%	1/30	14.8
Sailing	V> = 3	> = 20%	100%	1/6	98.0
Total					198.9

As Fenjie Island is located only 1.2 nautical miles or approximately 2.22 kilometres from the mainland, the duration of the four distinct ship states is relatively short. For the sake of convenience and to estimate carbon emissions, this article assumes the operation of a single ship based on the tourist numbers during the 2023 Spring Festival. It is important to note that this assumption does not consider whether one day is sufficient; rather, it simplifies the estimation process. Table 1 illustrates the power consumption of the host in these four states, as observed by Jun-wu (2015):

There are two main types of tourist traffic on Demarcation Islet, one is the cruise ship on the island, and the other is the electric vehicle in the scenic area. The cruise ships on the island mainly use diesel oil and 18 large express ships. Purchased in 2021×The MTU16V2000M72 main engine, For instance, the ship's total power rating is 2880 kW. Considering the short round-trip distance, a single engine typically handles the operation, and we consider only 1440 kW for our calculations. The ship has a rated fuel consumption of 683L per hour and can transport 199 tourists in a single trip. Building upon Yan Qing and Zhang Yunsong's methodology for estimating black carbon emissions from ship main engine load (Qing et al. 2022), we establish the carbon emission formula model 1. (1) ${\mathit{E}}_{\mathit{k}y}=\sum [({\mathit{M}}_{\mathit{i}j}{\mathit{D}}_{\mathit{i}j}{\mathit{F}}_{\mathit{i}j})]$(1) Where ${\mathit{E}}_{\mathit{k}y}\mathrm{is}\mathrm{the}\mathrm{waste}\mathrm{emission},\mathrm{kg}{\mathit{M}}_{\mathit{i}j}$ are the fuel consumption of the main engine in the four states of the ship, kg, respectively ${\mathit{D}}_{\mathit{i}j}$ is the working time of the ship in four states of anchoring, manoeuvring and sailing, respectively, t. ${\mathit{F}}_{\mathit{i}j}$ is the carbon emissions factor in the four states, kg/t. The emission factors for pollutants under the four states are shown in Table 2.Table 2).

Table 2. Standard marine low speed main engine, medium speed main engine and high speed main engine fuel emission factors.

Exhaust gas type	CO2/ kg/t	CO/ kg/t	HC/ kg/t	NOX/ kg/t	SOX/ kg/t	PM/ kg/t
Dock emission factor	3165.63	4.60	2.44	69.49	11.5	0.96
Low speed emission factor	3165.63	4.60	2.44	69.49	11.5	0.96
Medium speed mission factor	3147.7	3.59	1.74	44.93	10.5	1.02
High speed emission factor	3129.82	2.57	1.03	32.80	9.3	1.5

2.1.2. Estimation model of carbon emissions of electric vehicles in the island

Battery-powered cars on the Fenjie Island are mainly used for the transportation of visitors’ accommodation to the top of the mountain, as well as on-and-off sightseeing services for leisure tours on the island. There are currently 32 battery-powered cars with 8 seats on the island and 6 for 11 seats in the islet. The configurations of the two models are shown in Table 3.

Table 3. Table of parameters of the island battery car.

Model	Single cell	Battery voltage/V	Travel speed/ km/h	Climbing degree/%	Whole vehicle load/ kg
8 seats	6V180AH	48	25	20	600
11 seats	6V180AH	48	25	15	770

The electric vehicles in the island are all supplied with municipal electricity, and the Statistics Bureau of Hainan Province announced to the society in March 2021 that by the end of 2020, the clean energy generation in Hainan had accounted for 41.8% of all power generation. On 28 June 2021, Du Xiangwan, an academician of the Member of the Chinese Academy of Engineering and former vice president, said at the ‘National Forum: Energy China – China's Next Five Years’ that China's coal power generation efficiency has been greatly improved, and now only 308 grams of coal is consumed per kilowatt hour of power generation, in China's advanced coal power plants, only 270 grams of coal is consumed (Zhou 2020). (2) $E_{\mathrm{jy}}=W\ast Q\ast F_{\mathrm{ie}}$(2)

In equation 2, the $E_{\mathrm{jy}}$ is the i kind of substance emission of the scenic battery car, kg; W is the electric energy consumed by the battery car, kWh; Q is the proportion of electricity generated by coal power, taken as 58.2%. $F_{\mathrm{ie}}$ is the i kind of emission factor consumed by 1kWh of electricity, kg. Here Hainan thermal power is taken as the standard for the level of generating units above 1000 MW (Chunyang 2022) The study found that the average CO₂ emission factor of the whole power plant is 0.786 kg/kWh, which is significantly lower than the average CO₂ emission factor 0.997 of China's coal-fired power plants, that is, the actual production process of generating 1 kWh of electricity consumes less coal than our published value, and the specific emissions here are taken from Table 5 (Pingping et al. 2022). According to long-term statistics, when 38 battery-powered cars on the island are fully charged every night, as long as the battery attenuation is within the specified range, even if the island's accommodation areas are all in the mountains, the battery cars are in climbing conditions, and can basically maintain the passenger car for a day. If there is a holiday, it is necessary to use the temporary rest time to recharge, which can ensure the passenger car needs for a day. Combined with the characteristics of the battery, each battery car needs 263kWh of electric energy to charge 38 vehicles per day with 80% deep discharge standard.

2.2. Estimation model of CO₂ emissions from various tourism activities

2.2.1. Carbon emissions model of tourism accommodation

In the past two years, Fenjie Island has expanded the development of tourism resources, using the natural environment to attract tourists to live on the island, the current accommodation room types include the rooms like senior Linhai Court, sea fishing club rainforest room, Dolphin Bay Inn and so on, The beds include single bed, double bed, three bed, and multiple bed. For example, the room in the Sea Fishing Club Rainforest Room can be arranged up to eight beds, convenient for fishing friends to stay and rest. Tent accommodation is not supported on the island. The carbon emissions of tourism accommodation mainly include those generated by direct use of energy, mainly in air conditioning, hot water and lighting; The other is the secondary emissions and pollution caused by indirect utilisation, such as the emissions and pollution caused by cleaning the hotel's quilts, sheets, towels, etc. At the same time, we should also consider the emissions generated by the direct use of energy in the island enterprises, mainly the air conditioning system (refrigeration and heating), lighting system, elevator and escalator, computer and machine room, monitoring, audio, various lighting lights, hot water system, cold storage, small household appliances, etc.; The energy consumption of various electrical appliances including air conditioners, televisions, etc. in passenger accommodation rooms (Chow and Chan 1993). After practical verification, the statistics of administrative office energy-consuming equipment are recorded, and full and reasonable consideration is given to the use time. The actual theoretical calculation value is basically consistent with the actual value.

1. Emission estimation of energy consumption for office use within the enterprise

There are public offices, reception halls, training rooms, central computer rooms (with 10 kW Uninterruptible Power Supply) and other places in the enterprise of the Fenjie Island enterprise. In 2010, Deng S, Burnett J. studied the energy consumption of 1/3 of the hotels in Hong Kong and found that the most important energy consumption of Hong Kong tourism administration is the air conditioning system (Deng and Burnett 2000). This is largely consistent with the situation on the island, where most of the staff live on the opposite side of the island and only board the island during working hours. The island has three distribution rooms, eight transformers with an installed capacity of 13,600 kVA and 2000 kVA of diesel generators.

The visitor centre is equipped with three 45KW water-cooled units for the cooling needs of the office and conference areas, two 5 HP air conditioners for the server room, and split air conditioners for other areas. The overall administrative office is equipped with electrical appliances as follows Table 4.

Table 4. Administrative office power table of various types of electrical appliances.

Projects	Equipment	Quantity	Length of use	Power/kw	Total power/kW
Air conditioning system	Central air conditioning refrigeration units	2 sets	7	260	2600
	Air conditioning terminals	250W 8 sets, 100W 20 sets	10	4	40
	Inverter water pump (cooling, freezing)	6 sets	7	45	2700
	Split air conditioners	15 sets	14	3.7	777
Administrative office	Water dispenser with Self-drinker	sets	24	20	240
	LED big screen	3 pcs	24	11	264
	Printer	2 pcs of 500W, 20W 10 pcs	2	1.2	2.4
	copier	2 pcs	2	300	0.6
	Computers	80 units	10	340	272
Business centre	Large washing machine	2 pcs	4	11	88
	Dryer	4 pcs	8	13.2	422
Lighting & advertising	Street lights	110 pcs	12	44	52.8
	LED spotlights, downlights, candle lights in public areas	2.5W 3W 5W 10W and so on a set	12	5	60
	Audio	2 pcs	5	2	10
Data centre	Computers, air conditioners, UPS, servers, etc.		24	40	960
Total					5888

The actual emissions of energy consumption for office use within the enterprise can be obtained using Equation 2 in Table 5.

(2)	Estimation model of carbon energy consumption emission of tourist accommodation

Table 5. Calculation of daily carbon emissions of various types of appliances for administrative offices.

Exhaust gas type	SO2	NOX	Fume and dust	CO2
Emission factor	0.03	0.15	0.27	0.786

Tourism accommodation carbon emissions are concentrated in the lighting, ventilation, air conditioning, hot water supply, etc. of simple accommodation facilities, mainly in the indirect carbon emissions of electricity consumption. Zhang Hongxia et al. summarised the advantages and disadvantages of the top-down method and bottom-up method of accounting for carbon emissions in the accommodation industry (Hongxia, Qin, and Yuguo 2017) and combined with the quantitative calculation formula given by Yanyan (2020). Considering the several main pollutant emissions, the estimation model is established as the following Equation 3. (3) $E_{zs}=C\times \beta \times P\times Q\times F_{ie}$(3) Where,${\mathit{E}}_{\mathit{z}s}$ is the amount of carbon emissions from island accommodation, kg; C is the total number of beds; P is the weighted electricity consumption per B&B, kWh; 0.786 is the amount of CO₂ emitted from 1 kWh of electricity generated by standard coal, kg.

There are many types of accommodation on the island, but the layout of the rooms is basically the same, as shown in Table 6. The specific facilities are as follows: 200 rooms with 420 beds. According to the data before the epidemic in 2020, the average occupancy rate is about 70%, with an average of 294 beds per day, which should be converted into an average of 140 rooms per day, and 56 employees stay in the island every day to serve, a total of 27 rooms.

(3)	Model of tourism accommodation waste emission

Table 6. Usage of various electrical appliances in administrative offices.

Facilities	Quantity	Power/W	Time of use/h	Total power/kW
Energy saving lamps	6	15	12	1
Spotlights	2	50W	8	0.8
Incandescent lamps	1	40	8	0.32
TV 37 in.	1	180	12	2.16
Large 1.5 horse power air conditioner	1.5	1080W	20	21.6
Air water heater	1	2420	3	7.26
Electric kettle	1	1500	2	3
Small refrigerator	1	65	15	0.975
Total				37.2
167 rooms with daily emissions				6212.40

Tourism waste includes solid waste, sewage, feces, soot, SO₂, NOx, etc. According to Jian Yingmiao et al., solids include organic household waste such as food waste and paper generated from food and lodging, and inorganic waste such as plastic and metal packaging discarded during recreation (Yingmiao et al. 2012). The results of the study are summarised in the following table. The daily per capita waste generation of travellers was determined to be 3.5 kg/person/day, with food waste, park waste, and paper and textile waste each accounting for 1/3 of the total, according to the study by Dan et al. (2018). These wastes will be pulled out to land-based waste incineration plants, and waste incineration power generation mainly produces CO₂, CH₄, and N₂O. Combined with the results of carbon emissions study of waste incineration power generation projects by Bingkang et al. (2023). Combining the Intergovernmental Panel on Climate Change (IPCC) greenhouse gas inventory with the sewage treatment process, we obtain the CH₄ and N₂O emission calculation models as Equation 4, with a CH₄ emission factor of 11.9 kg/t and an N₂O emission factor of 0.97 kg/t. (4) $E_{fq}=N\times 3.5\times \sum _{i=1}^n(G_i\times {\delta }_i)$(4) where.$E_{gt}$ is the i emissions of tourism solid waste, 3.5 is the daily per capita waste production, 3.5 kg/-d.${\delta }_i$ is 1 kg of waste storage generated by CO₂, CH₄, N₂O and other emission factor, kg. then transported garbage emissions refer to the emissions of tourists boarding the island ship, here do not consider the emissions of car transport from land to the incineration plant, all types of emissions are in Table 7.

(4)	Indirect use of secondary emissions and pollution

Table 7. Comprehensive emission calculation of waste generated from tourism accommodation.

Total number of people	Total garbage generation 3.5 kg/person.d	Carbon emissions CO from transportation2 kg/kg	Incineration emission factor CO2 kg/kg	Carbon emissions SOX kg/kg from transportation	Incineration emission factor CH4 kg/kg	Carbon emissions from transportation NOX kg/kg	Incineration emission factor NOX kg/kg
7910	27,685	3.16563	0.385	0.115	0.0119	0.06949	0.00097

The washing wastewater of bed sheets, covers, towels, carpets and other linens in hotels and guesthouses is mainly composed of soap, grease, synthetic detergents, cleaning agents and a small amount of toxic and harmful substances such as bacterial coliforms and viruses, which has become an important source of water pollution, and the investigation and research of Member Jian, Niu Zhiqing, etc. concluded that more than 60% of hotel sewage wastewater is bathing and washing wastewater (Yuan, Niu, and Wang 2007) Washing wastewater has a high variation in organic concentration and high turbidity with a Biochemical Oxygen Demand (BOD) / Chemical Oxygen Demand (COD) ratio of about 0.45. Wastewater generated on the island is not subjected to recycling. Instead, it is directly discharged into a three-stage septic tank, a grease trap, and a 500m3/d wastewater treatment station located within the scenic area. Due to the absence of water storage equipment verification in the scenic area, it is assumed that the wastewater undergoes treatment to meet the required standards before discharge. The discharge standards for washing wastewater are in compliance with the ‘Comprehensive Discharge Standard for Sewage’ (GB8978-1996) and the ‘Sewage Discharge into Urban Sewerage Water Quality Standard’ (CJ343-2010), which corresponds to Grade B standards. According to Kejie Zhang's research, 5A hotel linens typically require six washing cycles, with each kilogram of dry clothes consuming approximately 50 kg of water (Kejie 2010). The daily weight of linens per room is presented in Table 8 below.

Table 8. Daily linen weight per room.

Linen items	Quantity	Unit weight/kg	Full weight/kg	Linen items	Quantity	Unit weight/kg	Full weight/kg
Large Bath Towel	2 bars	0.55	1.1	Bed Linen	2 bars	0.4	0.8
Face washcloth	2 bars	0.1	0.2	quilt cover	2 bars	0.8	1.6
Floor towel	1 Article	0.45	0.45	Pillowcase	4 articles	0.1	0.4
				Bathrobe	2 bars	1.8	3.6

From Table 8, it can be obtained that one room can produce 8.5 kg of linen in a day, including 27 staff accommodations, totalling 1419.5 kg of linen in 167 rooms. According to the study on the pollution of water bodies by laundry wastewater discharged from balconies by Shi-hao Shen, He-he Qin, etc., the characteristic pollution factors of laundry wastewater are COD and Total nitrogen (TN) (Shi-hao et al. 2020), COD, ammonia nitrogen, total nitrogen, total phosphorus, and BOD emission factors per litre of wastewater are shown in Table 9.

Table 9. Calculation of emissions from laundry water usage for guest room linens.

Emission targets	COD/kg-kg^−1	Ammonia nitrogen (NH3-N)/ kg-kg^−1	TN/ kg-kg^−1	Total phosphorus (TP)/ kg-kg^−1	DOD/kg-kg^−1
Wastewater emissions per kg of fabric	0.032	0.000378	0.000937	0.000068	0.00872

Then the following model equation can be used to derive the daily emissions of laundry linens on the island, where the total number of lodgers (5) $E_{xd}=C\times \beta \times Y\times 50\times F_{xd}$(5) Where ${\mathit{E}}_{\mathit{x}d}$ is the amount of carbon emissions from island accommodation, kg; C is the total number of beds.$\mathit{\beta }$ is the bed occupancy rate. $\mathit{Y}$ is the weight of linen produced per bed, here 8.15 kg.${\mathit{X}}_{\mathit{x}d}$ is the i substance emission factor mg-kg-1 per kg of laundry

2.2.2. Tourism restaurant carbon emissions model

The food and beverage in Fenjie Island is divided into two categories, one is the various kinds of gourmet snacks and drinks serving day-trip tourists, and the other is the hotel dine-in food serving accommodation guests. The special features are based on the special ingredients of the island, including all kinds of seafood, tropical fruits and beverages. There are five existing restaurants on the island, which can provide dining services for 600 people at the same time, among which, there are about 20 gourmet snacks, drinks and other businesses, and 2 hotel dine-in restaurants. Carbon emissions related to tourism catering primarily result from the consumption of natural gas, propane, electricity, and other energy sources. Given the diverse cooking methods employed by more than 20 restaurants, conducting a comprehensive survey is challenging. Therefore, we rely on data from the ‘Chinese Residents’ Household Energy Consumption Research Report,’ which indicates an annual per capita energy consumption of 612 kg of standard coal for Chinese households. This is roughly equivalent to 5.44 kWh of electricity. For the sake of conservative estimates, we use a slightly higher value of 6 kWh to calculate emissions. Additionally, we allocate energy consumption at a ratio of 1:2.5:2.5 for morning, midday, and evening periods. (6) $E_{cy}=(N\times L\times F_{ie})$(6) Where $E_{ft}$ is the amount of catering carbon emissions kg; N is the total number of tourists.$L$ for each meal converted electrical energy, kWh, to 2019 daily average of 7500 tourists plus all kinds of service staff 410 people, a total of 7910 people calculated, boarding island accommodation tourists including service, security only about 350 people, accounting for 4.4%, this part of the tourists consider eating three meals; Other staff members, on the other hand, typically consume between one and two meals. Considering the wide range of island entertainment options, numerous activities, and the significance of special food and beverage experiences within the tourism context, we use an intermediate value of 1.5 meals for this calculation. The energy consumption conversion and carbon emissions calculation for dining are shown in Table 10.

Table 10. Calculation of restaurant energy consumption and carbon emissions.

Number of accommodation and service staff Converted electricity			Number of other staff Converted electricity
Morning	Medium	Evening	Morning	Medium	Evening
350 people	350 people	350 people		7560 people	3780 people
350 kWh	700 kWh	700 kWh		15,120 kWh	7560 kWh
24,430 kWh

Tourism and catering are a major feature of the island. The island has a variety of ethnic and characteristic cuisine representing Hainan, the world-renowned South China Sea seafood, and Southeast Asian style bars. A lot of drinking water is needed to clean after meals, which is also a huge consumption of water resources for tourist attractions. Zhang Kejie uses the number of faucets actually configured in the kitchen, and takes the flow of faucets as the actual measurement, measuring that the daily consumption of drinking water for each person is 60L. Here, the average value of 50L of water consumption for seven types of restaurants given in the Building Water Supply and Drainage Design Manual is taken as the estimation basis. Table 10 serves as a reference for the various categories of diners. For the majority of passengers who do not stay overnight and typically depart after 6 pm, even though their island visit consists of just one meal, snacks become essential due to the abundance of games and activities available, making it a customary choice for every tourist. In the article guests in the hotel is calculated as a whole day, the tourists who eat both lunch and dinner can get 80% discount, and the tourists who only eat lunch can get 35% discount, so the total number of people who eat three meals per day is 4697. Chen Ziai and He Li conducted field verification on rural kitchens, and each item is given a range (Ziai et al. 2014). Here, considering the 5G scenic spot, the requirements for food cleaning and cooking should be high, and the highest and lowest values should be taken as a reference, as shown in Table 11.

Table 11. Calculation of water consumption and carbon emissions for tourism meals.

Three meals commuted to the number of people	Total water consumption	COD /kg-kg ^−1	NH3-N/kg-kg ^−1	TN /kg-kg ^−1	TP /kg-kg ^−1	BOD /kg-kg ^−1
4697	234,850	0.327	0.00044	0.00442	0.001163	0.23

2.2.3. Model estimation of water discharge from tourist accommodation

The main scenarios of water emissions from tourist accommodation are water for washing, water for toilets and water for drinking tea. Li Xu and Qin Yaochen's study concluded that tourists use more water per capita than local residents (Xu et al. 2013). China introduced tourist water consumption in 1999 according to the ‘Scenic Area Planning Code’ in the accommodation of tourist water consumption standards in general hotels for 100–200 litres / bed – day. Accommodation visitor water consumption indicators, summer and autumn take 200 litres / person – day, winter and spring take 150 litres / person – day 2017). However, this value spans a wide range and is not suitable for reference. According to Luo Yanju and Huang Yu et al. who conducted a study on water use for tourism tourists in Hainan (Yanju et al. 2010), it is considered reasonable to calculate the average water consumption of 0.5 t/person per overnight guest for hotel accommodation in Hainan, while the daily water consumption of day-trip tourists is 0.1 t/person. According to the statistics, 17-22% of the tourists in this island need to swim or dive in the sea, and they need to flush fresh water after swimming in the sea, and the amount of fresh water used for swimming in the sea is generally about 30 kg. Then the water consumption has. (7) $E_{ys}=(S_z+S_{fz}+S_{yy})\times F_{ie})$(7) where$E_{ys}$ is the different emissions generated by the water used by visitors.$S_z$ is the water consumption of accommodation visitors, kg.$S_{fz}$ is the amount of water used by non-accommodation tourists, kg.$S_{yy}$ is the amount of water used by swimming tourists, kg. effluent carbon emissions standard Referring to the above, the carbon emissions of water used for tourism accommodation can be calculated as shown in Table 12.

Table 12. Calculation of carbon emissions of water used in tourist accommodation.

$S_z$	$S_{fz}$	$S_{yy}$	COD /kg-kg^−1	NH3-N/kg-kg^−1	TN /kg-kg^−1	TP /kg-kg^−1	BOD /kg-kg^−1
175,000	756,000	38,500	0.032	0.000378	0.000937	0.000068	0.00872

2.2.4. Carbon emissions model of other activities in tourism

Other activities of the tour are mainly the experience of marine recreation programmes, including diving, sea flying boat, sea towing, sailing, sea fishing, underwater tour, marine animal theatre, etc. The carbon emissions here are mainly considered from the following aspects.

1. diving project, the main consideration of human sweat, skin oil, as well as people fall hair, skin flakes, etc. in the swimming very to the ocean, Wang Yuxin research found that the swimmer urinates about 3.5 ∼ 5.0% of swimmers, urine is one of the main sources of pool water pollution; summer swimming, with the increase in the amount of exercise in the amount of sweating increased, the sweating volume is generally 100 ml/h; the CO2 in the exhaled breath of swimmers and human secretions and excretions together can change the PH value of swimming pool water, while there are pathogenic bacteria such as dysentery bacillus, Pseudomonas aeruginosa, fungi, streptococci, etc. (Yuxin, Xiquan, and Wentao 1999). Luo Lan and He Zhongchen considered free residual chlorine, turbidity, pH, free residual chlorine of foot dipping pool, urea, total bacterial count, and coliform as the main health indicators of public swimming places, and a large number of people are exposed to them every day.(Lan et al. 2022).

2. sea blimp is composed of flying shoes, flying water pipe, jet ski / motorboat as a power entertainment projects, jet ski is generally 155 horsepower 110 kW, this kind of boat hourly consumption of diesel fuel amounted to about 40–60L. Other sea tugboats, kinetic blimp, sea motorboats, banana boats, water warriors, etc. are high-powered diesel generators for power, and their power is more than 100 kW.

3. The underwater tour is a semi-submersible boat, powered by a 1440 kW diesel engine, with a 20-minute tour cycle, as it is a free programme, it is dedicated to tourists who stay at night to see underwater creatures. It is sailing at full power for the whole journey.

4. The other submarine for underwater sightseeing is an all-submarine, with a length of 19.6 metres, a width of 3 metres, a diving depth of 20 metres, and a rated capacity of 48 visitors. Each time the ship goes to sea for 40 min, the active power of the ship is 100 kW power battery, and the main propulsion power is 10KW.

The whole recreational activity parameters and energy consumption calculation are shown in Table 13.

Table 13. Energy consumption of major recreational activities in the scenic area.

Projects	Dive	Sporty blimp	Parachute towing at sea	Beach bikes	Sailboat	Animal theatre	Flying dragon on water	Submarine tour (half dive)	Submarine tour (full dive)
Percentage of	15%	1%	0.8%	2%	0.2%	40%	1.2	5%
Number of people	1125	75	60	100	15	3000	90	380	300
Energy consumption/kg		806.25	645.00	716.28			967.50	100KWh	393.0.

Combined with the diesel carbon emissions parameters and battery carbon emissions parameters studied above, the highest emission factor is chosen to calculate considering the relatively poor performance of the engines used in recreational equipment. Then, the carbon emissions of the main recreational activities in the scenic area are calculated as shown in Table 14.

Table 14. Carbon emissions of major recreational activities in the scenic area.

Recreational activity fuel consumption/kg	Electricity consumption for recreational activities/kWh	SO2 /kg	NOX /kg	Soot/kg	CO2 /kg	CO/kg	PM/kg	HC/kg
3527	100	11.5 0.03	69.49 0.15	0.27	3129.82 0.786	4.6	1.02	2.44

Notes: The second row in the table is the mission factor of each power consumption. PM: particulate matter. HC: hydrocarbon.

3. Tourism structure carbon emissions analysis

3.1. Calculation results of carbon emissions of tourism activities

After the above analysis, the power resources consumed by Fenjie Island in a day with an average of 7500 visitors as a reference are shown in Table 15.

Table 15. One-day energy usage and comprehensive emission summary for Fenjie Island tourism operation.

Energy	Total consumption	CO2/kg	CO/kg	HC	NOX/kg	SO2/kg	PM/kg	Soot/kg
Diesel kg	79,487	136,211	1316	689	2211	408	524
Electricity kWh	39,470	15,280			1916.77	578.32		5203.43
Water kg	127,5325	COD/ kg-kg ^−1	NH3-N /kg-kg ^−1	TN/ kg-kg ^−1	TP/ kg-kg ^−1	BOD/ kg-kg ^−1
		110,091	496.63	2012.96	343.89	63088.44

3.2. Analysis of carbon emissions from various tourism activities

1. Table 14 reveals the substantial daily energy consumption on Fenjie Island, amounting to approximately 40,000 kWh of electricity. This results in a daily CO2 emission exceeding 15 tons from electricity generation. It's worth noting that the electricity pollution remains confined to the thermal power plant and does not directly impact the island. Nevertheless, this analysis serves as a reminder to both travellers and island management to prioritise electricity conservation.

2. The pollution of diesel fuel to this island is decisive, the amount of oil used in a day reaches about 80 tons, which directly produces more than 136 tons of CO₂, 1.3 tons of CO, more than 2.2 tons of NOX, 0.4 tons of SO2, 0.5 tons of PM; and all these pollutants are directly discharged into the sea or offshore air, which will cause serious consequences to the creatures of the sea.

3. Fenjie Island has a large number of visitors and uses more than 1245 tons of water per day. The huge amount of water will directly consume its fresh water resources. At the same time, the discharges produced will affect the island's environment. 110 tons of COD and 63 tons of BOD are required for sewage treatment. And the island is currently only a 500m3 septic tank root to be unable to meet such a huge amount of sewage treatment, cannot be treated and ultimately can only be discharged into the sea, the resulting ammonia nitrogen, total nitrogen, total phosphorus affect the light of the sea, seawater quality, seawater nutrient content. After a large number of discharge will lead to the ocean to the high requirements of water quality environment of the coral to bring disaster.

4. The island generates more than 27 tons of garbage every day, and although this garbage is hauled to the power plant for incineration every day, the pollutants produced by incineration cannot be ignored as a problem. Of course some of this garbage will be thrown into the sea by tourists and cannot be collected, which will become white pollution of the sea in the long run.

4. Fenjie Island abatement design and capacity study

Through theoretical and practical verification, the energy consumption of Fenjie Island is huge and the potential pollution problem is more serious. As a 5A tourist area, energy saving and emission reduction should be taken as an important matter in the island, specifically from the above two aspects.

4.1. Access to the island tourist capacity study

Many scholars have proposed the cask effect of tourist capacity in tourist attractions (Liu 2017), and proposed to use the capacity of water supply facilities as the main observation point to limit passenger capacity. This is not a scientific evaluation method. The current capacity of the water supply system is insufficient. Passengers may have to reduce their water consumption or consider increasing the capacity of the water supply infrastructure. Given the economic considerations, most individuals are willing to invest in expanding the water supply capacity.

For islands like Fenjie Island, with coral water quality as the evaluation basis, the maximum capacity of the island can be calculated. Under the current circumstances, the reference standard for tourist capacity in the scenic area must be based on the zero-emission standard of tourism carbon footprint. Specifically, subtracting the total emissions from the absorption capacity of trees covering an area of 0.41 square kilometres and the daily purification capacity of seawater. If the result is greater than zero, it will inevitably have an impact on the coral reefs in the ocean. This is an unbridgeable red line and the only criterion for assessing the sustainable development of tourist resources in the island for visitors. That is. (8) $\sum {\mathit{E}}_{\mathit{i}}-(\sum \mathit{S}{\mathit{L}}_{\mathit{i}}+\sum \mathit{H}{\mathit{S}}_{\mathit{i}})$(8)

In equation 8, the ${\mathit{E}}_{\mathit{i}}$ is the total daily emission of class i from tourism activities on Fenjie Island, kg.$\mathit{S}{\mathit{L}}_{\mathit{i}}$ is the sum of daily absorption i pollutants from the forest, kg. $\mathit{H}{\mathit{S}}_{\mathit{i}}$ is the sum of daily self-cleaning i pollutants from the ocean.

According to the data given by Punch.com, forests are air purifiers and are crucial to the global climate. Their ability to absorb dust is 75 times greater than that of bare earth; one hectare of forest can absorb 20-60t of dust a year. ₂and produces 730 kg of oxygen O₂. An adult person consumes 0.75 kg of oxygen and emits O.9 kg of carbon dioxide per day.(Chengcheng 2020). It can be seen that if we consider the CO₂ emission and adsorption, the forest in this scenic area adsorbs 42,000 kg of CO₂ per day, which is more than double.

COD is an important indicator of water quality in the ocean, which is supported by the fact that its average content is within the range of Class I seawater. In the process of chemical purification, the change of triple nitrogen content can be used to judge the self-purification ability of water bodies The change of triple inorganic nitrogen content can best indicate the self-purification ability of water bodies (Jun and Zhenji 1983). Xia, H. Y. and Li, X. L. took the biochemical degradation rate coefficient of COD at water temperature from 10 to 28°C (0.023-0.076 d⁻¹) and the concentration of BOD₅ at 0.6 mg/L as the Fenjie of self-purification capacity in Dapeng Bay (Hua-yong, Xu-lu, and Kang 2011). The empirical value of 1.317 mg/L is two times higher than this value. Obviously, the average daily vistor count of 7500 on the island in the current state is more than the environment can sustain, based on the adsorption capacity of the forest and the self-purification capacity of the ocean. An abatement design is needed.

4.2. Emission reduction recommendations

1. Fenjie Island is developed and utilised as an isolated island, and the number of visitors per day is enough to explain the value of other tourism utilisation. As the tourist destination that tourists want to visit, the manager must make good requirements for tourists to enter the island, and the local government must legislate for this purpose, so that every traveller should become the owner of energy conservation and emission reduction.

2. The organiser should do a good job of energy-saving renovation of the island, replacing energy-consuming products, and all employees should be leaders and practitioners of environmental protection. The island's energy-consuming equipment will use electricity whenever possible.

3. Replacement of visitor boats into the island for electric power system, through the island sightseeing of semi-submersible boats and full-submersible boats power system can be known, the use of electricity as power its energy saving and emission reduction effect is very obvious. The 100kWh power of the full-submersible boat can guarantee its 6-8 h of full load use. nearly 3000 bits of CO2 will be saved, and with the further expansion of the proportion of renewable energy power, electricity as will really become a low-energy commodity, so the organisers should act as soon as possible to eliminate the backward production capacity, as soon as possible to achieve the replacement of vistor boats in and out of the island for electric power system.

4. The island should expand the size of septic tanks as soon as possible, to ensure that all sewage can be treated and discharged up to standard.

5. The organisers should conduct a re-evaluation of the scenic tourist capacity measurement, not solely driven by economic considerations and unlimited expansion.

5. Discussion

The sustainable development of island tourism resources is a matter of great importance for mature governments, businesses, and society. Balancing economic growth and environmental protection is crucial to ensure that people can truly enjoy the benefits of development. In this paper, coral organisms, which have high environmental requirements in marine ecosystems, are used as indicators of environmental pollution. The study proposes using the standard of carbon neutrality and zero emissions in the scenic area to quantitatively determine the maximum number of daily tourist arrivals. This standard is relatively rigorous and high, which may have a certain impact on economic development and could potentially trigger various controversies in the industry. However, as an ecological red line, it should receive societal response and support.

Of course, the paper does not consider the influence of oceanic climatic characteristics on the environment, such as the magnitude of wind power, which can affect the level of pollution to some extent. In terms of analysing the self-cleansing capacity of the ocean, the paper only references existing literature as a benchmark and does not conduct relevant testing or verification. The calculations also do not consider the size and depth of the surrounding waters within a certain square kilometre range around the island, which is a comprehensive and important issue. It is hoped that more scholars from around the world can join in the discussion and contribute to the fundamental research for the scientific development of island tourism resources.

6. Conclusion

Based on an average daily tourist count of 7500 visitors, we conducted a comprehensive study on the carbon emissions of the 5A-rated Fenjie Island scenic area in Lingshui, Hainan, China. We established a carbon emission model and conducted both theoretical research and on-site verification analysis. The research findings indicate that the scenic area emits 151,000 kg of CO2 daily, with a daily COD water pollution emission of 110,000 kg, and a BOD₅ concentration of 1.317 mg/L. Taking into account the forest coverage on the island, the forest absorbs 42,000 kg of CO2 daily.

Furthermore, the BOD₅ concentration exceeds the self-purification capability of the surrounding seawater, which typically has a self-purification capacity of 0.6 mg/L. Additionally, emissions of other pollutants are also elevated, indicating that the comprehensive carbon emissions resulting from hosting 7500 tourists daily have exceeded the scenic area's capacity for adsorption and self-purification. To maintain the current status, it is imperative to implement artificial control measures on tourist numbers. Failure to upgrade tourism facilities on the island for energy efficiency and emission reduction will lead to a continual decline in the scenic area's carrying capacity. In the long term, this will cause immeasurable harm to the island's tourism resources and the surrounding marine environment.

The comprehensive zero-emission research method used in this study can serve as a reference for determining visitor limits on islands and in other tourist areas worldwide. It provides essential guidance for the orderly development of islands, environmental conservation, and the achievement of harmonious coexistence between humans and nature. However, it's important to note that most of the carbon emission factor standards for transportation, tourist lifestyles, dining facilities, and others cited in this study are based on previous research data. The accuracy and precision of these data may affect the final research results and should be used with caution in practical applications.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This paper was supported by Hainan Provincial Natural Science Foundation of China (121MS059).