Improvement in the Methodological Estimation of Sulfur Hexaﬂuoride Use in Electrical Equipment for Malaysia’s National Greenhouse Gas Inventory

: Sulfur hexaﬂuoride (SF 6 ) gas is one of the high global warming potential (GWP) gases regulated under the Kyoto Protocol. In Malaysia’s Biennial Update Report 3, the Revised 1996 Intergovernmental Panel on Climate Change Guidelines were followed to estimate the SF 6 emissions in the country, including the time series from 1990 to 2016. The majority of SF 6 emissions originate from the use of this gas in electrical equipment, where it is predominantly used in transmission switch gears, which have increased rapidly because of increasing electricity demand. SF 6 gas plays a signiﬁcant role in greenhouse gas emissions in Malaysia because this gas has a higher GWP than carbon dioxide. Hence, this SF 6 gas needs to be estimated using newer guidelines such as the 2006 IPCC Guidelines. Detailed activity data in the new methodology require stakeholders’ engagement with utility providers and government agencies. This paper describes the GHG inventory improvement plan, focusing on SF 6 emissions for Industrial Processes and Product Use for Malaysia through this transition of methodology.


Overview of SF 6 gas
Sulfur hexafluoride (SF 6 ) gas has been utilized as an insulating medium for highvoltage circuit breakers since the 1950s because of its exceptional dielectric and arcquenching properties, which stem from its high electronegativity and density. In addition, its high density has allowed the construction of smaller electrical equipment that is manageable and can bear safe high-voltage loads. However, SF 6 gas usage has a few disadvantages and operational constraints. For example, maintaining the required dielectric properties means that SF 6 gas needs to be kept at a minimum functional pressure. Operators must purchase additional gas to replace any leaked or lost SF 6 gas, which adds to a facility's costs. Moreover, exposure to moisture must be minimized because it can degrade the dielectric properties and cause dangerous by-products, such as hydrofluoric acid, to form from decomposed SF 6 gas. Lastly, SF 6 gas is a harmful greenhouse gas (GHG) that can persist in the atmosphere for up to 3200 years; 1 tonne of SF 6 gas emission is equivalent to 22,800 tonnes of CO 2 .
Despite these concerns, SF 6 has been used in electric power utilities for more than 40 years because of its remarkable electrical, thermal, physical, and chemical properties. To reduce SF 6 emissions into the atmosphere, the industry continues to concentrate on improving its SF 6 handling practices. Poor gas handling practices during equipment installation, maintenance, and decommissioning, as well as leakage from SF 6 containing gasinsulated equipment, are the main sources of SF 6 emissions. Closed-pressure equipment is prone to SF 6 emissions, while emissions in sealed-pressure equipment are more apparent In Malaysia's Biennial Update Report (BUR3) to the United Nations Framework Convention on Climate Change (UNFCCC), SF 6 gas is not considered a key category because the total emissions in this sector do not have a significant influence on the country's total inventory of GHG in terms of absolute level.
The motivation for improving the national GHG inventory is to better understand the sources and magnitude of these emissions, which is essential for developing effective climate change mitigation and adaptation policies. The significant contribution of this study is the establishment of methodologies to estimate SF 6 gas emissions from electrical equipment for Malaysia, which was achieved according to the requirement of IPCC 2006 Guidelines. Ultimately, this work fulfills the National Improvement Plan, which aims to uphold two main principles from the TACCC: transparency and accuracy. Figure 1 shows the total emissions for the sector of Industrial Processes and Product Use (IPPU) for Malaysia on the basis of GHG emissions reported in BUR3 [4]. Among the various sub-categories in this sector, the use of SF 6 gas is reported under the main category 2G: Other Product Manufacture and Use and within the specific sub-category 2G1b: Use of SF 6 gas in Electrical Equipment. This category recorded less than 1% of the total GHG emissions for 2016. Category 2G1 is not a key category, which is why the development of a country-specific emission factor (CSEF) is not a priority because the emissions are not considered significant. However, inventory compilers need to estimate this category based on the 2006 IPCC Guidelines [5] to consistently measure the GHG emissions of the country by using the same basis for comparison. Similarly, in the BUR3 report, all GHG are estimated using the 2006 IPCC Guidelines, except for SF6 gas used in 2G1 Electrical Equipment, which requires the adoption of the Revised 1996 Guidelines based on limitations of activity data during that period [4]. Table  1  Many sub-categories such as 2B9: Fluorochemical Production, 2C4: Magnesium Production, 2E2: TFT Flat Panel Display, and 2G2, namely, SF 6 and PFCs from Other Product Uses such as military and accelerators, among others, were not accounted for because no activities occurred pertaining to those industrial processes and use in Malaysia for that duration. In addition, categories such as 2E1: Integrated Circuit or Semiconductor and 2E3: Photovoltaics under the Electronics Industry were successfully estimated using the 2006 IPCC Guidelines based on default Tier 1 methodology. Hence, the only remaining sub-category using the Revised 1996 Guidelines in the national GHG inventory is this category because inadequate data were collected, given that the newer guidelines require more detailed activity data, as will be explained in the subsequent sections. In view of this situation, Malaysia initiated the National Inventory Improvement Plan for SF 6 emission estimation, concentrating on 2G1, because it is the only remaining sub-category that has yet to transition to the newer methodology of GHG emissions.
The main purpose of the National Inventory Improvement Plan is to improve climate change reporting through more precise methodological shifts, particularly for category 2G: Other Product Manufacture and Use, specifically sub-category 2G1: Electrical Equipment, which involves gas-insulated circuit breakers, switch gears, transformers, buses, and transformers. SF 6 gas has excellent insulation properties and is commonly used in the electrical equipment stated. Nonetheless, a risk of gas leakage exists during various stages of the life cycle of cylinder equipment, including manufacturing, shipping, storage, installation, operation, maintenance, decommissioning, disposal, or recycling.

SF 6 Sources in Malaysia
The electricity sector in Malaysia covers the generation, transmission, distribution, and sales of electricity in the country. The country has three main utility providers: Tenaga Nasional Berhad, Sabah Electricity Sdn. Bhd., and Sarawak Electricity Support Corporation (also known as Sarawak Energy). On the basis of the generation mix until the end of 2010, the total plant generating capacity is estimated at 26,265 MW, constituting 57% natural gas, 24.1% coal, 8.4% hydro, 6.4% oil/diesel, and 4.2% biomass/others [6].
According to the 2006 IPCC guidelines, SF 6 gas was emitted in each phase of the electric equipment life cycle, specifically during the manufacturing, installation, use, servicing, and disposal stages. A large quantity of SF 6 gas is usually used in gas-insulated transformers (GITs) in Asian countries. SF 6 gas is used in the power industry because of its exceptional electrical insulation and arc-quenching properties. However, the management and handling of SF 6 gas must be conducted properly because SF 6 gas is a GHG with a higher global warming potential (GWP) than CO 2 [7,8]. SF 6 gas is also heavily used in gas-insulated substations, where SF 6 -insulated circuit breakers, busbars, and monitoring equipment are housed. Among the most significant use of SF 6 gas is in high-voltage circuit breakers, where it serves as insulation and helps extinguish the arc from occurring when an energized circuit breaker operates. The quantity of SF 6 gas emissions from electric power systems is influenced by various factors, such as the type and age of the SF 6 -containing equipment and the handling and maintenance operating standards followed by utility providers. With its prolonged life span and high GWP, even a small amount of SF 6 gas can have a strong effect on the environment [9].
The gas is also used to detect a direct leak in an enclosed GIS substation. Indirect leak detection solutions are expensive because they require one monitoring device per gas compartment. Furthermore, the pressure/density switches that are currently used to monitor the SF 6 gas compartments for safety consideration lack sensitivity for rapid leak detection. Direct detection is normally preferred and more reliable because it relies on measuring trace concentration for leaking gas in the ambient air [10].
Poor and improper handling means that SF 6 emissions have the potential to occur during installation, maintenance, disposal, and equipment leakage. Leakages in closedpressure equipment predominantly occur during the manufacturing and disposal processes, while all equipment will release SF 6 gas at the disposal stage. Proper disposal procedures will be able to help reduce the emission of SF 6 into the atmosphere. In the manufacture of equipment, several process steps are performed, such as installing and testing the components and equipment. During the manufacture of electrical equipment, SF 6 emission is likely to occur while assembling and testing components before switch gears are obtained. To maintain the pressurized SF 6 gas, the manufacturer must first conduct the volume tightness test to test the circuit breaker capability.
The next potential SF 6 gas leakage can occur during the delivery of equipment or cylinders. This dry gas must be placed in the correct and safe position to ensure that no leakage occurs during the delivery process. During equipment installation, SF 6 gas can also be released without proper handling or if the refilling equipment is damaged. Electrical equipment, including closed-pressure equipment, should be disposed of meticulously. This equipment needs to be deactivated properly to reduce SF 6 gas leakage into the atmosphere. Used gas can only be either disposed of or reused. This process requires qualified workers from gas producers or specialized services. The risk of gas emissions is very high if untrained parties or different groups perform this process for closed-pressure and sealedpressure equipment [11]. 6 Regulation and Policy around the World SF 6 gas contributes to the high GWP of the power and semiconductor industries. As its application increases, countries have started planning to regulate this gas in various ways. This study reviews some of the regulations and policies in different countries and regions.

Review of the SF
The European Union (EU) has planned precautionary measures to decrease SF 6 gas because the emissions of fluorinated gases (F-gases) doubled from 1990 to 2014 [12]. In 2014, the European Commission enacted Regulation No. 517/2014, commonly referred to as the "2014 F-gas Regulation". The latest regulation sets requirements for products and sectors beyond the power industry and all hydrofluorocarbons; however, the following discussion focuses on the SF 6 gas requirements used in switch gears. According to the regulation, electrical switchgear is defined as "switching devices and their combination with associated control, measuring, protective and regulating equipment, and assemblies of such devices and equipment with associated interconnections, accessories, enclosures and supporting structures, intended for usage in connection with the generation, transmission, distribution, and conversion of electric energy" [13]. The EU is currently reviewing the effectiveness of the F-gas Regulation and exploring options to improve it. The Commission's proposal for a new regulation, which was expected by April 2022, includes a phase-out plan for SF 6 -, especially for medium-voltage applications.
The U.S. Environmental Protection Agency (US EPA) required reports on large SF 6 emissions in 2009. The California Air Resources Board (CARB) and the Massachusetts Department of Environmental Protection strengthened their SF 6 emission regulations, including emissions reporting standards and requirements for emission reduction. In 2009, in addition to the effort to reduce the emission rates, the US EPA established a Greenhouse Gas Reporting Program, which requires major suppliers and contributors of emissions to monitor and report their GHG emissions annually [14]. In addition, the CARB is tasked with protecting the public from air pollution and developing climate change programs. Their regulation was emulated by 14 other US states, where an SF 6 phase-out program will be enforced by 2025. In 2015, the Massachusetts Department of Environmental Protection enacted a regulation to ensure that all state utilities monitor and report their SF 6 emissions and inventory.
No SF 6 legislation in Asia specifically targets transmission and distribution businesses. Manufacturers and importers of fluorocarbon gases are urged to minimize their production and distribution while recycling fluorocarbon gases are recycled wherever practical in Japan. Through a national GHG inventory, South Korea maintains records of its yearly SF 6 emissions from the energy sector. In Japan's Fourth Biennial Update Report, filed in January 2019, SF 6 emissions declined by 83.4% from 1990 levels to 2.1 million tonnes of CO 2eq in 2017. This reduction is attributed to the improvements in gas recovery and management systems within the electrical utilities sector [15]. Japan has no laws that forbid the use of SF 6 gas in the power sector or that require the tracking and reporting of emissions. Instead, Japan established a voluntary action plan in the late 1990s for electric utilities and switchgear OEMs, with the goals of lowering emissions throughout the SF 6 life cycle, establishing and promoting recycling, improving SF 6 inventory tracking, and creating an alternative insulation technology [16].
In South Korea, SF 6 emissions were about 6.8 million tonnes of CO 2eq ., constituting at least 1.0% of the national GHG emissions in 2016. This value implies an increase of 3810.5% compared to 1990 [17]. This significant spike in percentage was due to the rapid development of various technology manufacturing subsectors over time, which called for the expansion of the electrical infrastructure. One subsector is the semiconductor industry, which uses SF 6 gas in its operations. South Korea also introduced a GHG emissions trading scheme in 2015, which also involves SF 6 gas. From an emissions baseline of the 2011-2013 levels, Phase 1 (2015-2017) requires 100% free allocations for the majority of the sectors; Phase 2 (2018-2020) requires 97% of the total allowance; and Phase 3 (2021-2025) will require around less than 90% free allowances [18]. The state-owned utility of South Korea, Korean Electric Power Corporation (KEPCO), reportedly signed a contract for joint usage of an SF 6 gas decomposition facility with the Korean National Railway, indicating the country's determination to shift away from SF6 [19]. The manufacturing facility will have a production capacity of 60 tonnes per year when finished, which was anticipated in June 2022. These six decomposition facilities, which would each process 300 tonnes annually, are all being built by KEPCO. The 6000 tonnes of SF6 gas that KEPCO reportedly releases are intended to be destroyed by these facilities by 2050.
In China, according to China's National Emission Inventory, the total amount of SF 6 emissions from 2012 reached 1000 tonnes, which is more than two times that in 2005 [20], 95% of which was attributed to electrical equipment [21]. The use of SF 6 gas in semiconductor production has been phased out to comply with environmental regulations, and the use of SF 6 gas as a safeguarding gas in magnesium manufacturing in China was stopped in 2010. Furthermore, given recent advancements in management and technology, leaking during SF 6 gas manufacturing might be insignificant. Electrical equipment continues to be the principal consumer of SF 6 gas and will be the primary contributor to SF 6 emissions in the future.
Limited information on SF 6 emissions is available in China's Second Biennial Update Report. However, China has shifted away from using SF 6 in GIS over the past 10 years. For instance, within the 12 kV voltage spectrum, including both primary distribution and secondary distribution, they have started to shift away from using SF 6 gas. While solidinsulated switchgear made up the first generation of SF 6 -free switchgear, the current trend is moving back to gas-insulated switchgear that uses substitute SF 6 gases. China is now exploring new rules or guidelines to further cut SF 6 petrol usage and emissions after the 2018 report. This approach involves a focused working group composed of utilities, oil and gas companies, and some of the top switchgear OEMs. This focused working group was established in October 2021 and is charged with investigating the application of SF 6 gas in the energy sector and possible approaches for regulating SF 6 and its substitutes. This working group is coordinated by China's Energy Research Society and the Ministry of Ecology and Environment [22].
An analysis of SF 6 gas emissions in Malaysia indicates that the country currently has no appropriate disposal option for reducing SF 6 gas [23]. Thus, at end-of-life, all the gases are released. Although the regulations mention the emission standard, the absence of containment and disposal facilities will eventually cause problems. Malaysia pledged at the UNFCCC 21st Conference of Parties to decrease its GHG emission intensity by 35% by 2030 when compared with the GDP in 2005. On the basis of the Third National Communication and Second BUR to UNFCCC, which was submitted in September 2018, the total national emissions and removals of SF 6 gas were 13,240.59 kg, which corresponds to 316.45 million kg of CO 2eq in 2014 [4]. The semiconductor industry and other businesses that largely rely on gas-insulated electrical equipment are the principal producers of products that consume and emit SF 6 gas.

SF 6 Emission Estimation Methodology
This section covers the methodology used to estimate SF 6 emissions from electrical equipment for insulation purposes in Malaysia. A detailed comparison is conducted between the methods proposed for the SF 6 emissions from electrical equipment using the Revised 1996 IPCC Guidelines and 2006 IPCC Guidelines. Until 2017, Malaysia had been using the revised 1996 IPCC Guidelines for the accounting and reporting SF 6 emissions. In recent reporting for 2018 to 2019, Malaysia shifted the method of reporting SF 6 emissions toward the 2006 IPCC Guidelines.
In general, the total activity data are the SF 6 emissions required during the manufacturing, installation, servicing, and disposal processes of electrical equipment that are widely used as insulators and circuit breakers or other uses and gas handling processes such as refilling and transportation. The selection method of emission calculation is purely dependent on the information available and the state of the country [11,12]. Inventory compilation is encouraged to contact chemical manufacturers and suppliers to assess the readiness of these stakeholders in providing information related to SF 6 emissions from electrical equipment.
The recommended best practices suggest using consumption data from users of SF 6 gas or import, export, or consumption data from SF 6 gas producers and distributors within Malaysia, disaggregated by the major type of SF 6 gas application. Tier 1 uses the default emission factor, and Tier 2 employs a country-specific technique. Tier 3 employs either a mass-balance or an emission-factor approach for various life cycle stages depending on the circumstances in each country.
The 2006 IPPC Guidelines include new gases and categories that were not mentioned in the Revised 1996 IPCC guidelines. The 2006 IPPC Guidelines provide clearer guidance on non-energy uses of fossil fuels, enabling the estimation of actual emissions of fluorinated compounds. The significant difference between the two guidelines is that all the estimates represent the actual emissions and not just the potential emissions as per the Revised 1996 IPCC Guideline. Overall, the IPCC 2006 Guidelines maintained the methods of earlier guidelines and integrated good practice guidance, thus reducing uncertainties.
The estimation methods for SF 6 gases from the electrical equipment used are influenced by three factors: choice of methods, choice of activity data, and choice of default emission factors. The tools that facilitate the choice of emission factor and reporting can be obtained from the IPCC emission factor database (EFDB). For Malaysia, the most suitable method is the Tier 1 method, which utilizes the sectoral activity data and default emission factor. The following section explains in detail the methodological steps for the successful estimation of SF 6 emission for Malaysia. It also compares the formulation for SF 6 where: Manufacturing emissions = manufacturing emission factor × total SF 6 consumption by equipment manufacturers; Equipment installation emissions = installation emission factor × total nameplate capacity of new equipment filled on site (not at the factory); Equipment use emissions = use emission factor × total nameplate capacity of installed equipment. Note: The use emission factor includes emissions due to leakage, servicing, and maintenance, as well as failures; Equipment disposal emissions = total nameplate capacity of retiring equipment × fraction of SF 6 remaining at retirement.
The SF 6 gas usage of equipment manufacturers and/or the nameplate capacity of the equipment at every stage of the life cycle after production in the country, as applicable, are multiplied by default regional emission factors to estimate emissions. If installation emissions are taken into account in the emission factor for emissions from production or use, then the term "installation emissions" may be discarded (for closed-pressure equipment, for example).
The activity data collected from the identified stakeholders are utilized in IPCC Inventory Software, which has the following sub-categories: The Revised 1996 IPCC Guidelines use the following SF 6 emission estimates formulation, shown in Equation (2). The emission factor, where applicable, is selected based on the regional values for Japan. The total SF 6 emissions are assumed to be approximately 1% of the total SF 6 gas contained in equipment such as GIS and circuit breakers. If the life span of the GIS equipment is 30 years, then the amount of SF 6 gas that will remain is estimated at 70% after retirement and will be released during disposal. The total SF 6 emission can be estimated using Equation (2) Emissions of SF 6 in year t = 1% of the total quantity of SF 6 This equation provides only the potential emissions of SF 6 gas, unlike the 2006 IPPC Guidelines, which enable the actual estimation of SF 6 emissions for Malaysia. Using the IPCC 2006 Guidelines provides more insights into the actual state and trend of SF 6 emissions in Malaysia with the time series analysis.

Emission Factor Selection
The design of the equipment (which varies based on when and where it was made), SF 6 gas handling procedures, the accessibility of cutting-edge handling technology, SF 6 gas costs, and laws (such as recovery requirements) are all factors that affect emission rates. Emission rates may vary over time or between countries depending on changes in any one of these factors. For the Tier 1 method, the suggested default emission factors are shown in Tables 2-4 and were developed for some regions. The recommended approach is to select default emission factors from regions and countries with similar equipment designs and SF 6 gas handling procedures to be applied to the country whose emissions are being evaluated. The electrical equipment most certainly comes from either Japan or Europe because both regions supply most of the global demand for electrical equipment. Regional default emission factors, apart from those for the United States, are those that were recorded for 1995, prior to the implementation of any unique industry emission reduction activities. Around 70% of the SF 6 employed to evaluate equipment during manufacturing in Japan in 1995 was retrieved and matches the values retrieved during equipment maintenance for equipment rated 110 kV or higher. Equipment rated less than 110 kV did not yield any gas [24]. In 1995, gas supply systems for equipment manufacture in Europe were usually decentralized, and filling tubes were not self-closing. Gas was recovered to approximately 0.05 bars absolute during manufacturing and maintenance [25].
With the formulation of the SF 6 emissions estimate given in the IPCC 2006 Guidelines, an appropriate emission factor that can best represent the country's state of emissions was obtained. The EFDB consists of emission factors that were developed for some regions. A good practice is to select default emission factors from countries and regions with equipment designs and SF 6 handling practices similar to those of the country whose emissions are being estimated. Japan and Europe supply most of the global demand for electrical equipment, which is why equipment designs are likely to be similar to those of either of these two countries. The emission factor chosen for Malaysia is based on regional figures for Japan. The emission factor was chosen as the data statistics by the Federation of Electric Power Companies (FEPC) and the Japan Electrical Manufacturers' Association (JEMA) (FEPC and JEMA, 2004) and did not differentiate between equipment types in reporting mean emission factors. As a result, the parameters can be applied to all types of equipment, including GITs, sealed-pressure systems, and closed-pressure systems, which are the most representative of the equipment types in Malaysia.

Activity Data Requirements
For Malaysia, SF 6 gas can be found in electrical equipment such as GIS substations and gas circuit breakers. Hence, emissions occur during every stage of the equipment's life cycle, including production, installation, usage, maintenance, and disposal. The various emission source types are divided according to the types of electrical equipment, namely, manufacture, use/installation, and disposal. In general, the activity data can be classified according to equipment basis: sealed-pressure, closed-pressure, and GITs. These categories are further divided into medium-voltage and high-voltage switch gears. The sample nameplate capacity of these switch gears is shown in Figure 2. namely, manufacture, use/installation, and disposal. In general, the activity data can be classified according to equipment basis: sealed-pressure, closed-pressure, and GITs. These categories are further divided into medium-voltage and high-voltage switch gears. The sample nameplate capacity of these switch gears is shown in Figure 2. Similar to other countries, Malaysia aims to reduce GHG emissions. Thus, the country has made more effort to obtain activity data year by year to improve its GHG reporting. Nevertheless, some gaps remain, which will require further improvement with assistance from government agencies to reduce uncertainty from the activity data while increasing accuracy. In GHG inventory accounting and reporting for 2018 and 2019, the identified gaps in the activity data on electrical equipment used at utilities are generalized as follows: o Leak detection and repair; Similar to other countries, Malaysia aims to reduce GHG emissions. Thus, the country has made more effort to obtain activity data year by year to improve its GHG reporting. Nevertheless, some gaps remain, which will require further improvement with assistance from government agencies to reduce uncertainty from the activity data while increasing accuracy. In GHG inventory accounting and reporting for 2018 and 2019, the identified gaps in the activity data on electrical equipment used at utilities are generalized as follows: Leak detection and repair; Use of recycling equipment; Employee education/training. Leak detection and repair require improvements to new equipment, which can be achieved by obtaining SF 6 monitoring tools and data management systems. Older equipment can be refurbished, and more efficient operation and maintenance techniques should be implemented. The past experience and lack of monitoring or handling of the SF 6 gases from the production at the manufacturers until disposal must be critically reviewed, and an appropriate and standardized management system should be considered. The employees' competency skills and knowledge in managing the SF 6 gases in the electrical equipment at functional locations can be increased through focused and continuous training with exposure to technologies for detecting leakages and systematic data logging. However, all these gaps require greater efforts and increased investments by the utility provider. The government can play a more significant role, such as offering incentives to electrical equipment utilities and manufacturers for reducing SF 6 . Critical reviews on Australia, the United States, and Japan show that these countries effectively address the same gaps that were identified for Malaysia, as indicated by the fact that SF 6 gas emissions are a key category in these countries' respective national GHG inventories [26][27][28].

Current Improvement for Malaysia and Moving to Higher Methodological Tiers
With the expected constraints, restrictions, and limitations in gathering the required activity data, the estimated SF 6 emissions are calculated only using the Tier 1 approach. Wherever possible, obtaining data for SF 6 emission estimates should involve government agencies and strong stakeholder engagement to ensure complete activity data. Doing so will enable Malaysia to progress further to the Tier 2 method and ultimately to the Tier 3 method in the future. The improvements in the recent GHG accounting and reporting involved shifting from the Revised 1996 IPCC Guidelines to the 2006 IPCC Guidelines, which requires collecting more detailed activity data. The following significant gaps were addressed in the transition from the Revised 1996 IPCC Guidelines to the 2006 IPCC Guidelines: The Revised 1996 IPCC Guidelines mention only two methods of estimating emissions of SF 6 gas from electrical equipment: A potential approach that equates emissions to chemical consumption; A simple emission factor-based approach that applies country-specific or global default emission factors to the quantities of SF 6 gas in operating and retiring equipment, respectively.
The Good Practice Guidance 2000 (GPG2000) [29] introduced three Tier 3 mass-balance methods and a more detailed Tier 2 emission factor-based approach that provides emission factors for each life cycle stage. In addition, the guidelines provided regional default emission factors for Tier 2; The 2006 IPCC Guidelines simplified the GPG2000 by replacing two Tier 3 massbalance methods with a single flexible Tier 3 method that contains both mass-balance and emission-factor-based components, which are summarized as follows: The country-level mass-balance method was moved to the Quality Assurance/Quality Control (QA/QC) section; The method for estimating potential emissions was moved from the Methodological Choice discussion and into a separate section where it can be used for QA/QC; The potential emissions approach was replaced with the default emissionfactor-based approach, which was moved from Tier 2 to Tier 1.
In aiming for a more accurate and transparent reporting of GHG emissions due to SF 6 gases, Malaysia has the potential to move to higher tiers in its national GHG accounting and reporting. This shift to a higher tier requires regulations and targeted policy development. Activity data gatherings from all electrical equipment sources require rigorous implementation. With targeted policy and regulations, activity data gatherings at all stages from production until disposal will be possible. Activity data management tools and skill enhancement training for data monitoring and management must be made available for the identified sources of SF 6 gas electrical equipment use or targeted group.
In terms of the emission factor, moving to Tiers 2 and 3 requires a CSEF. A focused working group can be formed to study and develop CSEFs related to SF 6 emissions at all stages. A substantial timeline must be considered to successfully derive well-defined CSEFs. Furthermore, sufficient funds and grants must be made available by the government to the relevant agencies and industries for accurate and transparent estimates of SF 6 emissions as part of the national effort to mitigate or reduce SF 6 emissions.

Transparency and Accuracy Inventory Reporting in Malaysia
The National Improvement Plan aims to uphold two main principles under the transparency, accuracy, consistency, comparability, completeness, and accuracy (TACCC) guiding principles of national GHG inventory reporting. The two main principles are transparency and accuracy, which are important for SF 6 emission estimation for the IPPU sector's GHG inventory reporting, particularly in the fulfillment of Malaysia's national obligation of inventory reporting to the UNFCCC.
Transparency is defined as the assumptions and methodologies used for an inventory mentioned in the reporting to facilitate the repetition of calculation and analysis of the inventory by inventory compilers [30]. Transparency reflects documentation that provides important information, where other personnel apart from the inventory compilers can comprehend how the inventory compilation takes place in accordance with the IPCC bestpractice requirements. Malaysia's efforts to champion transparency can be seen through transparent documentation, in which all technical annex reporting tables, Tables A1 to  A3, and Tables B1 to B21, including activity data, emission factors, entire time series, data sources, and tier methodology, are presented in the BUR3 [4].
Accuracy is a relative measure of the exactness of an emission or removal estimate. Estimates should be accurate in the sense that they should systematically neither overestimate nor underestimate the true emissions or removals and that uncertainties are reduced as much as possible. In this regard, the inventory compilers made efforts to engage with all relevant stakeholders within the 2G1: SF 6 in the Electrical Equipment category. Table 5 shows the sub-categories and the relevant stakeholders. Discussions in the form of focus group meetings were conducted with these stakeholders along with the lead ministry-the Ministry of Environment and Water-to obtain feedback on data collection activities. In addition to these engagement sessions, benchmarking with Singapore was performed for mutual learning experiences in calculating this sub-category [31]. These comprehensive inclusions of all stakeholders are important to ensure accurate estimations and reflect the use of SF 6 emissions in Malaysia.
In this perspective, though SF 6 is the most potent greenhouse gas, however, it does not fall into the key category for Malaysia. Thus, the use of SF 6 will continue to be used without substitution because of its high dielectric strength and thermal stability. It is also good to note that the stakeholders have initiated the effort to reuse or recycle the SF 6 gases.
Accurate and transparent inventory reporting faces a number of challenges. First, keeping track of inventory in a large, complex organization dating back to 1990, when the initial time series year started, can be difficult. Second, ensuring that the data and records are accurate and up to date can be difficult. Despite these challenges, transparency needs to be upheld, allowing stakeholders to clearly understand the country's inventory levels, particularly whether SF 6 gas should be phased out or replaced in the future.

Uncertainty Assessment
Uncertainty assessment is the attempt to compile an inventory of anthropogenic GHG emissions and removals and to understand trends over time. According to good practice, calculations should be reliable in the sense that they do not systemically overestimate or underestimate the actual emissions or removals to the extent that this can be determined, and they should be exact to the greatest possible extent.
Uncertainty assessment aims to comprehend and document the causes of uncertainty in individual estimates and overall totals qualitatively and quantitatively. This procedure delivers accurate and precise results. An element of uncertainty will always exist with each amount reported in an inventory. When data are being gathered, and emission or removal values are calculated, the uncertainty assessment is at its most effective. The formulas used for calculating emissions and removals are closely related to the combination of quantitative uncertainties estimates. Formulas that multiply activity data (AD) by an emission factor (EF) are the foundation of simple approaches.
A combination of the uncertainties in the emission factors for common sources and the associated activity data, or (more frequently) a function of instrument characteristics, calibration, and the sampling frequency for direct measurements, determines the estimated uncertainty of GHGs from individual sources. The best approach is to use probability density functions to express the uncertainty in the emission factors and activity data. The probability density function's shape should be determined objectively when data are sufficient.
The source category uncertainties need to be combined once they have been identified to obtain the uncertainty estimates for the whole inventory in any given year. The error propagation equation produces two useful rules for adding and multiplying uncorrelated uncertainty.
In general, both AD and EF can be the outcome of a few distinct parameters, and for more sophisticated Tier 3 approaches, models that use several equations and datasets that capture a variety of spatial-temporal scales may be used. Regardless of the method's complexity, the EF and AD uncertainties utilized in the equations affect the results' uncertainty. Therefore, a related qualitative and quantitative uncertainty assessment should be conducted for every piece of data that is gathered.
The uncertainty assessment results are not exact indicators of the general quality of the inventory. They reflect the proportions of sectors and categories in each country, even though the uncertainty estimation approach completely reflects the complexity of the emission and removal estimation equations (i.e., emission totals for some countries contain a higher proportion of emissions from categories that are inherently more uncertain). Despite this situation, uncertainty assessment is a helpful tool for inventory enhancement. It offers data for prioritizing methodology and data collecting enhancements across source and sink categories in conjunction with the key category analysis. The estimated uncertainties in the default emission factors for the Tier 1 method are illustrated in Table 6 and were published in the 2006 IPCC Guidelines [5]. For Malaysia, most equipment used by stakeholders is closed-pressure systems. Hence, the uncertainty default values for both AD and EF of ±30% will be used in the uncertainty analysis. The percentage uncertainty in total inventory is depicted using this method and was calculated as 0.19% for the 2019 inventory year. In addition, the Tier 1 method in the guidelines was adopted to estimate the trend uncertainty, with reference to the base year of 2005. The calculated trend uncertainty was 0.48% in sub-category 2G1b: Use of Electrical Equipment. The values calculated in the uncertainty assessment show that the confidence level in the SF 6 emission estimations is valid and acceptable.

The Way Forward for Malaysia in SF 6 Emission Estimation
As a result of the National Inventory Improvement Plan initiated for SF 6 estimation in Malaysia, the subsequent inventory reporting post-BUR3 will see the completion of the transition from the Revised 1996 IPCC Guidelines to the newer 2006 IPCC Guidelines for the 2018-2019 reporting year. This endeavor is a positive outcome of the strong cooperation between stakeholders. The remaining inventory years in the time series from 1990 to 2017 will be incorporated to reflect the methodological updates in the next report to the UNFCCC. The stakeholders did not have sufficient time to collect the time series data because only less than one year was given for this transition. However, efforts are already being made to obtain the time series data for the Biennial Transparency Report, to be reported in 2024.
The transition from the Revised 1996 IPCC Guidelines faced many challenges in view of the detailed activity data required in the 2006 IPCC Guidelines. The use of SF 6 gas in Electrical Equipment is not a key category in the national GHG inventory, which is why the Tier 1 method was adopted in the emission estimation. The activity data requirements include the nameplate capacity of each medium-voltage and high-voltage switch gear and GIT during the installation, use, and disposal stages. The emission factors were selected based on the closest geographical context provided by the default emission factors in the guidelines. Ensuring future improvement and completeness in obtaining time series activity data for SF 6 gas emission estimates will need the strong involvement of relevant stakeholders.
The recommendations for the way forward for the country to estimate SF 6 gas in strict accordance with TACCC principles and the 2006 IPCC Guidelines are as follows: Further engagement with stakeholders, particularly the utility providers, because they are the main key to assessing data and information for the recalculation of the time series from 1990 to 2017 by using the 2006 IPCC Guidelines; Workshop by technical experts and government agencies on the SF 6 gas outlook for the future, whether this gas will be retired or phased out gradually; Capacity-building activities to train all stakeholders in SF 6 gas estimation; Develop a method of collecting data on SF 6 gas handling and disposal because no disposal inventory systems are currently available to monitor the volume of SF 6 gas leakage; Integrate SF 6 gas with the Malaysian GHG Integrated Management System [32], which is a tool that enables GHG emission estimation and inventory compilation and contains an online emission database, a quality control system, documentation, and data archives for all stakeholders to utilize and plan their GHG emissions; Utilize the voluntary carbon market mechanism to encourage industries that use SF 6 to voluntarily report their GHG emissions, including SF 6 gas, for carbon tax incentives or carbon trading [33]. The guidelines will also assure industries that the emissions will not be double-counted when accounting for the achievement of Malaysia's Nationally Determined Contributions under the Paris Agreement. The emission reduction from the IPPU is included in this aspect; Establish technical guidance on mitigation actions that can be adopted within facilities [34], including tracking SF 6 gas in real time and utilizing high-accuracy weighing tools and mass flow scales to reduce discrepancies due to incorrect cylinder residual SF 6 in recovery equipment; Provide SF 6 gas management and handling courses to all stakeholders with incentives to encourage proper management and handling of this high-GWP gas. Courses are currently conducted internationally [35] and locally [8]. Provide regulation for the use of the gas, with reference to guidelines that have been implemented in other countries [36].

Conclusions
The National Inventory Improvement Plan for SF 6 emission estimation was successfully achieved. Malaysia was able to enhance its estimation methodology in the GHG inventory for the sub-category 2G1b: Use of SF 6 in Electrical Equipment of the IPPU sector for subsequent reporting post-BUR3. This exercise has strengthened the method of reporting for SF 6 emissions, which are minimal but have high GWP. SF 6 will continue to be utilized in Malaysia because it has excellent insulation properties, which are suitable for use in switch gears. This scenario can be mitigated by introducing transparent reporting on the use of this gas in the power sector, which will ensure that proper actions are in place to minimize the effect of this gas. The transition of the methodology from the Revised 1996 Guidelines to the newer 2006 Guidelines shows that Malaysia adheres to the reporting guidelines under the UNFCCC on the basis of the methodological requirement. Although a basic Tier 1 method is adopted, this estimation is sufficient because the sub-category 2G1 is not the source category in the overall inventory. The outcome of these activities in the National Inventory Improvement Plan for SF 6 emissions will facilitate the transparency and accuracy of Malaysia's GHG inventory reporting in the IPPU sector in keeping with the country's fulfillment of its national commitment to the UNFCCC.