Our previous article examined Phase 1 of GHG emissions accounting, Creating a GHG Inventory List. Once all the sources have been identified and categorized correctly, the next step is to collect activity data for each item in the GHG Inventory List.
This article delves into details of collecting activity data for Scope 1, Scope 2, and all the different categories in Scope 3 and the various recommended methods to convert the activity data into estimated GHG emissions.
Quantification methods for GHG emissions
GHG emissions can be quantified by the direct measurement method using direct monitoring, mass balance, or stoichiometry. Direct measurement is often unavailable or very expensive, so the more common approach is to collect activity data and use documented emission factors to convert the activity data into GHG emissions.
Examples of the type of activity data that can be used and available emission factors:
Scope 1 Data and Emissions Factors
Scope 1 emissions include carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) that are emitted from stationary and mobile combustion and inadvertent fugitive emissions. Fugitive emissions can also include hydrofluorocarbons (HFCs), perfluorinated compounds (PFCs), sulfur hexafluoride (SF6), and nitrogen trifluoride (NF3). The EPA website offers guidance on Scope 1 emissions and emission factors.
- Fuel Consumption Data: An organization needs to collect consumption data by fuel type in terms of fuel units either measured on-site or provided by a supplier. If only the cost of fuel purchase is available, then this needs to be converted into fuel units by dividing the costs by the average per unit price. The emissions are then computed by multiplying the fuel unit’s mass or volume with the fuel type’s emission factor. Emission factors are available from the EPA or other Emission Factor databases. The emission computation can be improved by using more accurate emission factors if carbon or heat content data is available.
- For mobile combustion, in addition to emissions from CO2, emissions from CH4 and NO2 also need to be computed. This can be computed by multiplying the appropriate emissions factor with the distance traveled for on-road equipment like cars, trucks and buses and or the volume of fuel consumed for nonroad equipment like forklifts, agricultural equipment, boats, rails or aircraft. This is converted to CO2 equivalent emissions by multiplying it with the Global Warming Potential (GWP) factor for methane and nitrous oxide.
- Fugitive emissions from refrigerants and air-conditioning equipment are calculated based on equipment-specific emission factors. Estimates are computed for the installation, operation, and disposal of equipment. Separate emission factors are also used to compute emissions from fire suppression equipment.
- Process emissions generally include emissions from the chemical transformation of raw materials. These processes include iron and steel, cement, petrochemical, and nitric acid production, among others. EPA guidance outlines that methodologies may vary, and reporters often choose the most appropriate method for their specific industrial category.
Scope 2 Data and Emission Factors
Scope 2 emissions are indirect emissions from purchased electricity, steam, heat, and cooling. GHG Protocol Scope 2 Guidance document provides details on computing scope 2 emissions. There are two methods for calculating emissions from purchased energy:
Location-based: A location-based method reflects the average emissions intensity of grids on which energy consumption occurs and uses grid-average emission factor data to compute the emissions.
Market-based: A market-based method reflects emissions from the electricity that companies have purposefully chosen through contractual instruments like RECs or PPAs.
For both the location-based and market-based methods, emissions are calculated by multiplying the purchased electricity by appropriate emission factors.
To calculate scope 2 emissions, the Corporate Standard recommends multiplying activity data (MWhs of electricity consumption) by source and supplier-specific emission factors to arrive at the total GHG emissions impact of electricity use.
Scope 3 Data and Emission Factors
Estimates for scope 3 categories can vary in accuracy depending on the available data and the organization’s quantification goal. The Corporate Value Chain (Scope 3) Accounting and Reporting Standard provides guidance on data and emissions for Scope 3 categories.
Categories 1 and 2: Purchased Goods and Services and Capital Goods
The spend-based method is the easiest method to estimate emissions for these categories. EPA’s supply chain GHG emission factors are based on US Environmentally-Extended Input-Output models and are presented in emissions per dollar of spend. The emission estimates can be improved by using the “Average-data method” by collecting data on the mass or relevant units of purchases. Even more accurate estimates can be computed using the supplier-specific or hybrid method where the product-level cradle-to-grave data is available for goods from the supplier.
Category 3: Fuel and energy-related activities
Emissions are computed using methods described in Scope 1 & 2 categories, by using the type of fuel and the appropriate emissions factor.
Categories 4 and 9: Upstream and downstream transportation and distribution and Categories 6 and 7: Business travel and employee commuting
For transportation-related categories like Upstream or Downstream Transportation and Distribution and Business Travel and Employee Commuting, fuel-based or distance-based methods can be used to compute emissions. In addition, hotel stay emissions need to be included in Category 6 and teleworking emissions from Scope 1 & 2 at the employee’s house are included in Category 7.
Categories 5 and 12: Waste generated in operations and end-of-life treatment of sold products
For the Waste category, emission factors are available for different types of waste (aluminum, plastic, steel, glass, etc.) and different disposal methods (landfill, compost, recycled or combusted, etc
Categories 8 and 13: Upstream and downstream leased assets, Category 14: Franchises
Category 8, 13, and 14 emissions are usually acquired from the leased assets or franchises by calculating the Scope 1 and Scope 2 emissions for the assets.
Category 15: Investments
This category includes scope 3 emissions associated with the company’s investments and depends on the type of investment: Equity investments, debt investments, project finance, or managed investments.
Data Collection and Management
Clearly defined data collection and management plans help meet the reporting and accounting principles of the GHG protocol: relevance, completeness, consistency, transparency, and accuracy.
- Identify data requirements for the source or operation; for example, the amount of fuel used, meter data, purchase records, or other internal tracking documents.
- Develop data collection procedures that allow the data to be collected efficiently annually.
- Maintain a record of calculation methods and emission factors.
- Roles and responsibilities of employees involved in the data collection and reporting process.
- Process for internal and external audits, verification, and security for the data collection and reporting process.
- Identify any missing data and estimates used for missing data and design procedures to improve data collection in subsequent cycles.
GHG emissions calculations tools
Several emission factor databases are available:
- Emission Factors from the Intergovernmental Panel on Climate Change (IPCC) Emission Factor Database (EFDB) are available at Emission Factor Database (EFDB)
- Emission Factors for Scope 2 in the US are found at US EPA Emissions and Generation Resource Integrated Database (eGRID).
- Worldwide Scope 2 emission factors at Institute for Global Environmental Strategies (IGES) List of Grid Emission Factors List of Grid Emission Factors
- Emission Factors for Scope 3 Categories can be found on the EPA website at:
- EPA’s supply chain GHG emission factors are based on US Environmentally-Extended Input-Output models and are presented in emissions per dollar of spend.
- EPA’s GHG Emission Factors Hub provides factors for most scope 3 categories. Some categories do not require specific emission factors, because the emissions-generating activities have associated scope 1 and scope 2 factors already available.
Several tools are also available that help with data collection and emissions calculations. For example, the GHG protocol and EPA provide free spreadsheet-based tools for basic emissions. Many companies offer GHG accounting software tools that contain links to emission factors and simplify data collection and emissions calculations.
Although it is a complex process, GHG emissions calculations provide a data-informed guide to an organization’s sustainability program. What gets measured gets managed. Accounting for emissions can help identify increased efficiency in operations, new products and services, and reduced risk from climate change. It can help differentiate you from your competitors.
