What are primary and secondary GHG data?
Primary data comes from a specific activity in your value chain. Examples include a 2025 meter export, utility bill, fuel invoice, purchased quantity, direct measurement, or product footprint tied to the supplier and item you bought. Supplier-specific data is primary only when the emissions, factor, or activity record represents that identified supplier's actual activity. Secondary data comes from somewhere else: industry averages, government statistics, life-cycle databases, financial factors, or a proxy from another site or product.
Why does primary vs secondary GHG data matter to you?
A customer may ask for the reporting period, product or site boundary, quantity unit, calculation method, factor source, and the percentage of Scope 3 emissions based on supplier data. ESRS E1-6 AR 46(g) asks covered companies to disclose the percentage calculated using primary data from suppliers or other value-chain partners. A customer preparing an ESRS report may therefore pass that request to you; the Germany requirements guide explains how supplier requests can flow down.
How does the emissions data hierarchy work?
Start with the decision the number must support. For a material category or reduction target, prefer direct measurement or product-, site-, and supplier-specific data that matches the reporting year and geography. Next comes specific physical activity data multiplied by a suitable secondary factor, such as purchased kilograms times an industry-average kg CO2e/kg factor. That is a hybrid calculation. Broader physical averages come next. If you lack physical quantities, use spend multiplied by an industry factor stated per unit of currency, or borrow data from a similar activity, as a last resort.
The hierarchy is not a rule that every primary file beats every secondary source. GHG Protocol Scope 3 Standard section 7.3 says to consider the goal, significance, availability, and quality of the data. Check technology, time, geography, completeness, and reliability. A current regional average can be more defensible than an incomplete supplier figure from the wrong product or year. Record the choice for every inventory line.
What mistakes should you avoid?
- Calling a supplier PDF primary without confirming that its figure covers the product, service, site, and period you bought.
- Calling all measured quantities primary when a quantity from one activity is being used as a proxy for another.
- Replacing a well-matched physical average with an old supplier number just because the source has a company name.
- Reporting primary-data coverage by supplier count or spend when the question asks for the percentage of emissions.
Is supplier-specific data always primary data?
No. A supplier-specific factor or emissions total is primary when it is tied to that supplier's relevant activity. If the supplier applied a generic industry average to your purchase, the result may be supplier-labelled but still depend on secondary data. Ask for the method, boundary, period, allocation rule, factor sources, and whether the underlying activity was measured or estimated.
Can secondary data be better than primary data?
Yes. Use the source that best represents the activity and your purpose. A current Japanese polymer average with a documented kg CO2e/kg boundary may be stronger than a supplier total covering a different resin, country, or year. Keep the limitation and your reason for choosing it beside the calculation.
What should you send when a customer asks how much primary data you used?
Send an inventory extract listing each source, period, unit, method, factor, geography, and primary, secondary, or hybrid classification. Calculate coverage using emissions, not supplier count: supplier-data emissions divided by the relevant disclosed emissions total. Include the meter files, bills, supplier method documents, database versions, assumptions, and the name of the reviewer who checked the classification.