How do I estimate Scope 3 emissions from purchased oxygen, nitrogen or argon?

Purchased oxygen, nitrogen and argon go in Scope 3 Category 1. Estimate them as cubic metres bought x the electricity the supplier's plant uses per cubic metre x the grid factor, 0.710 kg CO2 per kWh in India. Ask the supplier for its kWh per cubic metre; label any assumed figure as an estimate.

Why electricity is the whole story

Oxygen, nitrogen and argon are separated from air in an air separation unit. Nothing is burnt; the plant runs large compressors and chillers on electricity. So the footprint of the gas is, to a first estimate, the supplier's power use per cubic metre times the emission factor of that power. Cylinder filling, cryogenic tanker transport and cylinder returns add a little on top.

Getting the quantity into cubic metres

• Invoices in Nm3 or m3: use the figure as printed and note whether it is normal or standard conditions.
• Invoices in kg (common for liquid supply): divide by the gas density at 0 degrees C and 1 atmosphere: oxygen 1.429 kg per Nm3, nitrogen 1.251, argon 1.784.
• Cylinder supply: use the cubic metres per cylinder printed on the delivery challan, times the cylinders filled, not cylinders rented.
• Pipeline supply from an on-site plant run by the gas company: the plant's own meter reading of kWh is the best data.

What to ask the supplier

A supplier-stated figure counts as supplier-specific data. Without it, use an assumed kWh per cubic metre, say where it came from and mark the line as an estimate.

1. kWh per cubic metre for the product and supply mode you buy, because liquid gas needs much more power than gas piped straight from the plant.
2. Whether that power is grid, captive or renewable, with certificates if they claim renewable.
3. Whether the figure includes liquefaction, transport and cylinder handling.

Gases that are not Scope 3

Acetylene, LPG and propane bought for cutting or heating are burnt in your equipment, so they are Scope 1 fuel. Purchased CO2 used for welding shielding, beverages or dry ice is released at your site; treat it with its own rule rather than as an air gas. Keep these on separate lines.

Worked example: liquid oxygen for a foundry

• Purchased: 50,000 m3 of liquid oxygen in a year
• Assumed power use: 0.9 kWh per m3 (an estimate for liquid supply; replace with the supplier's figure)
• Electricity: 50,000 x 0.9 = 45,000 kWh
• 45,000 x 0.710 kg CO2 per kWh = 31,950 kg CO2, about 32 t CO2, Scope 3 Category 1

If the supplier states 0.6 kWh per m3 for the same product, the figure drops to 21.3 t CO2. The kWh per m3 is the number that matters.

What Senseible does here

Senseible reads industrial gas invoices with their quantity into the supplier evidence trail, separate from your Scope 1 and 2. A kWh per cubic metre figure from the supplier can be kept with that evidence as supplier-specific data.

• Using your supplier's product footprint
• Allocating supplier emissions to purchases
• Grid electricity factor for India

Sources: GHG Protocol Scope 3 Standard, Category 1 Purchased goods and services, CEA CO2 Baseline Database, version 21.0

Last reviewed 2026-10-17.