What is a greenhouse gas? Which gases count, and where they come from

A greenhouse gas absorbs infrared radiation reflected from the earth’s surface and so warms the planet. Water vapour is the most abundant, but human activity does not control it directly; climate policy addresses seven groups of gases released by human activity.

The gases in the Kyoto basket

• Carbon dioxide (CO₂) — fuel combustion and process reactions such as calcination. GWP = 1, the reference gas.
• Methane (CH₄) — natural gas leaks, landfill, ruminant livestock, rice paddies. GWP-100 ≈ 28.
• Nitrous oxide (N₂O) — nitrogen fertiliser application, nitric acid production, soil processes. GWP-100 ≈ 265.
• Hydrofluorocarbons (HFC) — refrigerants, foam blowing agents. GWP from hundreds to thousands.
• Perfluorocarbons (PFC) — anode effects in aluminium electrolysis, semiconductor manufacturing. GWP in the thousands.
• Sulphur hexafluoride (SF₆) — insulation in high-voltage switchgear. GWP-100 ≈ 23,500.
• Nitrogen trifluoride (NF₃) — electronics and flat panel manufacturing. GWP in the thousands.

Why small masses create large shares

A 50-tonne annual SF₆ leak at a plant looks negligible by mass. Multiplied by its GWP it becomes roughly 1.2 million tonnes CO₂e — more than the entire fuel emissions of a mid-sized factory. Screening out inventory lines that are small by mass is therefore the most dangerous shortcut.

Fugitive emissions: the most-missed line

Fuel consumption is read from invoices, electricity from a meter. Fugitive emissions appear nowhere: refrigerant leaking from cooling systems, SF₆ escaping switchgear, methane from wastewater treatment. They can only be calculated from equipment inventories and top-up records.

The practical method: the refrigerant added to a system during the year equals what leaked that year. Maintenance records are therefore an emissions data source.

The biogenic and fossil split

Chemically identical CO₂ is treated differently by origin. Carbon from fossil fuel adds to the atmosphere a stock that has been underground for millions of years. Carbon from biomass was taken from the atmosphere recently and is drawn back down as the plant regrows. Which is why EN 15804+A2 reports the two in separate rows.