Is there one CO2 figure per cubic metre of PSA oxygen?

The result depends on the plant's electricity per cubic metre and on the emission factor of its supply, and the European Environment Agency reports that grid intensity differs significantly between EU Member States.

Does a renewable electricity contract change the result?

Under the GHG Protocol market-based method, emission factors come from contractual instruments such as Guarantees of Origin or power purchase agreements; the location-based method uses grid-average factors.

How much CO2 does an on-site oxygen plant emit?

Q: How do you estimate the carbon footprint of a PSA oxygen plant from its electricity use?

To estimate a PSA oxygen plant's carbon footprint from its electricity use, multiply the electricity the plant consumes by the emission factor of its electricity supply, the method the GHG Protocol Scope 2 Guidance (2015) sets out for purchased electricity.

How do you estimate the carbon footprint of a PSA oxygen plant from its electricity use?

Step 1: the electricity the plant uses

WHO's 2020 interim guidance pointed to the manufacturer's technical specification for a detailed estimate of a PSA plant's power use, and Assist International (Open Critical Care) says to always refer to the manufacturer's specifications. Published reference figures for PSA plants include:

Source	Figure	Conditions
PATH and CHAI (2021)	About 1.2 kWh per Nm³ produced	Conventional PSA plant at 65 psig; consumption increases with higher service pressure and with cylinder filling
WHO, Oxygen sources and distribution for COVID-19 treatment centres (2020, interim)	1.22 kWh ±5% per m³ of total flow	Rule of thumb in COVID-19 guidance that states it expires two years after publication
Assist International (Open Critical Care)	1.5 kWh per m³ of oxygen	Example of one manufacturer's PSA plant

Pressure and purity change the figure: the ULTRAOX datasheet (2022) states that each extra bar of compressor pressure adds 7% to total electricity consumption, and the Global Fund purity note (2024) says that, for the same flow, a 95% (±1%) plant needs larger equipment with higher power consumption than a 93% (±3%) plant. See how much electricity a PSA plant uses.

Step 2: the emission factor

The GHG Protocol Scope 2 Guidance describes two methods. The location-based method reflects the average emissions intensity of the grids where the energy is consumed, using mostly grid-average emission factors. The market-based method derives emission factors from contractual instruments, such as Guarantees of Origin in the EU or power purchase agreements. Grid factors come from official sources, for example:

United Kingdom: the government conversion factors for company reporting, published by the Department for Energy Security and Net Zero (2026 factors published on 11 June 2026), applied to activity data such as kWh of electricity purchased.
United States: EPA's eGRID, which gives emissions and emission rates for almost all electric power generated in the country.
Other countries: the GHG Protocol lists IEA national electricity emission factors among location-based data.
European Union: the European Environment Agency reports that the greenhouse gas intensity of electricity production differs significantly between Member States, and that generating one kilowatt hour in the EU emitted 11% less in 2024 than in 2023.

Step 3: the calculation

The GHG Protocol procedure is to multiply the activity data by the emission factor for each applicable greenhouse gas, multiply the totals by their global warming potential to obtain CO2 equivalent, and report the result in metric tons for each method used. The UK conversion factors also cover activity data such as volume of fuel used, alongside kWh of electricity purchased, with Scope 1, 2 and 3 emissions reported separately.

Renewable electricity and UltraGreen

Global Fund sustainability guidance (2024) suggests considering renewable power instead of generators for operational and financial sustainability. Under the UltraGreen plan, an enrolled ULTRAOX runs on 100% renewable electricity, from on-site solar or certified green energy contracts, and Ultra Controlo states that each enrolled ULTRAOX unit avoids up to 130 tonnes of CO2 a year. See what UltraGreen is.