Developing an inventory of US hydrogen emissions

Hydrogen and particularly “clean hydrogen,” is expected to play a meaningful role in reducing climate impacts by reducing greenhouse gas (GHG) emissions from industry, energy producers, and downstream sectors. Hydrogen is not a direct GHG, but recent studies have shown that hydrogen itself has a potent indirect global warming effect in increasing levels of other GHGs, including methane and ozone. As a consequence, atmospheric emissions of hydrogen from venting and fugitive losses may offset the climate benefits of the energy transition to clean fuels. The first step in mitigating hydrogen losses is to understand sources of hydrogen emissions, develop methods and technologies for quantifying those losses, and develop a baseline emission inventory from which future trends in emissions can be tracked and reductions quantified.

In 2025, SLR contributed to a peer-reviewed paper, delivering the first baseline estimate of US hydrogen emissions from production, distribution, and storage by examining pure hydrogen emission sources, streams, and carriers.

Drawing on an extensive literature review, expert input, and best engineering estimates, researchers calculated total hydrogen emissions at approximately 0.063 million metric tons annually, representing an average leakage rate of 0.79% (0.26%–1.32%) of hydrogen produced. Key contributors include steam methane reforming (0.1–1% loss), electrolysis (2–4%), liquefaction (10–20%), and infrastructure such as pipelines, underground storage, and refueling stations. These findings underscore that even small percentages translate into significant volumes when scaled to national production capacity.

View the entire study on Frontiers: https://www.frontiersin.org/articles/10.3389/fenrg.2025.1650479

The importance of measurement-informed hydrogen emission inventories

In the natural gas value chain, methane emissions from equipment and operations have long been inventoried using bottom-up techniques based on industry average emission factors (mass emissions per activity) and activity factors (population counts, process rates, or consumption). In response to climate initiatives and other market-based incentives to reduce methane emissions from petroleum and natural gas systems, measurement-informed inventory techniques have been developed. A measurement-informed emission inventory results from quantitative direct measurement technologies and techniques to provide accurate site-specific emissions data used to benchmark emissions reduction trends and targets. Accurate emission inventories inform process design and operational practices to mitigate emissions.

Quantitative emission factors for hydrogen systems have not been developed due to the lack of measurement technologies (sensors and instrumentation) specific to hydrogen. In addition, hydrogen production, consumption, and other activity factors are not tracked by the government. Also, there are several incentives for developing clean hydrogen systems. Despite these challenges, hydrogen will play a role in a global energy transition. Characterizing hydrogen emission sources and quantifying emissions is critical to an emissions mitigation strategy. Quantitative hydrogen measurement technologies are evolving. In looking forward, source-specific hydrogen emission factors must be developed to inform bottom-up inventories, and technologies for facility-level measurements must be developed with the goal of a measurement-based inventory approach similar to that for natural gas systems. This paper is a first step toward understanding the current US inventory, data gaps, and the challenges for future improvements, building on the baseline.

To learn more about LCA in the natural gas industry, click here to read our article about Product-focused emission reductions (link)

With new technologies on the horizon, future research can aim to close the gaps outlined in this initial report and refine the broader understanding of emission measurement and the contribution of each source across the supply chain relative to the product.

For hydrogen producers, policymakers, and safety professionals, the work SLR has contributed to provides a starting point for emission control strategies in the US hydrogen market and reinforces the need for transparency as hydrogen as an energy source scales up in the US.