Global regulations and standards governing hydrogen combustion emissions are evolving as nations recognize the need to mitigate environmental impacts while transitioning to cleaner energy systems. Hydrogen combustion emits no carbon dioxide, but it can produce nitrogen oxides (NOx) depending on combustion conditions, making regulatory frameworks essential to control these emissions. Key regulatory bodies, including the U.S. Environmental Protection Agency (EPA) and the European Union, have established guidelines, though gaps remain in addressing the full spectrum of hydrogen-related emissions. Emerging certification schemes aim to define "low-emission" hydrogen combustion technologies, but industries face compliance challenges due to inconsistent standards and technological limitations.

In the United States, the EPA regulates NOx emissions from hydrogen combustion under the Clean Air Act, particularly through the New Source Performance Standards (NSPS) and National Emission Standards for Hazardous Air Pollutants (NESHAP). Stationary combustion turbines and industrial boilers using hydrogen must adhere to strict NOx limits, often requiring selective catalytic reduction (SCR) or other mitigation technologies. The EPA has also introduced tiered standards for fuel cells and hydrogen-based power generation, though these focus more on efficiency than direct emissions. However, the lack of specific hydrogen combustion guidelines in some sectors creates ambiguity, particularly for emerging applications like hydrogen blending in natural gas systems.

The European Union addresses hydrogen combustion emissions through directives such as the Industrial Emissions Directive (IED) and the Medium Combustion Plant Directive (MCPD). These frameworks set NOx limits for combustion plants, including those using hydrogen, but do not yet differentiate between hydrogen-specific and conventional fuel emissions. The EU’s Renewable Energy Directive (RED II) incentivizes low-carbon hydrogen but does not comprehensively regulate combustion byproducts. The upcoming Hydrogen and Decarbonized Gas Market Package aims to fill some gaps by introducing certification for renewable and low-carbon hydrogen, though combustion emissions remain a secondary focus.

Japan and South Korea have also developed hydrogen-specific regulations, particularly for fuel cells and transportation. Japan’s Basic Hydrogen Strategy includes emission standards for hydrogen turbines, while South Korea’s Hydrogen Economy Roadmap enforces NOx limits for hydrogen combustion in power generation. Both countries are piloting certification systems for clean hydrogen, but these are not yet fully integrated with combustion emission standards.

A significant gap in current policies is the lack of harmonized international standards for hydrogen combustion emissions. While organizations like the International Organization for Standardization (ISO) and the International Energy Agency (IEA) have published guidelines, these are not legally binding. The absence of a unified framework complicates compliance for multinational industries and hinders the development of global hydrogen markets.

Emerging certification schemes, such as the CertifHy initiative in Europe and the Clean Hydrogen Standard in the U.S., aim to define "low-emission" hydrogen but primarily focus on production rather than combustion. These schemes often exclude NOx emissions, focusing instead on carbon intensity. The Green Hydrogen Organization (GHO) is developing more comprehensive criteria, including combustion-related emissions, but widespread adoption remains uncertain.

Industries transitioning to hydrogen face several compliance challenges. First, existing infrastructure often cannot meet NOx limits without costly retrofits. For example, gas turbines designed for natural gas may produce higher NOx levels when switched to hydrogen. Second, monitoring and reporting requirements for hydrogen combustion are inconsistent across regions, creating administrative burdens. Third, the lack of clear standards for hydrogen blends in natural gas systems leaves operators uncertain about compliance.

The steel and cement industries, which are exploring hydrogen to reduce carbon footprints, encounter additional hurdles. High-temperature combustion in these sectors produces significant NOx, yet regulatory frameworks do not always account for the unique challenges of hydrogen use in industrial processes. Similarly, the maritime and aviation sectors, which are testing hydrogen combustion, lack tailored emission standards, relying instead on provisional guidelines.

Technological limitations further complicate compliance. While SCR systems can reduce NOx from hydrogen combustion, they are not always feasible for small-scale or mobile applications. Alternative mitigation strategies, such as lean premixed combustion, are still under development and not yet widely regulated. Additionally, the energy penalty associated with emission control technologies can offset the environmental benefits of hydrogen.

Efforts to address these gaps are underway. The International Partnership for Hydrogen and Fuel Cells in the Economy (IPHE) is working on global emission standards, while the European Commission is considering amendments to the IED to include hydrogen-specific provisions. In the U.S., the Department of Energy (DOE) is funding research into low-NOx hydrogen combustion technologies, which could inform future regulations.

Despite these efforts, industries must navigate a fragmented regulatory landscape in the short term. Companies investing in hydrogen combustion technologies should engage with policymakers to shape future standards and prioritize technologies that minimize NOx emissions. Collaborative initiatives, such as the Hydrogen Council, are advocating for more coherent policies, but progress depends on international cooperation.

In conclusion, while global regulations and standards for hydrogen combustion emissions are developing, significant gaps remain. Current policies often fail to address the unique challenges of hydrogen combustion, and emerging certification schemes are not yet comprehensive. Industries face compliance challenges due to inconsistent standards, technological limitations, and unclear guidelines for emerging applications. Harmonizing international standards and accelerating research into low-emission combustion technologies will be critical to realizing the full potential of hydrogen as a clean energy carrier.