The Federal Hydrogen Hub Community Guide
Glossary
Definitions of technical terms used in this Guide and/or in descriptions of Hydrogen Hub projects
Ammonia
Ammonia (NH3) is a colorless gas with a strong odor. Exposure to ammonia can irritate the nose, throat, and respiratory tract, which can also lead to respiratory issues. Chronic exposure increases risk of respiratory irritation, asthma symptoms, and impaired lung function. Studies suggest that exposure to high levels of ammonia may adversely affect the liver, kidney, and spleen. Ammonia also transforms into secondary PM2.5 (ammonium sulfate, ammonium nitrate, and ammonium chloride), causing the same health effects associated with exposure to particulate matter.
ATR
Autothermal Reforming is a chemical process in which methane (CH4) and water vapor (H2O) are reacted in pure oxygen (O2) to produce a synthetic gas, sometimes referred to as “syngas.” Syngas is composed of carbon oxides (carbon monoxide [CO] and CO2) and hydrogen gas (H2). ATR requires an Air Separation Unit (“ASU”) that separates pure oxygen from ambient air. In theory, ATR facilities should require less direct fossil fuel combustion to produce hydrogen than SMR facilities, but few have been built and this has yet to be verified in practice. ASUs can require a large amount of energy, either from on-site energy sources or from the electric grid.
Biomass
Biomass refers to materials that come from living things, such as leaves or stems from plants and crops, wood and bark from trees, or animal manure. These materials can be processed and used in ways that lead to meaningful decarbonization, but also in ways that increase carbon emissions.
Biogas
Biogas or biomethane is a particular type of biomass that is created in landfills, some wastewater treatment systems, and some livestock manure management systems when organic materials are broken down by bacteria in an oxygen-free environment. Biogas is 45%–65% methane, depending on how it was produced, and the rest is primarily CO2.
Blue hydrogen
Blue hydrogen is made from fossil methane most often using one of two technologies: steam methane reforming (SMR) or autothermal reforming (ATR), with the addition of carbon capture technology.
Carbon capture
Carbon capture refers to a set of industrial technologies designed to reduce CO2 emissions at the source (i.e., smokestack) of a facility and prevent on-site CO2 emissions from entering the atmosphere. The process involves three key phases:
- CO2 capture,
- CO2 transportation, and
- CO2 use and/or storage.
Carbon capture systems could be added to any point source that emits CO2. A facility with carbon capture technology captures some, but not all, of its CO2 emissions. Those captured CO2 emissions are then transported, typically by pipeline, from the emissions source to their eventual destination for use or storage in a deep underground geological formation. There are many different technologies that capture CO2, most of which are reliant on chemicals that readily bind to CO2, and most of these technologies require large amounts of Some of these technologies also require large volumes of water.
Carbon Monoxide (CO)
Carbon monoxide is a colorless, odorless gas. It reduces the ability of blood to carry oxygen, which then interferes with oxygen delivery to the body’s organs. This can pose a particular risk to those with anemia and those with a history of heart or respiratory disease.
Colors of hydrogen
Hydrogen can be produced from multiple sources, like water, fossil fuels, or biomass, using different kinds of technologies, like electrolysis or methane reforming. These different production methods can have substantially different community-level and climate impacts, and they are often characterized by colors. See:
Control technologies
Facilities that emit air pollution often must use control technology systems to keep their emissions below state or federal standards. These technologies can decrease the emissions of NOx, SO2, mercury, and other harmful air pollutants.
CO2 storage
CO2 storage, also known as sequestration, can refer to different things. When discussed in this guide, CO2 storage refers to storage in saline aquifers, which are deep underground and filled with salty water (brine).
Electrolysis
Electrolysis is the process of using electricity to drive a chemical reaction. In the case of hydrogen, electrolysis is used to split water into hydrogen and oxygen. The process takes place in a unit called an electrolyzer. Electrolyzers need large amounts of electricity to work. This electricity can be produced on- or off-site.
Gasification
Gasification (or pyrolysis) is a process through which complex carbon-based materials are converted into syngas, a gas mixture composed of carbon oxides (carbon monoxide [CO] and CO2) and hydrogen gas (H2). This is achieved through high temperatures and pressures, controlled levels of pure oxygen, and sometimes with the aid of a catalyst. Pyrolysis is very similar to gasification except that it occurs in the absence of oxygen. Gasification and pyrolysis can be achieved with a variety of feedstocks; according to available information, the Hydrogen Hubs will focus on the gasification or pyrolysis of biomass.
Gray hydrogen
Gray hydrogen is made from fossil methane most often using one of two technologies: steam methane reforming (SMR) or autothermal reforming (ATR).
Green hydrogen
Green hydrogen is made using 100% renewable electricity — like solar and wind — to split hydrogen from water molecules through a process called electrolysis, using a technology called an electrolyzer. To be truly clean, it must rely on sources of clean energy that are ‘new, now, and near’. These criteria — incrementality, hourly matching, and deliverability — are often called the “three pillars” of clean hydrogen production.
Heat pumps
Heat pumps use electricity to both heat and cool an indoor space. They move heat instead of burning fuel to generate heat, consuming less energy and increasing efficiency.
Methane
Methane (CH4) is a potent greenhouse gas, with a warming potential about 30 times that of CO2 over a 100-year period and a warming potential over 80 times that of CO2 over a 20-year period. Methane is often used as a feedstock to produce hydrogen, whether it is extracted as a fossil fuel or derived from biomass feedstocks.
“New, now, and near”
See: Truly clean hydrogen
NOx
NOx is the collective term for the nitrogen oxides NO and NO2. Exposure to NOx causes asthma and respiratory infections. NOx also reacts with other chemicals in the air to form ozone, which also harms the respiratory system. Both NO2 and ozone increase risk of early death. NOx indirectly contributes to the greenhouse effect, worsening atmospheric warming and climate disruption. NOx contributes to degradation of stratospheric ozone, which leads to higher UV levels and in turn causes increased skin cancers. NOx also transforms into secondary PM2.5, exposure to which can also harm health.
Nuclear energy production
Nuclear power can pose health risks to communities and the environment, largely due to the risk of an accident. These risks can be effectively minimized with proper regulation and safety standards. Nuclear energy production also creates a radioactive waste stream that must be appropriately stored to minimize impacts on communities and the environment. In these areas, nuclear energy has higher risks than renewables like wind, solar, and storage.
Particulate matter (PM)
PM is the term for small, inhalable solid particles and liquid droplets found in the air. PM2.5 represents the subset of PM that is smaller than 2.5 micrometers (1/30th the width of a single human hair). Exposure to PM can cause early death due to stroke, heart disease, respiratory infection, chronic obstructive pulmonary disease, lung cancer, and diabetes. Exposure to PM2.5 can also cause preterm births, low birth weights, new cases of asthma, asthma attacks leading to emergency room visits, and work absences. One in three Americans lives in a place with unhealthy levels of PM pollution. With increasing heat, drought, and wildfires, PM pollution at dangerous levels is a worsening problem.
Pink hydrogen
Pink hydrogen is made using nuclear energy to split hydrogen from water molecules through a process called electrolysis, using a technology called an electrolyzer.
Pre-processing of biomass feedstocks
Often, biomass feedstocks must be processed before they can be used for hydrogen production. For crops and forest residues, this may take the form of homogenizing the feedstock through processes like wood chipping. For biogas resources, digesters or other manure management technologies may need to be used, which can impact local air and water.
Pyrolysis
Gasification (or pyrolysis) is a process through which complex carbon-based materials are converted into syngas, a gas mixture composed of carbon oxides (carbon monoxide [CO] and CO2) and hydrogen gas (H2). This is achieved through high temperatures and pressures, controlled levels of pure oxygen, and sometimes with the aid of a catalyst. Pyrolysis is very similar to gasification except that it occurs in the absence of oxygen. Gasification and pyrolysis can be achieved with a variety of feedstocks; according to available information, the Hydrogen Hubs will focus on the gasification or pyrolysis of biomass.
SMR
Steam Methane Reforming is a chemical process in which methane (CH4) and water vapor (H2O) are reacted to produce a synthetic gas or syngas, a gas mixture composed of carbon oxides (carbon monoxide [CO] and CO2) and hydrogen gas (H2). Carbon is emitted from this process both in the syngas itself and from fossil fuels combusted to create the steam necessary for the reaction.
Sulfur Dioxide (SO2)
SO2 is a colorless gas that can harm the human respiratory system and make breathing difficult. People with asthma, particularly children, are sensitive to the effects of SO2. SO2 reacts with other compounds in the air to form particulate matter (PM).
Truly clean hydrogen
Truly clean hydrogen is hydrogen that is produced from water through electrolysis, where the electrolysis process is powered by sources of clean energy that are “new, now, and near”:
- New – The electrolyzer is powered by new, not existing, renewable resources. This requirement is often called “additionality” or “incrementality.”
- Now – Those new renewable energy sources produce electricity during the same hours that the electrolyzer is running. This requirement is often called “hourly matching” or “temporal matching.”
- Near – Those new renewable energy sources are located near the electrolyzer and can deliver power to the process. This requirement is often called “deliverability.”
These criteria are often called the “three pillars” of clean hydrogen production. Without these criteria, producing hydrogen from water will cause massive increases in CO2 and health-harming pollution.
Volatile Organic Compounds (VOCs)
VOCs are a group of chemicals typically used as industrial solvents that easily evaporate at room temperature and do not dissolve in water. Exposure to VOCs can harm the respiratory and central nervous systems. VOCs include many chemicals that cause severe health issues, such as Benzene, which causes cancer, particularly acute myeloid leukemia. Benzene also damages reproductive organs, bone marrow, and blood. VOCs also transform in the atmosphere to secondary PM2.5 and ozone.
Updated on October 11, 2024
Maps and graphics by Casey Chin / Earthjustice. Basemap data sources: Esri, HERE, Garmin, FAO, NOAA, USGS, EPA.
This guide is intended for informational purposes only and does not constitute legal advice. The information contained herein is not a substitute for professional legal counsel. Please consult with an attorney to discuss your specific legal needs.
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