Knowing Neurons
Science Policy

Protecting our Communities with Technology Standards for Future Hydrogen Fuel Combustion Facilities

Written by Bineh Ndefru

Natural gas-fired plants meet much of the electric power generation need in California. In 2020, natural gas plants generated over 48% of the state’s electricity and were responsible for 40.3 million metric tons of carbon dioxide (CO2; California Energy Commission, 2021). Increasing atmospheric CO2 is known to have many health and environmental impacts and was also recently shown to impair cognitive function (Xu, et al., 2011). In efforts to mitigate these growing threats to humans and the climate, California Senate Bill 100 in 2018 set the goals for the state’s transition to zero-carbon by 2045. President Biden recently set even more ambitious targets for the country to reach a carbon pollution-free power sector by 2035. Because of California’s deep reliance on natural gas, the state is considering alternatives to decommissioning plants to meet decarbonization goals. Many utility companies in California are planning to repurpose existing facilities to combust hydrogen gas rather than natural gas to meet net-zero targets, since burning hydrogen emits water rather than carbon.

The largest gas distribution utility company in the US, SoCalGas, has proposed Angeles Link, a plan to decarbonize by injecting hydrogen into existing natural gas infrastructure. Last year they successfully blended 20% hydrogen in a test natural gas system complete with natural gas residential appliances. Similar pilot studies are taking place at utilities across the country. Because hydrogen burns at a hotter temperature than natural gas and interacts with metals, causing pipeline degradation, the state’s energy agencies are also spending millions to assess infrastructure safety and reliability concerns.

However, beyond addressing these engineering and safety issues with the pipes, the impacts of hydrogen combustion on public health and climate have not been adequately addressed. Because hydrogen burns at such a high temperature, its combustion causes the formation of nitrogen oxides (NOx) as a byproduct, even though no carbon is emitted. Studies indicate that these NOx byproducts could be produced in quantities greater than those emitted by natural gas or other fossil fuels (Cellek & Pinarbasi, 2018; Igawa, Matsui, & Seo, 2011; Sadler, et. al. 2017).

“NOx promotes oxidative stress and inflammatory responses in the body and can interfere with signaling pathways in cells.”

NOx is a globally regulated air pollutant that is harmful on its own and is also a precursor to other pollutants such as fine particulate matter (PM2.5) and ozone. Indirectly, NOx and its byproducts can affect humans by damaging the ecosystems we rely on. Additionally, exposure to these pollutants has direct impacts on human health. These effects include breathing problems, headaches, chronically reduced lung function, eye and throat irritation, loss of appetite, diabetes, gastrointestinal disorders, pulmonary edema, capillary wall damage, asthma, and increased susceptibility to respiratory infections (Strak, et al., 2017; Kagawa, 1985; EPA, 2021; EPA, 2021). Exposure to NOx also results in increased susceptibility to respiratory infection. NOx promotes oxidative stress and inflammatory responses in the body and can interfere with signaling pathways in cells. High levels of oxidative stress have been associated with many diseases including heart attacks, and stroke (Kampa & Castanas, 2008; Luo, et al., 2016; Bourdrel, Bind, Béjot, Morel, & Argacha, 2017).

“NOx has also shown potential links to decreases in total gray matter and white matter volume in the brain, indicating the risk of neurodegen- eration.”

PM2.5 generated from NOx is inhaled or ingested, where it is then transported via the blood to the brain. These particulates have been shown to disrupt the integrity of the blood-brain barrier, allowing them to gain access to the central nervous system (Liu, et al., 2015). Therefore, beyond the respiratory inflammation that NOx may cause, many studies also indicate neurotoxicity, leading to decreases in cognitive and olfactory functions, auditory deficits, depressive symptoms, and altered memory among many other potential effects (Adams, et al., 2016; Yuan, Li, Tian, & Sun, 2022; Borroni, Pesatori, Bollati, Buoli, & Carugno, 2022). NOx has also shown potential links to decreases in total gray matter and white matter volume in the brain, indicating the risk of neurodegeneration (Erickson, Gale, Jacqueline, Brown, & Hedges, 2020). Many researchers have specifically linked NOx exposure to increased likelihood of neurodegenerative diseases such as dementia, Alzheimer’s and Parkinson’s diseases (Killin, Starr, Shiue, & Russ, 2016; Yan, Yun, Ku, Li, & Sang, 2016; You, Ho, & Chang, 2022). Further, the degeneration of neurons and loss of synapses caused by these pollutants may be more severe at early developmental stages or development in utero (Costa, Cole, Dao, Chang, & Garrick, 2019).

The formation of NOx as a byproduct of hydrogen combustion and these potential side effects are rarely discussed when discussing hydrogen as a future climate-friendly fuel. Touting hydrogen combustion as an emissions-free technology is especially problematic given that the natural gas facilities to be converted are often located in under-resourced communities facing socioeconomic disadvantage. Urban communities of color are already most burdened by pollutants, and the conversion from natural gas to hydrogen risks adding to the environmental and health burdens of these communities. The potential impacts on our most at-risk communities cannot be left out of the conversation.

The California Air Resources Board (CARB) sets emissions standards for stationary sources like natural gas facilities to protect air quality for our communities. They collaborate with air quality districts in the state such as the South Coast Air Quality Management District (AQMD) to manage air quality. This involves AQMDs adopting rules and guidelines, including specific types of equipment and processes to ensure compliance. One of these guidelines is for the Best Available Control Technology (BACT). California’s BACT guideline is a requirement to use technology to achieve the lowest possible emission rates for specific pollutants such as NOx. NOx-minimizing technology has been specified for natural gas facilities in the BACT guidelines, but at the levels and temperatures that hydrogen combustion emits NOx gases, current exhaust mitigation technologies have not yet been demonstrated and may not have the desired effect.

CARB and AQMDs have the authority to propose amendments to the BACT guidelines and to list acceptable control equipment for specific sources, as they have at recent board meetings (South Coast AQMD, 2021). It is necessary for these agencies to identify new technologies, evaluate their technical feasibility for hydrogen combustion, and develop hydrogen-specific BACT guidelines to limit NOx emissions. If safe levels cannot be obtained at an existing site, especially near sensitive areas, such as homes, hospitals, or schools, the California Energy Commission should assess the trade-offs between hydrogen and natural gas combustion. No conversion should be approved if a hydrogen-blended site could end up being worse for community health or the environment than the existing natural gas plant.

No conversion should be approved if a hydrogen-blended site could end up being worse for community health or the environment than the existing natural gas plant.

In approaching decarbonization, we must ensure that “zero carbon” does not result in other problems for air quality, health, and the environment. Not everyone was aware of the problems associated with developing fossil fuels that we face today. Many were trying to meet human needs in the moment, without thinking about potential social and ecological consequences. But, in trying to solve our current problems with hydrogen, we cannot keep making the same mistakes over and over again. We must consider the multitude of potential effects on respiratory, cardiovascular, and neurological health, especially for those in already vulnerable communities. We need to have proactive, evidence-based policy that will keep our energy systems reliable while keeping our communities healthy.


Written by Bineh Ndefru
Edited by Vincent Medina, Lauren Wagner, and Yuki Hebner


Become a Patron!


Adams, D. R., Ajmani, G. S., Pun, V. C., Wroblewski, K. E., Kern, D. W., Schumm, L. P., . . . Pinto, J. M. (2016). Nitrogen dioxide pollution exposure is associated with olfactory dysfunction in older U.S. adults. International Forum of Allergy & Rhinology, 1245-1252. doi:

Borroni, E., Pesatori, A. C., Bollati, V., Buoli, M., & Carugno, M. (2022). Air pollution exposure and depression: A comprehensive updated systematic review and meta-analysis. Environmental Pollution. doi:

Bourdrel, T., Bind, M.-A., Béjot, Y., Morel, O., & Argacha, J.-F. (2017). Cardiovascular effects of air pollution. Archives of Cardiovascular Diseases, 634-642. doi:

California Energy Commission. (2021). 2020 Total System Electric Generation. California. Retrieved from

Cellek, M. S., & Pinarbasi, A. (2018). Investigations on performance and emission characteristics of an industrial low swirl burner while burning natural gas, methane, hydrogen-enriched natural gas and hydrogen as fuels. International Journal of Hydrogen Energy, 1194-1207. doi:

Costa, L. G., Cole, T. B., Dao, K., Chang, Y.-C., & Garrick, J. M. (2019). Developmental impact of air pollution on brain function. Neurochem Int. doi:

EPA. (2021, June 7). Basic Information about NO2. Retrieved from United States Environmental Protection Agency:

EPA. (2021, May 27). Particle Pollution and Respiratory Effects. Retrieved from United State Environmental Protection Agency:

Erickson, L. D., Gale, S. D., J. E., Brown, B. L., & Hedges, D. W. (2020). Association between Exposure to Air Pollution and Total Gray Matter and Total White Matter Volumes in Adults: A Cross-Sectional Study. Brain Sciences. doi:doi:10.3390/brainsci10030164

Igawa, S., Matsui, T., & Seo, A. (2011). NOx Emission Reduction in Hydrogen Combustion. International Gas Union Research Conference. International Gas Union.

Kagawa, J. (1985). Evaluation of biological significance of nitrogen oxides exposure. The Tokai Journal of Experimental and Clinical Medicine, 348-353.

Kampa, M., & Castanas, E. (2008). Human health effects of air pollution. Environmental Pollution, 362-367.

Killin, L. O., Starr, J. M., Shiue, I. J., & Russ, T. C. (2016). Environmental risk factors for dementia: a systematic review. BMC Geriatrics. doi:

Liu, F., Huang, Y., Zhang, F., Chen, Q., Wu, B., Rui, W., . . . Ding, W. (2015). Macrophages treated with particulate matter PM2.5 induce selective neurotoxicity through glutaminase-mediated glutamate generation. J Neurochem. doi:

Luo, K., Li, R., Li, W., Wang, Z., Ma, X., Zhang, R., . . . Xu, Q. (2016). Acute Effects of Nitrogen Dioxide on Cardiovascular Mortality in Beijing: An Exploration of Spatial Heterogeneity and the District-specific Predictors. Sci Rep. doi:

Sadler, D. (2017). H21 Leeds CityGate Project Report. Leeds: H21 by Northern Gas Networks. doi:

South Coast AQMD. (Feb. 5 2021). Determine That Proposed Amendments to BACT Guidelines Are Exempt from CEQA and Amend BACT Guidelines. SCAQMD. Retrieved from

Strak, M., Janssen, N., Beelen, R., Schmitz, O., Vaartjes, I., Karssenberg, D., . . . Hoek, G. (2017). Long-term exposure to particulate matter, NO2 and the oxidative potential of particulates and diabetes prevalence in a large national health survey. Environ Int. doi:

Xu, F., Uh, J., Brier, M. R., John Hart, J., Yezhuvath, U. S., Gu, H., . . . Lu, H. (2011). The influence of carbon dioxide on brain activity and metabolism in conscious humans. J Cereb Blood Flow Metab., 58-67. doi:10.1038/jcbfm.2010.153

Yan, W., Yun, Y., Ku, T., Li, G., & Sang, N. (2016). NO2 inhalation promotes Alzheimer’s disease-like progression: cyclooxygenase-2-derived prostaglandin E2 modulation and monoacylglycerol lipase inhibition-targeted medication. Sci Rep. doi:

You, R., Ho, Y.-S., & Chang, R. C.-C. (2022). The pathogenic effects of particulate matter on neurodegeneration: a review. Journal ov Biomedical Science. doi:

Yuan, L., Li, D., Tian, Y., & Sun, Y. (2022). The Risk of Hearing Impairment From Ambient Air Pollution and the Moderating Effect of a Healthy Diet: Findings From the United Kingdom Biobank. Frontiers in Cellular Neuroscience. doi: