In post two of our series on nitrous oxide (N2O) abatement in nitric acid production, Calyx Global examines the greenhouse gas (GHG) integrity of these carbon projects, along with other impacts beyond emission reductions that are produced by N2O abatement projects. If you are new to the series, check out our first post, which outlines the fundamentals of this unique project type.

GHG integrity

Calyx Global assesses the GHG integrity of carbon projects in stages, beginning with assessing methodologies and ending with a deep project-level analysis. Our process is outlined in our explainer paper. In the first stage, we use our GHG Integrity Framework to assess three major CDM methodologies that facilitate N2O abatement in nitric acid plants. In this stage of the assessment, we identified the GHG integrity risks present for N2O abatement projects using these methodologies and whether these risks are likely to pose a significant challenge to the carbon credit integrity of these projects. 

In our next stage, we use our methodology assessments to develop a Project Assessment Framework specifically for N2O abatement in nitric acid projects. Our project frameworks are specific to mitigation activity and methodology combinations and help us focus on the most important elements of GHG integrity for that particular project type/methodology combination. Only once we have developed a Project Assessment Framework, and have the framework reviewed by sector or project-type experts, do we rate individual projects. 

In general, we find that nitric acid N2O abatement projects provide a strong case for greenhouse gas integrity: 

Financial risk of non-additionality

These projects are generally additional as they are unlikely to be implemented without carbon revenue due to the large financial burden of installing and maintaining the abatement technology. Since 2020, alternative policy instruments and financing, such as the Nitric Acid Climate Action Group (NACAG), have been explored for supporting N2O abatement technology installation, which could affect the financial additionality of these projects. However, the projects on our rating platform currently do not receive financial benefits beyond carbon revenue. In general, projects that do not receive external financial support (i.e. from NACAG) have a low risk of financial non-additionality.

Regulatory risk

Furthermore, Calyx Global reviewed the regulatory context of N2O abatement for nitric acid production plants at a global scale and for the country of each project we rated. If N2O abatement is legally required and regulations are enforced, projects are not additional. As of 2024, there are no international agreements requiring N2O abatement in nitric acid production facilities on a global scale. Pathways to international regulation of nitrous oxide have been considered by UNEP. In particular, the Montreal Protocol, an international treaty that regulates various high-GWP chemicals, could be amended to incorporate N2O abatement and regulation. However, currently, no such international regulation has been established. Furthermore, at the regional and country scale, none of the projects we rated were subject to N2O abatement regulations. 

Overestimated emission reduction risk

Another risk that influences carbon integrity can arise from the inaccurate (overestimated) calculation of emission reductions. Various approaches are applied by the relevant N2O abatement methodologies to quantify a project’s emission reductions. However, Calyx Global has concluded that the most recent nitric acid N2O abatement methodology- ACM0019- provides a strong foundation for the conservative calculation of baseline emissions. The older methodologies, AM0028 and AM0034, have more variability in their potential for an overestimated baseline risk. As we will discuss in our next post, an alternative review of the baseline calculation parameters is required for the latter methodologies in order to determine the legitimacy of emission reduction claims.

In general, nitric acid N2O abatement projects have a high potential for producing high-quality credits. While project-specific characteristics may still affect the GHG integrity of each project, on the whole, the project type has the potential to produce high-integrity emission reduction claims.

Co-benefits undercover

In addition to their overall GHG integrity, N2O abatement projects can also impact social good and environmental health. While this project type does not typically receive SDG certification, the benefits of N2O abatement projects can include ozone layer recovery, as well as air quality improvements due to collateral NOx reduction.

Ozone layer recovery

N2O emissions contribute to the depletion of the ozone layer[1]. Situated in the upper atmosphere, the ozone layer protects humans and other living organisms from hazardous UV rays. Exposure to UV rays increases the prevalence of skin cancer and changes biological processes in the environment[2]. Since the ‘ozone hole’ was discovered, an international effort has been made to reduce ozone-depleting substances and thus repair the ozone layer[3]. While most ozone-depleting substances were successfully regulated under the international treaty known as the Montreal Protocol, nitrous oxide remains one of the few exceptions to this regulation.  

Decreasing anthropogenic N2O emissions is currently seen as the most important factor for the long-term recovery of the ozone layer[3]. N2O is now the largest ozone-destroying gas, by weighted emissions, from anthropogenic activities[4]. With nitric acid production being a major industrial chemical source of N2O emissions[4], highly efficient emission abatement has the potential to contribute to ozone layer recovery. Ultimately, this can provide global benefits to human health (SDG 3: Good Health and Well-being) and contribute to restoring the natural balance to terrestrial (SDG 15: Life on land) and aquatic ecosystems (SDG 14: Life Below Water)[3].

Air quality 

Nitric acid production results in GHG emissions from both N2O and NOX gases. NOx gases, in particular, have adverse impacts on health and the environment and are a major contributor to acid rain. In some cases, NOx gases can be reduced collaterally through the installation of N2O abatement technology, which leads to less NOX pollution in the vicinity of a nitric acid plant.  

Environmental and social concerns

Abatement of N2O is applied in the broader context of nitric acid production, which can pose various health and environmental concerns throughout the process if the necessary precautionary safety measures are not implemented. Workers and nearby communities can face burns, irritation, and respiratory issues from nitric acid exposure. Environmental concerns, including air pollution and hazardous material handling, also arise from production, with pollutants like nitric oxide and nitrogen dioxide contributing to local air quality degradation. Pollutants like nitric oxide and nitrogen dioxide are emitted during production, contributing to local air quality degradation. However, nitric acid plants are usually subject to stringent safety and pollution measures, so these concerns are generally negligible. If a plant were to produce any of these outcomes, the impacts would be at a local scale. 

In addition, wastewater from production contains various substances posing risks of soil and water pollution and eutrophication. Nitric acid production also consumes significant amounts of water, which may contribute to the depletion of natural resources. However, we note that the project activity, which is to reduce N2O emissions, is not the cause of such issues; rather, the project is working to mitigate one problem of nitric acid plants, which may have pre-existing issues unrelated to the project activity.

Beyond these inherent risks, nitric acid production also carries indirect ethical considerations related to the end use of its primary products. The extensive use of nitrogen-based fertilizers stemming from nitric acid contributes to environmental risks such as runoff, algal blooms and water body "dead zones," endangering local drinking water quality, especially for vulnerable populations. Finally, given its role as an explosive precursor, nitric acid production is regulated by certain governments and agencies to prevent its misuse by terrorists and criminal organizations in the manufacture of explosives*. While most of the explosive products are used in the mining sector, it is crucial to conduct due diligence to ensure the traceability of nitric acid's intended end-use.

Final thoughts

N2O abatement projects provide a valuable pathway to reduce N2O emissions in the context of nitric acid production. Abatement technologies often require carbon credits in order to be implemented, and they often have the potential to produce legitimate and conservative emission reductions. These N2O abatement projects should be considered in the full context of nitric acid production in order to understand the diverse array of risks and benefits that the project facilitates. Stay tuned for the next post in the series, where we provide deeper insight into how we rate individual projects. 

*Such as: Convention of January 13, 1993 on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and on their Destruction (OPCW). United Nations Security Council Resolution 1540 of April 28, 2004, aimed at preventing the proliferation of weapons of mass destruction and, in particular, preventing and countering the acquisition and use by non-State actors of such weapons.
                                                                                                                                                                                                                                                                                                  

Citations

[1] Capala, P., Ruszak, M., Rudawska, A., Inger, M., and Wilk, M. (2023) The Technology of Tail Gases Purifying in Nitric Acid Plants and Design of deN20 and deNOx Reactors - Review. Appl. Sci 13(13).
[2] European Commission. Ozone Layer. Access Link. 
[3] Portmann, R.W., Daniel, J.S., and Ravishankara, A.R. (2012). Stratospheric ozone depletion due to nitrous oxide: influences of other gasses. Philosophical Transactions of the Royal Society B - Biological Sciences. 367(1593): 1256–1264.
[4] Davidson, E. A., & Kanter, D. (2014). Inventories and scenarios of nitrous oxide emissions. Environmental Research Letters, 9(10), 105012. https://doi.org/10.1088/1748-9326/9/10/105012