Air pollution impacts and trade-offs of ammonia as a road transportation fuel

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Ammonia shows great potential for decarbonizing the road transportation sector because it does not produce CO2 emissions during combustion. On the other hand, ammonia-fueled engines emit gases such as (unburned) ammonia (NH3), and nitrogen oxides (NO)x, which contribute to air pollution and adversely impact human health, among other environmental effects. The aim of this work is to investigate the air quality impacts and human health trade-offs associated with potential emissions from an ammonia-fueled road transportation fleet of different vehicle categories. Specifically, we create a simplified emissions tool to quantify the NH3 and NOx spatial emissions from state-of-the-art ammonia engine developments. Next, the emissions are combined with spatial sensitivities, obtained from the adjoint of GEOS-Chem, to estimate the corresponding air quality impacts in terms of PM2.5 formation and human health impacts with respect to premature mortalities.
The research findings indicate that the ammonia-fueled sector generally exhibits higher air quality and human health impacts compared to conventional transport. We estimate that the implementation of various ammonia engine configurations into the road transportation fleet in the USA in 2011 could lead to approximately 23 000 to 250 000 premature mortalities.
However, there is potential for mitigating air quality impacts of ammonia emissions through the use of post-combustion treatment methods or the adoption of ammonia-fueled heavy-duty vehicles. These approaches could help achieve air pollution levels comparable to those of fossil fuel vehicles while reducing the carbon footprint, offering future possibilities for an ammonia-fueled road transportation sector.