The idea behind green ammonia is to use renewable energy (solar, wind, etc.) to electrolyze water and produce hydrogen. The hydrogen can then be combined with nitrogen gas from the air in the Haber-Bosch process to produce ammonia. This is the same as what is done now, except that the most common process is to split the hydrogen off from natural gas, which results in carbon dioxide emissions.

Ammonia is used on a large scale as a fertilizer, so switching to this process would reduce emissions (and wouldn’t make the problem of excess nitrogen reaching our groundwater and surface water any worse, or better). I didn’t realize that ammonia could be burned for fuel. This article explains that even though burning it is less efficient than just burning the hydrogen gas, it is easier to move and store than hydrogen. Burning it does produce nitrogen oxide, which is also a greenhouse gas, but you can use a catalytic convertor to remove that.

It’s not mentioned in this article, but it should also be possible in principle to extract either nitrogen gas or ammonia directly from wastewater and farm waste, which if used as fertilizer would create a closed loop and actually help our ground and surface water at the same time it is helping our atmosphere. This sounds like a win-win-win for me, but it would have a cost, and the cost would have to be paid by the parties producing the pollution now rather than paid by all of us collectively in the future as we are impacted by the pollution, and that is the hard thing to explain and build political support behind.