While the world has focused on electric vehicles (EV) as part of a response to climate change, other technologies are being explored. Toyota and Chinese auto maker Guangzhou Automobile Group (GAC) have introduced an engine that is powered by ammonia. Similar to technology used in ships and trucks, these novel engines are said to be able to produce 161 horsepower with a 90 percent reduction in carbon emissions compared to conventional fuels. Ammonia-powered cars would likely be less expensive than EVs because they eliminate the environmental, production and disposal issues related to their batteries. 

Using ammonia as a fuel source does introduce challenges. It is a toxic substance that can dissolve some metals, and excessive exposure in gas or liquid form can be deadly. The slow-burning fuel has about half the energy density of gasoline, making it finicky for use in cars.   

When it burns, ammonia is carbon-free and produces no CO2, hydrocarbons or soot, but it could release nitrogen into the atmosphere, leading to acid rain and impaired breathing. GAC claims to have reduced nitrogen emissions by increasing the combustion pressure in the engine, so a safe and convenient infrastructure would need to be built to make its use viable. Also, the energy needed to manufacture sufficient quantities of ammonia would need to be factored into any calculation of net environmental impacts.