Ammonia (NH3) is an atmospheric pollutant that has complex and interesting effects on the environment.

Despite NH3 being alkaline, it contributes to soil and freshwater acidification by releasing of H+ ions during the microbial nitrification of Ammonium ions (NH4+) to Nitrate ions (NO3−). Interestingly it raises local levels of soil nitrogen, which may actually enhance soil fertility, however it also runs the risk of having excess NO3- leached out into the environment.

But where do agricultural ammonia emissions come from?

There are two main sources:

• Decomposition of nitrogenous livestock waste, e.g. waste that contains urea (cattle, sheep and pigs) or uric acid (poultry). Subsequent hydrolysis of the urea or uric acid by the enyzme urease produces NH3 and CO2. This results in a localised increase in pH which shifts the natural equilibrium between NH3 and NH4+ ions in liquid solution towards NH3. Gaseous ammonia emission then occurs due to the rapid volatilisation of this NH3 from solution.
• The other main source is from volatilisation of ammonium or urea-based fertilisers, potentially causing 10–20% losses in fertiliser N inputs. The process by which NH3 emissions enter the atmosphere is similar to the process nitrogenous livestock wastes.

Due to the means by which NH3 emissions are produced the best strategy for minimising NH3 emission is to limit the opportunity for volatilisation to occur. This can be done by reducing the contact of manure and slurry with the air. We can also reduce residual N in livestock waste by adjusting feed protein content to align more closely with livestock physiological requirements for the target level of production.

 

Sources:

• Merrington, G., Winder, L., Parkinson, R., & Redman, M. (2005). Agricultural Pollution Environmental: Environmental problems and practical solutions. Spon Press.
• Behera SN, Sharma M, Aneja VP, Balasubramanian R. Ammonia in the atmosphere: a review on emission sources, atmospheric chemistry and deposition on terrestrial bodies. Environ Sci Pollut Res Int. 2013 Nov;20(11):8092-131. doi: 10.1007/s11356-013-2051-9. Epub 2013 Aug 28. PMID: 23982822.