Ammonia

About: Ammonia is a research topic. Over the lifetime, 16217 publications have been published within this topic receiving 271940 citations. The topic is also known as: NH3 & azane.

Fossil Fuel Combustion-Related Emissions Dominate Atmospheric Ammonia Sources during Severe Haze Episodes: Evidence from 15 N-Stable Isotope in Size-Resolved Aerosol Ammonium

Abstract: The reduction of ammonia (NH3) emissions is urgently needed due to its role in aerosol nucleation and growth causing haze formation during its conversion into ammonium (NH4(+)). However, the relative contributions of individual NH3 sources are unclear, and debate remains over whether agricultural emissions dominate atmospheric NH3 in urban areas. Based on the chemical and isotopic measurements of size-resolved aerosols in urban Beijing, China, we find that the natural abundance of (15)N (expressed using δ(15)N values) of NH4(+) in fine particles varies with the development of haze episodes, ranging from -37.1‰ to -21.7‰ during clean/dusty days (relative humidity: ∼ 40%), to -13.1‰ to +5.8‰ during hazy days (relative humidity: 70-90%). After accounting for the isotope exchange between NH3 gas and aerosol NH4(+), the δ(15)N value of the initial NH3 during hazy days is found to be -14.5‰ to -1.6‰, which indicates fossil fuel-based emissions. These emissions contribute 90% of the total NH3 during hazy days in urban Beijing. This work demonstrates the analysis of δ(15)N values of aerosol NH4(+) to be a promising new tool for partitioning atmospheric NH3 sources, providing policy makers with insights into NH3 emissions and secondary aerosols for regulation in urban environments.

Oxygen isotopic exchange and fractionation during bacterial ammonia oxidation

Abstract: We examined the oxygen isotopic systematics for ammonia oxidation, the first step in the regeneration of nitrate from ammonium. In particular, oxygen isotopic fractionation and exchange with water were evaluated for their roles in determining the d18O of nitrite produced by four species of ammonia-oxidizing bacteria (AOB). Microbially catalyzed oxygen isotopic exchange between nitrite and water was less than 25% at low cell densities (106 cells mL21) and ammonium concentrations (less than 50 mmol L21). The amount of exchange was relatively constant for a given species of ammonia oxidizer but varied between 1% and 25% among the four species tested. The d18O value of nitrite produced at a given water d18O value also varied by nearly 10% among the different species. Isotopic fractionation, either during oxygen (O2) incorporation by ammonia monooxygenase and/or water incorporation by hydroxylamine oxidoreductase plays an important role in setting the d18O of nitrite produced by AOB. This work provides a detailed characterization of the oxygen isotopic systematics of ammonia oxidation by AOB, which will help us better interpret the oxygen isotopic distributions of nitrite, nitrate, and nitrous oxide in terrestrial and aquatic environments. Nitrogen is an essential macronutrient whose supply can limit primary production and carbon export from the surface ocean on seasonal, annual, decadal, and millennial time scales. Nitrate (NO { ) is the primary form of fixed nitrogen in the sea, and much research has focused on