Chinese scholars and overseas collaborators have made progress in the study of atmospheric ammonium nitrogen isotopes

With the support of the National Natural Science Foundation of China (grant numbers: 42125301, 41730855, 42073005), the team of Professor Liu Xueyan of Tianjin University and domestic and foreign collaborators have made progress
in the research of atmospheric ammonium nitrogen isotopes 。 The research results, titled "Significant contributions of combustion-related sources to ammonia emissions," were published
in the journal Nature Communications on December 13, 2022 。 Link to the paper: _istranslated="1">.

The change of nitrogen cycle is one of the causes of the surface ecological environment and climate change of the Anthropocene, which is related to the environmental quality of water-soil-gas, food production, structural function of ecosystems and climate feedback
.
Synthetic ammonia is the main raw material for chemical nitrogen fertilizer, and ammonia fuel is also a key substance
to achieve "carbon neutrality" in the field of energy and power.
However, since the Industrial Revolution, population growth and economic development have led to a continuous increase in atmospheric ammonia and ammonium concentrations, stocks, and sedimentation fluxes, and a correct understanding of the contribution of the main land-based sources of atmospheric ammonia is the key
to formulating ammonia emission reduction strategies and assessing the ecological, environmental and climate effects of anthropogenic ammonia.

Due to the high solubility and chemical reactivity of ammonia, its atmospheric lifetime is short, but the atmospheric transport of ammonium roots is obvious, resulting in complex sources and high mixing degree of atmospheric ammonium nitrogen at specific monitoring points and underlying
surfaces.
At regional and global scales, ammonia volatilization, mainly from agricultural nitrogen fertilizer application and aquaculture waste, has been considered to be the main source of
ammonium nitrogen in the atmosphere.
In recent years, more and more research evidence from experimental simulation, ground sampling analysis, satellite remote sensing monitoring, and more accurate emission inventory statistics shows that fossil energy mainly based on coal combustion (urban and surrounding industrial coal combustion, loose coal combustion in non-urban areas) and fuel oil (urban transportation as a hot spot, non-urban areas are also widely distributed), as well as biomass fuel combustion based on crop straw and natural fires, emits a large amount of ammonia
.
However, the emission factors and emission intensity of the widespread combustion-related ammonia are difficult to accurately constrain, resulting in uncertain emissions of combustion-related ammonia and its contribution to regional atmospheric ammonia
.

Since the fifties of last century, stable isotopes of nitrogen have gradually become a powerful tool for tracking the source of atmospheric ammonium nitrogen, and a large number of observations have been carried out in three high-nitrogen pollution areas in East Asia, North America and Europe (Figure).

However, how to clarify the nitrogen isotope change mechanism of atmospheric ammonium nitrogen and realize the quantitative evaluation of isotope of source contribution has always been a major problem
in atmospheric system nitrogen isotope geochemistry 。 Based on the above background and problems, the research team 1) constrained the nitrogen isotope effect between atmospheric ammonia, particulate ammonium and precipitated ammonium mixture and initial emission ammonia; 2) The nitrogen isotope ratio of the atmospheric initial emission ammonia mixture in East Asia, North America and Europe was reconstructed, and it was found that the nitrogen isotope ratio of the atmospheric initial emission ammonia mixture showed that of North America> Europe > East Asia, but the nitrogen isotope ratio of the atmospheric initial emission ammonia mixture in the three regions in the past few decades decreased, indicating that the relative proportion of combustion-related ammonia in North America was higher than that in Europe and East Asia, but the proportion of volatile ammonia in the three regions showed an increasing trend; 3) Combined with the nitrogen isotope terminal values and volatile ammonia emissions of mainly combustion-related ammonia and volatile ammonia, the proportion and emissions of combustion-related ammonia in three study areas were calculated using isotopic mass balance models: 40±21% (6.
6±3.
4 Tg N yr-1) in East Asia, 49±16% (2.
8±0.
9 Tg N yr-1) in North America, and 44±19% (2.
8±^1.
3 Tg N yr^{- 1}) (Figure).

These results reveal that combustion-related ammonia has an important contribution to atmospheric ammonium nitrogen, provide new regional ammonia emission data, and provide new scientific evidence
for the formulation of current and future atmospheric ammonia emission reduction strategies, settlement liquidation and effect evaluation.