Ammonia emissions are a leading contributor to PM2.5 formation in the atmosphere.
A new study has identified a more reliable method for measuring the natural nitrogen isotope signature of atmospheric ammonia, offering scientists a stronger tool for tracing pollution sources and improving air quality management.
In the atmosphere, ammonia reacts with acidic compounds to form PM2.5 particulate matter, which contributes to air pollution and climate effects. Identifying where ammonia originates from is essential for designing effective emission control strategies.
Researchers have long relied on nitrogen isotope signatures, commonly expressed as §15N, to distinguish between ammonia released from sources such as fertilizers, livestock waste, and agricultural activities. However, uncertainties during sample collection have limited the precision of these measurements.
In a new study published in Nitrogen Cycling, researchers evaluated how different acidic absorption solutions influence ammonia collection and isotope measurement accuracy. The research demonstrates that sulphuric acid provides significantly higher ammonia recovery and more stable isotope results than boric acid, which is also widely used in sampling techniques.
“Our goal was to improve the reliability of ammonia isotope measurements so researchers can better identify pollution sources,” said corresponding author Chaopu Ti. “By optimizing the collection process, we can generate more precise data to support environmental management and agricultural sustainability.”
To investigate the issue, the research team compared two commonly used absorption solutions, sulfuric acid and boric acid, using laboratory experiments and field sampling. They found that sulfuric acid achieved an average ammonia recovery rate exceeding 95 percent. In contrast, boric acid captured less than 90 percent of ammonia, increasing the risk of isotope distortion during sampling. The study also showed that sulfuric acid maintained stable isotope measurements even when ammonia concentrations were very low, a condition often encountered in real environmental monitoring.
Accurate isotope measurements depend heavily on preventing isotope fractionation, a process in which lighter and heavier nitrogen atoms are unevenly captured during sampling. Because sulfuric acid is a strong acid, it converts ammonia gas into stable ammonium more efficiently than weaker acids. This rapid conversion minimizes fractionation and improves measurement reliability across a wide range of sample concentrations.
The researchers further tested the optimized method in field studies involving major agricultural ammonia sources, including croplands, livestock facilities, orchards, and vegetable production systems. The results revealed clear differences in nitrogen isotope signatures among these emission sources. Cropland and livestock ammonia emissions displayed lower §15N values compared with orchard and vegetable production systems, demonstrating the method’s effectiveness for distinguishing pollution sources in real-world environments.
The findings have important implications for air pollution control and sustainable agriculture. Ammonia emissions are a leading contributor to PM2.5 formation. Improved source identification can help policymakers design targeted emission reduction strategies, optimize fertilizer use, and reduce environmental nitrogen losses.
