Isotopic Analysis of Atmospheric Nitrogen Compounds

Isotopic analysis of atmospheric nitrogen compounds centres on measuring variations in the ratios of stable isotopes of nitrogen (15N/14N) and oxygen (17O/16O, 18O/16O) within reactive nitrogen species such as nitrogen oxides (NOx), nitric acid (HNO3) and particulate nitrate (NO3−). By examining signatures such as δ15N, δ18O and the oxygen-17 excess (Δ17O), researchers can distinguish between emissions from fossil and non-fossil fuel combustion, soil microbial activity and biomass burning, as well as elucidate the dominant chemical pathways by which NOx is converted to nitrate. This approach underpins source apportionment, quantifies the efficiency of nocturnal versus daytime oxidant pathways and informs global models of nitrogen cycling. Advances in mass spectrometric techniques, coupled with atmospheric box and regional models, have enabled finer spatial and temporal resolution of isotopic measurements, yielding insights into hemispheric contrasts in oxidant chemistry, the impact of emission controls and the role of deposition in nutrient cycling and climate forcing.

Research from Nature Portfolio

Recent work compiled global precipitation nitrate δ15N observations to assess the contributions of fossil and non-fossil fuel NOx emissions. By applying isotope mass-balance alongside bottom-up emission inventories, it was shown that non-fossil fuel sources account for over half of total NOx emissions worldwide, with particularly large fractions derived from soil microbial processes in temperate regions and biomass burning in tropical zones. Spatial-temporal patterns in δ15N of wet nitrate highlight regional differences in human activity and underscore the need to integrate non-fossil sources into mitigation strategies. The study provides a robust isotopic framework for evaluating policy scenarios aimed at reducing atmospheric NOx pollution and its downstream impacts on air quality and nutrient deposition.

Isotopic Analysis of Atmospheric Nitrogen Compounds publication trend

The graph below shows the total number of articles in isotopic analysis of atmospheric nitrogen compounds across all publications each year (not limited to Nature Index journals).

Technical terms

NOx: Collective term for nitric oxide (NO) and nitrogen dioxide (NO2), key precursors to atmospheric nitrate.

δ15N, δ18O: Notation for per mille deviations in 15N/14N or 18O/16O ratios of a sample relative to international standards, indicating source signatures and fractionation.

Δ17O: Oxygen-17 excess anomaly, the deviation of a sample’s 17O/16O ratio from a mass-dependent relationship between 18O/16O and 17O/16O, used to trace ozone-mediated processes.

N2O5 hydrolysis: Heterogeneous reaction of dinitrogen pentoxide (N2O5) with water vapour or aerosol surfaces producing nitric acid, a major nocturnal nitrate formation pathway.

Heterogeneous reactions: Chemical processes occurring at interfaces between gas, liquid or solid phases, crucial for secondary aerosol formation.

References

1. Important contributions of non-fossil fuel nitrogen oxides emissions. Nature Communications (2021).
2. Hemispherical scale mechanisms of nitrate formation in global marine aerosols. npj Climate and Atmospheric Science (2024).
3. Investigating atmospheric nitrate sources and formation pathways between heating and non-heating seasons in urban North China. Environmental Research Letters (2023).
4. Nonlinear responses of particulate nitrate to NOx emission controls in the megalopolises of China. Atmospheric Chemistry and Physics (2021).