Ice core δ15N of Ammonium Reveals Changing Atmospheric Processing of NHx during European industrialisation
Abstract
Ammonia (NH3) is the main alkaline gas in the atmosphere and a key regulator of aerosol formation, nitrogen deposition, and air quality. Yet the relationship between NH3 emissions and deposited ammonium (NH4 + ) in remote archives, remains poorly constrained. Here, we present the first ice-core record of δ 15 N(NH4 + ), covering 1000 years of European atmosphere. Ice-core δ 15 N(NH4 + ) is systematically enriched relative to inventory-based δ 15 N(NH3), consistent with atmospheric isotopic fractionation between emitted NH3 and deposited NH4 + . The 10-year seasonally resolved record shows lower δ 15 N(NH4 + ) in winter than in summer, which is consistent with NH3-NH4 + partitioning integrated during transport, although no unique pathway can be identified as other mechanisms remain insufficiently constrained. Between 1900 and 1970, lower δ 15 N(NH4 + ) broadly coincides with higher acidity and lower neutralisation factor, consistent with increasing proportion of NH4 + through NH3-NH4 + partitioning, although cloud processing and other atmospheric processes cannot be separated. After 1980, this relationship breaks down, with a divergence between ice-core NH4 + and NH3 emission inventories, the isotope-concentration relationship disappears, and a decrease in apparent isotopic fractionation. Boundary layer observations suggest that a large underestimation of NH3 emissions is unlikely. This shift therefore indicates a change in the source-to-deposition atmospheric processes, although the responsible pathway remains unresolved. Ice-core δ 15 N(NH4 + ) therefore provides a long-term view of the source-to-deposition regime shifts, a perspective increasingly needed as Europe moves toward a less acidic, more NH3-rich atmosphere.
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BibTeX
@misc{lamothe2026core,
title = {{Ice core δ15N of Ammonium Reveals Changing Atmospheric Processing of NHx during European industrialisation}},
author = {Alexis Lamothe and Pete D Akers and Patrick Ginot and Wendell Walters and Sarah Albertin and Nicolas Caillon and Elsa Gautier and Joel Savarino},
howpublished = {HAL},
year = {2026},
month = oct,
doi = {10.5194/egusphere-2026-5825},
url = {https://hal.science/hal-05844130v1},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Ice core δ15N of Ammonium Reveals Changing Atmospheric Processing of NHx during European industrialisation
AU - Alexis Lamothe
AU - Pete D Akers
AU - Patrick Ginot
AU - Wendell Walters
AU - Sarah Albertin
AU - Nicolas Caillon
AU - Elsa Gautier
AU - Joel Savarino
PY - 2026
DA - 2026/10/13
PB - HAL
DO - 10.5194/egusphere-2026-5825
UR - https://hal.science/hal-05844130v1
AB - Ammonia (NH3) is the main alkaline gas in the atmosphere and a key regulator of aerosol formation, nitrogen deposition, and air quality. Yet the relationship between NH3 emissions and deposited ammonium (NH4 + ) in remote archives, remains poorly constrained. Here, we present the first ice-core record of δ 15 N(NH4 + ), covering 1000 years of European atmosphere. Ice-core δ 15 N(NH4 + ) is systematically enriched relative to inventory-based δ 15 N(NH3), consistent with atmospheric isotopic fractionation between emitted NH3 and deposited NH4 + . The 10-year seasonally resolved record shows lower δ 15 N(NH4 + ) in winter than in summer, which is consistent with NH3-NH4 + partitioning integrated during transport, although no unique pathway can be identified as other mechanisms remain insufficiently constrained. Between 1900 and 1970, lower δ 15 N(NH4 + ) broadly coincides with higher acidity and lower neutralisation factor, consistent with increasing proportion of NH4 + through NH3-NH4 + partitioning, although cloud processing and other atmospheric processes cannot be separated. After 1980, this relationship breaks down, with a divergence between ice-core NH4 + and NH3 emission inventories, the isotope-concentration relationship disappears, and a decrease in apparent isotopic fractionation. Boundary layer observations suggest that a large underestimation of NH3 emissions is unlikely. This shift therefore indicates a change in the source-to-deposition atmospheric processes, although the responsible pathway remains unresolved. Ice-core δ 15 N(NH4 + ) therefore provides a long-term view of the source-to-deposition regime shifts, a perspective increasingly needed as Europe moves toward a less acidic, more NH3-rich atmosphere.
ER -