Intra-event Variations of Nitrogen Isotopes of Ammonium in Wet Deposition
Abstract
Excess nitrogen is a major pollution problem threatening water quality and biodiversity in many urban estuaries. While many efforts have been made to reduce reactive nitrogen inputs from sewage treatment facilities, non-point source pollution such as atmospheric deposition remains challenging to quantify and monitor, especially with ammonia (NH3) emissions currently unregulated. Stable isotope compositions (δ15N) may provide an additional constraint for identifying the sources and reactions of reactive nitrogen species. The isotopic composition of ammonium (δ15N-NH4+) in wet deposition is becoming more frequently used as a source tracer for NH3 emissions. Past studies have typically compared precipitation δ15N-NH4+ to assumed δ15N-NH3emission source values to determine the relative contribution of each source. However, NH4+ source attribution based on isotope measurements is complicated by subsequent chemical and physical reactions in the atmosphere that may alter the original NH3 source signature, including wet-scavenging processes. Furthermore, few studies have simultaneously and accurately collected atmospheric NH3, p-NH4+, and w-NH4+ to characterize concentration, isotopic composition, and precipitation scavenging.
We present δ15N-NH4+ measurements of event-based wet-deposition collected over one year in Providence, RI. Preliminary results show that event-based records of δ15N-NH4+ do not show a significant relationship with air mass back trajectories, suggesting that precipitation NH4+ may be more influenced by local emission sources rather than transported emission sources. We have also monitored seasonal changes in dry deposited NH3 and p-NH4+, using laboratory-verified collection techniques suitable for isotopic analysis, which will serve as a useful comparison to understand seasonal drivers of δ15N in NH3, p-NH4+, and w-NH4+. To further understand NHx wet-scavenging, we are also collecting bulk NHx immediately before, during, and after precipitation events. This work will significantly improve our understanding of the controls on δ15N-NH4+ variability in wet deposition over the time course of rain events and improve our understanding of NHx wet-scavenging dynamics.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.A21M2918L
- Keywords:
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- 0322 Constituent sources and sinks;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0330 Geochemical cycles;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0365 Troposphere: composition and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0426 Biosphere/atmosphere interactions;
- BIOGEOSCIENCES