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2 years ago in Environmental Chemistry , Geochemistry By Aarav
How can sources of nitrate in precipitation be distinguished, particularly between polluted urban air and other sources?
Our precipitation samples show high nitrate, but the catchment has mixed influences: urban traffic, distant farmland, and natural soils. We need to move beyond simple concentration data to defensible source apportionment. I understand isotope ratios are key, but I'm unsure how to interpret the δ¹?N and δ¹?O signatures to untangle these overlapping sources effectively.
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By Abhay R Answered 2 years ago
You're right to focus on dual-isotope plots (δ¹?N vs. δ¹?O). From my work on atmospheric deposition, I've seen that different sources occupy distinct realms: vehicle NOx tends to have a low, clustered δ¹?N signature; soil emissions have a wider, often higher range; and fertilizer nitrate has a very low δ¹?N. The δ¹?O helps separate atmospheric processes. I would recommend analyzing co-existing ions like sulfate (for fossil fuel markers) and ammonium. Then, use a Bayesian mixing model (like SIAR or MixSIAR) with your local source end-members to quantify proportional contributions. It's rarely one source, but a mix the model can resolve
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