Sources and Processes Contributing to Nitrogen Deposition: An Adjoint Model Analysis Applied to Biodiversity Hotspots Worldwide

Citation:

Paulot, Fabien, Daniel J Jacob, and Daven K Henze. “Sources and Processes Contributing to Nitrogen Deposition: An Adjoint Model Analysis Applied to Biodiversity Hotspots Worldwide”. Environ. Sci. Technol. 47 (2013): , 47, 3226–3233. Web.

Number:

7

Date Published:

apr

Abstract:

Anthropogenic enrichment of reactive nitrogen (Nr) deposition is an ecological concern. We use the adjoint of a global 3-D chemical transport model ({GEOS-Chem)} to identify the sources and processes that control Nr deposition to an ensemble of biodiversity hotspots worldwide and two {U.S.} national parks (Cuyahoga and Rocky Mountain). We find that anthropogenic sources dominate deposition at all continental sites and are mainly regional (less than 1000 km) in origin. In Hawaii, Nr supply is controlled by oceanic emissions of ammonia (50%) and anthropogenic sources (50%), with important contributions from Asia and North America. Nr deposition is also sensitive in complicated ways to emissions of {SO2}, which affect Nr gas?aerosol partitioning, and of volatile organic compounds ({VOCs)}, which affect oxidant concentrations and produce organic nitrate reservoirs. For example, {VOC} emissions generally inhibit deposition of locally emitted {NOx} but significantly increase Nr deposition downwind. However, in polluted boreal regions, anthropogenic {VOC} emissions can promote Nr deposition in winter. Uncertainties in chemical rate constants for {OH} + {NO2} and {NO2} hydrolysis also complicate the determination of source?receptor relationships for polluted sites in winter. Application of our adjoint sensitivities to the representative concentration pathways ({RCPs)} scenarios for 2010?2050 indicates that future decreases in Nr deposition due to {NOx} emission controls will be offset by concurrent increases in ammonia emissions from agriculture.

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