Citation:

Walker, JohnT, M. Bell, A. Cole, G. Beachley, G. Lear, AND Z. Wu. NADP/TDep webinar series: Assessing uncertainty in total reactive nitrogen deposition estimates for North American critical load applications. NADP/TDep webinar series, NA, NC, April 15, 2020.

Impact/Purpose:

Determination of the amount of reactive nitrogen (Nr) deposition to an ecosystem in excess of the critical load requires an estimate of total deposition, which is typically derived from gridded chemical transport models (CTMs) or a combination of measurements and model output. The uncertainty of both the Nr deposition estimate and ecosystem response need to be understood to fully evaluate the risk to the ecosystem. Knowledge of these uncertainties is important in determining an appropriate policy action to manage ecosystem exposure.

Description:

In this presentation we review the state of the science with respect to the sources of uncertainty in total Nr deposition budgets used for critical loads assessments in North America. In the absence of methods to rigorously quantify uncertainty in total Nr deposition, a simple weighted deposition uncertainty metric (WDUM) is introduced for consideration in critical load assessments. Maps of the WDUM as applied to the National Atmospheric Deposition Program/Total Deposition (NADP/TDep) estimates show more uncertainty in areas where dry deposition makes a larger contribution to the budget, particularly for ammonia dry deposition in agricultural areas and nitrogen dioxide dry deposition in urban areas. Absence of organic N from the total deposition budget is an important source of uncertainty over much of the U.S. The new WDUM can be applied at the local scale to identify the most uncertain deposition components, prioritize research and monitoring activities, and guide more detailed investigations of deposition uncertainty.

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