Synthesizing the effects of N and S deposition on terrestrial biodiversity to inform air quality standards
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Atmospheric deposition of nitrogen (N) and sulfur (S) impacts terrestrial biodiversity in the United States (U.S.) and much of the developed world. There have been dramatic improvements from the deposition levels of the past, but in many areas N and S deposition remains above levels known to impact ecosystems. Here, we synthesize research from the U.S. on the sensitivity of different taxonomic groups (e.g., trees, lichen, herbs) to N and S deposition, and we put this in the context of federal decision-making to protect ecosystems from the effects of air pollution. Air pollution is regulated through the National Ambient Air Quality Standards (NAAQS), which are standards based on atmospheric concentrations. This can pose a challenge when assessing deposition impacts and relating those impacts to air concentrations. We will review the current science on the ecosystem impacts from S and N deposition and identify challenges and potential future research opportunities to help improve our understanding of these relationships. Although we continue to make progress in cleaning the air to protect ecosystems, we have more to do and will discuss the path forward from a scientific perspective.