Interview: Jill Baron- Nitrogen and Sulfur Deposition in US — Moving Beyond Air Quality

By Shinichi Asao, Andrew Tredennick, and Julie Kray

Tara Greaver of the Environmental Protection Agency and her colleagues recently published a study on the ecological effects of nitrogen and sulfur air pollution in the U.S. in Frontiers in Ecology and the Environment. They find that nitrogen and sulfur emissions from human activities contribute greatly to deposition (see video below for description, or here) of these elements to terrestrial systems. Unfortunately, the US Clean Air Act does not currently regulate deposition, just air quality. You can read the paper here.

We sat down with Jill Baron, a co-author and a senior research scientist of NREL and US Geological Survey to discuss nitrogen and sulfur deposition, how it is monitored, the effects it has on ecosystems, and ways to move forward. Here’s Jill describing her position and expertise.

Introduction to Jill Baron.


Q: This study is largely about nitrogen and sulfur pollution in terms of deposition as opposed to air quality.  What exactly is deposition?


Q: The way it was originally written, the Clean Air Act protected only air quality by regulating gas-phase pollutants but not necessarily what falls out of the air as deposition.  How has regulation evolved since then, and how does EPA regulate nitrogen and sulfur pollution now?

Want to learn more about the US Clean Air Act? Read about it here:


Q: Nitrogen and sulfur are essential nutrients for many organisms.  So why are increases in nitrogen and sulfur a concern for ecosystems?


Q: Nitrogen and sulfur deposition are monitored in several ways across many sites.  How is this information brought together to create a comprehensive picture of deposition in the U.S.?

Want to learn more about how nitrogen and sulfur deposition are monitored? Check these out: NADP, CASTNET, and CMAQ.


Q: Some parts of the U.S. are more affected by nitrogen and sulfur deposition than other parts.  For example California, and especially southern California, gets deposition of 30 – 90 kg nitrogen per hectare per year, compared to 1 – 4 kg per hectare per year in Colorado.  What other parts of the U.S. are most affected?

To see animated maps of nitrogen and sulfur deposition in the U.S. through time, check out these animations from NADP:


Q: What are the policy implications of this study?


Q: Are you optimistic that these changes will happen?


Our sincere thank you to Jill Baron.

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