The National Atmospheric Deposition Program: Lessons from a continental-scale monitoring network

Background/Question/Methods

Since 1978, the National Atmospheric Deposition Program (NADP) has tracked the status and changes in the many different chemical compounds within precipitation across the continent. The NADP monitors the removal of pollutants from the atmosphere; but more importantly, it monitors the addition of chemical compounds into the Biosphere and ecosystems of North America. Our primary charge has been to provide data for the determination of both spatial and temporal trends in chemical species and mercury wet-deposition fluxes for North America. And over the 30 years of monitoring, we have shown the value of consistent monitoring techniques, high quality assurance standards, and rigorous attention to procedures and data validation. This has allowed us to reliably quantify both small and large trends in several chemical species.

Results/Conclusions

It is clear that the addition of acidic compounds to ecosystems has dropped drastically over the past three decades, but that certain regions are still experiencing high acidic compound loading. Our data also show that nitrogen deposition is increasing, and in particular to very sensitive ecosystems. Additionally, we are noting the heavy regional increases is nitrogen deposition are due to ammonium increases. Finally, we can now show the approximate distribution of mercury input to ecosystems over North America and slight but quantifiable trends in this deposition. While mercury deposition is not important to human health while in the atmosphere, it is of extreme importance to human health as it moves through ecosystems.