CASTNET was established in 1991 to assess trends in ambient air quality and deposition of acidic pollutants due to emission reduction programs. CASTNET currently has more than 90 monitoring stations across the US and Canada. While CASTNET is managed by federal agencies (US EPA, National Park Service and Bureau of Land Management) there are more than 50 partners that are invaluable to the day-to-day operation of the network. These partnerships include universities, Native American tribes, and state agencies that provide site operator support, land, and their expertise in air monitoring research.

CASTNET has maintained three long-term tribal partnerships. In eastern Oklahoma the Cherokee Nation operates a CASTNET filter pack and ozone analyzer at their NCore station. This site has been operating as a CASTNET site since 2002. The Alabama-Coushatta tribe has operated a CASTNET site in eastern Texas since 2004, while the Santee Sioux in northern Nebraska have been operating a CASTNET site since 2006.

In 2012, CASTNET developed a small-footprint, low power monitoring site that does not require a temperature-controlled shelter. The small footprint site consists of a 10-m tower, a typical CASTNET filter pack with an enclosure located on the tower that includes a pump, MFC and telemetry. Since the development of the small-footprint site CASTNET has increased the number of monitoring sites by offering this low impact, low-cost setup for measuring weekly sulfur and nitrogen species. Two tribal partners, Kickapoo Nation located in Northeast Kansas and Red Lake Nation located in northern Minnesota joined CASTNET in 2013/2014 with the deployment of the small-footprint site.

EPA will continue their outreach efforts to existing tribal partners. Efforts will be expanded to other interested tribes in 2014. CASTNET will develop tools for viewing data, reports on air quality and deposition fluxes in tribal regions, and training documents and Frequently Asked Questions for tribal air monitoring groups.