The Clean Air Status and Trends Network (CASTNET) currently features more than 90 sites across the contiguous United States and Alaska. In recent years, CASTNET has taken the approach of expanding by adding new sites that are considered ‘small footprint’. These sites do not have traditional CASTNET shelters but instead use small, tower-mounted equipment boxes. Small footprint sites only include a filter pack system for measuring ambient concentrations and ambient temperature measurement for use in converting concentrations to local conditions. The equipment box houses the mass flow controller, pump, cellular modem, and data logger and is mounted at approximate chest height. The tower is a regular 10 meter CASTNET tilt-down tower used at traditional CASTNET sites. The first small footprint sites were installed in 2012 in the northeast, with two sites in the Adirondack Park in New York and one site in northern Vermont. Two additional small footprints sites were added in 2014. One site was installed in northeastern Kansas in February 2014 as part of the Kickapoo Tribe’s air monitoring program, and the second site began operations in late summer 2014 at the Red Lake Nation of Minnesota.

An alternative energy, ‘off-grid’ design for small footprint sites is currently being developed and tested at the AMEC field test site in Gainesville, Florida. This design will use a wind turbine and solar panel for generating electricity, which will be stored in two 12 volt AGM (absorbent glass mat) deep cycle batteries. The batteries will then be used to power the site. The first ‘off-grid’ site will be installed in late summer 2014 at the Coweeta Hydrologic Laboratory in North Carolina as part of a transect study designed to characterize concentrations in an Appalachian valley. The second site may be located in the northwestern United States and is scheduled to be deployed by the end of 2014. The ‘off-grid’ design will make it possible to do filter pack sampling in remote locations where electrical access is not possible or would be cost prohibitive.