As part of the Clean Air Status and Trends Network (CASTNet), dry deposition and ozone are sampled weekly at the GLEES Brooklyn monitoring site.

Established in 1987, CASTNet comprises 71 monitoring stations across the United States. The majority of the monitoring stations are operated under contract to EPA's Office of Air and Radiation. In conjunction with state and local monitoring efforts, the CASTNet monitoring network is used to determine the effectiveness of emissions control programs.

The CASTNet site at GLEES measures atmospheric concentrations of sulfate, nitrate, ammonium, sulfur dioxide, and nitric acid, continuous ambient ozone levels; and meteorological conditions required for calculating dry deposition rates. The GLEES site is equipped with a temperature controlled shelter, ozone analyzer, meteorological sensors, a filter pack sampling system, datalogger, and a radio phone modem. Filter packs are exposed for 1-week intervals (i.e., Tuesday to Tuesday) at a flow rate of 3.0 liters per minute and sent to a laboratory in Florida for chemical analysis.

Can NADP and CASTNet be used to evaluate total deposition on an annual time scale?
Zeller and others on our project compared and evaluated location-specific data from 3 different rural air monitoring programs: CASTNet (NDDN) network, the IMPROV (Interagency Monitoring of Protected Visual Environments) and the National Atmospheric Deposition Program (NADP/NTN). All 3 of these networks have sites located near each other at the Glacier Lakes Ecosystem Experiments Site (GLEES) in the Snowy Range Mountains of Wyoming. For both wet and dry deposition, spatial differences were evident. Higher elevation net deposition was greater even though higher elevation wet concentration values were lower. Wet deposition and wet concentration values between sites were not comparable on a weekly basis; but on an annual basis results were similar. Dry deposition concentration tended to be slightly higher at lower elevations. Air resource manager can use results from closely located NADP and NDDN sites to evaluate total deposition on an annual time scale with the caveat that spatial variability is expected.
Comparisons between NDDN and IMPROV sulfur concentration suggest that IMVROV data may be useful for estimating the dry concentration component used for estimating dry deposition. Although NDDN and IMPROV protocols are different, sulfate concentrations do correlate well.