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