A network of meteorological and chemical filterpack
monitoring stations has been in operation since the summer of 1984.
Additional towers have since been installed around the United States,
several towers have been removed, and at present there are 13 stations
actively operating as part of the dry deposition component of the
Atmospheric Integrated Research Monitoring Network (AIRMoN). ... Meteorological and surface condition data are collected, and 15-minute
averages are recorded. These parameters include radiation, winds
(speed & direction), temperature, relative humidity, rainfall, and
wetness. These data are used to infer weekly-average site-specific
dry deposition velocities for sulfur dioxide, ozone, nitric acid, and
sulfate using a procedure based on the resistance model of the dry
deposition process. Weekly-average concentration data are obtained
from the filters, using the measured sample flow rate. Concentrations
of the following ions are measured: chloride; nitrate; sulfate;
sodium; ammonium; potassium; magnesium; and calcium. Weekly-average
dry deposition fluxes for sulfur dioxide, nitric acid, sulfates, and
nitrates are then calculated from the product of the deposition
velocities and the measured concentrations. The adequacy of the
method is being tested by comparison to results from higher time
resolution chemical monitors located at three CORE research sites.
Direct eddy correlation measurements are also performed intermittently
at these CORE sites as a further test of the method, and to improve
the inferential model for the dry deposition velocity.
The dry deposition inferential measurement (DDIM) approach differs
from previous network measurement programs in that the data sets are
designed to permit extension from observations at a subset of research
sites to less intensive routine measurement sites. Hence a major goal
is the definition of a suitable set of supporting data from which dry
deposition rates can be inferred using air concentration data.