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METEORLOGICAL AND CHEMICAL DATA COLLECTED IN THE UNITED STATES TO INFER DRY DEPOSITION OF TRACE CONTAMINANTS
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The Atmospheric Turbulence and Diffusion Division is responsible for the operation of a prototype network developed to collect meteorological and surface condition data. The network of meteorological and chemical filterpack monitoring stations has been in operation since the summer of 1984. At present, there are 14 stations actively recording 15-minute averages of parameters which include radiation, winds (speed and 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.