Atmospheric deposition, measurement

Precipitation over North America gradually becomes more acidic from west to east, especially in industrialized areas of the Northeast. This acid rain may be a result of the release of nitrogen and sulfur oxides into the atmosphere. The colors and numbers (see key) indicate pH measured at field laboratories in 2004. Data from National Atmospheric Deposition Program/National Trends Network http //nadp.sws.uiuc.edu. 

Considerable work has been done on the behavior of pollutant species at air-water and air-soil interfaces. For example, wet and diy deposition measurements of various gaseous and particulate species have been made over a wide range of atmospheric and land-cover conditions. Still, the problem is of such complexity that species-dependent and particle-size-dependent rates of transfer from the atmosphere to water and soil surfaces are not completely understood. There is much to be learned about pollutant transfer at water-soil interfaces. Concern about groundwater contamination by mineral... 

Frescholtz 2002). Although ongoing and new planned field and laboratory studies are designed to further test this hypothesis, we feel that it is warranted at this time to develop a pilot-scale network of aimual ecosystem fluxes of THg in TF and LF as indicators of total atmospheric deposition. These fluxes can then be compared with measured wet plus modeled diy deposition based on both inferential and regional-scale models to develop independent estimates of total atmospheric deposition for forested catchments. We also believe that this approach could eventually be applied to a national network, such as the MDN. Although this method is best aimed at forested sites, ongoing research will address methods appropriate for other ecosystems. 

In marine ecosystems, the high copper levels measured in heavily contaminated coastal areas sometimes approach the incipient lethal concentrations for some organisms (Neff and Anderson 1977). Elevated copper concentrations in marine and estuarine environments may result from atmospheric deposition, industrial and municipal wastes, urban runoff, rivers, and shoreline erosion. Chesapeake Bay, for example, receives more than 1800 kg of copper daily from these sources (Hall et al. 1988). Copper concentrations in abiotic marine materials are generally higher near shore than... 

Ruhling, A. Tyler, G. 2004. Changes in the atmospheric deposition of minor and rare elements between 1975 and 2000 in south Sweden, as measured by moss analysis. Environmental Pollution 131.3, 417-23. 

Cole KL, Engstrom DR, Futyma RP, et al. 1990. Past atmospheric deposition of metals in northern Indiana measured in a peat core from Cowles Bog. Environmental Science and Technology 24 543-549. 

Dr. R.J. Wright at the Beltsville Agricultural Research Center, Beltsville, Maryland, is developing experimental approaches to allow direct measurement of pesticides including diazinon in wet and dry atmospheric deposition. The spatial and temporal distribution of airborne pesticide inputs to Chesapeake Bay will be determined to test predictive models of the atmospheric transport and deposition of agricultural chemicals. 

Eisenreich, S. J., W. A. Willford, and W. M. J. Strachan, The role of atmospheric deposition in organic contaminant cycling in the Great Lakes . In Intermedia Pollutant Transport Modelling and Field Measurements, D. Allen, Ed., Plenum Press, New York, 1989, pp. 19-40. 

Concentrations at surface sites are often affected by the proximity of the surface. The surface may emit the species, as is the case for NO, or the species may be deposited at the surface, as is the case for HN03. In either case, the atmospheric concentration measured within several meters of the surface may be significantly perturbed from the average for the troposphere as a whole or even for the boundary layer (the lowest layer of the troposphere in direct thermal contact with the surface its thickness varies from 102 m or less at night to 103 m or more during the day, at least over land). Therefore, the surface complicates the interpretation of concentration measurements. However, proper measurements near the surface can be used to determine surface fluxes of the species. 

Micrometeorological Flux Measurements. It is important to quantify the flux of the nitrogen species to or from the atmosphere due to surface emission or deposition. Measurements of fluxes of NO and N20 have been made by enclosure techniques, but the enclosures placed on a surface must be suspected of disturbing the flux that they are designed to measure. Fluxes... 

Our estimates of atmospheric deposition in preindustrial and modern times indicate that Hg inputs have increased by a factor of 3.4 in 130 years (3.7 to 12.5 xg/m2 per year). Alternatively, a factor of 3.7 is obtained by averaging the increase factor from each lake (Table II). The 3.7-fold increase translates to an average increase of about 2.2% per year, compared to an annual increase of 1.5% measured in air over the north Atlantic Ocean for the period 1977-1990 (26). 

Both local and long-range emission sources contribute to atmospheric deposition. Total atmospheric deposition is determined using both wet and dry deposition measurements. Although the term acid rain is widely recognized, the dry deposition portion ranges from 20 to 60 percent of total deposition. 

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