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Air Quality Management in the United States
mercury deposition. Nitrogen loading as a water quality problem has been addressed for several estuaries (for example, Long Island Sound and Tampa Bay) in the program but only to assess inputs from specific major stationary sources of concern.
The best examples of the integration of atmospheric deposition measurements with coastal effects can be found at specific sites where the research community and government agencies are actively engaged in understanding these problems. These efforts are usually multidisciplinary and involve cooperative efforts between university researchers and state or federal scientists to look holistically at a system plagued by problems, such as coastal eutrophication, associated with atmospheric deposition. For example, Neuse River estuary modeling and monitoring program involves researchers from several North Carolina universities as well as cooperation from the North Carolina Department of Environment and Natural Resources and Weyerhauser Corporation. This program has quantified not only the fluxes of atmospherically deposited nitrogen to the system (Whitall and Paerl 2001) but also the ecological effects of nitrogen loading from the atmosphere and from other sources (Peierls and Paerl 1997; Paerl et al. 1998). Similar efforts have been made for the Chesapeake Bay (Russell et al. 1998; CBADS 2001), including the development and application of the Chesapeake Bay eutrophication model (Cerco 2000).
Because of their direct economic import, the effects of air pollutants on agricultural crops are of particular concern. Probably the most comprehensive assessment of the agricultural losses incurred from exposure to air pollutants was conducted in the 1980s as part of the U.S. National Crop Loss Assessment Network (NCLAN) (Heck et al. 1988; Preston and Tingey 1988). NCLAN goals were (1) to conduct experiments using chambers with tops open to the atmosphere (see Figure 2-12 in Chapter 2) to relate doses of O3 to yields of economically important crops in several major areas in the United States; (2) to estimate actual crop losses over the United States by combining the O3-dose-to-crop-yield information with the data on crop acreage and pollutant levels in each county; (3) to assess dollar losses each year from these pollutant effects; and (4) to create models that relate yields to level of pollutant, water stress, stage of crop development, and temperature, using the results to determine the NAAQS based on injury thresholds.
There are three noteworthy aspects of the NCLAN study: (1) the data from this study are over two decades old and still represent the most comprehensive information on O3 effects on crops and are widely used to assess crop losses in the United States from air pollution; (2) the study found that crop yields are depressed substantially when O3 concentrations reach about