Regional scale impacts of Phases I and II of the Clean Air Act Amendments of 1990: The relationship between changes in emissions of SO2 and NOx, and wet and dry deposition of hydrogen ion, and sulfur and nitrogen compoundsEPA Grant Number: R826760
Title: Regional scale impacts of Phases I and II of the Clean Air Act Amendments of 1990: The relationship between changes in emissions of SO2 and NOx, and wet and dry deposition of hydrogen ion, and sulfur and nitrogen compounds
Investigators: Likens, Gene E. , Butler, Thomas J.
Institution: Cary Institute of Ecosystem Studies
EPA Project Officer: Hahn, Intaek
Project Period: September 21, 1998 through September 20, 2001
Project Amount: $172,860
RFA: Regional Scale Analysis and Assessment (1998) RFA Text | Recipients Lists
Research Category: Ecosystems , Ecological Indicators/Assessment/Restoration
This study will synthesize several regional data sets to quantify the relationship between changing emissions and precipitation and dry deposition in the eastern U.S. due to the Clean Air Act Amendments (CAAA) of 1990. Using this relationship, the impact on air and precipitation chemistry (hydrogen, sulfur and nitrogen species) of further reductions in emissions of SO2 and NOx due to Phase II of the CAAA will be predicted. Finally, deposition loads of H+, nitrogen and sulfur will be compared to "critical loads" for different acid sensitive regions to establish the overall effectiveness of federal regulations in protecting these areas. The impact on stream water of the Hubbard Brook Experimental Forest (HBEF) will be assessed as a case study. Implementation of Phase I, which began in 1995 for SO2 and 1996 for NOx, has led to a decline of approximately 18% in SO2 emissions in the eastern U.S. compared to 1994. Significant reductions in precipitation SO4- and H+ concentrations have been documented for 1995 (Lynch et al. 1996) and 1996 (Butler and Likens 1997) for the Ohio River Valley and the northeastern U.S. However, some areas considered "acid sensitive", such as the southern Appalachian Mt. region and the Upper Midwest, do not show noticeable improvement, especially for 1996.
We propose to: (1) Define the long-term relationship between changing SO2 and NOx emissions, with changing precipitation chemistry at approximately 80 sites in the eastern U.S. These analyses will be done at different levels of regional aggregation (i.e. New England, northeastern U.S., eastern U.S.). (2) Define the long-term relationship between changing SO2 and NOx emissions, and changing dry deposition and/or atmospheric concentrations (SO2, HNO3, SO4- and NO3-) for approximately 50 eastern dry deposition sites. Evaluate the regional representativeness of the CASTNet and AIRMoN-dry deposition networks by analyzing the spatial patterns these networks produce in relation to emission sources. (3) Combining the above information, estimate the impact of changing emissions on total deposition of H+, sulfur and nitrogen. This analysis assumes that the dry deposition sites are regionally representative. If the data suggest that dry deposition estimates are not representative regionally, we will examine the CASTNet and AIRMoN air concentration data, which are less subject to local effects, for regional representativeness; (4) Assess all sites for expected declines in chemical parameters have occurred because of implementation of the CAAA (H+, SO4- and NO3- for wet deposition; SO2, HNO3-, SO4- and NO3- for dry deposition or air concentration); and (5) Evaluate future predicted impacts on HBEF stream water (Likens et al. 1996).
The major results of this investigation will be to: (1) clarify where the CAAA are having a positive impact and where they are not; (2) develop statistical regression models to relate changing emissions to total deposition (or wet deposition if dry deposition is not regionally representative). These empirical models then can be used to (3) assess the ecological impact of further reductions in emissions under Phase II of the CAAA on a regional basis.