Grantee Research Project Results
1999 Progress Report: 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
EPA Grant Number: R826760Title: 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: Chung, Serena
Project Period: September 21, 1998 through September 20, 2001
Project Period Covered by this Report: September 21, 1998 through September 20, 1999
Project Amount: $172,860
RFA: Regional Scale Analysis and Assessment (1998) RFA Text | Recipients Lists
Research Category: Aquatic Ecosystems , Ecological Indicators/Assessment/Restoration
Objective:
The objective of this project is to assess the impact of the Clean Air Act Amendments of 1990 (CAAA) on precipitation and air chemistry for the eastern United States.Progress Summary:
Phase I of the CAAAs is nearly complete and has resulted in a significant reduction in SO2 emissions from utility power plants in the eastern United States. Reduced SO2 emissions, especially from the Ohio River Valley area, was a major focus of Phase I. Little or no improvement in NOX emissions reductions has occurred in this area, except for New York, New England, and Pennsylvania.
A major incentive for the passage of the CAAA was to reduce acidic deposition in the eastern United States and Canada, and ultimately to protect human health and acid-sensitive ecosystems in both the United States and Canada. We have assessed the impact of these SO2 emission reductions (and the lack of reductions in NOX emissions) in terms of precipitation and air chemistry, which are representative of atmospheric depositon. Several subregions of the eastern United States were evaluated individually, and relationships between emissions of SO2 and NOX to precipitation and air chemistry were established. Strong relationships were found in most regions evaluated (Northern New England and the Adirondacks, lower New York State, Pennsylvania, Mid-Atlantic Coast, Ohio, Illinois, and the Southern Appalachians). Declines in SO2 emissions from source regions (based on 15-hour back trajectories of air masses) led to comparable declines in precipitation sulfate and air concentrations of SO2 and particulate sulfate (representative of dry deposition). There also were strong linear relationships between declines in combined emissions (SO2 plus NOX) and precipitation acidity. The Illinois region showed somewhat weaker relationships for precipitation sulfate. The weakest relationships were found in the southern Appalachian region, where declines in SO2 emissions from appropriate source regions show no accompanying declines in precipitation acidity and small declines in precipitation sulfate concentrations. NOX emissions have increased in this area during the 1990s. Unfortunately, the southern Appalachians are an acid-sensitive region, where declines in acidic deposition are necessary to protect surface waters and high elevation forests.
We have used state-level SO2 and NOX emissions data from the Environmental Protection Agency (EPA) Emissions Inventory Group and 2 years of back trajectory analysis for seven different regions in the eastern United States to establish appropriate source regions and emissions from these regions. Three source areas of different scale were used for each region of interest. The smallest source region was based on 15-hour back trajectories of air masses. A mid-sized source region was based on 21-hour back trajectories, and a third, larger source region was based on an area in a northwest to south quadrant extending 1,500 km back from the area of interest. Emission changes were compared with changes in precipitation and air chemistry data from two wet deposition networks (NADP and the AIRMoN-wet subnetwork), and data from two dry deposition networks (CASTNET and AIRMoN-dry). To minimize seasonal and year-to-year climatic variability, the data have been summarized into multi-year means (1991 to 1994 and 1995 to 1997), representative of pre-CAAA and post-CAAA periods. Attempts to find consistent relationships between NOX emissions and nitrogen compounds associated with wet and dry deposition were not successful due to the very slight changes in NOX emissions for much of the eastern United States.
Based on 15-hour air mass back trajectories and data from 42 precipitation chemistry sites and 31 dry deposition sites, 1:1 relationships for emissions versus concentrations of precipitation sulfate and air concentration of SO2 and particulate sulfate (i.e., dry sulfur) exist for Northern New England and the Adirondacks (HB), lower New York State (NY), Pennsylvania (PA), and the mid-Atlantic Coast (DE). In some cases, greater percent declines in concentrations than in emissions have occurred in the 1990s. For the Ohio region, a 23 percent decline in emissions of SO2 has been accompanied by an 18 percent decline in precipitation sulfate and a 26 percent decline in dry sulfur. The Illinois region shows a 19 percent decline in emissions of SO2 compared with a 12 percent decline in precipitation sulfate and a 17 percent decline in dry sulfur.
One-to-one relationships exist for declines in combined emissions of SO2 and NOX and declines in H+ concentration (acidity) for lower New York State (NY), Pennsylvania (PA), the Mid-Atlantic Coast (DE), the Ohio region (OH), and the Illinois (IL) region. The northern New England and Adirondack region shows that a 17 percent decline in combined emissions of SO2 and NOX has led to a 14 to15 percent decline in precipitation acidity (H+ concentration) during implementation of Phase I.
For the southern Appalachian region (TN), back trajectories indicate that a 17 percent decline in SO2 emissions has led to only a 6 percent drop in precipitation sulfate and a 12 percent drop in dry sulfur. The removal of one outlier site brings the relationship much closer to 1:1 for dry sulfur. No relationship seems to exist between declines in combined emissions (approximately 10 percent) and declines in precipitation acidity (no change). The southern Appalachians are an acid-sensitive region that needs large declines in acidic deposition for surface waters and forests to be protected from acid rain.
A summary of declines in emissions, based on 15-hour back trajectories, and declines in mean concentrations for all regions is presented in Table 1. The details of this table are described in the accompanying caption.
(a) | (b) | (c) | (d) | (e) | (f) | |
91-94
vs 95-97 |
NOX
% change |
SO2
% change |
2S+N (moles)
% change |
Sulfate wet
% change |
S dry
% change |
H+ % wet
change |
NE | -10 | -20 (-19) | -17 | -24 | -28 | -14 |
NY | -6 | -21 (-20) | -16 | -24 | -- | -22 |
PA | -3 | -21 | -16 | -21 | -21 | -17 |
DE | +1 | -18 | -12 | -21 | -- | -16 |
OH | +3 | -23 | -15 | -18 | -23 | -16 |
IL | +4 | -19 | -11 | -12 | -17 | -17 |
TN | +4 | -17 | -10 | -6 | -12 | <-1 |
Table 1. Declines in emissions of (a) NOX, (b) SO2, and (c) combined emissions, expressed as percents; and mean declines, also expressed as percents, in (d) precipitation sulfate concentrations, (e) SO2 and particulate sulfate air concentrations (sources of dry S deposition), and (f) precipitation acidity (H+ concentrations) for several areas of the eastern United States. The years 1991 through 1994 (pre-CAAA implementation) are compared with 1995 through 1997 (post-CAAA implementation). The regions of study include northern New England and the Adirondack Mountains (NE), New York, not including the Adirondack Mountains (NY), Pennsylvania (PA), the mid-Atlantic (DE), Ohio (OH), Illinois (IL), and the southern Appalachians (TN). The number of wet depositon sites (W) and dry deposition sites (D) for each region are as follows: NE W = 7 D = 7, NY W = 7, PA W = 6 D = 7, DE W = 4, OH W = 7 D = 4, IL W = 7 D = 5, and TN W = 7 D = 8. Combined emissions (c) include two times the moles of SO2 (each mole of SO2 has the potential to generate two moles of H+ in precipitation) plus moles of NOX. The percent change in parenthesis for NE and NY under (b) represent changes in emissions when the Canadian province of Ontario is included as part of the source region*. Including the Canadian emissions has little impact on the analysis. * small source region
While Phase I of the CAAA has led to improvements in air quality and declines in acid deposition for large areas of the eastern United States, the improvements have not translated into significant decreases in acidification for many sensitive ecosystems.
Future Activities:
Future efforts will focus on the implementation of Phase II impacts and how these may translate to improvements in surface water quality.Journal Articles:
No journal articles submitted with this report: View all 7 publications for this projectSupplemental Keywords:
acid rain, CASTNET, precipitation, acid deposition, SO2, NOX, northeast, southeast, mid-atlantic, NY, TN, PA, OH., RFA, Scientific Discipline, Water, Ecosystem Protection/Environmental Exposure & Risk, Nutrients, Environmental Chemistry, Ecosystem/Assessment/Indicators, Ecosystem Protection, Restoration, Ecological Effects - Environmental Exposure & Risk, Environmental Monitoring, Ecological Risk Assessment, Ecology and Ecosystems, Aquatic Ecosystem Restoration, Ecological Indicators, aquatic ecosystem, hydrological stability, precipitation, ecological exposure, monitoring, nutrient sensitive ecosystems, regional economies, bioavailability, chemical transport, Sulfur dioxide, sulfur, emissions, hydrogen ion, atmospheric nitrogen deposits, nitrogen oxide, nutrient stress, wet and dry deposition, SO2, sulfur compounds, precipitation chemistry, ecosystem, Clean Air Act, nitrogen compounds, water quality, ecosystem stress, rainfall, public policy, regulations, ecological impact, acid rain, climatology, nitrogenRelevant Websites:
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.