Grantee Research Project Results
2000 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, 1999 through September 20, 2000
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 CAAA is complete and has resulted in a significant reduction in SO2 emissions from utility power plants in the eastern United States (as of 1998, the last year that emissions data are available). Reduced SO2 emissions, especially from the Ohio River Valley area, were 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 acid 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 deposition. Several subregions of the eastern United States were evaluated individually, and relations between emissions of SO2 and NOx to precipitation and air chemistry were established. In most regions evaluated (Northern New England and the Adirondack Mt. region, lower New York State, Pennsylvania, Mid-Atlantic, Ohio and vicinity, Illinois and vicinity, and the Southern Appalachians). Strong relations were found in all regions except the Southern Appalachians. Declines in SO2 emissions from source regions (based on 15-hour back trajectories of air masses for the New England area and 9-hour back trajectories of air masses for the remaining study areas) led to comparable declines in precipitation SO42-, and air concentrations of SO2 and particulate SO42- (representative of dry deposition). There were also strong linear relations between declines in combined emissions (SO2 plus NOx) and precipitation acidity. The Illinois region showed somewhat weaker relations for precipitation SO42-. The weakest relations were found in the southern Appalachian Mt. region where declines in SO2 emissions from appropriate source regions show no accompanying declines in precipitation acidity and small declines in precipitation SO42- concentrations. NOx emissions have increased in this area during the 1990s. The southern Appalachian Mountains are an acid sensitive region where declines in acidic deposition are necessary to protect surface waters and high elevation forests.
When data from all study areas are combined to obtain a representative estimate of relations for emissions and concentrations for the eastern United States as a whole (not including the deep south, which was not evaluated in this study) there are near 1:1 relations for SO2 emissions vs. precipitation SO42- concentrations, SO2 emissions versus air concentrations of SO2 and particulate SO42- (i.e., dry deposition components), and for combined emissions of SO2 and NOx versus H+ concentrations (acidity).
We have used state level SO2 and NOx emissions data from the EPA Emissions Inventory Group and 2 or more years of air-mass, back trajectory analysis for seven different regions in the eastern United States to establish appropriate source regions and emissions from these regions. Four emission source regions of different scale were used for each of the seven study areas. The source regions were based on 9-hour, 15-hour, and 21-hour back trajectories of air masses. A final, largest source region was based on an area in a northwest to south quadrant extending 1500 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/NTN and the AIRMoN-wet subnetwork) and data from two dry deposition networks (CASTNET and AIRMoN-dry). In order to minimize seasonal and year-to-year climatic variability we summarized the data into multi-year means (1991 to 1994 and 1995-1997) representative of pre-CAAA and post-CAAA periods, respectively. Attempts to find consistent relations between NOx emissions and nitrogen compounds associated with wet and dry deposition were not successful due to the very small changes in NOx emissions for much of the eastern United States.
Based on 15-hour air mass back trajectories for the New England and Adirondack Mountain area, and 9-hour source regions for the other 6 study areas, and data from 47 precipitation chemistry sites and 34 dry deposition sites, 1:1 relations or near 1:1 relations for emissions versus concentrations of precipitation sulfate and air concentration of SO2 and particulate- SO42- (i.e., dry sulfur) exist for Northern New England and the Adirondack Mountain region (NE), lower New York State (NY), Pennsylvania (PA), and the Mid-Atlantic coast (MA). In some cases greater percent declines in concentrations than in emissions have occurred in the 1990s. For the OH region, a 23 percent decline in emissions of SO2 was accompanied by an 18 percent decline in precipitation SO42- and a 23 percent decline in dry sulfur. The Illinois region showed a 20 percent decline in emissions of SO2 compared with 12 percent declines in precipitation SO42- and a 20 percent decline in dry sulfur.
Near 1:1 relations 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 Illinois (IL) region. The Northern New England and Adirondack Mountain region showed that a 17 percent decline in combined emissions of SO2 and NOx led to a 14-15 percent decline in precipitation acidity (H+ concentration) during implementation of Phase I.
For the southern Appalachian Mountain region (SA) back trajectories indicate that a 20 percent decline in SO2 emissions led to only a 12 percent drop in precipitation SO42-, but a 20 percent drop in dry sulfur. No relations were found between declines in combined emissions (approximately 10 percent) and declines in precipitation acidity (no change). The southern Appalachian Mountains are an acid sensitive region which need large declines in acid deposition in order for surface waters and forests to be protected.
A 1:1 relation between emissions and concentrations means that a certain percentage decline in emissions leads to an equal percentage decline in concentrations. For example, a 1:1 relation means a 20 percent decline in SO2 emissions will lead to a 20 percent decline in precipitation SO42- concentrations. If the relation is 1: 0.8 then a 20 percent decline in emissions will lead to a 16 percent decline in precipitation SO42-, and so forth. Using the data for all the study areas, for the eastern United States as a whole (not including the deep south) the relations are as follows:
1:0.85 +0.06 for SO2 emissions vs. precipitation SO42-
1:0.88 +0.14 for SO2 emissions vs. dry sulfur species
1:0.96 +0.10 for SO2 plus NOx emissions vs. H+
If the southern Appalachian Mountains, which show the weakest relations, are removed from the analysis then the relations are:
1:0.92 +0.06 for SO2 emissions vs. precipitation SO42-
1:1.07 +0.10 for SO2 emissions vs. dry sulfur species
1:1.08 +0.08 for SO2 plus NOx emissions vs. H+
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.
Examination of the long-term (1965-1997) precipitation SO42- concentration at the Hubbard Brook Experimental Forest, NH, and SO2 emissions based on 15-hour air mass back trajectories shows a strong relation (R2 = 0.74) between emissions and concentrations. The decline in concentrations due to the CAAA of 1990 is not unusual within the perspective of the long-term record.
Future Activities:
Future efforts will focus on: (1) establishing the relation between NOx emissions and their impacts on precipitation NO3- (a major source of acid deposition), and (2) how implementation of Phase II may translate to improvements in surface water quality.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
| Other project views: | All 7 publications | 3 publications in selected types | All 3 journal articles |
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Likens GE, Butler TJ, Buso DC. Long-and short-term changes in sulfate deposition: effects of the 1990 Clean Air Act Amendments. Biogeochemistry 2001;52(1):1-11. |
R826760 (2000) R826760 (2001) R826760 (Final) |
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Supplemental Keywords:
acid rain, acidic deposition., RFA, Ecosystem Protection/Environmental Exposure & Risk, Scientific Discipline, Water, Restoration, Ecological Indicators, Ecological Risk Assessment, Ecosystem Protection, Aquatic Ecosystem Restoration, Environmental Chemistry, Ecosystem/Assessment/Indicators, Ecological Effects - Environmental Exposure & Risk, Nutrients, Ecology and Ecosystems, Environmental Monitoring, bioavailability, precipitation, regional economies, ecological impact, Clean Air Act, emissions, hydrogen ion, climatology, nutrient stress, water quality, ecosystem, precipitation chemistry, aquatic ecosystem, nutrient sensitive ecosystems, wet and dry deposition, monitoring, nitrogen compounds, atmospheric nitrogen deposits, sulfur, SO2, public policy, sulfur compounds, ecosystem stress, hydrological stability, nitrogen oxide, ecological exposure, dry deposition, chemical transport, rainfall, nitrogen, regulations, acid rainRelevant 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.