An Introduction to Aggregate Air-Water Exchanges

Transcription

1 An Introduction to Aggregate Air-Water Exchanges Air Directors Meeting March 25, 2013 Lewis Linker CBP Modeling Coordinator 1

2 In the Chesapeake TMDL exchanges of nitrogen are allowed among basins, among point and nonpoint sources, between nitrogen and phosphorus, and between air and water sources. In the assessment of air-water exchanges we need to use the CBP integrated models of the airshed, watershed, and tidal Bay. 5

3 Modeling Information Using Average Hydrology Approximately 267 million pounds nitrogen delivered to Bay in 2011

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6 Nutrient Allocation Decision Support System Airshed Model Watershed Model Bay Model Criteria Assessment Procedures CFD Curve Percent of Time Area of Criteria Exceedence Area of Allowable Criteria Exceedence Percent of Space Effects Allocations 6

7 Nutrient Allocation Decision Support System Airshed Model Watershed Model Bay Model Criteria Assessment Procedures CFD Curve Percent of Time Area of Criteria Exceedence Area of Allowable Criteria Exceedence Percent of Space Land Use Model Used to Assess Air-Water Exchanges Effects Used to Assess TMDL Achievement Allocations 7

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9 Flow-adjusted Total Nitrogen Trends at 31 sites (68%) down 2 up (6%) 8 not significant (26%)

10 In the Chesapeake TMDL the water quality standards of Deep Water, Deep Channel, and Open Water dissolved oxygen (DO) are key for the protection of living resources. Chlorophyll h ll and SAV/clarity standards are also designed to protect living resources. 10 From Batiuk (2003)

11 Chesapeake Bay TMDL Based on 7 Watershed Implementation Plans 11

12 Standard Air Exchange Decision Rules We re looking for air exchange decision rules that are: straight forward consistent equitable flexible 12

13 Standard Air Exchange Decision Rules The method needs to give credit for air program reductions beyond the current best assessment of air controls in 2025 (when the TMDL implementation is completed) and take into account improvements in accounting with refined and updated scenarios in the 2017 Midpoint Assessment. 13

14 Recap: The discounting that takes place in the delivered load to the Bay The 1% Credit Atmo Dep About 70% of the emission NOx load is removed in conversion of NO 2 to units of N. Example: 100 tons of emissions reduced to 30 tons. About 50% of NOx atmo dep emitted in the CB watershed Is deposited in the CB watershed. Example: 30 tons reduced to 15 tons. Forest, Cropland, Pasture, and Pervious Developed Land Use The 1% Credit About 10% of NOx atmo dep deposited to pervious land use land use (~95% of area) is exported to rivers and streams. Example: 15 tons reduced to 1.5 tons On average about 50% of Rivers and Streams NOx atmo dep exported to rivers and streams is delivered to the Bay. Example: tons reduced to 0.75 tons.

15 Case Study of PA Diesel Rule Phase II WIP Decision Rules Conversion to Reduction of Reduction of Conversion of % Emissions Conversion of N tons of pounds of molecules l NOx returned to deposited d to N NOx emissions NOx emissions (NO 2 ) to atoms N CB Watershed delivered to Bay 736 1,472, ,224 39,600 4,384 UNITS tons pounds pounds pounds pounds FACTOR As Given (* 2000) (0.3045) (0.0883) 0883) (0.1107) Conversion to N from N0 2 - The (N/NO 2 ) factor: / = Percent of Emissions Returned to the Chesapeake Bay Watershed - The (deposited/emitted) factor: Emitter State Receptor State Delaware Maryland New York Pennsylvania Virginia West Virginia Deposition to Wshed % of Emiss% of Emissions % of Emissions % of Emissions % of Emissions % of Emissions DE-watershed MD-watershed NY-watershed PA-watershed VA-watershed WV-watershed Ches Bay Watershed Overall Deposition to CB Watershed from CB States = Conversion of pound N deposited to pound N delivered by State - The (deliverered N/deposited N) factor: State Ratio DE DC MD NY PA VA WV

16 Lew Linker event/19335/