Exchanges of Aggregate Air Nitrogen Emissions and Watershed Nitrogen Loads Robin L. Dennis, Sergey L. Napelenok Atmospheric Modeling and Analysis Division, NERL, EPA Lewis Linker EPA Chesapeake Bay Program Mary Jane Rutkowski Maryland Department of the Environment CERF 22 nd Biennial Conference San Diego, California November 5, 2013

1 Exchanges of Aggregate Air Nitrogen Emissions and Watershed Nitrogen Loads The Chesapeake Bay TMDL sets limits on the load that can be delivered from tributaries and the air to the Bay. These limits are costly and not easy to achieve. The TMDL takes into account nitrogen deposition reductions from current national air rules, such as the Clean Air Interstate Rule (CAIR). States may go beyond national Clean Air Act (CAA) rules to meet local air quality standards It is important to the costly, water-oriented TMDL process to take advantage of air emissions reductions that would occur in addition to national air rules and look for opportunities for trading between air and water sources of nutrients Outline of Talk Brief background on air deposition Outline the approach to air-water trading Present underlying numeric transfer factors Give an example application of the approach and factors Provide the results of a test of the method

2 Atmospheric Deposition Plays a Role 2 The atmospheric contribution to nutrient loading to estuaries can be significant Air (15-40%) Models estimate that air accounts for 1/3 rd of N loading to Chesapeake Bay (both indirect and direct) CAA-reductions in oxidized-N deposition from reducing NO X emissions are included in the Chesapeake Bay TMDL Nitrogen loading to Estuaries by Source Type

Oxidized-N = Ox-N = sum of all species in the oxidation of NO X expressed as N (= NO + NO 2 + HNO 3 + NO PAN + higher PAN’s + N 2 O 5 + HONO + etc.) NO X Emissions 2002 CMAQ Oxidized-N Deposition Atmospheric Models Turn Emissions into Deposition 12km Grid

4 Special Versions of the Air Quality Models Can Track Individual State and State-sector Contributions to the Oxidized-N Deposition: Pennsylvania Example PA Mobile Sources PA Power Plants PA Off Road PA Total PA Industry Fraction

5 PA Total Fraction VA Total Fraction Special Versions of the Air Quality Models Can Track Individual State and State-sector Contributions to the Oxidized-N Deposition: 4 Bay States MD Total NY Total

State Attribution to Chesapeake Bay Watershed (12km) State% New York5.5 Pennsylvania16.3 Maryland8.7 Virginia15.0 Delaware1.1 West Virginia5.2 D.C States+DC Combined52.5 The emissions from watershed states account for a little over half of the Ox-N deposition to the watershed 6 Bay States+DC Fraction of Ox-N Deposition Derived from Bay State NO X emissions Fraction

7 Approach Convert annual NO X emissions to tons-N emitted/year Sources can be state sectors or state total Use state total NO X emissions here as source Calculate deposition by source to specified area kg-N/year Receptor can be a tributary area; watershed area in a state; total watershed; Bay Use total watershed and full Bay (advantageous) Calculate Transfer Functions for each state Annual kg-N deposited to area per ton-N emitted in state Calculate attenuation fractions for portion of deposited N that is delivered as N-load to Bay from defined watershed Use the set of factors to calculate how a change in NO X emissions results in a change in N-load to Bay

8 Transfer Functions at the Watershed Level by State Fraction & Location in Watershed Matters kg-N deposited / ton-N emitted

9 Fraction of State-Area and Total Watershed Deposition that Reaches the Bay to Result in Load Delivered to the Bay Receptor Basin DelawareMarylandNew YorkPennsylvaniaVirginiaW. Virginia Bay Watershed fraction State-Basin Attenuation State Basin Attenuation Fractions to Calculate the kg-N Delivered Load Change Only a small fraction of deposited N is delivered to the Bay

10 Transfer Functions for the Tidal Bay by State Proximity to Bay is Important kg-N deposited / ton-N emitted

11 EXAMPLE: State of Virginia Honeywell Nylon Consent Decree Emissions decrease = 5,693.4 tons NO X = 1,732.8 tons N Watershed: Deposition decrease = VA Transfer Fn x Emissions = (kg-N/ton-N) x 1,732.8 (ton-N) = 246,404 kg-N/yr Load decrease = Attenuation Fraction x Deposition = x 246,404 kg-N/yr = 17,554 kg-N/yr Bay: Deposition decrease = VA Transfer Fn x Emissions = (kg-N/ton-N) x 1,732.8 (ton-N) = 18,766 kg-N/yr Watershed + Bay: Total = 17, ,766 = 36,320 kg-N/yr = 80,072 lbs-N/yr

12 State Level Tons-N Emissions Reduced Emitter DelawareMarylandNew YorkPennsylvaniaVirginiaW. Virginia Sector tons-N Mobile = Total391.32,952.76,931.75,051.43, Testing Inferred Deposition Change Against A Formal NO X Emission Sensitivity Simulation Associated with a Mobile Source Proposed Rule Inferred Change in Deposition to Watershed and Bay due to Change in State Emissions (multiply emissions by transfer function) Emitter DelawareMarylandNew YorkPennsylvaniaVirginiaW. Virginia Receptor kg-N Dep Watershed Deposition 29, , , , , , ,986,656.4 Bay Deposition 3, , , , ,288.62, ,286.8

13 Testing Inferred Deposition Change (cont.) Watershed Inferred reduction in deposition (kg-N) = 1,986,656.4 Base deposition (kg-N) = 68,431,692.5 Mobile sensitivity change (kg-N) = 3,250, % of deposition explained by Bay States = 1,703,076.8 Inference/Sensitivity = 117% Bay Inferred reduction in deposition (kg-N) = 122,286.8 Base deposition (kg-N) = 3,791,919.9 Mobile sensitivity change (kg-N) = 173, % of deposition explained by Bay States = 83,877.4 Inference/Sensitivity = 146%

Summary A sophisticated air quality model can be used to create realistic, simplified equations approximating the complex relationship of an incremental emissions change in a state (or specified geographic region) to an incremental deposition change in designated watersheds or sub-watersheds These simplified equations can be used in a TMDL process to facilitate air-water trading and allow States to take credit for additional air reductions required to meet human health standards and enhance efficiency and cost-effectiveness of the TMDL process At the 2017 Midpoint Assessment, the new bi-directional CMAQ and updated scenarios of State SIPS and national programs would replace previous air-water exchanges 14

Thanks Questions? 15

Use CMAQ with DDM-3D Adapted for Deposition DDM-3D calculates in the forward sense: how a specific source or sources impacts the domain DDM-3D for deposition estimates the fraction of the total deposition attributed to emissions from a particular source type or region We track NO X emissions (oxidized nitrogen deposition) for a 2020 CAIR future We use the CMAQ DDM-3D version with 12km grids over the airshed domain We then create simplified state-level delta emissions–to-delta atmospheric deposition transfer coefficients by major source sectors within a state 16

17 Transfer Functions at the Watershed Level by Sector are Similar