Relative Responsibility Assessment of Sectors and States:

Oxidized-Nitrogen Deposition in 2020

Robin L. DennisNOAA/EPA

Atmospheric SciencesModeling Division

January 10, 2007Chesapeake Bay Modeling Subcommittee Meeting

Annapolis, MD

Decrease

Total Ox-N Deposition Decreases SignificantlyBetween 2001 and 2020 Due to Air Regulations

Increase

Decrease

However:Decreases in total ox-N deposition areseverely mitigated by increases intotal red-N deposition, driven by drydeposition. Note: We believe red-N dry deposition is too high in CMAQ. Also,OAQPS will no longer grow NH3 emissions in its new 2020 projections.

Time Trend in Proportions of Ox-N and Red-Nfrom ExtRADM (1990) and CMAQ

(averaged over Chesapeake Bay watershed)

1990 2001 2010 2020

High Low High Low High Low

Oxidized-N 67% 62% 64% 48% 52% 40% 44%

Reduced-N 33% 38% 36% 52% 48% 60% 56%

Low = Reduced dry deposition of ammonia (adapted from sensitivity study) + less growth over time. These are judged to be more “realistic” conditions than the Base Case, which is the High case.

The Average Proportion of 40:60 for 2020 isHighly Variable Across the Chesapeake Watershed

Old 1990 Sector Maps: Utilities

Oxidized-Nitrogen Deposition2020 Sector Responsibility: Power Plants

%

Old 1990 Sector Maps: Mobile

Oxidized-Nitrogen Deposition2020 Sector Responsibility: Mobile Sources

%

Old 1990 Sector Maps: Industry

Note scale change

Old 1990 Sector Maps: Other

Note scale change

Oxidized Nitrogen DepositionSector Responsibility

Watershed

1990 2020Preliminary

Power Plants (EGU’s) 40% 17%

Mobile Sources (on-road) 30% 32%

Industry 8% 20%

Other (off-road-construction; residential & commercial) 21% 31%

Oxidized-Nitrogen Deposition2020 Sector Responsibility: Industry

%

Oxidized Nitrogen DepositionSector Responsibility

(Preliminary)

Water-shed

Above-FallLine

Below-FallLine

Bay

EGU’s 17% 17% 15% 15%

Mobile 32% 31% 34% 31%

Industry 20% 20% 18% 17%

Other 31% 31% 32% 36%

Above the Fall Line

75% of total watershed ox-N deposition

Top 3 Basins (85% of Above Fall Line Deposition)

EGU's Mobile Industry Other

James 18% 28% 25% 30%

Potomac 18% 30% 20% 31%

Susque-hanna

17% 33% 19% 32%

Oxidized Nitrogen DepositionSector Responsibility

(Preliminary)

Oxidized Nitrogen DepositionSector Responsibility

(Preliminary)

Below the Fall Line

25% of total watershed ox-N deposition

Top 5 Basins (84% of Below Fall Line Deposition)

EGU's Mobile Industry Other

E. Shore 16% 33% 18% 34%

James 17% 31% 21% 32%

Potomac 14% 38% 16% 32%

W. Shore 12% 37% 16% 35%

York 18% 32% 21% 30%

Relative Responsibility for Ox-N Deposition to Watershed: Airshed and Bay States

1990 Results from ExtRADM

Relative Responsibility:Airshed and Bay States

2001 and 2020 Results from CMAQYet to Come –

Suspicion: Both %’s will increase by 2020

Airshed

Emissions

Bay State

Emissions

76% 50%

Problem with Bay State Calculations

We ran into a nonlinearity in the brute-force sensitivity approach we use to assess relative responsibility. CMAQ has more up-to-date dynamics for the gas-particle partitioning.

• The result is an overestimate of the relative responsibility for each member. Thus, when we add together the individual responsibility percentages, they sum to much more than 100.

• This affected the localized State responsibility results more than the across-the-board Sector responsibility results.

We believe the sensitivity to the nonlinearity is significantly enhanced for 2020 conditions, compared to 1990, due to the increased relative importance of ammonia.

We will need to employ a more accurate mathematical approach to replace the brute-force sensitivity approach. We have a new approach available for set up with CMAQ.

Distribution of Bay State Responsibilityfor Bay State Deposition to the Watershed

(NOT a % of overall responsibility)

1990 2020

Maryland 18.5% 24.2%

Pennsylvania 34.1% 28.0%

Virginia 21.0% 22.8%

Delaware 1.8% 1.2%

New York 9.7% 10.5%

West Virginia 15.0% 13.4%

Relative responsibility stays pretty similar over time.But, Maryland and Pennsylvania get closer together.

Future Work/Next StepsRelated to Responsibility Determinations

• Bay State Contributions Using More Advanced Technique– 2001 (to get a more current estimate)– 2020 (to see where we are going)

• Sector Contributions Using More Advanced Technique– 2001– 2020 (better establish the change identified to date)

• Airshed Contribution Using More Advanced Technique– 2001– 2020 (we expect a change between 2001 and 2020)

• Ammonia– Trend in emissions: Harmonize with Bay Program– Better dry deposition rate in CMAQ