1. Impact of Reduced Nitrogen on Air Quality: Fine Scale Simulation, Evaluation, and Sensitivity Study
Kristen Olsen and Yang Zhang
Department of Marine, Earth, and Atmospheric Sciences, NC State University, Raleigh, NC
John Walker
Division of Air Pollution Prevention and Control, US EPA, RTP, NC
Wayne Robarge
Department of Soil Science, NC State University, Raleigh, NC
The 7th Annual CMAS Conference
Chapel Hill, NC, October 6-8, 2008

2. Monthly Mean NH3 Emission
Motivation
Monthly Mean NH3 Emission
Ammonia (NH3) emissions from large number of animal feeding operations in southeast U.S., particularly in eastern North Carolina (NC)
Impact of NH3
An alkaline species with odors
Modulation of soil nutrient and nitrogen cycles
Neutralization of acids in the air
Formation of fine particulate matter (PM2.5)

3. Objectives
Intercompare the performance of two air quality models in simulating the fate and transport of reduced nitrogen (NHx = NH3 + NH4+) at fine grid scales
Evaluate the sensitivity of air quality predictions to a 50% reduction of emissions of agricultural livestock NH3 (AL-NH3)
Examine model sensitivity to horizontal grid resolution (12-, 4-, and 1.33-km)

4. Model Setup Period: January and July 2002
Horizontal/Vertical Resolutions: 4- and 1.33-km / 19 layers
Air Quality Models: CMAQ v4.51, CAMx v4.42
Meteorology Model: MM5 v3.7 with FDDA
Emission Inventory: developed by VISTAS, processed through SMOKE v2.1
IC/BC: VISTAS 12-km simulations
Dataset for Evaluation: NCDENR North Carolina Department of Environment and Natural Resources NC CRONOS NC Climate Retrieval and Observations Network of the Southeast Database CASTNET Clean Air Status and Trends Network NADP National Acid Deposition Program STN Speciation Trends Network SEARCH Southeastern Aerosol Research and Characterization IMPROVE Interagency Monitoring of Protected Visual Environments AIRS – AQS Aerometric Information Retrieval System – Air Quality Subsystem
CMAQ – Community Multiscale Air Quality model, CAMx – Comprehensive Air Quality Model with extensions, MM5 – the 5th generation Mesoscale Model, FDDA – Four Dimensional Data Assimilation, VISTAS – Visibility Improvement State and Tribal Association of the Southeast, SMOKE – Sparse Matrix Operator Kernel Emission

5. Model Treatments CMAQ CAMx Version
4.51 with ENVIRON’s revised SOA module
4.42
Gas-Phase Chemistry
CB-IV
Horizontal Advection
PPM
Vertical Advection
Yamartino
PM2.5 Size Representation
3 lognormal modes
2 sections
Aerosol Chemistry
AE4 / ISORROPIA
CF / ISORROPIA
Aqueous Chemistry
RADM
Dry Deposition
M3Dry / RPM
Wesely
Wet Deposition
Aerosol and gas scavenging; Henry’s Law;
accumulation/coarse PM in cloud water, Aitken slowly absorbed
all PM in cloud water
CB-IV – Carbon Bond IV, PPM – Piecewise Parabolic Method, RADM – Regional Acid Deposition Model,
CF – Coarse/Fine, RPM – Regional Particulate Model

6. Meteorology Evaluation
Jan.
Jul.
Variable
Network
Data # MB
NMB (%) T2
(°C)
CASTNET
5157
-0.9
-11.0
7410
1.0
4.4
STN 60
0.6
8.9
134
-0.5
-1.7
SEARCH
1360
-3.0
-30.2
1393
-2.5
-8.8
RH2
(%)
6857
6.3
6741
-5.7
-7.4
1455
10.7
15.3
1164
-3.4
WSP10
(m s-1)
4877
1.1
18.7
3251
31.0
1067
0.4
3.5
571
0.8
22.8
WDR10
(°)
7098
12.1
6.0
7140
0.9
0.5
0.3
1182
-6.5
-2.9
Prec (mm)
NADP 72
-3.2 84
45.6
151.3
T2 – Temperature at 2-m, RH2 – Relative humidity at 2-m, WSP10 – Wind speed at 10-m, WDR10 – Wind direction at 10-m, Prec – Precipitation, MB – Mean Bias, NMB – Normalized Mean Bias

7. O3 and PM2.5 Normalized Mean Bias
CMAQ
CAMx
Jan.
Jul.

8. PM2.5 Temporal Variation
Jan.
Jul.
Atlanta, GA
Raleigh, NC
Kinston, NC

9. % Conversion of NH3 to NH4+ (NH4+/NHx)
CMAQ
CAMx
Jan.
Jul.

10. Impacts of NH3 Control in July 2002
Base Case - Monthly Mean
Impact of NH3 Control – Abs. Difference
PM2.5
AdjGR
AdjGR = ([NO3-]+[NH3]) / ([NO3-]+[HNO3])
NO3-

11. Sensitivity to Grid Resolution (CMAQ, July)

12. NH4+/NHx Sensitivity to Grid Resolution (CMAQ, July)
12-km
4-km
1.33-km

13. Summary
MM5 performance is reasonably good, except for precipitation in July. CMAQ and CAMx perform similarly for O3 but differently for PM2.5 and composition, with worse performance for NO3- and OC by CMAQ in both months, others better by CMAQ in Jan. but by CAMx in Jul.
Compared to CMAQ, CAMx gives similar conversion rates of NH3 to NH4+ in Jan., but higher rates in Jul., possibly due to differences in vertical mixing, deposition, and aerosol treatments.
50% AL-NH3 emission reduction in Jul. leads to lower PM2.5 by up to 8% via decreasing NH4NO3 and an increased role of transport via increasing ratios of NH4+/NHx near the source.
The use of 4- and 1.33-km resolutions without adequate NH3 source treatments does not improve model performance in Jul.

14. Acknowledgments
This project is supported by National Research Initiative Competitive Grant no from the USDA Cooperative State Research, Education, and Extension Service Air Quality Program
Pat Brewer, Mike Abraczinskas, George Bridgers, Bebhinn Do, Chris Misenis, Hoke Kimball, and Wayne Cornelius, NCDENR
Don Olerud, Baron Advanced Meteorological Systems
Dennis McNally and Cyndi Loomis, Alpinephysics, Inc.
Ryan Boyles, NC State Climate Office
Alice Gilliland, Steve Howard, and Shao-Cai Yu, U.S. EPA
Shiang-Yuh Wu, Clark County Department of Air Quality and Environmental Management

15. Extras

16. Wet Deposition of NH4+/NHx
Jan.
Jul.
CMAQ
CAMx

17. Impacts of NH3 Control in July 2002: AdjGR
Base Case
Reduction of AL-NH3
AdjGR = ([NO3-]+[NH3])
([NO3-]+[HNO3])

18. Impacts of NH3 Control in July 2002: NH4+/NHx
Base Case
Reduction of AL-NH3
% Difference

19. Impacts of NH3 Control in July 2002

20. Impacts of NH3 Control in July 2002

21. [NH3]emis, 50% AL-NH3 / [NH3]emis, base

22. Sensitivity to Grid Resolution (CMAQ, July)
Variable
Network
Data #
Mean
Obs
Mean Sim
NMB (%)
12-km
4-km
PM2.5
IMPROVE 55
15.8
7.9
6.7
-50.1
-57.8
STN
127
19.3
10.3
9.7
-46.1
-49.6
NH4+
CASTNET 40
2.3
1.1
-50.3
-52.4 9
1.7
0.9
0.7
-48.4
-57.3
135
2.0
1.3
1.2
-37.3
-41.2
SO42-
8.3
7.3
6.3
-12.3
-23.9 56
7.1
5.4
4.3
-23.6
-39.1
7.2
5.9
4.7
-18.0
-34.3
NO3-
0.2
0.0
0.1
-81.4
-73.4
-80.2
-61.8
-89.9
-86.9 BC 43
0.3
-42.5
-46.6
134
0.4
0.5
20.8
37.6 OC
0.6
-70.3
-72.5
4.8
1.4
-74.1
-71.6

23. Sensitivity to Grid Resolution (CMAQ, July)
Variable
Network
Data #
Mean
Obs
Mean Sim
NMB (%)
12-km
4-km O3
(1-hr max)
AIRS
3216 71 65 62
-8.6
-12.6
CASTNET
300 66 61 60
-7.0
-8.8
(8-hr max)
3215 63 56
-3.4
-10.1 58
-1.0
-5.0
WD_NH4
NADP 69
0.3
0.2
-45.0
-23.2
WD_SO4
2.2
1.7
3.0
-18.9
38.3
WD_NO3
1.6
0.5
0.9
-69.6
-43.5
Prec 84
30.1
63.8
75.7
111.9
151.3
WD_NH4 – Wet deposition of NH4+, WD_SO4 – Wet deposition of SO42-,
WD_NO3 – Wet deposition of NO3-
12-km
4-km

24. PM2.5 Sensitivity to Grid Resolution (CMAQ, July)
12-km
4-km
1.33-km