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

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)

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)

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

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

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

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

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

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

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-

Sensitivity to Grid Resolution (CMAQ, July)

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

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.

Acknowledgments This project is supported by National Research Initiative Competitive Grant no. 2008-35112-18758 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

Extras

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

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

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

Impacts of NH3 Control in July 2002

Impacts of NH3 Control in July 2002

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

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

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

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