Why is it useful to look at model results for nitrogen & sulfur wet deposition?

1. An Evaluation of WRAP’s 2002 Air Quality Simulation for Nitrogen & Sulfur Wet Deposition in the Pacific Northwest. Robert Kotchenruther, Ph.D. EPA Region 10

2. Why is it useful to look at model results for nitrogen & sulfur wet deposition? • regional haze relevance: NO3 & SO4 are important haze causing species, so wet deposition as a main removal mechanism in the model is one means to diagnose how well the model is performing. • A model that performs adequately when evaluated against monitoring data can be used with greater confidence to estimate values in unmonitored areas. • Concern over excess nitrogen and sulfur deposition in National Parks is increasing the importance of model predictions to better understand and estimate possible adverse ecosystem effects in unmonitored areas.

3. When performing a model evaluation, comparing models to the monitored values, it’s important to note that both models and monitors have issues. Not all forms of wet deposition are captured by either. Wet deposition: rain snow fog rime ice CMAQ model: yes yes no no NADP monitors: yes yes no no (but poor collection)

4. 30-year Average Heavy Fog Frequency (visibility < 0.25miles)1961-1990 • How important might fog be to deposition? • Likely significant in coastal areas and higher elevations. • Some Class 1 Areas in WRAP more heavily effected than others. 8 in WRAP with > 25 annual heavy fog days. • Because this map is generated from measured data, it likely under represents the impact of fog at higher elevations (which is also where ecosystems are more sensitive). OLYM NOCA MORA CRLA REDW LABE PINN SEKI Class I Areas > 25 Fog Days (8 in WRAP) Source: NOAA National Climatic Data Center Slide courtesy of Elizabeth Waddell, NPS

5. NADP Monitor • Some Details on the National Atmospheric Deposition Program (NADP) Wet Deposition Monitoring Network • ~ 220 monitors nationwide • 20 sites in the Pacific Northwest • Measurements are weekly sums of species including sulfate, nitrate, and ammonium. • Measures primarily deposition through rainfall (poor collection efficiency of snow). • Because of poor snow capture, NPS is often lead to site monitors at lower elevations, which may lead to biases. • Open bucket collection method mean that sample is also open to volatilization during the collection, which could lead to underreporting. NADP Network in the Pacific Northwest

6. Details on the WRAP 2002 Model Predictions • base02b EI estimates actual emissions. • For the prediction of wet deposition, the precipitation predictions from the meteorological model (MM5) are very important. • Historically, MM5’s ability to accurately predict the amount and location of precipitation has been poor ---- likely to be especially true for the WRAP 36km simulation in the PNW because much of the precipitation is generated by topography, which is poorly represented at a 36km resolution. • The model predicts deposition through both rain and snow, but not cloud deposition (fog and rime ice). • Model makes hourly predictions. MM5 2002 Meteorology Emissions base02b CMAQ Photochemical Model Wet Deposition Prediction

7. WRAP 2002 Wet Deposition Performance Analysis • How did I conduct my performance analysis? • Aggregated the model data to match the time frequency of each weekly monitor measurement in the PNW domain. • Compared weekly measurements with weekly aggregated model estimates. • Summed both measurements and model over the year to compare yearly estimates from model and monitor. NADP Network in the Pacific Northwest

8. Example – weekly deposition performance – NADP Site ID11 – NH4 Reynolds Creek - Owyhee County, Idaho (SW Idaho) (looks similar for NO3 and SO4) r2 = 0.03 mean bias = -0.005 kg ha-1

9. Example – weekly deposition performance – NADP Site WA99 – NO3 Mount Rainier National Park - Pierce County, Washington (looks similar for NH4 and SO4) r2 = 0.13 mean bias = 0.000 kg ha-1

10. Model performance for total monitored wet deposition in 2002 – NO3 and NH4 • Each data point represents a NADP monitoring location & the summed deposition. • Model values were aggregated to match only valid monitoring periods. • Roughly a factor of two agreement. • NH4 r2 effected by outlier. 2002 NO3 Wet Dep Performance 2002 NH4 Wet Dep Performance NO3 mean bias = -0.69 kg ha-1 r2 = 0.15 NH4 mean bias = -0.09 kg ha-1 r2 = 0.03

11. Model performance for total* monitored wet deposition in 2002 – N and S • Each data point represents a NADP monitoring location & the summed deposition. • Model values were aggregated to match only valid monitoring periods. • Roughly a factor of two agreement. • Low r2 effected by outliers. 2002 N Wet Dep Performance 2002 S Wet Dep Performance N mean bias = -0.22 kg ha-1 r2 = 0.06 S mean bias = -0.21 kg ha-1 r2 = 0.03

12. Model summed wet deposition for the PNW - N WRAP 2002 base02b Total Predicted N Wet Deposition from NO3 and NH4 • Model predicted total deposition – as opposed to aggregated to match monitor in previous slides. • Increased deposition near urban centers and upwind side of Cascade mountains. • Deposition ‘shadow’ on leeward side of Cascades. • Hot spot near Vancouver BC likely due to higher NH3 emissions.

13. Model summed wet deposition for the PNW - S WRAP 2002 base02b Total Predicted S Wet Deposition from SO4 • Model predicted total deposition – as opposed to aggregated to match monitor in previous slides. • Increased deposition near urban centers and upwind side of Cascade mountains. • Deposition ‘shadow’ on leeward side of Cascades. • Evidence of ship emissions in deposition along coasts?

14. Conclusions: • WRAP base02b model results for weekly N & S wet deposition in the Pacific Northwest seems to capture the overall magnitude of N & S deposition on par with NADP measurements, but correlations are poor. • Total modeled wet deposition for 2002 (aggregated to match monitoring record) generally agrees within a factor of 2 with the monitored value, with a number of noted outliers.

15. Thank you! Questions?

16. Supplementary Slides

17. Weekly deposition performance examples – NADP Site ID11 Reynolds Creek - Owyhee County, Idaho (SW Idaho)

18. Weekly deposition performance examples – NADP Site WA99 Mount Rainier National Park - Pierce County, Washington