The Impact of Deposition Velocity and Concentration Covariance on Weekly Flux Estimates

1. The Impact of Deposition Velocity and Concentration Covariance on Weekly Flux Estimates Melissa Pulchowski Gary Lear Tom “Big Idea Man” Butler

2. Concentration-weighted Deposition Velocities • CMAQ v4.7 Average 2002 – 2006 • Calculated the average covariance for each site and each parameter Covariance = (Sum(Conc * Vd) – Sum(Vd) * Sum(Conc)/n)/n • Normalized covariance (correlation coefficient) – shows strength of the linear relationship between concentration and Vd • Calculate weighted deposition flux Weighted Weekly Flux = no. of hours * (cov + avg(conc) * avg(vd)) • Compare the weighted flux to the flux calculated from hourly concentrations and deposition velocities and average weekly concentrations and deposition velocities

3. Calculating Weekly Averages Vd • Compared • “true” sum of hourly deposition • Product of weekly averages • “Corrected” product using coefficient of covariance • Variables: NH3, HNO3, SO2, NH4+, NO3-, SO42- Concentration Hour of day Error due to covariance Week of year

4. SO2 Beltsville, MD • The product of means is a good estimator of the product of individual pairs only if pairs are independent and random • When concentration and Vd are uncorrelated, the product of the weekly means are reasonably accurate -7% annual bias

5. HNO3 Great Smokies NP, TN • Diurnal patterns aren’t a problem as long as there is no covariance between Vd and Concentration +2% annual bias

6. HNO3 Cherokee Nation, OK • Diurnal patterns aren’t a problem as long as there is no covariance between Vd and Concentration • With positive correlation, weekly product significantly underestimates true deposition -34% annual bias

7. NH3 Cherokee Nation, OK • Diurnal patterns aren’t a problem as long as there is no covariance between Vd and Concentration • With positive correlation, weekly product significantly underestimates true deposition • With negative correlation, weekly product significantly overestimates true deposition +17% annual bias

8. Seasonal Variability in NH3 Concentration and Deposition Velocity at CHE185

9. NH3 Connecticut Hill, NY

10. Concentration-weighted Deposition Velocities • Calculated the average covariance for each site and each parameter Covariance = (Sum(Conc * Vd) – Sum(Vd) * Sum(Conc)/n)/n • Normalized covariance (correlation coefficient) – shows strength of the linear relationship between concentration and Vd • Calculate weighted deposition flux Weighted Weekly Flux = no. of hours * (cov + avg(conc) * avg(vd)) • Compare the weighted flux to the flux calculated from hourly concentrations and deposition velocities and average weekly concentrations and deposition velocities

11. Next Steps • Compare modeled results to hourly measurements from MARGA, hourly SO2 and bi-weekly AMoN concentrations • Include bi-directional deposition velocities for NH3 from CMAQ v5? • Next iteration will be based on CMAQ 0708 runs. Total deposition maps will be corrected using results from these runs.