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CMAQ Sensitivity to Winter-Time Ground Surface Albedo

CMAQ Sensitivity to Winter-Time Ground Surface Albedo. Tyler Cruickshank State of Utah Department of Environmental Quality Division of Air Quality. CMAS Annual Conference October 6-8, 2008 Chapel Hill, North Carolina Last Talk, Last Day, 4:30 PM. λ 2. ∫.

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CMAQ Sensitivity to Winter-Time Ground Surface Albedo

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  1. CMAQ Sensitivity to Winter-Time Ground Surface Albedo Tyler Cruickshank State of Utah Department of Environmental Quality Division of Air Quality CMAS Annual Conference October 6-8, 2008 Chapel Hill, North Carolina Last Talk, Last Day, 4:30 PM

  2. λ2 ∫ јA = σA(λ,T)ФA(λ,T)I(λ) dλ λ1 Objective 1: Derive each term of the first-order rate constant for winter-time photolysis where, јAis the First-order rate constant for photolysis (јA )

  3. Objective 2: Disregard Objective 1. How do you get outa’ here?! You want to be here. You are here. Google says 21 minutes to the airport.

  4. Seriously Though … Q: Why are we interested in winter-time ground surface albedo? A:Increased photolysis = Higher O3 & Higher secondary PM2.5. Important to Utah Because: ~ Up to 90% of PM2.5 is NH4NO3 ~ High winter O3 This Is An Awareness Talk: ● Winter-time modeling of O3 or secondary PM ●This issue is likely a bigger concern in the Western United States

  5. Photolysis In Action Incident Scattered O3 How reflective is the ground surface to ultraviolet radiation (UV)? Reflection

  6. United States Snow Cover – February 23, 2008 Winter Photochemistry Can Be Significant Logan, UT: 60 ug/m3 NH4NO3 51 ppb O3 Boulder, WY: 109 ppb O3

  7. Estimated UV Albedo Values Croplands: 0.37 Grasses: 0.72 CMAQ/JPROC Uses 0.05 Evergreens: 0.27 “Bare” Ground: 0.83 Data from Tanskanen and Manninen (2007)

  8. CMAQ Photolysis Rate Calculation Step 1: Look-up table of photolysis rates created by JPROC. Step 2: Grid cells adjusted for exact location Step 3: CCTM adjusts rates for atmospheric attenuation (i.e. clouds). BUT, Land use not accounted for. Snow cover not accounted for. Result is grossly underestimated

  9. JPROC Albedo Test Results July 18 January 18

  10. CMAQ Results – O3 @ 1400 MST 0.75 0.55 0.65 0.85

  11. CMAQ Results – HNO3 & NH4NO3 @ 1400 MST 0.85 0.85 HNO3 NH4NO3

  12. CMAQ Results – Impressive Increases Maximum Hourly Concentration Change Units: ppb, ug/m3

  13. Conclusions ●Winter-time UV albedo is a significant issue for winter-time modeling ● Significant underestimation of O3, NH4NO3 ●Hard coded albedo adjustments are necessary in the short term. ●A comprehensive approach UV albedo is needed in CMAQ: ► Need to Incorporate: land use type snow cover depth snow cover age

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