CMAQ Sensitivity to WinterTime Ground Surface Albedo Tyler

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

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

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.

Seriously Though … Q: Why are we interested in winter-time ground surface albedo? A: Increased photolysis = Higher O 3 & Higher secondary PM 2. 5. Important to Utah Because: ~ Up to 90% of PM 2. 5 is NH 4 NO 3 ~ High winter O 3 This Is An Awareness Talk: ● Winter-time modeling of O 3 or secondary PM ● This issue is likely a bigger concern in the Western United States

Photolysis In Action t c In n e d i Scattered O 3 How reflective is the ground surface to ultraviolet radiation (UV)? Reflection

United States Snow Cover – February 23, 2008 Winter Photochemistry Can Be Significant Logan, UT: 60 ug/m 3 NH 4 NO 3 51 ppb O 3 Boulder, WY: 109 ppb O 3

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)

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

JPROC Albedo Test Results July 18 January 18

CMAQ Results – O 3 @ 1400 MST 0. 55 0. 75 0. 65 0. 85

CMAQ Results – HNO 3 & NH 4 NO 3 @ 1400 MST 0. 85 HNO 3 NH 4 NO 3

CMAQ Results – Impressive Increases Maximum Hourly Concentration Change Albedo O 3 HNO 3(p) NH 4 NO 3 0. 55 +27% +14% +33% +22% +30% 0. 65 +34% +17% +43% +29% +38% 0. 75 +41% +21% +54% +36% +48% 0. 85 +49% +26% +66% +45% +59% Units: ppb, ug/m 3

Conclusions ● Winter-time UV albedo is a significant issue for winter-time modeling ● Significant underestimation of O 3, NH 4 NO 3 ● 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