Transcript 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.

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
λ2
∫
јA = σA(λ,T)ФA(λ,T)I(λ) dλ
λ1
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 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
Photolysis In Action
Scattered
O3
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/m3 NH4NO3
51 ppb O3
Boulder, WY: 109 ppb O3
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
NO2 Photolysis Rates
NO2 Photolysis Rate
July 18
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
January 18
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
UV Albedo
CMAQ Results – O3 @ 1400 MST
0.55
0.75
0.65
0.85
CMAQ Results – HNO3 & NH4NO3 @ 1400 MST
0.85
0.85
HNO3
NH4NO3
CMAQ Results – Impressive Increases
Maximum Hourly Concentration Change
Albedo
O3
HNO3
NO3(p)
NH4(p)
NH4NO3
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/m3
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