CMAQv5.0.2 CSQY DATA Files

Snow Correction Factors

Brief Description

• Studies over the Utah and Wyoming Basins have shown that CMAQ model underpredicts the surface albedo for non-wooded and sparsely wooded areas when covered with snow. The model then underpredicts photolysis rates that produce to high ozone concentrations when emissions of volatile organic compounds are high.
• To better match observations and values expected for snow albedo of non-wooded and sparsely wooded land use classes, snow corrections factors are increased for several MODIS Land Use Classes: CLOSED SHRUBS, WOODY SAVANNA, SAVANNA, GRASSLAND, CROPLAND, CROP MOSIAC, and BARREN/DESSERT.

Significance and Impact

According to Rodriguez et. al (2014) and internal tests by CMAQ developers, the changes increase photolysis rates over snow cover areas and produce higher ozone concentration under conditions mentioned above.

Affected files

The 5.0.1 version of CSQY_DATA_* files under MECHS/saprc07tb_ae6_aq, MECHS/saprc07tc_ae6_aq, MECHS/cb05tucl_ae6_aq, MECHS/cb05tump_ae6_aq directories.

References

Rodriguez, M., J. Reed, C.J. Chein, C. Taylor, 2014. Ozone Modeling Results and Analysis for Sublete County, Sweetwater County and Lincoln County, Wyoming-Interim Report. Wyoming Department of Environmental Quality, Air Quality Division.

Errors in the Cross-Sections and Quantum Yields

Brief Description

• Inspection of the CSQY_DATA file for the CB05 and SAPRC07T based mechanism revealed the following problems or bugs.
• An error in the data for N2O5 and MGLY photolysis rates was found in CB05 based mechanisms and caused the rates to be over and under estimated, respectively. The data was replaced based on the intended values.
• Photolysis rates that share the same molecular cross-section had inconsistent values for the cross-section over the wave bands. The molecular and radical paths for HCHO photolysis rates is example. The cross-sections were replaced to be consistent to the original references for each mechanism.

Affected files

The 5.0.1 version of CSQY_DATA_* files under MECHS/saprc07tb_ae6_aq, MECHS/saprc07tc_ae6_aq, MECHS/cb05tucl_ae6_aq, MECHS/cb05tump_ae6_aq directories.

Significance and Impact

How photolysis affects species concentration will be more consistent to the original references.

References

• Whitten et al., a new condensed toluene mechanism for Carbon Bond: CB05-TU. Atmospheric Environment, 44, 5346-5355, 2010.
• Sarwar, et al., impact of a new condensed toluene mechanism on air quality model predictions in the US, Geosci. Model Dev.,4, 1-11, 2011.
• Carter, W.P.L., 2010a. Documentation of the SAPRC-07 chemical mechanism and updated ozone reactivity scales. Report to the California Air Resources Board, January 27, 2010. Available at www.cert.ucr.edu/~carter/SAPRC.

Carter, W.P.L., 2010b. Development of the SAPRC-07 Chemical Mechanism. Atmospheric Environment 44, 5336-5345.

Mapping for USG24 Land Use Scheme

Brief Description

• Surface albedo parameters of the USGS24 land use classes are derived from or mapped to values for the MODIS land use classes.
• The definition of USGS24 Shrubland class allows a large fraction of non-woody plants (up to 70%) and corresponds more to the "OPEN SHRUBS" class in MODIS land use scheme but is the "CLOSED SHRUBS" class.
• The mapping for the USGS24 land use scheme was then changed for Shrubland to "OPEN SHRUBS" from "CLOSED SHRUBS." It is now indentical that is used by Mixed Shrubland-Grassland class in the USGS24.

Significance and Impact

The change will increase talbedo for the altered USGS24 land use class when covered with snow. Under such condition, photolysis rates increase and higher ozone concentrations are possible when VOC concentration are high.

Affected files

The 5.0.1 version of CSQY_DATA_* of files under MECHS/saprc07tb_ae6_aq, MECHS/saprc07tc_ae6_aq, MECHS/cb05tucl_ae6_aq, MECHS/cb05tump_ae6_aq directories.

References

None

NLCD40 Compatibility

Brief Description

The meteorological inputs for the CMAQ can now be based on the NLCD40 land use classes. Data were then added to calculate to the surface albedo under these circumstances.

Significance and Impact

The surface albedo algorithm used by the in-line photolysis calculation has greater functionality regarding the meteorologcal inputs.

Affected files

The 5.0.1 version of CSQY_DATA_* files under MECHS/saprc07tb_ae6_aq, MECHS/saprc07tc_ae6_aq, MECHS/cb05tucl_ae6_aq, MECHS/cb05tump_ae6_aq directories.

References

None

Contact

William T. Hutzell, Atmospheric Modeling and Analysis Division, U.S. EPA