“The height of the mixing zone…is significant primarily when calculating NO$_{x }$emissions  rather than hydrocarbons or CO. If NO x  emissions are an important component of the  inventory, site-specific data must be gathered on mixing heights . If NO$_{x }$ emissions are  unimportant, mixing height will have little effect on the results and the default value of  3,000 feet can be used for more generalized results.”  The EPA  Guideline on Air Quality Models  also identifies four options for establishing the  mixing height based on the type and amount of data available as well as its application. These  options are summarized below:  77 EPA, Mixing Heights,  Wind Speeds, and Potential for Urban Air Pollution Throughout the Contiguous United  States , 1972 (also called the “Holzworth” report),  http://nepis.epa.gov/Exe/ZyNET.exe/20013CDS.TXT?ZyActionD=ZyDocument&Client=EPA&Index=Prior+t  o+1976&Docs=&Query=&Time=&EndTime=&SearchMethod=1&TocRestrict=n&Toc=&TocEntry=&QField  =&QFieldYear=&QFieldMonth=&QFieldDay=&IntQFieldOp=0&ExtQFieldOp=0&XmlQuery=&File=D%3A  %5Czyfiles%5CIndex%20Data%5C70thru75%5CTxt%5C00000005%5C20013CDS.txt&User=ANONYMOU  S&Password=anonymous&SortMethod=h%7C- &MaximumDocuments=1&FuzzyDegree=0&ImageQuality=r75g8/r75g8/x150y150g16/i425&Display=p%7Cf  &DefSeekPage=x&SearchBack=ZyActionL&Back=ZyActionS&BackDesc=Results%20page&MaximumPages  =1&ZyEntry=1&SeekPage=x&ZyPURL.  78 EPA,  Procedures for Emission Inventory Preparation , Volume IV, Chapter 5, Section 5.2.2, December, 1992,  EPA-420-R-92-009], http://www.epa.gov/otaq/models/nonrdmdl/r92009.pdf.  79 More recent regulatory update also mentions checking the STIP/TIP if mixing height is provided (EPA 40 CFR  93.153).  80 AERSURFACE is a tool that proce sses land cover data to determine the surface characteristics for use AERMET.  81 The roughness length is approximately one-tenth of the height of the surface roughness elements. For example,  short grass of height 0.01 m has a roughness length of approximately 0.001 m. Surfaces are rougher if they have  more protrusions. Forests have much larger roughness lengths than tundra, for example. Roughness length is an  78$_{ }$ D.2.3.3 Surface Roughness Length, Albedo, Bowen Ratio  • NCDC Data : These data are site -specific and based upon the most recent set of “real - world” measurement data near an airport.  • Support Center for Regulatory Air Models (SCRAM) Data : These data are available from  the EPA Office of Air Quality Planning and Standards SCRAM Bulletin Board. Although  these data are based on NCDC measurements, they were collected during the late 1980’s  and early 1990’s and are not the most recent available.  • EPA’s  Mixing Heights, Wind Speeds, and Potential for Urban Air Pollution Throughout  the Contiguous United States : This 1972 publication (also called the “Holzworth” report)  contains data and graphs depicting mixing heights for mean annual morning and mean  summer afternoon conditions across the U.S., by season (i.e., winter, summer, etc.). 77  • 3,000 feet Mixing Height:  This value is recommended by EPA when no site-specific data  is available and is the “default” value contained in EDMS/AEDT. $_{78}$,$_{79 }$ APPENDIX D$_{ }$ AERSURFACE 80  should be used to assess the land use cover and determine the appropriate  surface roughness length 81 , Bowen ratio 82 , and albedo 83  based on land use cover, soil moisture,  and seasonal conditions. 