These files "STEM-Aerosol.TRACEP-90x60.Mar.nc" and "STEM-Aerosol.TRACEP-90x60.Mar31-Apr15.nc"
includes STEM-2K3 chemical and RAMS meteorological fields for TRACE-P and ACE-Asia periods. 
All the data files are in EPA IOAPI format (http://www.baronams.com/products/ioapi/AA.html#conventions),
 a convention of NetCDF. You can read them with NetCDF code. Their coordinate
 information can be found in (http://www.baronams.com/products/ioapi/INCLUDE.html#parms).
 You can use ncdump to view this information, too. For example, under UNIX

$ ncdump  -h STEM-Aerosol.TRACEP-90x60.Mar.nc

You will the following print out :

dimensions:
        TSTEP = UNLIMITED ; // (241 currently)
        DATE-TIME = 2 ;
        LAY = 17 ;
        VAR = 17 ;
        ROW = 60 ;
        COL = 90 ;

which means that this file includes 241 time steps, X-dimension (COL) is 90,
Y-dimension (ROW) is 60, and Z-dimension (LAY) is 17. You will also find

// global attributes:
                :IOAPI_VERSION = "2.2 2002080 (March 21, 2002)" ;
                :EXEC_ID = "????????????????                                                                " ;
                :FTYPE = 1 ;
                :CDATE = 2005017 ;
                :CTIME = 180738 ;
                :WDATE = 2005017 ;
                :WTIME = 180738 ;
                :SDATE = 2001060 ;
                :STIME = 0 ;
                :TSTEP = 30000 ;

"SDATE" is file starting date in YYYYDDD, where DDD is the julian day, and 2001061
is March 1, 2001; "STIME" is the start time in HHMMSS, and "TSTEP" is time step also in
HHMMSS.	In the following grid information,

 :VGTOP = 22379.39f ;
 :VGLVLS = 75.f, 240.f, 438.f, 675.6f, 960.72f, 1302.864f, 1713.437f, 2206.125f, 2797.349f, 3506.819f, 4358.184f, 5379.82f, 6605.785f, 8076.942f, 9779.392f, 11579.39f, 13379.39f, 15179.39f
 
 You will find that the model vertical grid (RAMS's sigma-z) has sigma-top at 22379.39 m,
 and its half-sigma level over sea surface is 75m, 240m, ........................ 
 Please view the webpage meantioned above and the sample reading program "read-stem-rams-1.f" and
 "read-stem-rams-1.cs" for detailed information. To compile the reading program, you need
 install netcdf and EPA IOAPI (http://www.baronams.com/products/ioapi/AVAIL.html).
 
STEM-2K3 (Tang et al., 2004, JGR 109, D19S23, doi:10.1029/2003JD004201)
has 4-bin aerosols: 0.1-0.3um, 0.3-1.0um, 1.0-2.5um, and 2.5-10um in diameter. In these files,
BC1 means the black carbin in 0.1-0.3um, and Na4 is the sodium in the bin of 2.5-10um.

 If you have any question about the data. contact Youhua Tang (ytang@cgrer.uiowa.edu)