These files "STEM-Aerosol.ICARTT-90x60.July.nc" and "STEM-Aerosol.ICARTT-90x60.Aug.nc"
includes STEM-2K3 chemical and MM5 meteorological fields for ICARTT 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.ICARTT-90x60.July.nc

You will the following print out :

dimensions:
        TSTEP = UNLIMITED ; // (250 currently)
        DATE-TIME = 2 ;
        LAY = 21 ;
        VAR = 17 ;
        ROW = 62 ;
        COL = 97 ;

which means that this file includes 250 time steps, X-dimension (COL) is 97,
Y-dimension (ROW) is 62, and Z-dimension (LAY) is 21. You will also find

// global attributes:
                :IOAPI_VERSION = "2.2 2002080 (March 21, 2002)" ;
                :FTYPE = 1 ;
                :CDATE = 2005179 ;
                :CTIME = 190820 ;
                :WDATE = 2005179 ;
                :WTIME = 190820 ;
                :SDATE = 2004183 ;
                :STIME = 0 ;
                :TSTEP = 30000 ;

"SDATE" is file starting date in YYYYDDD, where DDD is the julian day, and 2004183
is July 1, 2004; "STIME" is the start time in HHMMSS, and "TSTEP" is time step also in
HHMMSS.	In the following grid information,

 VGTOP = 1.f ;
:VGLVLS = 0.99900001f, 0.99650002f, 0.99250001f, 0.98500001f, 0.97000003f, 0.94499999f, 0.90999997f, 0.87f, 0.82500005f, 0.76999998f, 0.71000004f, 0.64999998f, 0.59000003f, 0.52999997f, 0.47f, 0.41f, 0.34999999f, 0.285f, 0.21000001f, 0.125f, 0.039999999f, 0.f
 
 You will find that the model vertical grid (MM5's sigma-p in reference atmosphere instead of
 realistic atmosphere). You can find corresponding height in meter above ground level in 
"mm5height.m97x62-icartt-21Layer.nc". The grid geographic information can be found in 
"TOPO-icartt-m97x62.nc".

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)