for the geoschem 2x2.5 degrees run which corresponds to NY_DP in my paper (see table 4)
/glade/p/acd/alma/GEOSCHEM_ncl/outputs_2015/average_2005_2008/PHOT

I extracted a smaller grid 180W to 0E, and the first model level for january + february months averaged over 2005-2008 years

To visualize NETCDF data install the NASA tool (I never used that), and this will make it very easy (apparently) to extract everything you want by just clicking with your mouse!
<http://www.giss.nasa.gov/tools/panoply/>

You can also do do 
ncdump -v IJ_AVG_S__CO file.nc ; and that will output you CO concentrations from the file


Netcdf file (ncdump -h file.nc) looks like this:
dimensions:
	time = UNLIMITED ; // (1 currently)
	lev = 1 ;
	lat = 33 ;
	lon = 73 ;
variables:
	float IJ_AVG_S__CO(time, lev, lat, lon) ;
		IJ_AVG_S__CO:long_name = "CO tracer" ;
		IJ_AVG_S__CO:units = "ppbv" ;
	float IJ_AVG_S__O3(time, lev, lat, lon) ;
		IJ_AVG_S__O3:long_name = "Pure O3 tracer" ;
		IJ_AVG_S__O3:units = "ppbv" ;
	float IJ_SOA_S__BC(time, lev, lat, lon) ;
		IJ_SOA_S__BC:long_name = "BCPI + BCPO" ;
		IJ_SOA_S__BC:units = "ug C/m3" ;
	float IJ_SOA_S__NH4(time, lev, lat, lon) ;
		IJ_SOA_S__NH4:long_name = "ammonium" ;
		IJ_SOA_S__NH4:units = "ug/m3" ;
	float IJ_SOA_S__NIT(time, lev, lat, lon) ;
		IJ_SOA_S__NIT:long_name = "nitrate" ;
		IJ_SOA_S__NIT:units = "ug/m3" ;
	float IJ_SOA_S__OC(time, lev, lat, lon) ;  this is to calculate POA as POA = 2.1 * IJ_SOA_S__OC
		IJ_SOA_S__OC:long_name = "OCPI + OCPO" ;
		IJ_SOA_S__OC:units = "ug C/m3" ;
	float IJ_SOA_S__SAL(time, lev, lat, lon) ;
		IJ_SOA_S__SAL:long_name = "SALA + SALC" ;
		IJ_SOA_S__SAL:units = "ug/m3" ;
	float IJ_SOA_S__SO4(time, lev, lat, lon) ;
		IJ_SOA_S__SO4:long_name = "sulfate" ;
		IJ_SOA_S__SO4:units = "ug/m3" ;
	float IJ_SOA_S__TotalPM(time, lev, lat, lon) ;
		IJ_SOA_S__TotalPM:long_name = "OC + BC + SOA + NH4 + NIT + SO" ;
		IJ_SOA_S__TotalPM:units = "ug/m3" ;
	float IJ_SOA_S__sumASOA(time, lev, lat, lon) ;
		IJ_SOA_S__sumASOA:long_name = "Sum of anthropogenic SOA" ;  !! this is from the anthropogenic and biomass burning traditional VOC
		IJ_SOA_S__sumASOA:units = "ug/m3" ;
	float IJ_SOA_S__sumBSOA(time, lev, lat, lon) ;
		IJ_SOA_S__sumBSOA:long_name = "Sum of biogenic SOA" ;    !! from biogenic VOCs
		IJ_SOA_S__sumBSOA:units = "ug/m3" ;
	float IJ_SOA_S__sumOA(time, lev, lat, lon) ;
		IJ_SOA_S__sumOA:long_name = "Sum of organic aerosol" ;
		IJ_SOA_S__sumOA:units = "ug/m3" ;
	float IJ_SOA_S__sumOC(time, lev, lat, lon) ;
		IJ_SOA_S__sumOC:long_name = "Sum of organic carbon" ;
		IJ_SOA_S__sumOC:units = "ug C/m3" ;
	float IJ_SOA_S__sumOCstp(time, lev, lat, lon) ;
		IJ_SOA_S__sumOCstp:long_name = "Sum of organic carbon @ STP" ;
		IJ_SOA_S__sumOCstp:units = "ug C/sm3" ;
	float IJ_SOA_S__sumSPOA(time, lev, lat, lon) ;                      !!! SOA from anthropogenic and biomass burning S/IVOC 
		IJ_SOA_S__sumSPOA:long_name = "Sum of semi-volatile POA" ;
		IJ_SOA_S__sumSPOA:units = "ug/m3" ;
	float lat(lat) ;
		lat:long_name = "Latitude" ;
		lat:units = "degrees_north" ;
	float lev(lev) ;
		lev:long_name = "Eta Centers" ;
		lev:units = "sigma_level" ;
	float lon(lon) ;
		lon:long_name = "Longitude" ;
		lon:units = "degrees_east" ;
	float time(time) ;
		time:long_name = "Time" ;
		time:units = "hours since 1985-1-1 00:00:0.0" ;
		time:delta_t = "0000-01-00 00:00:00" ;