def _get_optional_diags(print_diag_options: bool = False,) :
    """Function to list. get all optional Diagnostic Quantites you can get with Planeflight.""" 
    # grabbed from: http://wiki.seas.harvard.edu/geos-chem/index.php/Planeflight_diagnostic
    # and from inside planeflight_mod.f90
    
    diag_dict= dict({"RO2": "Concentration of RO2 family", 
                     "AN": "Concentration of AN family", 
                     "NOy": "Concentration of NOy family",
                     "GMAO_TEMP":"Temperature",
                     "GMAO_ABSH":"Absolute humidity",
                     "GMAO_SURF":"Aerosol surface area",
                     "GMAO_PSFC":"Surface pressure", 
                     "GMAO_UWND":"Zonal winds",
                     "GMAO_VWND":"Meridional winds", 
                     "GMAO_IIEV":"GEOS-Chem grid box index, longitude", 
                     "GMAO_JJEV":"GEOS-Chem grid box index, latitude",
                     "GMAO_LLEV":"GEOS-Chem grid box index, altitude", 
                     "GMAO_RELH":"Relative humidity", 
                     #"GMAO_PVRT":"Ertel's potential vorticity", # Currently disabled, State_Met%PV is not defined.
                     "GMAO_PSLV":"Sea level pressure", 
                     "GMAO_AVGW":"Water vapor mixing ratio", 
                     "GMAO_THTA":"Potential temperature",
                     "GMAO_PRES":"Pressure at center of grid box", 
                     "AODC_SULF":"Column aerosol optical depth for sulfate", 
                     "AODC_BLKC":"Column aerosol optical depth for black carbon",
                     "AODC_ORGC":"Column aerosol optical depth for organic carbon",
                     "AODC_SALA":"Column aerosol optical depth for accumulation mode sea salt",
                     "AODC_SALC":"Column aerosol optical depth for coarse mode sea salt", 
                     "AODC_DUST":"Column aerosol optical depth for dust", 
                     "AODB_SULF":"Column aerosol optical depth for sulfate below the aircraft",
                     "AODB_BLKC":"Column aerosol optical depth for black carbon below the aircraft",
                     "AODB_ORGC":"Column aerosol optical depth for organic carbon below the aircraft",
                     "AODB_SALA":"Column aerosol optical depth for accumulation mode sea salt below the aircraft",
                     "AODB_SALC":"Column aerosol optical depth for coarse mode sea salt below the aircraft",
                     "AODB_DUST":"Column aerosol optical depth for dust below the aircraft",
                     "HG2_FRACG":"Fraction of Hg(II) in the gas phase", "HG2_FRACP":"Fraction of Hg(II) in the particle phase",
                     "ISOR_HPLUS":"ISORROPIA H+", 
                     "ISOR_PH":"ISORROPIA pH (non-ideal system, so pH can be negative)",
                     "ISOR_AH2O":"ISORROPIA aerosol water", 
                     "ISOR_HSO4":"ISORROPIA bifulfate",
                     "TIME_LT":"Local time", 
                     "GMAO_ICE00": "the fraction of each grid box that has 0% to +10% of sea ice coverage",
                     "GMAO_ICE10" :"the fraction of each grid box that has 10% to +20% of sea ice coverage",
                     "GMAO_ICE20" : "the fraction of each grid box that has 20% to +30% of sea ice coverage",
                     "GMAO_ICE30" : "the fraction of each grid box that has 30% to +40% of sea ice coverage",
                     "GMAO_ICE40" : "the fraction of each grid box that has 40% to +50% of sea ice coverage",
                     "GMAO_ICE50" : "the fraction of each grid box that has 50% to +60% of sea ice coverage",
                     "GMAO_ICE60": "the fraction of each grid box that has 60% to +70% of sea ice coverage",
                     "GMAO_ICE70" : "the fraction of each grid box that has 70% to +80% of sea ice coverage",
                     "GMAO_ICE80": "the fraction of each grid box that has 80% to +90% of sea ice coverage",
                     "GMAO_ICE90": "the fraction of each grid box that has 90% to +100% of sea ice coverage",
                     #"GAMM_EPOX":"Uptake coefficient for EPOX", # don't currently work with flexchem
                     #"GAMM_IMAE":"Uptake coefficient for IMAE", 
                     #"GAMM_ISOPN":"Uptake coefficient for ISOPN", 
                     #"GAMM_DHDN":"Uptake coefficient for DHDN", 
                     #"GAMM_GLYX":"Uptake coefficient for GLYX", 
                     "AQAER_RAD":"Aqueous aerosol radius", 
                     "AQAER_SURF":"Aqueous aerosol surface area"})
    
    # Print off the optional diagnostics... 
    if print_diag_options is True: 
        k=[*diag_dict]
        print('Diagnositic options for planeflight.dat are as follows:')
        for i in range(0, len(k)):
            v=diag_dict.get(k[i])
            print("{:<15} {:<100}".format(k[i], v))
            
    return diag_dict