Why the PM_TOT not equal to the sum of PM species?

!! PM2.5 species computed using modeled size distribution
PM25_HP ,ug/m3 ,(AH3OPI[1]*PM25AT[3]+AH3OPJ[1]*PM25AC[3]+AH3OPK[1]*PM25CO[3])*1.0/19.0
PM25_CL ,ug/m3 ,ACLI[1]*PM25AT[3]+ACLJ[1]*PM25AC[3]+ACLK[1]*PM25CO[3]
PM25_EC ,ug/m3 ,AECI[1]*PM25AT[3]+AECJ[1]*PM25AC[3]
PM25_NA ,ug/m3 ,ANAI[1]*PM25AT[3]+ANAJ[1]*PM25AC[3]+ANAK[0]*PM25CO[3]
PM25_MG ,ug/m3 , AMGJ[1]*PM25AC[3]+AMGK[0]*PM25CO[3]
PM25_K ,ug/m3 , AKJ[1] *PM25AC[3]+AKK[0] *PM25CO[3]
PM25_CA ,ug/m3 , ACAJ[1]*PM25AC[3]+ACAK[0]*PM25CO[3]
PM25_NH4 ,ug/m3 ,ANH4I[1]*PM25AT[3]+ANH4J[1]*PM25AC[3]+ANH4K[1]*PM25CO[3]
PM25_NO3 ,ug/m3 ,ANO3I[1]*PM25AT[3]+ANO3J[1]*PM25AC[3]+ANO3K[1]*PM25CO[3]
PM25_OC ,ugC/m3 ,AOCI[0]*PM25AT[3]+AOCJ[0]*PM25AC[3]
PM25_OM ,ug/m3 ,AOMI[0]*PM25AT[3]+AOMJ[0]*PM25AC[3]
PM25_SOIL ,ug/m3 ,ASOILJ[0]*PM25AC[3]+ASOIL[1]*PM25CO[3]
PM25_SO4 ,ug/m3 ,ASO4I[1]*PM25AT[3]+ASO4J[1]*PM25AC[3]+ASO4K[1]*PM25CO[3]
PM25_TOT ,ug/m3 ,ATOTI[0]*PM25AT[3]+ATOTJ[0]*PM25AC[3]+ATOTK[0]*PM25CO[3]
PM25_UNSPEC1 ,ug/m3 ,PM25_TOT[0]-(PM25_CL[0]+PM25_EC[0]+PM25_NA[0]+PM25_NH4[0]

I find that the PM_TOT not equal to the sum of PM25_HP,PM25_CL,PM25_EC, PM25_NA, PM25_MG, PM25_K, PM25_CA, PM25_NH4, PM25_NO3, PM25_OC, PM25_OM, PM25_SOIL and PM25_SO4.

The version is CMAQ5.2. And the chemical mechanism is cb05tucl_ae6_aq.
Thanks for your reply.

Based on the species you have listed here, I assume that your reconstructed PM25_TOT is always greater than the PM25_TOT coming from this combine tool? If so, I would guess the main explanation is that you have summed PM25_OC and PM25_OM both into your PM25_TOT metric. Note that PM25_OM includes both organic carbon mass (PM25_OC) and noncarbon mass (PM25_NCOM, if you will). So you have likely added PM25_OC twice.

Best regards,