This approach estimates retained organic carbon FRM mass and explicitly accounts for

the following important and difficult to estimate carbon mass properties: (1) regional and urbanrural

differences in the mix of carbonaceous aerosols, i.e. the amount of oxygen, hydrogen, etc;

(2) retained water associated with hygroscopic carbon compounds (Saxena, 1996; Yua, 2004);

(3) volatile carbonaceous material measured by speciation samplers, but not retained in FRM

mass; and (4) uncertainties associated with blank corrections of measured organic carbon.

Organic Carbon Mass by mass balance (OCMmb) is defined as ,

OCMmb = PM2.5 - { [SO4] + [NO3FRM] + [NH4FRM] + [water] + [EC] + [OPP] + [0.5] } [5.5]

In this expression, all of the above components represent the mass retained on FRM Teflon


This approach completely accounts for FRM mass43 and OCMmb is often greater than the

43The OC by mass balance technique assumes that all other mass is accounted for and

therefore all remaining mass is OCM. This may not always be a good assumption. The results

of the technique should be carefully evaluated to ensure that OC mass is not overestimated (and

therefore other mass components are underestimated). This may be a problem in areas that do

not have nearby speciation data and have relatively large concentrations of primary PM2.5. The

OC by mass balance technique may inadvertently apportion mass to organic carbon which may

actually be EC or “other” primary PM2.5 mass. All available ambient data and modeling data



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