The recommended equation is as follows:

Other primary PM2.5 mass = 3.73 × [Si] + 1.63 × [Ca] + 2.42 × [Fe] + 1.94 × [Ti]

Blank mass

The other quantifiable components of PM2.5 mass include passively collected mass,

represented by a field blank concentration of 0.3-0.5ug/m3 (U.S. EPA, 2002a). This appears to

constitute a contamination of the filter resulting from handling or contact with the FRM cassette.

This value is deemed to be an important constituent of PM2.5 mass (it is assumed to not be

dependent on pollutant emissions). We recommend using a default nominal blank mass value of

0.5 ug/m3. This value can be modified based on local FRM blank mass measurements. The

blank mass is assumed to remain constant through time (RRF=1.0).

42IMPROVE estimates fine soil as: 2.2 × [Al] + 2.49 × [Si] + 1.63 × [Ca] + 2.42 × [Fe]

+ 1.94 × [Ti]

Calculation of Carbonaceous Mass

Organic carbon mass is typically estimated from blank corrected speciation data, where

organic carbonaceous mass is first estimated by multiplying the organic carbon concentrations

by 1.4 or alternative factors to account for the oxygen, hydrogen and other elements associated

with ambient carbon particles.

There are many uncertainties in estimating carbonaceous mass from carbon

measurements (Turpin, 2001; Chow, 2004). Uncertainties include differences in carbon

measurement protocol between urban and rural monitoring locations; a relatively “bumpy”

surface of urban carbon concentrations as derived from urban and rural organic carbon

measurements; and lack of carbon measurements at all FRM locations. We therefore

recommend an alternative approach to estimate the organic carbon contribution to PM2.5 mass.

The recommended SMAT approach estimates organic carbon by mass balance. Precisely

measured FRM PM2.5 mass (U.S. EPA, 2003a) is compared to the sum of its non-organic carbon

components. The latter are sulfates, ammonium, nitrates, estimated particle bound water,

elemental carbon, estimated other primary PM2.5 material plus 0.5 ug/m3 blank mass as

discussed earlier.



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