Table 1.
Summary of the 11 mass reconstruction equations and their major chemical components
| Equation No. (reference)/study area | Inorganic ions | Organic mass/organic carbon (OM/OC) ratio | Elemental carbon (EC) | Geological mineralsa | Saltb | Trace elementsc | Others |
|---|---|---|---|---|---|---|---|
| Equation 1 (Macias et al. 1981)/Page, AZ | (NH4)2SO4 + NH4NO3 | 1.5d | Yes | 1.89Al + 2.14Si + 1.4Ca + 1.2K + 1.43Fe (assuming Al2O3, SiO2, CaO, K2O, and Fe2O3) | None | 1.25Cu + 1.24Zn + 1.08Pb (assuming CuO, ZnO, and PbO) | None |
| Equation 2 (Solomon et al. 1989)/Los Angeles, CA | SO4 = + NO3 − + NH4 + | 1.4 | Yes | 1.89Al + 2.14Si + 1.4Ca + 1.43Fe (no oxides were specified) | None | Sum of all species measured by XRF (excluding S, Al, Si, Ca, and Fe) plus Na+ and Mg++ measured by AAS | None |
| Equation 3 (Chow et al. 1994b)/Los Angeles, CA | SO4 = + NO3 − + NH4 + | 1.4 | Yes | As in Eq. 2 (assuming Al2O3, SiO2, CaO, and Fe2O3) | None | Sum of 40 elements (Na to U) by XRF excluding S, Al, Si, Ca, and Fe | None |
| Equation 4 (Malm et al. 1994)/IMPROVE network | 4.125S as (NH4)2SO4 | 1.4 | Yes | 2.2Al + 2.49Si + 1.63Ca + 1.94Ti + 2.42Fe (assuming Al2O3, SiO2, CaO, Fe2O3, and FeO (in equal amounts), TiO2, and K2O (assuming that soil K is 0.6Fe), with all oxide multipliers by 1.16 to account for other missing compounds) | None | None | None |
| NO3 − was excluded due to the concern that NO3 − can volatilize from the Teflon-membrane filters but not from the Nylon filter | |||||||
| Equation 5 (Chow et al. 1996)/San Joaquin Valley, CA | SO4 = + NO3 − + NH4 + | 1.4 | Yes | As in Eq. 2 | Na+ + Cl− | As in Eq. 2: also excluding Na+, K+, and Cl− | None |
| Equation 6 (Andrews et al. 2000)/Great Smoky Mountains National Park, TN | SO4 = + NO3 − + NH4 + | 1.4 | Yes | As in Eq. 2 plus 1.67Ti (assuming Al2O3, SiO2, CaO, K2O, TiO2, and Fe2O3) | None | Sum of remaining species (excluding S, Al, Si, Fe, Ti, Ca, and K; see Table S-1 of Andrews et al. 2000) | None |
| (MOUDI sampler NH4 + was estimated by HEADS SO4 =/NH4 + ratio) | |||||||
| Equation 7 (Malm et al. 2000); original IMPROVE Eq.)/ IMPROVE network | 4.125S (as (NH4)2SO4) + 1.29NO3 − (as NH4NO3) | 1.4 | Yes | As in Eq. 4 | None | None | None |
| Equation 8 (Maenhaut et al. 2002)/Melpitz, Germany | SO4 = + NO3 − + NH4 + | 1.4 | Yes | As in Eq. 4 | Cl + 1.4486Na | Sum of all non-sea salt and non-crustal elements, excluding S and K. | Non-crustal K (K − 0.6Fe) |
| Equation 9 (DeBell et al. 2006)/IMPROVE network | 4.125S (as (NH4)2SO4) + 1.29NO3 − (as NH4NO3) | 1.8 | Yes | As in Eq. 4 | None | None | None |
| Equation 10 (Hand et al. 2011; revised IMPROVE Eq.)/IMPROVE network | 1.375 SO4 = (as (NH4)2SO4)e + 1.29NO3 − (as NH4NO3) | 1.8 | Yes | As in Eq. 4 | 1.8Cl− | None | None |
| Equation 11 (Simon et al. 2011)/IMPROVE network | (NH4)2SO4 + NH4NO3 | 1.8 | Yes | 3.48Si + 1.63Ca + 2.42Fe + 1.94Ti | 1.8Cl− | None | Non-crustal K = 1.2 × (K − 0.6Fe) |
(NH 4 ) 2 SO 4 ammonium sulfate, NH 4 NO 3 ammonium nitrate, S sulfur, SO 4 = sulfate, NH 4 + ammonium, NO 3 − nitrate, MOUDI, Multi-Orifice Uniform Deposit Impactor, HEADS Harvard-EPA Annular Denuder System
aGeological minerals include: aluminum (Al), aluminum oxide (Al2O3), silicon (Si); silicon oxide (SiO2), potassium (K); potassium oxide (K2O); calcium (Ca); calcium oxide (CaO), titanium (Ti), titanium oxide (TiO2), iron (Fe), ferric oxide (FeO), and ferrous oxide (Fe2O3)
bSalt includes: sea salt, chloride (Cl−), potassium ion (K+), and sodium ion (Na+)
cTrace elements include: barium (Ba), chromium (Cr), copper (Cu), lead (Pb), vanadium (V), zinc (Zn), copper oxide (CuO), lead oxide (PbO), and zinc oxide (ZnO); measurement methods are X-ray fluorescence (XRF) and atomic absorption spectroscopy (AAS)
dBased on assumed organic compound composition proportional to CH2O0.25
eHand et al. (2011) estimated (NH4)2SO4 from the SO4 = concentration as 1.375 × SO4 = to account for unmeasured NH4 +