Source apportionment models

Because certain sources emit particles with characteristic elemental signatures, in principle one ought to be able to measure the composition of particles in the atmosphere and then work backward to calculate how much each source contributed to obtain the final, observed particle composition. This approach involves the use of receptor models, defined as models that assess contributions from various sources based on observations at sampling sites (the receptors) (Gordon, 1988). 

There are a number of different types of source apportionment models, including the chemical mass balance method, factor analysis, multiple linear regression analysis, and Lagrangian modeling. The chemical 

Cjj is the concentration of species i in the /th source and Sj is the source strength for source j (e.g., as mass m ) contributed by particles from that particular source. This assumes there are no loss processes for the element between source and receptor, e.g., reactions and or volatilization. If the concentration profiles for the various contributing sources (i.e., the Cjj) are measured, as well as the total concentration OC, at the receptor, the set of simultaneous equations represented by (II) can be solved to obtain s., the contribution of each source for that particular element. 

This approach has been used to show, for example, that non-catalyst-equipped vehicles are the major source of fine particles in the area around Sao Paul, Brazil (Alonso et al., 1997), and in Mexico City (Vega et al., 1997). 

A third common approach is multiple linear regression analysis. In this approach, multiple linear regressions of the form 

---

In addition, in view of the results of Schwartz, et al. (32), on filter artifacts associated with the fraction, further studies are warranted before developing a source apportionment model. 

Multiple Regression Source Apportionment Models for Airborne Particulate Organic Matter in New York City... 

The source apportionment models proposed for the CYC and ACE fractions were ... 

A COMPARISON OF SOURCE APPORTIONMENT MODELS FROM AMBIENT AND DISPERSION NORMALIZED DATA ... 

Source Apportionment Models for the Cyclohexane-Soluble Fraction of Respirable Suspended Particulate Matter. Stepwise multiple regression analysis was used to determine the coefficients of the source tracers for the models proposed for CYC in equations (7)-(9). These models are shown in Table IV. As expected from the factor analyses, the coefficient for V, accounting for the greatest proportion of the variance of CYC, was fitted first into the equation. Equation (14) was the simplest and the F value was slightly higher than for equations (15) and (16). In addition, as will be discussed later in this paper, the coefficient for PB was in reasonable agreement with the ratio of CYC /PB for samples collected in the Allegheny Tunnel. 

SOURCE APPORTIONMENT MODELS FOR CYCLOHEXANE-SOLUBLE PARTICULATE ORGANIC MATTER ... 

Multivariate source. apportionment models have been developed for two fractions of respirable particulate organic matter which together constitute about 90% of the total organic solvent-extractable mass. The independent variables used for developing the models were trace metals, water-soluble sulfate and meteorological variables. Two of the three POM fractions extracted sequentially with cyclohexane (CYC), dlchloromethane (DCM) and acetone (ACE) were used as individual dependent variables. 

Daisey, J. M., J. L. Cheney, and P. J. Lioy, Profiles of Organic Particulate Emissions from Air Pollution Sources Status and Needs for Receptor Source Apportionment Modeling, J. Air Pollut. Control Assoc., 36, 17-33 (1986b). 

State-of-the-art methods include the combination of source apportionment models with high time-resolved source apportionment techniques for organic aerosols datasets using the Aerodyne Aerosol Mass Spectrometer (AMS), obtaining contributions from primary organic emissions from traffic [60, 61]. 

Thus for risk assessment in health effect studies or for aerosol source apportionment modeling local emission source profiles and emission factors are mandatory. 

---