The dispersion model is run with emissions and meteorology for year 3 (the

70

center year of the 5 year period). The maximum quarterly values from the 5 years which are

equal to or less than the 98th percentile concentration are as follows (from example 5.2):

(1) It is believed that several steel mills in the area are contributing to the local

component of PM2.5 at the monitor

(2) Based on comparison to other monitors in the area, it is believed that the primary local PM2.5

component at the monitor (on high PM days) is the following for each of the quarters in 2001:

Quarter 1: 15 ug/m3

Quarter 2: 13 ug/m3

Quarter 3: 8 ug/m3

Quarter 4: 20 ug/m3

It is believed that this is representative of the other four years within the 5-year period.

(3) Using receptor modeling, it is determined that the steel mills are contributing a local

PM2.5 component (on high PM days) of the following for each of the quarters in 2001:

Quarter 1: 8 ug/m3

Quarter 2: 4 ug/m3

Quarter 3: 4 ug/m3

Quarter 4: 5 ug/m3

It is believed that this is representative of the other four years within the 5-year period.

(4) Modeling with a dispersion model shows the following contribution at the monitor from the

identified local sources (steel mills) for total primary PM2.5 in each of the quarters in 2001:

Quarter 1: Base: 11.7 ug/m3 Future: 8.3 ug/m3

Quarter 2: Base: 6.3 ug/m3 Future: 4.4 ug/m3

Quarter 3: Base: 5.3 ug/m3 Future: 3.1 ug/m3

Quarter 4: Base: 8.3 ug/m3 Future: 6.2 ug/m3

For each quarter, we computed the 24-hr average for each day and computed the mean of the

high days for each quarter to get the base and future year concentrations.

(5) Based on the results from the modeling in (4), the RRF values are:

Quarter 1: 8.3/11.7 = 0.709

Quarter 2: 4.4/6.3 = 0.698

Quarter 3: 3.1/5.3 = 0.585

Quarter 4: 6.2/8.3 = 0.747

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deutsch: DIS CUS  DES  RAD

castellano: DIS CUS DES  RAD   english: DIS CUS DES RAD

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