APPROACH FOR MODELING POM 

Issues with modeling POM 

Not all POM reported to EPA’s national emission inventory (NEI) are speciated into individual 

compounds. As a result, we must apply some simplifying assumptions in order to model and 

assess the risk from the individual pollutants that comprise POM. This involves establishing 

different POM “groups” and modeling them as separate pollutants. In establishing these groups, 

we considered the need to provide the most detailed information about risks from the individual 

pollutants within POM while taking into account the inconsistencies in how much speciation is 

reported in the inventory. We used a more refined method to establish POM groups for the 1999 

NATA than we did for the 1996 NATA to reflect improvements in the speciation of POM within 

the inventory. Specifically, for the 1996 NATA we had two overlapping POM groups and for 

the 1999 NATA we have eight distinct groups. 

1996 NATA Approach 

For the 1996 NATA, we had two POM groups: (1) 7-PAH and (2) total POM. Note that the two 

groups overlap one another in that the total POM also contains pollutants in the 7-PAH group. 

We chose these groups in order to provide a range of the risk estimate. This is because the bulk 

of the POM was reported in the inventory as unspeciated POM. In addition, in some cases, the 

inventory contained more than one PAH group for the same stack (e.g., unspeciated POM, 

unspeciated 7-PAH in the same stack). For 7-PAH, we included only those pollutants that either 

were individual constituents of the 7-PAH group, such as benzo(a)pyrene, or were reported as 

“7-PAH” in the inventory. This would potentially be the low range since it did not include any 

pollutants identified as total POM, which presumably include some 7-PAH. The total POM 

group included all individual compounds belonging to POM as well as unspeciated POM and 

PAH groups. In addition, the total POM group included the compound “naphthalene” which is 

listed as a separate HAP in the Clean Air Act list of 188, but was not inventoried this way in the 

1996 inventory. The total POM group could conceivably double count emissions from stacks in 

which multiple POM groups were reported. Additional explanations for the approach can be 

found in Appendix D of the EMS-HAP User’s Guide, Version 2.0, which can be downloaded 

from www.epa.gov/ttn/emch/models. An explanation of the risk assumptions for these two 

groups can be found at http://www.epa.gov/ttn/atw/nata/nettables.pdf. As is stated in the latter 

document, the risk from the 7-PAH group was found to be significantly lower than that from the 

total POM group, and the 7-PAH group was subsequently dropped from the assessment. 

1999 NATA Approach 

For the 1999 NATA, we used a very different, more refined approach to group POM to reflect 

the improvements in the inventory. There are three main 1999 NEI improvements related to 

POM. First, a larger quantity of the 1999 NEI emissions is speciated into individual POM 

compounds. Second, there is no double-counting of POM groups from individual stacks in the 

point source inventory. There was still an inventory issue relating to double counting of 7-PAH 

and 16-PAH from numerous non-point sources (e.g., animal cremation, human cremation) and 

nonroad (e.g., 2-stroke logging equipment). We fixed this issue prior to ASPEN modeling by 

creating a “new” inventory pollutant, whose emissions are the difference between 16-PAH and 

7-PAH. Third, naphthalene is inventoried as a separate HAP and is not included nor summarized 

in any PAH group. 
APPROACH FOR MODELING POM 

The approach taken to assess POM for the 1999 NATA is to group inventory POM species into 

non-overlapping categories for which we can associate similar inhalation risks based on the unit 

risk estimate (URE). Unit risk estimates were obtained from the toxicity table 

http://www.epa.gov/ttn/atw/toxsource/table1.pdf (version dated October 2003) for the individual 

POM compounds. Table 1 shows the 8 POM groups and the associated URE assignments. 

Note that naphthalene is not included within any of the 8 POM groups for the 1999 NATA. For 

the 1999 NATA, naphthalene is modeled and treated as a separate HAP; it is not combined with 

other pollutants considered to be POM. 
APPROACH FOR MODELING POM 

Table 1. POM groups for the 1999 National Scale Air Toxics Assessment POM GROUP (EMSHAP code) 

Names Used in NATA Website 

Description of Group URE for 

Risk Characterization 

Basis for U

71002 

POM, Group 1: Unspeciated POM_Group_1_unspec

Group contains unspeciated POM, no URE is associated with them 

5.5 * 10 -5

Assume same for total POM g5% of risk from 

72002 

POM, Group 2: No URE data POM_Group_2_nodata 

Group contains individual POM species that have no URE associated with them 5.5 * 10 -5

Assume same unspeciated P

73002 

POM, Group 3: 5e-2<URE<5e-1 POM_Group_3_vhigh1 

Group contains individual POM species in which the UREs are between:  5e-2<URE<5e-1 1 * 10 -1

Midpoint of ran

74002 

POM, Group 4: 5e-3<URE<5e-2 POM_Group_4_high2 

Group contains individual POM species in which the UREs are between:  5e-3<URE<5e-2 1 * 10 -2

Midpoint of ran

75002 

POM, Group 5: 5e-4<URE<5e-3 POM_Group_5_mhigh3 

Group contains individual POM species in which the UREs are between: 5e-4<URE<5e-3 1 * 10 -3

Midpoint of rangroup that con

76002 

POM, Group 6: 5e-5<URE<5e-4 POM_Group_6_med4 

Group contains individual POM species in which the UREs are between: 5e-5<URE<5e-4 1 * 10 -4

Midpoint of ran

77002 

POM, Group 7: 5e-6<URE<5e-5 POM_Group_7_mlow5 

Group contains individual POM species in which the UREs are between: 5e-6<URE<5e-5 1 * 10 -5

Midpoint of ran

78002 

POM, Group 8: Unspeciated 7-PAH POM_Group_8_Unspec_7 

Group contains pollutant reported as “7-PAH” 

2 * 10 -4 Assume same 

7-PAH from 19risk from Benz
APPROACH FOR MODELING POM 

Table 2 shows the assignment of the POM in the 1999 NEI to the eight POM modeled pollutant 

groups. Note that summaries of POM in the 1999 NEI are provided for a different set of groups 

that don’t have a one-to-one relationship to the modeled groups. Column 4 of Table 2 shows 

how the 1999 NEI POM groups relate to the modeled groups. Table 2 also shows the nationwide 

(50 States, Puerto Rico and Hawaii) emissions of the various POM reported in the inventory1

. 

In Table 2, the pollutant called “16-PAH-7-PAH” was created from the 1999 NEI version 3 prior 

to modeling by subtracting 7-PAH (inventory pollutant code 40) from 16-PAH (inventory 

pollutant code 75). It was assigned a pollutant code of 75040, but because it is not in the NEI, it 

does not have an associated “POM category in 1999 NEI” entry. 

Table 2. Mapping of NEI HAPs belonging to POM into the modeled POM groups 

And 1999 NEI National-level Emissions 

POM 

group 

Pollutant 

code Description of Pollutant 

POM 

category 

in 1999 

NEI 

Point 

inventtory 

Nonpoint 

inventory 

Onroad 

inventory 

Nonroad 

inventory Total 

 Tons/Year 

71002 103 Benz(a)Anthracene/Chrysene 

POM as 

7-PAH 0 0.00267 0 0 0.00267

71002 234 total PAH 

POM as 

7-PAH 54.85 976.96 0 0 1031.81

71002 246 Polycyclic Organic Matter 

POM as 

7-PAH 3314.58 644.09 0 0 3958.67

71002 40 16-PAH 

POM as 

non-15 

PAH 13.12 320.38 0 0 333.5

71002 75040 16PAH-7PAH 0 132.42 0 1.4012 133.8212

72002 120127 Anthracene 

POM as 

15-PAH 38.1 332.92 31.91 15.2 418.13

72002 129000 Pyrene 

POM as 

15-PAH 399.16 617.33 46.37 35.2 1098.06

72002 191242 Benzo[g,h,i,]perylene 

POM as 

15-PAH 2.04 283.7 9.35 9.91 305

72002 192972 Benzo[e]pyrene 

POM as 

non-15 

PAH 0.59 184.69 0 0 185.28

72002 195197 Benzo(c)phenanthrene 

POM as 

non-15 

PAH 0 152.71 0 0 152.71

72002 198550 Perylene 

POM as 

non-15 

PAH 2.3 35.4 0 0 37.7

 

1 Also note that the non-point inventory benzo-a-pyrene emissions in Table 2, which are based on the 1999 NEI 

version 3.0 (Fall 2003) are greatly overestimated. After the initial ASPEN modeling was completed, it was found 

that the State of Oregon mistakenly used a wrong emission factor for estimating its wildfire emissions (SCC = 

2810001000) that caused an overestimation of benzo(a)pyrene by about factor of 4. The ASPEN results were 

adjusted to reflect this error, but the emissions were not changed. 
APPROACH FOR MODELING POM 

POM 

group 

Pollutant 

code Description of Pollutant 

POM 

category 

in 1999 

NEI 

Point 

inventtory 

Nonpoint 

inventory 

Onroad 

inventory 

Nonroad 

inventory Total 

 Tons/Year 

72002 203123 Benzo(g,h,i)Fluoranthene 

POM as 

non-15 

PAH 0 7.5 0 0 7.5

72002 203338 Benzo(a)fluoranthene 

POM as 

non-15 

PAH 

0.00001

7 101.81 0 0 101.81

72002 206440 Fluoranthene 

POM as 

15-PAH 231.63 523.85 33.26 30.49 819.23

72002 208968 Acenaphthylene 

POM as 

15-PAH 1.42 1744.67 139.2 66.04 1951.33

72002 2381217 1-Methylpyrene 

POM as 

non-15 

PAH 0 354.36 0 0 354.36

72002 2422794 12-Methylbenz(a)Anthracene 

POM as 

non-15 

PAH 0 0.51 0 0 0.51

72002 247 Methylbenzopyrenes 

POM as 

non-15 

PAH 

0.00003

5 114.51 0 0 114.51

72002 248 Methylchrysene 

POM as 

non-15 

PAH 0 305.61 0 0 305.61

72002 

2691418

1 Methylanthracene 

POM as 

non-15 

PAH 0.63 322.43 0 0 323.06

72002 

5683273

6 Benzofluoranthenes 

POM as 

7-PAH 0.03 205.14 0 0 205.17

72002 779022 9-Methylbenz(a)Anthracene 

POM as 

non-15 

PAH 0 1.01 0 0 1.01

72002 832699 1-Methylphenanthrene 

POM as 

non-15 

PAH 0 7.58 0 0 7.58

72002 83329 Acenaphthene 

POM as 

15-PAH 39.77 309.59 26.42 26.07 401.85

72002 85018 Phenanthrene 

POM as 

15-PAH 175.02 1085.44 90.99 100.74 1452.19

72002 86737 Fluorene 

POM as 

15-PAH 59.73 254.13 55.29 51.32 420.47

72002 91576 2-Methylnaphthalene 

POM as 

non-15 

PAH 9.53 20.76 0 0 30.29

72002 91587 2-Chloronaphthalene 

POM as 

non-15 

PAH 0.09

0.00000

0737 0 0 0.090001

73002 57976 

7,12-

Dimethylbenz[a]anthracene 

POM as 

non-15 0.1 1.93 0 0 2.03
APPROACH FOR MODELING POM 

POM 

group 

Pollutant 

code Description of Pollutant 

POM 

category 

in 1999 

NEI 

Point 

inventtory 

Nonpoint 

inventory 

Onroad 

inventory 

Nonroad 

inventory Total 

 Tons/Year 

PAH 

74002 189559 Dibenzo[a,i]pyrene 

POM as 

non-15 

PAH 

0.00000

176 0 0 0 1.76E-06

74002 189640 Dibenzo[a,h]pyrene 

POM as 

non-15 

PAH 

0.00001

69 0 0 0 1.69E-05

74002 56495 3-Methylcholanthrene 

POM as 

non-15 

PAH 0.00016 0.25 0 0 0.25016

75002 192654 Dibenzo[a,e]Pyrene 

POM as 

non-15 

PAH 

0.00095

4 0 0 0 0.000954

75002 3697243 5-Methylchrysene 

POM as 

non-15 

PAH 0.00021

0.00000

405 0 0 0.000214

75002 50328 Benzo[a]pyrene(7PAH) 

POM as 

7-PAH 15.67 1073.9 4.84 3.19 1097.6

75002 53703 Dibenzo[a,h]anthracene 

POM as 

7-PAH 0.87 7.12

0.00098

5 0.07 8.060985

76002 102 Benzo[b+k]fluoranthene 

POM as 

7-PAH 0.01 0.19 0 0 0.2

76002 193395 Indeno[1,2,3-c,d]pyrene 

POM as 

7-PAH 0.43 178.2 2.58 3 184.21

76002 205823 B[j]fluoranthen 

POM as 

non-15 

PAH 

0.00136

3 0 0 0 0.001363

76002 205992 Benzo[b]fluoranthene 

POM as 

7-PAH 4.95 85.87 5.32 2.57 98.71

76002 207089 Benzo[k]fluoranthene 

POM as 

7-PAH 2.07 143.53 5.32 2.37 153.29

76002 224420 Dibenzo[a,j]Acridine 

POM as 

non-15 

PAH 0.0001 0 0 0 0.0001

76002 56553 Benz[a]anthracene 

POM as 

7-PAH 109.4 433.97 7.97 4.85 556.19

77002 218019 Chrysene 

POM as 

7-PAH 30.23 388.2 4.18 3.09 425.7

78002 75 7-PAH 

POM as 

7-PAH 66.26 39.96 0 1.38069 107.6007