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. Author manuscript; available in PMC: 2016 Nov 21.
Published in final edited form as: Res Rep Health Eff Inst. 2012 Dec;(172):5–82.

Table 13.

Principal Component Analysis Results for Upwind Concentrations at Six Truck Terminals with Repeat-Site Visitsa

Philadelphia, PA (59 Observations)
Component Eigenvalue Difference Proportion Cumulative
1 10.41148 8.72907 0.6941 0.6941
2 1.68240 0.56236 0.1122 0.8063
3 1.12004 0.60590 0.0747 0.8809
4 0.51414 0.15714 0.0343 0.9152
Eigenvectors: Variable 1 2 3
Trimethylpentane 0.29303 −0.08129 0.12258
Dimethylpentane 0.30119 −0.04845 0.04001
2-Methylhexane 0.29746 −0.03064 −0.09313
Methylpentane 0.28291 −0.06777 0.03750
3-Methylhexane 0.29599 −0.03356 −0.07716
Methylcyclohexane 0.28915 0.06748 −0.21077
Benzene 0.22826 −0.05374 0.38971
Ethylbenzene 0.29374 −0.11086 −0.01200
m&p-Xylenes 0.29325 −0.13020 0.02429
o-Xylene 0.29020 −0.12509 −0.02509
Styrene 0.23589 −0.11354 0.17484
Toluene 0.27730 0.02761 −0.25639
Acetone 0.04900 0.33342 0.78699
Acetaldehyde 0.13029 0.64569 −0.21651
Formaldehyde 0.15222 0.62475 −0.08452
Columbus, OH (32 Observations)
Component Eigenvalue Difference Proportion Cumulative
1 8.06425 5.91380 0.5376 0.5376
2 2.15045 0.51269 0.1434 0.6810
3 1.63776 0.66599 0.1092 0.7902
4 0.97177 0.29168 0.0648 0.8549
Eigenvectors: Variable 1 2 3
Trimethylpentane 0.32007 0.07282 −0.01997
Dimethylpentane 0.26094 0.30355 −0.12524
2-Methylhexane 0.26046 0.27159 −0.15337
Methylpentane 0.09789 −0.01519 0.73713
3-Methylhexane 0.17612 0.24369 0.55146
Methylcyclohexane 0.30933 0.09364 −0.22378
Benzene 0.32060 0.01536 0.16374
Ethylbenzene 0.31362 −0.21091 −0.03663
m&p-Xylenes 0.32407 −0.20009 −0.01163
o-Xylene 0.31756 −0.21312 0.00709
Styrene 0.29831 −0.07938 −0.06648
Toluene 0.28533 −0.03521 −0.14613
Acetone −0.17283 0.43333 −0.05872
Acetaldehyde 0.01017 −0.45945 −0.03063
Formaldehyde 0.13398 0.47310 −0.06598
Milwaukee, WI (41 Observations)
Component Eigenvalue Difference Proportion Cumulative
1 9.23479 7.53026 0.6157 0.6157
2 1.70452 0.66138 0.1136 0.7293
3 1.04314 0.08008 0.0695 0.7988
4 0.96306 0.23954 0.0642 0.8630
Eigenvectors: Variable 1 2 3
Trimethylpentane 0.31610 −0.07041 −0.01190
Dimethylpentane 0.29324 −0.15527 −0.05706
2-Methylhexane 0.31451 −0.09587 0.02867
Methylpentane 0.29862 −0.22527 0.05575
3-Methylhexane 0.31609 −0.05347 0.03297
Methylcyclohexane 0.27616 0.08393 −0.19560
Benzene 0.29981 −0.12261 0.13578
Ethylbenzene 0.26641 0.37402 −0.08243
m&p-Xylenes 0.29839 0.15380 −0.07171
o-Xylene 0.29422 0.11832 −0.08677
Styrene 0.05586 0.66751 −0.16334
Toluene 0.29305 0.11518 0.08584
Acetone 0.01958 0.25005 0.74578
Acetaldehyde 0.12571 −0.42539 −0.11561
Formaldehyde 0.09045 −0.07871 0.55841
Phoenix, AZ (36 Observations)
Component Eigenvalue Difference Proportion Cumulative
1 11.26329 9.34352 0.7509 0.7509
2 1.91977 1.22864 0.1280 0.8789
3 0.69113 0.31270 0.0461 0.9249
4 0.37843 0.09569 0.0252 0.9502
Eigenvectors: Variable 1 2 3
Trimethylpentane 0.28558 −0.02203 −0.23326
Dimethylpentane 0.28752 −0.09283 −0.20793
2-Methylhexane 0.26749 −0.12707 −0.23521
Methylpentane 0.24485 −0.00478 −0.39223
3-Methylhexane 0.27090 −0.11620 −0.22928
Methylcyclohexane 0.27959 −0.01475 −0.05949
Benzene 0.28807 −0.02361 −0.04127
Ethylbenzene 0.27549 −0.17208 0.30997
m&p-Xylenes 0.27259 −0.13325 0.40123
o-Xylene 0.26820 −0.20424 0.34675
Styrene 0.27555 −0.03287 0.35122
Toluene 0.28328 −0.07054 −0.14151
Acetone 0.16989 0.51784 −0.20786
Acetaldehyde 0.19567 0.50786 0.21358
Formaldehyde 0.15580 0.58244 0.16081
Portland, OR (50 Observations)
Component Eigenvalue Difference Proportion Cumulative
1 9.14751 6.97432 0.6098 0.6098
2 2.17318 0.92761 0.1449 0.7547
3 1.24557 0.38155 0.0830 0.8378
4 0.86402 0.08821 0.0576 0.8954
Eigenvectors: Variable 1 2 3
Trimethylpentane 0.31347 0.06429 −0.01009
Dimethylpentane 0.28401 0.19744 −0.29654
2-Methylhexane 0.31445 0.06256 −0.06918
Methylpentane 0.26424 0.20242 −0.38733
3-Methylhexane 0.31318 0.10114 0.01309
Methylcyclohexane 0.24131 −0.13917 0.40271
Benzene 0.29442 −0.01268 0.28767
Ethylbenzene 0.31637 −0.14423 0.07562
m&p-Xylenes 0.30686 −0.15987 −0.04215
o-Xylene 0.30939 −0.12220 −0.05931
Styrene 0.12952 −0.39503 0.29146
Toluene 0.31573 0.01045 −0.10893
Acetone 0.03383 0.39158 0.58616
Acetaldehyde 0.03915 0.33411 0.24623
Formaldehyde 0.01627 0.63232 0.00268
Denver, CO (58 Observations)
Component Eigenvalue Difference Proportion Cumulative
1 6.89480 3.57083 0.4597 0.4597
2 3.32397 1.66795 0.2216 0.6813
3 1.65602 0.57094 0.1104 0.7917
4 1.08508 0.38902 0.0723 0.8640
Eigenvectors: Variable 1 2 3
Trimethylpentane 0.30564 0.10609 0.02605
Dimethylpentane 0.14512 0.47277 0.25268
2-Methylhexane 0.09940 0.48869 0.25914
Methylpentane 0.25088 0.21168 −0.27846
3-Methylhexane 0.08364 0.48412 0.29259
Methylcyclohexane 0.31545 −0.04321 −0.04290
Benzene 0.35347 −0.03896 −0.10308
Ethylbenzene 0.35215 −0.14362 0.02057
m&p-Xylenes 0.35577 −0.08746 −0.12541
o-Xylene 0.35677 −0.09249 −0.10090
Styrene 0.18614 −0.11281 0.00024
Toluene 0.35595 −0.00617 −0.10613
Acetone 0.07476 −0.24213 0.43245
Acetaldehyde 0.05974 −0.28182 0.56485
Formaldehyde 0.18133 −0.23706 0.38606
a

Each factor has an eigenvalue (also called its latent root) associated with it that is related to the amount of variability it explains; these are ranked from the highest to the lowest. The eigenvectors or factor loadings represent the importance of each individual compound to each factor (only the primary three eigenvalues are reported here). Compounds with eigenvectors closer to one are more strongly related to a given factor, whereas values closer to zero show weak associations.