Assessment of heterogeneity of metal composition of fine particulate matter collected from eight U.S. counties using principal component analysis

Figures & data

Figure 1. Map showing locations of the sampling sites and sampling periods in the United States.

Table 1. Description of sampling locations

	Sacramento	Maricopa	Anoka	Harris	Pinellas	Jefferson	Allegheny	Queens
	CA	AZ	MN	TX	FL	KY	PA	NY
Sampling period	Jan–Mar 2008	Jun–Jul 2008	Sep–Oct 2008	Jan–Feb 2009	Apr–May 2009	Aug–Sep 2009	Oct–Nov 2009	Nov 2009– Jan 2010
Coordinates (longitude, latitude)	38.68327, −121.16443	33.48388, −112.14256	45.13759, −93.20789	29.66996, −95.12848	27.98625, −82.78207	38.13774, −85.57651	40.42065, −79.94591	40.73854, −73.82352
County population ^a	1,400,949	4,023,132	331,582	4,070,989	909,013	721,597	1,218,494	2,306,712
Area (km^2)	2577	23,890	1156	4605	1575	1033	1929	462
EPA land use description	Residential	Residential	Commercial	Residential	Residential	Residential	Residential	Residential
Note: ^aPopulation estimated from U.S. Census Data 2009.

Table 2. Summary of average PM_2.5 and metal concentrations at each sampling location

	>LOD ^b	Mean ± SD
		CA	AZ	MN	KY	FL	TX	PA	NY
Element ^a	(%)	(n = 6)	(n = 6)	(n = 5)	(n = 6)	(n = 6)	(n = 6)	(n = 5)	(n = 5)
PM2.5	100	6.86 ± 2.50	9.33 ± 1.96	7.92 ± 3.02	11.27 ± 2.60	5.77 ± 1.21	8.68 ± 2.98	10.32 ± 2.81	8.21 ± 2.50
Na	98	427 ± 374	405 ± 592	5.11 ± 4.86	2.78 ± 1.77	158 ± 61.2	81.6 ± 30.6	38.1 ± 21.4	53.0 ± 17.2
Ca	100	21.9 ± 6.67	205 ± 83.3	37.0 ± 11.5	29.8 ± 5.89	46.7 ± 18.8	63.4 ± 30.2	51.5 ± 26.2	56.3 ± 24.5
Fe	100	36.9 ± 12.2	518 ± 158	38.4 ± 7.48	46.8 ± 5.96	23.3 ± 8.17	48.0 ± 19.7	172 ± 106	63.1 ± 18.0
Al	100	25.8 ± 14.5	167 ± 103	17.5 ± 10.2	35.8 ± 15.8	29.8 ± 9.95	33.5 ± 27.6	29.1 ± 15.4	21.1 ± 14.5
K	100	63.1 ± 15.0	326 ± 87.1	42.0 ± 15.9	50.9 ± 9.14	47.1 ± 13.1	66.3 ± 21.3	77.8 ± 34.6	38.5 ± 9.01
Mg	100	17.0 ± 9.42	29.8 ± 30.4	7.01 ± 2.93	9.38 ± 3.53	37.9 ± 14.5	18.9 ± 13.6	12.2 ± 7.32	10.0 ± 3.28
Zn	100	8.97 ± 4.41	20.4 ± 6.51	7.91 ± 1.89	6.90 ± 0.82	3.14 ± 1.47	11.1 ± 4.97	66.2 ± 53.2	44.9 ± 30.9
Ti	96	2.16 ± 0.96	81.7 ± 65.6	4.12 ± 6.25	3.20 ± 1.00	5.88 ± 6.97	7.79 ± 13.8	2.99 ± 1.42	2.44 ± 0.58
Mn	100	0.82 ± 0.29	13.4 ± 4.06	1.10 ± 0.22	2.50 ± 2.18	0.39 ± 0.19	1.64 ± 0.63	10.7 ± 7.28	2.61 ± 1.35
Cu	100	1.72 ± 0.33	8.36 ± 2.20	1.50 ± 0.24	1.92 ± 0.54	0.57 ± 0.19	3.01 ± 1.49	4.98 ± 2.66	5.14 ± 1.37
Pb	100	1.23 ± 0.45	2.15 ± 0.74	9.85 ± 5.01	2.21 ± 0.56	0.88 ± 0.42	1.72 ± 0.57	12.1 ± 6.73	3.09 ± 1.08
Ni	76	0.05 ± 0.05	10.5 ± 4.65	0.13 ± 0.12	0.03 ± 0.01	0.30 ± 0.08	1.30 ± 0.82	0.53 ± 0.36	8.13 ± 4.39
V	100	0.17 ± 0.09	2.36 ± 0.74	0.14 ± 0.07	0.23 ± 0.05	1.22 ± 0.24	4.21 ± 1.36	0.30 ± 0.14	2.12 ± 1.08
Cr	98	0.15 ± 0.09	3.37 ± 1.08	0.55 ± 0.41	1.15 ± 0.97	0.25 ± 0.07	0.86 ± 0.51	1.95 ± 1.08	0.37 ± 0.14
Sb	96	0.49 ± 0.12	1.30 ± 0.95	0.61 ± 0.12	0.77 ± 0.23	0.16 ± 0.06	0.51 ± 0.20	1.67 ± 0.79	3.75 ± 1.38
Mo	87	0.18 ± 0.06	1.00 ± 0.35	0.18 ± 0.07	0.25 ± 0.11	0.11 ± 0.07	0.88 ± 0.40	1.91 ± 1.20	1.69 ± 1.00
Sn	98	0.95 ± 0.41	1.00 ± 0.36	0.70 ± 0.26	0.51 ± 0.12	0.14 ± 0.06	0.79 ± 0.74	1.51 ± 0.74	0.89 ± 0.22
Se	82	0.02 ± 0.01	0.16 ± 0.05	0.29 ± 0.10	3.92 ± 4.19	0.42 ± 0.08	0.55 ± 0.24	2.81 ± 1.10	0.55 ± 0.28
As	100	0.66 ± 0.27	0.42 ± 0.15	1.24 ± 0.73	1.21 ± 0.41	0.39 ± 0.18	1.39 ± 0.90	1.59 ± 0.71	0.43 ± 0.07
Co	42	0.02 ± 0.01	0.54 ± 0.15	0.02 ± 0.01	0.02 ± 0.01	0.02 ± 0.01	0.04 ± 0.02	0.05 ± 0.02	0.62 ± 0.32
Cd	76	0.05 ± 0.02	0.05 ± 0.03	0.13 ± 0.05	0.01 ± 0.01	0.05 ± 0.03	0.09 ± 0.03	0.49 ± 0.29	0.08 ± 0.03
Ag	0	0.21 ± 0.04	0.20 ± 0.05	0.23 ± 0.06	0.23 ± 0.07	0.21 ± 0.04	0.22 ± 0.07	0.20 ± 0.03	0.22 ± 0.06
Cs	22	0.02 ± 0.01	0.18 ± 0.06	0.02 ± 0.01	0.01 ± 0.01	0.02 ± 0.01	0.02 ± 0.01	0.07 ± 0.05	0.02 ± 0.01
Tl	8.9	0.02 ± 0.01	0.02 ± 0.01	0.02 ± 0.01	0.03 ± 0.02	0.02 ± 0.01	0.02 ± 0.01	0.07 ± 0.05	0.02 ± 0.01
Be	0	0.02 ± 0.01	0.02 ± 0.01	0.02 ± 0.01	0.02 ± 0.01	0.02 ± 0.01	0.02 ± 0.01	0.02 ± 0.01	0.02 ± 0.01
Notes: CA: Sacramento County, CA; AZ: Maricopa County, AZ; MN: Anoka County, MN; KY: Jefferson County, KY; FL: Pinellas County, FL; TX: Harris County, TX; PA: Allegheny County, PA; NY: Queens County, NY.
^aUnit: μg/m^3 for PM2.5 and ng/m^3 for 25 metals. ^bLOD = limit of detection.

Figure 2. Average concentrations of selected elements for eight U.S. counties. Error bars represent standard deviations: (a) Na, (b) Ca, (c) Fe, (d) Al, (e) Zn, (f) Ti, (g) Pb, (h) Ni, (i) V, and (j) Se.

Table 3. Standardized rotated factor loading and communalities from PCA in PM_2.5

Component 1		Component 2		Component 3		Component 4		Component 5
Metal	Loadings	Metal	Loadings	Metal	Loadings	Metal	Loadings	Metal	Loadings
K	0.955	Cd	0.942	Sb	0.869	Na	0.782	V	0.761
Fe	0.952	Pb	0.825	Co	0.852	Se	−0.638	Mg	0.644
Cr	0.923	Zn	0.804	Ni	0.738	As	−0.562	Al	0.364
Ca	0.88	Sn	0.695	Mo	0.591	Mg	0.427	Ca	0.335
Al	0.862	Mo	0.98	Cu	0.488	Pb	−0.172	Ti	−0.217
Mn	0.808	As	0.578	Zn	0.45	K	0.168	Pb	−0.190
Ti	0.75	Mn	0.519	V	0.366	Cr	−0.155	Se	−0.183
Cu	0.73	Sb	0.374	As	−0.305	Al	0.137	Mo	0.169
Ni	0.627	Cu	0.37	Ca	0.233	Mo	−0.136	Cu	0.144
Co	0.446	Cr	0.268	Mg	−0.186	Co	0.134	K	0.138
Mg	0.333	Se	0.266	Sn	0.185	Fe	0.123	Ni	0.129
Sn	0.282	Ti	−0.229	Fe	0.177	Ca	0.097	As	0.091
V	0.183	Fe	0.163	Mn	0.16	Cd	−0.093	Co	0.089
Na	0.163	V	−0.136	Se	−0.159	V	−0.081	Fe	0.076
Mo	0.161	Ni	−0.104	Ti	0.148	Cu	0.065	Cr	0.051
Zn	0.102	Mg	−0.043	Na	−0.143	Sb	−0.042	Sb	0.041
As	−0.096	Ca	0.036	K	0.096	Ni	0.038	Na	−0.036
Sb	0.056	Co	−0.029	Al	0.082	Ti	0.031	Cd	−0.031
Se	0.053	K	0.023	Cr	0.062	Zn	−0.020	Sn	−0.024
Cd	0.021	Na	0.006	Pb	−0.058	Sn	−0.017	Zn	−0.014
Pb	−0.010	Al	−0.005	Cd	−0.034	Mn	−0.015	Mn	0.008
Eigen ^a	8.51	Eigen	4.25	Eigen	2.1	Eigen	1.2	Eigen	1
var ^b (%)	42.5	Var (%)	21.3	Var (%)	10.5	Var (%)	5.9	Var (%)	5
Notes: ^aEigen = eigenvalue. ^bVar = variance explained.

Figure 3. Average principal component (PC) scores for eight U.S. counties. Closed circles represent average PC scores. Error bars represents standard deviations: (a) average PC score 1, (b) average PC score 2, (c) average PC score 3, (d) average PC score 4, and (e) average PC score 5.