Indoor-Outdoor Relationships and Infiltration Behavior of Elemental Components of Outdoor PM_2.5 for Boston-Area Homes

Figures & data

TABLE 1 Summary of indoor–outdoor PM_2.5 compositional data for 12 h nighttime samples

	Outdoor conc. (ng/m^3)					Indoor conc. (ng/m^3)					I/O Ratios
Constituent	N > LOD	Mean	SD	Median	Maximum	N > LOD	Mean	SD	Median	Maximum	N	Mean	SD	% > 1.15	I/O correlations Spearman R
Total PM2.5	49	13717	7203	11843	41402	49	10820	6815	9300	30986	49	0.78	0.21	10	0.82
Al	36	17	13	13	65	29	17	11	14	49	24	1.19	0.84	42	0.39
As	0					4	5	2	5	7			NC		NC
Ba	1	133	NC	133	133	0							NC		NC
Br	26	4	2	3	8	23	3	1	3	5	16	0.81	0.23	6	0.78
Ca	35	23	12	19	51	46	27	12	25	63	35	1.46	0.75	51	0.48
Cl	0					6	122	114	85	316			NC		NC
Cu	19	5	2	4	11	18	6	6	5	31	12	1.27	1.29	25	0.12
Fe	48	41	25	33	117	49	29	18	24	80	48	0.81	0.43	10	0.78
K	46	42	20	39	84	48	37	23	34	169	45	1.01	0.47	31	0.73
Mg	10	25	12	22	46	14	24	12	20	45			NC		NC
Na	23	109	38	91	192	33	121	63	95	285	18	1.24	0.72	39	0.28
Ni	34	6	2	6	12	24	6	3	4	11	22	0.80	0.25	9	0.72
P	12	16	10	13	34	16	11	4	10	19			NC		NC
Pb	20	8	3	7	15	10	7	2	7	11	8	0.81	0.25	13	0.62
Pd	2	14	0.3	14	14	1	15	NC	15	15			NC		NC
Se	18	4	2	4	9	8	2	0.4	2	3	7	0.52	0.27	0	0.54
Si	49	64	41	54	225	49	59	29	53	173	49	1.09	0.61	35	0.62
Sr	1	2	NC	2	2	0							NC		NC
S	49	1510	1184	1072	6356	49	1212	1175	830	4955	49	0.74	0.23	4	0.92
Zn	46	14	8	12	38	47	10	5	10	21	45	0.83	0.31	18	0.79
Zr	0					3	3	0.4	3	3			NC		NC
The following elements were not detected above their uncertainty limits in any sample: Ti, Va, Cr, Mn, Co, Ga, Rb, Yt, Mo, Ag, Cd, In, Sn, Sb, La, Au, Hg, Tl, and Ur.
Only Al, P, and S were detected above their uncertainty limits in field blanks and thus required blank corrections.
One indoor zinc measurement was removed from the dataset because it was determined to be a statistical outlier.
Due to particle size effects for Mg and Na, concentrations of these elements should not be considered quantitative.
I/O ratios and correlations are presented when the number of matched I/O samples > 5.
NC = not calculated.
Correlations in bold indicate statistical significance (p < 0.05).

TABLE 2 PM_2.5 and elemental correlation coefficients for outdoor and indoor datasets

	S	Ni	Zn	Fe	K	Si	Ca	Al
Outdoors
S		0.38	−0.13	−0.10	−0.24	0.005	0.07	0.43
Ni	0.38		0.36	0.35	0.09	0.33	0.24	0.15
Zn	−0.13	0.36		0.59	0.68	0.48	0.31	−0.03
Fe	−0.10	0.35	0.59		0.66	0.86	0.70	0.17
K	−0.24	0.09	0.68	0.66		0.64	0.50	0.20
Si	0.005	0.33	0.48	0.86	0.64		0.82	0.31
Ca	0.07	0.24	0.31	0.70	0.50	0.82		0.47
Al	0.43	0.15	−0.03	0.17	0.20	0.31	0.47
Indoors
S		0.37	−0.06	0.09	−0.10	0.16	−0.11	0.43
Ni	0.37		0.26	0.34	0.20	0.17	0.19	0.33
Zn	−0.06	0.26		0.71	0.61	0.65	0.66	0.17
Fe	0.09	0.34	0.71		0.68	0.87	0.69	0.09
K	−0.10	0.20	0.61	0.68		0.71	0.70	0.13
Si	0.16	0.17	0.65	0.87	0.71		0.77	0.30
Ca	−0.11	0.19	0.66	0.69	0.70	0.77		0.27
Al	0.43	0.33	0.17	0.09	0.13	0.30	0.27
Indoors—excluding indoor data where I/O > 1.15
S		0.52	−0.03	0.09	−0.03	0.33	−0.11	0.53
Ni	0.52		0.31	0.29	0.08	0.08	0.29	0.38
Zn	−0.03	0.31		0.72	0.71	0.65	0.65	0.13
Fe	0.09	0.29	0.72		0.71	0.91	0.65	0.11
K	−0.03	0.08	0.71	0.71		0.72	0.77	0.18
Si	0.33	0.08	0.65	0.91	0.72		0.78	0.36
Ca	−0.11	0.29	0.65	0.65	0.77	0.78		0.34
Al	0.53	0.38	0.13	0.11	0.18	0.36	0.34
Correlations in bold indicate statistical significance (p < 0.05).

FIG. 1 Distributions of elemental indoor/outdoor ratios stratified by low and high AER conditions.

FIG. 2 Relationships between elemental indoor/outdoor ratios and AERs. Filled circles represent spring–summer samples, while open circles represent fall–winter samples.

TABLE 3 Summary of indoor–outdoor mixed-model regression and correlation analyses

		All data ^b mixed-model coefficients				Low AER mixed-model coefficients				High AER mixed-model coefficients
Constituent	N	Slope	Intercept	Spearman R	N	Slope	Intercept	Spearman R	N	Slope	Intercept	Spearman R
Sulfur	47	0.83 ^a	−0.10	0.91 ^a	25	0.67	0.09	0.92	22	0.87	−0.09	0.95
Nickel	20	0.94 ^a	−0.001	0.89 ^a	8	0.81	−0.0008	0.83	12	1.13	−0.002	0.92
Zinc	37	0.49 ^a	0.004	0.87 ^a	20	0.45	0.004	0.79	17	0.68	0.001	0.85
Iron	43	0.56 ^a	0.006	0.83 ^a	22	0.44	0.008	0.79	21	0.65	0.005	0.90
Potassium	31	0.64 ^a	0.005	0.87 ^a	14	0.59	0.005	0.91	17	0.69	0.005	0.92
Silicon	32	0.69 ^a	0.006	0.88 ^a	17	0.70	0.003	0.84	15	0.67	0.01	0.94

FIG. 3 Indoor/outdoor PM_2.5 ratios versus elemental I/O ratios. Filled circles represent samples collected during high AER conditions, while open circles represent samples collected during low AER conditions.

FIG. 4 Mean deviations between elemental I/O ratios and I/O ratios for discrete particle size intervals.

FIG. 5 I/O size-resolved data versus I/O nickel. Filled circles represent samples collected during high AER conditions, while open circles represent samples collected during low AER conditions. N = 20 for all plots. (Continued)