Spatial differences in ambient coarse and fine particles in the Monterrey metropolitan area, Mexico: Implications for source contribution

Figures & data

Table 1. Sum of CODs for PM_2.5 and PM₁₀ in the MMA.

Station/year	2011		2012		2013		2014
	PM2.5	PM10	PM2.5	PM10	PM2.5	PM10	PM2.5	PM10
SE	0.94	0.95	0.70	0.87	0.67	1.16	0.75	1.34
NE	0.66	0.86	0.64	0.74	0.68	1.05	0.65	1.07
CE	0.63	0.98	0.59	1.09	0.64	1.40	0.60	1.05
NW	0.65	0.89	0.54	0.76	0.55	1.07	0.59	0.98
SW	0.72	1.07	0.68	*	0.67	1.13	0.63	1.24
NW2	*	1.26	*	1.06	*	1.40	*	1.15
N	*	1.04	*	0.83	*	1.14	*

Notes. NW = Northwest; NW = Northwest 2; N = North.

*No data were available to calculate the corresponding COD.

Figure 1. Location of all monitoring stations in the MMA, with sampling sites (red circles) and nonsampling sites (gray circles) for PM_2.5 and PM_c.

Figure 2. Wind rose diagrams for all sampling sites in the MMA.

Table 2. Average ambient concentrations of PM₁₀ and PM_2.5.

		PM10 (μg m^-3)						PM2.5 (μg m^-3)
Site	N	Average	Median	Minimum	Maximum		N	Avearage	Median	Minimum	Maximum
SW	7	36	37	24	49		7	8.9	8.8	6.2	12
CE	7	38	37	25	53		7	7.7	8.2	4.7	10
NE	7	55	58	46	65		7	7.9	7.6	4.6	12
SE	7	87	90	63	106		7	8.2	8.1	4.4	12

Figure 3. Time series for airborne particle concentrations. Gaps in the time series indicate that samples were not taken on those dates due to the movement and maintenance of the sampling equipment.

Table 3. Individual correlations (R²) for each sampling site.

	OC vs. EC		K vs. K^+		S vs. SO4^2–		Cations vs. anions		Sum 35 metals vs. PM2.5		Cl vs. Cl^–
Site	PM2.5	PMc	PM2.5	PMc	PM2.5	PMc	PM2.5	PMc	PM2.5	PMc	PM2.5	PMc
SW	0.54	0.85	0.66	0.95	0.74	0.61	0.99	0.01	0.11	0.99	*	0.75
CE	0.29	0.64	0.42	0.79	0.85	0.95	0.99	0.52	0.92	0.66	*	0.87
NE	0.00	0.09	0.92	0.83	0.98	0.99	0.95	0.26	0.88	0.95	*	0.99
SE	0.00	0.22	0.74	0.73	0.91	0.99	0.98	0.00	0.52	0.95	*	0.97

Notes. In bold are those correlations that are statistically significant (p value < 0.05) at a confidence level of 95%.

*Correlation was not calculated because Cl and Cl^– concentrations were below the detection limit.

Figure 4. Overall correlations and comparisons between sampling sites for PM_c: (a) OC vs. EC, (b) K vs. K+, (c) S vs. SO₄^2–, (d) cations vs. anions, (e) sum of 35 metals vs. PM_c, and (f) Cl vs. Cl^–. The average errors are OC (16 ± 3%), EC (22 ± 5%), K (19 ± 6%), K⁺ (14 ± 3%), S (20 ± 2%), SO₄^{2 –} (24 ± 3%), cations (> 100%), anions (19 ± 4%), metals (20 ± 5%), and PM_2.5 (8 ± 1%).

Figure 5. Overall correlations and comparisons between sampling sites for PM_2.5: (a) OC vs. EC, (b) K vs. K⁺, (c) S vs. SO₄^2–, (d) cations vs. anions, (e) sum of 35 metals vs. PM_2.5. The average errors are OC (9.5 ± 0.6%), EC (12 ± 2%), K (43 ± 14%), K⁺ (7.1 ± 0.6%), S (11 ± 0.6%), SO₄^{2 –} (7.1 ± 0.02%), cations (9.5 ± 1.2%), anions (7.4 ± 0.1%), metals (51 ± 12%), and PM_2.5 (7.9 ± 1.2%).

Table 4. Average elemental sulfur (S) to sulfate-sulfur (SS) ratios for each sampling site across the MMA.

	S/SS
	PM2.5		PMc
SW	0.66		1.78
CE	0.65		1.63
NE	0.75		1.37
SE	0.70		1.27

Figure 6. Relative contribution (%wt) of the chemical species in the PM_c samples at each site.

Figure 7. Relative contribution (%wt) of the chemical species in the PM_2.5 samples at each site.

Table 5. Comparison of PM_2.5 and PM_c contributions with those reported by other MMA studies.

	PM2.5			PMc
Reference	Martínez et al. (2012)	Blanco and Mizohata (2015)	This study	Blanco and Mizohata (2015)	This study
Component/Period	November–December 2007	October–December 2014	June–July 2015	October–December 2014	June–July 2015
GM	11	26	6	42	45
TE	1	3	2	3	1
OM*	42	25	30	18	13
Salts	3	2	0	2	1
NH4NO3	13	11	1	8	3
(NH4)2SO4	23	23	54	5	11
EC	7	7	4	2	2
Other	0	2	3	20	24

Notes. *Martínez et al. (2012) used an OM/OC = 1.2; Blanco and Mizohata (2015) used an OM/OC = 1.5; and the present study used an OM/OC = 1.4.

Table 6. Average OC and EC concentrations and OC/EC ratios for PM_c and PM_2.5.

Station	PMc			PM2.5
	OC (μg m^–3)	EC (μg m^–3)	OC/EC	OC (μg m^–3)	EC (μg m^–3)	OC/EC
SW	3.3 ± 0.6	0.77 ± 0.14	4.3 ± 1.1	2.1 ± 0.2	0.36 ± 0.04	5.8 ± 0.9
CE	3.2 ± 0.5	0.68 ± 0.13	4.7 ± 1.2	1.7 ± 0.2	0.35 ± 0.04	4.9 ± 0.9
NE	4.1 ± 0.6	0.61 ± 0.12	6.7 ± 1.7	1.8 ± 0.2	0.32 ± 0.04	5.6 ± 0.9
SE	5.3 ± 0.7	0.44 ± 0.12	12.0 ± 3.6	1.5 ± 0.2	0.42 ± 0.05	3.6 ± 0.5

Table 7. Average SOA contributions for PM_c and PM_2.5 in the MMA.

Site	(SOA)PMc (μg m^–3)	(SOA/OA)PMc	SOA/PMc	(SOA)PM2.5 (μg m^–3)	(SOA/OA)PM2.5	SOA/PM2.5
SW	1.4 ± 1.6	0.2 ± 0.1	0.04 ± 0.03	2.5 ± 0.7	0.8 ± 0.2	0.3 ± 0.1
CE	1.2 ± 1.5	0.2 ± 0.1	0.03 ± 0.03	1.9 ± 0.6	0.8 ± 0.3	0.3 ± 0.1
NE	4.0 ± 1.4	0.5 ± 0.2	0.04 ± 0.03	2.1 ± 0.6	0.8 ± 0.3	0.3 ± 0.1
SE	5.3 ± 1.2	0.6 ± 0.2	0.04 ± 0.01	1.5 ± 0.7	0.7 ± 0.3	0.2 ± 0.1

Figure 8. Enrichment factor value for PM_c using the concentration of the trace elements in the four sampling sites in the MMA, taking Ca as reference element.

Figure 9. Enrichment factor value for PM_2.5 using the concentration of the trace elements in the four sampling sites in the MMA, taking Ca as reference element.

Martínez, M. A., P. Caballero, O. Carrillo, A. Mendoza, and G. M. Mejía. 2012. Chemical characterization and factor analysis of PM2.5 in two sites of Monterrey, Mexico. J. Air Waste Mange. Assoc. 62:817–27. doi:10.1080/10962247.2012.681421.

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