Ozone sensitivity to its precursor emissions in northeastern Mexico for a summer air pollution episode

Figures & data

Figure 1. The MMA and location of air quality monitoring stations (Obispado: Downtown [DT], La Pastora: Southeast [SE], Santa Catarina: Southwest [SW], San Nicolás: Northeast [NE], San Bernabé: Northwest [NW]).

Figure 2. Nested modeling domains defined for the MM5 application (labeled as D01, DO2, and DO3).

Figure 3. Emission reduction combinations of NOx and COVs (•) used in the control scenarios evaluated. The top right corner represents the base case.

Figure 4. Ozone concentrations for August 26 at the time of modeled peak O₃ concentration (19:00 UTC) at the MMA.

Figure 5. Ozone isopleths for August 26 at (a) NW, (b) NE, (c) DT, and (d) SE stations. The top right corner represents the base case.

Table 1. Peak O₃ concentrations (ppbv) for the basecase, VOC-only and NOx-only emission reduction scenarios

	Station
	Obispado (DT)		San Nicolas (NE)		San Bernabe (NW)		La Pastora (SE)
	August 25	August 26	August 25	August 26	August 25	August 26	August 25	August 26
Base-case peak O3 concentration	56	77	62	76	61	81	58	72
Peak O3 concentration for the 25% VOCs reduction case	56 (−0.9)	72 (−7.3)	61 (−1.3)	73 (−4.7)	60 (−1.6)	77 (−4.4)	57 (−0.7)	70 (−3.6)
Peak O3 concentration for the 50% VOCs reduction case	55 (−1.8)	67 (−13.4)	60 (−2.6)	70 (−8.3)	59 (−3.3)	73 (−9.8)	57 (−1.4)	67 (−7.6)
Peak O3 concentration for the 25% NOx reduction case	59 (+4.5)	83 (+7.3)	63 (+1.8)	79 (+3.6)	63 (+3.5)	89 (+10.5)	59 (+2.5)	79 (+9.5)
Peak O3 concentration for the 50% NOx reduction case	61 (+8.0)	96 (+23.6)	63 (+2.8)	84 (+9.9)	65 (+5.4)	95 (+17.0)	60 (+4.7)	83 (+15.2)
Note: Values in parentheses represent percent increment or reduction in peak O3 concentration with respect to the base-case run.

Figure 6. Ozone difference maps for VOC-only emission reduction scenarios: (a) 25% VOC reduction, (b) 50% VOC reduction.

Figure 7. Ozone difference maps for NOx-only emission reduction scenarios: (a) 25% NOx reduction, (b) 50% NOx reduction (color figure available online).

Figure 8. Model-derived VOC/NOx ratios for (a) the MMA and (b) the modeling domain.

Table 2. Model-derived O₃/NOy ratios at 19:00 UTC and the location of the air quality monitoring stations in the MMA

Station		August 25		August 26
Obispado (DT)		3.5		2.9
San Nicolas (NE)		5.9		5.5
San Bernabe (NW)		4.4		4.3
La Pastora (SE)		5.2		4.3

Figure 9. Model-derived O₃-to-NOy ratios for the modeling domain.

Figure 10. Model-derived O₃-to-NOy ratios for (a) the MMA, (b) Monclova, and (c) Nava–Piedras Negras–Acuña for August 26, 2005, at 19:00 UTC (see text for details).

Figure S1. Main urban locations in Northeastern Mexico.

Figure S2. Classification tree used for episode selection.

Table S1. Statistical model performance evaluation for MM5 when applied to the D03 domain.

Meteorological parameter	Statistical parameter	August 23	August 24	August 25	August 26	August 27	Episode	Guidance value^(a)
Wind velocity	RMSE^(b) (m/s)	1.36	1.74	1.49	1.26	1.25	1.42	≤2 m/s
	Bias (m/s)	0.41	0.78	0.51	0.22	−0.36	0.31	N/A
	IOA^(c)	0.77	0.72	0.70	0.76	0.72	0.74	≥0.6
Wind direction	Gross error (degrees)	25.6	20.2	27.1	30.1	47.6	30.1	≤20°
	Bias (degrees)	11.0	10.0	14.7	8.8	16.3	12.2	N/A
Temperature	Gross error (K)	1.60	1.53	1.46	1.47	1.87	1.59	≤2 K
	Bias (K)	1.06	0.41	0.43	0.86	1.05	0.76	≤±0.5 K
	IOA	0.94	0.94	0.94	0.95	0.93	0.94	≥0.7
Specific Humidity	Gross error (g/kg)	1.82	1.76	2.26	1.61	1.56	1.80	≤2 g/kg
	Bias (g/kg)	−1.17	−0.36	−1.77	−1.16	−0.37	−0.97	±1 g/kg
	IOA	0.78	0.74	0.67	0.81	0.78	0.76	≥0.7
^(a) According to Emery et al. (2001). ^(b) RMSE: Root Mean Square Error. ^(c) IOA: Index of Agreement. Definition of statistical parameters can be found in Emery et al. (2001).

Table S2. O₃ model performance evaluation for stations within the MMA^(a).

Statistical parameter	Daily performance				Monitoring station performance				Overall episode performance	Guidance value^(b)
	August 24	August 25	August 26	August 27	Obispado (DT)	San Nicolas (NE)	San Bernabe (NW)	La Pastora (SE)
Peak accuracy	−36	−20	−4	14	−8	41	12	10	−8	±20%
Mean normalized bias	3	14	13	24	0	33	11	13	14	±15%
Normalized gross error	21	23	16	27	15	33	17	23	21	35%
Normalized mean bias	−3	9	11	23	−3	32	9	11	11	±13%
Normalized mean error	22	21	15	26	15	32	16	22	20	20%
No. of observations	17	13	29	23	20	20	25	17	82
^(a) Model performance is with respect to 1-hr average O3 concentration. A 40 ppbv cutoff was used for all statistics, except for peak accuracy prediction. ^(b) According to US EPA guidelines (US EPA, 1991, 2008).

Figure S3. Time series for simulated and observed O₃ concentrations at the Obispado station (Julian day 236, 2005 = August 24, 2005).

Figure S4. Simulated vs observed O₃ scatterplot for the entire modeled episode (cutoff at 40 ppbv).

Figure S5. O₃ concentration in and around the MMA for August 26, 2005. Diamonds represent the monitoring stations in the MMA.

Figure S6. Ozone difference maps for combined VOC reductions with a 25% NOx reduction: a) 25% VOC reduction, b) 50% VOC reduction.

Figure S7. Ozone difference maps for combined VOC reductions with a 50% NOx reduction: a) 25% VOC reduction, b) 50% VOC reduction.

Figure S8. Domain-wide O₃/NOz ratio.

Figure S9. Domain-wide O₃/HNO₃ ratio.

Figure S10. Domain-wide H₂O₂/HNO₃ ratio.