1

Appendix A. Supplementary Data

Table S1. Selected national and regional air pollution control programs implemented since 2000

Scope Program or 

Regulation Description Year phased in References

National

National Tier 2 

Vehicle and 

Gasoline Sulfur 

Program

The tailpipe standards were set at an 

average standard of 0.07 grams per mile 

for nitrogen oxides for vehicles weighing 

less than 6000 pounds. Refiners will meet 

a 30 ppm average sulfur level with a 

maximum cap of 80 ppm.

2004 - 2007 http://www.epa

.gov/tier2/

National Low 

Emission Vehicle 

Program and 

Ozone Transport 

Commission 

(OTC) LEV

NOx will be reduced by 538 tons per day 

nationwide in 2005 and 1,699 tons per 

day in 2015. Non-methane organic gases 

(NMOG) will be reduced by 350 tons per 

day nationwide in 2005 and 1,030 tons 

per day in 2015.

Since 2000

http://www.epa

.gov/oms/levnlev.htm#imple

mentation

Heavy-Duty 

Highway Diesel 

Program

2.6 million tons of smog-causing nitrogen 

oxide emissions will be reduced each 

year. Soot or PM will be reduced by 

110,000 tons a year.

2007 - 2010

http://www.epa

.gov/oms/highw

ay-diesel/

Acid Rain 

Program Phase II 

The final 2010 SO2 cap that may be 

emitted by electric generating units 

(EGUs) in the contiguous United States 

was set at 8.95 million tons, a level of 

about one-half of the emissions from the 

power sector in 1980. NOx rule will 

achieve an additional reduction of 

890,000 tons of NOx annually, increasing 

the overall annual reductions to 2.1 

million tons. 

Since 2000

http://www.epa

.gov/airmarkets

/programs/arp/

Regional: 

under the 

Texas State 

Implementation 

Plan (SIP)

Nitrogen 

Oxides(NOx) 

Mass Emissions 

Cap and Trade 

(MECT) 

Overall 80% NOx reduction from existing 

industrial sources and utility power 

plants, implemented through a cap and 

trade program.

2003 - 2007

http://www.tce

q.state.tx.us/air

quality/sip/hgb/

sip-hgb

Texas Low 

Emission Diesel 

(TxLED)

Requires all diesels for both on-road and 

non-road use to have a lower aromatic 

content and a higher cetane number.

Since 2005

Texas Emissions 

Reduction Plan

Provides grant funds for on-road and 

non-road heavy-duty diesel engine 

replacement/retrofit.

Since 2002
2

Table S2. Descriptive statistics for PM2.5 and its components in Greater Houston, Texas, during 2000 - 2011.

Pollutanta Sampling period N Mean SDb IQRc Min P25 Median P75 Max

PM2.5

1/01/2000 - 12/30/2005 2086 13.547 5.801 6.760 1.900 9.600 12.600 16.360 57.500

1/02/2006 - 12/30/2011 2072 13.448 5.443 6.775 2.100 9.600 12.600 16.375 44.200

1/01/2000 - 12/30/2011 4158 13.498 5.625 6.760 1.900 9.600 12.600 16.360 57.500

Al

2/15/2000 - 12/30/2005 630 0.071 0.192 0.037 0.001 0.005 0.010 0.041 1.866

1/02/2006 - 12/29/2011 688 0.100 0.212 0.058 0.003 0.013 0.031 0.071 1.720

2/15/2000 - 12/29/2011 1318 0.086 0.203 0.052 0.001 0.006 0.023 0.058 1.866

Br

2/15/2000 - 12/30/2005 630 0.003 0.002 0.003 0.000 0.002 0.003 0.004 0.023

1/02/2006 - 12/29/2011 688 0.003 0.004 0.003 0.000 0.002 0.003 0.004 0.076

2/15/2000 - 12/29/2011 1318 0.003 0.003 0.003 0.000 0.002 0.003 0.004 0.076

Cr

2/15/2000 - 12/30/2005 630 0.001 0.001 0.001 0.000 0.000 0.001 0.001 0.012

1/02/2006 - 12/29/2011 688 0.001 0.010 0.001 0.000 0.000 0.001 0.001 0.255

2/15/2000 - 12/29/2011 1318 0.001 0.007 0.001 0.000 0.000 0.001 0.001 0.255

Cu

2/15/2000 - 12/30/2005 630 0.003 0.005 0.003 0.000 0.001 0.002 0.004 0.095

1/02/2006 - 12/29/2011 688 0.012 0.022 0.010 0.000 0.001 0.002 0.011 0.197

2/15/2000 - 12/29/2011 1318 0.008 0.017 0.005 0.000 0.001 0.002 0.006 0.197

ECd

2/15/2000 - 12/30/2005 626 0.347 0.205 0.218 0.045 0.210 0.300 0.428 2.025

1/02/2006 - 4/13/2009 385 0.411 0.252 0.269 0.049 0.245 0.350 0.513 2.200

2/15/2000 - 4/13/2009 1011 0.372 0.226 0.235 0.045 0.220 0.315 0.455 2.200

Fe

2/15/2000 - 12/30/2005 630 0.079 0.112 0.048 0.002 0.027 0.042 0.075 0.979

1/02/2006 - 12/29/2011 688 0.092 0.134 0.056 0.001 0.032 0.052 0.088 1.120

2/15/2000 - 12/29/2011 1318 0.086 0.124 0.054 0.001 0.030 0.048 0.084 1.120

K

2/15/2000 - 12/30/2005 630 0.076 0.061 0.057 0.001 0.036 0.057 0.093 0.637

1/02/2006 - 12/29/2011 688 0.079 0.077 0.051 0.001 0.040 0.057 0.091 1.004

2/15/2000 - 12/29/2011 1318 0.077 0.070 0.054 0.001 0.038 0.057 0.092 1.004

Mn

2/15/2000 - 12/30/2005 630 0.002 0.002 0.001 0.000 0.001 0.001 0.002 0.014

1/02/2006 - 12/29/2011 688 0.002 0.002 0.002 0.000 0.001 0.002 0.003 0.022

2/15/2000 - 12/29/2011 1318 0.002 0.002 0.002 0.000 0.001 0.001 0.002 0.022

Na+

2/15/2000 - 12/30/2005 587 0.222 0.259 0.199 0.006 0.065 0.128 0.264 2.160

1/02/2006 - 12/29/2011 692 0.268 0.274 0.291 0.006 0.071 0.175 0.362 2.115

2/15/2000 - 12/29/2011 1279 0.247 0.268 0.253 0.006 0.068 0.157 0.321 2.160

NH4

+

2/15/2000 - 12/30/2005 617 1.247 0.928 1.000 0.001 0.630 0.970 1.630 8.760

1/02/2006 - 12/29/2011 692 0.986 0.753 0.779 0.003 0.486 0.782 1.265 7.040

2/15/2000 - 12/29/2011 1309 1.109 0.850 0.881 0.001 0.550 0.875 1.430 8.760

Ni

2/15/2000 - 12/30/2005 630 0.002 0.002 0.001 0.000 0.001 0.001 0.002 0.035

1/02/2006 - 12/29/2011 688 0.002 0.003 0.001 0.000 0.001 0.001 0.002 0.066

2/15/2000 - 12/29/2011 1318 0.002 0.003 0.001 0.000 0.001 0.001 0.002 0.066

NO3

-

2/15/2000 - 12/30/2005 623 0.784 0.752 0.531 0.036 0.371 0.542 0.902 5.840

1/02/2006 - 12/29/2011 692 0.755 0.602 0.464 0.022 0.404 0.586 0.868 4.800

2/15/2000 - 12/29/2011 1315 0.769 0.677 0.487 0.022 0.388 0.565 0.875 5.840
3

Table S2. Descriptive statistics for PM2.5 and its components in Greater Houston, Texas, during 2000 - 2011.

OCd

2/15/2000 - 12/30/2005 595 3.429 2.136 2.572 0.555 1.825 2.851 4.397 17.544

1/02/2006 - 4/13/2009 316 2.894 1.868 2.436 0.422 1.463 2.323 3.899 10.758

2/15/2000 - 4/13/2009 911 3.243 2.062 2.516 0.422 1.714 2.710 4.230 17.544

Si

2/15/2000 - 12/30/2005 630 0.229 0.402 0.136 0.002 0.062 0.104 0.197 4.067

1/02/2006 - 12/29/2011 688 0.255 0.466 0.164 0.002 0.050 0.095 0.214 3.920

2/15/2000 - 12/29/2011 1318 0.242 0.436 0.146 0.002 0.055 0.100 0.202 4.067

SO4

2-

2/15/2000 - 12/30/2005 623 3.707 2.419 2.510 0.003 2.100 3.194 4.610 26.000

1/02/2006 - 12/29/2011 692 2.950 1.637 2.065 0.002 1.735 2.613 3.800 10.400

2/15/2000 - 12/29/2011 1315 3.309 2.079 2.245 0.002 1.910 2.896 4.155 26.000

V

2/15/2000 - 12/30/2005 630 0.004 0.003 0.003 0.000 0.002 0.003 0.005 0.022

1/02/2006 - 12/29/2011 688 0.005 0.004 0.005 0.001 0.002 0.004 0.007 0.023

2/15/2000 - 12/29/2011 1318 0.004 0.004 0.004 0.000 0.002 0.004 0.006 0.023

Zn

2/15/2000 - 12/30/2005 630 0.008 0.010 0.008 0.000 0.003 0.005 0.011 0.122

1/02/2006 - 12/29/2011 688 0.008 0.008 0.007 0.000 0.003 0.005 0.010 0.099

2/15/2000 - 12/29/2011 1318 0.008 0.009 0.008 0.000 0.003 0.005 0.010 0.122

a The unit for all pollutants is μg/m3

. b Standard deviation. c Interquartile range. dWe included a shorter sampling 

period for EC and OC due to sampling method change in the year 2009 (see Methods for details).
4

Table S3. Pearson correlation coefficientsa of PM2.5 and its components.

PM2.5 Al NH4

+ Br Cr Cu Fe Mn Ni NO3- K Si SO42- V Zn Na+ b

EC bOC

PM2.5 1.00

Al 0.28 1.00

NH4

+ 0.67 -0.14 1.00

Br 0.34 -0.15 0.30 1.00

Cr 0.00 0.03 -0.02 0.02 1.00

Cu 0.06 0.00 -0.01 0.01 0.23 1.00

Fe 0.33 0.92 -0.11 -0.12 0.20 0.07 1.00

Mn 0.34 0.69 0.02 -0.01 0.29 0.17 0.79 1.00

Ni 0.13 -0.05 0.19 0.14 0.70 0.17 0.08 0.24 1.00

NO3

- 0.26 -0.07 0.35 0.28 0.00 0.04 -0.02 0.09 0.19 1.00

K 0.47 0.54 0.08 0.29 0.00 0.02 0.57 0.44 -0.02 0.10 1.00

Si 0.31 0.93 -0.12 -0.15 0.01 0.01 0.95 0.67 -0.07 -0.05 0.57 1.00

SO4

2- 0.71 -0.04 0.92 0.32 -0.02 -0.05 -0.02 0.04 0.14 0.14 0.19 -0.02 1.00

V 0.29 0.09 0.26 0.16 0.00 0.02 0.13 0.20 0.29 0.31 0.16 0.09 0.21 1.00

Zn 0.26 -0.08 0.27 0.18 0.04 0.16 0.01 0.19 0.11 0.30 0.07 -0.07 0.17 0.13 1.00

Na+ 0.09 0.16 -0.16 0.30 -0.02 -0.17 0.13 0.00 -0.07 -0.08 0.32 0.16 0.03 0.00 -0.28 1.00

EC 0.31 -0.10 0.22 0.19 0.25 0.22 0.02 0.25 0.18 0.34 0.06 -0.10 0.11 0.30 0.60 -0.32 1.00

OC 0.55 -0.17 0.51 0.29 0.14 0.16 -0.08 0.13 0.21 0.33 0.15 -0.13 0.43 0.15 0.54 -0.33 0.66 1.00

a Data used to calculate these correlations include the entire sampling period from 2000 to 2011; b EC and OC measurements 

during 2001-2009 were used.
5

Fig. S1. Federal Reference Method (FRM) PM2.5 monitoring sites in Greater Houston, Texas. (Speciation 

samples (red hexagon) were collected at the Houston Deer Park site. Mass samples were collected from 

16 sites within Greater Houston. Among them, 3 sites (blue triangles) have been operating actively

throughout the entire study period from 2000 to 2011. Other sites (red triangles) only operated for a 

certain period of time during the study period).
6

Fig. S2. Boxplots of daily mean concentrations of PM2.5 mass and major components by year (EC and OC measurements during 2001-2009 were 

used).

PM2.5 NH4(+) NO3(-)

SO4(2-) EC OC

0

20

40

60

0.0

2.5

5.0

7.5

0

2

4

6

0

10

20

0.0

0.5

1.0

1.5

2.0

0

5

10

15

200020012002200320042005200620072008200920102011

2000

2001

2002

200320042005

2006

2007

2008

2009

2010

2011

2000

2001

2002200320042005200620072008200920102011

200020012002200320042005200620072008200920102011200020012002200320042005200620072008

2009

201020112000200120022003200420052006200720082009

20102011

μg/m3
7

Fig. S3. Box-plots of daily mean temperature and mean dew point temperature by season. 

Daily Mean Temperature Daily Mean Dew Point Temperature

0

10

20

30

-10

0

10

20

SP SU F W SP SU F W

celsius (°C)
8

Fig. S4. Percent increase in mortality (95% CI) associated with an IQR increase in the PM2.5 components on the previous day by sampling period. 

All, period from 2000 to 2011; 1, period from 2000 to 2005; 2, period from 2006 to 2011 (IQRs were calculated based on all-year data; Otherwise 

as Fig. S2).

PM2.5 Al Br Cr Cu EC

Fe K Mn Na(+) NH4(+) Ni

NO3(-) OC Si SO4(2-) V Zn

-2

0

2

-2

0

2

-2

0

2

All 1 2 All 1 2 All 1 2 All 1 2 All 1 2 All 1 2

Percent increase in mortality for IQR incre
9

Fig. S5. Percent increase in mortality (95% CI) associated with an IQR increase in the PM2.5 components at lag time day 0, 1, 2, and 3 (Otherwise 

as Fig. S4).

PM2.5 Al Br Cr Cu EC

Fe K Mn Na(+) NH4(+) Ni

NO3(-) OC Si SO4(2-) V Zn

-1

0

1

-1

0

1

-1

0

1

0 1 2 3 0 1 2 3 0 1 2 3 0 1 2 3 0 1 2 3 0 1 2 3

Percent increase in mortality for IQR incre
10

Fig. S6. Percent increase in mortality (95% CI) associated with an IQR increase in the PM2.5 components by age groups. Age groups: All, all ages 

included; >=65, persons with the mortality age ≥ 65 (Otherwise as Fig. S4).

PM2.5 Al Br Cr Cu EC

Fe K Mn Na(+) NH4(+) Ni

NO3(-) OC Si SO4(2-) V Zn

-2

-1

0

1

2

-2

-1

0

1

2

-2

-1

0

1

2

All >=65 All >=65 All >=65 All >=65 All >=65 All >=65

Percent increase in mortality for IQR incre
11

Fig. S7. Percent increase in mortality (95% CI) associated with an IQR increase in the PM2.5 components on the previous day by season in Greater 

Houston, Texas, during 2000 - 2011. Warm, (April - September); Cool, (October - March) (Otherwise as Fig. S4).

PM2.5 Al Br Cr Cu EC

Fe K Mn Na(+) NH4(+) Ni

NO3(-) OC Si SO4(2-) V Zn

-1

0

1

2

-1

0

1

2

-1

0

1

2

Warm Cool Warm Cool Warm Cool Warm Cool Warm Cool Warm Cool

Percent increase in mortality for IQR incre
12

Fig. S8. Box-plots of daily mean PM2.5 mass and the major PM2.5 components by season (Otherwise as Fig. S4).

PM2.5 NH4(+) NO3(-)

SO4(2-) EC OC

0

20

40

60

0.0

2.5

5.0

7.5

0

2

4

6

0

10

20

0.0

0.5

1.0

1.5

2.0

0

5

10

15

SP SU F W SP SU F W SP SU F W

SP SU F W SP SU F W SP SU F W

μg/m3
13

Fig. S9. Wind roses based on measurements at the weather station located in at the George Bush 

Intercontinental Airport, Houston, during 2000-2011.

Spring Summer

Fall Winter

W

S

N

E

5%

10%

15%

20%

25%

30%

0 - 2 2 - 4 4 - 6 6 - 25

(m/s)

W

S

N

E

5%

10%

15%

20%

25%

0 - 2 2 - 4 4 - 6 6 - 25

(m/s)

W

S

N

E

2%

4%

6%

8%

10%

12%

14

0 - 2 2 - 4 4 - 6 6 - 25

(m/s)

W

S

N

E

2%

4%

6%

8%

10%

12%

14%

0 - 2 2 - 4 4 - 6 6 - 25

(m/s)