APPENDIX X 

MATES III 

FINAL REPORT 

Weekday/Weekend PM2.5 Speciation Project 

Author

Jason Low
MATES III Final Report

Appendix X-1 

APPENDIX X 

Weekday/Weekend PM2.5 Speciation Project 

X-1 Background 

A major focus of MATES II and III is the estimation of ambient diesel particulate matter levels. 

Currently, diesel particulate matter is being estimated by quantifying the EC and other 

components of PM2.5 samples. Although the MATES III Program assesses the annual South 

Coast Air Basin average risk associated with selected toxic air contaminants using monitoring 

data averaged over a year, emissions vary from day to day and especially from weekday to 

weekend, following variation of anthropogenic activity. Since this variation exists, additional 

weekend specific data on toxic air compounds could provide additional information on pollution 

sources. One of the most notable phenomena is the “ozone weekend effect” whereby 

concentrations of ozone are greater on the weekends than on the weekdays in the South Coast 

Basin. The weekend effect has become more pronounced over the last decade and is indicative 

of varying emissions sources as a function of the day of the week. Studies have also shown the 

reverse trend for VOCs, particulate matter (PM10 and PM2.5), and carbon monoxide (CO) 

whereby high concentrations are observed during the weekdays and drop significantly (10 to 

25%) on the weekends (ARB, 2004). 

In an effort to investigate the weekday/weekend differences found, ARB initiated an emission 

source activity study characterized by day of the week which obtained data for on-road mobile 

sources, off-road mobile and area sources, and point sources which would include toxic air 

contaminant emissions (ARB, 2004). Through telephone and mail surveys, in-vehicle sensors 

checking driving activity, traffic volume observations on surface streets and freeways, 

continuous emissions monitoring, and on-site field surveys, it was shown that activity levels for 

on-road mobile sources, commercial off-road mobile sources, and commercial area sources 

declined on the weekends relative to weekdays, but activity levels for recreational off-road 

mobile sources and recreational sources increased on weekends relative to weekdays. The study 

included roadway loop sensor data which suggested that surface street traffic declined 20-27% 

on Saturdays and 27-33% on Sundays, but heavy-duty diesel traffic declined more, 67-83% 

(Figure X-1). Also, the study analyzed Caltrans Weigh-In-Motion (WIM) data for 2002 and 

observed that total freeway traffic declined 11% on Saturdays and 26% on Sundays (Figure X-2), 

but heavy-duty traffic declined 50-75% on weekends (Figure X-3). Different activity patterns 

exist for Friday, Saturday and Monday which is reflective of the transition from weekday to 

weekend activities and vice versa. According to ARB (Larsen, 2004), the preliminary 

observations for 2004 traffic patterns do not deviate significantly from those in 2002. Through 

surveys, activities such as boating, off-road driving, painting and barbecuing increased 25-165% 

from weekdays to weekends, but business activities declined 60-90% on the weekends, almost 

ceasing on Sunday (ARB, 2004). 
MATES III Final Report

Appendix X-2 

X-2 Introduction 

A special study was conducted in addition to the MATES III fixed site measurements to 

specifically compare weekday and weekend differences in elemental carbon, a marker for diesel 

exhaust, and later was expanded to include PM2.5 mass and other compounds. Multiple-Channel 

Fine Particulate (MCFP) samplers from the PM Technical Enhancement Program (PTEP) were 

deployed to the Central Los Angeles, West Long Beach, and Rubidoux sites which were also 

selected for the PAH and the organic tracers measurements conducted as part of MATES III. The 

purpose of the extra samplers was to allow consistent Wednesday and Sunday sampling without 

interfering with the MATES III fixed-site sampling schedule and being able to acquire more day 

specific data than the fixed site sampling schedule. For the purpose of this study, Wednesday 

was chosen as the representative “weekday” because on-road vehicular activity was shown to be 

consistent from Tuesday through Thursday. Sunday was chosen as the representative “weekend” 

because it is the day with the lowest on-road vehicular activity within the South Coast Basin. 

Sampling by the MCFP samplers commenced in the high PM season starting in October 2004 

and proceeded through March 2005 and then again from October 2005 through March 2006. 

X-3 Methodology 

The MCFP samplers collected a 24-hour integrated sample onto one Teflon filter and three 

quartz filters at the rate of 8 L min-1 (11,500 L per sample). Channel II of each MCFP sampler 

was equipped with a Teflon-coated cyclone for PM2.5 size selective sampling. Information on 

the MCFP samplers can be found in Kim, et. al (2000). The sampler differs from the SASS 

samplers used in the routine sampling at the MATES III sites in the cyclone and flow rates. The 

MCFP sampler has been shown to produce comparable results to FRM samplers for mass and 

nitrates (Teffera,et. al, 1998). After mass was determined, metals were analyzed on the Teflon 

filters using X-ray Fluorescence Spectroscopy (XRF). EC/OC analysis duplicates were done on 

one of the quartz filters requiring two circular punches with a 5 mm diameter from the sample. 

After EC/OC analysis, the punched filters were stored with the collocated filters at 4o C to await 

the organic tracer analysis. The two quartz filters with the most convergent EC concentrations 

on a given sampling day were selected to contribute to the monthly composite sample for the 

organic speciation analysis. 

Volatile organic compound data and PM2.5 filter data from the fixed site data were also used for 

day-of-week analysis and were measured using the methods described in Section 2.5; PAH 

measurement methods are depicted in Appendix IV; and PM2.5 particulate-bound organic 

compound analysis is described in Appendix V. 

X-4 Results and Discussion 

In addition to normal quality control checks, the data from the MCFP samplers were compared to 

the data from the fixed sites for the days that there was overlap. The MCFP mass concentrations 

showed a positive bias from the SASS mass concentrations (Figure X-4). The bias was greater 

than 20% in all samplers. QC checks on the MCFP metals data indicated that there were 

unusually high concentrations of copper, zinc, nickel and other metals that were not seen in the 
MATES III Final Report

Appendix X-3 

SASS metal data. A source of contamination was found in the brass fittings that were used 

upstream of the denuder tubes. Brass is an alloy consisting primarily of copper (~65%) and zinc 

(~35%) and other trace metals. When the total mass of the metals was compared to the 

overlapping samples, a positive bias was found in the MCFP sampler data. When that metal sum 

bias was subtracted from the MCFP PM2.5 mass data, the adjusted mass MCFP concentration 

averages were comparable to the SASS mass data averages. 

Because of the known metals contamination of the MCFP samples, the MCFP data was not used 

further for data analysis on PM2.5 mass and metal content. Instead, the SASS sample data was 

used for the day-of-week comparisons for PM2.5 filter data. The SASS data provides a complete 

data set over two years which provides around 35 data points for comparison for each day of the 

week for each site compared to the 24 data points originally conceived for the special project for 

one year with the MCFP. Also, it allows for seasonal comparisons as well as providing 

resolution to see Friday, Saturday, and Monday transition effects on the data. 

The PM2.5 EC and OC data from the MCFP samplers were relatively unaffected by the metals 

contamination as would be expected. The average EC and OC MCFP data was within 15%, the 

precision of the carbon analyzer at ambient concentrations, of the SASS averages with exception 

to the Rubidoux OC data which was within 25%. Thus, it can be inferred that the data for the 

PM2.5 particle-bound speciated organic compound analysis is not significantly affected by the 

metals contamination. 

Figure X-5 shows the day-of-week SASS PM2.5 mass pattern for the seasonal data of West Long 

Beach, Los Angeles, and Rubidoux. The summer designation is for data collected in the months 

of April through September, and the winter designation is used for data collected in the months 

of October through March. The West Long Beach mass data shows that the annual weekend 

mass average (19.52 μg m-3) is 10% higher than the weekday average (17.88 μg m-3), but the 

average concentration is highest on Saturday (21.57 μg m-3). This pattern was also observed in 

Rubidoux, Los Angeles, and also in the total regional average of all fixed station PM2.5 mass data. 

When looking at the seasonal mass data, there is less of a change between weekend mass in the 

summer whereas there is a 30-50% increase in the winter between the three sites which accounts 

for most of the difference observed in the annual data. In the winter, the day-of-week trend 

indicates the maximum average mass concentrations on Saturday and the lowest on Monday with 

a 40 – 60% difference. Comparison of the stations confirms other observations that Rubidoux 

has higher average PM2.5 concentrations relative to the western portions of the South Coast Air 

Basin. 

This Saturday effect observed with the mass was also observed in the SASS PM2.5 NO3 and SO4

data (Figure X-6 and Figure X-7) in all three sites with increases of 30% and 14% respectively 

for the annual average, but the larger differences (40 – 70%) were observed in the winter data. 

For comparison to other studies, average summer concentrations of NO3 in this study were three 

to four times higher than the 0.54 to 0.82 μg m-3 concentrations reported by the three-week 

summer time study by Lough, et al. (2003). The seasonal NO3 and SO4 trends are comparable to 

those reported by ARB, 2005. Concentrations of NO3 were higher in the winter than in the 

summer and increase going from west to east which agrees with other studies which have shown 

secondary particulate formation downwind of NH3 sources (Russell and Cass, 1986; Neuman, et 
MATES III Final Report

Appendix X-4 

al., 2003). NH4 concentrations day-of-week patterns matched the NO3 patterns for the three sites. 

Conversely, SO4 concentrations were higher, especially during the weekdays, closer to the 

industrial and traffic sources in the western side of the Basin. MATES III SO4 summer average 

concentration of 4.97 μg m

-3 agrees well with Los Angeles concentrations reported in the Lough, 

et al., Study (2003) which reported 4.4 ±1.8 μg m-3. Also, 60 to 100% higher SO4 concentrations 

were observed in the summer than in the winter at the three sites. The SO4 average 

concentrations declined progressing eastward. 

Average Wednesday to Sunday comparisons of selected organic speciated compounds from the 

MATES III Study were compared to PAH special study average data if the compounds were 

measured in both studies. Average concentrations of the fall PAH data to the organic speciated 

data for pyrene, indeno[1,2,3-cd]pyrene and benzo[g,h,i]perylene are within 95%, 14% and 30% 

respectively. The high discrepancy for pyrene would be expected as the particulate-bound 

heavier PAHs will retain to the filter while the more volatile pyrene would have less recovery on 

a filter compared to XAD-2, the absorbent used in the PAH study. 

In the organic tracer data, pyrene, a stronger marker for diesel, shows a greater than 40% 

decrease on Sundays relative to Wednesdays for West Long Beach, Los Angeles and Rubidoux; 

benzo[g,h,i]perylene, a marker for light-duty vehicles, decreases from 40% in West Long Beach 

to 13% in Rubidoux; indeno[1,2,3-cd]pyrene, a tracer for older, higher polluting vehicles, 

decreases at West Long Beach and Los Angeles, but increase in Rubidoux; coronene, another 

tracer for light-duty vehicles decreases between 30 and 40%; and levoglucosan, a tracer for 

biomass combustion, increases at West Long Beach, Los Angeles and Rubidoux, with the largest 

increase at West Long Beach (Figure X-8). Pyrene, indeno[1,2,3-cd]pyrene, and indeno[1,2,3-

cd]pyrene at West Long Beach have variable higher concentrations during Monday through 

Friday and decrease on the weekend. Other tracers of vehicle combustion such as benzene, 

toluene and m+p xylenes showed a similar pattern at West Long Beach (Figure X-9), but were 

different at Los Angeles (Figure X-10) and Rubidoux (Figure X-11). West Long Beach showed 

a 20 to 30% decrease between the average weekday to weekend concentrations and Rubidoux 

showed more modest changes (Figure X-12), whereas increases in concentrations of these 

volatile tracers increased during the weekend at Los Angeles, mostly attributed to a Saturday 

maximum. 

OC average concentrations (Figure X-13) did not vary from weekend to weekday except at 

Rubidoux where both Saturday and Sunday concentrations were 20% higher than the weekday 

average. However, the seasonal pattern at West Long Beach and Los Angeles shows that 

fall/winter concentrations were 42% higher and 27% higher respectively. Rubidoux did not 

exhibit a seasonal difference. 

EC average annual day-of-week concentration data showed concentrations drop 40 to 45% from 

Wednesdays to Sundays (Figure X-14). The day-of-week pattern shows an 18 to 30% drop from 

weekdays to weekends. The percentage differences were more enhanced in the summer. Also, 

over 50% differences between fall/winter and EC concentration were observed at the three sites. 

EC concentrations for the three sites were similar from Friday through Sunday, but showed 

variation Monday through Thursday whereby EC progressively decreases going eastward from 

West Long Beach to Rubidoux. 
MATES III Final Report

Appendix X-5 

PM2.5 metal concentration differences between Wednesdays and Sundays were observed in some 

of the metals (Figure X-15). Zinc (Zn) and Manganese (Mn) concentrations decreased at all 

three stations with the most significant decrease occurring at the Los Angeles station. Nickel (Ni) 

concentrations increased on Sundays. Other differences in concentrations from metals such as 

arsenic (AS), cadmium (CD), lead (Pb), and vanadium (V) were not consistent across all the 

stations. However, PM2.5 V concentrations did exhibit a maximum concentration on Saturdays 

and showed a distinct presence in West Long Beach compared to the other two sites (Figure X16). 

X-5 Conclusions 

The two years of fixed site data was substantial enough to perform a day-of-week comparison. 

The sampling that was originally designated for the weekday/weekend special study provided a 

good quality control check for EC, OC and also the mass, if corrected for the metals 

contamination. As hypothesized from the activity data, the MATES III PM2.5 data evaluated 

from West Long Beach, Los Angeles and Rubidoux confirms that Wednesday data is reflective 

of concentrations observed on average with Tuesday through Thursday. However, Sunday 

average data did not always demonstrate to have the minimum concentrations in the week as 

shown with the PM2.5 mass. This is added evidence that indicates that studies designed to 

consider weekday versus weekend effects in the South Coast Basin should require both Saturday 

and Sunday measurements. Also, for some of the PM2.5 speciated components, the seasonality 

has a significant effect upon concentration and day-of-week patterns which should also be 

reflected in data sets, as many activity studies are based upon a time scale that would not capture 

seasonal effects. 

Known compounds associated with vehicular traffic such as EC, benzene, toluene, and PAHs 

showed a reduction in concentrations from the weekdays to a minimum on Sunday average. 

PM2.5 EC average concentrations decreased from weekday to weekend, with a greater than 40% 

decrease from the maximum on Wednesdays to the minimum on Sundays. This EC decrease 

corresponds with the reduction on the weekends from sources such as diesel exhaust and 

commercial stationary sources, especially on Sunday. The day-of-week difference was stronger 

than the observed seasonality effects, although the day-of-week differences were more enhanced 

in the fall/winter time periods. Also, the EC weekend decrease is similar to trends observed in 

benzene, toluene, and m+p xylene at West Long Beach, but was only observed slightly in 

Rubidoux and not consistent with the trend observed in Los Angeles. 

Sunday average data did not always show the minimum concentrations in the week as shown 

with the PM2.5 mass, OC and associated inorganic ions and metals. PM2.5 mass average day-ofweek patterns for Rubidoux, Los Angeles, and West Long Beach differed from earlier 

observations of enhanced concentrations on the weekends relative to weekdays (Motallebi et al., 

2003), but only during the winter/fall time period. The decrease in mass of EC on the weekends 

is small compared to the large increase in the secondary pollutants, NO3 and SO4, contributing to 

the increased overall PM2.5 mass. Nitrate contributed more PM2.5 mass downwind of NH3 

sources and the SO4 contributed to PM2.5 mass closer to the commercial and traffic sources. The 
MATES III Final Report

Appendix X-6 

data shows a peak maximum on Saturdays for PM2.5 mass, NO3, SO4 and a minimum on 

Mondays. 

Vanadium exhibited weekday to weekend variability, which shared a similar trend with SO4 in 

seasonal, day of week, and seasonally at the West Long Beach site. Although vanadium day-ofweek trends were similar across the three stations, there were significant differences in 

concentration among the three stations, with the highest concentrations located in West Long 

Beach and the lowest in Rubidoux. If it can be inferred that vanadium concentrations can be 

connected to the cargo ship activity due to the ships’ use of residual fuel containing vanadium; 

the vanadium data suggests that emissions due to these ships is highest on Saturdays which may 

correlate to the high Saturday PM2.5 SO4 and NO3 formed by the oxidation of SO2 and NOx that 

may also be generated by the ships. 

Further studies can be done to compare traffic data at a higher resolution using traffic counts 

from the WIM Program to better source apportion traffic activity by vehicle type to the chemical 

analysis which will improve the geographic correlation between the data and the traffic observed. 

The data was not obtainable in the time scale for this report, but data can be obtained for a future 

data analysis. 

Figure X-1: Average day-of-week traffic patterns of differing vehicle classes observed for 

surface streets in 2002 (ARB, 2004). 
MATES III Final Report

Appendix X-7 

Figure X-2: Diurnal time series for light-duty vehicles by day of week. 

Figure X-3: Diurnal time series for heavy-duty vehicles by day of week. 
MATES III Final Report

Appendix X-8 

0

5

10

15

20

25

30

West Long

Beach

Los Angeles Rubidoux

SASS

MCFP

Figure X-4: Average of day-to-day comparisons (N= 17) of PM2.5 mass data taken from SASS 

samplers from the fixed site data and the special purpose MCFP samplers. 
MATES III Final Report

Appendix X-9 

 

West Long Beach

0

5

10

15

20

25

30

MonTuesWedThur

Fri

SatSun

Ave: M-F

Ave: Sat-Sun

 [PM2.5 Mass] ug/m

3

Annual Winter Summer

Central Los Angeles

0

5

10

15

20

25

30

MonTuesWedThur

Fri

SatSun

Ave: M-F

Ave: Sat-Sun

 [PM2.5 Mass] ug/m

3

Annual Winter Summer

Rubidoux

0

5

10

15

20

25

30

35

MonTuesWedThur

Fri

SatSun

Ave: M-F

Ave: Sat-Sun

 [PM2.5 Mass] ug/m

3

Annual Winter Summer

Figure X-5: Average day-of-week PM2.5 mass concentrations by season for West Long Beach,

Los Angeles and Rubidoux. 
MATES III Final Report

Appendix X-10 

West Long Beach

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

MonTuesWedThur

Fri

SatSunAve: Mon-FriAve: Sat-Sun

[NO3] ug/m

3

Annual Winter Summer

Central Los Angeles

0.0

2.0

4.0

6.0

8.0

10.0

MonTuesWedThur

Fri

SatSunAve: Mon-FriAve: Sat-Sun

[NO3] ug/m

3

Annual Winter Summer

Rubidoux

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

MonTuesWedThur

Fri

SatSunAve: Mon-FriAve: Sat-Sun

[NO3] ug/m

3

Annual Winter Summer

Figure X-6: Average day-of-week NO3 concentrations by season for West Long Beach, Los 

Angeles and Rubidoux. 
MATES III Final Report

Appendix X-11 

West Long Beach

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

MonTuesWedThur

Fri

SatSunAve: Mon-FriAve: Sat-Sun

 [ SO4 ] ug/m

3

Annual Winter Summer

Central Los Angeles

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

MonTuesWedThur

Fri

SatSunAve: Mon-FriAve: Sat-Sun

[SO4] ug/m

3

Annual Winter Summer

Rubidoux

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

MonTuesWedThur

Fri

SatSunAve: Mon-FriAve: Sat-Sun

[SO4] ug/m

3

Annual Winter Summer

Figure X-7: Average day-of -week SO4 concentrations by season for West Long Beach, Los 

Angeles and Rubidoux. 
MATES III Final Report

Appendix X-12 

-75%

-50%

-25%

0%

25%

50%

75%

PYRBGHIPE

IN123PYRCORENELEVGU 

 % 

West Long Beach Los Angeles Rubidoux

Figure X-8: Percentage change from Wednesday to Sunday of concentrations of selected organic 

tracer components at West Long Beach, Los Angeles, and Rubidoux during the fall 

and winter time. 

West Long Beach

0.0

0.5

1.0

1.5

2.0

2.5

MonTuesWed

ThurFriSat

Sun

Ave: Mon-FriAve: Sat-Sun

[ ] ppb

Methylene Chloride

Benzene

Toluene

Ethyl benzene

(m+p)-Xylenes

o-Xylene

2-butanone (MEK)

Figure X-9: Average selected VOC concentrations for West Long Beach by day. 
MATES III Final Report

Appendix X-13 

Central Los Angeles

0.0

0.5

1.0

1.5

2.0

2.5

3.0

MonTuesWedThur

Fri

SatSunAve: Mon-FriAve: Sat-Sun

[ ] ppb

Methylene Chloride

Benzene

Toluene

Ethyl benzene

(m+p)-Xylenes

o-Xylene

2-butanone (MEK)

Figure X-10: Average selected VOC concentrations for Central Los Angeles by day. 

Rubidoux

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

MonTuesWed

ThurFriSat

Sun

Ave: Mon-FriAve: Sat-Sun

[ ] ppb

Methylene Chloride

Benzene

Toluene

Ethyl benzene

(m+p)-Xylenes

o-Xylene

2-butanone (MEK)

Figure X-11: Average selected VOC concentrations for Rubidoux by day. 
MATES III Final Report

Appendix X-14 

-40%

-30%

-20%

-10%

0%

10%

20%

Methylene Chloride

Benzene

Toluene

Ethyl benzene(m+p)-Xyleneso-Xylene2-butanone (MEK)

 %

West Long Beach LA Rubidoux

Figure X-12: Percentage difference of average weekday to weekend concentrations for select 

VOCs at West Long Beach, Los Angeles, and Rubidoux.
MATES III Final Report

Appendix X-15 

West Long Beach

0

1

2

3

4

5

6

7

8

9

MonTuesWedThur

Fri

SatSun

Ave: M-F

Ave: Sat-Sun

 [OC] ug/m

3

Annual Winter Summer

Central Los Angeles

0

1

2

3

4

5

6

7

8

9

10

MonTuesWedThur

Fri

SatSun

Ave: M-F

Ave: Sat-Sun

 [OC] ug/m

3

Annual Winter Summer

Rubidoux

0

1

2

3

4

5

6

7

8

9

10

MonTuesWedThur

Fri

SatSun

Ave: M-F

Ave: Sat-Sun

 [OC] ug/m

3

Annual Winter Summer

Figure X-13: Average day-of-week OC concentrations by season for West Long Beach, 

Los Angeles and Rubidoux. 
MATES III Final Report

Appendix X-16 

West Long Beach

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

MonTuesWedThur

Fri

SatSun

Ave: M-F

Ave: Sat-Sun

 [EC] ug/m

3

Annual Winter Summer

Central Los Angeles

0.0

0.5

1.0

1.5

2.0

2.5

3.0

MonTuesWedThur

Fri

SatSun

Ave: M-F

Ave: Sat-Sun

 [EC] ug/m

3

Annual Winter Summer

Rubidoux

0.0

0.5

1.0

1.5

2.0

2.5

3.0

MonTuesWedThur

Fri

SatSun

Ave: M-F

Ave: Sat-Sun

 [EC] ug/m

3

Annual Winter Summer

Figure X-14: Average day-of-week EC concentrations by season for West Long Beach, 

Los Angeles and Rubidoux. 
MATES III Final Report

Appendix X-17 

-100%

-80%

-60%

-40%

-20%

0%

20%

40%

60%

As Cd Cu Pb Mn Ni Zn

Element Name

Change of Wed to Sun (%)

W. LB LA Rub

Figure X-15: Percentage differences from Wednesday to Sunday concentrations for PM2.5

metals. A negative percentage indicates a drop in concentration on Sunday 

compared to the Wednesday concentration. 
MATES III Final Report

Appendix X-18 

West Long Beach

0

5

10

15

20

25

30

MonTuesWedThur

Fri

SatSunAve: Mon-FriAve: Sat-Sun

 [ V ] ng/m

3

Annual Winter Summer

0

5

10

15

20

25

MonTuesWedThur

Fri

SatSunAve: Mon-FriAve: Sat-Sun

 [ V ] ng/m

3

West Long Beach Los Angeles Rubidoux

Figure X-16: Vanadium day-of-week average concentrations for West Long Beach by season 

and also in comparison to day-of-week trends with Los Angeles, and Rubidoux. 
MATES III Final Report

Appendix X-19 

X-6 References 

Atmospheric and Environmental Research, Data Analysis for a Better Understanding of the 

Weekday/Weekend Ozone and PM Differences, 2001. 

Kim, B.M., Teffera, S., Zeldin, M., Characterization of PM2.5 andPM10 in the South Coast Air 

Basin of Southern California: Part 1 – Spatial Variations, J. Air & Waste Manage. Assoc, 50, 

2034-2044, 2000. 

California Air Resources Board, Collection and Analysis of Weekend/Weekday Emissions 

Activity Data in the South Coast Air Basin, 2004. 

ftp://ftp.arb.ca.gov/carbis/aqd/weekendeffect/STI_WE-WD_FR_5-7-04.pdf. 

California Air Resources Board, Characterization of Ambient PM10 and PM2.5 in California: 

Technical Report June 2005, http://www.arb.ca.gov/pm/pmmeasures/pmch05/pmch05.htm, 

viewed April 16, 2008. 

Larsen, Larry, California Air Resources Board, Personal Communication, August 31, 2004. 

Lough, G.C., Schauer, J.J., and Lawson, D.R., Day-of-Week trends in carbonaceous aerosol 

composition in the urban atmosphere, Atmospheric Environment, 40, 2006, 4137-4149. 

Motallebi, N., Tran, H., Croes, B.E., and Larsen, L., Day-of-week patterns of particulate matter 

and its chemical components at selected sites in California, J. Air & Waste Manage. Assoc., 53, 

876-888. 

Neuman, J. A., Nowak, J. B., Brock, C. A., Trainer, M., Fehsenfeld, F.C., Holloway, J. S., 

Hubler, G., Hudson, P.K., Murphy, D.M., Nicks, Jr., D. K., Orsini, D., Parrish, D. D., Ryerson, T. 

B., Sueper, D. T., Sullivan, A., and Weber, R., Variability in ammonium nitrate formation and 

nitric acid depletion with altitude and location over California, J. Geophys. Res., 108, D17, 4557, 

2003. 

Teffera, S., Barbosa, S., and Eden, R., Collocated PM2.5 Mass and Nitrate Measurements Using 

The New EPA PM2.5 FRM and South Coast Air Quality Management District’s PTEP MultiChannel Samplers, SCAQMD, 1998.