## APPENDIX X MATES III

FINAL REPORT

Weekday/Weekend PM 2.5 

## Speciation Project



## Author Jason Low

### MATES III Final Report

Appendix X-1 

## APPENDIX X

Weekday/Weekend PM 2.5 

## 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 estim ated by quantifying the EC and other components of PM 2.5 

### samples. Although the MATES III Program assesses the annual South Coast Air Basin average risk associated with select ed 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 activ ity. 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 pronounc ed over the last decade and is indicative of varying emissions sources as a function of the d ay of the week. Studies have also shown the reverse trend for VOCs, particulate matter (PM 10 

### and PM 2.5 

### ), 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 dif ferences found, ARB initiated an emission source activity study characterized by day of the w eek which obtained data for on-road mobile sources, off-road mobile and area sources, and poin t sources which would include toxic air contaminant emissions (ARB, 2004). Through telepho ne and mail surveys, in-vehicle sensors checking driving activity, traffic volume observati ons 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 o n weekends relative to weekdays. The study included roadway loop sensor data which suggested t hat 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 W eigh-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 refl ective of the transition from weekday to weekend activities and vice versa. According to AR B (Larsen, 2004), the preliminary observations for 2004 traffic patterns do not devia te significantly from those in 2002. Through surveys, activities such as boating, off-road drivi ng, 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).

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Appendix X-2 X-2 Introduction

A special study was conducted in addition to the MA TES III fixed site measurements to specifically compare weekday and weekend difference s in elemental carbon, a marker for diesel exhaust, and later was expanded to include PM 2.5 

### mass and other compounds. Multiple-Channel Fine Particulate (MCFP) samplers from the PM Techni cal Enhancement Program (PTEP) were deployed to the Central Los Angeles, West Long Beac h, and Rubidoux sites which were also selected for the PAH and the organic tracers measur ements conducted as part of MATES III. The purpose of the extra samplers was to allow consiste nt 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 wa s chosen as the representative “weekend” because it is the day with the lowest on-road vehic ular 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 fro m October 2005 through March 2006.

X-3 Methodology

The MCFP samplers collected a 24-hour integrated sa mple 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 sa mpler was equipped with a Teflon-coated cyclone for PM 2.5 

### 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 r esults to FRM samplers for mass and nitrates (Teffera,et. al, 1998). After mass was de termined, 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 pu nches with a 5 mm diameter from the sample. After EC/OC analysis, the punched filters were stor ed with the collocated filters at 4 o 

### C to await the organic tracer analysis. The two quartz filter s 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 PM 2.5 

### filter data from the fixed site data were also use d for day-of-week analysis and were measured using the me thods described in Section 2.5; PAH measurement methods are depicted in Appendix IV; an d PM 2.5 

### particulate-bound organic compound analysis is described in Appendix V.

X-4 Results and Discussion

In addition to normal quality control checks, the d ata from the MCFP samplers were compared to the data from the fixed sites for the days that the re was overlap. The MCFP mass concentrations showed a positive bias from the SASS mass concentra tions (Figure X-4). The bias was greater than 20% in all samplers. QC checks on the MCFP me tals data indicated that there were unusually high concentrations of copper, zinc, nick el and other metals that were not seen in the

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Appendix X-3 SASS metal data. A source of contamination was fou nd in the brass fittings that were used upstream of the denuder tubes. Brass is an alloy co nsisting 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 t he MCFP sampler data. When that metal sum bias was subtracted from the MCFP PM 2.5 

### mass data, the adjusted mass MCFP concentration averages were comparable to the SASS mass data aver ages.

Because of the known metals contamination of the MC FP samples, the MCFP data was not used further for data analysis on PM 2.5 

### mass and metal content. Instead, the SASS sample data was used for the day-of-week comparisons for PM 2.5 

### filter data. The SASS data provides a complete data set over two years which provides around 35 da ta points for comparison for each day of the week for each site compared to the 24 data points o riginally conceived for the special project for one year with the MCFP. Also, it allows for season al comparisons as well as providing resolution to see Friday, Saturday, and Monday tran sition effects on the data.

The PM 2.5 

### EC and OC data from the MCFP samplers were relativ ely 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 concent rations, 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 PM 2.5 

### particle-bound speciated organic compound analysis is not significantly affected by the metals contamination.

Figure X-5 shows the day-of-week SASS PM 2.5 

### mass pattern for the seasonal data of West Long Beach, Los Angeles, and Rubidoux. The summer desi gnation is for data collected in the months of April through September, and the winter designat ion 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 μ g m -3 

### ) is 10% higher than the weekday average (17.88 μ g m -3 

### ), but the average concentration is highest on Saturday (21.57 μ g m -3 

### ). This pattern was also observed in Rubidoux, Los Angeles, and also in the total region al average of all fixed station PM 2.5 

### mass data. When looking at the seasonal mass data, there is le ss of a change between weekend mass in the summer whereas there is a 30-50% increase in the wi nter between the three sites which accounts for most of the difference observed in the annual d ata. In the winter, the day-of-week trend indicates the maximum average mass concentrations o n Saturday and the lowest on Monday with a 40 – 60% difference. Comparison of the stations confirms other observations that Rubidoux has higher average PM 2.5 

### concentrations relative to the western portions of the South Coast Air Basin.

This Saturday effect observed with the mass was als o observed in the SASS PM 2.5 

### NO 3 

### and SO 4 

### 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 con centrations of NO 3 

### in this study were three to four times higher than the 0.54 to 0.82 μ g m -3 

### concentrations reported by the three-week summer time study by Lough, et al. (2003). The sea sonal NO 3 

### and SO 4 

### trends are comparable to those reported by ARB, 2005. Concentrations of NO 3 

### were higher in the winter than in the summer and increase going from west to east which a grees with other studies which have shown secondary particulate formation downwind of NH 3 

### sources (Russell and Cass, 1986; Neuman, et

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Appendix X-4 al., 2003). NH 4 

### concentrations day-of-week patterns matched the NO 3 

### patterns for the three sites. Conversely, SO 4 

### concentrations were higher, especially during the weekdays, closer to the industrial and traffic sources in the western side of the Basin. MATES III SO 4 

### summer average concentration of 4.97 μ g m -3 

### agrees well with Los Angeles concentrations report ed in the Lough, et al., Study (2003) which reported 4.4 ±1.8 μ g m -3 

### . Also, 60 to 100% higher SO 4 

### concentrations were observed in the summer than in the winter at t he three sites. The SO 4 

### 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 o f 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 woul d be expected as the particulate-bound heavier PAHs will retain to the filter while the mo re volatile pyrene would have less recovery on a filter compared to XAD-2, the absorbent used in t he PAH study.

In the organic tracer data, pyrene, a stronger mark er 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 vehic les, decreases from 40% in West Long Beach to 13% in Rubidoux; indeno[1,2,3-cd]pyrene, a trace r for older, higher polluting vehicles, decreases at West Long Beach and Los Angeles, but i ncrease 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, L os 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 c oncentrations 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 i ncreases in concentrations of these volatile tracers increased during the weekend at Lo s Angeles, mostly attributed to a Saturday maximum.

OC average concentrations (Figure X-13) did not var y from weekend to weekday except at Rubidoux where both Saturday and Sunday concentrati ons were 20% higher than the weekday average. However, the seasonal pattern at West Lon g 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 sh owed concentrations drop 40 to 45% from Wednesdays to Sundays (Figure X-14). The day-of-we ek pattern shows an 18 to 30% drop from weekdays to weekends. The percentage differences w ere more enhanced in the summer. Also, over 50% differences between fall/winter and EC con centration 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 progre ssively decreases going eastward from West Long Beach to Rubidoux.

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Appendix X-5 PM 2.5 

### metal concentration differences between Wednesdays and Sundays were observed in some of the metals (Figure X-15). Zinc (Zn) and Mangane se (Mn) concentrations decreased at all three stations with the most significant decrease o ccurring at the Los Angeles station. Nickel (Ni) concentrations increased on Sundays. Other differe nces in concentrations from metals such as arsenic (AS), cadmium (CD), lead (Pb), and vanadium (V) were not consistent across all the stations. However, PM 2.5 

### V concentrations did exhibit a maximum concentrati on on Saturdays and showed a distinct presence in West Long Beach c ompared to the other two sites (Figure X16).

X-5 Conclusions

The two years of fixed site data was substantial en ough 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 d ata, the MATES III PM 2.5 

### data evaluated from West Long Beach, Los Angeles and Rubidoux conf irms 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 PM 2.5 

### mass. This is added evidence that indicates that studies designed to consider weekday versus weekend effects in the Sout h Coast Basin should require both Saturday and Sunday measurements. Also, for some of the PM 2.5 

### 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 ar e based upon a time scale that would not capture seasonal effects.

Known compounds associated with vehicular traffic s uch as EC, benzene, toluene, and PAHs showed a reduction in concentrations from the weekd ays to a minimum on Sunday average. PM 2.5 

### EC average concentrations decreased from weekday t o weekend, with a greater than 40% decrease from the maximum on Wednesdays to the mini mum 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 week end 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 PM 2.5 

### mass, OC and associated inorganic ions and metals. PM 2.5 

### mass average day-ofweek patterns for Rubidoux, Los Angeles, and West L ong Beach differed from earlier observations of enhanced concentrations on the week ends 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 seco ndary pollutants, NO 3 

### and SO 4, 

### contributing to the increased overall PM 2.5 

### mass. Nitrate contributed more PM 2.5 

### mass downwind of NH 3 

### sources and the SO 4 

### contributed to PM 2.5 

### mass closer to the commercial and traffic sources. The

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Appendix X-6 data shows a peak maximum on Saturdays for PM 2.5 

### mass, NO 3 

### , SO 4 

### and a minimum on Mondays.

Vanadium exhibited weekday to weekend variability, which shared a similar trend with SO 4 

### in seasonal, day of week, and seasonally at the West L ong 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 hi ghest concentrations located in West Long Beach and the lowest in Rubidoux. If it can be inf erred that vanadium concentrations can be connected to the cargo ship activity due to the shi ps’ use of residual fuel containing vanadium; the vanadium data suggests that emissions due to th ese ships is highest on Saturdays which may correlate to the high Saturday PM 2.5 

### SO 4 

### and NO 3 

### formed by the oxidation of SO 2 

### and NO x 

### 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 tra ffic activity by vehicle type to the chemical analysis which will improve the geographic correlat ion between the data and the traffic observed. The data was not obtainable in the time scale for t his 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).

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Appendix X-7 Figure X-2: Diurnal time series for light-duty veh icles by day of week.

Figure X-3: Diurnal time series for heavy-duty vehi cles by day of week.

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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= 1 7) of PM 2.5 

### mass data taken from SASS

samplers from the fixed site data and the special p urpose MCFP samplers.

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Appendix X-9 West Long Beach

0 5 10 15 20 25 30

M on Tues Wed Thur Fr

i S at S un Ave:

M

- F A v e: S at -Sun[PM2.5Mass] ug/m3

Annual Winter Summer
Central Los Angeles

0 5 10 15 20 25 30

Mon Tues Wed Thur Fri Sat Sun Ave: M-

F Ave: S

a t-Sun[PM2.5Mass] ug/m3

Annual Winter Summer

Rubidoux

0 5 10 15 20 25 30 35

Mon Tues W

e d Thur F

ri Sat Sun Ave: M-F Ave: Sat

- Sun[PM2.5Mass] ug/m3

Annual Winter Summer



### Figure X-5: Average day-of-week PM 2.5 

### mass concentrations by season for West Long Beach,

Los Angeles and Rubidoux.

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Appendix X-10 West Long Beach

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0

M

on Tues W

ed Thur Fr

i S at S un Ave: Mon-Fri

A v e: Sat -Sun[NO3] ug/m3

Annual Winter Summer
Central Los Angeles

0.0 2.0 4.0 6.0 8.0 10.0

Mon T

u es Wed T

h ur Fri S

a t Sun Ave: Mon-Fri

Ave: Sat-Sun[NO3] ug/m3

Annual Winter Summer

Rubidoux

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

Mon T

u es W e d Thur Fr

i Sat Sun Ave: Mon-

F ri Ave: Sat-Sun[NO3] ug/m3

Annual Winter Summer



### Figure X-6: Average day-of-week NO 3 

### concentrations by season for West Long Beach, Los

Angeles and Rubidoux.

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Appendix X-11 West Long Beach

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0

M

on Tues We

d Thur Fri S

at S un Ave: Mon-Fri

Ave: S at-Sun[ SO4] ug/m3

Annual Winter Summer

Central Los Angeles

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0

Mon Tues Wed Th ur Fri Sat Sun Ave: M o n- Fr i Ave: S

a t-Sun[SO4] ug/m3

Annual Winter Summer

Rubidoux

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0

Mon Tu

es W e d Th ur Fri Sat Sun Ave: M o n -Fri Ave: Sa

t - S un[SO4] ug/m3

Annual Winter Summer



### Figure X-7: Average day-of -week SO 4 

### concentrations by season for West Long Beach, Los

Angeles and Rubidoux.

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Appendix X-12 -75% -50% -25% 0% 25% 50% 75%

P

YR B

GHIP
E IN123P

Y R C O R EN E LEVGU%

West Long Beach Los Angeles Rubidoux



### Figure X-8: Percentage change from Wednesday to Sun day 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

Mon Tues Wed Thur Fri Sat S un A

v e: M on-Fr

i A v e: Sat-S

u n[ ] ppb Methylene Chloride
Benzene
Toluene Ethyl benzene (m+p)-Xylenes o-Xylene 2-butanone (MEK)



### Figure X-9: Average selected VOC concentrations fo r West Long Beach by day.

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Appendix X-13 Central Los Angeles

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Mo

n Tues We

d Th u r Fri Sa

t Sun A ve : Mo n -Fr i Ave: Sat-Sun[ ] ppb Methylene Chloride

Benzene
Toluene Ethyl benzene (m+p)-Xylenes o-Xylene 2-butanone (MEK)



### Figure X-10: Average selected VOC concentrations f or 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

Mon Tues Wed Thur Fri Sat S un A

v e: M on-Fr

i A v e: Sat-S

u n[ ] ppb Methylene Chloride
Benzene
Toluene Ethyl benzene (m+p)-Xylenes o-Xylene 2-butanone (MEK)



### Figure X-11: Average selected VOC concentrations f or Rubidoux by day.

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Appendix X-14 -40% -30% -20% -10% 0% 10% 20%

Me

t hyl e ne Chlori

d e B e nz en e Tolu en e Ethyl benzene (m+ p ) - Xyl e n es o- X ylen
e 2-but

a none ( ME K )%

West Long Beach LA Rubidoux



### Figure X-12: Percentage difference of average weekd ay to weekend concentrations for select

VOCs at West Long Beach, Los Angeles, and Rubidoux.

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Appendix X-15 West Long Beach

0 1 2 3 4 5 6 7 8 9

Mon Tues Wed Thur Fr i Sat S

u n Ave:

M-F Ave: S a t -Sun[OC] ug/m3

Annual Winter Summer

Central Los Angeles

0 1 2 3 4 5 6 7 8 9 10

M o n Tues W

e d Th ur Fri Sat Su

n Av

e: M

- F Ave: Sa

t -Sun[OC] ug/m3

Annual Winter Summer

Rubidoux

0 1 2 3 4 5 6 7 8 9 10

Mon T

ues W e d T hur Fri S

at Sun Av

e : M- F A ve: S at

- Su n[OC] ug/m3

Annual Winter Summer



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

Los Angeles and Rubidoux.

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Appendix X-16 West Long Beach

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Mon T

ues W e d Th ur F r i Sat Sun Ave: M-F Ave: Sat

- Sun[EC] ug/m3

Annual Winter Summer
Central Los Angeles

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Mon Tu

es W e d T hur F r i Sat S

un A

v e: M-F A ve: S at

- Su n[EC] ug/m3

Annual Winter Summer

Rubidoux

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Mon T

u es Wed Th

u r Fri Sa

t S un A

ve: M-F Av e : S a t - Sun[EC] ug/m3

Annual Winter Summer



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

Los Angeles and Rubidoux.

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Appendix X-17 -100% -80% -60% -40% -20% 0% 20% 40% 60%



# As Cd Cu Pb Mn Ni Zn

Element NameChange of Wed to Sun (%)



### W. LB LA Rub



### Figure X-15: Percentage differences from Wednesday to Sunday concentrations for PM 2.5



### metals. A negative percentage indicates a drop in concentration on Sunday compared to the Wednesday concentration.

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Appendix X-18 West Long Beach

0 5 10 15 20 25 30

Mon Tues W

ed Thu

r F ri Sat Sun A ve : M on -Fr i Ave

: Sat- S un[ V ] ng/m3

Annual Winter Summer

0 5 10 15 20 25

M

on T ue s W ed T hur Fri Sat S

un A

ve: M

o n-Fri A ve: Sat-Sun[ V ] ng/m3

West Long Beach Los Angeles Rubidoux



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

and also in comparison to day-of-week trends with L os Angeles, and Rubidoux.

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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., Characterizatio n of PM 2.5 

### andPM 10 

### in the South Coast Air Basin of Southern California: Part 1 – Spatial Vari ations, J. Air & Waste Manage. Assoc , 50, 2034-2044, 2000.

California Air Resources Board, Collection and Anal ysis of Weekend/Weekday Emissions Activity Data in the South Coast Air Basin, 2004. ftp://ftp.arb.ca.gov/carbis/aqd/weekendeffect/STI_W E-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.h tm
, viewed April 16, 2008.

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

Lough, G.C., Schauer, J.J., and Lawson, D.R., Day-o f-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 Ca lifornia, 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., Var iability in ammonium nitrate formation and nitric acid depletion with altitude and location ov er 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 M anagement District’s PTEP MultiChannel Samplers, SCAQMD, 1998.