California Environmental Protection Agency 

Air Resources Board

Air Quality Impacts of the Use of Ethanol

 in California Reformulated Gasoline

Appendix C

Baseline and Future Air Quality

Concentrations

December 1999
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Table of Contents

C-1. Introduction........................................................................................................... 1

C-2. Data Sources Used ................................................................................................ 1

C-2.1. Criteria Pollutant Monitoring Network........................................................... 2

C-2.2. Toxic Air Contaminant (TAC) Monitoring Network ..................................... 2

C-2.3. Desert Research Institute Study...................................................................... 2

C-2.4. Los Angeles Sepulveda Tunnel Study............................................................ 3

C-2.5. Bay Area Caldecott Tunnel Study.................................................................. 3

C-2.6. Data Quality.................................................................................................... 3

C-2.7. Emission Inventory Data................................................................................. 3

C-3. Establishing Baseline Air Quality Concentrations................................................ 4

C-3.1. Criteria Pollutants........................................................................................... 4

C-3.1.1. Carbon Monoxide..................................................................................... 4

C-3.1.2. Nitrogen Dioxide...................................................................................... 4

C-3.1.3. Ozone........................................................................................................ 4

C-3.1.4. Particulate Matter (PM10, PM2.5).............................................................. 4

C-3.2. Toxic Pollutants.............................................................................................. 4

C-3.2.1. Benzene, 1,3-Butadiene, and MTBE........................................................ 5

C-3.2.2. Acetaldehyde and Formaldehyde ........................................................... 22

C-3.2.3. Toluene, Xylenes, Isobutene, n-Hexane, and n-Heptane ....................... 28

C-3.3. Ethanol.......................................................................................................... 37

C-3.3.1. Maximum Daily Average....................................................................... 37

C-3.3.2. Maximum One-Hour Average ............................................................... 39

C-3.3.3. Population-Weighted Annual Exposure................................................. 39

C-3.4. Alkylates....................................................................................................... 40

C-3.4.1. Ratio Between Total Alkylates and CO................................................. 40

C-3.4.2. Estimated 1997 Concentrations.............................................................. 43

C-3.5. PAN and PPN............................................................................................... 43

C-4. Methods to Estimate Future Air Quality Concentrations.................................... 44

C-4.1. Basic Procedure for all Pollutants................................................................. 44

C-4.1.1. Maximum Daily and One-Hour Averages............................................. 44

C-4.1.2. Population-Weighted Annual Exposure................................................. 45

C-4.2. Special Procedures for Criteria Pollutants.................................................... 45
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C-4.3. Special Procedures for Toxic Pollutants....................................................... 45

C-5. Results................................................................................................................. 46

C-6. References........................................................................................................... 51

List of Tables

Table 3.1 Calculated Atmospheric Lifetimes and MIRs for Selected Compounds........... 6

Table 3.2 Linear Regression Parameters for Correlations Between Ambient

Concentrations of Benzene and CO ................................................................... 8

Table 3.3 Linear Regression Parameters for Correlations Between Ambient

Concentrations of 1,3-Butadiene and CO ........................................................ 12

Table 3.4 Linear Regression Parameters for Correlations Between Ambient

Concentrations of MTBE and CO.................................................................... 16

Table 3.5 Linear Regression Parameters for Correlations Between Ambient

Concentrations of Toluene and CO.................................................................. 30

Table 3.6 Linear Regression Parameters for Correlations Between Ambient

Concentrations of m&p-Xylene and CO.......................................................... 31

Table 3.7 Linear Regression Parameters for Correlations Between Ambient

Concentrations of o-Xylene and CO................................................................ 32

Table 3.8 Linear Regression Parameters for Correlations Between Ambient

Concentrations of Isobutene and CO ............................................................... 33

Table 3.9 Linear Regression Parameters for Correlations Between Ambient

Concentrations of n-Hexane and CO................................................................ 34

Table 3.10 Linear Regression Parameters for Correlations Between Ambient

Concentrations of n-Heptane and CO .............................................................. 35

Table 3.11 Estimated Maximum Annual and One-Hour Toxics Concentrations

using CO as a Surrogate ................................................................................... 36

Table 3.12 Linear Regression Parameters for Correlations Between Ambient

Concentrations of Ethanol and CO................................................................... 38

Table 3.13 Weight Percentage of Each Alkylate of the Total Alkylates Observed

at Each Monitoring Site.................................................................................... 41

Table 3.14 Linear Regression Parameters for Correlations Between Ambient

Concentrations of Total Alkylates and CO...................................................... 42

Table 3.15 Estimated Maximum Annual-Average and One-Hour-average

Alkylate Concentrations Using CO as a Surrogate .......................................... 43

Table 3.16 PAN and PPN Concentrations Measured and Modeled at Azusa.................. 43

Table 3.17 Estimated Maximum 1-Hour-Average and Daily-Average 1997 PAN

and PPN Concentrations................................................................................... 44

Table 5.1 Estimated 1997 Annual-Average Primary and Secondary Acetaldehyde

Based on Different Ratio Assumptions (Concentrations in ppb)..................... 47

Table 5.2 Estimated 1997 Annual-average Primary and Secondary Formaldehyde

Based on Different Ratio Assumptions (Concentrations in ppb)..................... 47

Table 5.3 Estimated Pollutant Concentrations for 1997 and 2003 in the SoCAB........... 48
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List of Figures

Figure 3.1 Benzene versus CO for SoCAB (Four TAC Sites, 1996)................................. 9

Figure 3.2 Benzene versus CO for SoCAB (Three DRI Sites, 1996).............................. 10

Figure 3.3 Benzene versus CO for LA Sepulveda Tunnel (1996)................................... 11

Figure 3.4 1,3-Butadiene versus CO for SoCAB (Four TAC Sites, 1996)...................... 13

Figure 3.5 1,3-Butadiene versus CO for SoCAB (Three DRI Sites, 1996)..................... 14

Figure 3.6 1,3-Butadiene versus CO for LA Sepulveda Tunnel (1996).......................... 15

Figure 3.7 MTBE versus CO for SoCAB (Three TAC Sites, 1996)................................ 17

Figure 3.8 MTBE versus CO for SoCAB (Three DRI Sites, 1996)................................. 18

Figure 3.9 MTBE versus CO for LA Sepulveda Tunnel (1996)...................................... 19

Figure 3.10 Formaldehyde to CO Ratio versus CO for SoCAB (TAC Winter

Data, 1996 and 1997)....................................................................................... 24

Figure 3.11 Formaldehyde to CO Ratio versus CO for SoCAB (Three DRI Sites,

1996)................................................................................................................. 25

Figure 3.12 Acetaldehyde to CO Ratio versus CO for SoCAB (TAC Winter Data,

1996 and 1997)................................................................................................. 26

Figure 3.13 Acetaldehyde to CO Ratio versus CO for SoCAB (Three DRI Sites,

1996)................................................................................................................. 27
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C-1. Introduction

This appendix discusses the methods used to estimate baseline and future air quality

concentrations of important pollutants associated with the phase-out of methyl

tertiary-butyl ether (MTBE) from gasoline. Analyses were only done for the South Coast

Air Basin (SoCAB), the most populated and most polluted air basin in California and the

area with the greatest wealth of air quality data. Separate sections are included on data

sources, methods for establishing baseline concentrations, methods for estimating future

air quality, and results.

C-2. Data Sources Used

The criteria pollutants studied included carbon monoxide (CO), nitrogen dioxide

(NO2), ozone (O3), and particulate matter (PM10). The key toxic air contaminants studied

were benzene, 1,3-butadiene, MTBE, acetaldehyde, and formaldehyde. Ethanol,

peroxyacetyl nitrate (PAN), and peroxypropionyl nitrate (PPN) were also studied. Some

additional compounds (e.g., toluene, xylenes, isobutene, n-hexane, n-heptane, alkylates)

were evaluated for baseline concentrations but were dropped from further analysis

because the potential differences in concentrations due to the use of different fuels

relative to risk levels would not pose a significant health concern. Ambient data for

criteria pollutants in 1996-1998 were used to represent the 1997 baseline to account for

natural year-to-year meteorological fluctuations while only 1996-1997 toxics data were

used to represent the 1997 baseline since 1998 data were not readily available at the time

of data analysis. Data from before 1996 were not used because the fuels used then did

not satisfy the requirements of California Phase 2 Reformulated Gasoline (CaRFG).

Data from the following sources were used in our analysis:

• 1996-1998 Criteria Pollutant Monitoring Network in the SoCAB.

• 1996-1997 ARB Toxic Air Contaminant Network in the SoCAB (TAC data).

• 1996 SoCAB VOC Monitoring Study by Desert Research Institute (DRI data).

• 1996 Desert Research Institute Sepulveda Tunnel Study.

• 1996 and 1997 UC Berkeley Caldecott Tunnel Studies.

• 1997 ARB Emission Inventory for the SoCAB.

These data sets are described briefly below. Because 1997 Southern California

Ozone Study-NARSTO (SCOS97-NARSTO) and Multiple Air Toxics Exposure Study

(MATES) II data were not readily available at the time of data analysis, data from these

studies were not included in our analysis. Although data from a 1999 UC Berkeley

Tunnel Study were proposed to be used in the initial work plan, these data were not

available at the time of our data analysis, and therefore also were not used.
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C-2.1. Criteria Pollutant Monitoring Network

Criteria pollutants are those that have national or state ambient air quality standards.

The Air Resources Board (ARB), in conjunction with local districts, operates a criteria

pollutant monitoring network throughout California. Currently, there are thirty-one

monitoring sites in the SoCAB, monitoring one or more of the pollutants included in our

analysis. Further details regarding each monitoring site can be found in the ARB State

and Local Air Monitoring Network Plan (ARB, 1998a). Data from the statewide network

are stored in the ARB ambient air quality database, Aerometric Data Analysis and

Management (ADAM). The 1996-1998 data used in our analysis were extracted from the

ADAM database in July 1999 and were used to represent our baseline year of 1997.

Hence, changes to data that may have occurred since that time would not be reflected in

our analysis, but these are expected to be small.

C-2.2. Toxic Air Contaminant (TAC) Monitoring Network

The California Air Resources Board operates a toxics sampling network, which

consists of twenty-one monitoring sites throughout California. This network measures

sixty-four pollutants including some of the compounds used in our analysis.

Twenty-four-hour toxics samples are collected on a 1-in-12-day basis. The sampling

sites in the SoCAB are Burbank-West Palm Avenue, Los Angeles-North Main Street,

North Long Beach, Riverside-Rubidoux, and Upland. Both 1996 and 1997 TAC data

used in this study were extracted in December 1998 from ADAM and stored on a

CD-ROM available to the public (ARB, 1998b). 1998 data were not available in time to

use in our analysis. The exception is data for MTBE, which were not on the CD-ROM

and were extracted from ADAM in July 1999.

C-2.3. Desert Research Institute Study

Zielinska et al. (1999) at Desert Research Institute (DRI) undertook a study entitled

“Air Monitoring Program for Determination of the Impacts of the Introduction of

California Phase 2 Reformulated Gasoline on Ambient Air Quality in the SoCAB” in

1995-1996. The objective of this study was to conduct ambient measurements of

speciated hydrocarbons, oxygenated organic gases, methane, carbon monoxide, and

carbon dioxide during the summers of 1995 and 1996 in the SoCAB for providing data

required to determine air quality impacts of CaRFG. In the study, samples were collected

from two source-dominated sites (Burbank-West Palm Avenue and Los Angeles-North

Main Street), a downwind receptor site (Azusa), and a background site (Santa Monica

Beach) for forty-two days (six weeks) throughout the summers (i.e., from July to the end

of September) of 1995 and 1996. Two three-hour samples were taken per sampling day,

one in the morning (600 to 900) during rush hour traffic and one in the afternoon (1300 to

1600). Results for 1996 were used in our analysis.
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C-2.4. Los Angeles Sepulveda Tunnel Study

Gertler et al. (1997) at DRI conducted an impact study of California Phase 2

Reformulated Gasoline at the Los Angeles Sepulveda Tunnel in 1995-1996. The

objectives of this study were to quantify automotive emission rates of CO, NMHC,

speciated hydrocarbons, NOX, and CO2 following the introduction of CaRFG. The

Sepulveda Tunnel runs under part of the Los Angeles International Airport (LAX).

Eighteen sampling experiments were performed in 1996 over the period of July 23 to July

25 during the hours of 0600 to 2000. One-Hour samples were collected at both ends of

the tunnel and analyzed for CO, NMHC, various hydrocarbon species, and NOX. Results

from 17 of the 18 sampling experiments were reported by DRI and used in our analysis.

C-2.5. Bay Area Caldecott Tunnel Study

Kirchstetter et al. (1999a; 1999b; 1999c) at the University of California at Berkeley

performed a similar CaRFG air quality impact study at the Caldecott tunnel, east of San

Francisco Bay on State Highway 24, during the summers of 1994 through 1997. The

tunnel was heavily used during commute hours. In the study, two-hour samples were

collected for analyzing speciated hydrocarbon and carbonyls during the afternoon

commute period (1600 to 1800). On selected days, additional measurements were also

performed earlier in the afternoon. Concentrations of CO2, CO, and NOX were measured

continuously and each was recorded as a five-minute average concentration. The data

collected from 1996 and 1997 were used in our analysis.

C-2.6. Data Quality

The air monitoring data used in this evaluation and described above underwent

various degrees of quality assurance procedures at the time the data were collected. The

quality assurance procedures that apply to the data obtained from the ARB database

(criteria and TAC pollutants) is described in the Quality Assurance Manual of the ARB

Monitoring and Laboratory Division (ARB, 1999a). The procedures used in the special

studies described above are documented in the various reports also referenced above.

C-2.7. Emission Inventory Data

Emission inventories representing summer emissions in 1997 and 2003 for the

SoCAB were extracted from the California Emission Forecasting System (CEFS) (ARB,

1999b) in late May 1999. We speciated the hydrocarbon data and produced summer

inventories as described in Appendix A. Additionally, 1997 annual and winter emission

inventories were extracted from CEFS in late July 1999.
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C-3. Establishing Baseline Air Quality Concentrations

C-3.1. Criteria Pollutants

The criteria pollutants evaluated in this study were carbon monoxide, nitrogen

dioxide, ozone and particulate matter (PM10 and PM2.5). Baseline concentrations to

represent 1997 were based on 1996-1998 data drawn from the ARB ADAM database.

C-3.1.1. Carbon Monoxide

The maximum measured one-hour and eight-hour concentrations over the 1996-1998

period were 22.5 ppm and 17.5 ppm, respectively. Both were measured at the Lynwood

monitoring station.

C-3.1.2. Nitrogen Dioxide

The maximum measured one-hour and daily-average concentrations over the

1996-1998 period were 0.255 ppm and 0.117 ppm, respectively. The one-hour maximum

was measured at the Banning monitoring station and the maximum daily-average

concentration was measured at the Los Angeles-North Main monitoring station. A

maximum annual-average concentration of 0.043 ppm was measured at the Pomona

monitoring station.

C-3.1.3. Ozone

The maximum measured one-hour and eight-hour concentrations over the 1996-1998

period were 0.244 ppm and 0.206 ppm, respectively. Both were measured at the Lake

Gregory monitoring station.

C-3.1.4. Particulate Matter (PM10 and PM2.5)

The maximum measured PM10 daily-average concentration over the 1996-1998

period was 227 μg/m3, measured at the Banning monitoring station. The maximum PM10

annual geometric mean concentration of 56 μg/m3 was measured at the RiversideRubidoux monitoring station. The maximum measured PM2.5 daily-average

concentration over the 1996-1998 period was 81 μg/m3, measured at the North Long

Beach monitoring station. The maximum PM2.5 annual average concentration of

25.9 μg/m3 was measured at the Riverside-Rubidoux monitoring station.

C-3.2. Toxic Pollutants

The toxic pollutants evaluated in our analysis included benzene, 1,3-butadiene,

MTBE, acetaldehyde, formaldehyde, toluene, and xylenes. Isobutene, n-hexane, and nheptane are also discussed in this section because estimates for these three compounds

involve the same analytical procedures. Baseline pollutant concentrations to represent

1997 were based on 1996-1997 data drawn from the ARB toxics database, from DRI

data, and from correlation analyses using these same data, tunnel study results and
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criteria pollutant data. Different approaches were used for different groups of toxic

compounds.

C-3.2.1. Benzene, 1,3-Butadiene, and MTBE

Two different approaches were used to estimate benzene, 1,3-butadiene, and MTBE

concentrations representative of 1997. First, we used measured concentrations directly

from the toxics sampling network. In addition, we developed ratios between these toxic

compounds and carbon monoxide and used them to estimate concentrations at locations

where there were no direct toxics measurements, but there were CO measurements. This

latter approach allowed us to estimate pollutant concentrations at nineteen locations,

rather than the five locations for which toxics sampling data are available. The two

approaches provide a range in estimates. The next section discusses the rationale for

correlating CO with other compounds. The section after that describes the method and

results.

C-3.2.1.1. Rationale for Using Ratios of CO to Other Compounds

The concept of establishing a relationship between CO and other pollutants is based

on the premise that these pollutants are principally emitted from mobile sources and that

for the most part they are primary pollutants. Thus, if CO concentrations are high at a

particular site, the related pollutants can be expected to be high as well. This premise is

reasonably straightforward for compounds that are primary pollutants and for compounds

with low reactivity. However, the relationship holds as well for 1,3-butadiene, which has

much higher reactivity. In part, this is because the peak concentrations for both CO and

1,3-butadiene occur during the winter months when photochemistry is minimal.

Additionally, the continual infusion of fresh emissions, the ubiquitous presence of mobile

sources, and their relatively close proximity to monitoring sites means that there is little

time for atmospheric reaction prior to being measured.

Ultimately, we found good correlation between CO and benzene, 1,3-butadiene,

MTBE, toluene, n-heptane, n-hexane, isobutene, the three xylenes, and the alkylates. The

specific application of the resulting relationships is discussed in the following sections

covering the respective pollutants. Table 3.1 presents the lifetime and the maximum

incremental reactivity MIR of selected compounds.

C-3.2.1.2. Development of Ratios Between Toxic Compounds and CO

To estimate toxics concentrations at locations other than those where toxic

compounds are sampled, we developed ratios between toxic compounds and CO. The

general procedure for determining the ratio between a TAC and CO is described below.

The same procedure was applied to all TACs except the aldehydes.

The first step was to extract the TAC and CO data from the aforementioned data sets

and select sites where both TACs and CO were measured. CO was not measured at the

Upland site (one of five sites in the TAC monitoring network in the SoCAB) in 1996 or

1997, so data collected at Upland were not used in the subsequent calculations. As for

the DRI data set, both the AM data and the combined AM plus PM data were analyzed
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Table 3.1 Calculated Atmospheric Lifetimes and MIRs for Selected Compounds

separately in this study to consider possible differences between the morning period of

direct source contribution and overall behavior during the day.

Then we estimated representative background concentrations and subtracted them

from the extracted data. The background subtraction was to facilitate development of a

single basin-wide ratio between a TAC and CO. Because there was no significant natural

sources for the toxic compounds studied (except aldehydes), atmospheric background for

each TAC was determined to be negligible (zero). However, for CO the background was

estimated to be 100 ppb, based on measurements at Santa Catalina Island, Point

Conception, and San Nicholas Island during SCOS97-NARSTO.

The next step was to exclude concentrations below the level of detection (LOD) and

some outliers because such values could distort the ratios being calculated. For the TAC

monitoring network data set, for example, 19 benzene data values and two CO data

values (out of 109 pairs of matched data values collected in the SoCAB in 1996) were

below their LOD values (ARB, 1998b). As for outliers, two exceptionally high benzene

concentrations, observed on July 7, 1996 (AM) and July 8, 1996 (PM) in the DRI data,

were also excluded in subsequent calculations.

Compound Atmospheric Lifetimea MIRb 

(daylight hours) (g ozone/g NMOG)

Acetaldehyde 5.9 7.25

Alkylates 9.3-92.6 1.0-2.3

Benzene 75.3 0.91

1,3-Butadiene 1.4 12.88

Carbon Monoxide 440.9 0.066

Ethanol 28.3 1.88

Formaldehydec 9.9 9.27

n-Hexane 17.0 1.71

n-Heptane 13.2 1.48

Isobutene 1.8 6.59

MTBE 31.5 0.88

Toluene 15.5 4.24

m-Xylene 3.9 11.04

o-Xylene 6.8 7.87

p-Xylene 6.5 4.56

a. The atmospheric lifetime for each compound was calculated based on

 the recommended OH rate constants (Atkinson, 1994) and a 12-hr average

 OH radical concentration of 3.0x106

 molecule/cm3.

b. Maximum Incremental Reactivity (Carter W.P.L, 1999.)

c. The atmospheric lifetime for formaldehyde is estimated based on the photolysis rate

 of formaldehyde, which dominates over gas-phase reaction with OH radicals.
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Finally, a least-square linear regression technique was applied to the TAC and CO

data and the regression line forced through the origin. Then, the TAC to CO ratios and

correlation coefficients were calculated.

The specific application of these procedures to develop ratios to CO for benzene,

1,3-butadiene, and MTBE are discussed further below.

C-3.2.1.2.1. Benzene

Table 3.2 summarizes the ratios and correlation coefficients between benzene and CO

derived from the five data sets. Ratios calculated from the emission data were based on

ratios of benzene emissions to CO emissions estimated for all sources and for just

on-road sources, respectively. In general, good correlation between benzene and CO data

was observed, except for the 1997 Caldecott data set. No significant difference in ratios

was observed between the DRI AM and AM plus PM data sets. Except for those derived

from the Caldecott data sets, the benzene to CO ratios range from 0.81 to 1.21 (ppb/ppm).

Statewide ratios between benzene and CO derived from TAC data collected throughout

the state in 1996 and 1997 are 1.03 and 0.88 (ppb/ppm), respectively. A ratio of 1.0

(ppb/ppm) was selected as a reasonable ratio of benzene to CO.

Figure 3.1 shows a scatterplot of benzene versus CO for the SoCAB TAC samples

collected in 1996. Data collected in different sites are represented by different symbols.

Scatterplots of benzene versus CO for the DRI data and the Sepulveda tunnel data are

shown in Figure 3.2 and Figure 3.3, respectively.

C-3.2.1.2.2. 1,3-Butadiene

Table 3.3 summarizes the ratios and correlation coefficients for 1,3-butadiene to CO

derived from the aforementioned data sets. Good correlation between 1,3-butadiene and

CO was observed for all data sets except the two tunnel studies and Riverside data. The

ratios range from 0.22 to 0.34 (ppb/ppm), except those obtained from Caldecott tunnel

data. Statewide ratios calculated from TAC data collected throughout California in 1996

and 1997 are 0.29 and 0.28 (ppb/ppm), respectively. A ratio of 0.30 (ppb/ppm) was

selected as a reasonable ratio of 1,3-butadiene to CO. Scatterplots of 1,3-butadiene

versus CO are presented in Figure 3.4, Figure 3.5, and Figure 3.6 for 1996 TAC data,

DRI data, and Sepulveda tunnel data, respectively.

C-3.2.1.2.3. MTBE

Table 3.4 summarizes the ratios and correlation coefficients for MTBE to CO derived

from the same data sets described above. Good correlation was observed for the DRI

data set and the 1997 TAC data. However, correlation was poor for the Caldecott tunnel

data and the 1996 Long Beach data. The ratios obtained from the TAC network data and

the DRI data range from 2.6 to 4.6 (ppb/ppm), while the ratios derived from emission

inventory and tunnel data are substantially lower. Based on these results, a ratio of 3.0

(ppb/ppm) was selected as a reasonable ratio of MTBE to CO. Scatterplots of MTBE

versus CO are shown in Figure 3.7, Figure 3.8, and Figure 3.9 for 1996 TAC data, DRI

data, and Sepulveda data, respectively.
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Table 3.2 Linear Regression Parameters for Correlations Between Ambient Concentrations of Benzene and COa

Ratio R

2 Ratio R2 Ratio R2 Ratio R2 All Sources On-road Sources 

1996

California Statewidec1.03 0.61

South Coast Air Basinc0.90 0.76 1.10 0.93 1.11 0.91 1.21 1.18

Burbank 0.86 0.66 1.14 0.98 1.14 0.98

Los Angeles 0.84 0.92 1.03 0.89 1.05 0.90

Long Beach 1.13 0.81

Riverside 0.98 0.69

Azusa 1.17 0.95 1.19 0.86

Sepulveda Tunnel 1.10 0.96

Caldecott Tunnel 0.59 0.76

1997

California Statewidec0.88 0.82

South Coast Air Basinc0.80 0.89

Burbank 0.78 0.84

Los Angeles 0.82 0.95

Long Beach 0.81 0.88

Caldecott Tunnel 0.53 0.46

Emission InventorybTAC Network DRI Data (AM) DRI Data (AM&PM) Tunnel Data

a. Concentration units are ppmv for CO and ppbv for benzene. CO background of 100 ppb was subtracted in CO measurements. 

 Below-LOD values were excluded in ratio calculation. Regression line was forced through zero.

b. Emission ratios were obtained by using SoCAB emission inventory data in 1997.

c. Statewide and basin-wide ratios and correlation coefficients were calculated using the data collected statewide and in the SoCAB, respectively. 
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Figure 3.1 Benzene versus CO for SoCAB (Four TAC Sites, 1996)

Four TAC Sites, 1996

0.00.51.01.52.02.53.03.54.0

0.0 1.0 2.0 3.0 4.0 

CO (ppmv)

Benzene (ppbv) Burban

LALBRiversi

y=0.90xR2=0.76
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Figure 3.2 Benzene versus CO for SoCAB (Three DRI Sites, 1996)

SoCAB (Three DRI Sites, 1996) 

0.01.02.03.04.05.06.0

0.0 1.0 2.0 3.0 4.0 5.0 

CO (ppmv)

Benzene (ppbv) Azusa Burbank LA

y=1.11xR2=0.91
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Figure 3.3 Benzene versus CO for LA Sepulveda Tunnel (1996)

LA Sepulveda Tunnel (1996)

y = 1.10xR2 = 0.96

05

101520253035

0 5 10 15 20 25 

CO (ppmv)

Benzene (ppbv)
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Table 3.3 Linear Regression Parameters for Correlations Between Ambient Concentrations of 1,3-Bu

Ratio R2 Ratio R2 Ratio R2 Ratio R2 All S

1996California Statewidec 0.29 0.79

South Coast Air Basinc 0.27 0.84 0.26 0.76 0.24 0.71 0Burbank 0.26 0.85 0.26 0.78 0.23 0.72Los Angeles 0.27 0.90 0.25 0.68 0.24 0.72Long Beach 0.34 0.68Riverside 0.26 0.46Azusa 0.27 0.83 0.22 0.64Sepulveda Tunnel 0.24 0.57Caldecott Tunnel 0.13 0.021997California Statewidec 0.28 0.81South Coast Air Basinc 0.28 0.82 Burbank 0.25 0.84 Los Angeles 0.30 0.90 Long Beach 0.30 0.74 Caldecott Tunnel 0.15 0.28

TAC Network DRI Data (AM) DRI Data (AM&PM) Tunnel Data

a. Concentration units are ppmv for CO and ppbv for 1,3-butadiene. CO background of 100 ppb was subtracted in CO measu Below-LOD values were excluded in ratio calculation. Regression line was forced through zero.b. Emission ratios were obtained by using SoCAB emission inventory data in 1997.c. Statewide and basin-wide ratios and correlation coefficients were calculated using the data collected statewide and in the S
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Figure 3.4 1,3-Butadiene versus CO for SoCAB (Four TAC Sites, 1996)

SoCAB (Four TAC Sites, 1996)

0.00.51.01.52.02.5

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0

CO (ppmv)

1,3-Butadiene (ppbv) Burbank LALB

Riverside

y=0.27xR2=0.84
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Figure 3.5 1,3-Butadiene versus CO for SoCAB (Three DRI Sites, 1996)

SoCAB (Three DRI Sites, 1996) 

0.00.20.40.60.81.01.21.4

0.0 1.0 2.0 3.0 4.0 5.0 6.0

CO (ppmv)

1,3-butadiene (ppbv) Azusa Burbank LA

y=0.24xR2=0.71
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Figure 3.6 1,3-Butadiene versus CO for LA Sepulveda Tunnel (1996)

LA Sepulveda Tunnel (1996)

y = 0.24xR2 = 0.57

0.02.04.06.08.0

0 5 10 15 20 25 

CO (ppmv)

1,3-Butadiene (ppbv)
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Table 3.4 Linear Regression Parameters for Correlations Between Ambient Concentrations of MTBE and COa

Ratio R

2 Ratio R2 Ratio R2 Ratio R2 All Sources On-road Sources

1996

South Coast Air Basinc2.90 0.59 4.06 0.84 4.13 0.83 1.82 2.31

Burbank 3.07 0.71 4.56 0.96 4.61 0.95

Los Angeles 2.66 0.72 3.43 0.81 3.51 0.84

Long Beach 3.37 0.10

Riverside

Azusa 4.45 0.90 4.59 0.79

Sepulveda Tunnel 2.28 0.93

Caldecott Tunnel 0.88 0.35

1997

South Coast Air Basinc3.00 0.88

Burbank 3.25 0.90

Los Angeles 2.59 0.93

Long Beach 3.12 0.91

Caldecott Tunnel 0.62 0.33

Emission InventorybTAC Network DRI Data (AM) DRI Data (AM&PM) Tunnel Data

a. Concentration units are ppmv for CO and ppbv for MTBE. CO background of 100 ppb was subtracted in CO measurements. 

 Below-LOD values were excluded in ratio calculation. Regression line was forced through zero.

b. Emission ratios were obtained by using SoCAB emission inventory data in 1997.

c. Basin-wide ratio and correlation coefficient were calculated using the data collected in the SoCAB. 
C-17

Figure 3.7 MTBE versus CO for SoCAB (Three TAC Sites, 1996)

SoCAB (Three TAC Sites, 1996)

0

3

6

9

12

15

18

0.0 1.0 2.0 3.0 4.0 5.0 6.0

CO (ppmv)

MTBE (ppbv)

Burbank

LA

LB

y=2.90x

R2=0.59
C-18

Figure 3.8 MTBE versus CO for SoCAB (Three DRI Sites, 1996)

SoCAB (Three DRI Sites, 1996) 

05

10152025

0.0 1.0 2.0 3.0 4.0 5.0 

CO (ppmv)

MTBE (ppbv) Azu

BurbLA

y=4.13xR2=0.83
C-19

Figure 3.9 MTBE versus CO for LA Sepulveda Tunnel (1996)

LA Sepulveda Tunnel (1996)

y = 2.28xR2 = 0.93

0

102030405060

0 5 10 15 20 25 

CO (ppmv)

MTBE (ppbv)
C-20

C-3.2.1.3. Estimated 1997 Concentrations

In our analyses, we estimated 1997 benzene, 1,3-butadiene, and MTBE

concentrations for the maximum daily average, the maximum one-hour average, and the

population-weighted annual exposure.

C-3.2.1.3.1. Maximum Daily Average

The maximum measured daily-average benzene concentration in the SoCAB from

1996 to 1997 was 7.4 ppb, measured at Burbank on January 10, 1996. The maximum

measured daily-average CO concentration in the SoCAB between 1996 and 1998 was

9.6 ppm, measured at Lynwood on November 1, 1997. Subtracting 0.1 ppm background

from this and multiplying it by the benzene to CO ratio of 1.0 (ppb/ppm), the estimated

maximum daily-average benze ne concentration at Lynwood is 9.5 ppb.

The maximum measured daily-average 1,3-butadiene concentration in the SoCAB

from 1996 to 1997 was 2.0 ppb, measured at Burbank on January 10, 1996. Multiplying

the background-adjusted maximum daily-average CO concentration (9.5 ppm) by the

1,3-butadiene to CO ratio of 0.3 (ppb/ppm), the estimated maximum daily-average

1,3-butadiene concentration at Lynwood is 2.9 ppb.

The maximum measured daily-average MTBE concentration in the SoCAB from

1996 to 1997 was 13 ppb, measured at Burbank on November 24, 1997. Multiplying the

background-adjusted maximum daily-average CO concentration (9.5 ppm) by the MTBE

to CO ratio of 3.0 (ppb/ppm), the estimated maximum daily-average MTBE

concentration at Lynwood is 29 ppb.

C-3.2.1.3.2. Maximum One-Hour Average

The maximum measured daily-average benzene concentration in the SoCAB from

1996 to 1997 was 7.4 ppb, measured at Burbank on January 10, 1996. The corresponding

maximum one-hour and daily-average CO concentrations at Burbank on this day were

11.6 ppm and 7.43 ppm, respectively. Assuming that benzene concentrations vary during

the day in proportion to CO concentrations (since they are both primarily emitted by

motor vehicles and affected by the same meteorology), the estimated maximum one-hour

benzene concentration at Burbank is 11.6 ppb. The maximum measured

one-hour-average CO concentration in the SoCAB between 1996 and 1998 was

22.5 ppm, measured at Lynwood on January 6, 1996. Subtracting 0.1 ppm background

from this and multiplying it by the benzene to CO ratio of 1.0 (ppb/ppm), the estimated

maximum benzene concentration at Lynwood is 22.4 ppb.

The maximum measured daily-average 1,3-butadiene concentration in the SoCAB

from 1996 to 1997 was 2.0 ppb, measured at Burbank on January 10, 1996. The

corresponding maximum one-hour and daily-average CO concentrations at Burbank on

this day were 11.6 ppm and 7.43 ppm, respectively. Assuming that 1,3-butadiene

concentrations vary during the day in proportion to CO concentrations (since they are

both primarily emitted by motor vehicles and affected by the same meteorology), the

estimated maximum one-hour 1,3-butadiene concentration at Burbank is 3.1 ppb.
C-21

Multiplying the background-adjusted maximum one-hour-average CO concentration

(22.4 ppm) by the 1,3-butadiene to CO ratio of 0.3 (ppb/ppm), the estimated maximum

1,3-butadiene concentration at Lynwood is 6.7 ppb.

The maximum measured daily-average MTBE concentration in the SoCAB from

1996 to 1997 was 13 ppb, measured at Burbank on November 24, 1997. The

corresponding maximum one-hour and daily-average CO concentrations at Burbank on

this day were 5.9 ppm and 4.03 ppm, respectively. Assuming that MTBE concentrations

vary during the day in proportion to CO concentrations (since they are both primarily

emitted by motor vehicles and affected by the same meteorology), the estimated

maximum one-hour MTBE concentration at Burbank is 19 ppb. Multiplying the

background-adjusted maximum one-hour-average CO concentration (22.4 ppm) by the

MTBE to CO ratio of 3.0 (ppb/ppm), the estimated maximum MTBE concentration at

Lynwood is 67 ppb.

C-3.2.1.3.3. Population-Weighted Annual Exposure

In calculating health risks, the Office of Environmental Health Hazard Assessment

(OEHHA) uses population-weighted annual pollutant exposure as an indicator of the

concentration to which a typical person is exposed to toxic substances. For benzene,

1,3-butadiene, and MTBE, population-weighted annual-average exposure was calculated

two ways.

The first way used available data from the five toxics monitoring sites in the SoCAB.

Annual averages for 1996 and 1997 were averaged for the individual monitoring sites.

Then the population-weighted annual-average concentration was estimated by

interpolating between the five monitoring sites using a previously developed technique

(ARB, 1993). This interpolation process starts with population data by census tract and

an associated centroid. Then data for any monitoring site within 50 kilometers of the

centroid is used in determining a representative concentration to which people in the

census tract are exposed. In determining this representative concentration, the

contribution from each monitoring site is weighted in proportion to the inverse of the

square of the distance from the population centroid to the monitoring site. To determine

the population-weighted exposure, the population of individual census tracts is multiplied

by their representative concentration, summed over all census tracts and then divided by

the total population across all census tracts. The resulting population-weighted

annual-average concentrations calculated to represent the SoCAB in 1997 were 1.1 ppb

for benzene, 0.34 ppb for 1,3-butadiene, and 3.9 ppb for MTBE, respectively.

The second way used an average of annual-average CO conc entrations for 1996-1998

to calculate benzene, 1,3 butadiene and MTBE concentrations at nineteen monitoring

locations in the SoCAB using the ratios to CO described in Section C-3.2.1.2 applied to

the background-adjusted CO concentrations. Population-weighted annual-average

concentrations of 1.2 ppb benzene, 0.36 ppb 1, 3-butadiene, and 3.6 ppb MTBE were

calculated using the interpolation and averaging procedure described in the paragraph

above.
C-22

C-3.2.2. Acetaldehyde and Formaldehyde

Three different approaches were considered in estimating acetaldehyde and

formaldehyde concentrations representative of 1997. First was the use of measured

concentrations directly from the toxics sampling network. Second was the use of results

from the air quality model simulations. Third was developing relationships between

aldehydes and CO and oxidant so aldehyde concentrations could be estimated at many

more locations than are sampled with the toxics monitoring network. Our attempt to

correlate aldehydes with CO and oxidant was not considered sufficiently reliable and was

abandoned. A brief discussion of that effort is presented in Section C-3.2.2.2.

C-3.2.2.1. Estimated 1997 Concentrations

In our analyses, we estimated 1997 acetaldehyde and formaldehyde concentrations

for the maximum daily average, the maximum one-hour average, and the

population-weighted annual exposure.

C-3.2.2.1.1. Maximum Daily Average

The maximum measured daily-average acetaldehyde concentration in the SoCAB

from 1996 to 1997 was 5.1 ppb, measured at Upland on August 13, 1996. The maximum

measured daily-average formaldehyde concentration in the SoCAB from 1996 to 1997

was 14.0 ppb, measured at Upland on August 13, 1996. In addition, the regional air

quality model simulation for 1997 predicted the basin-wide maximum acetaldehyde and

formaldehyde concentrations to be 6.2 ppb and 11.35 ppb, respectively. Since the

maximum formaldehyde concentration predicted is lower than the maximum measured

value, we considered the measured value to be more representative of the maximum

concentration.

C-3.2.2.1.2. Maximum One-Hour Average

The maximum one-hour aldehyde concentrations were estimated three ways using

three data sources.

First, three-hour DRI data were used as a basis. The maximum three-hour

acetaldehyde concentration measured was 13.88 ppb at Azusa on August 28, 1996

between 1300 and 1600 PDT. Corresponding three-hour and maximum one-hour ozone

concentrations for this period are 0.11 ppm and 0.14 ppm, respectively. Assuming that

acetaldehyde concentrations vary in the afternoon in proportion to ozone concentrations

(since both are strongly influenced by atmospheric chemical reactions at this time of

day), the estimated maximum one-hour acetaldehyde concentration at Azusa is 17.7 ppb.

Similarly for formaldehyde, the maximum 3-hour measurement of 18.17 ppb was in the

afternoon on August 29, 1996 in Burbank. The corresponding estimated one-hour

maximum is 20.3 ppb.

Second, TAC daily-average data were used. The maximum daily-average

acetaldehyde concentration at Upland, measured on August 13, 1996, was 5.1 ppb. The

average ratio of maximum one-hour average to daily-average ozone for monitors

operating in the SoCAB on August 13, 1996 was 2.7. Assuming that acetaldehyde
C-23

concentrations at Upland in August vary in proportion to ozone concentrations

(photochemical model simulations indicate that over 90% of the acetaldehyde and 85% of

the formaldehyde at Upland is from atmospheric chemical reactions on high ozone days),

the maximum one-hour acetaldehyde concentration estimated for Upland is 13.8 ppb.

Similarly, the maximum daily-average formaldehyde concentration at Upland, measured

on August 13, 1996, was 14 ppb and the corresponding estimated maximum one-hour

concentration is 37.8 ppb.

Third, the regional air quality model simulation for 1997 predicted the basin-wide

maximum acetaldehyde and formaldehyde concentrations to be 9.2 ppb and 22.7 ppb,

respectively. Since the model maximum one-hour acetaldehyde concentration of 9.2 ppb

was less than the maximum three-hour measured value, we considered the estimates

made using the measured values to be more representative of maximum concentrations.

C-3.2.2.1.3. Population-Weighted Annual Exposure

There are five monitoring sites in the SoCAB at which acetaldehyde and

formaldehyde measurements were made between 1996 and 1997. The

population-weighted annual-average concentrations were calculated using the

interpolation and averaging procedure described in Section C-3.2.1.3.3 above. The

resulting population-weighted annual-average concentrations calculated to represent the

SoCAB in 1997 are 1.75 ppb for acetaldehyde and 4.65 ppb for formaldehyde.

C-3.2.2.2. Attempt to Correlate Aldehydes with CO and Oxidant

To provide a broader base of data for estimating aldehyde concentrations, an attempt

was made to correlate acetaldehyde and formaldehyde concentrations with carbon

monoxide and oxidant (O3+NO2) concentrations. CO was used as an index of primary

aldehyde emissions and oxidant as an index of the secondary aldehyde produced through

chemical reactions in the atmosphere. To develop a relationship with CO, we plotted

aldehydes versus CO using both the TAC data and 0600 to 0900 data for 1996 from the

DRI study. Because some of the measured acetaldehyde and formaldehyde may be

secondary in origin, we opted to estimate a ratio between primary aldehydes and CO by

plotting the aldehyde to CO ratio versus CO and identifying the minimum ratio that

generally had most if not all of the points above it. For formaldehyde from the toxics

monitoring network, the minimum ratio was 1.4 ppb/ppm CO (see Figure 3.10). For DRI

formaldehyde data, the minimum ratio was 2.1 (see Figure 3.11). For acetaldehyde, the

minimum ratio was 0.50 (see Figure 3.12) for TAC data and 0.95 (see Figure 3.13) for

the DRI data. In developing these minimum ratios we first subtracted background

concentrations of 0.1 ppm CO and 0.5 ppb acetaldehyde or formaldehyde from the

measured values. These background concentrations were determined from measurements

at Santa Catalina Island, Point Conception, and San Nicholas Island during

SCOS97-NARSTO.
C-24

Figure 3.10 Formaldehyde to CO Ratio versus CO for SoCAB (TAC Winter Data, 1996 and 1997)

SoCAB (TAC Winter Data, 1996 and 1997)

0.0

1.0

2.0

3.0

4.0

5.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

CO (ppmv)

Formaldehyde/CO (ppbv/ppmv)

Minimal Ratio=1.4
C-25

Figure 3.11 Formaldehyde to CO Ratio versus CO for SoCAB (Three DRI Sites, 199

SoCAB (Three DRI Sites, 1996)

05

10152025

0.0 1.0 2.0 3.0 4.0 5.0 

CO (ppmv)

Formaldehyde/CO (ppbv/ppmv) Minimal Ratio=2.1
C-26

Figure 3.12 Acetaldehyde to CO Ratio versus CO for SoCAB (TAC Winter Data, 1996 an

SoCAB (TAC Winter Data, 1996 and 1997)

0.00.40.81.21.62.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 

CO (ppmv)

Acetaldehyde/CO (ppbv/ppmv) M inim alR atio=0.50
C-27

Figure 3.13 Acetaldehyde to CO Ratio versus CO for SoCAB (Three DRI Sites, 199

SoCAB (Three DRI Sites, 1996)

0369

12

0.0 1.0 2.0 3.0 4.0 5.0 

CO (ppmv)

Acetaldehyde/CO 

(ppbv/ppmv) Minimal Ratio=0.95
C-28

To determine a factor relating aldehydes to oxidant, we assembled carbon monoxide

and oxidant (O3+NO2) data to match aldehyde measurements from the toxics monitoring

network in the SoCAB. First, we used the aldehyde to CO ratios determined above to

estimate primary acetaldehyde. Then we subtracted this from the measured aldehyde

concentration to obtain a residual aldehyde amount (presumably secondary in origin).

Then we plotted the residual aldehyde versus oxidant, after subtracting a background

concentration of 0.03 ppm oxidant. This background concentration was determined by

looking at the distribution of oxidant concentrations measured in the SoCAB between

1996 and 1998. More than 98.6 % of the measured daily-average concentrations were

0.03 ppm or higher. Using the acetaldehyde to CO ratio of 0.50, a best fit oxidant slope

was determined to be 40 for the TAC data. Using the ratio of 0.95 from the DRI data, the

best fit oxidant slope for TAC data was determined to be 31. Using the formaldehyde to

CO ratio of 1.4, a best fit oxidant slope was determined to be 73 for the TAC data. Using

the ratio of 2.1 from the DRI data, the best fit oxidant slope for TAC data was determined

to be 80. For residual acetaldehyde our R

2

 regression coefficients were .50 to .54,

depending on which slope factors were used. For residual formaldehyde our R

2

regression coefficients were .12 to .37, depending on which slope factors were used.

When we tried applying the CO and oxidant ratios to predict daily aldehyde

concentrations, the maximum predicted concentrations at the toxics monitoring sites in

the SoCAB on actual sampling days were 75% or more higher than measured maximum

values. Therefore, we decided that this approach did not provide sufficiently reliable

estimates to use in our analysis.

C-3.2.3. Toluene, Xylenes, Isobutene, n-Hexane, and n-Heptane

OEHHA requested information on annual exposure and maximum one-hour

concentrations for toluene, xylenes, isobutene, n-hexane, and n-heptane. In response to

this, we did a sensitivity evaluation of 1997 concentrations for these compounds. A key

part of the sensitivity evaluation involved developing ratios between the compounds of

interest and CO. This is discussed below, followed by estimates of 1997 pollutant

concentrations.

After reviewing the estimated 1997 concentrations relative to chronic Reference

Exposure Levels (RELs), OEHHA concluded that even a few-fold difference in

concentration from the use of one fuel over the other is not going to be a significant

health concern. This was because current concentrations of these compounds are one to

two orders of magnitude below their chronic RELs. Thus, airshed modeling analysis was

not performed to predict future air quality concentrations of these compounds.

C-3.2.3.1. Ratio Between Compounds and CO

Following a procedure similar to that described in Section C-3.2.1.2, we developed

ratios between the compounds of interest and CO. The results for each of the compounds

evaluated follow:
C-29

C-3.2.3.1.1. Toluene

Table 3.5 summarizes the ratios and correlation coefficients between toluene and CO

derived from TAC data, DRI data, Sepulveda data, and the emission inventory. This

includes ratios derived from each monitoring site as well as sites combined (basin-wide)

in the same data set. In general, good correlation was observed in all cases except the

Riverside site. The ratios derived from air quality data range from 2.3 to 4.6.

C-3.2.3.1.2. Combined meta- and para-Xylenes

Table 3.6 summarizes the ratios and correlation coefficients between combined metaand para-xylene (m&p-xylene) and CO derived from the same data sets. In general, good

correlation was observed for all data sets. The ratios obtained range from 1.1 to 1.9.

C-3.2.3.1.3. o-Xylene

Table 3.7 summarizes the ratios and correlation coefficients between o-xylene and

CO derived from the same data sets. In general, good correlation was observed for all

data sets. The ratios obtained range from 0.4 to 1.8.

C-3.2.3.1.4. Isobutene

Table 3.8 summarizes the ratios and correlation between isobutene and CO derived

from DRI data, the Sepulveda tunnel study, and the emission inventory. This compound

is not measured in our TAC network. In general, good correlation was observed for all

data sets except Los Angeles. The ratios derived range from 0.9 to 1.6.

C-3.2.3.1.5. n-Hexane

Table 3.9 summarizes the ratios and correlation coefficients between n-hexane and

CO derived from DRI data, the Sepulveda tunnel study, and the emission inventory. Like

isobutene, n-hexane is not measured in our TAC network. In general, good correlation

was observed for all data sets. The ratios derived range from 0.5 to 1.0.

C-3.2.3.1.6. n-Heptane

Table 3.10 summarizes the ratios and correlation coefficients between n-heptane and

CO derived from DRI data, the Sepulveda tunnel study, and the emission inventory. Like

isobutene and n-hexane, n-heptane is not measured in our TAC network. Good

correlation was observed for most of the data sets. The ratios derived range from 0.1 to

0.3.

C-3.2.3.2. Estimated 1997 Concentrations

We made estimates of expected maximum annual-average and maximum

one-hour-average concentrations for toluene, m&p-xylene, o-xylene, isobutene, n-hexane,

and n-Heptane. These were done using available measurements from the toxics

monitoring network and by establishing a ratio to carbon monoxide and multiplying that

ratio by maximum CO concentrations.
C-30

Table 3.5 Linear Regression Parameters for Correlations Between Ambient Concentrations of Toluene and COa

Ratio R

2 Ratio R2 Ratio R2 Ratio R2 All Sources On-road Sources

1996

South Coast Air Basinc2.73 0.84 3.91 0.82 3.96 0.78 3.74

Burbank 2.84 0.85 4.26 0.94 4.35 0.89

Los Angeles 2.55 0.82 3.24 0.89 3.29 0.86

Long Beach 2.77 0.86

Riverside 3.11 0.31

Azusa 4.56 0.88 4.57 0.77

Sepulveda Tunnel 2.27 0.95

Caldecott Tunnel

1997

South Coast Air Basinc2.49 0.76

Burbank 2.66 0.65

Los Angeles 2.36 0.80

Long Beach 2.55 0.75

Caldecott Tunnel

Emission InventorybTAC Network DRI Data (AM) DRI Data (AM&PM) Tunnel Data

a. Concentration units are ppmv for CO and ppbv for toluene. CO background of 100 ppb was subtracted in CO measurements. 

 Below-LOD values were excluded in ratio calculation. Regression line was forced through zero.

b. Emission ratios were obtained by using SoCAB emission inventory data in 1997.

c. Basin-wide ratio and correlation coefficient were calculated using the data collected in the SoCAB. 
C-31

Table 3.6 Linear Regression Parameters for Correlations Between Ambient Concentrations of m&

Ratio R2 Ratio R2 Ratio R2 Ratio R2 All So

1996South Coast Air Basinc 1.29 0.93 1.83 0.87 1.76 0.85 1

Burbank 1.27 0.91 1.90 0.91 1.85 0.94Los Angeles 1.31 0.96 1.68 0.82 1.63 0.84Long Beach 1.38 0.82Riverside 1.32 0.67Azusa 2.00 0.91 1.88 0.79Sepulveda Tunnel 1.33 0.97

Caldecott Tunnel1997South Coast Air Basinc 1.15 0.84 

Burbank 1.16 0.62 Los Angeles 1.15 0.92 Long Beach 1.13 0.88 Caldecott Tunnel

TAC Network DRI Data (AM) DRI Data (AM&PM) Tunnel Data

a. Concentration units are ppmv for CO and ppbv for m&p-xylene. CO background of 100 ppb was subtracted in CO measure Below-LOD values were excluded in ratio calculation. Regression line was forced through zero.b. Emission ratios were obtained by using SoCAB emission inventory data in 1997.c. Basin-wide ratio and correlation coefficient were calculated using the data collected in the SoCAB. 
C-32

Table 3.7 Linear Regression Parameters for Correlations Between Ambient Concentrations of o-

Ratio R2 Ratio R2 Ratio R2 Ratio R2 All So

1996South Coast Air Basinc 0.46 0.96 0.66 0.89 0.64 0.87 0

Burbank 0.46 0.98 0.69 0.92 0.67 0.95Los Angeles 0.45 0.97 0.60 0.85 0.59 0.87Long Beach 0.48 0.87Riverside 0.49 0.72Azusa 0.73 0.92 0.70 0.83Sepulveda Tunnel 1.79 0.97Caldecott Tunnel1997South Coast Air Basinc 0.41 0.84 Burbank 0.41 0.67 Los Angeles 0.42 0.93 Long Beach 0.39 0.70 Caldecott Tunnel

TAC Network DRI Data (AM) DRI Data (AM&PM) Tunnel Data

a. Concentration units are ppmv for CO and ppbv for o-xylene. CO background of 100 ppb was subtracted in CO measurement Below-LOD values were excluded in ratio calculation. Regression line was forced through zero.b. Emission ratios were obtained by using SoCAB emission inventory data in 1997.c. Basin-wide ratio and correlation coefficient were calculated using the data collected in the SoCAB. 
C-33

Table 3.8 Linear Regression Parameters for Correlations Between Ambient Concentrations of Isob

Ratio R2 Ratio R2 Ratio R2 Ratio R2 All Source

1996South Coast Air Basinc 1.05 0.54 0.95 0.62 1.24

Burbank 1.11 0.68 0.99 0.68Los Angeles 0.97 0.40 0.96 0.54Long BeachRiversideAzusa 1.10 0.58 0.89 0.61Sepulveda Tunnel 1.55 0.92Caldecott Tunnel1997South Coast Basin-wide BurbankLos AngelesLong BeachCaldecott Tunnel

TAC Network Tunnel Data Emis

DRI Data (AM) DRI Data (AM&PM)

a. Concentration units are ppmv for CO and ppbv for isobutene. CO background of 100 ppb was subtracted in CO measurem Below-LOD values were excluded in ratio calculation. Regression line was forced through zero.b. Emission ratios were obtained by using SoCAB emission inventory data in 1997.c. Basin-wide ratio and correlation coefficient were calculated using the data collected in the SoCAB. 
C-34

Table 3.9 Linear Regression Parameters for Correlations Between Ambient Concentrations of n-H

Ratio R2 Ratio R2 Ratio R2 Ratio R2 All S

1996South Coast Air Basinc 0.87 0.58 0.91 0.62 0

Burbank 0.96 0.73 1.02 0.65Los Angeles 0.70 0.60 0.74 0.71Long BeachRiversideAzusa 1.03 0.73 1.03 0.74Sepulveda Tunnel 0.49 0.92Caldecott Tunnel1997South Coast Air Basinc

Burbank Los Angeles Long Beach Caldecott Tunnel

TAC Network DRI Data (AM) DRI Data (AM&PM) Tunnel Data

a. Concentration units are ppmv for CO and ppbv for n-hexane. CO background of 100 ppb was subtracted in CO measurem Below-LOD values were excluded in ratio calculation. Regression line was forced through zero.b. Emission ratios were obtained by using SoCAB emission inventory data in 1997.c. Basin-wide ratio and correlation coefficient were calculated using the data collected in the SoCAB. 
C-35

Table 3.10 Linear Regression Parameters for Correlations Between Ambient Concentrations of n-H

Ratio R2 Ratio R2 Ratio R2 Ratio R2 All S

1996South Coast Air Basinc 0.10 0.64 0.10 0.44 0

Burbank 0.10 0.72 0.12 0.36Los Angeles 0.08 0.76 0.08 0.80Long BeachRiversideAzusa 0.12 0.73 0.12 0.54Sepulveda Tunnel 0.27 0.95Caldecott Tunnel1997South Coast Air Basinc

Burbank Los Angeles Long Beach Caldecott Tunnel

TAC Network DRI Data (AM) DRI Data (AM&PM) Tunnel Data

a. Concentration units are ppmv for CO and ppbv for n-heptane. CO background of 100 ppb was subtracted in CO measure Below-LOD values were excluded in ratio calculation. Regression line was forced through zero.b. Emission ratios were obtained by using SoCAB emission inventory data in 1997.c. Basin-wide ratio and correlation coefficient were calculated using the data collected in the SoCAB. 
C-36

C-3.2.3.2.1. Estimated Maximum Using Ratio to CO

We calculated ranges of maximum annual-average and one-hour toxic compound

concentrations using maximum measured CO concentrations in the SoCAB for

1996-1998 and the range of ratios to CO established in Section C-3.2.3.1. The

background-adjusted maximum annual-average and one-hour CO concentrations were

both measured at Lynwood in 1996 and are 2.4 ppm and 22.4 ppm, respectively. The

calculated maximums for the various compounds are shown in Table 3.11.

Table 3.11 Estimated Maximum Annual and One -Hour Toxics Concentrations

using CO as a Surrogate

Compound Annual Average (ppbv) One-Hour Average (ppbv)

Toluene 6-11 52-103

m&p-Xylene 2.6-4.6 25-43

o-Xylene 1.0-4.3 9-40

Isobutene 2.2-3.8 20-36

n-Hexane 1.2-2.4 11-22

n-Heptane 0.2-0.7 2-7

C-3.2.3.2.2. Maximum One-Hour Averages Extrapolated from Maximum Daily

Averages

We estimated the maximum one-hour concentrations by extrapolating from measured

maximum daily concentrations. For toluene and o-xylene the measured maximum daily

concentrations for 1996-1997 in the SoCAB were 19 ppb and 3.5 ppb, respectively, and

were measured at Burbank on January 10, 1996. For m&p-xylene the maximum daily

concentration was 9.7 ppb, measured on January 10, 1996 at Los Angeles-North Main.

We used measured CO daily and maximum one-hour CO concentrations at Burbank and

Los Angeles on January 10, 1996 to extrapolate to maximum one-hour toxics

concentration assuming proportionality between CO and toxics concentrations at each

location. At Burbank the daily and maximum one-hour CO concentrations were

7.43 ppm and 11.6 ppm, respectively. The calculated maximum one-hour-average

toluene and o-xylene concentrations are 29.7 ppb and 5.5 ppb, respectively. At Los

Angeles the daily and maximum one-hour CO concentrations were 7.0 ppm and

10.3 ppm, respectively. The calculated maximum one-hour m&p-xylene concentration is

14.3 ppb. Isobutene, n-hexane, and n-heptane are not measured as part of the TAC

monitoring program, and no estimates were made for these three compounds.

C-3.2.3.2.3. Maximum Measured Annual Average

Based on TAC data for 1996-1997, the maximum measured annual-averages for the

SoCAB were measured at Burbank in 1996 and were 5.12 ppb for toluene, 2.2 ppb for

m&p-xylene, and 0.77 ppb for o-xylene.
C-37

C-3.3. Ethanol

The only ethanol air quality data readily available were those collected by DRI in the

summers of 1995 and 1996. We used the 1996 data as the basis for estimating

representative population-weighted annual and maximum daily average and maximum

one-hour average for 1997. The 1995 data were not used because cleaner burning

gasoline was not widely available until 1996. The highest ethanol concentrations are

expected in winter. Given only summer data, it was challenging to estimate

concentrations in a different season. We opted to use CO as an index of mixing and

dispersion to extrapolate from measured maximum ethanol concentrations in the summer

to a different season.

Similar to other pollutants, we attempted to correlate ethanol with CO. The results

summarized in Table 3.12 showed poor correlation. This was not surprising, given that

on-road vehicles currently emit less than one percent of the estimated ethanol emissions

in the SoCAB (see Appendix A). Correlations with various organic compounds (not

shown) were equally unsuccessful.

C-3.3.1. Maximum Daily Average

The maximum daily-average ethanol concentration is expected to occur in winter, and

was calculated using one procedure with two different assumptions. The general

equation for calculating the maximum daily-average concentration is as follows:

In the equation above, the CO air quality concentrations are divided by the relevant

seasonal (winter or summer) emission estimates to adjust for the effects of higher CO

emissions in winter. This is because CO is being used as an index of dispersion and

mixing under the assumption that CO emissions are kept constant.

This procedure was applied two ways -- once using only data for Los Angeles (the

monitoring site with the highest ethanol measurements), and once using the CO data for

Lynwood (the site with the highest CO concentrations) and ethanol data for Los Angeles.

The latter application was made attempting to represent conditions of very limited mixing

and dispersion that occur at Lynwood. A maximum daily-average ethanol concentration

of 47 ppb was calculated using the Los Angeles maximum as follows:

A similar calculation yielded 51 ppb using Lynwood CO data.

Summer CO Emission

Summer Matching 6hr CO Air Quality

Winter CO Emissions

Annual Maximum 24hr Avg. CO

Ethanol (Max 24hr) = Ethanol(Hi 6hr Ave.) ×

47 ppb

5283 tons/day

3.10 ppm

6520 tons/day

7.0 ppm

Ethanol (Max 24hr) = 25.7 ppb× =
C-38

Table 3.12 Linear Regression Parameters for Correlations Between Ambient Concentrations of Ethanol and COa

Ratio R

2 Ratio R2 Ratio R2 Ratio R2 All Sources On-road Sources

1996

South Coast Air Basinc4.55 0.22 4.43 0.27 3.75 0.04

Burbank 4.25 0.12 4.32 0.23

Los Angeles 4.37 0.17 4.34 0.23

Long Beach

Riverside

Azusa 5.27 0.35 4.71 0.34

Sepulveda Tunnel

Caldecott Tunnel

1997

South Coast Air Basinc

Burbank

Los Angeles

Long Beach

Caldecott Tunnel

Emission InventorybTAC Network DRI Data (AM) DRI Data (AM&PM) Tunnel Data

a. Concentration units are ppmv for CO and ppbv for ethanol. CO background of 100 ppb was subtracted in CO measurements. 

 Below-LOD values were excluded in ratio calculation. Regression line was forced through zero.

b. Emission ratios were obtained by using SoCAB emission inventory data in 1997.

c. Basin-wide ratio and correlation coefficient were calculated using the data collected in the SoCAB. 
C-39

C-3.3.2. Maximum One-Hour Average

The maximum one-hour-average ethanol concentration is expected to occur in winter

and was calculated using one procedure with two different assumptions. The general

equation for calculating the maximum one-hour average is as follows:

This procedure was applied two ways -- once using only data for Los Angeles (the

monitoring site with the highest ethanol measurements), and once using the maximum

one-hour-average CO from Lynwood (the site with the highest CO concentrations) and

the rest of the data from Los Angeles. The latter application was made attempting to

represent conditions of very limited mixing and dispersion that occur at Lynwood. A

maximum one-hour-average ethanol concentration of 78 ppb was calculated using the

Los Angeles maximum as follows:

A similar calculation yielded 108 ppb using Lynwood CO data.

C-3.3.3. Population-Weighted Annual Exposure

There were three sites for which data were collected in the DRI study -- Azusa,

Burbank and Los Angeles -North Main. For each site, an estimated annual-average

ethanol concentration was calculated using carbon monoxide concentrations as an index

of ventilation and dispersion. The following equation was used:

The time period for averaging the summer 1996 CO data was 600-900 and 1300-1600

PDT for July 7, 1996 through September 29, 1996. This corresponds to the time period

over which the DRI ethanol data were collected. Applying the above equation to

Burbank data, we obtain:

Summer CO Emissions

Summer Matching 3hr CO Air Quality

Winter CO Emissions

Annual Maximum 1hr Avg. CO

Ethanol (Max 1hr) = Ethanol (Hi 3hr Ave.) ×

Summer CO Emissions

Summer 1996 CO Air Quality

Annual CO Emissions

Annual CO Air Quality

Ethanol (Annual) = Ethanol (Summer 1996 Avg.) ×

78 ppb

5283 tons/day

3.97 ppm

6520 tons/day

10.3ppm

Ethanol (Max 1hr) = 37.0 ppb× =
C-40

The population-weighted annual-average concentration was calculated using

annual-average data for the three monitoring sites and the procedure described in Section

C-3.2.1.3.3 above. The population-weighted annual-average concentration calculated to

represent the SoCAB in 1997 is 5.4 ppb ethanol.

C-3.4. Alkylates

Similar to the analysis performed for toluene, we also did a sensitivity evaluation of

1997 concentrations for the class of organic compounds known as alkylates. Alkylates is

a class of C6+ branched alkanes and cycloalkanes present in motor vehicle fuels. Based

on the ambient measurements by DRI in the SoCAB in 1996, there were thirty-two

alkylates observed in the atmosphere, which are listed in Table 3.13, together with the

weight percentage of each alkylate of the total alkylates observed at each monitoring site.

We used the DRI data and measured CO concentrations in 1996-1998 to estimate

annual-average and maximum one-hour total alkylate concentrations, using a procedure

similar to that used in Section C-3.2.3 for isobutene, n-hexane, and n-heptane. Below we

discuss the development of a ratio between the total alkylates and CO followed by an

estimate of the 1997 pollutant concentration.

We provided the 1997 estimated pollutant data for alkylates to OEHHA. Since

OEHHA concluded that there are no data that would indicate a toxicological problem

with any of the alkylates, primarily due to lack of data, there was no need to model air

quality concentrations for the 2003 scenarios.

C-3.4.1. Ratio Between Total Alkylates and CO

Following a procedure similar to that described in Section C-3.2.1.2, we developed

ratios between the total alkylates and CO. Both DRI data and Sepulveda Tunnel data

were used in our analysis. Alkylates are not measured in the TAC monitoring network.

Table 3.14 summarizes the ratios and correlation coefficients between total alkylates

and CO derived from DRI data and Sepulveda data. Excellent correlation was observed

for all data sets. The ratios obtained range from 6.5 to 9.6

5.04 ppb

5283 tons/day

1.651ppm

5782 tons/day

1.705 ppm

Ethanol (Annual) = 5.35 ppb× =
C-41

Table 3.13 Weight Percentage of Each Alkylate of the Total Alkylates Observed

at Each Monitoring Site

Chemical Name Azusa Burbank LA-North Main

2,2-Dimethylbutane 3.31% 3.20% 3.34%

2,3-Dimethylbutane 0.08% 0.11% 0.05%

2-Methylpentane 15.93% 15.35% 15.88%

3-Methylpentane 9.36% 9.13% 9.29%

Methylcyclopentane 0.00% 0.00% 0.00%

Methylcyclopentane 9.46% 9.52% 10.06%

2,4-Dimethylpentane 4.26% 4.53% 4.25%

2,2,3-Trimethylbutane 0.20% 0.19% 0.17%

3,3-Dimethylpentane 0.66% 0.62% 0.65%

2,3-Dimethylpentane 6.48% 7.31% 6.73%

1,3-Dimethylcyclopentane 2.06% 2.09% 2.18%

3-Ethylpentane 2.90% 2.78% 3.96%

2,2,4-Trimethylpentane 14.16% 12.65% 12.03%

Methylcyclohexane 6.15% 7.92% 5.78%

2,5-Dimethylhexane 1.68% 1.64% 1.51%

2,4-Dimethylhexane 3.65% 3.61% 3.36%

2,3,4-Trimethylpentane 4.78% 4.14% 3.95%

2-Methylheptane 2.42% 2.70% 2.56%

4-Methylheptane 0.99% 1.04% 1.03%

3-Methylheptane 2.00% 2.18% 2.20%

2,2,5-Trimethylhexane 0.52% 0.52% 0.56%

1,1-Dimethylcyclohexane 0.01% 0.01% 0.02%

2,3,5-Trimethylhexane 1.51% 2.15% 3.36%

2,4-Dimethylheptane 0.13% 0.11% 0.13%

4,4-Dimethylheptane 0.48% 0.48% 0.52%

2,6-Dimethylheptane 0.63% 0.56% 0.61%

2,5-Dimethylheptane 1.75% 1.57% 1.67%

3,3-Dimethylheptane 0.95% 0.72% 0.82%

2-Methyloctane 1.39% 1.36% 1.41%

3-Methyloctane 1.20% 1.12% 1.18%

2,6-Dimethyloctane 0.17% 0.18% 0.16%

3,6-Dimethyloctane 0.73% 0.53% 0.60%

Total 100.00% 100.00% 100.00%
C-42

Table 3.14 Linear Regression Parameters for Correlations Between Ambient Concentrations of Total Alkylates and COa

Ratio R

2 Ratio R2 Ratio R2 Ratio R2 All Sources On-road Sources 

1996

South Coast Air Basinc8.79 0.86 8.88 0.83

Burbank 9.49 0.96 9.64 0.91

Los Angeles 7.77 0.82 7.90 0.85

Long Beach

Riverside

Azusa 9.55 0.92 9.53 0.80

Sepulveda Tunnel 6.53 0.95

Caldecott Tunnel

1997

South Coast Air Basinc

Burbank

Los Angeles

Long Beach

Caldecott Tunnel

Emission InventorybTAC Network DRI Data (AM) DRI Data (AM&PM) Tunnel Data

a. Concentration units are ppmv for CO and ppbv for total alkylates. CO background of 100 ppb was subtracted in CO measurements. 

 Below-LOD values were excluded in ratio calculation. Regression line was forced through zero.

b. Emission ratios were obtained by using SoCAB emission inventory data in 1997.

c. Basin-wide ratio and correlation coefficient were calculated using the data collected in the SoCAB. 
C-43

C-3.4.2. Estimated 1997 Concentrations

We made estimates of expected maximum annual-average and maximum

one-hour-average concentrations for the total alkylates. These were done by using

maximum measured CO concentrations in the SoCAB from 1996-1998 and the range of

ratios to CO established above. The background-adjusted maximum annual-average and

one-hour CO concentrations, both measured at Lynwood in 1996, are 2.4 ppm and

22.4 ppm, respectively. The calculated maximum for the total alkylates is shown in

Table 3.15.

Table 3.15 Estimated Maximum Annual-Average and One-Hour-average

Alkylate Concentrations Using CO as a Surrogate

Compound Annual Average (ppbv) One-Hour Average(ppbv)

Total Alkylates 15.6-23.0 146-216

C-3.5. PAN and PPN

Information used to establish 1997 baseline concentrations for peroxyacetyl nitrate

(PAN) and peroxypropionyl nitrate (PPN) is contained in a separate document (Grosjean,

1999). Table 3.16 compares PAN and PPN measurements made at Azusa during a

special study in 1993 and SCOS97-NARSTO with model predictions for the 1997

baseline scenario. The PPN model species represents higher acyl peroxy nitrates in

addition to peroxypropionyl nitrate. The measured PPN concentrations should be

doubled to roughly approximate the PPN modeled species (Grosjean, personal

communication). Based on these data, we established the range of estimated 1997 PAN

and PPN concentrations, shown in Table 3.17.

Table 3.16 PAN and PPN Concentrations Measured and Modeled at Azusa

Compound Year Max. 1-hr Ave. (ppbv) Max. Daily Ave. (ppbv) Average (ppbv)

1993 9.9 5.0 3.0

1997 4.8 2.1 0.9

PAN

Model 1.9 1.4 -

1993 1.5 0.9 0.5

1997 0.7 - 0.3

PPN

Modela0.3 0.5 -

aThe PPN model species represents higher acyl peroxy nitrates in addition to peroxypropionyl nitrate.
C-44

Table 3.17 Estimated Maximum 1-Hour-Average and Daily-Average 1997

PAN and PPN Concentrations

Compounds Max. 1-hr Ave. (ppbv) Max. Daily Ave. (ppbv)

PAN 5-10 2.5-5.0

PPNa1.5-3.0 1.0-2.0

aThe PPN model species represents higher acyl peroxy nitrates in addition to peroxypropionyl nitrate.

C-4. Methods to Estimate Future Air Quality

Concentrations

C-4.1. Basic Procedure for all Pollutants

Future air quality concentrations were estimated using estimated 1997 concentrations

(Section C-3) and results from the photochemical simulation model for the specific

pollutant of concern in 2003. Unlike the 1997 estimates, we did not use correlations

between CO and toxic compounds to estimate 2003 concentrations. Separate model

simulations were made using 1997 and 2003 baseline (MTBE-based CaRFG), 2003

ethanol at 2.0 wt% oxygen, 2003 ethanol at 3.5 wt% oxygen, and 2003 non-oxygenate.

Although the model simulation covered three days, the only day deemed suitable for

comparison was the third day. This was because results on the first and second day are

strongly affected by the choice of initial conditions. The general procedure for

calculating 2003 air quality was:

Departures from this basic procedure are discussed in Sections C-4.2 and C-4.3.

C-4.1.1. Maximum Daily and One -Hour Averages

For estimating 2003 maximum daily and one-hour-average concentrations, we

normally used the maximum concentrations for the highest grid cell in the modeling

region for the third day of the model simulation as the model air quality parameter in the

equation above. In applying this general procedure, the grid cell with the modeled peak

concentration and the time at which the peak occurred are not required to be the same in

the numerator and denominator of the equation.

Notable exceptions to his general procedure are estimates for benzene, 1,3-butadiene,

carbon monoxide, ethanol, and MTBE. For these, we used the modeled daily average

and one-hour average for the grid cell containing Lynwood, the monitoring site with the

highest measured CO concentrations. The use of the Lynwood grid cell concentrations

was because these pollutants are primary pollutants and Lynwood was the site of the

highest estimated concentrations for these pollutants in 1997.

Modeled 1997 Air Quality

Modeled 2003Air Quality for Fuel X

2003 Air Quality for Fuel X =1997 Air Quality ×
C-45

C-4.1.2. Population-Weighted Annual Exposure

For the population-weighted annual-average exposure, we normally used the

region-wide population-weighted average of the daily-average model results for the third

day of the model simulation as the model air quality parameter in the equation above.

This was believed reasonable for any compound that is a primary pollutant.

Acetaldehyde and formaldehyde have substantial contributions from secondary reactions

in the atmosphere and were treated differently as discussed below.

C-4.2. Special Procedures for Criteria Pollutants

Generally we followed the basic procedures for estimating 2003 air quality

concentrations except as follows:

For 2003 maximum daily and maximum one-hour-average concentrations for CO, we

used the model values for the grid cell containing Lynwood, as discussed above. For

estimating 2003 maximum eight-hour-average ozone concentrations, we used the

maximum grid cell eight-hour-average model results. For maximum eight-hour CO

concentrations, we used model values for the grid cell containing Lynwood.

C-4.3. Special Procedures for Toxic Pollutants

Generally we followed the basic procedures for estimating 2003 air quality

concentrations except as follows:

For maximum daily and maximum one-hour-average concentrations for benzene,

1,3-butadiene, ethanol and MTBE, we used the model values for the grid cell containing

Lynwood, as discussed above.

For ethanol, the maximum daily and maximum one-hour-average concentrations for

Los Angeles-North Main were calculated using model values from the grid cell

containing the Los Angeles-North Main monitoring site.

For acetaldehyde and formaldehyde, we used the basic procedure for the maximum

daily and maximum one-hour averages. This was deemed reasonable because in 1997 the

maximum daily and maximum one-hour concentrations occurred in August, the month of

the model simulation. For calculating the maximum daily and maximum

one-hour-average concentrations, we used total aldehyde concentrations from the model.

For the population-weighted annual-average, a different procedure was needed because

the contribution from primary emission sources versus secondary formation in the

atmosphere was expected to be different in different seasons of the year. The basic

equation for estimating 2003 aldehydes was as follows:

Modeled1997Secondary Air Quality 

Modeled 2003Secondary Air Quality 1997Secondary Air Quality 

Modeled1997 Primary Air Quality 

Modeled 2003Primary Air Quality 1997Primary Air Quality 

2003Air Quality 0.5 ppbbackground

+ ×

+ ×

=
C-46

This requires that the amount of primary and secondary aldehyde be known for 1997

and for the model results. The model was set up so secondary aldehydes were tracked

separately from primary aldehydes. The 1997 Primary Air Quality and 1997 Secondary

Air Quality were determined from 1996-1997 aldehyde and CO data using the following

procedure:

1. Determine primary aldehyde to CO ratio representative of 1997 -- this was done

in Section C-3.2.2.2.

2. Determine average CO for month using all CO measurements at each monitoring

site, adjusted to remove 0.1 ppm background.

3. Determine average CO for each site-month combination using just aldehyde

sampling days, adjusted to remove 0.1 ppm background.

4. Determine average aldehyde (acetaldehyde or formaldehyde) for site-month

combination, adjusted to remove 0.5 ppb background.

5. Estimate average primary aldehyde by month = #1 x #2 unless this exceeds

(#4 / #3) x #2, in which case substitute (#4 / #3) x #2.

6. Estimate average secondary aldehyde by month =( ( #4 - ( #1 x #3 ) ) / #3) x #2;

unless #1 x #2 exceeds (#4 / #3) x #2, in which case substitute zero.

7. Estimate annual-average primary aldehyde = #5 averaged over 12 months of the

year.

8. Estimate annual-average secondary aldehyde = #6 averaged over 12 months of the

year.

This procedure was applied separately to the DRI based and TAC Network based

aldehyde-to-CO ratios developed in Section C-3.2.2.2. The resulting estimated 1997

annual-average primary and secondary aldehyde concentrations are listed in Table 5.1 for

acetaldehyde and Table 5.2 for formaldehyde. To obtain population-weighted results,

2003 aldehyde concentrations were estimated for the four monitoring locations shown in

the tables, and then these values were weighted by population.

C-5. Results

The resulting air quality estimates for 1997 and the different fuel scenarios in 2003

are shown in Table 5.3. In general, the table shows the estimated population-weighted

annual exposure, maximum daily average, and maximum one-hour average for benzene,

1,3-butadiene, acetaldehyde, formaldehyde, carbon monoxide, nitrogen dioxide, ozone,

PM10, PM2.5, ethanol, MTBE, PAN, PPN, and nitric acid. In some cases the pollutant

averaging times are adjusted to show different averaging times. For example, maximum

eight-hour averages instead of maximum daily averages are included for carbon

monoxide and ozone since there are eight-hour standards for these two pollutants. In

addition, the maximum predicted one-hour-average and daily-average concentrations for

nitric acid are also included for 1997 and the various 2003 fuel scenarios. A column on

the table indicates whether each row of the table was used (Y) or was not used (N) in
C-47

producing summaries of the estimated maximum pollutant concentrations. Two reasons

that a particular row may not have been used in a summary are that it reflected summer

concentrations and winter concentrations were higher, or that it reflected 1997 model

results that were lower than estimated 1997 maximum concentrations.

Table 5.1 Estimated 1997 Annual-Average Primary and Secondary Acetaldehyde

Based on Different Ratio Assumptions (Concentrations in ppb)

Table 5.2 Estimated 1997 Annual-average Primary and Secondary

Formaldehyde Based on Different Ratio Assumptions (Concentrations in ppb)

Acetaldehyde Estimated Estimated Estimated Total

Location / Ratio Source to CO Ratio Background Primary Secondary Acetaldehyde

Burbank

TAC Data 0.50 0.50 0.82 0.98 2.30

DRI Data 0.95 0.50 1.36 0.44 2.30

Los Angeles - North Main

TAC Data 0.50 0.50 0.65 0.92 2.07

DRI Data 0.95 0.50 1.10 0.47 2.07

North Long Beach

TAC Data 0.50 0.50 0.44 0.38 1.32

DRI Data 0.95 0.50 0.71 0.11 1.32

Riverside - Rubidoux

TAC Data 0.50 0.50 0.33 0.90 1.73

DRI Data 0.95 0.50 0.57 0.65 1.73

Formaldehyde Estimated Estimated Estimated Total

Location / Ratio Source to CO Ratio Background Primary Secondary Formaldehyde

Burbank

TAC Data 1.40 0.50 2.31 4.01 5.33

DRI Data 2.10 0.50 3.34 2.91 5.33

Los Angeles - North Main

TAC Data 1.40 0.50 1.95 3.95 5.14

DRI Data 2.10 0.50 2.85 2.99 5.14

North Long Beach

TAC Data 1.40 0.50 1.25 2.56 3.51

DRI Data 2.10 0.50 1.88 2.02 3.51

Riverside - Rubidoux

TAC Data 1.40 0.50 1.03 3.15 4.02

DRI Data 2.10 0.50 1.53 2.57 4.02
C-48

Table 5.3 Estimated Pollutant Concentrations for 1997 and 2003 in the SoCAB

Used for 1997 2003 2003 2003 2003

Range? MTBE MTBE Et2.0% Et3.5% NonOxy Comments

Benzene, ppbV

Population Weighted Annual Exposure

Based on Measured Values Y 1.07 0.72 0.70 0.73 0.69

Projected Level based on CO levels Y 1.19 0.80 0.78 0.81 0.76

Model Output Pop Wt Summer Daily N 0.82 0.55 0.54 0.56 0.53 Summer

Maximum Daily Average

Measured Daily Max. Y 7.4 5.3 5.1 5.3 4.9

Projected Maximum based on CO levels Y 9.5 6.8 6.5 6.8 6.4

Model Output - Lynwood N 0.69 0.49 0.47 0.49 0.46 Summer

Maximum from Model Output N 1.72 1.10 1.09 1.10 1.06 Summer

Maximum One-hour Average

Extrapolated from Measured Daily Max. Y 11.6 7.4 7.4 7.4 7.4

Projected Maximum based on CO levels Y 22.4 14.3 14.3 14.3 14.3

Model Output - Lynwood N 1.1 0.7 0.7 0.7 0.7 Summer

Maximum from Model Output N 3.4 1.9 1.9 2.0 1.9 Summer

1,3-Butadiene, ppbV

Population Weighted Annual Exposure

Based on Measured Values Y 0.34 0.19 0.19 0.19 0.19

Projected Level based on CO levels Y 0.36 0.20 0.20 0.20 0.20

Model Output Pop Wt Summer Daily N 0.074 0.042 0.041 0.041 0.041 Summer

Maximum Daily Average

Measured Daily Max. Y 2.0 0.8 0.8 0.8 0.8

Projected Maximum based on CO levels Y 2.9 1.2 1.2 1.2 1.2

Model Output - Lynwood N 0.05 0.02 0.02 0.02 0.02 Summer

Maximum from Model Output N 0.88 0.87 0.87 0.87 0.87 Summer

Maximum One-hour Average

Extrapolated from Measured Daily Max. Y 3.1 1.6 1.6 1.6 1.6

Projected Maximum based on CO levels Y 6.7 3.4 3.4 3.4 3.4

Model Output - Lynwood N 0.2 0.1 0.1 0.1 0.1 Summer

Maximum from Model Output N 3.0 3.0 3.0 3.0 3.0 Summer

Acetaldehyde, ppbV

Population Weighted Annual Exposure

Based on Measured Values 

TAC Based Value and Projection Y 1.75 1.59 1.60 1.74 1.58

DRI/TAC Based Projection Y 1.55 1.58 1.79 1.54

Model Output Pop Wt Summer Daily N 3.23 2.81 2.81 2.93 2.78 Summer

Maximum Daily Average

Measured Daily Max. Y 5.1 5.1 5.1 5.1 5.1

Maximum from Model Output Y 6.2 6.2 6.2 6.2 6.2

Model Output - Upland N 4.43 3.83 3.86 3.99 3.83

Maximum One-hour Average

Extrapolated from DRI Measured Three-hour Max.using O3 Y 17.7 16.7 16.9 17.1 16.9

Extrapolated from Measured Daily Max.using O3 Y 13.8 13.1 13.2 13.4 13.2

Maximum from Model Output N 9.2 8.7 8.8 8.9 8.8

Model Output - Upland N 6.4 5.6 5.5 5.7 5.5
C-49

Used for 1997 2003 2003 2003 2003

Range? MTBE MTBE Et2.0% Et3.5% NonOxy Comments

Formaldehyde, ppbV

Population Weighted Annual Exposure

Based on Measured Values 

TAC Based Value and Projection Y 4.65 4.22 4.06 4.14 4.04

DRI/TAC Based Projection Y 4.12 3.97 4.04 3.95

Model Output Pop Wt Summer Daily N 6.85 5.95 5.74 5.86 5.70 Summer

Maximum Daily Average

Measured Daily Max. Y 14.0 12.2 11.8 12.1 11.7

Maximum from Model Output N 11.35 9.90 9.57 9.79 9.49

Model Output - Upland N 9.13 7.96 7.73 7.90 7.66

Maximum One-hour Average

Extrapolated from DRI Measured Three-hour Max.using O3 Y 20.3 20.6 20.3 20.5 20.3

Extrapolated from Measured Daily Max.using O3 Y 37.8 38.3 37.8 38.1 37.8

Maximum from Model Output Y 22.7 23.0 22.7 22.9 22.7

Model Output - Upland N 13.9 11.8 11.5 11.6 11.4

Carbon Monoxide, ppmV

Maximum Eight-hour Average

Measured Eight-hour Max. Y 17.5 14.3 14.3 13.4 14.7

Model Output - Lynwood N 1.010 0.828 0.828 0.773 0.846 Summer

Maximum from Model Output N 2.43 1.82 1.82 1.66 1.87 Summer

Maximum One-hour Average

Measured One-hour Max. Y 22.5 19.2 19.2 18.0 19.7

Model Output - Lynwood N 1.11 0.95 0.95 0.89 0.97 Summer

Maximum from Model Output N 3.02 2.19 2.19 1.97 2.26 Summer

Nitrogen Dioxide, ppmV

Maximum Annual Average Exposure

Based on Measured Values Y 0.043 No significant difference expected among 2003 scenarios

Maximum Daily Average

Measured Daily Max. Y 0.117 0.098 0.097 0.097 0.097

Maximum from Model Output N 0.073 0.061 0.060 0.060 0.060 Summer

Maximum One-hour Average

Measured One-hour Max. Y 0.255 0.235 0.235 0.235 0.235

Maximum from Model Output N 0.105 0.097 0.097 0.097 0.097 Summer

Ozone, ppbV

Maximum Eight-hour Average

Measured Eight-hour Max. Y 0.206 0.196 0.196 0.196 0.196

Maximum from Model Output N 0.187 0.178 0.178 0.178 0.178

Maximum One-hour Average

Measured One-hour Max. Y 0.244 0.230 0.228 0.228 0.228

Maximum from Model Output N 0.236 0.222 0.220 0.220 0.220
C-50

Used for 1997 2003 2003 2003 2003

Range? MTBE MTBE Et2.0% Et3.5% NonOxy Comments

Particulate Matter (10 μm or less), μg/m3 

Maximum Annual Geometric Mean

Based on Measured Values Y 56 No significant difference expected among 2003 scenarios

Maximum Daily Average

Measured Daily Max. Y 227 No significant difference expected among 2003 scenarios

Particulate Matter (2.5 μm or less), μg/m3 

Maximum Annual Geometric Mean

Based on Measured Values Y 25.9 No significant difference expected among 2003 scenarios

Maximum Daily Average

Measured Daily Max. Y 81 No significant difference expected among 2003 scenarios

Ethanol, ppbV

Population Weighted Annual Exposure

Estimated from Summer Measurements Y 5.4 5.1 7.6 8.8 5.1 Whole Year

Model Output Pop Wt Summer Daily N 2.05 1.95 2.87 3.35 1.94 Summer

Maximum Daily Average

Extrapolated Daily Summer Max. N 21 20 29 33 20 Summer

Estimated Daily Winter Max.

Lynwood Y 51 49 71 81 49 Winter

LA-N Main Y 47 45 64 75 45 Winter

Model Output

Lynwood N 1.86 1.77 2.58 2.96 1.77 Summer

LA-N Main N 4.60 4.40 6.29 7.30 4.38 Summer

Maximum from Model Output N 19.1 17.3 17.9 18.1 17.4 Summer

Maximum One-hour Average

Extrapolated One-hour Summer Max. N 42 39 56 64 39 Summer

Estimated One-hour Winter Max.

Lynwood Y 108 101 145 165 101 Winter

LA-N Main Y 78 74 114 140 74 Winter

Model Output

Lynwood N 3.2 3.0 4.3 4.9 3.0 Summer

LA-N Main N 5.7 5.4 8.3 10.2 5.4 Summer

Maximum from Model Output N 45.6 41.4 42.3 42.8 41.4 Summer

MTBE, ppbV

Population Weighted Annual Exposure

Based on Measured Values Y 3.9 2.6 0 0 0

Projected Level based on CO levels Y 3.6 2.4 0 0 0

Model Output Pop Wt Summer Daily N 1.09 0.72 0 0 0 Summer

Maximum Daily Average

Measured Daily Max. Y 13 9 0 0 0

Projected Maximum based on CO levels Y 29 20 0 0 0

Model Output - Lynwood N 0.97 0.67 0 0 0 Summer

Maximum from Model Output N 2.63 1.67 0 0 0 Summer

Maximum One-hour Average

Extrapolated from Measured Daily Max. Y 19 13 0 0 0

Projected Maximum based on CO levels Y 67 46 0 0 0

Model Output - Lynwood N 1.6 1.1 0 0 0 Summer

Maximum from Model Output N 6.1 3.9 0 0 0 Summer
C-51

Used for 1997 2003 2003 2003 2003

Range? MTBE MTBE Et2.0% Et3.5% NonOxy Comments

PAN, ppbV

Maximum Daily Average

Upper Baseline Y 5.0 4.8 4.8 4.9 4.7

Lower Baseline Y 2.5 2.4 2.4 2.4 2.4

Maximum from Model Output N 2.12 2.03 2.02 2.06 2.00

Maximum One-hour Average

Upper Baseline Y 10.0 9.5 9.3 9.5 9.1

Lower Baseline Y 5.0 4.8 4.7 4.8 4.5

Maximum from Model Output N 4.4 4.2 4.1 4.2 4.0

"Model PPN", ppbV

Maximum Daily Average

Upper Baseline Y 2.0 2.0 2.0 2.0 2.1

Lower Baseline Y 1.0 1.0 1.0 1.0 1.0

Maximum from Model Output N 0.579 0.575 0.588 0.571 0.600

Maximum One-hour Average

Upper Baseline Y 3.0 3.0 3.0 3.0 3.0

Lower Baseline Y 1.5 1.5 1.5 1.5 1.5

Maximum from Model Output N 1.4 1.4 1.4 1.4 1.4

Nitric Acid, ppb (Model Output Only)

Population Weighted Summer Daily Exposure

From Model Y 12.4 11.0 11.0 11.0 11.0

Maximum Daily Average

Maximum from Model Output Y 36.7 32.4 32.3 32.2 32.3
C-52

C-6. References

ARB (Air Resources Board) (1993) “Guidance for Using Air Quality-Related Indicators

in Reporting Progress in Attaining the State Ambient Quality Standards,” Resolution

93-49, Technical Support Division, July.

ARB (Air Resources Board) (1998a) “California State and Local Air Monitoring

Network Plan,” Report TSD 98-005, Planning and Technical Support Division, Air

Quality Data Branch, October (http://www.arb.ca.gov/aqd/namslams/namslams.htm).

ARB (Air Resources Board) (1998b) “California Ambient Air Quality Data 1980-1997,”

CD Number: PTSD-98-010-CD, Planning and Technical Support Division, Air

Quality Data Branch, Client Support Services Section, December.

ARB (Air Resources Board) (1999a) “Air Monitoring Quality Assurance Manual,”

Monitoring and Laboratory Division, June

(http://www.arb.ca.gov/aaqm/qmosqual/qamanual/qamanual.htm).

ARB (Air Resources Board) (1999b) “California Emission Inventory Data,” Planning and

Technical Support Division, Emission Inventory Branch, July

(http://www.arb.ca.gov/emisinv/emsmain/emsmain.htm).

Atkinson, R. (1994) “Gas-Phase Tropospheric Chemistry of Organic Compounds,”

Journal of Physical and Chemical Reference Data, Monograph No. 2.

Carter, W.P.L. (1999) “Documentation of the SAPRC-99 Chemical Mechanism for VOC

Reactivity Assessment,” Draft Report to California Air Resources Board, Contract

92-329 and 95-308, September.

Gertler A.W., J.C. Sagebiel, W.A. Dippel, J.A. Gillies, F. Gofa, and C.M. O’Connor

(1997) “Comparison of 1995 and 1996 Emissions at the Los Angeles Sepulveda

Tunnel Including the Impact of California Phase 2 RFG,” Final Report to

Coordinating Research Council, Inc. and South Coast Air Quality Management

District, Contract No. E-27, October.

Grosjean D. (1999) “Ambient Levels of Peroxyacetyl Nitrate in Southern California,”

Draft Report to California Air Resources Board, September.

Grosjean, D. (1999) Personal Communication, October.

Kirchstetter T.W. and R.A. Harley (1999a) “Impact of Reformulated Fuels on Particle

and Gas-Phase Emissions from Motor Vehicle,” Final Report to California Air

Resources Board, Contract No. 95-330, March.

Kirchstetter T.W., B.C. Singer, R.A. Harley, G.R. Kendall, and M. Traverse (1999b)

“Impact of California Reformulated Gasoline on Motor Vehicle Emissions: 1. Mass

Emission Rates,” Environmental Science & Technology, 33: 318-328.

Kirchstetter T.W., B.C. Singer, R.A. Harley, G.R. Kendall, and M. Traverse (1999c)

“Impact of California Reformulated Gasoline on Motor Vehicle Emissions 2. Volatile

Organic Compound Speciation and Reactivity,” Environmental Science &

Technology, 33: 329-336.
C-53

Zielinska B., J. Sagebiel, G. Harshfield, and E. Fujita (1999) “Air Monitoring Program

for Determination of the Impacts of the Introduction of California’s Phase 2

Reformulated Gasoline on Ambient Air Quality in the SoCAB,” Final Report to

California Air Resources Board, Contract No. 94-322, February.