OEHHA REPORT ON ETHANOL IN GASOLINE - 02/15/00

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ADDENDUM

Estimating atmospheric concentrations and the resulting risks posed by the chemicals

of concern for the South Coast Air Basin is a very complex and dynamic process. As

more information is obtained on atmospheric chemistry fate and health effects of these

chemicals, there is the expectation that the modeled atmospheric concentrations and

health risk values will change. Ultimately, the goal is to provide a more accurate analysis

and lower the uncertainty involved in the process. Thus, CARB performed a

supplementary “upper-bound model” simulation on the five fuel scenarios that formed

the original basis of the health impacts assessment. The additional model inputs included

the effects of emission uncertainty and chlorine chemistry, uses updated MTBE and

ethanol rate constants, and corrects boundary conditions for several substances.

The resulting atmospheric concentration estimates are shown in Table A-1, and our

conclusions are as follows:

• The “upper-bound model atmospheric concentrations” presented here are generally

lower than the original atmospheric concentrations presented in Table 4. Thus, the

cumulative hazard indices and cumulative cancer risks are predicted to be lower

under this modified model simulation.

• The only increased atmospheric levels under the modified model simulation were for

ethanol. In some cases these were nearly double the original predicted atmospheric

concentrations. However, the increased ethanol concentrations are expected to have

no impact on health due to ethanol’s low anticipated health risk relative to other fuelrelated chemicals.

• Comparing the atmospheric concentrations among the year 2003 fuel scenarios under

the modified model, there are higher concentrations of acetaldehyde in the scenario

with ethanol (3.5% oxygen) fuel. This difference was less marked in the predictions

of the previous version of the model. However, the health impact of the higher

acetaldehyde concentrations is negligible due to its relatively low health risk

compared to other chemicals of concern.

• Under the modified model, the upper range estimates of PAN concentrations are

higher in the scenario with ethanol (3.5% oxygen) fuel. This difference also was less

marked with the previous version of the model. If the atmospheric concentrations of

PAN were in fact to be substantially increased, this would be of concern since PAN

has a relatively high health impact for acute eye irritation. However, given the total

range of the predicted PAN concentrations and the uncertainty in the model

prediction, it is unclear whether PAN results in a greater health risk under the ethanol

(3.5% oxygen) fuel scenario.

• It appears that the modified model simulations are more sensitive to fuel composition

in the predictions of ethanol, acetaldehyde, and PAN concentrations (and therefore of

the associated health impacts) compared to the other chemicals of concern.
OEHHA REPORT ON ETHANOL IN GASOLINE - 02/15/00

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• There are no indications of substantial differences between the 2003 fuel types in

cancer or noncancer health impacts of airborne exposures, whether the original or

modified model is used. Therefore, there are no grounds to recommend one fuel over

another based on health impacts of air pollution. Similarly, there is no indication that

any of those fuel choices would result in worse health impacts than the current

situation.

In addition to predicted values for PM10, CARB also included in their latest report

predicted values for PM2.5. As with PM10, CARB states that they expect no difference

among 2003 scenarios, and therefore only provided a maximum daily average (81 μg/m3)

and a maximum annual average (25.9 μg/m3) for the 1997 MTBE fuel scenario for PM2.5.

Currently, although U. S. EPA has proposed standards for PM2.5, there are no state or

federal standards in place for this material. However, it is commonly assumed that the

ratio of PM2.5/PM10 is 0.5. Use of the California PM10 standards (30 μg/m3 for the annual

average; 50 μg/m3 for the 24-hr average standard) results in values of 15 and 25 μg/m3,

respectively, as guidance for interpreting the significance of the predicted PM2.5

concentrations. While it is known that these guidance values for particulates are

frequently exceeded in California, according to CARB's report, there is no difference

expected among the 2003 scenarios.

Further discussion and analysis of the atmospheric concentration estimates based on

the modified model simulations can be found in section 4.2.2 of CARB’s “Air Quality

Impacts of the Use of Ethanol in California Reformulated Gasoline. Final Report to the

California Environmental Policy Council. December, 1999”.
OEHHA REPORT ON ETHANOL IN GASOLINE - 02/15/00

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Table A-1. Atmospheric Concentration Estimates: Range of Predicted 1997 and 2003 Air Quality for

the South Coast Air Basin Using “Upper-Bound Model Simulations” a

1997

MTBE

2003

MTBE

2003

Et2%

2003

Et3.5%

2003

Non-Oxy

Acetaldehyde (ppb)

Population-Weighted Annual Exposure

Upper 1.8 1.5 1.5 1.8 1.5

Lower 1.8 1.4 1.5 1.7 1.4

Maximum Daily Average

Upper 11.0 7.9 8.1 8.5 8.0

Lower 5.1 3.7 3.8 4.0 3.7

Maximum 1 Hour Average

Upper 17.7 12.4 12.7 13.6 12.3

Lower 13.8 9.7 9.9 10.6 9.6

Benzene (ppb)

Population-Weighted Annual Average

Upper 1.19 0.68 0.67 0.69 0.63

Lower 1.07 0.61 0.60 0.62 0.57

Maximum Daily Average

Upper 9.5 5.6 5.6 5.7 5.2

Lower 7.4 4.4 4.3 4.4 4.1

Maximum 1 Hour Average

Upper 22.4 13.1 13.1 13.1 12.1

Lower 11.6 6.8 6.8 6.8 6.3

Butadiene (ppb)

Population-Weighted Annual Average

Upper 0.36 0.20 0.19 0.20 0.20

Lower 0.34 0.19 0.18 0.19 0.18

Maximum Daily Average

Upper 2.9 1.5 1.5 1.5 1.5

Lower 2.0 1.1 1.1 1.1 1.1

Maximum 1 Hour Average

Upper 6.7 4.0 4.0 4.0 4.0

Lower 3.1 1.9 1.9 1.9 1.9

Ethanol (ppb)

Population-Weighted Annual Average

Upper 5.4 5.1 10.9 14.2 5.1

Maximum Daily Average

Upper 51 48 98 125 48

Lower 47 45 93 121 44

Maximum 1 Hour Average

Upper 108 101 213 268 101

Lower 78 74 191 267 74
OEHHA REPORT ON ETHANOL IN GASOLINE - 02/15/00

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Table A-1 (continued). Atmospheric Concentration Estimates: Range of Predicted 1997 and 2003 Air

Quality for the South Coast Air Basin Using “Upper-Bound Model Simulations”a

1997

MTBE

2003

MTBE

2003

Et2%

2003

Et3.5%

2003

Non-Oxy

Formaldehyde (ppb)

Population-Weighted Annual Average

Upper 4.7 3.7 3.4 3.5 3.4

Lower 4.7 3.6 3.4 3.5 3.4

Maximum Daily Average

Best 14.0 9.8 9.2 9.6 9.1

Maximum 1 Hour Average

Upper 37.8 26.5 25.1 25.9 24.9

Lower 20.3 14.2 13.5 13.9 13.4

MTBE (ppb)

Population-Weighted Annual Average

Upper 3.9 2.4 0 0 0

Lower 3.6 2.2 0 0 0

Maximum Daily Average

Upper 29 18 0 0 0

Lower 13 8 0 0 0

Maximum 1 Hour Average

Upper 67 41 0 0 0

Lower 19 12 0 0 0

PAN (ppb)b

Maximum Daily Average

Upper

Lower

5.0

2.5

3.3

1.7

3.2

1.6

3.4

1.7

3.1

1.6

Maximum 1 Hour Average

Upper

Lower

10.0

5.0

6.3

3.1

6.0

3.0

6.5

3.2

5.7

2.9
OEHHA REPORT ON ETHANOL IN GASOLINE - 02/15/00

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Table A-1 (continued). Atmospheric Concentration Estimates: Range of Predicted 1997 and 2003 Air

Quality for the South Coast Air Basin Using “Upper-Bound Model Simulations”a

1997

MTBE

2003

MTBE

2003

Et2%

2003

Et3.5%

2003

Non-Oxy

Carbon Monoxide (ppm)

Maximum 8 Hour Average

Best 17.5 12.7 12.7 12.1 13.1c

Maximum 1 Hour Average

Best 22.5 16.1 16.1 15.3 16.6c

Nitrogen Dioxide (ppm)

Maximum Annual Average

Best 0.043 CARB reported, “No difference expected among 2003 scenarios” d

Maximum Daily Average

Best 0.117 0.095 0.095 0.095 0.095

Maximum 1 Hour Average

Best 0.255 0.207 0.207 0.207 0.207

Ozone (ppm)

Maximum 8 Hour Average

Best 0.206 0.165 0.159 0.162 0.159

Maximum 1 Hour Average

Best 0.244 0.190 0.182 0.186 0.182

Particulate Matter (10 microns or less) (mg/m3)

Maximum Annual Geometric Mean

Best 56 CARB reported, “No difference expected among 2003 scenarios” d

Maximum Daily Average

Best 227 CARB reported, “No difference expected among 2003 scenarios” d

a

 Source: Table 4.9 of “Air Quality Impacts of the Use of Ethanol in California Reformulated Gasoline. Final Report to the

California Environmental Policy Council. December, 1999. California Air Resources Board, Cal/EPA”

b

 A population-weighted annual average for PAN was not determined because consistent long-term measurements of

atmospheric PAN have not been performed. See CARB report for details.

c This apparent increase is a function of the emission assumptions. Due to the wintertime oxygenate requirement for the

SoCAB, CO concentrations within the nonattainment area of Los Angeles County will not differ from the 2003 MTBE

baseline.

d

 No significant change compared to 1997 MTBE-fuel scenario. See CARB report for details.
OEHHA REPORT ON ETHANOL IN GASOLINE - 02/15/00

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Tables A-2 and A-3 display the non-cancer Hazard Quotients (HQs) generated from

the modeled atmospheric concentrations in Table A-1. The relatively marginal increase

in the acute atmospheric acetaldehyde concentrations under the 3.5% ethanol fuel

scenario relative to the other fuel scenarios did not translate into a proportionally higher

HQ. This was primarily due to acetaldehyde’s relatively low HQ. In contrast, the upper

range atmospheric PAN concentrations under the 3.5% fuel scenario exhibited a

proportionally increased HQ compared to the other fuel scenarios. Although the

proportional increases in upper range PAN and acetaldehyde concentrations were similar

under this fuel scenario, there is likely greater concern for PAN’s acute effects because of

its relatively high HQ. However, it is not clear how real this difference is because the

lower range PAN HQ is proportionally similar to the lower range PAN HQs in the other

fuel scenarios. Given the total range of the PAN HQs and the uncertainty in the model

prediction, it is unclear whether PAN results in a greater health risk under the 3.5%

ethanol fuel scenario.
OEHHA REPORT ON ETHANOL IN GASOLINE - 02/15/00

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Table A-2. Range of Estimated Maximum Noncancer Hazard Quotients (HQ) for Various Scenarios in

the South Coast Air Basin Based on ARB’s “Upper-Bound Model Simulations”

1997

MTBE

2003

MTBE

2003

Et2%

2003

Et3.5%

2003

NonOxy

Acetaldehyde

Upper 0.4 0.3 0.3 0.4 0.3

Chronic HQ Lower 0.4 0.3 0.3 0.3 0.3

Upper 0.3 0.2 0.2 0.2 0.2

Acute HQ Lower 0.2 0.1 0.2 0.2 0.1

Benzene

Upper 0.06 0.03 0.03 0.03 0.03

Chronic HQ Lower 0.05 0.03 0.03 0.03 0.03

Upper 0.06 0.03 0.03 0.03 0.03

Acute HQ Lower 0.03 0.02 0.02 0.02 0.02

Butadiene

Upper 0.09 0.05 0.05 0.05 0.05

 Chronic HQ Lower 0.09 0.05 0.05 0.05 0.05

Upper 0.05 0.03 0.03 0.03 0.03

 Acute HQ Lower 0.02 0.01 0.01 0.01 0.01

Ethanol

Best 0.0001 0.0001 0.0002 0.0003 0.0001

 Chronic HQ

Upper 0.002 0.002 0.004 0.005 0.002

 Acute HQ Lower 0.001 0.001 0.004 0.005 0.001

Formaldehyde

Upper 2.4 1.9 1.7 1.8 1.7

 Chronic HQ Lower 2.4 1.8 1.7 1.8 1.7

Upper 0.5 0.3 0.3 0.3 0.3

Acute HQ Lower 0.3 0.2 0.2 0.2 0.2

MTBE

Upper 0.005 0.003 0.0 0.0 0.0

 Chronic HQ Lower 0.005 0.003 0.0 0.0 0.0

Upper 0.01 0.006 0.0 0.0 0.0

Acute HQ Lower 0.003 0.002 0.0 0.0 0.0

PAN*

Upper 5.5 3.5 3.3 3.6 3.2 Acute HQ

Lower 2.7 1.7 1.7 1.8 1.6

* A population-weighted annual average for PAN was not determined because consistent long-term measurements of

 atmospheric PAN have not been performed. See CARB report for details.
OEHHA REPORT ON ETHANOL IN GASOLINE - 02/15/00

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Table A-3. Range of Estimated Maximum Noncancer Hazard Quotients (HQ) for Various Scenarios in

the South Coast Air Basin Based on ARB’s “Upper-Bound Model Simulations” – Criteria Air

Pollutants

1997

MTBE

2003

MTBE

2003

Et2%

2003

Et3.5%

2003

NonOxy

Carbon Monoxide

Acute 8 hour HQ 1.9 1.4 1.4 1.3 1.5

Acute 1 hour HQ 1.1 0.8 0.8 0.8 0.8

Nitrogen Dioxide

Chronic HQ 0.8 concentrations not estimated by CARB since no significant

change in Maximum 1-Hour*

Acute 1 hour HQ 1.0 0.8 0.8 0.8 0.8

Ozone

Acute 8 hour HQ 2.6 2.1 2.0 2.0 2.0

Acute 1 hour HQ 2.7 2.1 2.0 2.1 2.0

Particulate Matter (PM10)

Chronic HQ 1.9

Acute 24 hour HQ 4.5

CARB reported, “No significant change expected among

2003 scenarios” for both annual and daily concentrations*

* compared to exposure estimates for the 1997 MTBE-fuel scenario (see CARB report for details)

With regard to the chemicals that are predicted to pose a cancer risk (Table A-4), the

modified model simulation does not change the existing conclusions that, (1) we have

more confidence in the relative risks estimates than the absolute values of concentrations

and risk, and (2) there are no substantial differences between the 2003 fuel types with

regard to the cumulative lifetime cancer risk estimates. As expected, the marginal

increase in atmospheric acetaldehyde concentrations under the 3.5% ethanol fuel scenario

relative to the other fuel scenarios did not result in a significant increase in cumulative

cancer risk. This is primarily due to acetaldehyde’s considerably lower cancer risk

relative to other carcinogens such as benzene.
OEHHA REPORT ON ETHANOL IN GASOLINE - 02/15/00

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Table A-4. Lifetime Cancer Risk from Individual Chemicals and Cumulative Lifetime Cancer Risk for

Each of the Five Fuel Scenarios Based on ARB’s “Upper-Bound Model Simulations”

Chemical 1997

MTBE

2003

MTBE

2003

Et2%

2003

Et3.5%

2003

NonOxy

Upper 8.6 E-6 7.2 E-6 7.2 E-6 8.6 E-6 7.2 E-6 Acetaldehyde

Lower 8.6 E-6 6.7 E-6 7.2 E-6 8.1 E-6 6.7 E-6

Upper 1.1 E-4 6.3 E-5 6.2 E-5 6.4 E-5 5.9 E-5 Benzene

Lower 1.0 E-4 5.7 E-5 5.6 E-5 5.8 E-5 5.3 E-5

Upper 1.3 E-4 7.4 E-5 7.0 E-5 7.4 E-5 7.4 E-5 Butadiene

Lower 1.3 E-4 7.0 E-5 6.7 E-5 7.0 E-5 6.7 E-5

Upper 3.3 E-5 2.6 E-5 2.4 E-5 2.5 E-5 2.4 E-5 Formaldehyde

Lower 3.3 E-5 2.5 E-5 2.4 E-5 2.5 E-5 2.4 E-5

Upper 3.6 E-6 2.2 E-6 0 0 0

MTBE

Lower 3.3 E-6 2.0 E-6 0 0 0

Cumulative Lifetime Upper 2.9 E-4 1.7 E-4 1.6 E-4 1.7 E-4 1.6 E-4

Risk Lower 2.7 E-4 1.6 E-4 1.5 E-4 1.6 E-4 1.5 E-4

Excess Cancer Cases Upper 290 170 160 170 160

Per Million Individuals Lower 270 160 150 160 150

For non-cancer cumulative impacts, the toxicological endpoints of concern, acute eye

irritation (Table A-5), acute respiratory irritation (Table A-6), and chronic respiratory

irritation (Table A-7), remained the same under the modified model simulations. The

only noticeable difference among the fuel scenarios was that for acute eye irritation, the

2003 MTBE and 3.5% ethanol fuels had slightly higher upper range acute HIs relative to

the other year 2003 fuels. The secondary pollutant PAN was primarily responsible for

the increased disparity, due to the higher upper range estimate of its HQ under these two

fuel scenarios. However, the lower range of the cumulative HIs does not show as great a

disparity among the fuel scenarios. There is considerable uncertainty involved in the

model predictions, including both the range of estimates with this “upper bound model”

and the differences between this model and the earlier one. It cannot therefore be

definitely concluded that the 3.5% ethanol fuel will result in greater eye irritation relative

to the other fuels. Improvement in atmospheric modeling and measurement may

eventually resolve this uncertainty.
OEHHA REPORT ON ETHANOL IN GASOLINE - 02/15/00

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Table A-5. Maximum Acute Hazard Quotients (HQ) and Cumulative Acute Hazard Indices (HI) for Eye

Irritation for Each of the Five Fuel Scenarios Based on ARB’s “Upper-Bound Model Simulations”

Chemical 1997

MTBE

2003

MTBE

2003

Et2%

2003

Et3.5%

2003

NonOxy

Upper 0.3 0.2 0.2 0.2 0.2 Acetaldehyde

Lower 0.2 0.1 0.2 0.2 0.1

Upper 0.002 0.002 0.004 0.005 0.002 Ethanol

Lower 0.001 0.001 0.004 0.005 0.001

Upper 0.5 0.3 0.3 0.3 0.3 Formaldehyde

Lower 0.3 0.2 0.2 0.2 0.2

Upper 0.01 0.006 0 0 0

MTBE

Lower 0.003 0.002 0 0 0

Upper 5.5 3.5 3.3 3.6 3.2 PAN

Lower 2.7 1.7 1.7 1.8 1.6

Nitrogen dioxide Best 1.0 0.8 0.8 0.8 0.8

Ozone Best 2.7 2.1 2.0 2.1 2.0

Cumulative HI Upper 10.0 6.9 6.6 7.0 6.5

Lower 6.9 4.9 4.9 5.1 4.7

Table A-6. Maximum Acute Hazard Quotients (HQ) and Cumulative Acute Hazard Indices (HI) for

Respiratory Irritation For Each of the Five Fuel Scenarios Based on ARB’s “Upper-Bound Model

Simulations”

Chemical 1997

MTBE

2003

MTBE

2003

Et2%

2003

Et3.5%

2003

NonOxy

Upper 0.3 0.2 0.2 0.2 0.2 Acetaldehyde

Lower 0.2 0.1 0.2 0.2 0.1

Upper 0.002 0.002 0.004 0.005 0.002 Ethanol

Lower 0.001 0.001 0.004 0.005 0.001

Upper 0.01 0.006 0 0 0

MTBE

Lower 0.003 0.002 0 0 0

Nitrogen dioxide Best 1.0 0.8 0.8 0.8 0.8

Ozone Best 2.7 2.1 2.0 2.1 2.0

Cumulative HI Upper 4.0 3.1 3.0 3.1 3.0

Lower 3.9 3.0 3.0 3.1 2.9
OEHHA REPORT ON ETHANOL IN GASOLINE - 02/15/00

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Table A-7. Maximum Chronic Hazard Quotients (HQ) and Cumulative Chronic Hazard Indices (HI) for

Respiratory Irritation for Each of the Five Fuel Scenarios Based on ARB’s “Upper-Bound Model

Simulations”

Chemical 1997

MTBE

2003

MTBE

2003

Et2%

2003

Et3.5%

2003

NonOxy

Upper 0.4 0.3 0.3 0.4 0.3 Acetaldehyde

Lower 0.4 0.3 0.3 0.3 0.3

Best 0.0001 0.0001 0.0002 0.0003 0.0001 Ethanol

Upper 2.4 1.9 1.7 1.8 1.7 Formaldehyde

Lower 2.4 1.8 1.7 1.8 1.7

Nitrogen dioxide Best 0.8 0.8 0.8 0.8 0.8

PM10 Best 1.9 1.9 1.9 1.9 1.9

Cumulative HI Upper 5.5 4.9 4.7 4.9 4.7

Lower 5.5 4.8 4.7 4.8 4.7

In conclusion, the modified model simulation did not change the original finding that

the different fuel types are substantially the same with regard to airborne cancer and

noncancer health risks. However, given that we have more confidence in the relative risk

estimates than the absolute values of the risks, the slight increase in atmospheric PAN

concentration resulting with the new model input should be further explored.

While the modified model simulation resulted in lower cancer risks and noncancer

health effects under all 2003 fuel scenarios relative to the original model simulation, it

should be emphasized that these changes are modest and do not diminish the need for the

existing regulatory action on automobiles. With the complexities involved in predicting

atmospheric concentrations, it is uncertain whether further refinements of the

atmospheric modeling will increase or decrease the overall health risks. Ultimately, the

differences for cancer and noncancer health risks are not substantial enough between the

2003 fuel types to recommend one fuel over another based on airborne exposure, nor is

there any indication that any of those fuel choices would result in worse health impacts

than the current situation.