P.1 

OAR Box 1856 

Prepped by Keeia Richards 

Document Number: 

70) ll-A-07 

Docket Number: 

A-87-11 

Printed 11/24/2008 12:41:50 PM Sheet 70 of 82 
P.2 

m i 

EPA-AA-SDSB-86-01 

Technical Report 

Factors Influencing Benzene Emissions 

from Passenger Car Refueling 

By 

Paul M. Laing 

May 1986 

NOTICE 

Technical Reports do not necessarily represent final E.PA 

decisions or positions. They are intended to present 

technical analysis of issues using data which are 

currently available. The purpose in the release of such 

reports is to facilitate the exchange of technical 

information and - to inform the public of technical 

developments which may form the basis for a final EPA 

decision, position or regulatory action. 

Standards Development and Support Branch 

Emission Control Technology Division 

Office of Mobile Sources 

Office of Air and Radiation 

U. S. Environmental Protection Agency 
P.3_ 

- 2 -

Table of Contents 

Page 

I. Introduction 3 

II. Experimental Approach 3 

III. Sampling and Analytical Technique 4 

IV. Experimental Results , 7 

V. Other Sources of Data 9 

VI. Combined Analysis 12 

VII. Current Benzene Refueling Emission Rates 

and Inventory 16 

VIII. Possible Future Benzene Refueling Emission 

Rates 23 

IX. Summary 25 
P.4 

-3-

I. Introduction 

Hydrocarbon emissions occur during the refueling of 

gasoline-fueled vehicles. These emissions arise from the 

displacement of fuel tank vapors and the evaporation of 

dispensed and spilled liquid fuel. Benzene, which has been 

listed as a hazardous air pollutant based on evidence of 

carcinogenicity, is among the hydrocarbons emitted during 

refueling. In an effort to characterize this problem, EPA 

conducted a test program to measure the amount of benzene 

emitted during a refueling event. The test program conducted 

by EPA was relatively limited in scope, so, to broaden the data 

base for analysis, EPA's data were supplemented with other 

sources of similar data. A combined data analysis resulted in 

the development of an empirical relationship between benzene 

refueling emissions and three parameters that significantly 

affect these emissions. This relationship was used to estimate 

average national benzene refueling emission rates, and the 

effects of lead phase-down and potential fuel RVP controls on 

benzene refueling emissions. 

II. Experimental Approach 

Recommended refueling emissions test procedures were 

adapted for use in the EPA test program. [1]* However, to 

provide the test program with a reliable overall approach for 

measuring uncontrolled benzene refueling emissions, a benzene 

emission measuring system was added to the SHED. 

The benzene measurement system utilized charcoal 

collection tubes to capture hydrocarbons from air samples 

pumped from the SHED (using a small Accuhaler Low Flow Pump) 

during each test. The benzene content of each tube was 

determined by an independent local laboratory (Environmental 

Research Group, Inc.) using Standard NIOSH Method #S311.[2] 

The mass of benzene captured in each tube and the volume of the 

air sampled from the SHED were used to calculate the SHED 

benzene concentration (mass/volume). 

All EPA tests were run on a 1983 4-door Cutlass Supreme 

with an 18.*1 gallon rear fill fuel tank and a fill height of 

about 4 inches. 

Two different fuels were used in the test program. These 

included an Indolene fuel (9.0 psi RVP and 1.36 wt. percent 

benzene) and a commercial unleaded fuel (11.9 psi RVP and 1.49 

wt. percent benzene). Liquid fuel benzene concentrations were 

determined by the local laboratory that performed the charcoal 

tube analyses. 

Numbers in brackets designate references at the end of 

this report. 
^ 5 _ 

_4_ 

Fuel dispensing rates ranged from 5 to 7 gallons/minute, 

with total dispensed volumes ranging from 14.9 to 15.3 gallons 

of gasoline (95 percent fill). As is discussed later, 

dispensed fuel temperatures ranged from 79.8°F to 93°F, and 

tank temperatures ranged from 9l°F to 120°F. 

The refueling emission tests were performed in the manner 

outlined in Table 1. The test vehicle was pushed into the SHED 

"cold," i.e., at ambient temperature. At this point there was 

a ten percent fill in the tank. With the SHED open, the 

vehicle's fuel tank was then raised by heating blankets to the 

desired temperature. 

At the end of the heating phase, the heating blankets were 

unplugged, the fuel nozzle was inserted into the fuel neck, the 

mixing fans were started, and the SHED was sealed. A 

background HC reading was taken inside the sealed SHED prior to 

the refueling operation using a FID (Flame Ionization 

Detector). The refueling was then performed by turning on the 

fuel cart from outside the SHED. The benzene sampling pump was 

then started to draw an air sample across the charcoal 

collection tube. The refueling ended at a 95 percent fill. A 

final FID sample reading was taken, and the fuel tank cap was 

reinstalled. The benzene sampling pump was operated long 

enough to insure that the charcoal collection tube captured 

enough benzene to meet analysis detection and quantification 

limits (usually about 30 minutes). During the charcoal tube 

sampling period the SHED remained closed and sealed. 

Temperature sensors were located at three points inside 

the tank, in the fuel cart, and at various other places in the 

testing setup. Temperature values were recorded approximately 

every two minutes throughout the test. Upon completion of the 

test, the heating blankets and thermocouples were disconnected, 

and the vehicle was removed from the SHED. 

Ill. Sampling and Analytical Technique 

HC levels were measured before and after each refueling 

operation using standard FID techniques. Overall HC emissions 

were calculated by taking the difference between these two 

measurements. 

The following procedure was devised to determine benzene 

emissions. A charcoal collection tube was used to capture 

hydrocarbons from an air sample pumped out of the SHED. The 

tube was then analyzed for benzene content by a local 

laboratory using Standard NIOSH Method #S311.[2] The air 

volume sampled was calculated by multiplying the calibrated 

pump stroke volume by the number of strokes made- during each 

run. (The pump stroke volume was calibrated with the sampling 

equipment train in place.) The benzene concentration in the 

SHED was calculated by dividing the mass of emissions measured 
P.6 

-5-

Table 1 

Test Sequence 

1. Drain and refuel tank to 10 percent of fuel capacity. 

2. Push vehicle into SHED. 

3. Connect heating blankets and thermocouples. 

4. Heat vehicle tank to desired temperature. 

5. Insert fuel nozzle. 

6. Close SHED and start mixing fans. 

7. Take initial HC sample reading (using FID). 

8. Begin refueling. 

9. Start benzene sampling pump. 

10. End refueling when tank is charged to 95 percent of 

capacity. 

11. Take final FID sample reading, and reinstall the fuel tank 

cap. 

12. Operate benzene sampling pump until charcoal collection 

tubes capture enough benzene to meet analysis 

quantification limits (usually about 30 minutes). 

13. Shut off benzene sampling pump and disconnect 

thermocouples and heating blankets. 
P.7 

-6-

by the air volume sampled. The total mass of benzene refueling 

emissions was calculated by multiplying the benzene 

concentration in the SHED by the SHED volume. SHED volume was 

adjusted to take into account the space occupied by the vehicle. 

This procedure is presented more concisely by the 

following equation: 

grams benzene emitted (Vs) 

= (BT) * (1) 

refueling event (VA) 

Where: 

BT = Charcoal tube benzene content, grams 

Vs = SHED volume = 41.8 mJ 

= (Total SHED volume) - (Standard Vehicle Correction 

Factor) 

= (48.1 m3) - (6.3 m3) = 41.8 m3 

VA = Volume of air sample removed from SHED, m3 

= (Ns) * (VP) 

(Ns = Number of pump strokes) 

(VP = Calibrated volume of each pump stroke 

= 6.61 x 10"S m3) 

Equation (1) is based on the following four assumptions: 

i) Benzene levels are relatively constant throughout the SHED. 

ii) The charcoal tube is an efficient trap, allowing no 

significant amount of benzene to escape, 

iii) No significant amount of benzene exists in the SHED prior 

to refueling. 

iv) Temperature and pressure corrections to standard 

conditions were not necessary. 

Benzene refueling emissions (BRE) on a grams 

benzene/gallon basis were obtained by dividing the results from 

Equation (1) by the volume of fuel dispensed into the tank 

during each test. The' concentration of benzene emitted from 

the fillneck in units of parts per million (ppm) can be 

approximated by the following conversion. 

Benzene Cone.(ppm) = 82,700 * BRE(grams benzene/gallon) (2) 

There is one final note about, the use of this technique to 

measure benzene emissions. Very low benzene concentrations 

were experienced throughout the test program. Prior to 

refueling, it was not possible to measure a benzene background 

level with this technique. Benzene levels were only detectable 

after refueling. The local lab's analytical equipment had a 

minimum quantification level of 12 ug (1.25 ppm for a 3 liter 
P.8 

-7-

sample) so sampling times (and air volumes) on the order of 30 

minutes (1-3 liters) were needed to capture the minimum mass of 

benzene which could be accurately quantified. EPA's 

experiments produced benzene mass levels that ranged between 22 

and 32 ug. 

IV. Experimental Results 

EPA determined in earlier work[3] that the following three 

factors significantly influence overall HC refueling emissions: 

1. Dispensed fuel temperature: TD 

2. Difference between tank fuel temperature (TT) and 

dispensed fuel temperature (TD): AT 

3. Fuel volatility: expressed as RVP 

As a result of this earlier work, measurements were made 

throughout the benzene test program to determine what effect 

(if any) these three parameters would have on benzene 

emissions. A fourth factor, liquid fuel benzene concentration, 

was also studied to determine its impact on benzene emissions. 

Table 2 contains the experimental conditions and results 

of the fourteen tests run by EPA. Fuel specifications along 

with tank and dispensed temperature conditions are shown for 

each run. Overall HC emissions in all fourteen runs were 

determined using standard FID techniques. Benzene emissions 

were calculated using Equation (1) for all but two of the 

fourteen runs. In the runs labeled 5A and 5B, unusually high 

HC background levels (over 1600 ppm) existed in the SHED prior 

to refueling. It would seem likely that benzene levels were 

also unusually high at the beginning of these two test runs. 

(Although it not possible to know this for certain because 

background benzene measurements were not taken.) Equation (1), 

which is based on insignificant benzene background levels, was 

therefore not applicable to Runs 5A and 5B. However, it was 

possible to modify Equation (1) to provide a reasonably good 

estimate of the benzene emissions occurring in these two runs. 

The modified equation that follows is based upon the assumption 

that the benzene mass fraction of the background hydrocarbons 

was equal to that found in the refueling vapors. 

adjusted grams benzene (Vs) (HC2 - HCi) 

refueling event (VA) (HC*) 

Where: 

BT, Vs, and VA are the same as in Equation (1). 

HCi = SHED hydrocarbon level prior to refueling, ppm 

HC2 = SHED hydrocarbon level after refueling, ppm 
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This correction appears reasonable given the cause of the 

background emissions (excess emissions related to high tank 

temperatures), the consistency of the final results, and the 

fact that there were no significant differences between 

statistical analyses performed on datasets which did and did 

not include Runs 5A and 5B. 

At the conclusion of the planned effort, it soon became 

apparent that the EPA test program was too limited to produce a 

meaningful relationship among the test parameters. Too few 

tests were run, and the fuel benzene and temperature ranges 

evaluated were too limited. Therefore, other sources of data 

were sought to supplement the EPA data. 

V. Other Sources of Data 

Benzene refueling emission information was found in the 

following five published sources: "Onboard Control of Vehicle 

Refueling Emissions, Demonstration of Feasibility," API 

Publication #4306;[4] "Benzene Emissions from Motor Vehicles," 

Clarke;[5] "Factors Influencing the Composition and Quantity 

of Passenger Car Refueling Emissions - Part I," Lemmons and 

Gabele;[6] "Composition of Vapor Emitted from a Vehicle Gas 

Tank During Refueling," SAE Technical Paper Series #860086;[7] 

and "Benzene Emissions From Passenger Cars," CONCAWE Report 

#12/83.[8] As is discussed further below, three of these five 

sources (API #4306, Clarke, and Lemmons and Gabele) contained 

data that were compatible with EPA's data and were used in the 

final analysis of benzene rates. Table 3 contains the data 

taken from these three other sources. The following five 

paragraphs describe the procedures and the compatibility of the 

experiments performed in each of these reports. 

The data from API report #4306[4] were collected using 

standard SHED techniques and two different vehicles. The test 

fuel was spiked to 4.99 wt. percent benzene to make measurement 

of benzene concentration by gas chromatography possible. The 

vehicles were charged with a 90 percent fill of test fuel at 

85°F following a diurnal test. This procedure is comparable to 

the approach used in the EPA test program. Two tests at 

identical temperature conditions were performed on each vehicle 

providing four data points with units of grams benzene/gallon. 

The Clarke report[5] involved six tests on two California 

specification vehicles. The tests were performed using 

standard SHED refueling procedures with a fuel containing 0.83 

wt. percent benzene. This report contained a total of six data 

points in units of grams benzene/gallon. 

The data cited in the Lemmons and Gabele report[6] were 

also obtained using standard SHED techniques. This report was 

obtained in draft form with a caution from the authors about 

the applicability of the data to the vehicle fleet in general 
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due to the extreme temperature conditions at which some of the 

experiments were run. Therefore, these data were inspected for 

consistency with theoretical expectations and other comparable 

data. In total, eleven test points were available from this 

source. Based upon trends in this and other data sources, 

ideal vapor-liquid behavior, past experience, and engineering 

judgment, most of the data was found to be reasonable and 

consistent. However, one of the experiments involving extreme 

temperature conditions did produce unexpected results. The 

experiment involving the combination of vehicle tank and 

dispensed temperatures which should have resulted in the 

highest total HC emissions based on earlier EPA work,[3] 

actually had the lowest overall HC emission level in the 

Lemmons and Gabele work. This "abnormal" result could be due 

to excessive fuel weathering at the high temperature prior to 

refueling. This one data point was eliminated. In the end, 

ten data points remained on a grams benzene/gallon basis. 

The data presented in SAE Paper #860086[7] were obtained 

from four test runs using standard SHED techniques. These 

tests differed from the other sources in two general ways. 

First, they were bench tests performed on a side fill fuel tank 

mounted on a stand. Also, no attempt was made during these 

experiments to determine the quantity of the refueling 

emissions; only the composition of these emissions was 

measured. Therefore, these data were only available on a mass 

fraction basis (in units of grams benzene/grams HC) and could 

not be used in the final analysis because they were not 

available in the proper format (grams benzene/gallon). 

The CONCAWE report[8] obtained data using fuels and 

vehicles of European specifications. The experiments were run 

using modified SHED techniques to measure refueling emissions. 

These data were not compatible with the other sources because 

an unusual test procedure was used in these experiments. The 

fuel tank was preconditioned with a 40 percent charge of test 

fuel prior to the refueling test to saturate the tank's vapor 

space. This initial charge was drained from the tank, and then 

the tank was refueled to 40 percent. The drain of this initial 

charge is inconsistent with standard procedures and has 

indeterminable effects on the results. One likely problem in 

this test approach is that the vapor space in the fuel tank 

would not be saturated prior to refueling. Therefore, the 

CONCAWE data were not used in this report. 

The end result of combining the EPA data with the three 

compatible sources was the formation of a combined data set 

obtained from a broader set of test conditions. Tables 2 and 3 

show these data sets which contain a total of 34 data points 

and are in units of grams benzene/gallon. 
P.13 

-12-

VI. Combined Analysis 

A primary goal of this study was the development of an 

empirical relationship between benzene refueling emissions and 

fuel/temperature conditions. This relationship has several 

important uses such as the estimation of a national benzene 

emission rate and the prediction of fuel alteration effects. A 

relationship between benzene refueling emissions and three 

significant parameters was developed by fitting a multivariate 

linear regression model to the data in Tables 2 and 3. This 

relationship has the following form: 

grams benzene/gallon = (.035 * %Bz) - (1.60 x 10"* * T0) 

- (4.24 x 10-4 * AT) (4) 

Where: 

%Bz = Fuel benzene concentration (wt.%), expressed as 

percent not decimal fraction. 

TD = Dispense fuel temperature (°F). 

AT = Difference between fuel tank temperature and 

dispensed fuel temperature (F°) 

R

2

 = 0.9607 

SE = 0.0092 

Each of the parameters included in the regression model is 

statistically significant at a confidence of at least 99 

percent, i.e., the probability that any of the three parameters 

has no effect upon benzene refueling emissions is less than one 

percent. The correlation coefficients among the predictor 

variables ranged from 0.04 to 0.30 which indicates a high 

degree of predictor variable independence. 

A regression model that included fuel RVP as a factor was 

also fitted to this data and showed RVP to have a relatively 

insignificant effect , on benzene refueling emissions 

(significance = 0.40). Also, for reasons not fully understood, 

this regression model showed T0 to have a fairly 

insignificant effect on refueling emissions (significance = 

0.46). This model is not recommended for use, but it is 

included in Appendix A for those who may be interested. 

Of the three equation parameters, fuel benzene content 

expressed in weight percent (%Bz) has by far the greatest 

impact on benzene refueling emissions. Stated in another way, 

small changes in %Bz greatly affect the amount of benzene 

emitted during refueling. The degree to which this phenomenon 

occurs can be seen graphically in Figure l. Figure 1 is a plot 

of Equation 4. Each of the three lines in this figure is the 
P.14 

-13-

result of varying one of the three equation parameters (%Bz, 

T0» or AT), while keeping the other two equation parameters 

constant at current national annual average conditions. This 

figure clearly shows that fuel benzene content has the greatest 

influence on benzene refueling emissions. This is also obvious 

by a comparison of the %Bz, T0, and AT coefficients in 

equation 4. 

It is also interesting to note the effect that T0 has on 

benzene refueling emissions. Figure 1 shows a weak inverse 

relationship between T0 and benzene refueling emissions. 

While it is expected that TD should have only a minor effect 

on benzene refueling emissions because all of the refueling 

tests were performed at temperatures well below the 175°F 

boiling point of benzene, it is counterintuitive to expect that 

benzene refueling emissions should decrease with increasing 

dispensed fuel temperature. However, this result is easily 

explained. It is important to remember that the effect TD 

has on benzene refueling emissions (i.e., the sign and 

magnitude of the coefficient) was determined by a multivariate 

statistical analysis. Such an analysis attempts to account for 

the effects of several different influences by determining the 

coefficients of the parameters in the prediction equation which 

are best able- to predict the actual results of the emission 

tests. Sometimes the effects of the individual influences are 

not completely separable, and the regression analysis tends to 

distort their individual influences especially when one of the 

parameters has only limited effects. With all of the refueling 

tests being performed at temperatures well below the boiling 

point of benzene, it is possible that other, more substantial, 

variability exists which is not taken into account by the 

prediction equation (such as fuel delivery rate and vehicle 

fuel system configuration). These other effects have the 

potential to distort the contribution of T0 and cause a 

negative TD coefficient to provide the best fit line. 

Figure 2 shows the degree to which the prediction equation 

fits the actual data. In this figure, the residuals (actual 

benzene refueling emissions minus predicted benzene refueling 

emissions) are plotted against the predicted benzene refueling 

emissions. • Most of the predicted values are seen to fall 

within 0.01 grams benzene/gallon of the actual values. 

Although this range is quite reasonable, it is also apparent 

that a certain amount of variability exists in the results. 

Much of this variability can be explained by influences such as 

differences in vehicle fuel system configuration, fuel delivery 

rate, analytical measurement variability, and a certain degree 

of inherent test to test and vehicle to vehicle test 

variability. 

It is interesting to note that the two largest residuals 

(+0.025 and -0.016 grams benzene/gallon), both from the Lemmons 

and Gabele report,[6] are the result of experiments which 

involved dispensed fuel temperatures at the outer limits of 
P.15 

-14-

Figure 1 

Benzene- Itefueling Bnissions Fran Prediction Equaticn 4 

(Displacement Loss cnly) 

0.14 -r0.12 - -

0.10 . _ 

S 

& 0.08 

03 

& 

0.06 __ 

with T & AT constant .@ nat'n avg. conditions 

•with % BztTQ constant @ nat'n avg. conditions 

with % BZIAT constant @ nat'n avg. conditi 

0.04 __ 

0.02 _ . 

Wt. % Bz 0 

(in fuel) 

T (F°) 

_C lit -t & ~""+t +to +15 +20 

TD CF) 

52 * 

h 

62 J h 

72 ^ 

h 

82 87 
4 

t* 

FIGURE: 2 

Residual Values Vs. Predicted Values 

+ 0.025 _i 

+ 0.020 J 

+ 0.015 J 

+ o.oio 4 

+ 0.005 H 

- 0.005 -J 

- 0.010 J 

- 0.015 J 

t 

++ 

+ 

0.03 

I 

0.01 

0.05 

• I l i • i 

0.07 0.09 0.11 0.13 0.15 0.17 

Predicted Baission (grains benzene/gallcn) 

0.19 

ui I 
P.17 

-16-

values tested (92 and 45°F, respectively). The large residual 

at 45°F suggests that the assumption of linearity is not valid 

at such low temperatures. This deviation from linearity is not 

unique. Similar results have been observed in studies of total 

hydrocarbon refueling emissions. For example, in "A Study of 

Variables that Effect the Amount of Vapor Emitted During the 

Refueling of Automobiles,"[9] refueling emissions are seen to 

deviate from linearity as AT grows increasingly negative. In 

fact, this study showed that at large negative ATs, actual 

refueling emissions were far less than the prediction of a 

linear model. This result compares closely with the large 

negative residual of -0.016 grams benzene/gallon (when TD = 

45°F and AT = -30F°) found in this report. The other large 

residual mentioned above (+0.025 grams benzene/gallon when TD 

= 92°F) is due possibly to the prediction equation's potential 

distortion of TD's contribution to overall benzene refueling 

emissions. As was discussed earlier, it is likely that as TD 

increases, benzene refueling emissions will also increase. 

However, this is in opposition to the prediction equation 

estimate, and therefore, at high dispensed fuel temperatures 

(when the actual contribution of TD is expected to be 

substantially positive) a large residual results. 

It is also interesting to compare Figure 2 with a similar 

figure (Figure 3) that depicts the total HC refueling emission 

prediction equation residuals .from "Refueling Emissions from 

Uncontrolled Vehicles".[3] Both figures show similar point 

scatters with the majority of predicted emission rates falling 

within approximately 25 percent of their actual value. The 

biggest difference between the two figures is that Figure 2 

lacks data points in the mid-range of its predicted emission 

values (the result of having only a limited number of different 

gasoline benzene concentrations). In general, Figure 2 shows 

the prediction equation to fit the data quite well. 

At this point it should be noted that because Equation (4) 

is an empirical relationship developed specifically for the 

range of test fuel and temperature conditions used in the 

various experimental studies, the accuracy of its use outside 

this test range has not been evaluated, and caution should be 

used when applying this equation to conditions outside of the 

following parameter ranges: 

%Bz: 0.8 to 5.0 wt.%, 

T„: 50 to 90°F, 

AT: -15 to +20F°, 

Fuel RVP: 9 to 12 psi; 

VII. Current Benzene Refueling Emission Rates and Inventory 

An important use of Equation (4) is the estimation of 

current national benzene refueling emission rates. This is 

accomplished by obtaining average national values for the three 

parameters in this equation. 
a 

] 

(grans HC/gallcn) 

I 

9 

.•00 0 

I.WMM * 

l.ftOOO * 

1.000 0 • 

.MOOO * 

.0000 0 

-.MOOO 

-t.OOOO 

-i.tooo 

. a oooo 

FIGURE 3 * 

RESIDOAL VALUES vs . PREDICTED VMJJBS 

• 

• 

• • 

• 

• 

•• 

..oow * ^ JUOO° 

2.0000 

• • 

• 

• 

• 

• 

• 

• • 

• » • •• 

• * • 

* • 

• 

• - . . . 

• • 

• •• i • 

• . . • • -

• * ••..* • 

• . 2 • • • 

» * / . 

. •• • 

• • •• • .••• • 

• 

* 

• • 

• • 

• • 

• 

""wMffl l (^ams IE/gallon) 

, , ., w H-„I~ * " Rothman and Johnson, U.S. EPA, OAR, OMS, 1985. * "Refueling Emissions fran Uncontrolled Vehxcles, Rothman an 

1 ' 1 • 

( 

-17-

1 
P.19 

-18-

NIPER gasoline surveys[10] and gasoline sales reports from 

"Petroleum Marketing Monthly"[11] can be used to calculate a 

sales-weighted national average benzene content in gasoline. 

Table 4 shows leaded and unleaded gasoline sales volumes for 

the winter of 1984-1985 and the summer of 1985. Table 5 

combines this sales information with data from NIPER gasoline 

surveys to calculate average national gasoline benzene 

concentrations (seasonal and annual). 

National averages for the other two equation parameters 

(TD and AT) were developed in an earlier EPA report on 

refueling emissions[3] and are shown below. This data, 

together with the fuel benzene content averages, provide the 

information needed to calculate current benzene refueling 

emission rates for summer, winter, and an overall twelve month 

average using Equation (4). The results of these calculations 

are shown in Table 6. 

National Average Parameter Values 

Parameter Summer Winter Annual 

T0 (°F) 76.2 60.3 68.9 

AT (F°) +8.8 -0.8 +4.4 

In the "Evaluation of Air Pollution Regulatory Strategies 

for Gasoline Marketing Industry,"[12] theoretical benzene 

emission rates were developed from the ideal gas law without 

the use of empirical data. It is interesting to compare the 

empirical benzene refueling emission rate calculated in this 

report (0.0428 grams benzene/gallon) with the theoretical rate 

developed in the Gasoline Marketing Study.[12] This comparison 

is slightly more complicated than it first seems because the 

two benzene refueling emission rates are in different units 

(the emission rate in the Gasoline Marketing Study[12] is 

expressed as 0.0066 grams benzene/grams HC). This complication 

can be eliminated by converting the units of the emission rate 

in this report to the units of the emission rate in [12] 

through the use of a national average HC refueling emission 

rate in units of grams HC/gallon. The current national average 

HC refueling emission rate is estimated at 5.4 grams HC/gallon 

by substituting the following three current national average 

parameter values into the EPA HC refueling emission prediction 

equation[3]: 1) Fuel RVP = 11.6 psi,[10] 2) AT = 4.4F°,[3] 

and 3) TD = 68.9°F.[3] Therefore, the national average 

benzene refueling emission rate developed in this report can 

also be expressed as (0.0428/5.4) or approximately 0.0079 grams 

benzene/grams HC. These two rates (0.0079 and 0.0066 grams 

benzene/grams HC), which only differ by twenty percent, are 

quite similar. As a matter of fact, much of the twenty percent 

difference can be explained by 1) the difference in gasoline 

benzene concentrations used to estimate these rates (1.59 wt. % 

in this report, and 1.54 wt. % in [12]), and 2) the fact that 
P.20 

-19-

Table 4 

Gasoline Sales Volumes* 

Fuel Type 

Leaded Regular: 

Unleaded Regular 

Premium: 

Total: 

WINTER SALES 

(millions 

21, 

25, 

8, 

of 

177 

054 

345 

qallons) 

6 

3 

8 

Percent of 

Winter Sales 

(38.8%) 

(45.9%) 

(15.3%) 

54,577.7 

Fuel Type 

Leaded Regular: 

Unleaded Regular 

Premium: 

Total: 

SUMMER SALES 

(millions of qallons) 

22,042 

27,645 

9,019 

7 

1 

5 

Percent of 

Summer Sales 

(37.5%) 

(47.1%) 

(15.4%) 

58,707.3 

Fuel Type 

Leaded Regular: 

Unleaded Regular 

Premium: 

Total: 

ANNUAL SALES 

(millions of qallons) 

43,220.3 

52,699.4 

17,365.3 

113,285.0 

Percent of 

Annual Sales 

(38.2%) 

(46.5%) 

(15.3%) 

"Petroleum Marketing Monthly," Energy 

Administration, October 1984 to September 1985 

Information 
P.21 

-20-

Table 5 

National Average Gasoline Benzene Concentrations 

SUMMER 

Fuel Type 

Regular unleaded 

Premium unleaded 

Leaded regular 

Percent 

Sales* 

47.1 

15.4 

37.5 

Avg. Bz 

Content 

(Wt. %)»« 

1 

1 

1 

57 

59 

60 

Seasonal Average Bz Content: 1.58 wt. % 

Seasonal Sales Volumes: 51.8 % 

Annual Average Bz Content: 1.59 wt. % 

WINTER 

Percent 

Sales*** 

Avg. Bz 

Content 

(Wt. %)*** * 

45.9 

15.3 

38.8 

1 

1 

1 

38 

68 

84 

1.60 wt. % 

48.2 % 

* "Petroleum Marketing Monthly," Energy Information Administration, 

April 1985 to September 1985. 

** "Motor Gasolines, Summer 1984," NIPER, Shelton and Dickson, 

February, 1985. 

*** "Petroleum Marketing Monthly," Energy Information Administration, 

October 1984 to March 1985. 

**** "Motor Gasolines, Winter 1984-85," NIPER, Shelton and Dickson, June, 

1985. 
P.22 

-21" 

Table 6 

Predicted Benzene Refueling Emission Rates 

(Grams Benzene/Gallon) 

Summer* 

Winter** 

Annual*** 

Displacement 

Loss Only 

0.0394 

0.0467 

0.0428 

Total Loss 

(Includes Spillage) 

0.0441 

0.0515 

0.0475 

April to September 

October to March. 

*** Twelve months. 

* * 
P.23 

-22-

the Gasoline Marketing Study[12] rate was developed under the 

assumption that static conditions apply, and therefore, it does 

not account for possible dynamic effects such as liquid/vapor 

turbulence or vapor growth/shrinkage effects associated with 

non-zero ATs. This comparison shows that theory and 

experiment compare quite closely. 

It is also interesting to calculate the average 

concentration of benzene emitted during refueling and compare 

it with benzene concentrations reported in the recent SAE Paper 

"Vehicle Evaporative and Exhaust Emissions as Influenced by 

Benzene Content of Gasoline".[13] An average benzene refueling 

emission concentration can be calculated in the following 

manner through the use of Equation (2): 0.0428 x 82,700 = 3,540 

ppm or 0.354 percent by volume. The SAE Paper[13] shows that 

the concentration of benzene in the head space of a vehicle's 

fuel tank averages 0.324 percent by volume for a liquid fuel 

benzene concentration of 1.5 volume percent. This head space 

concentration (0.324 volume percent) compares quite closely 

with the benzene refueling emission concentration calculated in 

this report (0.354 volume percent). 

The benzene refueling emission values developed thus far 

are for displacement losses only. A total benzene refueling 

emission factor must also consider spillage losses. From EPA's 

emission factor document (AP-42)[14], refueling spillage losses 

are estimated to be about 0.3 grams HC/gallon of gasoline 

dispensed. Assuming the spilled gasoline completely 

evaporates, benzene spillage emissions can be calculated by 

multiplying the liquid fuel's benzene weight content (%Bz from 

above divided by 100) by the HC spillage emission rate (0.3 

grams HC/gallon). Total benzene refueling emission rates are 

obtained from Equation 5 (below) which adds the spillage factor 

(.003 * %Bz) to the displacement emission equation. This 

calculation was performed using national average summer, 

winter, and annual fuel/temperature conditions, and the results 

are shown in Table 6. 

grams benzene/gallon = (.038 * %Bz) - (1.60 x 10"4 * TD) 

- (4.24 x 10"4 * AT) (5) 

• 

Equation (5) predicts a national annual benzene refueling 

emission rate of 0.048 grams benzene/gallon. Using this 

average and a 10 gallon fill, a national average value of 0.48 

grams benzene/refueling event was calculated. 

A current annual benzene refueling emission inventory was 

obtained by multiplying the average annual emission rate by the 

total gallons of gasoline sold in this period. At present, it 

is estimated that 5,440 megagrams of benzene are emitted each 

year as a result of refueling. In a GAO (U.S. General 

Accounting Office) report on air pollution,[15] the total 

benzene emission inventory is estimated as 253,600 megagrams. 
-23-

Therefore, benzene refueling emissions account for roughly two 

percent of the total benzene emission inventory. 

Lastly, it should be noted that the NIPER fuel surveys 

show that gasoline benzene content varies significantly from 

sample to sample ranging in value from 0.1 to 5.0 wt. percent. 

This range, when incorporated into Equation (5), indicates that 

at current national average temperature conditions benzene 

refueling emissions can range from near zero up to 0.177 grams 

benzene/gallon. 

VIII. Possible Future Benzene Refueling Emission Rates 

Another important use of benzene emission prediction 

equation is the estimation of future emission rates. In order 

to use Equation (5) for this purpose, future fuel and 

temperature conditions must be evaluated. Although temperature 

conditions have inherent variability, future seasonal averages 

should be similar to current averages. The only parameter that 

has a potential to significantly affect future benzene 

refueling emissions is fuel composition. Future fuel can be 

affected by lead phase-down and potential RVP control. The 

possible effects of these fuel changes on benzene refueling 

emissions are discussed below. 

In an EPA final regulatory impact analysis, "Costs and 

Benefits of Reducing Lead in Gasoline,"[16], a DOE refining 

model predicted that lead phase-down would not change the 

benzene content of the entire gasoline pool (leaded and 

unleaded combined), but it would cause a shift in benzene 

content between the leaded and unleaded pools. The DOE model 

predicted that lead phase-down would increase benzene content 

in unleaded gasoline and decrease benzene content in leaded 

gasoline. Lead phase-down would therefore not have any 

significant effect on overall benzene refueling emissions, but 

it would create a greater benzene exposure potential to the 

users of unleaded gasoline. Also, it should be mentioned that 

lead phase-out is a future possibility. With lead phase-out is 

the potential for an increase in the entire gasoline pool's 

benzene content as a means to increase octane.[17] Therefore, 

lead phase-out could possibly increase benzene refueling 

emissions, but whether or not any significant increase occurs 

depends on the refiner's blending decisions. 

Potential fuel RVP control is another-way in which future 

fuel may be altered. Currently, EPA is considering whether 

fuel volatility should be regulated as a means of controlling 

HC emissions. It has been estimated that a fuel's benzene 

content increases slightly with decreasing RVP as shown in 

Table 7.[18] Using these potential changes in weight percent 

with the national average temperature conditions, it is 

estimated that the most stringent RVP control would increase 

benzene refueling emissions by about 0.002 grams benzene/gallon 
P.25 

-24-

Table 7 

Potential RVP Effects on Gasoline Benzene Content* 

and Benzene Refueling Emissions 

Refueling Emission 

RVP (psi) Benzene (wt.%) Rate (g Benz/gallon)** 

11.5 1.59 .0475 

10.5 1.60 .0479 

9.5 1.64 .0494 

9.0 1.65 .0498 

* "Study of Gasoline Volatility and Hydrocarbon Emissions 

From Motor Vehicles," EPA-AA-SDSB-85-5, November, 1985. 

** Calculated using Equation (5) 
P.26 

-25-

(4.9 percent). The effects of RVP control on benzene refueling 

emissions are shown in Table 7. Therefore, RVP control could 

possibly increase benzene refueling emissions slightly. 

IX. Summary 

To characterize uncontrolled benzene refueling emissions, 

an in-house EPA test program was conducted to measure benzene 

refueling emissions for fuels with different RVPs and benzene 

contents under varying temperature conditions. To broaden the 

data base for analysis, three other sources of benzene 

refueling emission data were combined with the "in-house" 

data. Two other sources were studied but determined 

incompatible with the other sources due to test procedure 

differences. 

A regression model was fitted to the combined data set 

producing the benzene refueling emission prediction equation 

shown below. The model found the following parameters 

significantly influence benzene refueling emissions: fuel 

benzene content (%Bz), dispensed fuel temperature (T0), and 

the difference between tank fuel temperature and dispensed fuel 

temperature (AT). Fuel RVP was not found to be a 

statistically significant influence. 

grams benzene/gallon = (.038 * %Bz) - 1.60 x 10'4 * T0) 

- (4.24 x 10"4 * AT) 

At current national average conditions including the 

effects of spillage, the prediction equations yields an average 

benzene refueling emission of 0.048 grams/gallon. 

Lead phase-down should not alter overall benzene refueling 

emissions but could create a greater benzene exposure to the 

users of unleaded fuel. Lead phase-out could possibly increase 

overall benzene refueling emissions. Lastly, potential fuel 

RVP control may slightly increase benzene refueling emissions. 
P.27 

-26-

acknowledgments 

The author wishes to recognize Tony Barth and Carl Fuller 

for the special effort they contributed to make the test 

procedure a succeessful undertaking. 

The author also wishes to thank Fred Holbert for his 

technical guidance and Glenn Passavant for his continual 

support ind special effort to make this project a success. 

Onbo01^ 

f\taf^' 

-k 
P.28 

-27-

References 

1. "Instrumentation and Techniques for Vehicle 

Refueling Emissions Measurement," SAE Recommended Practice 

J1045, August, 1973. 

2. NIOSH Manual of Analytical Methods, Volume 3, Second 

Edition, 1977. 

3. "Refueling Emissions from Uncontrolled Vehicles," 

Rothman and Johnson, U.S. EPA,OAR,OMS, 1985, Public Docket No. 

A-84-7. 

4. "Onboard Control of Vehicle Refueling Emissions, 

Demonstration of Feasibility," API Publication No. 4306, 

October, 1978. 

5. "Benzene Emissions from Motor Vehicles," P.J. 

Clarke, Exxon, April 21, 1978, Public Docket No. A-84-7. 

6. "Factors Influencing the Composition and Quantity of 

Passenger Car Refueling Emissions - Part I," J. N. Braddock, 

T.J. Lemmons, and P.A. Gabele, U.S. EPA, RTP, N.C. (Submitted 

to SAE for October 1986 publication). 

7. "Composition of Vapor Emitted From a Vehicle 

Gasoline Tank During Refueling," SAE Paper # 860086, Furey and 

Nagel, General Motors Research Laboratories, February, 1986. 

8. "Benzene Emissions from- Passenger Cars," CONCAWE 

Report No. 12/83, August 21, 1984. 

9. "A Study of Variables that Effect the Amount of 

Vapor Emitted During the Refueling of Automobiles," Edward M. 

Liston, API Report CEA-21, May, 1975. 

10. "Motor Gasolines, Summer 1984," and "Motor 

Gasolines, Winter 1984 - 85," NIPER, Shelton and Dickson, 

February and June, 1985. 

11. ''Petroleum Marketing Monthly," Energy Information 

Administration, October, 1984 to September, 1985. 

12. "Evaluation of Air Pollution Regulatory Strategies 

for Gasoline Marketing Industry," EPA-450/3-84-012a, July, 1984. 

13. "Vehicle Evaporative and Exhaust Emissions as 

Influenced by Benzene Content of Gasoline," SAE Technical Paper 

Series K860531, Seizinger, Marshall, Cox, and Boyd, NIPER, 

February, 1986. 

14. "Compilation of Air Pollutant Emission Factors," 

(AP-42), U.S. EPA, OAWM, OAQPS, 1977. 
P.29 

-28-

15. "AIR POLLUTION - EPA's Strategy to Control Emissions 

of Benzene and Gasoline Vapor," GAO/RCED-86-6, December, 1985. 

16. "Costs and Benefits of Reducing Lead in Gasoline," 

EPA Final Regulatory Impact Analysis, February, 1985. 

17. Lead Phase-Out and Octane Enhancement," V.E. Pierce 

and B.B. Bansal, The M.W. Kellogg Co., Chemical Engineering 

Processes, March, 1986. 

18. "Study of Gasoline Volatility and Hydrocarbon 

Emissions From Motor Vehicles," EPA-AA-SDSB-85-5, November, 

1985. 
P.30 

-29-

Appendix A 

Regression Model with RVP as a Parameter 

(Using the data from Tables 2 and 3) 

grams Bz/gallon = (.0346 * Bz) - (7.71 x IO"5 * T0) 

- (4.38 X 10"4 * AT) - (5.77 x IO"4 * RVP) 

R

2

 = 

SE = 

Parameter 

Bz 

To 

AT 

RVP 

0.9616 

.00927 

Significance 

0.0000 

0.4653 

0.0002 

0.4026