UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

RESEARCH TRIANGLE PARK, NC 27711 

NOV 2 0 2013 

OFFICE OF 

AIR QUALITY PLANNING 

AND STANDARDS 

MEMORANDUM 

SUBJECT: 

FROM: 

THRU: 

TO: 

Revisions to the Photochemical Assessment Monitoring Stations Compound Target List 

Kevin A. Cavender, P AMS Program Manage~__......,...-

Ambient Air Monitoring Group (C304-06) JY--

Lewis Weinstock, Leader @J 

Ambient Air Monitoring Group (C304-06) 

State and Local Monitoring Agencies 

The purpose of this memorandum is to summarize changes being made to the Photochemical 

Assessment Monitoring Stations (P AMS) compound target list. Prior to this change, the P AMS target 

list contained 57 compounds. This memorandum divides the previous list into two categories -priority 

compounds and optional compounds. In addition, seven new compounds are being added to the target 

list as priority compounds. Table 1 contains the revised target list. The list contains 34 priority 

compounds and 29 optional compounds. 

The revisions to the target list are a product of a collaborative effort by EPA and state and local 

monitoring agencies. A workgroup was formed to evaluate the target list comprised of EPA 

representatives (EPA-OAQPS, EPA-ORD, and EPA-Regions 1, 2, 3, 6, 8, 9) and state and local 

monitoring agencies (including Arizona, City of Denver, Georgia, LADCO, Maine, Maryland, 

Massachusetts, New York, Texas, and South Coast AQMD). In addition, the EPA consulted with the 

Clean Air Science Advisory Committee's Air Monitoring and Methods Subcommittee (CASACAMMS) on potential revisions to the target list. Finally, the revised list has been reviewed by the 

National Association of Clean Air Agencies' Monitoring Steering Committee (MSC). 

EVALUATION OF EXISTING TARGET COMPOUNDS 

The existing target compounds were evaluated to determine if any of the existing compounds could be 

removed, or made optional, due to low importance. A decision matrix was used to rank the relative 

importance of each compound based on several criteria. A decision matrix allows for assigning 

importance to a compound by scoring each compound based on one or more factors. The initial score is 

multiplied by a weighting for the factor being evaluated. The weighted score for each factor is then 

summed to provide a total score for each compound. Figure 1 summarizes the results of the decision 

matrix analysis for the P AMS target compounds where the compounds are sorted from highest 

importance to least importance. The factors considered in this analysis, and relative weight assigned, 

included: 

Internet Address (URL) • http://www.epa.gov 

Recycled/Recyclable • Printed wnh Vegetable 011 Based Inks on Recycled Paper (Minimum 25% Postconsumer) 
• Overall reactivity adjusted average concentration (30 percent); 

• Reactivity adjusted average concentration during 9 am morning rush hour on high ozone days 

(30 percent); 

• Reactivity adjusted average concentration based on geography (e.g., NE, SE, SW, MW, W) (30 

percent); 

• If the compound was a hazardous air pollutant (HAP) (5 percent); and 

• If the compound was a high priority secondary organic aerosol precursor (5 percent). 

The first three factors attempt to identify the compounds most important to ozone formation. The last 

two factors recognize that the measurements of the target compound may be important for other air 

quality programs. The rationale for selecting each factor and the approach used to score the target 

compounds for each of the factors are summarized in the following paragraphs. 

Overall Reactivity Adjusted Average Concentration 

The overall reactivity adjusted average concentration was selected as a factor to represent the 

importance of the compound to ozone formation. In general, higher Volatile Organic Compound (VOC) 

concentrations lead to increased ozone formation potential. The 2010 P AMS data (downloaded from 

the AQS system) was used to calculate average concentration for each target compound. For each 

compound, the data from all sites and days were averaged. Due to differences in reactivity of the 

individual target compounds, the measured concentrations for each compound were multiplied by the 

Maximum Incremental Reactivity (MIR, Carter 2010) ofthe compounds to obtain their overall average 

reactivity adjusted concentration. 

Each compound was then scored based on a proportional weighting, where the compound with the 

highest reactivity adjusted average concentration was awarded 100 points, and the compound with the 

average score was awarded 0 points. Those compounds in between the highest and lowest were scored 

based on the following calculation: 

Score = (Target Average - Minimum)/(Maximum- Minimum)* 100 

Where: 

Target Average= the average MIR adjusted concentration for the compound being scored 

Minimum =the lowest average MIR adjusted concentration for all compounds 

Maximum= the highest average MIR adjusted concentration for all compounds 

Figure 2 summarizes the scores for each target compounds based on the overall average MIR adjusted 

concentration. 

Reactivity Adjusted Average Concentration During 9 am on High Ozone Days 

This factor was selected in recognition that for some VOC compounds, their concentration (and 

therefore their importance to ozone formation) may be higher during high ozone episodes than at other 

times of the year. Only data from days where the maximum 8-hour ozone concentration exceeded 75 

ppb in the county the P AMS site was located in were used in an attempt to better identify those 

2 
compounds which are most responsible for elevated ozone concentrations. In addition, only the data 

collected during the 9 am hour (near the end of the "morning rush hour") was used to further focus on 

those compounds that would be most responsible for ozone formation during that high ozone day as it 

represents concentrations during the morning rush hour and concentrations present as ozone formation 

is beginning to increase. The data for each compound were then averaged across all sites, and then 

multiplied by their respective MIR value to give the reactivity adjusted average concentration during 

9 am on high ozone days. Each compound was then scored based on a proportional weighting as 

described above. Figure 3 summarizes the reactivity adjusted average concentrations for the target 

compounds during the 9 am hour on high ozone days. 

Reactivity Adjusted Average Concentration Based on Geographic Location 

This factor was selected in order to recognize that some target compounds may be more important to 

ozone formation in certain parts of the country than in others. The 2010 P AMS data were divided into 

five geographic regions (i.e., NE, SE, MW, SW, and W) depending on the state that the data were 

collected in. The data for each compound were averaged across all sites within that geographic region, 

and then multiplied by their respective MIR value to give the reactivity adjusted average concentration 

for that region. Each compound was then scored based on a proportional weighting for each geographic 

region. The maximum score for each compound over all of the geographic regions was then used for 

the score for that compound for this factor. Figure 4 summarizes reactivity adjusted average 

concentrations for the target compounds in each of the regions reviewed. 

Hazardous Air Pollutants 

Several of the existing P AMS target compounds are also HAP. This factor was added to account for the 

added benefit to the air quality program of measuring these HAP compounds in the P AMS program. 

The HAP list was cross referenced verses the P AMS target list, and those P AMS target compounds 

identified as HAP were given an additional 5 percent to their final score for this factor. Table 2 lists the 

P AMS target compounds that were identified as HAP. 

Secondary Organic Aerosol Precursor 

Several of the existing P AMS target compounds are also important secondary organic aerosol 

precursors (SOAP). This factor was added to account for the added benefit to the air quality program of 

measuring these SOAP compounds in the P AMS program. A list of the 18 most important SOAP 

compounds was obtained from the literature (Derwent, 2010). This list was cross referenced verses the 

P AMS target list, and those P AMS target compounds on the SOAP list were given an additional 5 

percent to their final score for this factor. Table 3 lists the P AMS target compounds that were identified 

as SOAP compounds. 

Summary of Results and Selection of Priority Compounds 

Figure 1 summarizes the overall score and ranking of the existing target compounds, with the most 

important compounds on the left with decreasing importance moving to the right. As can be seen, many 

of the existing compounds have very low importance based on this scoring approach. However, this 

approach does not by itself identify a "cut point" to separate priority compounds from optional 

compounds. In order to identify a point to separate the compounds into priority and optional lists, a 

running sum of the individual scores of each compound was created for each compound. The running 

sum was made up of the target compound's score plus the score of all higher ranked compounds. For 

example, the running sum for ethylene is the sum of the score for ethylene plus the scores for 

3 
formaldehyde and isobutane. The running sum for the least important compound includes the scores for 

all compounds, and is referred to here as the "total value." By dividing the running sum for a given 

compound by the total value and multiplying by 100, you obtain an estimate of the percent of the total 

value obtained by measuring that compound and all higher ranked compounds. 

Figure 5 graphically represents this calculation for all current target compounds. As can be seen, a 

point is reached where measuring each additional compound adds little value. A decision to obtain 90 

percent of the value would lead to a cut point between p-ethyltoluene and o-ethyltoluene. The cut point 

between the priority list and the optional target list was selected after o-ethyltoluene to avoid cutting 

the lists between these two isomers. In addition, cis-2-butene was included in the priority list to avoid 

separating it from its isomer trans-2-butene. Table 1 provides the revised priority and optional target 

lists. 

CONSIDERATION OF COMPOUNDS TO ADD 

Three considerations were made in evaluating if additional compounds (compounds not currently on 

the PAMS target list) should be added: 

1. If any VOC compounds important to ozone formation were not included in the original target 

list, 

2. If any VOC compounds important to air toxic risks or secondary organic aerosols (SOA) 

formation were not included in the original target list, and 

3. If the existing measurement technologies being used at P AMS sites are capable of measuring 

the candidate VOC compound. 

With respect to important ozone forming VOC compounds that are not included, we note that biogenics 

have been identified as important to ozone formation (especially in the east) (Samet, 2011). However, 

isoprene is the only biogenic on the target list. Alpha and beta pinene have also been identified as 

important biogenic compounds for ozone formation. The existing gas chromatographs (GC) used in the 

P AMS program are capable of measuring both alpha and beta pinene; however, concerns have been 

raised about the methods capability of accurately differentiating between alpha and beta pinene. This 

issue has been addressed before with other VOC isomers, such as m-xylene and p-xylene where 

separation of the two isomers is difficult. As with m/p-xylene, alpha and beta pinene can be measured 

and the total be reported as a/~-pinene. As such, alp-pinene is being added to the priority compound 

list. 

In addition to biogenics, the CASAC monitoring subcommittee also suggested measuring ethanol as a 

marker for biofuel usage. The use of biofuels has been increasing in recent years, and measuring 

ethanol will allow for tracking the potential impact on ozone formation due to changes in fuel usage. 

As such, ethanol is being added to the priority compound target list. 

For air toxics, the 2005 NATA (EPA, 2011) was reviewed in order to identify air toxic compounds 

considered to be either national cancer risk drivers or contributors. Six compounds were identified as 

national cancer risk drivers or contributors that can be measured using the existing measurement 

technologies, including - 1,3 butadiene, acrylonitrile, carbon tetrachloride, ethylene oxide, 

tetrachloroethylene, and 1 ,4-dichlorobenzene. Of these six compounds, the National Air Toxics Trends 

Sites (NATTS) program currently measures 1,3 butadiene, carbon tetrachloride, and 

tetrachloroethylene. For consistency with the NATTS, these three compounds are being added to the 

priority compound target list. 

4 
The list of SOA compounds discussed above was reviewed again to identify if any compounds should 

be considered for addition to the target list. Only benzaldehyde was identified as a compound that was 

considered an important SOA but that was not on the current target list. Benzaldehyde can be measured 

along with the other carbonyls currently on the target list (formaldehyde, acetaldehyde, and acetone). 

As such, benzaldehyde is being be added to the priority compound target list. 

IMPLEMENTATION OF LIST CHANGES 

Based on this guidance, P AMS monitoring agencies could begin reporting just the existing priority 

compounds listed in Table 1 as early as the 2014 P AMS season. Continued reporting of the optional 

compounds may continue on a voluntary basis but should be reviewed in the overall context of agency 

reporting burdens. 

The EPA is evaluating the ability of the existing equipment to measure the new priority compow1ds 

listed in Table 1. These compounds will be evaluated as part of an auto-GC evaluation currently 

planned for the winter of 2013 and the EPA will be soliciting volunteers from state and local 

monitoring agencies to assist in the evaluation during the 2014 P AMS season. In addition, the current 

P AMS retention time cylinders do not include the new priority compounds, which would make it more 

difficult for monitoring agencies to identify the peaks for the new priority compounds. As such, 

monitoring agencies should wait until the EPA/state evaluation is complete to begin measuring and 

reporting the new priority compounds listed in Table 1, by which time the EPA will have completed the 

review of the new compounds and appropriate retention time cylinders will be available. 

Table 1 lists four carbonyl compounds as priority compounds. It should be noted that under the current 

regulatory requirements for P AMS, carbonyls are only required to be measured at P AMS areas 

classified as severe and above nonattainment areas for ozone. This guidance does not supersede the 

regulatory requirements. However, due to the importance of carbonyl measurements in understanding 

ozone formation, P AMS monitoring agencies are encouraged to consider measuring carbonyls at their 

PAMS sites. 

REFERENCES 

Carter, W. P. L., Development of the SAPRC-07 Chemical Mechanism. Atmospheric Environment 

2010, 44, (40), 5324-5335. 

Samet, Jonathan M., "Review of EPA's Photochemical Assessment Monitoring Stations (PAMS) 

Network Re-engineering Project." 

http://yosemite.epa.gov/ ab/sabproduct.nsf/264cbl227d55e02c85257402007446a4/8412 

Derwent, D., Chemical Mechanism Development and the Relative Policy Importance of Ozone and PM 

Formation in Europe and USA, presented at the 2010 Air Chemical Mechanism Conference. 

http://airguality.ucdavis.edu/pages/events/2010/acm/DERWENT.pclf 

USEPA, 2011, Summary of Results for the 2005 National Scale Assessment. 

http://www.epa.gov/ttn/atw/nata2005/05pdf/sum results.pdf 

Attachments 

5 
Table 1. Revised PAMS Target Lise 

Existing Priority Compounds Optional Compounds 

1 ,2,3-Trimethylbenzene 1.3,5-Trimethylbenzene 

1,2,4-Trimethylbenzene 1-Pentene 

1-Butene 2,2-Dimethylbutane 

2,2,4-Trimethylpentane 2, 3,4-Trimethylpentane 

Acetaldehydeb 2,3-Dimethylbutane 

Aceto neb 2, 3-Dimethylpentane 

Benzene 2 4-Dimethylpentane 

Cis-2-Butene 2-Methylheptane 

Ethane 2-Methylhexane 

Ethyl benzene 2-Methylpentane 

Ethylene 3-Methylhej:)tane 

Formaldehydeb 3-Methylhexane 

lsobutane 3-Metllylpentane 

I so pentane Acetylene 

Isoprene. Cis-2-Pentene 

M/P Xylene Cyclohexane 

M-Ethyltoluene Cyclopentane 

N-Butane lsopropylbenzene 

N-Hexane M-Diethylbenzene 

N-Pentane Methylcyclohexane 

0-Ethyltoluene Methylcyclopentane 

0-Xylene N-Decane 

P-Ethyltoluene N-Heptane 

Propane N-Nonane 

Propylene N-Octane 

Styrene N-Propylbenzene 

Toluene N-Undecane 

Trans-2-Butene P-Diethylbenzene 

Trans-2-Pentene 

New Priority Compounds 

a/13-Pinene 

1,3 Butadiene 

Benzaldehydeb 

Carbon Tetrachloride 

Ethanol 

Tetrachloroethylene 

"This table only includes individual target compounds. Monitoring 

agencies are encouraged to continue measuring and reporting total nonmethane organic compounds (TNMOC) 

b These compounds are carbonyls and are only required to be measured 

at P AMS sites in ozone nonattainment areas classified as serious or 

above for the 8-hour ozone standard. 

1 
Table 2. P AMS Targets that are HAP Compounds 

2,2,4-Trimethylpentane 

Acetaldehyde 

Benzene 

Ethyl benzene 

Formaldehyde 

Isopropyl benzene 

M/P Xylene 

N-Hexane 

0-Xylene 

Styrene 

Toluene 

Table 3. P AMS Targets Identified as Important SOAP Compounds 

1,2,3-Trimethylbenzene 

1,2,4-Trimethylbenzene 

Benzene 

Ethyl benzene 

M/P Xylene 

M-Ethyltol uene 

N-Propylbenzene 

0-Ethyltoluene 

0-Xy!ene 

P-Ethyltoluene 

Styrene 

Toluene 

2 
Score 

0 9 0 0 0 0 0 0 0 0 ..... 0 ..... ;., w ~ i.n a. :... Co io 0 0 0 0 0 0 0 0 0 0 0 0 

Formaldehyde 

lsobutane 

Ethylene 

Isoprene 

Propylene 

_, 

Acetaldehyde 

M/P Xylene 

Toluene 

lsopentane 

'Tj N-Butane 

ac;· 0-Xylene 

= 1, 2,3-Trimethylbenzene 

""' 

(1) 

...... Propane 

1,2,4-Trimethylbenzene 

0 M-Ethyltoluene 

< 

(1) N-Pentane 

""' 

~ Ethyl benzene 

~ Benzene 

$:>) Styrene 

= :;>;" N-Hexane 

s· Acetone OCI 

0 1-Butene >-+, Ethane 'i:l 

> 2,2,4-Trim ethyl pentane 

a;:: Trans-2-Butene C/). P-Ethyltoluene >-i w ~ 0-Ethyltoluene 

OCI 1,3 

,5-Trimethylbenzene (1) - Trans-2-Pentene 

"' 

t:;O lsopropylbenzene $:>) N-Propylbenzene "' 

(1) 

0.. Cis-2-Butene 

0 Methylcyclopentane = 

tj 2-Methylpentane 

(1) 3-Methylpentane () 

u;· Methylcyclohexane 

a· 1-Pentene 

= 

a;:: Cis-2-Pentene 

~ Acetylene 

""' 

3

-Methylhexane ~· 

C/). Cyclopentane 

() Cyclohexane 0 

""' M-Diethylbenzene s· 

OCI N-Heptane 

2,3-Dimethylpentane 

2-Methylhexane 

P-Diethylbenzene 

2,4-Dimethylpentane 

2,3

-Dimethylbutane 

N-Octane 

2,3 ,4-Trimethylpentane 2,2-Dimethylbutane 

3-Methylheptane 

N-Decane 

2

-Methylheptane 

N-Nonane 

N-Undecane 
>-rj 

oq' 

~ .... 

(1) 

!'J 

r:/1 

~ 

s 

s 

~ 

~ 

0 

....., 

0 

< 

(1) 

.... 

~ - -!:> ~ (1) 

.... 

~ 

(Jq 

(1) 

a;:: 

:;a 

> 

a: 

~ 

VJ 

....... 

(1) 

0.. 

n 

0 

1:1 

(') 

(1) 

ij 

~ 

c;· 

1:1 

0 "' .... 

0 

MIR Adjusted Average Concentration (ppbC) ,_. 

(J1 !:5 N 

"' w 

0 w 

VI 

.,. 

0 ~ 

Formaldehyde liiiiiiiiiiiiiiii~iiiiiiiiiiiiiiiiii~iiiiiiiiiiiiiiiiiiiljliiiiiiiiiiiiiiiiii.iiiiiiiiiiiiiiiiii~iiiiiiiiiiiiiiiiii~iiiiiiiiiiii~iiiiiiiiiiiiiiiiiiilfiiiiii ~ lsobutane 

Ethylene _ 

Isoprene 

Propylene 

Acetaldehyde 

M/P Xylene 

Toluene 

lsopentane 

N-Butane 

0-Xylene )...... 

1, 2,3-Trimethylbenzene 

Propane 

1, 2,4-Trimethylbenzene 

M-Ethyltoluene ).--

N,Pentane 

Ethylbeo""' Benzene b. 

Styrene 

N-Hexane 

Acetone 

1-Butene 

Ethane 

2,2,4-Trimethylpentane P... 

Trans-2-Butene 

0-Ethyltoluene 

P-Ethyltol"'"' b 

1,3,5-Trimethylbenzene 

Trans-2-Pentene 

lsopropylbenzene 

N-Propylbenzene 

Cis-2-Butene 

Methylcyclopentane 

2-Methylpentane 

3-Methylpentane 

Methylcyclohexane 

1-Pentene 

Cis-2-Pentene 

Acetylene 

3-Methylhexane 

Cyclopentane 

Cyclohexane 

M-Diethylbenzene 

N-Heptane 

2,3-Dimethylpentane 

2-Methylhexane 

P-Diethylbenzene 

2,4-Dimethylpentane 

2,3-Dimethylbutane 

N-Octane 

2,3,4-Trimethylpentane 

2,2-Dimethylbutane 

3-Methylheptane 

N-Decane 

2-Methylheptane 

N-Nonane 

N-Undecane 
MIR Adjusted Average Concentration (ppbC) 

.... "' w .&» Vl <1\ ..... 00 

0 0 0 0 0 0 0 0 0 

-1-

Formaldehyde 

lsobutane 

Ethylene 

Isoprene 

Propylene 

Acetaldehyde 

>-rj 

M/P Xylene 

oc;· Toluene 

s:::: lsopentane ...., 

('D N-Butane w 0-Xylene 

(/) 1,2

,3-Trimethylbenrene s:::: 

s Propane 

s 1,2

,4-Trimethylbenzene ~ M-Ethyltoluene 1- ~ 

0 N-Pentane ......., Ethylbenzene a;:: 

_. Benzene 

?0 Styrene 

> N-Hexane 

&: Acetone s:::: 

VJ !-Butene (t 

~ Ethane 

> 2, 2,4-Trimethylpentane < 

('D Trans-2-Butene ...., 

~ P-Ethyltoluene ~ ('D 0 -Ethyltoluene (') 1,3,5-Trimethylbenzene 0 U'l l::l Trans-2-Pentene (') 

('D lsopropylbenzene a 

...., N-Propylbenzene 

~ Cis-2-Butene o· 

l::l Methylcyclopentane 

t/ 

2

-Methylpentane s:::: 3-Methylpentane ...., 

s· 

~ Methylcyclohexane 

1.0 1-Pentene 

~ Cis-2-Pentene s Acetylene ::r: 

0 3-Methylhe

xane 1: Cyclopentane ...., 

0 Cyclohexane l::l 

:I: M-Diethylbenzene 

oc;· N-Heptane 

=r 2,3-Dimethylpentane 

0 

N 

2

-Methylhe

xane 

0 

P-Diethylbenzene l::l 

('D 

2

,4-Dimethylpentane 

t/ 

2

,3-Dimethylbutane 

~ VJ N-Octane 

2,3,4-Trimethylpenta ne 2,2-Dimethylbutane ) 

3-Methylheptane 

N-Decane 

2-Methylheptane 

N-Nonane 

N-Undecane 
Maximum Score Based on Geographical Evalua~ion 

0 0 !=' !=' 0 0 0 0 

b b ..... ..... ;.., ;.., w LJ 0 "' 0 

"' 0 

"' 0 

"' -1-

Formaldehyde 

lsobutane 

Ethylene 

Isoprene 

"Tl Propylene 

ciQ' Acetaldehyde 

., 

~ M/P Xylene (I) Toluene 

""" lsopentane 

[f) N-Butane ~ 

s 0-Xylene 

s 1, 2,3-Trimethylbenzene 

~ Propane 

0 1, 2,4-Trimethylbenzene ......, M-Ethyltoluene [f) 

(') N-Pentane 0 

., 

[/) 

(I) Hhylb'"""' Benzene E. 

8" ., Styrene 

~ N-He

xane 

- Acetone ::0 

> 1-Butene 

&: Ethane 

~ [/) 

.... 

(I) 

2

,2,4-nlm"hYIP'"""' 

Trans-2-Butene 

b 

0.. 

P-Ethyltoluene 

> 

0'1 < 0-Ethyltoluene (I) 

., 

1

,3 

,5-Trimethylbenzene l=ll 

CIQ Trans-2-Pentene (I) 

(1 lsopropylbenzene 

0 

N

-Propylbenzene :::3 

(') Cis-2-Butene (I) 

:::3 Methylcyclopentane ~ 

~ 

2

-Methylpentane 

s· 3-Methylpentane 

:::3 Methylcyclohexane t:ci 

l=ll 1-Pentene [/) 

(I) Cis

-2-Pentene 

Cl. Acetylene 0 

:::3 

3

-Methylhe

xane 

Cl Cyclopentane (I) 

0 Cyclohexane CIQ ., M-Diethylbenzene l=ll 

"0 N-Heptane ::r 

c=;· 2,3

-Dimethylpentane 

L' 2-Methylhe

xane 0 

(') 

P-Diethylbenzene 

~ 2,4-Dimethylpentane c;· 

:::3 

2

,3-Dimethylbutane 

N-Octane 

2,3,4-Trimethylpenta ne 2,2-Dimethylbutane 

3-Methylheptane 

N-Decane 

2-Methylheptane 

N-Nonane 

N-Undecane 
"Tj 

aa· 

= 

..., 

(1) 

~ 

VJ 

s 

= 

s 

$:>) 

~ 

0 

H) 

~ 

= 

= 

s· -..J 

{Jq 

VJ 

s 

= 

0 

H) 

........ 

= 

0.. 

:;::· 

0.: 

a 

= 

VJ 

('") 

0 

..., 

(1) 

"' 

Formaldehyde 

lsobutane 

Ethylene 

Isoprene 

Propylene 

Acetaldehyde 

M/P Xylene 

Toluene 

lsopentane 

N-Butane 

0-Xylene 

1, 2,3-Trimethylbenzene 

Propane 

1, 2,4-Trimethylbenzene 

M-Ethyltoluene 

N-Pentane 

Ethylbenzene 

Benzene 

Styrene 

N-Hexane 

Acetone 

1-Butene 

Ethane 

2, 2,4-Trimethylpenta ne 

Trans-2-Butene 

P-Ethyltoluene 

0-Ethyltoluene 

1,3,5-Trimethylbenzene 

Trans-2-Pentene 

lsopropylbenzene 

N-Propylbenzene 

Cis-2-Butene 

Methylcyclopentane 

2-Methylpentane 

3-Methylpentane 

Methylcyclohexane 

1-Pentene 

Cis-2-Pentene 

Acetylene 

3-Methylhexane 

Cyclopentane 

Cyclohexane 

M-Diethylbenzene 

N-Heptane 

2,3-Dimethylpentane 

2-Methylhexane 

P-Diethylbenzene 

2,4-Dimethylpentane 

2,3-Dimethylbutane 

N-Octane 

2,3,4-Trimethylpenta ne 

2,2-Dimethylbutane 

3-Methylheptane 

N-Decane 

2-Methylheptane 

N-Nonane 

N-Undecane 

..... IV w 0 0 0 0 

%of Cumulative Score 

~ (J1 0 "' 0 

...., 

0 Oo 0 lO 

0 

... 

g