UNITED STATES ENVIRONMENTAL PROTECTION AGENCY RESEARCH TRIANGLE PARK, NC 27711


## NOV 2 02013

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, PAMS 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 ofthis memorandum is to summarize changes being made to the Photochemical Assessment Monitoring Stations (PAMS) compound target list. Priorto this change, the PAMS 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 1contains the revised target list. The list contains 34 priority compounds and 29 optional compounds. The revisions to the target list are aproduct ofa collaborative effort by EPA and state and local monitoring agencies. A workgroup was formed to evaluate the target list comprised ofEPA representatives (EPA-OAQPS, EPA-ORD, and EPA-Regions 1, 2, 3, 6, 8, 9) and state and local monitoring agencies (including Arizona, City ofDenver, Georgia, LADCO, Maine, Maryland, Massachusetts, New York, Texas, and South Coast AQMD). In addition, the EPA consulted withthe 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 ofCleanAir Agencies' Monitoring Steering Committee (MSC). EVALUATION OF EXISTING TARGET COMPOUNDS The existing target compounds were evaluatedto determine ifany ofthe existing compounds could be removed, or made optional, due to lowimportance. A decision matrix was used to rank the relative importance ofeach 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 atotal score for each compound. Figure 1 summarizes the results ofthe decision matrix analysis for the PAMS 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 morningrush hour onhigh ozone days (30 percent);

• Reactivity adjusted average concentrationbased on geography (e.g., NE, SE, SW, MW, W) (30 percent);

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

• Ifthe compound was a high priority secondary organic aerosol precursor (5 percent). The first three factors attempt to identify the compounds most importantto ozone formation. The last two factors recognize that the measurements ofthe target compound may be importantfor other air quality programs. The rationale for selecting each factor and the approach used to score the target compounds for each ofthe factors are summarized in the following paragraphs. 

### OverallReactivityAdjustedAverage Concentration The overall reactivity adjusted average concentration was selected as a factor to represent the importance ofthe compound to ozone formation. In general, higher Volatile Organic Compound (VOC) concentrations lead to increased ozone formation potential. The 2010 PAMS 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 ofthe individual target compounds, the measured concentrations for each compound were multiplied by the Maximum Incremental Reactivity (MIR, Carter 2010) ofthe compounds to obtaintheir overall average reactivity adjusted concentration. Each compound was then scored based on aproportional 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 onthe 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 MIRadjusted concentrationfor all compounds Maximum=the highest average MIR adjusted concentration for all compounds Figure 2 summarizes the scores for eachtarget compounds based on the overall average MIRadjusted concentration. 

### ReactivityAdjustedAverage Concentration During9 am on High OzoneDays This factor was selected in recognition that for some VOCcompounds, their concentration (and therefore their importance to ozone formation) may be higher during high ozone episodes than at other times ofthe year. Only data from days where the maximum 8-hour ozone concentration exceeded 75 ppb in the county the PAMS site was located in were used in an attempt to better identify those 2compounds which are most responsible for elevated ozone concentrations. In addition, only the data collected during the 9 am hour (nearthe end ofthe "morning rush hour") was used to further focus on those compounds that would be most responsible for ozone formation during thathigh 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 bytheir 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. 

### ReactivityAdjustedAverage Concentration Basedon GeographicLocation This factor was selected in orderto recognize that some target compounds may be more important to ozone formation in certainparts ofthe country than in others. The 2010 PAMS data were divided into five geographic regions (i.e., NE, SE, MW, SW, and W) depending onthe state thatthe data were collected in

. The data for each compound were averaged across all sites within that geographic region, and then multiplied by their respective MIRvalue to give the reactivity adjusted average concentration for thatregion. Each compound was then scoredbased on aproportional weighting for each geographic region. The maximum score for each compound over all ofthe 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 ofthe regions reviewed. 

### HazardousAirPollutants Several ofthe existing PAMS target compounds are also HAP. This factor was added to account for the added benefitto the air quality program ofmeasuring these HAP compounds inthe PAMS program. The HAP listwas cross referenced verses the PAMS target list, and those PAMS target compounds identified as HAP were given an additional 5 percentto their final score for this factor. Table 2 lists the PAMS target compounds that were identified as HAP. 

### Secondary OrganicAerosolPrecursor Several ofthe existing PAMS 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 PAMS program. A list ofthe 18 most important SOAP compounds was obtained from the literature (Derwent, 2010). This list was cross referenced verses the PAMS target list, and those PAMS target compounds on the SOAP list were given an additional 5 percentto their final score for this factor. Table 3 lists the PAMS target compounds that were identified as SOAP compounds. 

### Summary of Results andSelection of Priority Compounds Figure 1summarizes the overall score and ranking ofthe existing target compounds, with the most important compounds onthe left with decreasing importance moving to the right. As can be seen, many ofthe existing compounds have very lowimportance based on this scoring approach. However, this approach does not by itselfidentify a "cutpoint"to separatepriority compounds from optional compounds. In orderto identify a pointto separate the compounds into priority and optional lists, a running sum ofthe individual scores ofeach compound was created for each compound. The running sum was made up ofthe target compound's score plus the score ofall higher ranked compounds

.For example, the running sum for ethylene is the sum ofthe score for ethylene plus the scores for 3formaldehyde 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 compoundbythe total value and multiplyingby 100, you obtain an estimate ofthe percent ofthe total value obtainedbymeasuring that compound and all higher ranked compounds. Figure 5 graphically represents this calculationfor all current target compounds. As canbe seen, a point is reached where measuring each additional compound adds little value. A decisionto obtain 90 percent ofthe value would leadto a cutpointbetween 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 itfrom its isomer trans-2-butene. Table 1provides the revised priority and optional target lists. CONSIDERATION OF COMPOUNDS TO ADD Three considerations were made in evaluating ifadditional compounds (compounds notcurrently on the PAMS target list) should be added: 1. Ifany VOC compounds importantto ozone formation were not included in the original target list, 2. Ifany VOC compounds importantto air toxic risks or secondary organic aerosols (SOA) formation were not included inthe original target list, and 3. Ifthe existing measurement technologies being used at PAMS sites are capable ofmeasuring the candidate VOC compound. Withrespect to important ozone forming VOC compounds that are notincluded, we note that biogenics have been identified as importantto ozone formation (especially in the east) (Samet, 2011). However, isoprene is the only biogenic onthe target list. Alpha and betapinene have also been identified as importantbiogenic compounds for ozone formation. The existing gas chromatographs (GC) used in the PAMS program are capable ofmeasuringboth alpha and betapinene; however, concerns have been raised about the methods capability ofaccurately differentiating between alpha and betapinene. This issue has been addressed before with other VOC isomers, such as m-xylene and p-xylene where separation ofthe two isomers is difficult. As with m/p-xylene, alpha and betapinene 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 ofbiofuels has been increasing in recent years, and measuring ethanol will allow for tracking the potential impact on ozone formation due to changes infuel usage. As such, ethanol is being added to the priority compoundtarget list. For air toxics, the 2005 NATA (EPA, 2011) was reviewed in orderto identify air toxic compounds consideredto be either national cancerrisk drivers or contributors. Six compounds were identified as national cancerrisk drivers or contributors that can be measuredusing the existing measurement technologies, including

- 1,3 butadiene, acrylonitrile, carbon tetrachloride, ethylene oxide, tetrachloroethylene, and 1,4-dichlorobenzene. Ofthese six compounds, the National Air Toxics Trends Sites (NATTS) program currently measures 1,3 butadiene, carbontetrachloride, and tetrachloroethylene. For consistency with the NATTS, these three compounds are being added to the priority compoundtarget list. 4The list ofSOA compounds discussed above was reviewed again to identify ifany compounds should be considered for additionto the target list. Only benzaldehyde was identified as a compoundthat was considered an important SOA butthat was not on the currenttarget 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 addedto the priority compound target list. IMPLEMENTATION OF LIST CHANGES Based onthis guidance, PAMS monitoring agencies could beginreportingjustthe existing priority compounds listed in Table 1 as early as the 2014 PAMS season. Continuedreporting ofthe optional compounds may continue on a voluntarybasis but should be reviewed inthe overall context ofagency reporting burdens. The EPA is evaluating the ability ofthe existing equipmentto measure the newpriority compow1ds listed in Table 1. These compounds will be evaluated as part ofan auto-GC evaluation currently planned for the winter of2013 and the EPA will be soliciting volunteers from state and local monitoring agencies to assistin the evaluation during the 2014 PAMS season. In addition, the current PAMS retention time cylinders do not include the newpriority compounds, whichwould make it more difficult for monitoring agencies to identifythe peaks for the newpriority compounds. As such, monitoring agencies shouldwait until the EPA/state evaluation is complete to beginmeasuring and reporting the newpriority compounds listed in Table 1, by which time the EPA will have completed the review ofthe new compounds and appropriate retention time cylinders will be available. Table 1lists four carbonyl compounds as priority compounds. It should be notedthat under the current regulatory requirements for PAMS, carbonyls are onlyrequiredto be measured at PAMS areas classified as severe and above nonattainment areas for ozone. This guidance does not supersede the regulatory requirements. However, due to the importance ofcarbonyl measurements inunderstanding ozone formation, PAMS monitoring agencies are encouragedto consider measuring carbonyls attheir PAMS sites. REFERENCES Carter, 

### W. P. L., Development ofthe SAPRC-07 Chemical Mechanism. Atmospheric Environment 2010, 44, (40), 5324-5335. Samet, Jonathan M., "ReviewofEPA's Photochemical Assessment Monitoring Stations (PAMS) NetworkRe-engineering Project." http:// yosemite.epa.gov/ ab/sabproduct.nsf/264cbl227d55e02c85257402007446a4/8412
Derwent, D., Chemical Mechanism Developmentandthe Relative Policy Importance ofOzone and PM Formation in Europe and USA, presented atthe 2010Air Chemical Mechanism Conference. http://airguality.ucdavis.edu/pages/events/2010/acm /DERWENT.pclf USEPA, 2011, Summary ofResults 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 Acetoneb 2,3-Dimethylpentane Benzene 2 4-Dimethylpentane Cis-2-Butene 2-Methylheptane Ethane 2
-Methylhexane Ethylbenzene 2-Methylpentane Ethylene 3-Methylhej:)tane Formaldehydeb 3-Methylhexane lsobutane 3-Metllylpentane Isopentane 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) bThese compounds are carbonyls and are only required to be measured at PAMS sites in ozone nonattainment areas classified as serious or above for the 8-hour ozone standard

. 1

### Table 2. PAMS Targets that are HAP Compounds 2,2,4-Trimethylpentane Acetaldehyde Benzene Ethylbenzene Formaldehyde Isopropylbenzene M/P Xylene N-Hexane 0-Xylene Styrene Toluene



### Table 3. PAMS Targets Identified as Important SOAP Compounds
1 ,2,3-Trimethylbenzene 1 ,2,4-Trimethylbenzene Benzene Ethylbenzene M/P Xylene M-Ethyltoluene N-Propylbenzene 0-Ethyltoluene 0-Xy!ene P-Ethyltoluene Styrene Toluene

2Score 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 < N-Pentane (1) ""' **~** 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""' b. Benzene Styrene N-Hexane Acetone 1-Butene Ethane 2,2,4-Trimethylpentane P... Trans-2-Butene P-Ethyltol"'"' b 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- Trimethylpentane 2,2-Dimethylbutane 3-Methylheptane N-Decane 2-Methylheptane N-Nonane N-UndecaneMIR 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 ......., Ethylben z ene 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 x ane 1: Cyclopentane ...., 0 Cyclohexane l::l :I: M-Diethylbenzene oc;· N-Heptane =r 2,3-Dimethylpentane 0 2 - Methylhe x ane N 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-UndecaneMaximum 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 ., Hhylb'"""' E. (I) [/) Benzene 8" Styrene ., **~** N-He x ane - Acetone ::0 > 1-Butene &: Ethane **~** 2 , 2,4-nlm"hYIP'"""' b [/) .... Trans-2-Butene (I) 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 [/) Cis - 2-Pentene (I) Cl. Acetylene 0 :::3 3 - Methylhe x ane Cl Cyclopentane (I) 0 Cyclohexane CIQ ., M - Diethylbenzene l=ll "0 N-Heptane ::r c=;· 2,3
- Dimethylpentane L' 2-Methylhe x ane

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