UNITED STATES ENVIRONMENTAL PROTECTION AGENCY RESEARCH TRIANGLE PARK NC 27711

June 14, 2012

OFFICE OF A IR QUALITY PLANNING A ND STANDARDS

MEMORANDUM

SUBJECT: Recommendations to Users of CSN and IMPROVE Speciation Data Regarding Sampling Artifact Correction for PM 2.5 Organic Carbon

FROM: Neil Frank, Air Quality Analysis Group, EPA (C304-04) /s/

TO: PM NAAQS Review Docket EPA-HQ-OAR-2007-0492

As part of the review of the national ambien t air quality standards (NAAQS) for particulate matter (PM) completed in 1997, EPA established a PM 2.5 Chemical Speciation Network (CSN) to conduct routine speciation m onitoring, primarily in urban areas across the United States (U.S.). Similar to the CSN, the Interagency Monitoring of PROtected Visual Environments (IMPROVE) program, a cooperative measuremen t effort managed by a steering committee composed of representatives from federal, re gional, and state organi zations, also conducts routine PM 2.5 speciation monitoring, primarily in non-urban areas across the U.S. 1

For a number of years, EPA and IMPROVE St eering Committee representatives have been working together to ensure uniformity between th e measurement and analytical procedures used in the CSN and IMPROVE programs.

In 2011, a committee was formed by the IMPROVE Steering Committee to review the existing procedures used by the IMPROVE program to adjust PM 2.5 organic carbon (OC) measurements for sampling artifact and to iden tify appropriate procedures that might be adopted for the U.S. EPA’s CSN data to ensure comparability and c onsistency with the similar data collected by IMPROVE. The committee consists of representativ es of EPA, National Park Service, Desert Research Institute, Cooperative Institute for Rese arch in the Atmosphere (CIRA) and University of California-Davis. IMPROVE pub licly reports its OC data with an adjustment for sampling artifact; while the EPA currently reports it OC data without such an adjustment. The attached document, issued in January 2012, provides the Committee’s rationale and recommendations for those adjustments.

1 The IMPROVE Steering Committee includes representativ es from EPA, the National Oceanic and Atmospheric Administration, the Fish and Wildlife Service, the Bureau of Land Management, the National Park Service, the U.S. Forest Service, National Park Servi ce, the National Association of Clean Air Agencies, Northeast States for Coordinated Air Use Management, Western States Air Resources Council, Mid-Atlantic Regional Air Management Association, and the State of Arizona.Prior to the Committee’s reco mmendations being issued, EP A reflected on the ongoing carbon measurement work of the IMPROVE program when conducting analyses as part of its ongoing review of the PM NAAQS. Specifi cally, in considering the adequ acy of the current secondary (welfare-related) PM standards to provide protec tion against PM-related visibility impairment as well as alternative standards that were appropriate to consider ba sed upon the availa ble scientific information, the EPA staff made a nominal adju stment to the CSN’s measured OC based on sampler-specific network-wide field bla nks (US EPA, 2011, Chapter 4, Appendix G). 2

For the aforementioned policy assessment, a nominal value of 0.4 μg/m3 was used to adjust OC measurements which were derived with EPA’s IMPROVE-like monitoring method in the CSN. However, the attached technical committee repor t describes lower adjustment values based on monthly median backup filters or field blanks. Those would result in adjustments of ~0.32 μg/m 3 and 0.12 μg/ m 3 , respectively, and the latter approach is tentatively recommended to adjust the data from both networks. Assuming a multiplier of 1.4 to convert adjusted OC into estimated extinction, the use of the two adjustment approach es both result in slight ly higher estimate of organic mass (+0.1 to + 0.4 ug/m 3 ) and estimated extinction (+ 0.4 to + 1.6 Mm-1). Nevertheless, the latter change in visibility for locations with higher calculated extinction is extremely small for either approach when the results are expresse d in deciview (dv) units. If the total aerosolbased extinction using the IMPROVE algorithm is 160 Mm-1 (28.3 dv), the change in calculated extinction using the alternative backup filter or field blank derived OC adjustment both result in a value of 28.4 dv (+ 0.1 dv). Thus, the tentat ively recommended field blank approach is reasonable for the purposes of PM -related visibility assessment.

Attachment

2 US EPA (2011). Policy Assessment for the Review of th e Particulate Matter National Ambient Air Quality Standards. Office of Air Quality Planning and Standards. U.S. Environmental Protection Agency, Research Triangle Par k, NC. EPA 452/R-11-003. April 2011. Available: http://www.epa.gov/ttn/naaqs/standards/pm/s_pm_2007_pa.html

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### Rationale and Recommendations for Sampling Artifact Correction for PM 2.5 

### Organic Carbon

Ann M. Dillner 1 , Mark Green 2
Bret Schichtel 3 , Bill Malm 4 , Joann Rice 5 , Neil Frank 5

, Judy Chow 2 , John Watson 2 , Warren White 1 , Marc Pitchford 2 January 2012

1 University of California, Davis 2 Desert Research Institute, 3 US Park Service, 4 Cooperative Institute for Research in the Atmosphere – CIRA, 5 US Environmental Protection Agency.

Background Organic sampling artifacts occur during PM 2.5 sampling in the U.S. long-term urban Chemical Speciation Network (CSN) and non-urban Inte ragency Monitoring of PROtected Visual Environments (IMPROVE) networks. Organic sa mpling artifacts are interferences in the collection and quantificati on of particulate organic carbon (OC) due to adsorption and desorption of volatile organic compounds (VOCs) and semi- volatile organic compounds (SVOCs) on to the quartz-fiber filter substrate. Estimates of organi c sampling artifacts and their uncertainties are needed to estimate the mass contribution of partic ulate carbon in the calcul ation of aerosol-based light extinction with the IMPROVE algorithms in ur ban or rural areas (Pitchford et al., 2007). Inaddition, estimates of sampling artifacts are needed to understand compliance with the massbased PM 2.5 National Ambient Air Quality Standard (NAAQS) and to determine long-term trends and chemical mass closure.

Organic vapor adsorption can occur during activ e sampling (with air drawn through the filter) and passive exposure (zero face velocity) (Chow et al., 2010; Watson et al., 2009). These vapors leave the sample during thermal an alyses (Chow et al., 2007; 2011) a nd are interpreted as part of the measured particulate OC. This positive (addi tive) OC artifact yields higher values for PM 2.5 OC samples than exist in ambient air. SVOCs can be initially collected as particles, but portions can evaporate during sampling beca use of increases in temperature or decreases of their gasphase concentrations in the sampled air, causing the particles to leave the filter and become part of the gas stream (Mader and Pankow, 2001). Ev aporated SVOCs from sa mpled particles yield negative OC artifacts which tend to be multiplicative and could be reported as part of the particulate mass to represent ambient concentrati ons. A large number of inve stigations have been performed to address organic sampling artifact s based on: passive fiel d blanks (FB), backup quartz-fiber filters (QBQ) placed behind the front quartz-fiber filter (QF), pre-filter organic denuders, and OC to PM 2.5 mass regression analyses, but the re sults are not consistent among the different studies.

CSN and IMPROVE Sampling, Analys is and Artifact Corrections Efforts have been made since 2007 to obtain consistency of PM 2.5 carbon sampling and analyses between CSN and the IMPROVE network. As of October 2009, the URG3000N sampler (URG Corporation, Chapel Hill, NC; modified IM PROVE carbon sampler) has been operating at all CSN sites. The sampler uses 25 mm Pallflex® Tissuquartz TM filters at a nominal flow rate of 22 L/min for OC and elemental carbon (EC) detection following the IMPROVE_A thermal/opticalreflectance (TOR) protocol (Chow et al., 2007). Th is approach is consistent with procedures applied in the IMPROVE network.

Currently, carbon data is not artifact-corrected for CSN. Fo r the IMPROVE network, monthly median OC from the quart z-fiber backup filter (OC QBQ ) is subtracted from all front filters in the network to correct positive organic sampling arti fact. This approach assumes negative sampling artifacts are negligible. No artifact correction is made for EC.

For CSN, FB and QBQ filters were collected at a frequency of 20 percent at all sites during 2007–2010 and then reduced to a 10 percent freq uency as of January 2011. For IMPROVE, QBQ were collected at six sites (1988 to August 2008), which increased to 12 sites with 13 sets of blanks (including 3 urban sites and one collo cated sampler in Phoenix, AZ) from September 2008 onward. FB were collected at ~2–5 percent frequency at all sites from 1988 to 2008, and switched to the 12 QBQ sites after August 2008. Analysis of OC FB and OC QBQ for CSN and IMPROVE showed that:

• For CSN, median OC FB (0.12 μg/m 3 ) is about 60 percent lower than median OC QBQ (0.32 μg/m 3 ), accounting for 6.7 percen t and 17.9 percent of OC QF concentrations (1.79 μg/m 3

, n=5043) during 2008–2010.

• For IMPROVE during 2005-2006, the median OC FB (0.24 μg/m 3 ) was ~12 percent lower than OC QBQ (0.28 μg/m 3 ) accounting for 24 percent and 26 percent of OC QF concentrations (1.03 μg/m 3 , n=41588) respectively. From September, 2008 through December 2010, the median OC FB (0.13 μg/m 3 ) was 43 percent lower than OC QBQ (0.22 μg/m 3 ) accounting for 16 percent and 28 percent of OC QF concentrations (0.81 μg/m 3 , n=47526) respectively.

• OC FB levels are independent of front quartz-fiber filter OC, for both the CSN and the IMPROVE networks.

• OC FB levels are lower than OC QBQ so they represent a lowe r bound on the additive artifact.

• OC QBQ increase with increasing OC QF concentrations at some CSN and at all 12 QBQ IMPROVE sites and therefore overestimate the additive artifact.

• OC FB are more consistent between s ites and by season or day than OC QBQ
.
. • There is a decreasing trend in median OC F, OC FB and OC QBQ from 2005 to 2010 for the IMPROVE sites. Median OC F was 1.07 μg/m 3 in 2005 and 0.80 μg/m 3 in 2010. OC QBQ was 0.29 μg/m 3 in 2005 and 0.22 μg/m 3 in 2010. OC FB was 0.25 μg/m 3 in 2005, and 0.12 μg/m 3
in 2010.

• A sharp decrease in IMPROVE OC FB was found during August 2008 as network FB collection is switched from a random selection of 2–5 percent of the sites to the 12 QBQ sites. Data analysis shows that changing the s ites of collection for the FB is not likely the cause of the decrease.

Recommendation

Based on the above preliminary analyses, we tentatively recommend applying a monthly network median OC FB for artifact correction for the CSN and IMPROVE networks, based on each networks OC FB data. The use of OC FB appears to adequately address the additive artifact. A data adjustment for the multiplicative artifact can be incorporated into the multiplicativeconversion of particulate organic carbon into particulate organic mass. For the original IMPROVE algorithm, this adjustment uses a 1.4 multiplier. The revised IMPROVE algorithm uses 1.8 (Pitchford et al, 2007). For its ur ban locations, CSN uses a 1.4 multiplier.

Additional Measurements and Analyses

It is recognized that thes e proposed artifact corrections utilizing a monthly median OC FB may change upon additional field experiments and da ta analyses. The following questions will be addressed to better understa nd the behavior of the OC FB in IMPROVE and CSN:

• Have there been changes in th e physical properties of the quart z-fiber filters used by both CSN and IMPROVE (manufacturer and product purchased has not changed during the time periods addressed in this report) that caused changes in the OC FB , particularly the sharp decrease observed in 2008? Test s to address this question incl ude (but are not limited to):

o Weigh archived laboratory quartz-fiber filter blanks from different manufacturer lots used in IMPROVE (2005-2010) and CSN (2008- 2010) as an indicato r of the reactive surface area available for organic vapor adsorption.

o Perform optical microscopy and possibly othe r analyses on the archived filters to evaluate if physical pr operties have changed.

o Determine if there is a relationship between mass or other properties of the filter and measured OC FB
.

• Did operational changes (changes from singl e to double quartz filter blanks, changes in sampler operations) in the IMPROVE network ca use the sharp decrease in QF values 2008? Tests to address this question include (but are not limited to):

o Single field blanks and double field blanks will be colle cted in parallel in the IMPROVE network and evaluated for differences.

o Samples collected using the old sampler prot ocol and with the new sampler protocol will be collected in parallel and evaluated for differences.

o Data from IMPROVE sites with FBs will be ev aluated just prior to and just after the change in sampler protocol.
References

Chow, J.C.; Watson, J.G.; Chen, L.-W.A.; Chang, M.C.O.; Robinson, N.F.; Trimble, D.L.; Kohl, S.D. (2007). The IMPROVE_A temperature protocol for thermal/optical carbon analysis: Maintaining consistency with a longterm database. J. Air Waste Manage. Assoc.

, 57 (9): 1014-1023. http://pubs.awma.org/gsearch/journal/2007/9/10.3155-1047-3289.57.9.1014.pdf

. Chow, J.C.; Watson, J.G.; Chen, L.W.A.; Rice, J.; Frank, N.H. (2010). Quantification of PM2.5 organic carbon sampling artifacts in US networks. Atmos. Chem. Phys.

, 10 (12): 5223-5239. http://www.atmos-chemphys.net/10/5223/2010/acp-10-5223-2010.pdf

. Chow, J.C.; Watson, J.G.; Robles, J.; Wang, X.L.; Chen, L.-W.A.; Trimble, D.L.; Kohl, S.D.; Tr opp, R.J.; Fung, K.K. (2011). Quality assurance and qua lity control for thermal/optical analys is of aerosol samples for organic and elemental carbon. Anal. Bioanal. Chem.

, 401 (10): online. DOI 10.1007/s00216-011-5103-3. http://www.springerlink.com/c ontent/a60122x13p757421/fulltext.pdf

. Mader, B.T.; Pankow, J.F. (2001). Gas/solid partitioning of semivolatile organic compounds (SOCs) to air filters - 3. An analysis of gas adsorption artifact s in measurements of atmospheric SOCs and organic carbon (OC) when using Teflon membrane filters and quartz fiber filters. Environ. Sci. Technol.

, 35 (17): 3422-3432. Pitchford M; Maim W; Schichtel B; Kumar N; Lowenthal D; Hand J (2007). Revised algorithm for estimating light extinction from IMPROVE particle speciation data. J Air Waste Manag Assoc, 57: 1326-36. 098066Watson, J.G.; Chow, J.C.; Ch en, L.-W.A.; Frank, N.H. (2009). Methods to assess carbonaceous aerosol sampling artifacts for IMPROVE and other long-term networks. J. Air Waste Manage. Assoc.

, 59 (8): 898-911. http://pubs.awma.org/gsearch/journal/2009/8/10.3155-1047-3289.59.8.898.pdf

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