## Federal Reference Method s for NO y 

## and p

- SO 4 

## for the N ew

C ombined NO

x 

## and SO

x 

## S econdary N AAQS

Research Plan

January 20, 2011



### Project Period: J uly 20 10 to July 20 12

United States Environmental Protection Agency

Office of R esearch and D evelopment National Exposure Research Laboratory Human Exposure and Atmospheric Sciences Division

Investigators: Russell Long, Surender Kaushik

, Tad Kleindienst, Robert W. Vanderpool

, and Fred Dimmick2

I. Acronyms

AIM

- Ambient Ion Monitor

APS

- Aerodynamic Particle Sizer

CASTNET

- Clean Air Status and Trends Network

FEM

- Federal Equivalent Method

FP

- Filter Pack

FRM

- Federal Reference Method

GPT

- Gas Phase Titration

H 2 O (g) - Water Vapor

HEASD

- Human Exposure and Atmospheric Sciences Division

HNO 2 - Nitrous Acid

HNO 3 - Nitric Acid

IPN

- Isopropyl Nitrate NAAQS

- National Ambient Air Quality Standard

NCORE

- Multi

- pollutant Network

NERL

- National Exposu re Research Laboratory

NH 3 - Ammonia

NO

- Nitric Oxide

NO 2 - Nitrogen Dioxide

NO

x - Oxides of Nitrogen (NO

x = NO + NO 2 )

NO y - Total Reactive Nitrogen

NO

z - Reacted Oxides of Nitrogen (NO

z = NO y - NO

x )

NPN

- N

- Propyl Nitrate

O 3 - Ozone

OAP

- Office of Atmospheric Programs OAQPS

- Office of Air Quality Planning and Standards

OAR

- Office of Air and Radiation

ORD

- office of research and Development

PAN

- P eroxyacetyl N itrate

p

- NH 4 - Particulate Ammonium

p

- NO 3 - Particulate Nitrate

p

- S O 4 - Particulate Sulfate QAPP

- Quality Assurance Project Plan

SO 2 - Sulfur Dioxide

SOP

- Standard Operating Procedures

SO

x - Oxides of Sulfur

t

- NO 3 - Total Nitrate (t

- NO 3 = HNO 3 + p

- NO 3 )

UVF

- Ultrav iolet Fluorescence

VOAG

- Vibrating Orifice Aerosol Generator3

I I. Abstract Summary Information

Title: Federal Reference Methods for NO y and p

- SO 4 for the N ew C ombined NO

x and SO

x S econdary NAAQS Project Lead: Russell W. Long , Ph.D., ORD/NERL/HEASD Key Collaborators and Interested Parties : Surender Kaushik, Tad Kleindienst, Robert W. Vanderpool, and Fred Dimmick, OAR/OAQPS, OAP , State/local air agencies, Teledyne API, American Ecotech, Thermo Environmental Project Period: July 2010

- July 2012 Project Summary: EPA has been considering an indicator with a combination of measurements (SO 2 , p

- SO 4 , and NO y ) that form the NAAQS measured component of a new combined NO

x and

SO

x secondary standard

. Federal reference and/or equivalent methods (FRM/FEM) are currently available only for SO 2

. H owever, p

- SO 4 is measured at over 500 sites nationally, most often through the use of a filter pack sampler followed by off

- line ion chromatographic analysis.

Based on an initial survey of available information

, methods of this type are reliable and provi de

consistent data. The determination of NO y is attempted in near real time using optical monitors employing an externally locate catalytic converter to convert all NO y species to NO

, prior to possible line losses, which can then be detected using O 3 - chem iluminescence. T his NO y methodology is now being deployed in EPA’s national NCORE network. However, a large degree of uncertainty exists as to the quality of the NO y data

, the ability to measure total NO y , and the applicability of this method for routine regulatory use

.

This research will result in the d evelop ment and evaluat ion of sampling and analytical methods required to support the promulgation of the proposed NO

x and SO

x secondary NAAQS

. It is anticipat ed that these newly developed/evaluated methods will be promulgated as the federal

reference methods for the combined standard. For SO 2 , no work is needed as a designated FRM already exists for the primary standard. For p

- SO 4 , the CASTNET filter pack (FP ) method will be adopted and modified as needed to make it suitable for use as an FRM. The catalytic

conversion/ chemiluminescence based method f or NO y , will require significant research to assess its adequacy for use as an FRM. K ey unresolved science que stions associated with this method need to be identified and studies performed to address these questions. After the available data

and information on NO y measurement methods is compiled, HEASD will be able to describe the accuracy, precision, and reliability of the NO y method. Measurement uncertainties associated with existing NO y methods fall mainly in these important areas: total NO y capture (i.e.,

par ticulate NO 3 ); converter performance ( efficiency with respect to individual NO y species, consistency ( i.e., changes in efficiency over time ); inlet placement (i.e., vertical distribution of

NO y in ambient air); potential interferences; and instrument calib ration, and challenge (zero, span, precision) procedures.

Following procurement and evaluation of commercially available NO y monitors, HEASD will

conduct field and laboratory based stud ies to address the above mentioned measurement

uncertainties and to ev aluate the method for use as a FRM. It is anticipated that t est results and developed procedures will provide guidance to regional, s tate and local monitoring agencies in deployment and operation of the proposed NO

x and SO

x secondary FRM monitoring network

. In addition, t hese approved measurement methods will ser ve as important tools for monitoring agencies towards development of effective implementation plans aimed at deposition of acidic species into aquatic systems.4

I I I

. Project Implementation Plan

A. Objectives

1. Adopt FRM specifications for SO 2 b ased upon current FRM for primary SO 2 NAAQS.

2. Propose and f

inalize FRM specifications for p

- SO 4 b ased upon adop tion of CASTNET FP method for p

- SO 4

. 3. Evaluate t he catalytic conversion/ chemiluminescence based method as a potential

FRM for NO y .

a. Quantify overall uncertainties associated with the NO y method

b. Identify and quantify interferences and measurement challenges associated

with the NO y measurement method

.

c. Investigate vertical NO y distribution in a representative air shed to establish

inlet placement criteria

. d. Develop calibration and challenge procedures for NO y method

e. Evaluate commercially available chemiluminescence based NO y monitors for

use as FRMs

4. Propose and f

i nalize FRM specifications for NO y .

B. Technical Approach Adopt FRM specifications for SO 2

. The existing FRM for the primary SO 2 NAAQS is based upon ultra

- violet fluorescence (UVF) 1 . FRM analyzers using this UVF technique can provide the needed detection limits, precision, and accuracy and thus fulfill all purposes of an FRM. As a result, no work will be done on the current SO 2 FRM and it will be adopted as the FRM for the

SO 2 indi cator of the proposed secondary standard.

Additionally, some interest has been expressed by OAR/OAQPS in pursuing the CASTNET FP

method for SO 2 2, 3 as an additional FRM or possible FEM due to the expected prohibitive cost associated with equipping a site with UVF FRM monitors. As a result, HEASD will use the substantive, readily available data and information available for the FP SO 2 method. HEASD will provide a technical summary of the data and develop the basis/rationale for making it an

FRM/FEM. HEAS D will prepare docket materials, proposal preambles, response to comments, and the FRM in regulatory text format.

Propose and finalize FRM specifications for p

- SO 4

. HEASD w ould use the readily available and documented data, procedures and information a vailable for the CASTNET p

- SO 4 FP method 2, 3

. HEASD will provide a technical summary of the data and supporting information and develop the basis/rationale for adopting it as an FRM. HEASD will prepare docket materials, proposal preambles, response to co mments, and the FRM in regulatory text format. This approach for a p

SO 4 FRM when combined with the above two approaches for a SO 2 FRM will provide scientifically defendable methods where SO

x deposition is involved

.

Evaluate the catalytic conversion/chemiluminescence based method as a potential FRM for NO y . Current NO y instruments based upon catalytic conversion and chemiluminescence detection methodology are available commercially but have not been assessed thoroughly enough to develop as an FRM. As a result, HEASD has identified measurement uncertainties and key5

unresolved science questions associated with this method. These uncertainties and associated questions are:

(1) Total NO y capture

– It iis well established that the proposed m ethod is capable of the near quantitative capture of certain key gaseous components of NO y such as NO and NO 2 . However, there are questions about this methods capability in capturing the two components of NO y most relevant to nitrogen deposition, nitric a cid (HNO 3 ) and particulate nitrate (p

- NO 3 ).

(2) Converter efficiency

– The catalytic converter most often employed in instrumentation of this type is a heated molybdenum converter wherein the more highly oxidized oxides of nitrogen (NO 2 , HNO 3 , HNO 2 , p

- NO 3 , PAN) are converted to NO which can then be detected via O 3 - chemiluminescence. It is well established for the species NO 2 , that the converter efficiency is
≥98% thus the basis for use of this method as the FRM for the NO 2 primary NAAQS. However,

what i s not known is how efficient the molybdenum converter is in converting other oxides of nitrogen to NO for detection. This particular aspect will be important as these proposed FRMs will be deployed in air sheds with differing NO y compositions. In additio n, uncertainties also exist associated with the stability of the converter over extended periods of time with respect to

total NO y and the individual components.

(3) Inlet placement

– It is standard practice in the determination of total NO y to locate the molybdenum converter externally, very near to the point of sampling to reduce sample transfer line losses of species such as p

- NO 3 and HNO 3 . Most often the converter and inlet probe are placed at a height of 10 m to eliminate any bias associated with ver tical concentration gradients

of HNO 3 and p

- NO 3 . However, additional research needs to be performed to identify and quantify potential vertical gradients in total NO y . This research will result in the inlet siting criteria for the proposed FRM.

(4) Inte rferences

– potential interfering species in the catalytic conversion/chemiluminescence

determination of NO y include certain hydrocarbon s , H 2 O (g) and NH 3 . However, the extent to which, and under what circumstances these species interfere is not known and must be identified and quantified

.

(5) Calibration/challenge procedures

– Although not an uncertainty, detailed method calibration and operating procedures must be developed and demonstrated as part of the FRM process. This includes procedures to test t he performance of the FRM (i.e., zero, span, precision checks). It is anticipated that calibration procedures will be similar to those used in t he NO 2 primary NAAQS FRM with slight modification to account for the elevated converter height. However, performance challenge criteria will have to be identified that best represent the mixture of NO y species that are expected to be present in the various air sheds across the U.S.

To address the above mentioned science questions, uncertainties and measurement challenges, the following approach will be taken:

(1) Qu antify overall uncertainties associated with the NO y method

– Overall uncertainty will be quantified by collocated pair sampling to determine precision, bias and comparability between

identical instruments under laboratory and ambient conditions . The laboratory based studies will6

allow these figures of merit to b e determined for individual NO y species and various NO y mixes under controlled laboratory conditions using simulated NO y species while the ambient studies will result in an assessment of precision, bias, and comparability under conditions that the FRMs

wou ld experience upon routine deployment . All ambient air studies will be conducted at the AIRS sampling site on EPAs RTP, NC campus as it is anticipated that this site is representative of the proposed sites in the NO

x and SO

x combined secondary standard ne twork. There are currently three commercially available NO y instruments (Teledyne API, Thermo Environmental, and American Ecotech) that will be evaluated for use as FRMs . Table 1 gives an inventory of the instrumentation/equipment to be used during the l aboratory based and ambient studies.

Table 1. Inventory of instrumentation/equipment for laboratory and ambient studies.

Instrument Species Analyzed Parameters Investigated

Thermo 42i

- Y NO y Monitor NO, NO y , NO 2 +NO

z precision, bias, Total NO y , speciated

NO y , NO y capture, converter efficiency/stability, vertical NO y flux

American Ecotech 9843 NO y Monitor NO, NO y , NO 2 +NO

z precision, bias, Total NO y , speciated

NO y , NO y capture, converter efficiency/stability, vertical NO y flux Teledyne API T200U NO y Monito r NO, NO y , NO 2 +NO

z precision, bias, Total NO y , speciated

NO y , NO y capture, converter efficiency/stability, vertical NO y flux Teledyne API 200EU Photolytic NO 2 Monitor NO, NO 2 , NO

x speciated NO y

URG 9000D Ambient Ion

Monitor p

- NO 3 , p

- NH 4 , HNO 3 , HNO 2 , NH 3 speciated NO y , interfering species

GC

- based PAN PAN speciated NO y TSI VOAG p

- NO 3 , p

- NH 4 speciated NO y , NO y capture, converter efficiency, interfering species

Perm Tube Oven HNO 3 , NH 3 speciated NO y , NO y capture, converter efficiency, interfering species Dynamic Dilution Gas

Manifold gas phase species speciated NO y , NO y capture, converter efficiency, interfering species

(2) Identify and quantify interferences and measurement challenges associated with the NO y measurement method

– P otential measurement challenges and interferences will be identified, quantified and documented through rigorous laboratory based and ambient method evaluations. In the laboratory based studies these include using state of the science equipment and facilities to challenge the NO y instrumentation with simulated individual NO y species and mixtures of species to gain an understanding of NO y capture (inlet and sampling losses), molybdenum converter efficiency and stability with respect to individual NO y species and total NO y , and measurement interferences of other atmospherically relevant species in the NO y determination. A TSI Vibrating Orifice Aerosol Generator (VOAG) will be used to generate test aerosols of

known particle size, composition, and concentration to introduce to th e candidate method as shown in Figure 1. A TSI Aerodynamic Particle Sizer (APS) will be used to monitor the7

Figure 1

. Schematic representation of the aerosol generation system to be used during the

ambient studies.

a erodynamic diameter of the generated particles and a filter pack sample will be used as a reference. The filter pack sample will be collected and analyzed according to EPAs Compendium of Methods for the Determination of Inorganic Compounds in Ambient Air, IO

- 2 4

and IO

- 3 5 . A dynamic dilution system will be used to provide gas phase species to the candidate method as shown in Figure 2. The source gas will be obtained either through compressed gas cylinders (NO, NO 2 ) or thorough the use of permeation tubes (HNO 3 , HNO 2 , NH 3 ). An annular denuder sample collected and analyzed according to EPAs Compendium of Methods for the

Determination of Inorganic Compounds in Ambient Air, IO

- 4 6 will be used as a reference. The aerosol and gas generation systems will allow HEASD to produce individual NO y components and potential interfering species under extremely controlled conditions. Ambient studies will confirm laboratory findings under conditions that the potential FRMs will experience upon deployment. During the amb ient based studies, NO y will be speciated into its individual components and summed for comparison with results obtained with the method for total NO y . This comparison will allow for the assessment of the capability of the method in determining

NO y as an FRM and identify any sampling shortcomings. Currently, HEASD has the capability for the high time resolution determination of the majority of the NO y components including the most atmospherically and deposition relevant p

- NO 3 and HNO 3 and the most abundan t
component

, NO 2 (Table 1).8

Figure 2

. Schematic representation of the dynamic dilution gas generations system to be used during the laboratory based studies

(3) Investigate vertical NO y distribution in a representative air shed to establ ish inlet placement

criteria

– The vertical distribution of NO y concentrations will be investigated using collocated sampling with comparable instruments w here inlet probes and converter boxes are located at differing heights along a 10m telescoping or lean down tower. As stated previously, the results of this investigation will provide data for inlet siting criteria of the proposed FRM.

(4) Develop calibration and challenge procedures for NO y me thod

– Currently, the FRM for the primary NO 2 NAAQS is based on internally located molybdenum conversion and chemiluminescence detection technology 7 . Per the FRM, detailed calibration and challenge procedures are given. Since the proposed NO y method is b ased upon similar technology, HEASD will investigate and develop calibration procedures based upon those for the NO 2 FRM. However, the more complex composition of NO y will result in the need for investigation and development of new procedures for challeng ing the NO y FRMs calibration

. This includes

identification and testing of existing gases (i.e., NO 2 by GPT, IPN, and NPN) to establish representative test gas es to assess the molybdenum converter efficiency.

(5) Evaluate commercially available chemilumi nescence based NO y monitors for use as FRMs

– The commercially available instrumentation will be evaluated primarily in an ambient setting over a period of at least 1 year to assess the applicability of each monitor as an FRM. During the evaluations, the monitors will be calibrated, operated and challenged as if they were FRMs according to a detailed SOP that will be developed during the evaluation process.

Propose and finalize FRM specifications for NO y . After compilation of the generated data and

information on the NO y measurement method, HEASD will be able to describe the accuracy, precision, and reliability of the NO y instruments and their applicability as FRM. Therefore,9

HEASD will provide a technical summary of the data and supporting informat ion and develop the basis/rationale for adopting it as an FRM. HEASD will prepare docket materials, proposal preambles, response to comments, and the FRM in regulatory text format.

Based upon results from literature searches and available data and in formation, it was the original intent of HEASD researchers to pursue a FRM based upon the most deposition relevant species of total nitrate (t

- NO 3 , p

- NO 3 + HNO 3 ) as the indicator. As a result HEASD may consider, as resources allow, the CASTNET FP method f or t

- N O 3 2, 3 as an additional FRM or possible FEM with the surrogate indicator of t

- NO 3 due to the expected prohibitive cost associated with equipping a site with NO y monitors . HEASD may use the substantive, readily

available data and in formation availabl e for the FP t

- N O 3 method and provide a technical summary of the data and develop the basis/rationale for making it a surrogate FRM/FEM.

HEASD w ould prepare docket materials, proposal preambles, response to comments, and the FRM in regulatory text format.

C

. P roject S chedule and P lanned P roducts Propose and finalize FRM specifications for SO 2

. This effort began in July 2010

. HEASD is recommending that the current UVF FRM for the primary SO 2 NAAQS be designated as the FRM for the SO 2 secondary standard

. Therefore, HEASD will provide this recommendation by the initial rule making date in July 2011. HEASD will provide response to comments and a final recommendation by the final rule making date in

March 2012.

Alternatively, HEASD is currently collect ing available data and information for the FP SO 2 method. HEASD will provide a technical summary of the data and develop the basis/rationale for making it an FRM/FEM by April 2011. HEASD will prepare docket materials, proposal preambles and provide the F RM in regulatory text format by the initial rulemaking date of July 2011. HEASD will provide response to comments and the final FRM in regulatory text format by the March 2012 final rule making date

. Results from this effort will serve as the basis of th e SO 2 FRM.

Propose and finalize FRM specifications for p

- SO 4

. This effort began in July 2010. HEASD is currently collecting available data and information for

the FP p

- SO 4 method. HEASD will provide a technical summary of the data and develop the basis/rationale for making it an FRM/FEM by April 2011. HEASD will prepare docket materials, proposal preambles and provide the FRM in regulatory text format by the initial

rulem aking date of July 2011. HEASD will provide response to comments and the final FRM for p

- SO 4 in regulatory text format by the March 2012 final rule making date

. Results from this

effort will serve as the basis of the p

- SO 4 FRM.

Evaluate the catalytic conversion/chemiluminescence based method as a FRM for NO y . Field and laboratory evaluation of the NO y method relative accuracy, precision, and correlation beg a n in May 2010 and will continue through May 2012 . Following data analysis, data validation, and data interpretation, a summary report of the results will be completed by July

2012 . Results fro m this research effort will be published in a peer

- reviewed journal article (s)

.10

Propose and finalize FRM specifications for N O y . Concurrent to the NO y FRM development and evaluation research, HEASD will provide a technical summary of the available data and develop the basis/ra tionale for making it an FRM by May 2011. HEASD will prepare docket materials, proposal preambles and provide a description of the proposed NO y FRM in regulatory text format by the initial rulemaking date of July 2011. Method evaluations will continue during the period between initial and final rule making (July

2 0 11

- March 2012). HEASD will provide response to comments and the final FRM for NO y in regulatory text format by the March 2012 final rule making

. Results fro m this effort will serve as the basis for the NO y FRM

.

Alternatively, HEASD is collecting available data and information for the FP t

- NO 3 method. HEASD will provide a technical summary of the data and develop the basis/rationale for making

it an alternative FRM by April 2011. HEASD will prepare docket materials, proposal preambles

and provide the FRM in regulatory text format by the initial rulemaking date of July 2011. HEASD will provide response to comments and the final FRM in regulatory text format by the

March 2012 final rule making date

. Results from this effort will serve as the basis of the t

- NO 3 FRM.

D. E xpected R e sults and B enefits

T he U.S. EPA plans a 20 12 promulgation of a new combined NO

x and SO

x secondary NAAQS

, which w ill require sampling and analysis methods that are capable of measuring these metrics with known quality and thus ensure accurate compliance determinations. Developing, proposing

and f inalizing the FRM s for p

- SO 4 and NO y will be a critical component of th e final ruling.

T hese approved measurement methods will ser ve as important tools for monitoring agencies towards development of effective implementation plans aimed at deposition of acidic species into aquatic systems.

Following promulgation of the new s econdary NAAQS for NO

x and SO

x , s tates will be required to develop state implementation plans which will outline measures designed to achieve compliance with the new NAAQS. In order to effectively develop these plans, States must first

have an understandi ng of the factors influencing deposition of nitrogen and sulfur containing species within specific airsheds. Included in these factors is the capability to accurately determine the concentrations of these species in the ambient air. Thus, HEASDs evaluati on of these potential FRMs and development of sampling criteria will establish the tools needed for in

SO 2 , p

- SO 4 and NO y determination. In addition, t his information will be valuable to future multiple air pollutant exposure studies and provide key data for source apportionment modeling

and deterministic model evaluations. The NO y method research will also provide valuable methodology and data to assess the role of NO y species in key atmospheric chemistry processes.

E. Collaboration

HEASD will collaborate with key personnel from OAR /OAQPS during the research and development work as well as the regulatory writing tasks associated with this project. HEASD responses to the public comments, as they relate to finalizing the proposed FRM regulations, will be reviewed by OAR

. Laboratory and field evaluation of the NO y monitors will involve collaboration with their respective manufacturers and potentially State/local air agencies

.11

HEASD will collaborate with OAP (managers for CASTNET) on adoption and m odification of

the CASTNET FP method for SO 2 , p

- SO 4 and t

- NO 3 as FRMs.

I V

. Quality Assurance and Communication Strategy

A. Quality assurance (QA)

The detailed quality assurance project plan (QAPP) “ Identification, Evaluation, and Intercomparison of Methods for Oxides of Nitrogen and Sulfur” (QAP P

- KDO

- 10

- 01 ) will address QA consistent with EPA’s Quality Manual for Environmental Programs (found at http://www.epa.gov/quality/qs

- docs/5360.pdf ). The proposed research and subsequent d ata analysis in this project have a strong foundation in quality assurance in that they come from an existing organization/system with rigorous QA requirements and ha ve been used extensively by

the HEASD team. The derived data from the proposed research will be evaluated and review extensively by HEASD researchers in th eir corresponding areas of expertise

B. Communication Strategy The project will use a variety of communication methods . There will be reg ular meetings to discuss progress and periodic meetings with a larger group to provide updates and ensure the team is meeting expectations. Materials will be produced to inform all stakeholders of the project. Scientific outputs will be produce in the fo rm of reports, manuscripts, symposium/conference presentations to inform the scientific community and general public of the project technical outcomes.

V. Appendices

A. References

1. Reference Measurement Principle and Calibration Procedure for the Measurement of Sulfur Dioxide in the Atmosphere (Ultraviolet Fluorescence Method)

, 40 CFR Part 50 Appendix A

- 1

. 2. Clean Air Status and Trends Network

, Quality Assurance Project Plan

, Revision 6.0

, Appendix 1: CASTNET Field Standard Operating Procedures

, November 2009

. http://epa.gov/castnet/javaweb/docs/qapp_v6_App_01_Field_SOP.pdf

3. Clean Air Status and Trends Network, Quality Assurance Project Plan, Revision 6.0, Appendix 4: CASTNET Laboratory Standard Operating Procedures, November 2009

. http://epa.gov/c astnet/javaweb/docs/qapp_v6_App_04_Laboratory_SOP.pdf

4. Compendium of Methods for the Determination of Inorganic Compounds in Ambient Air, Chapter IO

- 2, Integrated Sampling of Suspended Particulate Matter (SPM) in

Ambient Air

, http://www.epa.gov/ttn/amtic/in org.html

. 5. Compendium of Methods for the Determination of Inorganic Compounds in Ambient Air, Chapter IO

- 3

, Chemical Species Analysis of Filter

- Collected Suspended Particulate Matter (SPM), http://www.epa.gov/ttn/amtic/inorg.html

. 6. Compendium of Methods for the Determination of Inorganic Compounds in Ambient Air, Chapter IO

- 4

, Determination of Reactive Acidic and Basic Gases and Strong Acidity of Atmospheric Fine Particles in Ambient Air Using the Annular Denuder Technology

, http://w ww.epa.gov/ttn/amtic/inorg.html12

7. Measurement Principle and Calibration Procedure for the Measurement of Nitrogen Dioxide in the Atmosphere (Gas Phase Chemiluminescence)

, 40 CFR Part 50 Appendix

F.