United States
Environmental Protection
Agency
Office of Air Quality
Planning and Standards
Research Triangle Park NC 27711
EPA-450/4-80-011
June 1980
Air
Guidance for Collection
of Ambient Non-Methane
Organic Compound
(NMOC) Data for Use
in 1982 Ozone SIP
Development, and
Network Design  and
Siting Criteria for the
NMOC and NOX Monitors

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                               EPA-450/4-80-011
 Guidance for Collection of Ambient
  Non-Methane Organic Compound
(NMOC) Data for Use in 1982 Ozone
 SIP Development, and Network and
         Siting Criteria for the
      NMOC and NOX  Monitors
                    by

            Monitoring and Data Analysis Division
           U.S. ENVIRONMENTAL PROTECTION AGENCY
             Office of Air, Noise, and Radiation
           Office of Air Quality Planning and Standards
           Research Triangle Park. North Carolina 27711

                   June 1980

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This report is issued by the Environmental  Protection Agency to report
technical data of interest to a limited  number  of  readers.   Copies are
available free of charge to Federal employees,  current EPA contractors
and grantees, and nonprofit organizations - in  limited quantities - from
the Library Services Office (MD-35),  U.S. Environmental Protection Agency,
Research Triangle Park, North Carolina   27711;  or,  for a fee,  from the
National Technical Information Service,  5285 Port  Royal Road,  Springfield,
Virginia  22161.
This document has been reviewed by  the  Office  of  Air  Quality Planning and
Standards, U.S. Environmental Protection Agency,  and  approved for publi-
cation.  Subject to clarification,  the  contents reflect current Agency
thinking.
                             EPA-450/4-80-011
                                    ii

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                                PURPOSE

     The purpose of this document is to provide guidance for collection of
ambient non-methane organic compound (NMOC) data and siting of the monitoring
instruments.  Ambient NMOC data will be needed as input to various photochemical
ozone models which may be used for the 1982 ozone SIPs.  Special guidance on
NMOC  monitoring is needed because:

     (1)  ambient NMOC monitoring has not been previously required, nor is it
routinely performed in more than a few areas of the Nation;
     (2)  NMOC monitoring is needed, not to determine compliance with a NMOC
ambient air quality standard, but to aid in control  strategy planning activi-
ties associated with achievement of the ozone ambient standard;
     (3)  the nature and extent of NMOC monitoring varies depending on which
of several NMOC-03 relationships (models) is used for control  strategy
planning.
     (4)  NMOC monitoring presents unique problems not generally encountered
in monitoring for other criteria pollutants; and,
     (5)  significant technical, logistical, and other problems exist with
currently available NMOC monitoring methodology.

     This guideline attempts to explain these circumstances more completely
and provide guidance in effectively carrying out an ambient NMOC monitoring
program.

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                              BACKGROUND

     Prior to the initial setting of National  Ambient Air Quality Standards
(NAAQS) in 1971, few agencies outside of California performed air monitoring
for organic compounds.  Even with the setting  of the 0.24 ppm NAAQS, to be
used as a "guide" toward achieving the former  0.08 ppm oxidant standard, NMHC
(or NMOC) monitoring was not required because  NMHC* is not a criteria pollu-
tant (health or welfare based standard) for which the NAAQS must be achieved.

     In the early to mid-1970s, many State and local  agencies began measuring
ambient NMOC, despite the fact that such measurements were not required by
EPA.  Some agencies reported the measured values to the National Aerometric
Data Bank (NADB), but the accuracy of the NMOC data has often been questioned
because the early NMOC methodology was unreliable.   The lack of a NMOC moni-
toring requirement and the unreliability of the methodology in routine field
use prompted a memorandum from OAQPS (in 1975  - copy attached), recommending
a moratorium on purchase of new NMOC instruments.   This recommendation was
based on results of a contractor study of NMOC instrument user experience**
and some unpublished work carried out by EPA in North Carolina.  Anticipating
a subsequent time when NMOC monitoring might be needed,  the memorandum
recommended that existing NMOC analyzers be retained  and that agencies con-
tinue to operate such analyzers for trend purposes,  if desired.  Indeed, some
agencies continued to monitor NMOC routinely.
*   Henceforth in this document,  non-methane  hydrocarbons  (NMHC)  will  be
    referred to as NMOC, since the various  methods of analysis  also measure
    organics other than hydrocarbons.
**  EPA-650/4-75-08, December 1974,  "Survey of Users of  the  EPA Reference
    Method for Measurement of NMHC in Ambient Air"

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     While  there has been little further commercial development of continuous
NMOC monitoring instruments since the 1975 memorandum, this is not to imply
that nothing  has been done in the interim about improving the measurements.
An EPA contractor study investigated the fundamentals of FIDs (flame-ionization
detector) used in NMOC analyzers, and also compared the responses of various
commercial  instruments to ambient atmospheres.*  In addition, ORD/RTP has
maintained  a  program for evaluating new NMOC measurement methods.  ORD/RTP has
also attempted to identify the principal reasons for lack of reproducibility
of NMOC measurements between various instruments.  Unfortunately, due to
inherent problems in measuring NMOC, any new measurement techniques which have
substantially better characteristics than the present continuous FID method
may not be  available for several  years.   On the other hand, some presently
available instruments are thought to be capable of yielding acceptable data at
concentrations above about 0.5 ppmC if they are carefully maintained and
calibrated.

                    AMBIENT NMOC MONITORING METHODS
     Two general  categories of NMOC monitoring methods are available:
These are a)  "continuous" and b)  "discrete" or sometimes called "grab sample"
analysis.

Continuous  Methods
     Continuous methods provide hourly average NMOC concentrations, up to
24 per day, at fixed sites.  They are somewhat analogous to N0/N09/N0
*   EPA-600/4-77-033, June 1977, "Evaluation of the EPA Reference Method for
    the Measurement of Non-Methane Hydrocarbons - Final Report".

                                     3

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analyzers in that they provide separate measurements of total  organic compounds
(TOC) and of methane (CH.).  The difference between the TOC and CH. measure-
ments is (defined as) the NMOC measurement.  Most NMOC analyzers are designed
to perform the subtraction automatically and provide a direct NMOC output.

     The TOC and CH. measurements are made with a FID, but two methods for
separating the CH. from the TOC are in general  use.  Chromatographic analyzers
use adsorbent columns to separate the CH. from  all other organic compounds.
These analyzers tend to be rather complex, require special operating pro-
cedures, and provide up to 12 analyses per hour rather than a truly continuous
measurement.  Other analyzers use a catalytic process to separate CH. by
oxidizing all hydrocarbons other than CH. in a  special control led-temperature
oxidizer.  They may be either dual  channel, in  which the TOC and CH. are
measured simultaneously, or cyclic, where TOC and CH. are measured alter-
nately.  Aside from operational complexity, both Chromatographic and catalytic
types of continuous NMOC analyzers are equally  acceptable, subject to the
limitations discussed below.

     Continuous NMOC analyzers suffer from a number of inherent technical
problems which limit the reproducibility of data which they provide.  Chief
among these is the necessity of subtracting two comparably-sized numbers to
obtain a measure of the NMOC.  Because the difference between the TOC and CH.
measurements—i.e., NMOC—is usually considerably smaller than either of the
individual TOC or CH. concentrations, small errors in the TOC or CH. measure-
ments may become large percent errors in the NMOC difference.   Furthermore,

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ambient TOC and CH. concentrations must be measured on broad,  relatively
insensitive ranges of the instrument in order to accommodate the frequent wide
excursions of the TOC and CH^ ambient concentrations.*  Also,  FIDs  are sensi-
tive to changes in operating conditions such as flow rates,  temperature,
burner cleanliness, etc., which may result in zero and span  drift.   These
characteristics make careful calibration and accurate balance  of the TOC and
CH. channels imperative.  However, with good operational  and quality control
procedures which include careful attention to gas pressures  and  frequent zero,
span and calibration checks, the analyzers should yield useful measurements at
concentrations above about 0.5 ppmC.

     Other NMOC analyzer problems over which the operator may  have  little or
no control include measurement of TOC and CH* in different samples  of air due
to sequential, cyclic operation (usually not a problem for hourly averages),
non-uniform sensitivity to various organic compounds and  from  one analyzer
design to another, operational complexity, and potential  safety  hazard from
hydrogen gas which all FIDs require.

     There is currently no reference or equivalent method for  NMOC,  nor is one
expected in the near term (3-5 years).   However, it is recommended  that
analyzers selected for NMOC monitoring in the next one to two  years  be of the
conventional FID type described above,  using either chromatographic  or cata-
lytic separation of CH..  Several such analyzers are currently available from
*  For example, NMOC instruments are usually set to measure  full-scale
   concentrations of TOC of 10 ppm.  If the TOC concentration were  5 ppm
   and the CH4 concentration were 4 ppm, NMOC would be 1  ppm.  Assuming
   a 10% error in the TOC measurement--0.5 ppm—this would result in a
   50% error—1 + 0.5 ppm—in the NMOC computations.

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manufacturers, such as the Bendix Corporation (Lewisburg, WV), Byron Instru-
ment Co. (Raleigh, NC), Meloy Laboratories, Inc. (Springfield, VA) and Mine
Safety Appliances Company (Pittsburgh, PA).  In addition, older, out-of-
production analyzers such as the Beckman 6800 may be used if still in
servicable condition.

     The use of a non-conventional  NMOC analyzer may be considered, provided
its NMOC measurements have been characterized and found to be reasonably
relatable to sum-of-species measurements provided by sophisticated GC analysis
(see next section) or are otherwise deemed suitable for the application for
which the NMOC data will be used.  Such non-conventional  analyzers might be
based on techniques such as direct-reading backflush chromatography, processes
which convert all NMOC compounds to CH,, etc.  Additional guidance on the
advantages and suitability of these new techniques will be forthcoming from
EPA as test, characterization and comparison data for them become available.

"Discrete" or "Grab-Sample" Analysis
     More accurate and sensitive NMOC measurements can be obtained by analysis
of ambient air samples using a sophisticated, multi-component gas chromato-
graphic (GC) analysis system.  The  cost and complexity of such a system pre-
cludes jji^ situ monitoring; hence, ambient air samples must be collected in
plastic bags or stainless steel canisters and subsequently analyzed in a
laboratory.   Furthermore, because of these costs and complexities, analysis
of ambient NMOC by this method is limited to short-term (1-2 months) studies
rather than year round monitoring.   Discrete samples can  be collected by
integration over a period of one hour or more,  or grab samples can be collected
in a few seconds.  They are transported to the chromatograph and analyzed

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within a few hours to minimize losses or contamination from the bag or
container.

     The analysis yields individual species concentrations of low-to-medium
carbon number compounds (Co-Cif)). commonly found in ambient air.  Individual
compounds may be combined into functional groups, such as paraffins, olefins,
aromatics, etc., if desired.  A simple total NMOC measurement may be obtained
by summing the concentrations of the various individual compounds and groups
in the sample.  This measurement provides accuracy superior to the continuous
NMOC measurement, especially at concentrations below 0.5 ppmC.  The concen-
tration of individual compounds may be useful information for other air
pollution studies, also.

     The sophisticated GC analysis of discrete samples and the high level of
expertise necessary for these complex procedures are a serious problem which
limits the usefulness of this method in routine applications.  Such capability
cannot be developed in a few weeks, or even months, by an agency or private
laboratory.  Standardized published techniques are not yet available; thus,
skill is acquired only by apprenticeship and experience.  Even the number of
university or contractor laboratories presently able to perform these analyses
competently is very limited.*  EPA will attempt to widen contractor support
capabilities by the summer of 1981.  A guidance document outlining the pro-
cedures which should be followed in collecting, handling and analyzing samples
has recently been prepared.**
*   Much of the current capability will be utilized in the Northeast
    Corridor and other studies in the summer of 1980.
**  EPA-45Q/4-8Q-008, April 1980, Guidance for the Collection and Use of
    Ambient Hydrocarbon Species Data in Development of Ozone Control Strategies.

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                 CURRENT NMOC MONITORING REQUIREMENTS

     Current NMOC ambient monitoring requirements stem entirely from the need
to control hydrocarbons as precursors to the photochemical formation of ozone.
Recent advancements in the development and verification of quantitative models
(e.g., photochemical dispersion models)  relating NMOC emissions and NMOC
ambient concentrations to photochemical  ozone concentrations now allow improved
estimation of the degree of NMOC control  necessary to achieve the NAAQS for
ozone.  Thus, NMOC data have become a necessary input to models that are used
to develop the ozone NAAQS attainment strategy.  Current models (e.g., city-
specific EKMA* and sophisticated photochemical  dispersion models) require NMOC
as input.

Method Applicability
     Photochemical dispersion modeling is the most sophisticated type of
modeling.  Photochemical  models require  detailed organic species data in
order to establish initial and boundary  conditions -  as well as continuous
NMOC data - for trouble shooting and verification of  the model  in each new
application.   Organic species data  are also needed to check the accuracy of
emission inventory estimates in various  portions of the modeling region.
Grab samples  of organic species taken by  aircraft are needed as input and to
verify organic concentrations aloft in the model.

     EKMA requires continuous measurements of the higher NMOC levels in the
polluted air  mass in the areas of highest precursor emission density.   Some
*  Empirical  Kinetic Modeling Approach
                                        8

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measure of organic compounds upwind is needed to assess transport into the
area if this is thought to contribute significantly to the area's NMOC burden.
Because of possible inaccuracies of continuous measurements at lower concen-
trations, (i.e., < 0.5 ppmC), discrete sampling techniques and the summing of
non-methane organic species concentrations are recommended for upwind NMOC
measurements.

     The NMOC data are to be collected during the season of peak ozone con-
centrations (summer).  NMOC concentrations are often high in central  urban
locations and at those times of the day (early morning) when accurate measure-
ments are required for the models.  Also, NMOC concentrations are most often
high on those days when high values of ozone are measured later in the day.
Consequently, (with the exception of upwind measurements) NMOC concentrations
are more frequently expected to exceed the 0.5-1.0 ppmC threshold where the
continuous NMOC analyzer's accuracy is thought to be satisfactory for model
needs.  Continuous NMOC measurements below 0.5 ppmC may be inaccurate for use
in the 03 models, even when the instruments are operated under the best quality
control procedures.

Additional Technical  Assistance To Be Available
     As noted earlier, errors due to variability with currently available
continuous NMOC analyzers are a problem, and limit their usefulness to higher
concentration measurements.  To minimize these errors and to obtain maximum
usefulness of the continuous NMOC data, careful attention to calibration,
operational  procedures, and quality assurance is necessary.  Technical
guidance in these areas will be provided in a Technical Assistance Document

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(TAD) to be prepared by EMSL at Research Triangle Park,  North Carolina.
Regional Offices will  be notified and supplied copies of this TAD as soon
as it is available (expected in November 1980).   For NMOC measurements to be
made in Summer 1980, interim guidance is given in an appendix to this document.

     As the EPA's Environmental Monitoring Systems Laboratory (EMSL) develops
guidance on standard calibration procedures,  quality assessment and quality
control procedures for existing NMOC analyzers,  OAQPS plans to develop and to
present workshops on this material,  as well  as video tapes of such workshops,
in order to transfer the newly developed procedures and  information to State
and local agencies in  a timely fashion.

     General  technical guidance on organic species analysis by GC (including
recommendations for standardized procedures)  has been developed for use by
State and local agencies (see Footnote on Page 7).  However, it is generally
recommended that a competent contractor be sought to carry out this part of
the NMOC measurements, rather than for a State or local  agency to attempt
such a measurement program,  particularly if they have not had previous
experience with GC techniques.

     Another reference source for monitoring  guidance for NMOC includes the
May 10, 1979, Part 58, Monitoring Regulations.  Further, the guidance docu-
ment, "Site Selection  for the Monitoring of Photochemical Air Pollutants,"
EPA-450/3-78-013, April 1978, provides additional detailed guidance for
location of NMOC monitors and classifying spatial scales of representativeness.
                                      10

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                        FUTURE NMOC MONITORING

     Beyond the development of the 1982 SIPs, there will  be a continuing  need
for NMOC ambient monitoring data.  Agencies should continue to utilize  their
NMOC monitors to assess trends in ambient NMOC and ozone  levels relative  to
hydrocarbon emission reductions.  This information will provide an additional
means (besides ozone trends) to assess the effectiveness  of hydrocarbon  (and
NO ) control strategies.  Also, these trend data will provide further insight
  A
into the projection capabilities of the models used.

     Under the current SIP surveillance plan requirements, State and local
agencies will be conducting ambient monitoring at SLAMS*  or NAMS* sites for the
various criteria pollutants.  In view of the continuing needs for NMOC monitor-
ing, NMOC monitoring may be required as part of the NAMS  networks.  Thus,
analyzers purchased in earlier special monitoring efforts for the 1982 ozone
SIPs may eventually be incorporated into the NAMS network, with the resulting
data to be submitted to EPA for control strategy evaluation.  It is anticipated
that Part 58 rulemaking revisions pertaining to NAMS NMOC monitoring would not
occur before calendar year 1982.  During the time period  after a State or local
agency has collected NMOC data for the 1982 SIPs, and up  until the NMOC revi-
sions to Part 58, it is recommended that control agencies continue operating
and submitting NMOC data to EPA.
*   SLAMS  State/Local Air Monitoring System
**  NAMS   National Air Monitoring System
                                   11

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       NETWORK DESIGN AND SITING  CRITERIA  FOR  NMQC/NOX MONITORS
A.   General  Conclusions






     Two general  considerations  for  all  sites  are recommended  before discussing



specific criteria.






     1.   NMOC and NO  analyzers should  be collocated;  and,
                     A





     2.   NMOC and NO  levels  and/or ratios  should not  be  predominantly
                     A


          influenced by the emissions from a single  street or  source.
B.   Type and Location of Site





     Although the following types of sites are  listed  in a  general  priority



order, it will  be up to each specific user to determine the appropriate  number



and mix of sites in the development of his individual  SIP.   Siting  recommen-



dations for use in the EKMA model have been made  in EPA-450/2-77-021a  and



EPA-450/2-77-021b.







     1.   Maximum Emissions Density Site  -  This site should  be  located in



the area of maximum emissions.  Automobile traffic density  can be used as a



surrogate for NMOC/NO  emissions.  In an absence  of traffic density maps,
                     A


the commercial  business district of the urban area may be used to reflect the



area of maximum emissions.  If  there is a predominant  summer morning wind



direction associated with the area, the downwind  fringe of  the area of maximum



emission density is preferable.  If there is no predominant wind  direction,



the centroid of these areas is  preferable.  Since the  conversion  of NMOC/NO
                                                                           A


to oxidants occurs over a wide  area and at elevated altitudes, the  monitoring



site should reflect this, as well, and not merely be representative of the
                                     12

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emissions of a single street.  Therefore, the minimum height acceptable for
this type of monitoring is 10 meters.  Minimum setbacks from roadways will be
the same as those found in the Part 58 guidance for N02 monitoring sites,
except that the setback requirements may be met by horizontal, vertical or
slant distance.  These setbacks are reproduced in Table 1.  Spacing from
obstructions is covered in Section C below.
Table 1.  Minimum Separation Distance for NMOC/NO  Stations and Roadways
                         (edge of nearest traffic lane)

Roadway Average Daily Traffic,          Minimum Separation Distance Between
     Vehicles Per Day                   Roadways and Stations, Meters

     110,000                                 >10a
      15,000                                  20
      20,000                                  30
      40,000                                  50
      70,000                                 100
    >110,000                                >250

a Distances Should Be Interpolated Based on Traffic Flow
     2.   Industrial Source Emissions Site  -  Although the bulk of NMOC/NO
             "         ~^^^"~              ~ ™^^^™                                 j\
emissions comes from transportation sources, some urbanized areas have appre-
ciable emissions from the industrial sector.  As with the maximum emission
density site, a downwind fringe area would be preferable.  The spacing from
obstructions, height and setback criteria would be identical to the maximum
emission density site, with the additional restriction that the site should
not be within 200 meters of the 10° plume sector from a point source
constructed along the prevailing summertime morning wind direction.
                                    13

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     3.   .Upwind background Site  -  Th'is *si;te is'used tn "some trode'Ting'appli-
 cations that call for the ^incoming NMOC/NO  to be handled 'differently from  the
                                          •/\
 locally generated pollutants.  'As such, the 3 i tie should be located 10-35 km
 upwind of the urbanized area in the most frequent summer wind direction.  The
 site should comply with setback requirements as shown in Table 1.  Since the
 upwind site should not be affected by local sources, the height criteria can be
 less restrictive.  Accordingly, the recommended height is 3-15 meters.  The
 spacing from obstructions is covered in Section C below.

     4.   Downwind Edge of City Site  -  This site is located further downwind
 than the area of maximum emissions and, therefore, has had a chance for more
mixing than the maximum emission site.  The specific siting criteria should
conform to that for the upwind background site.

C.   Spacing from Obstructions

     Buildings, trees and other obstacles may possibly scavenge N0?.   In order
to avoid this kind of interference,  the station must be located well  away from
such obstacles so that the distance  between obstacles and the inlet probe is at
least twice the height that the obstacle protrudes above the probe.  For similar
reasons, a probe inlet along a vertical wall is undesirable because air moving
along that wall may be subject to possible removal mechanisms.   The inlet probe
should also be at least 20 meters from trees.  There must be unrestricted
airflow in an arc of at least 270° around the inlet probe,  and  the predominant
wind direction for the season of greatest pollutant concentration potential
must be included in the 270° arc. If the probe is located  on the side of the
building, 180° clearance is required.
                                      14

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                                SUMMARY
     The following points summarize the guidance related to NMOC data
collection for 1982 SIPs:

          NMOC data collection is needed for modeling to support development
          of 1982 ozone SIPs.

          NMOC monitoring activities will  differ, depending upon the type
          of ozone model  to be used for control  strategy development.
          Requirements for use with EKMA are identified in EPA-450/2-77-021a
          and EPA-450/2-77-021b.

          NMOC data collection should take place during the oxidant
          season, if not all  year.

          Continuous analyzers used for NMOC monitoring in the next one
          to two years should be  of the conventional  selective oxidation or
          chromatographic FID type.  New,  unconventional  NMOC techniques may
          be considered if characterization data are  available to show suita-
          bility.

          Continuous monitors provide data useful for modeling at higher
          concentrations  (> 0.5-1 ppmC).   Improved maintenance/operating/
          quality assurance procedures are being developed to provide greater
          assurance that acceptable data are collected.

          Measurements made with  continuous NMOC monitors are generally
          expected to be  useful,  since many of them will  be made during peak
          NMOC season, at peak NMOC time during  the day,  and in the area of
          peak NMOC emission density when  ambient NMOC concentrations are
          expected to be  high.

          Some organic species measurements may  also  be needed, especially
          for determining upwind  NMOC concentrations  and  for use in sophis-
          ticated photochemical dispersion models if  a State chooses to use
          one of these models.

          NMOC instruments should be collocated  with  NO  instruments.
          Monitoring sites should be carefully chosen in  order to minimize
          undue influence of emissions from single sources.

          Additional guidance is  available on:

          -  NMOC species data collection  (EPA-450/4-80-008);

          -  maintenance/operating procedures for continuous analyzers
             (in preparation  - available by November  1980).

          Long-range EPA  plans call for considering requiring routine NMOC
          monitoring at selected  NAMS in major metropolitan areas.
                                     15

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                INTERIM GUIDANCE FOR NMOC MEASUREMENTS

     NMOC analyzers should be set up and operated according to the manu-
facturer's instructions.  Special attention should be given to matching or
balancing the TOC and CH^ responses, particularly on dual-FID analyzers, so
that the CH. is accurately subtracted from the TOC (whether done internally
by the analyzer or external to the analyzer).   Flow rates, as well as other
operational parameters, should be measured to  assure that they are correct.
For chromatographic analyzers, initial and periodic manual chromatograms
should be obtained to verify that the gating and operational sequences are
properly timed.  Also, all maintenance procedures should be carried out
according to the manufacturer's instructions.

     NMOC measurements should always be reported in ppmC (explained later)
and be referenced to a propane standard.   This is because FID analyzers
respond differently to different organic  compounds, and propane provides a
response close to the average FID response of  the organic compounds in the
atmosphere.  NMOC measurements referenced to propane are comparable to
total NMOC measurements made by GC species analysis and are appropriate
for use in EKMA.

     The way that NMOC analyzers are referenced to propane differs, depend-
ing on the design of the analyzer.   Analyzers  having a direct NMOC output
with an individual span control  may be physically calibrated directly with
propane.  However, the TOC and CH^ responses may have to be first calibrated
                                 16

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with CH. to insure that the CH. measurement is correctly subtracted from
the TOC measurement.  Other analyzers must be calibrated with CH^.  Then
the (TOC - CH.) reading (obtained either from the analyzer or by external
subtraction) must be corrected to propane as follows:
               NMQC -      -      - A
where M and A are the least squares slope and intercept, respectively, of
the analyzer's response to a multipoint calibration with propane after the
physical calibration with CH^.

     Familiarization with the instrument is essential to obtain accurate
calibration and to avoid unnecessary adjustments that would waste calibration
gas mixtures and complicate the procedure.

     Cylinders containing compressed gas mixtures of known concentrations of
hydrocarbons in air are used for calibration of the analyzer.  These concen-
tration standards should be certified by the supplier to be traceable to NBS
Standard Reference Materials (SRM) or should be otherwise referenced to such
SRM's.  NMOC concentrations are expressed in parts per million carbon (ppmC),
which is simply the volumetric concentration (ppmV) multiplied by the carbon
number (number of carbon atoms per molecule) of the hydrocarbon compound (see
example below).

     Two separate hydrocarbon standards are generally needed — a CH.-in-air
standard for calibrating and matching the CH. and TOC responses, and a
propane-in-air standard to calibrate the NMOC response.  As an example, the
following standards would be appropriate for a 0 to 10 ppmC scale range:
                                 17

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Standard          ppmV     Carbon Number     ppmC    Used to Calibrate
methane in air     8             1            8      CH^, TOC response
propane in air     3             3            9      NMOC response

     A single gas cylinder containing both methane and propane standard con-
centrations may be used for periodic  span checks between calibrations, but
such a combined standard will  not allow the channel  balance to be checked or
adjusted.   Furthermore, a two  component mixture is usually more expensive
and may not be as accurate as  separate hydrocarbon standards.  The following
examples are appropriate for combined standards, if this procedure is chosen:

Compound                           ppmV      Carbon Number       ppmC

Subtracting Analyzer:
     methane                       8              1              8
     propane                       339
     CH, channel response:                                        8
     NMOC channel response:                                       9

Nonsubtractjng Analyzer:
     methane                       3              1              3
     propane                       236
     Total                                                        9
     CH4 channel response:                                        3
     TOC channel response:                                        9

All methane standards should be specified to have less than 0.1 ppmC total
of other hydrocarbons as impurities.   Absence of hydrocarbon impurities is
                                 18

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important for precise analyzer balance and accurate calibration; all methane
standards should be checked for impurities before use.

     Calibration concentrations may be provided directly by gas cylinders
containing the appropriate concentration levels.  For multi-point calibration,
a separate cylinder is needed for each concentration level.

     Greater economy can be realized by obtaining calibration concentrations
by dilution, since many different concentration levels may be provided from
a single standard cylinder, and consumption of the standard is greatly
reduced.  In this case, the standard should have a concentration level of
several hundred ppmC.  An ample source of clean, hydrocarbon-free zero air
is, of course, required.  The dilution system must have suitable means to
control and accurately measure the flow rates of the standard and the zero
air, and the two flows must be thoroughly mixed.

     All calibration gases should be introduced into the analyzer at atmo-
spheric pressure through the sample inlet.   This can be facilitated by
installing a ''tee" fitting between the analyzer sample inlet and the cali-
bration source, with one leg of the tee left open to the atmosphere as a
yent.  The flow of calibration gas must exceed the flow demand of the
analyzer at all times, with the excess released at the atmospheric pressure
yent.  This atmospheric vent flow should be about 20 to 50% of the analyzer
flow to assure adequate venting without excessive waste of calibration gas.
Additional guidance or more specific information on the operation of NMOC
analyzers may be obtained from EMSL, Research Triangle Park, NC by calling
(919) 541-3791 (FTS 629-3791) or (919) 541-2622 (FTS 629-2622).

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               UNITED SIAHIS ENVIRONMENT 1. I'HOTLCTION AGLNCY
              Office of Air Quality Pic n.imj and  Standards
              Research Triangle Park, N rth Carolina   27711
M';;.|l.(  i.  The Unreliability of Non-Methan,/  Hydrocarbon  IMTK:   i >> nnv -\o7r
        Analyzers and its Impact on IIC/O>: Strategies               y'J

i-KOM:    c.  J. Stei'jerwald, Director
        Office of Air Quality Planning and Standards

TO:      Roger Strclow, Assistant /vdministrator
        for Air and V;aste Management

        Surveillance and Analysis Division Directors,  Regions
        Air and Hazardous Materials Division Directors,  Regions I-X

            Recent studies with commercial non-methane hydrocarbon
        (NMIIC) analyzers have established the fact  that these
        instruments yield unreliable data.  Not only  do instru-
        ments from different manufacturers produce  different results,
        even instruments  from the same manufacturer,  with  supposedly
        the s£ime characteristics, yield data sometimes differing
        by a factor of two.   (For comparison, measurements  made witli
        different S02 instruments have a  correlation  coefficient
        of better than O.G5).  These studies were carried  out by
        i;PA laboratories  as well as contractors,  and  the results
        are thus thought  to be conclusive.

            Iii an attempt to identify  the source  of trouble, one of
        the NERC/RTP laboratories is contracting  for  a 15  month
        study of the NMIIC instrumental technique.  At this  time,
        it js thought that  the solution  lies in  rigid specification
        of the design and construction of the  NMIIC analyser as well
        as a strJct protocol for its operation.   The  contractor will
        .'submit his report about January  1977.   In the meantime,
        however, the consequences of these  studies and the distant
        solution cause EPA  concern  in  the following areas:

             1.  The doubt cast on the  Appendix J curve.

             2.  The enforced delay  in  possibility of developing area
        specific upper  limit  1IC/OX  curves.

             3.  The  validation  of  HC/0X  models.

             4.  The  lack of knowledge  about true NMIJC concentrations
        and  their  trends in urban  areas.

             All of  these arc  interrelated,  of  course.  Accepting
         the  situation  as it exists, KPA's position on these  areas
        of concern should be as follows:
 EPA Form 1370-6 (Rr». 6-72)

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                                2

      Any doubt which may  arise <.:<>;icerninq  the  Appendix J curve
is misplaced .  LJata used  to construct  Appendix  J did not co-mo
from these instruments — rather, from total  hydrocarbon measure-
ments, in general.  Under  any  circumstances,  there is an abun-
dance of evidence from many other experimental  programs shpwing
a relation between ambient hydrocarbons and photochemical
oxidants.  Thus, despite  the acknowledged deficiencies in the
Appendix J curve, it should still be used where appropriate in
11C/C,. reduction strategies.

      A better relation may exist between non-methane hydrocarbon
and ozone, but the data are not available.   There is reason to
believe, too, that such a  relation  differs  from one metropolitan
area to another.  V.'c had  hopes of cons true timj  arca-r.pccif ic
.Appendix J-like curves;  and using  these to better define required
hydrocarbon  ei.'.i ssion reductions for the various areas.  V/c
believe  the  idea  is  still  a cjood  one,  but we suggest delaying
its i mpj eiuen ta tion until  we have  reliable MH11C data from good
instruments.

      iMost of our  laboratory work and  field studies on IIC/0,,
relations arc not affected by  this  discovery of the faulty
I-.'MliC  instrumental  method.   Usually  gas chromatographic procedures
were  used which  are  accurate  for  specific hydrocarbons.  It is
onJy v; lie IT ambient hydrocarbon  measurements are made by the
IJHIIC  technique  that  we  lose  accuracy.

       As  you know,  MH11C measurements are not required  from  the
 states  at  the  present  time.   In forthcoming revisions  to
 40  CFR 01.17,  we had considered requiring  those metropolitan
 areas  where  ozone concentrations  are estimated  to be  above  the
 N/\/K.i!j  in  1977  to begin monitoring for Ni'iilC.  This requirement
 has now been deleted from the  draft regulation  but  will  be
 reconsidered at  the  appropriate time.

       It is  our  belief that the reference  method  for  M-iliC,
 detailed in  <10 CFK 130.10 7\ppendix E, doer,  not  need  to be
 rescinded at this time, however,  both because  it  never had
 the force of being a required procedure  for a  criteria pollu-
 tant and also because the basic procedure  may  still be valid.
 'The specifications may just need to be  Lightened  up.   OnJy
 after the i:j;KC/KTP experimental program  has been  completed
 will we knew whether it is necessary.

       For those agencies  which already  have NfMlC  anoly/ers,
 it is ucbatabJe whether or not _thei.r  use should be  continued.
 I'erh.ips "Hi-,.' "trend data would  be interes t.i ng .   However, it
 is J mi rob.ib] e that past or present values  have the  required
 accuracy for any absolute moaning  at  this  time.  On the

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other hand, Lliir; is not to say 'hat the .1 MS truments should
be junked.  Depending on what j.:; i'ound within  the next  few
months, it may be possible to modify present instruments  to
make their measurements meaningful.  However,  we certainly
cannot encourage the purchase of new NMIIC analyzers at  this
time .

     This memo has addressed only the subject  of ambient  NMIIC
analyses.  Neither mobile source testing nor stationary source
testing is affected by this discovery of unreliable data  from
these instruments since other analytical methods arc  used.

     In summary, because of design differences between  various
NM1IC analyzers, data from these instruments are unreliable.
The questioned accuracy of the data obtained from such  instru-
ments should in no v:ay discredit the belief that hydrocarbons
arc a major factor in the generation of photochemical oxidants.
Irradiation chamber studies, as well as ambient measurements
using gas chromatographic techniques, which do provide  accurate
hydrocarbon data, have documented the role of  hydrocarbons
in smog reactions.

cc:  D. Dorchers

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                                    TECHNICAL REPORT DATA
                            (Please read Instructions on the reverse before completing)
1. REPORT NO.
  EPA-450M-8Q-011
                              2.
                                                             3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE Guidance for  Collection of Ambient Non-
  methane Organic Compound Data for Use In 1982  SIP Devel
  opment, and  Network Design and Siting Criteria for the
  NMOC and NOx Monitors	
                                                             5. REPORT DATE
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
                                                             8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
  Monitoring  and Data Analysis  Division
  Office of Air Quality Planning and Standards
  US Environmental Protection Agency
  Research Triangle Park, NC  27711
                                                             10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
                                                             13. TYPE OF REPORT AND PERIOD COVERED
                                                             14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
  Project Officer;   Dr. Harold G.  Richter
16. ABSTRACT
       Guidance is given on the  selection, siting and use of NMOC monitoring
  instruments  for use in preparing 1982 Ozone SIPs.   Some of the commercially  available
  NMOC continuous monitors can provide data useful for modeling  and for development of
  NMOC abatement strategies,  if  they are carefully maintained and calibrated.
  Collection of grab samples  of  ambient air for  subsequent analysis by GC methods may be
  needed if a  photochemical model is to be used,  but this may be better done by  a
  contractor.
17.
                                KEY WORDS AND DOCUMENT ANALYSIS
                  DESCRIPTORS
                                               b.lDENTIFIERS/OPEN ENDED TERMS  C. COSATI Field/Group
  NMOC Monitoring Strategies
  NMOC Monitoring
  1982 SIP Development
18. DISTRIBUTION STATEMENT
                                               19. SECURITY CLASS (This Report)
              21. NO. OF PAGES
                   25
                                               20. SECURITY CLASS (Thispage/
                                                                           22. PRICE
EPA Form 2220-1 (Rev. 4-77)   PREVIOUS EDITION is OBSOLETE

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