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                                  CONTENTS
1.  INTRODUCTION 	   1
    1.1  PURPOSE AND SCOPE	   1

2.  EPISODE MONITORING 	   3
    2.1  STAGGERED SAMPLING  	   3
    2.2  SHORT-TIME INTERVAL SAMPLING  	   5

3.  ALTERNATIVES TO THE REFERENCE METHOD 	   7
    3.1  ESTABLISHING ACCEPTABILITY  	   7
    3.2  ALTERNATIVE METHODS 	   8
         3.2.1  Soiling Index  	   8
         3.2.2  Photometers and Transmissometers 	   9
         3.2.3  Beta Gauge	   9
         3.2.4  Piezoelectric Principle	  10
         3.2.5  TEOM-Tapered Element Oscillating Microbalance  .  11
    3.3  SITE- AND SEASON-SPECIF 1C RELATIONSHIP	12
    3.4  OPERABLE SIZE RANGES FOR PARTICULATE INSTRUMENTS  ...  12

4.  REFERENCES	15

APPENDICES

A.  REFERENCE METHOD FOR THE DETERMINATION OF PARTICULATE
      MATTER AS PM^ IN THE ATMOSPHERE	16
    1.0  APPLICABILITY	16
    2.0  PRINCIPLE   	16
    3.0  RANGE   	17
    4.0  PRECISION	18
    5.0  ACCURACY	  18
    6.0  POTENTIAL SOURCES OF ERROR  	  19
    7.0  APPARATUS	20
    8.0  CALIBRATION	24
    9.0  PROCEDURE   	25
   10.0  CALCULATIONS	28
   11.0  REFERENCES	29

B.  ESTABLISHING RELATIONSHIP OF ALTERNATIVE SAMPLING METHODS
      TO THE REFERENCE METHOD	32
    1.0  OCCASIONS WHEN RELATIONSHIP MUST BE ESTABLISHED ....  32
    2.0  TEST CONDITIONS FOR TAKING MEASUREMENTS 	  34
    3.0  METHODS FOR CALCULATING AND DISPLAYING THE RELATIONSHIP  36
    4.0  METHODS FOR ASSESSING THE RELATIONSHIP  	  41
                                   -m-

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                             1.  INTRODUCTION

     The EPA requirements which are prescribed in Title 40 Code of Federal
Regulations (40 CFR) Part 58 for ambient air quality monitoring for purposes
of State Implementation Plans (SIPs)  are being revised, and will  include
revisions to the emergency episode monitoring requirements now described  in
Appendix C of 40 CFR Part 58.  The emergency episode guidance  provided  in
Federal Regulation Part 51.16 and Appendix L will  be amended to reflect the
new requirements.  The new regulations would permit the use of two modified
versions of Appendix B of 40 CFR, Part 50 - Reference Method for the
Determination of Particulate Matter in the Atmosphere.   The regulations
will  also permit the use of non-reference methods provided that specific
site relationships to the reference method have been determined and docu-
mented and that these methods provide for short-term measurements.

1.1  PURPOSE AND SCOPE
     The procedures specified in the  reference method are for  a 24-hour
sample collection period and a 24-hour equilibrium period before  weighing.
Therefore, the use of the reference method is not responsive to emergency
episodes because of the 48-hour delay in determining the concentrations.
During episode monitoring conditions, the concentrations must  be  available
on a more current basis than provided for in the reference method  for
pollutant index calculations and/or corrective actions  where necessary.
     There are two purposes for this  guideline.   The first is  to  explain
the priciples of operation of the two episode particulate monitoring methods
which are modifications of the reference method:   (1)  sampling  over short

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sampling time intervals;  and (2)  staggered sampling.   These methods may be
used by an agency in their participate matter  episode  network without
further testing in most cases.
     Secondly, a procedure is described for establishing  a site-  and season-
specific relationship between the reference method  and  particulate methods
other than the two mentioned above.

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                          2.  EPISODE MONITORING
     The reference method for measurement of PM^Q requires the  use of an
air sampler designed to pull  air through a filter media in order  to collect
the entrained particles.  The average concentration of PM^Q collected over
a 24-hour period is calculated by determining the mass of the particles
collected and dividing the mass by the volume of air sampled.   Appendix A
provides information on the key topics that are included in the text of the
PM^g reference method.
     Two approaches recommended for episode monitoring require  modifica-
tions to the reference method in order to reduce the time from  the start
of the sampling period to the reporting of the concentration results and/or
to reduce the time between subsequent measurements at the same  sampling
location.  One approach uses short sampling intervals, and the  other uses
staggered sampling intervals.  Both methods rely on greatly reduced
equilibration time for the filter moisture content.

2.1  STAGGERED SAMPLING
     Staggered high-volume sampling is a method that provides the  opportunity
to update the information system at intervals more frequently than every 24
hours, but involves a short period for equilibration of the high-volume
filters.   The method requires the use of multiple monitors  at the  site.
Operationally, the method involves staggered starting of the high- volume
samplers at a constant time interval, running the sampler for 24 hours,
then allowing the filter to equilibrate for 2 hours before  determining the
final  weight of the filter.  As an example, if it is determined that an

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update of the PM^g concentration is required every 4 hours, six high- volume
samplers would be necessary.  Samplers would be started at 4-hour intervals
after the first one is started.   Twenty-four hours after the first sampler
is started, the filter from that sampler is removed, equilibrated for 2
hours, then weighed and the PM^Q concentration determined; hence, the first
concentration is determined approximately 26 hours after the start of
sampling, then an updated concentration is available and the facilities
available to accommodate multiple samplers, the PM^o concentration can be
updated at any desired time increment.  More than six samplers  at one site
are probably not practical; consequently, increments of 4 hours are the
shortest practical  interval .
     Some obvious precautions to be made when employing multiple samplers
include arrangement of the samplers so they sample the same atmosphere but
do not interfere with each other when operating simultaneously.  Operation
of a number of samplers will  also require an electrical  power supply capable
of operating the samplers simultaneously without appreciably affecting the
voltage as samplers turn on and  turn off.
     The principal  advantages of staggered PM^Q sampling are obvious:
     §  Rigorous performance testing  is  not required  for  implementation,
        because it is primarily based on the reference method.
     •  The method is compatible with analytical  facilities dedicated
        to the reference method.
     •  Relatively rapid data reporting  promotes  a  near real-time
        basis for contingency plan  response and public information.
     However, staggered PM^Q sampling  is  not  without disadvantages when
compared with the reference method.  For  discussion purposes, these
disadvantages are separated into (1) predictable  shortcomings and (2)
uncertainties.  Predictable shortcomings  are  those problems that can be

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assessed prior to implementation.  They include the following:
     •  Increased demands of equipment, expendable inventory, electrical
        power, and labor may place an unacceptable strain on monitoring
        resources.
     t  The physical  aspects of the monitoring site may preclude acceptable
        siting of multiple samplers.
     •  Data from the initial  sample will  not be available for  26 hours
        after the sampling start time.
     The principal area of uncertainty  that cannot be properly  assessed
prior to implementation lies in the shortened filter equilibration  period.
Equilibration is necessary to standardize  the moisture condition of the
filter/sample matrix  so that inferred sample mass is not unduly biased  by
retained moisture.  Moisture retention  arises from two processes:
hygroscopicity (differential  absorption of water vapor onto  hydrophilic
materials) and retention of unbound moisture (i.e.,  water droplets  sampled
as if they were PM^o).
     Problems associated with hygroscopicity can be suppressed  by using
nonhygroscopic filtration material, but in many cases chemical  and  physical
properties of the particles must be accounted for.
2.2  SHORT-TIME INTERVAL SAMPLING
     With this method,  an abbreviated sampling period and filter equili-
bration period are used.  A 4-hour sample  period followed by a  2-hour
filter equilibration  is suggested for a reasonable sampling  duration.   The
shorttime interval sampling method requires that a clean  tared  filter be
installed on the sampler after every 4-hour sampling period.  After  removal
from the sampler, the filter is conditioned in a dessicator  for 2 hours,
then weighed.  The PM^o concentration can  be determined 6  hours after
starting the sample.   Trends of PM^o concentrations  can be determined if

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at least four successive sample values indicate  changes  in  the  same  direc-
tion.
     The obvious advantage to using the short- time interval  is  the oppor-
tunity for quicker results from the start of sampling; hence, it is  more
representative of the most recent conditions and only one sampler is required
(compared with six samplers needed for the staggered- sampl ing scheme).
The filter and sample may be less subject to errors introduced, due  to the
abbreviated equilibration time when compared with  the staggered-sampl ing
method.
     Some disadvantages that should be considered  in conjunction with the
short-time samples include the following:
     •  A larger bias in the PM^Q  concentration may occur due to artifact
        particle formation on the  filters.   (Bias, due  to artifact particle
        formation,  will  be reduced with  proper selection of filter material ,
        e.g., by use of quartz or  Teflon filters.)
     •  The possiblity for human error is greater due to the increased number
        of filter changes required.
     •  The average of six 4-hour  concentration values  is only an estimate
        of the true 24-hour continuous sample value.

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                 3.  ALTERNATIVE TO THE REFERENCE METHOD
     Atmospheric aerosols may be monitored or measured  with  instruments
that use several principles for detection other than the reference method.
The advantage of these other instruments is primarily that they  provide
real-time readout of atmospheric aerosol  concentrations.
     A disadvantage of using the nonreference technique is the necessity
of developing a site-specific correlation of an alternative  monitoring
technique with the reference method.
3.1  ESTABLISHING ACCEPTABILITY
     Alternative methods of PM^Q sampling may be acceptable  if a  site- and
season-specific relationship is established between  the alternate  method
and the reference method.  The guidance provided for establishing  the
relationship is adapted from similar requirements for TSP monitoring.  The
evaluation procedure requires simultaneous side-by-side sampling  using the
reference method and the candidate method.  A comparison of  at least 10
simultaneous samples (or sample periods)  is required.   The data resulting
from the simultaneous samples are analyzed to determine if a useful
statistical  relationship exists that will  allow the  use of the alternate
method.  Details of the procedure for evaluating the acceptability of
candidate methods are provided in Appendix B.
     The coefficient of correlation between the reference method and
alternative method being compared should  have a value of 0.85 or greater
in order to accept the alternative method.

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     Several factors should be considered when collecting samples or analyzing
data to determine the correlation of the measurement technique.   Among the
factors to consider are the following:

     •  Influences of seasonal variations
     •  Influences from local  sources
     t  Wind direction

Siting factors and similar considerations are discussed in  a companion
guideline document--"Network Design and Optimum Site Exposure Criteria for
Particul ate Matter".
3.2  ALTERNATIVE METHODS
     The leading methods that may be considered as alternatives  to  the
reference method are discussed in the remainder of this section.
     3.2.1  Soiling Index is a sampling method that has been used in air
monitoring stations for many years and has been relied  upon  to determine
the onset of TSP episodes.  Soiling index is determined by  using  an  auto-
mated tape sampler that draws sample air through a filter tape and  then by
evaluating the change in transmittance or reflectance of light through the
spot on the filter where the sample was collected.   The transmittance  or
reflectance of light is highly variable depending on the type of  aerosol
collected.  The optical  properties of the aerosol  sampled must remain
constant in order to develop a good correlation between mass concentration
and light transmittance.  Site-specific studies would have  to conducted
to show the uniformity of aerosols sampled before an adequate correlation
with the reference method could be developed.

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     Regan et al .  (1979) have reported finding excellent correlation
between fine participate concentrations and COM values.   Regan's  study
included correlation of COH values (average of six  2-hour samples)  compared
against the concentration of fine particules collected on 12-hour  samples
using a high-volme sampler equipped with an Andersen  size-fractionating
sample head.  Total  particle concentrations from the  high-volume  samplers
were corrected to  represent particles less than 15  ym.   Correlation coeffi-
cients for the concentrations from five stages of the size-fractionated
samples ranged from 0.947 to 0.971.  A regression analysis was run  to
establish a quantitative relationship between COH and fine particulate
data.  A good correlation was found in the instance reported, but the
results cannot be  legitimately transferred to other sites without establish-
ing the relationship at each site.
     3.2.2  Photometers and Transmissometers are included in this text
primarily because  they have been  used experimentally  to  attempt to  determine
suspended particle concentrations.  Aerosol  measurement  with optical tech-
niques is most effective for particles that are about 2  urn diameter or
smaller, where the light effect is most pronounced.   In  transmissometers,
particles in the light path attenuate a light beam  and a  signal responsive
to the changes in  light at the detector.  Integrating nephelometers also
depend on changes  in light intensity as the detection principle; however,
in the integrating nephelometer,  scattered light is detected, rather an
attenuated light beam.   Some success has been reported with correlating
atmospheric mass concentration the response of the  integrating nephelometer
(Butcher 1972).
     3.2.3  The Beta Gauge, produced in various models by the GCA
Corporation, operates on the principle of collecting  particles on a

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filter media that is located over a beta particle emitter.   As  the  particles
are collected on the filter material, fewer beta  particles  penetrate  the
accumulated mass.  A correlation between the attenuation  of beta  particles
and the collected particle mass allows the instrument to  provide  real-time
indication of particle concentration.  The typical  sampling period  for  the
beta gauge is 4 minutes; hence, a series of sample must be  averaged to
obtain a value corresponding to a long-term samples using a PM^o  reference
method.  A continuously cycling measurement mode  is available with a  printer
to record each sample result.  Jaklevic et al .  (1981) have  reported the
beta gauge method is equivalent in accuracy to  gravimetric  methods when
proper attention is paid to instrument design and calibration procedures.
The conclusion is based on a study that included  comparison of  data using
the beta gauge, a dichotomous sampler, and a high volume  sampler.
     3.2.4  The Piezoelectric principle has been  used in  other  instruments
designed to sample airborne particles and automatically display or record
a mass concentration, such as the piezobalance  produced by  TSI, Incorporated.
The standard piezopbalance is available with a  3.5  urn particle  diameter
cutoff option, but the instrument can be ordered  with particle  selectors
with cutpoint up to 10 pm.  The piezobalance operates using a piezoelectric
quartz crystal  that oscillates at a constant frequency  under static conditions.
As particles are collected on the detecting crystal,  the  frequency of the
oscillations changes in respect to the mass of  particles  collected.  The
change in frequency is detected and compared with  the frequency at the
initiation of the sampling period, and a concentration  is calculated at
the end of a 2-minute sampling period.  The concentration is displayed at
the end of the sample period until  the beginning of the next period.  The
                                     10

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piezobalance is available in a portable, manually operated version and  a
fixed-location, fully automated version that is capable of continuously
cycling (i.e., sampling, data recording, and automated cystal  cleaning).
     The beta attenuation and the piezoelectric quartz crystal  instruments
provide the short-term sampling options that are desirable for episode
monitoring.  Some caveats must be recognized when considering  the  use of
these instruments.  The effect of the moisture collected in the sample  is
not compensated for by either instrument.   The effect of moisture  collection
is likely to have a more significant effect on the piezoelectric instrument.
Particle collection efficiencies of the instruments must also  be evaluated.
Although the instruments are considered to  be useful  for collecting  particles
up to 10 ym aerodynamic diameter, ambient conditions  may considerably alter
the actual  size of particles collected.  Fairchild (1980)  has  evaluated
both types of instruments and compared results with those  from  gravimetric
sampling.  The report indicates the instruments evaluated  accurately sample
particles with +^25 percent of the gravimetric concentration when  four or
more instrument readings were averaged.  The report also stated that the
piezoelectric quartz crystal  collected particles greater than 6  m aerodynamic
diameter with poor efficiency due to poor mechanical  coupling  with the
quartz crystal.
     3.2.5  TEOM-Tapered Element Oscillating Microbalance
     A report of a recently designed instrument to detect  fine  particles
and determine the concentration after a 30-minute sampling  period  indicates
the instrument may be useful  for short-term  measurement  of  fine particles.
The instrument must undergo further development, but  is  to  be commercially
available.   The TEOM works by collecting particles on  a  filter cartridge
that is attached to the narrow end of hollow tapered  tube.  The wide end
                                     11

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of the tube is attached to the instrument.  The tapered tube oscillates
during the sampling period, with frequency of the oscillation being accurately
monitored.  Loading of particles in the filter cartridge causes a shift in
the oscillation frequency, which is interpreted and translated into a
concentration by a microprocessor.
     The system that has been developed and reported on is equipped with a
2.5 ym cutpoint cyclone preseparator, so the measurment relates to the fine
aerosol portion of airborne particle mass.  The TEOM can be operated for a
long time period with printer output programmed on a 1/2- to 1-hour schedule.
A heater element in the intake maintains a constant temperature of the
incoming aerosol  to provide frequency stability and minimize the effect of
humidity on the measurement.
     The TEOM is a new device that has not been proven in field use.  The
device reportedly has resolved difficulties that exist with the quartz
crystal micrebalance instruments.
3.3  SITE- AND SEASON-SPECIF 1C RELATIONSHIP
     Any of the automated aerosol measurement units must be compared with
the PMiQ reference method to obtain a site- and season-specific relationship
before the measurements from the nonreference method can be accepted for
episode monitoring.  Guidance for developing the site- and  season-specific
relationship is provided in Appendix B.
3.4  OPERABLE SIZE RANGES FOR PARTICIPATE  INSTRUMENTS
     The Lawrence Berkeley Laboratories  (LBL)  has compiled  an  inventory  of
the specifications and capabilities for  a  variety of air pollutant monitoring
instruments.  The LBL document describing  particle-collecting  or  detecting
instruments provides the following table,  Table 1,  to  indicate  possible
combinations of instruments that will  detect particles over a  wide  range of
                                     12

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particle sizes.  The instruments  are  described in generic terms, but the
listing can give valuable guidance  to  possible instrument types that may
be feasible for PM^Q episode  monitoring.
                                    14

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                               4.   REFERENCES
1.  Acton, F.S,   1959.   Analysis of straight-line data.   New  York:  John
    Wiley and Sons.

2.  Butcher, S.S., and  Charlston, R.J.   1972.   An Introduction  to  air
    chemistry.   New York:   Academic Press.

3.  Fairchild,  C.I.; Tillery, M.I.; and Ettinger, H.J.   1980.   An  evaluation
    of fast response aerosol  mass monitors.  LA  8220  ,  Los  Alamos Scientific
    Laboratory,  Los Alamos, N. Mex.

4.  Kramer, D.N., and Mitchel, P.W.  1967.   Eavluation of  filters  for
    high-volume sampling of atmospheric particulates.  J. Am.  Ind.  Hyg. Assoc.
    (28)3:224-28.

5.  Lewis, C.W.  1981.  The tapered element  oscillating micrebalance:  a
    monitor for  short-term measurement  of fine  aerosol mass measurement.
    EPA Report  600/S2-81-146.  Environmental  Sciences  Research  Laboratory,
    Research Triangle Park, NC  27711.

6.  Lippmann, M.; Kleinman, M.T.; and Bernstein,  D.M.  1979.  Size-mass
    distributions of the New York summer aerosol. Ann. N.Y. Acad.  Sci.
    322:29-44.

7.  Natrella, M.G., ed. 1963.  Experimental  statistics, handbook 91.
    National  Bureau of  Standards, Washington, D.C.

8.  Regan, G.F.; Goranson, S.K.; and Larson,  L.L. 1979.   Use of tape
    samplers as  fine particulate monitors.  J.  Air Pol. Control Assoc.
    (29) 1158-1160.

9.  U.S. Environmental  Protection Agency.   1979.   Guidance for  selecting
    TSP episode  monitoring methods.  EPA Report 450/4-79-U07, Office of
    Air Quality  Planning and Standards, U.S.  Environmental Protection Agency,
    Research Triangle Park, MC  27711.
                                     15

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                                 APPENDIX A
           REFERENCE METHOD FOR THE DETERMINATION OF PARTICULATE
          MATTER AS PM10 IN THE ATMOSPHERE - Appendix J  40 CFR 50
              (Reproduced as proposed in the Federal Register)
1.0  APPLICABILITY
     This method provides for the measurement of the mass concentration
of particulate matter with an aerodynamic diameter less  than  or  equal  to
a nomimal 10 micrometers (PM^Q)  in ambient air over a 24-hour period  for
purposes of determining attainment and maintenance of the primary  and
secondary national  ambient air quality standards for particulate matter
specified in §50.6 and §50.7 of this chapter.  The measurement process is
nondestructive, and the PM^g sample can be subjected to  subsequent physical
and chemical analyses.  Quality assurance procedures and guidance  are
provided in Part 58,.Appendices  A and B, of this chapter and  in  References
1 and 2.
2.0  PRINCIPLE
2.1  An air sampler draws a measured quantity of ambient air  at  a  constant
flow rate into a specially shaped inlet where the suspended particulate
matter is inertially separated into one or more size fractions within  the
PM]_Q size range.  Each size fraction in the PM^Q size range is then
collected on a separate filter over the specified sampling period.  The
particle size discrimination characteristics (sampling effectiveness and
50 percent cutpoint) of the sampler inlet over the PM^Q  size  range are
functional  specifications described in Part 53 of this chapter.
2.2  Each filter is weighed (after moisture equilibration) before  and
after use to determine the net weight (mass)  gain due to  collected "PM^o-
The total volume of air sampled,  corrected to EPA reference conditions (25°

                                     16

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C, 101.3 kPa), is determined from the measured volumetric flow rate and the


sampling time.  The concentration of PM10 in the ambient air is computed as


the total mass of collected particles in the PM10 size range divided by the


volume of  air sampled,  corrected to reference conditions, and is expressed


in micrograms  per  standard cubic meter (ug/std m3).  For samples collected


at temperatures  and pressures  significantly different  from  EPA reference


conditions,  these  corrected concentrations  can differ  substantially from


actual concentrations  (in  micrograms  per actual cubic meter), particularly


at high  elevations.  The actual PM10 concentration  can  be  calculated from


the  corrected concentration,  using  the  actual  temperature  and  pressure


during the sampling period.


2.3   A  method based  on  this  principle will  be  considered a  reference


method only  if (a)  the associated sampler meets the requirements specified

                                       •
in this  appendix  and those in  Part  53  of this chapter  and  (b)  the method


has been designated as  a  reference method  in accordance with  Part  53 of


this chapter.


3.0   RANGE


      The lower limit of the mass concentration range can be estimated from


the repeatability of filter  tare weights, assuming  the  nominal  air sample


volume for the sampler.   The upper limit of the concentration range cannot


be specified.   For  samplers  having a filter-changing  mechanism,  there may


be  no  upper  limit.   For  samplers  that  do  not  have  a  filter-changing


mechanism, the upper limit is  determined by the point at which the sampler


no  longer maintains the  specified  operating  flow rate due  to increased


pressure drop  across the loaded filter(s).   This limit cannot be specified


because  it  is a complex and undetermined  function of  particle size dis-


tribution  and  type,   humidity,  filter  type,  and  perhaps  other  factors.



                                  17

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4.0   PRECISION

      The reproducibil ity  of  PM10  samplers must be 15 percent or better as

required by  Part 53  of this chapter,  which prescribes  a reproducibility

test  procedure  that  determines the  variation .in the  PM10  concentration
                                 i
measurements  of  identical  samplers   under  typical  sampling  conditions.

Other  specifications  are  provided in  Part  S3 for  the particle  size  dis

crimination  characteristics  and the  flow rate  stability of  the  sampler.

Continual assessment  of the  precision via collocated  samplers  is  required

by  Part  58  of  this  chapter for PM10 samplers used  in certain monitoring

networks.

5.0   ACCURACY

      Because the  sizes  of  the particles  making up  ambient  particulate

matter vary  over a wide  range  and  the concentration  of particles  varies

with particle size,  it is difficult to define the absolute accuracy of PM10

samplers.  Part 53 of this chapter provides a specification for the sampling

effectiveness of PM10  samplers.  This sampling effectiveness specification

requires that the expected mass concentration measurement calculated for a

candidate PM10  sampler, when  sampling a specified typical ambient particle

distribution, be within ± 10 percent of that calculated for an ideal  sampler

whose  sampling  effectiveness  is explicitly  specified.   Also,  the  particle

size for 50  percent  sampling  effectiveness is required to be 10 ± 1 micro-

meters  (urn).    Other  specifications  related  to  accuracy  apply  to  flow

measurement and calibration,  filter media, analytical  (weighing) procedures,

loss  of  volatiles, and artifact  and  nonsampled particulate  matter.   The

flow rate accuracy of PM10 samplers used in certain monitoring networks is

required by  Part 58  of this  chapter to be  assessed  periodically  via flow

rate audits.
                                   18

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6.0   POTENTIAL SOURCES OF ERROR


6.1   Loss of  Volatile  Particles:   Volatile particles collected on filters


can  be  lost during  shipment and/or  storage of  the  filters prior  to the


postsampling weighing3.   Although shipment  and storage  of  loaded filters


are sometimes unavoidable, filters should be reweighed as soon as practical


to minimize these losses.


6.2   Artifact Particulate Matter:  Positive errors in particle mass measure-


ments can  result from  retention of  gaseous species  on  filters4'  5.  Such


errors include the  retention of sulfur dioxide and nitric acid.   Retention


of sulfur  dioxide  on filters, followed by oxidation to sulfate is referred


to as artifact particulate sulfate formation, a phenomenon which increases


with increasing  filter  alkalinity6.   Artifact particulate nitrate, result-


ing primarily  from  retention of nitric acid, occurs  to  varying  degrees on


many filter types,  including glass fiber, cellulose ester, and many quartz


fiber filters5'  7>  8>  9> 10.  Filters  that  meet  the  alkalinity specifica-


tion (section  7.2.4) should  show little or  no  artifact  sulfate.   Negative


artifact  is  the  loss  of collected particulate  matter during sampling  by


volatilization or  chemical reaction11.  Loss of  true atmospheric particu-

                                         IS\
late nitrate has been  observed on Teflon  filters8 and inferred for quartz


fiber filters11.   The  significance of this  problem for  PM10 mass measure-


ments will vary  with location and ambient temperature.   However,  for most


sampling locations,  PM10  mass concentration errors due to nitrate artifact


are expected to be small.


6.3   Nonsampled Particulate  Matter:   Particulate matter can be deposited


on  filters  during   periods   when  the  sampler   is  inoperative12.   Timely


installation and retrieval of filters prior to and following the sampling


period should help to minimize this problem.
                                  19

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6.4   Humidity:  The effects of ambient humidity on the sample are unavoid-



able.   The  moisture conditioning  procedure  in section 9.0  is  designed to



minimize the effects of moisture on the filter medium.



6.5   Filter Handling:   Careful handling of filters between presampling and



postsampling weighing  is  necessary to avoid errors due to damaged filters



or  loss  of  particles   from  the  filters.   Use  of a  filter cartridge or



cassette may reduce the magnitude of these errors.



6.6   Flow Rate Variation:  Variations in the sampler's operating flow rate



can alter  the  particle size discrimination characteristics  of  the sampler



inlet.   The magnitude  of  this  error will depend on  the  sensitivity of the



inlet to  variations in flow rate  and on the particle distribution  in the



atmosphere  during  the sampling  period.   The  use  of an  automatic  flow



controller (section 7.1.4) is required to minimize  this error.



6.7   Air  Volume  Determination:   Errors in  the air  volume determination



can result  from errors in the  flow rate and/or sampling  time measurements.



The automatic flow controller also serves to minimize errors in  the average



flow rate  determination.   The  use  of an elapsed time meter (section 7.1.5)



is required to minimize the error in sampling time.



7.0   APPARATUS



7.1   PM10 Sampler



7.1.1     The sampler shall be  designed to:



          a.   Draw the air sample, via reduced internal  pressure, into the



               sampler  inlet and through the  filter(s)  at  a uniform face



               velocity.



          b.   Hold and seal  the filter(s) in a horizontal  position so that



               sample air is  drawn downward  through the filter(s).
                                  20

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          c.   Allow the filter(s) to be installed and removed conveniently.



          d.   Protect  the filter(s)  and  sampler  from 'precipitation and



               prevent insects and other debris from being sampled.



          e.   Minimize  leaks  that  would  cause error in the measurement of



               the air volume passing through the filter(s).



          f.   Discharge  exhaust air  at  a sufficient  distance  from the



               sampler  inlet  to minimize  the  sampling  of  exhaust  air.



          g.   Minimize the collection of dust from the supporting surface.



7.1.2     The sampler  shall  operate at a controlled flow rate specified by



its  designer  or manufacturer,  and it  shall   have  an  inlet system  that



provides  particle  size  discrimination  characteristics  meeting  all  of the



applicable performance specifications prescribed in Part 53 of this chapter.



The  sampler inlet  shall  show no  significant wind  direction dependence.



This  requirement can  generally  be  satisfied  by  an  inlet shape  that  is



circularly symmetrical about a vertical axis.



7.1.3     The sampler  shall  provide a  means to measure the total flow rate



during  the  sampling  period.   A  continuous  flow recorder  is  recommended.



The sampler may  be  equipped with additional flow measurement devices if it



is designed to collect more than one particle size fraction.



7.1.4     The  sampler  shall  have an automatic  flow  control  device capable



of  adjusting  and  maintaining  the  sample  flow  rate  within  the  limits



specified for the sampler  inlet over normal variations in line voltage and



filter pressure  drop.   A convenient means must be provided to temporarily



disable  the automatic  flow control  device to allow  calibration of  the



sampler's flow measurement device.



7.1.5     A  timing/control device  capable of starting  and  stopping  the



sampler  shall  be used  to  obtain an elapsed  run-time of 24 ± 1 hr (1,440
                                  21

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± 60 nrin).   An elapsed time meter, accurate to within 15 minutes, shall be
used to  measure sampling  time.   This meter is  optional  for samplers with
continuous  flow recorders  if  the  sampling  time measurement  obtained by
means of the recorder meets the ± 15 minute accuracy specification.
7.1.6     The  sampler  shall  have  an  associated operation  or instruction
manual  as  required  by §53.4 of this  chapter  and which includes either the
text or a reproduction  of this appendix.
7.2   Filters
7.2.1     Filter Medium:   No  commercially available filter medium is ideal
in all respects  for all samplers.  The  user's  goals in sampling determine
the relative importance of various filter evaluation criteria (e.g., cost,
ease of  handling,   physical  and chemical  characteristics,  etc.)  and, con-
sequently,  determine the  choice  among  acceptable  filters.   Furthermore,
certain  types  of filters  may  not be suitable for  use  with some  samplers,
particularly under   heavy  loading  conditions  (high  mass  concentrations),
because  of  high  or  rapid increase in the filter flow resistance that would
exceed the capability of the sampler's automatic flow controller.   However,
samplers  equipped  with automatic filter-changing mechanisms  may  allow use
of  these types  of  filters.   The  specifications  given below  are minimum
requirements to  insure  acceptability of the filter  medium for measurement
of PM10  mass  concentrations.   Other filter evaluation  criteria  should be
considered to meet  individual sampling and analysis objectives.
7.2.2     Collection  Efficiency:   >_  99  percent  as measured  by   OOP test
(ASTM-2986) with 0.3 urn particles at the sampler's operating face velocity.
7.2.3     Integrity:  ± 5  ug/m3  (assuming  sampler's nominal  24-hour air
sample volume),  measured as the  concentration  equivalent  corresponding to
the difference between the  initial  and  final  weights of  the filter when
weighed  and handled  under simulated  sampling  conditions (equilibration,
                                  22

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initial weighing,  placement on inoperative  sampler,  removal  from sampler,
reequalibration, and final weighing).
7.2.4     Alkalinity:   <0.005  milliequivalents/gram of  filter as measured
by ASTM-D202  following  at least two months  storage  at ambient temperature
and relative humidity.
7.3   Flow Rate Transfer Standard
7.3.1     A flow  rate  transfer standard, suitable for the flow rate of the
sampler and calibrated against a primary standard that is traceable to NBS,
must be used to calibrate the sampler's flow measurement device.
7.3.2     The reproducibility  and  resolution of the transfer standard must
be 2 percent or less of the sampler's operating flow rate.
7.3.3     The flow  rate transfer  standard must include a means to vary the
sampler  flow  rate  during  calibration  of  the sampler's  flow measurement
device.
7.4   Filter Conditioning Environment
7.4.1     Temperature range:  15 to 30° C.
7.4.2     Temperature control:   ± 3° C.
7.4.3     Humidity: 45 ± 5 percent relative humidity.
7.5   Analytical Balance
7.5.1     The analytical balance must be suitable for weighing the type and
size of filters required by the sampler.  The  range and sensitivity required
will  depend on  the filter  tare  weight  and mass loading.   Typically,  an
analytical balance with a sensitivity of 0.1 mg is required for high volume
samplers  (flow  rates >  0.5 mVmin).  Lower volume  samplers  (flow rates <
0.5 mVmin) will require a more sensitive balance.
                                   23

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8.0   CALIBRATION



8.1   General Requirements



8.1.1     Calibration of  the  sampler's flow measurement device is required



to establish traceability of the flow measurement to a primary standard.  A



flow  rate  transfer standard  calibrated against  a  primary  flow  or volume



standard shall  be  used  to calibrate the sampler's  flow measurement device



at the field site.



8.1.2     The  particle  size  separation characteristics  of  PM10 samplers



usually require  that  specific air velocities be  maintained  in the separa-



tion system.  Therefore, the sampler must be set to operate at and maintain



the  specified  volumetric  flow rate,  measured  under  the  actual  ambient



conditions of  use  (Qa).   In contrast,  the  mass  concentration of PM10 must
                     cl


be computed  using  the flow rate based  on the standard volume at EPA refer-



ence conditions (Qstd).



8.2  Flow Rate Calibration Procedures



8.2.1     The  calibration  procedure given  here is based  on  flow rates at



ambient conditions  (Q )  and serves to  illustrate the steps involved in the
                      3


calibration  process.   Alternative  procedures   based  on other  measures of



flow  rate  (e.g., Qstcf)  "iay be  used  provided  the  requirements of section



8.1  are  met.   Consult  the sampler  manufacturer's instruction  manual  for



specific guidance on  calibration.   Reference 13 provides additional infor-



mation on  the  use  of the  commonly  used measures  of flow  rate  and their



interrelationships.



8.2.2     Calibrate the  flow  rate transfer standard against a primary flow



or volume  standard  traceable  to NBS.    Establish a calibration relationship



(e.g., an  equation  or   family  of  curves)  such  that traceability  to  the



primary standard is  accurate  over the  expected range of ambient conditions





                                   24

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(i.e., temperatures  and pressures) under which  the  transfer standard will



be  used.   Recalibrate the transfer standard  periodically  (minimum of once



per year).



8.2.3     Disable  the sampler's flow controller  during  calibration of the



sampler's flow measurement device.



8.2.4     Install  a  clean  filter (or filters) in  the  sampler.   Remove the



sampler  inlet  and connect  the transfer standard  to the sampler such that



the  transfer  standard  accurately  measures  the  sampler's  flow rate.   Make



sure  there  are  no  leaks  between  the  transfer  standard and  the sampler.



8.2.5     Choose three  flow  rates  evenly spaced  over  a  range  of ± 10 per-



cent  of  the sampler's  specified operating flow  rate  (actual  mVmin), and



by suitable adjustment  of the sampler flow rate, obtain  a calibration  curve



of flow  rate  (actual mVmin) versus the sampler's flow  indicator reading.



Record the  barometric pressure and ambient temperature.   Daily or seasonal



temperature and  daily or average pressure corrections for subsequent flow



indicator readings may  be  required for certain  types of  flow measurement



devices (see NOTE  following step 9.6).



8.2.6     Re-enable  the  flow  controller,  adjust the  flow  rate (actual



m3/min)  to  the manufacturer's  specified operating set  point,  and use the



transfer  standard to  verify  that the  flow  rate  is  correct with  a   clean



filter (or filters)  in  place.



8.2.7     Replace  the sampler inlet.



9.0   PROCEDURE



9.1   The  sampler   shall  be  operated  in  accordance  with  the  general



instructions given here and  with the specific instructions provided in the



sampler  manufacturer's  instruction manual.   NOTE:   This procedure assumes
                                  25

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that the  sampler's  flow rate calibration was performed using flow rates at



ambient conditions (Q ).
                     a


9.2   Inspect each filter for pinholes, particles, and other imperfections;



establish  a  filter  information record and  assign  an identification number



to each filter.



9.3   Equilibrate each  filter  in  the conditioning environment for at least



24-hours.



9.4   Following equilibration, weigh each filter, and record the presampling



weight with the filter identification number.



9.5   Install a preweighed filter (or filters) in the sampler following the



instructions provided  in the  sampler  manufacturer's instructional  manual.



9.6   Turn  on  the  sampler  and  adjust  (if necessary)  the  automatic  flow



controller to  the manufacturer's  specified operating set  point.   Run the



sampler for  at  least  5 minutes  to establish  run-temperature  conditions.



Record the flow  indicator  reading and, if  needed,  the  barometric pressure



and  ambient  temperature.    Determine  the  sampler  flow  rate   (in  actual



m3/min) using the sampler's flow rate calibration curve.



NOTE:     No onsite  pressure or temperature  measurements  are  necessary if



the  sampler  flow  indicator  does  not  require pressure  or  temperature



corrections or if average barometric pressure and seasonal average tempera-



ture for  the  site are  incorporated  into  the  sampler calibration (see step



8.2.5).   For  individual pressure and  temperature  corrections,  the  ambient



pressure  and temperature can be obtained by  onsite  measurements or from a



nearby weather  station.  Barometric  pressure readings obtained from air-



ports  must  be station  pressure,  not corrected to sea level, and may need



to be  corrected  for differences in  elevation  between the sampler site and



the airport.



                                   26

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9.7   If the  sampler flow  rate (actual mVmin)  is  outside the acceptable



range specified  by the  sampler manufacturer, check  the  sampler for leaks



and, if  necessary, adjust  the automatic flow controller set point.   Stop



the sampler.



9.8   For samplers  without continuous  flow recorders, record  the initial



flow rate (in actual mVmin) as Qa/-*nl-* \-



9.9   Set the timer to start and stop the sampler at appropriate times.  Set



the elapsed time meter to zero.



9.10  Record the  sample  information  (filter identification number(s), site



location or identification number, sample date, and starting time).



9.11  Sample for 24 ± 1 hours.



S.12  For samplers'without  continuous  flow recorders, as soon as practical



following the  sampling  period,  run  the  sampler for  5  minutes  to  again



establish run-temperature conditions.   Record  the flow  indicator reading



and, if  needed,  the barometric pressure and ambient temperature.  Stop the



sampler.    Determine  the  final  flow  rate  (in   actual  mVmin)  using  the



sampler's flow  rate calibration  curve and  record  as Qa(f-jna-i ^  (see NOTE



following step  96).   If  Qa/-f^naT\  is outside  the  sampler manufacturer's



specified  operating  range,   the  sample must be  invalidated.    For  valid



samples, calculate the  average  flow rate  (in  actual m3/min),  and record



as Qa.



9.13  For samplers with continuous flow recorders, examine the flow record.



If Q  is outside the sampler  manufacturer's  specified  operating range for
    a


more than   6  hours of  the  24-hour  sampling  period, the  sample  must be



invalidated.  For valid  samples,  record the  average  flow recorder reading



during the  sampling period.   If  needed, estimate  the  average temperature



and pressure at  the site during the sampling period from weather bureau or
                                   27

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other available  data.   Determine the average flow  rate  (in actual m3/min)



using the  sampler's  flow rate calibration curve and record as Q   (see NOTE
                                                                3


following step 9.6).

                                 \

9.14  Carefully  remove  the filter (or filters)  from  the sampler  following



the  sampler manufacturer's  instructions.   Touch only  the outer  edges  of



the filter.



9.15  Place the  filter(s)  in a protective holder or container (e.g., petri



dish, glassine envelope, or manila folder).



9.16  Record  the elapsed  time  on  the  filter  information record and  any



other  factors,  such as  meteorological   conditions,  construction   activity,



fires or  dust storms,  etc.,  that might be pertinent  to the measurement.



If the sample is known to be defective,  void it at this time.



9.17  Transport  the  exposed  sample  filter  (or  filters) to the  filter



conditioning  environment as  soon as possible  for  equilibration  and  sub-



sequent weighing.



9.18  Equilibrate the exposed filter(s)  in the conditioning environment for



24-hours.



9.19  Immediately after equilibration, reweigh the filter(s) and record the



weight(s)  with the filter identification number(s).



10.0  CALCULATIONS



10.1  Calculate the average flow rate over the sampling period corrected to



EPA reference conditions as Q ...  When the sampler's flow rate calibration



and operation is based on flow rates at ambient conditions,



calculated as:
                    * r *  r
                      'a    Kstd
                                  28

-------
where:   'Qstd = avera9e ^low rate at EpA reference conditions, std m3/min;

            Q  = average flow rate at ambient conditions, mVmin;
             a

            P.  = average barometric pressure for the site or average
                 barometric  pressure  during  the  sampling  period,  1
-------
 3.  Clement,  R.  E. ,  and  F.  W.  Karasek1.   Sample  Composition Changes  in



     Sampling  and  Analysis  of  Organic Compounds  in Aerosols. Int. J.  En-



     viron. Analyt.  Chem.,.7:109, 1979.



 4.  Lee,  R.  E. , Jr.,  and  J.  Wagman.  A  Sampling Anomaly  in the Deter-



     mination of Atmospheric Sulfate Concentration.  Amer.  Ind. Hyg. Assoc.



     J.,  27:266, 1966.



 5.  Appel, B. R., S. M. Wall, Y. Tokiwa, and M. Haik.   Interference Effects



     in  Sampling Participate  Nitrate  in  Ambient  Air.   Atmos.   Environ.,



     13:319, 1979.



 6.  Coutant,  R.  W.   Effect of  Environmental  Variables  on  Collection  of



     Atmospheric Sulfate.   Environ. Sci. Techno!.,  11:873,  1977.



 7.  Spicer, C. W., and P.  Schumacher.  Interference in  Sampling Atmospheric



     Particulate Nitrate.   Atmos. Environ., 11:873,  1977.



 8.  Appel, B. R., Y. Tokiwa, and M. Haik.  Sampling of  Nitrates in Ambient



     Air.  Atmos. Environ., 15:283, 1981.



 9.  Spicer, C. W., and P.  M. Schumacher.   Particulate Nitrate:  Laboratory



     and  Field  Studies of  Major  Sampling  Interferences.   Atmos.   Environ.,



     13:543, 1979.



10.  Appel, B. R.  Private  Communication, 1982.



11.  Pierson, W.  R. , W.  W. Brachaczek, T.  J.   Korniski,  T.  J. Truex,  and



     J.   W.  Butler.   Artifact  Formation of  Sulfate, Nitrate,  and  Hydrogen



     Ion on Backup Filters:  Allegheny Mountain  Experiment.   J. Air. Pollut.



     Control Assoc., 30:30, 1980.



12.  Chahal,  H.  S.,  and  D.  J.  Romano.    High-Volume   Sampling  Effect  of



     Windborne  Particulate Matter  Deposited  During Idle  Periods.  J.  Air



     Pollut. Control Assoc., 26:885, 1976.
                                   30

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13.   Smith, F. ,  P.  S. Wohlschlegel,  R.  S.  C. Rogers,  and D.  J. Mulligan.



     Investigation of  Flow  Rate Calibration Procedures Associated with the



     High Volume Method for Determination of Suspended Particulates.



     EPA-600/4-78-047,  U.S.   Environmental   Protection  Agency,  Research



     Triangle Park,  North Carolina 27711, 1978.
                                  31

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                                APPENDIX B
                 ESTABLISHING RELATIONSHIP OF ALTERNATIVE
                 SAMPLING METHODS TO THE REFERENCE METHOD

1.0  OCCASIONS WHEN RELATIONSHIP MUST BE ESTABLISHED
     Whenever a method other than staggered high-volume sampling or short time
interval sampling is to be used for episode monitoring, a specific site relation-
ship with the reference method must be established and documented.
     The advantage of using the staggered sampling or short time interval
sampling methods is that these methods use the principle of the reference
method.  Consequently, in most cases, a specific site relationship need not
be determined, thus reducing the testing time, testing cost, and the need
perhaps for skilled personnel or expensive equipment.
     The advantage of other methods over the two methods suggested above may be
the advantage of automation, which could minimize the loss of time between air
samples and important strategy decisions.
     Requirements (see Table B-l) that must be satisfied to determine whether
a method can be designated as equivalent to a reference method are found in
Subpart C of 40 CFR Part 53.  Comparability for a candidate method is demon-
strated if all the differences between corresponding measurements made by the
candidate method and by a reference method on simultaneously collected PM-|g
samples at each of the three test sites are less than 15 percent of the
reference method value.  In addition, a candidate method must exhibit perfor-
mance better than, or equal to, the requirement stated in Subpart D of 40 CFR 53.
                                        32

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            TABLE B-l.  TEST SPECIFICATIONS FOR PM1QMETHODS
Concentration range, yg/m3                                    30 to 150
Minimum number of test sites:                                         3
Minimum number of candidate method samplers per site:                  3
Minimum number of 24-hour measurements per sampler per site:           5
Minimum number of sample sets:                                       15
Acceptable difference, percent of reference method:                  +15
                                    33

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These criteria define what good comparable performance is for a monitoring
method.  A careful review of the full text of 40 CFR Part 53 should be made
before testing for comparability of two methods in order to ensure that the
most current rules are being applied.  However, failure of a method to meet
the specifications for comparability to a reference method does not render the
data from the candidate method useless.  The procedure described below may be
used to determine the correlation of the candidate method with a reference
method and consequently allow those data to be assessed with respect to
applicability to episode"monitoring.
     The remainder of this Appendix* describes the procedures that should be
followed to collect test data and to calculate, display, and assess a specific
site relationship between a candidate method and the reference method.
2.0  TEST CONDITIONS FOR TAKING MEASUREMENTS
    The reference method uses the filtration method described in Appendix A.
The procedures described in Appendix A should be followed when sampling is
done using the reference method.  Sampling using alternate methods (candidate
methods) for which the specific site relationship is to be established should
be conducted according to the applicable manuals (e.g., manuals produced by
instrument vendors that produce the instrument to be tested).
     At least 10 ambient air measurements should be made simultaneously by
the candidate and the reference method.  The air samples should be taken
*  It is important to note here that much of the text included in the remainder
   of this chapter follows very closely the text provided in an EPA document
   (EPA 450/4-79-007) referenced previously.
                                        34

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simultaneously in the same area (i.e., within 2-3 meters of each other) with-
out interference between samples or instruments.  It is preferable to take all
measurements during a single season, because site-specific relationships may
vary with season.  If more than one season is covered by the sampling period,
then 10 or more measurements per season should be made and results analyzed on
a season-specific basis.  The definition of a season is left to the discretion
of those determining a site-specific relationship.  In most areas of the contig-
uous United States, December through February is considered the winter season,
with subsequent 3-month groupings comprising the remaining three seasons.
     These measurements should be made on ambient air containing PM-jg  con-
centrations in the range that the candidate method will be subjected to during
an episode.  To accomplish this, the measurements could initially be performed
in nonepisodic (normal) atmospheric conditions to establish the relationship,
but resumed during an episode to determine if the established relationship
changes significantly.  The relationship may be a function of the pollutant
source, such as coal combustion, dust storms, or fuel  use.  If such is the
case, then the relationship should be established under different source
strengths.
     If the candidate method has a shorter measuring time interval  than the
reference method, a sufficient number of sequential  interval  measurements
should be made to equal the time period of the reference method (24 hours).
The  PM,Q concentration as determined by the reference method and the PM,Q
concentration determined by the candidate method (or the mean of sequential
determinations by the candidate method)  are considered a "test pair."
                                        35

-------
     All records, test data, procedural description and details, and other
documentation obtained from (or pertinent to) tests made for the purpose of
testing a candidate method should be identified, dated, and signed by the
tester.  Test data are to be compiled and forwarded to the U.S. EPA Regional
Office for approval.
3.0  METHODS  FOR  CALCULATING AND  DISPLAYING  THE RELATIONSHIP
     The test pairs are used to estimate the functional relationship between
the candidate and the reference methods.  For a full season of 24-hour mea-
surements taken every sixth day, 15 or 16 test pairs would be available in
the absence of missing data.  Hypothetical data (16 pairs) that are used to
illustrate appropriate analytical  methods appear in Table B-2.  The method
suggested for estimating a functional relationship between the candidate method
(X) and the reference method (Y) is linear regression.  Figure B-l shows all
calculations required to produce regression estimates and associated outputs
from the inputs in Table B-2.   The method suggested for displaying a relation-
ship between values from the two methods is a scattergram, as illustrated in
Figure B-2.  The latter figure also includes the estimated regression line.
     The essential outputs from the regression procedure are the estimated
slope (Step 12 in Figure B-l),  intercept (Step 13), and correlation coefficient
(Step 14).  The slope and intercept are required in order to make subsequent
predictions based on  the regression estimates (Step 15).   The correlation
coefficient is useful in assessing the strength of the association between
values from the two methods.  The residual mean square (Step 11) and sum of
squared deviations about T (Step 6) are necessary if one wishes to construct
                                        36

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TABLE B-2.  SIMULATED DATA FOR CANDIDATE AND REFERENCE METHODS
x - PMJO
ug/m-3
Response measured
by candidate method
357
392
311
281
240
287
259
233
231
237
209
161
199
152
115
112
Y = PM1Q
ug/nr
Response measured
by reference method
459
419
375
334
310
305
309
319
304
273
204
245
209
189
137
114
                                 37

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X denotes Candidate Method Response, Y denotes Reference Method Response
     a)   2X  =  Sum  of X
             =  3776
     b)   Y =  2X/n  = Average of X
           =  236
     c)   n =  Number of test pairs
           =  16
                               d)  2Y = Sum of Y
                                       = 4505
                               e)  T = 2y/n =  Average  of Y
                                     = 281.5625
Step (1):
2XY = Sum  of X  times Y
     = 1,170,731
Step (2):
(2X)  (2Y)/n
* 1,063,180
Step (3):       S   = 2 (X - Y) (Y - T)  or 2XY  -  (2X)(2Y)/n
               Step (1) - Step (2}
               =  107,551

Step (4):       2X2 =  Sum of each X squared
               =  985,740
Step (5):       (2X)2/n = a2/c
               = 891,136
Step (6);  '     Sxx = 2 (X - IT = Step (4)  -  Step (5)
               =  94,604
Step (7):       2Y2 = Sum of each Y squared
               =  1,404,543
         Figure  B-l.  Basic Worksheet Showing the Calculation Steps
                                       38

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Step (8):      CSY)2/n - d2/c
               = 1,268,439

Step (9);      S   =  2(Y - T)2 = Step (7)  - Step (8)
               = 136,104

                   A     2
Step (10) :       2 (Y - Y)  = Residual  sum of squares  (sum of squared
                              differences between predicted and actual
                              y values)
               = S(Y - Y)2 - [(X -~X)(Y -~Y)]2/Z(X  -
               = Step (9)  - [Step (3)]2/Step (6)
               * 136,104 - (107,5512/94,604)
               * 13,834

Step (11):     S2 = [2(Y  - Y)2]/(n - 2)  = Residual  mean  square
               = Step (10)/(c - 2)
               = 13,834/14 = 988
Step (12):      Z = S  /S   = Slope of the regression  curve
               = Step (3) /Step (6)
               = 107,551/136,104 = 1.137
Step (13);      I = T - Z T = Y intercept
               = e - Step (12)b
               =* 281.5625 - 1.137(236)  = 13.23

Step (14):.     r = Correlation coefficient
               * S  / VT~ VT~
                  xyj     xx    yy
               » Step (3)/[Step (6)]1/2  [Step  (9)]1/2
               = 107,551/[136104]1/2  [94604]1/2
               ' 0.948
Figure B-l.   Basic Worksheet Showing  the Calculation Steps (Continued)
                                        39

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Step (15);   Prediction of Reference Method Value from Candidate
             Method Value
             (a)  Equation of regression line
                  Y = I + ZX
                  Y = 13.23 + 1.137 X
             (b)  Sample prediction
                  Let X0 » 240
                  Y0 = 13.23 + 1.137(240)
                  = 286.1
Step (16):    95 Percent Confidence Interval  for Predicted Value (Y0)
             (a)  Equation for interval
             Interval  = Y0 +_ tn_2, 0.05 (s ^ + 1/n + (xo - "^2/   i.Q6267
                      = 286.1 +_ 69.5
                      = (216.6, 355.6)

   Figure B-l.   Basic Worksheet Showing the Calculation Steps  (Concluded)
                                        40

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confidence intervals around predicted reference method values  (Step  16).  The
value of t, used for a 95 percent confidence interval, varies  with the  number
of test pairs.  The appropriate number can be found in a table of t-values,
which appears in most statistical texts.
     Advanced slide-rule calculators with statistical capability can be used to
quickly obtain estimates of the slope, intercept, and correlation coefficient.
With such a calculator, one needs only to input the test pairs.  The estimates
are retrievable by pushing specified keys on the calculator.   With some alge-
braic manipulation, the residual mean square and sum of squared deviations can
be derived from intermediate outputs, which are retrievable from selected
memory areas within the calculator.
4.0  METHODS FOR ASSESSING THE RELATIONSHIP
     The regression procedure illustrated in Figure B-l should be used only
if the relationship between candidate and reference method values appears to
be reasonably linear over the range of interest.  A visual assessment of the
degree of linearity can be made upon the basis of the scattergram (Figure B-2).
     In cases where the relationship does not appear to be linear over the
entire range of interest, other techniques for relating the two methods may be
used.  For example, some agencies have found that a piece-wise linear function
is superior to a single linear function.  Tests of significance are not as
straightforward as for the linear case and require care in interpretation.
Often, it is possible to linearize a nonlinear relationship by transformation
of variables (e.g., -^x7 log X, etc.).  In such cases, the procedures outlined
in the previous section" of this Appendix may be applied to the transformed
                                        41

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      450   -
      400   t
      350
•3
J
a
2
 u
<*•
 a
si
300   -
£     250    i

      200
      ISO
      100
                                        200             250            300
                                           Values for Candidate Method
                                                                               350
400
                 Figure B-2.  Graph of Relationship Between Candidate and Reference Method Values
                                                          42

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variables.  In some rare cases, it may be necessary to use nonlinear regression
techniques to properly fit the measured data.
     The visual assessment of linearity should precede all calculations.  Once
a reasonable approximation to linearity has been achieved in the original or
transformed data, the calculations shown in Figure B-l can be performed.  The
resultant regression equation can be used to draw the regression line through
the data, as in Figure B-2.  This line can be drawn by predicting Y values from
X values at low and high extremes, plotting the resultant (X,Y) pairs, and
connecting these plotted points.  Any apparently nonrandom pattern of residuals
about the regression line should then be readily discernible.
     The strength of the association between the candidate and reference method
values can be discerned by examining the correlation coefficient.  In the case
of 16 pairs, a correlation coefficient of 0.5 or greater is statistically
significant at the 5 percent level.  A coefficient of this magnitude, however,
is of limited practical significance.  The square of the correlation coefficient
is a measure of the proportion of the variation in the reference method values
explained by regression on the candidate method values.  Thus, a correlation
coefficient of 0.5 means that only 25 percent of the variation in reference
method values is explained.  A correlation coefficent of 0.7 means that approx-
imately 50 percent of the variation is explained.  Consequently, agencies are
not advised to use a candidate method whenever the coefficient of correlation
is less than 0.7.  A more stringent cutoff level  for candidate method accept-
ability would be a correlation coefficient of 0.85, which means that nearly
75 percent of the variation is explained.
                                        43

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