United States                 EPA-600/2-81-039
               Environmental Protection
               Agency                    March 1981
&EPA        Research  and
               Development
               RECEPTOR MODELS RELATING
               AMBIENT SUSPENDED PARTICIPATE MATTER
               TO SOURCES
               Prepared  for
               Office of Air Quality Planning and Standards
               Prepared  by
               Industrial Environmental Research
               Laboratory
               Research Triangle Park NC 27711

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                 RESEARCH REPORTING SERIES


Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and  application of en-
vironmental technology. Elimination  of  traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:

    1. Environmental Health Effects Research

    2. Environmental Protection Technology

    3. Ecological Research

    4. Environmental Monitoring

    5. Socioeconomic Environmental Studies

    6. Scientific and Technical Assessment Reports (STAR)

    7. Interagency Energy-Environment Research and Development

    8. "Special" Reports

    9. Miscellaneous Reports

This report has been assigned to the  ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series describes research performed to develop and dem-
onstrate instrumentation, equipment,  and methodology to repair or prevent en-
vironmental degradation from  point and non-point sources of pollution. This work
provides the new or improved technology required for the control and treatment
of pollution sources to meet environmental quality standards.
                       EPA REVIEW NOTICE
This report has been reviewed by the U.S. Environmental Protection Agency, and
approved for publication. Approval does not signify that the contents necessarily
reflect the views and policy of the Agency, nor does mention of trade names or
commercial products constitute endorsement or recommendation for use.

This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.

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Document No. P-A422
March 1981
Contract No. 68-02-2542 Task 8
Prepared for
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
           The State of the Art of
                   Receptor Models
                  Relating  Ambient
           Suspended Particulate
                  Matter to Sources
ERT
ENVIRONMENTAL RESEARCH & TECHNOLOGY, INC.
ATLANTA - CHICAGO • CONCORD, MA • FORT COLLINS, CO
HOUSTON • LOS ANGELES • PITTSBURGH • WASHINGTON, DC

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                 EPA Project Officers
                     John 0. Milliken
                     Robert K. Stevens

                       Prepared by

                     John G. Watson
                   with assistance from
William Baasel
John  Bachman
Neil Berg
Glenn  Cass
John  Cooper
John  Core
Russell Crutcher
Lloyd  Currie
Joan  Daisey
Stuart Dattner
Briant  Davis
Ronald Draftz
Alan Dunker
Thomas Dzubay
Robert Eldred
Edward  Fasiska
Sheldon Friedlander
Donald Gatz
Glen Gordon
Bruce Harris
Ronald Henry
George  Hidy
Philip Hopke
Reginald Jordan
Ted Kneip
Nick Kolak
Ross Leadbetter
Richard  Lee
Charles  Lewis
Carol  Lyons
John Milliken
Jarvis Moyers
John Overton
Thompson Pace
Skip Palenik
Terry Peterson
William  Pierson
Kenneth  Rahn
Philip Russell
John Spengler
Robert  K. Stevens
Warren  White
Jack Winchester
John Woodward
John Yocom

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                            ACKNOWLE DGEMENTS

     This report is the product of many minds,  as  evidenced by  the
authorship on the title page.
     It results from a two and one half day meeting in which  these
researchers and users of receptor models came together in  formal  and
informal sessions at the Quail's Roost Conference  Gaiter of the
University of North Carolina located in Rougemont,  North Carolina.
The intimate, tranquil setting and the southern hospitality of  the
Quail's Roost was a major ingredient in the success of the meeting,
and the staff, under the leadership of Mr.  Charlie Philips, merits
special appreciation.
     John Cooper of the Oregon Graduate Center, Ed Macias  of
Washington University, John Milliken of EPA,  Ron Henry and
John Watson, both of Environmental Research & Technology,  Inc.
organized the meeting and moderated its formal  sessions.   Glen Gordon
of University of Maryland, Jarvis Moyers of University of  Arizona,
Skip Palenik of McCrone & Associates, George  Hidy  of Environmental
Research & Technology, Inc., Phil Hopke of  University  of Illinois, and
Ed Macias of Washington University led and  summarized  the  task  force
discussions to define the state-of-the-art  and  research needs that
formed the outline of this report.
     Special review presentations were prepared by John Cooper,
John Watson, Ron Henry, Rich Lee of U.S. Steel, Tom Dzubay of EPA, and
Sheldon Friedlander of UCLA.
     Summaries of daily activities were prepared by Ted Kneip of
New York University, Bill Pierson of Ford Motor Co., and Jack Winchester
of Florida State University.
     Bob Stevens, Tom Dzubay and Chuck Lewis, all  of EPA,  and
Peter Mueller and Ron Henry of ERT provided critical review of  the
initial drafts of this document which resulted in  substantial
improvements.
     The typing and editing support of Marge  Hagy, Audrey  Rose  and
Judith Chow of ERT, above all in the compilation of the bibliography
and reproduction of equations, deserves particular recognition.
                                   111

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     The final acknowledgement goes to those pioneers of receptor
modeling who did not participate in the Quail Roost meeting but upon
whose efforts the science is being developed.  As much as possible,
relevant references to their work have been included in the
bibliography.
                                   IV

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                                ABSTRACT

     Receptor Models are used to determine the source contributions to
ambient particulate matter loadings at a sampling site based on common
properties between source and receptor.  This is in contrast to a
source model which starts with emission rates and meteorological
measurements to predict an ambient concentration.
     Three generic types of receptor model have been identified,
chemical mass balance, multivariate, and microscopical
identification.  Each one has certain requirements for input data to
provide a specified output.  An approach which combines receptor and
source models, source/receptor model hybridization, has also been
proposed, but it needs further study.
     The input to receptor models is obtained from ambient sampling,
source sampling, and sample analysis.  The design of the experiment is
important to obtain the most information for least cost.  Sampling
schedule, sample duration and particle sizing are part of the ambient
sampling design.  Analysis for elements, ions, carbon, organic and
inorganic compounds are included in the sample analysis design.  Which
sources to sample and how to sample them are part of the source
sampling design.
     In order for receptor modeling to become a useful tool, it must
be developed in five major areas:
          General Theory - The generic types of receptor model  are
          related to each other, but that relationship has  not  been
          generally established.  A general theory of receptor  models,
          including the input data uncertainties, needs to  be
          constructed.
          Validation - Simulated data sets created from known source
          contributors and perturbed by random error need to be
          presented to models, and their source contribution
          predictions should be compared to the known contributions.
          Several models need to be applied to the same data set and
          their results compared.
          Standardization - Validated models need to be placed  in
          standard form for easy implementation and use.

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Measurement Methods - Ambient and source sampling and
analysis methods need to be developed, tested and
standardized.

Documentation and Education - Users need to be informed of
the powers and limitations of these models and instructed in
their use.
                       VI

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                            TABLE  OF  CONTENTS
                                                                Page

ACKNOWLEDGEMENTS                                                iii
ABSTRACT                                                        v
TABLE OF CONTENTS                                               vii
LIST OF ILLUSTRATIONS                                           ix
1.   INTRODUCTION                                                1
2.   THE RECEPTOR MODELS                                         7
     2.1  The Chemical Mass Balance Receptor Model               8
     2.2  Multivariate Models                                   14
     2.3  Microscopical Identification Models                   19
     2.4  Hybrid Source/Receptor Models                         22
3.   RECEPTOR MODEL INPUT DATA                                  27
     3.1  Field Study Design and Data Management                27
     3.2  Source Characterization                               33
     3.3  Analytical Methods                                    37
4.   RECEPTOR MODEL NEEDS                                       47
BIBLIOGRAPHY                                                    50
                                  vn

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Vlll

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                         LIST OF ILLUSTRATIONS

Figure                    Title                                 Page

1         Source Model vs. Receptor Model Block Diagram          4

2         Plot of Predicted vs.  Observed Concentration
          for Regression                                       24

3         Example of Source-Receptor Model Hybrid               26

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                         CHAPTER 1:   INTRODUCTION

      There is  a need today to quantify the effects of aerosol sources
 on  ambient particulate matter loadings.  Over one hundred air quality
 maintenance areas in the United States are not meeting primary and
 secondary Total Suspended Particulate (TSP)  Matter Standards.  These
 areas must submit state implementation plans showing how they will
 come  into attainment within a specified time period.  This  involves
 the identification of major causes  of 24 hour and/or annual standard
 violations and the application of a control  strategy to eliminate
 those causes.   The source identification step rarely receives as  much
 attention as  the control of "assumed" sources.   The result  of this
 imbalance can  result in expensive controls with little or no effect  on
 ambient  air quality.  Industry is reluctant  to make expenditures  when
 it  sees  no hard evidence that it is a major  contributor to
 violations.  Airshed residents balk at higher taxes and burning and
 driving  restrictions in the absence of a clear relationship between
 those activities and air quality.
      As  the condition of the environment improves,  people become
 concerned about certain amenities in addition to health effects.
 Industrial sources are often charged as the  cause of soiling,
 deposition or  visibility degradation in a community or area.   The
 verification of these charges is often left  to  emotional pleas rather
 than  to  hard technical evidence.  When an industry  admits culpability,
 it still  needs  to  determine which part of its process  is the  major
 contributor.
      Standards  for suspended particulate matter must be reevaluated
 every ten years.   At the  present time the Environmental Protection
Agency is  proposing  a size-selective aerosol  standard  (Miller,  et
 al, 1979).  The economic  and monitoring impacts of  such a standard
 cannot be  assessed without  determining relative source contributions
 to the size-range  under  consideration.

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      Identifying the major sources of ambient particulate matter
 loadings was a fairly simple process when values exceeded 500 yg/m
 and stack  emissions  were  plainly visible.  Control of  these emitters
 was forthcoming and  effective.  At levels of 150 to 200 |_ig/nH, the
 use of  annual  emission  inventories focused further regulatory efforts
 on  major sources which  have resulted in more successful reductions.
      Presently, at levels around 75-100 yg/m3, the uncertainties
 involved in  these  assessments of source contributions  are greater than
 the contributions  themselves.
      Source-oriented atmospheric dispersion modeling has been the
 major tool used in attributing  ambient concentrations  to source
 emissions.  With extensively researched emission inventories and
 adequate meteorological information, these models have done a credible
 job of  predicting non-reacting  gaseous pollutant concentrations  at
 receptors  due  to specific sources.  Many  times, however, predicted
 concentrations do not compare well with ambient measurements (e.g.,
 Guldberg and Kern, 1978).
      These source models have not proved  themselves adequate for
 suspended  particulate matter for several  reasons.  First, particulate
 matter  emissions are widely dispersed and hard to quantify.  Whereas
 most  gaseous emissions  can be confined to specific points (even  auto
 tailpipes, though numbering in  the millions, are identifiable and
 confined to roadways and  parking lots), particulate matter  is produced
 from  point and nonpoint sources; every square inch of  surface crossed
 by  wind is a potential  emitter.  Emission factors for  area  sources  are
hard  to estimate and display wide variability.
     Second, the transport of aerosol is highly dependent on particle
size, with larger particles settling out closer to the emission point
than  smaller ones or impacting  out on surfaces such as trees or
buildings.  The particle size distributions of many aerosol sources
are inadequately characterized  or highly  variable.  Even if the
distributions were available, few source models have developed
mechanisms for aerosol  removal.  There are source models in which
 total reflection at ground level occurs!

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     Finally,  the  complexities  of  aerosol  chemistry,  —  the
condensation and adsorption  of  organic  vapors  —  the  conversion  of
S*^ to  sulfate species  —  is not a part of the standard  source
models.  Though these models may potentially provide  useful insights,
their results  must  not  be  relied upon as the definitive  statement.
     With  the  development  of inexpensive and rapid  chemical analysis
techniques for dividing ambient and source  particulate matter into its
components has  come  another  approach, the  receptor model.
     While the source-oriented model begins with measurements at the
source  (i.e.,  emission  rates for the period under study), and
estimates  ambient  concentrations,  the receptor-oriented model begins
with the actual ambient measurements and estimates  the source
contributions  to them.  Figure  1 illustrates the  difference between
source  and receptor  models.
     The receptor model relies  on  properties of the aerosol which are
common  to  source and receptor and  that  are  unique to  specific source
types.  These  properties are composition,  size and variability.
     The composition of material from one  source  type is different
from that  of another.   Auto  exhaust particles  contain significant
amounts of lead and  bromine  not found in aerosol  from other sources.
The shapes, birefringences and x-ray diffraction  patterns of certain
minerals can identify which  aggregate storage  pile  they come from if
the piles  contain  different  minerals.
     The particle  size  distribution is  dictated by  the processes which
generate the aerosol, the most useful size  distinction being between
particles  greater  than  and less than  2 /^m.  Willeke  and
Whitby  (1975),  after hundreds of particle  size measurements in urban
situations, have found  that  the mass of most aerosols appears to be
concentrated into two size ranges, commonly termed  the coarse
(particles >2/im) and fine (particles <2jLtm) particle modes.  Coarse
particles are  primarily the  result of grinding and errosive
operations, the breaking up  of  larger material into smaller pieces.
Geological material  tends  to dominate this mode.  Fine particles are
formed by the  condensation of gases to  particles, chemical reactions
between gases  yielding  particles, and the  coagulation of still smaller

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     KNOWN
    SOURCE
   EMISSIONS
     KNOWN
   DISPERSION
CHARACTERISTICS
SOURCE
 MODEL
   ESTIMATED
    AMBIENT
CONCENTRATIONS
                       SOURCE MODELS
  SOME KNOWN
    SOURCE
CHARACTERISTICS
KNOWN
AMBIENT '
CONCENTRATIONS
^
*.
S
RECEPTOR
MODEL


ESTIMATED
SOURCE
IMPACTS
  SOME KNOWN
   DISPERSION
CHARACTERISTICS
                      RECEPTOR  MODELS

Figure 1.  The source model uses source emissions as inputs, calculates ambient concentrations.
        The receptor model uses ambient concentrations as inputs, calculates source contributions.
        (From Watson, 1979)

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particles.  A dichotomous mass sample, the measurement of the fraction
of the total mass contributed by  the  coarse and  fine modes, is a good
indicator  (Dzubay and Stevens, 1975)  of the relative contributions
from these two broad source  categories.  It appears (Heisler et
al., 1973) that finer gradations  of particle size at source and
receptor could make these classifications more specific.
     The variation of particulate matter properties, both temporally
and spatially, corresponds  to variations of source emissions and to
the variability of meteorological transport between source and
receptor.  Increases in  ambient lead  and bromine  concentrations during
rush hour  could correspond  to a known increase in auto exhaust during
those  time periods.  Rheingrover  and  Gordon (1980) show spatial
variability of aerosol component  concentrations varying precisely with
wind direction, implicating  upwind  sources known  to emit those
components.  When the effects of  changing meteorology are taken into
account, sources with diurnal, weekly, and seasonal emission
variations will engender similar  variations of the components they
contribute to a receptor.   Source/receptor distance and wind related
transport  cause all source  contributions to vary with receptor
location.
     The examination of  these properties to identify source
contributions is not new.   Throgmorton and Axetell (1978) have done a
credible job of tabulating  and generalizing applications of receptor
models in  the past and Cooper and Watson (1980)  and Gordon  (1980)
offer excellent reviews  of  current work.  Receptor modeling is an
active area of research  which is  on the verge of  becoming a useful
tool in the ambient monitoring and regulatory process.  However, it
needs a unified focus to direct its development.
     In an attempt to provide this focus, forty-seven active receptor
model users from government, university, consulting and industry met
for 2 1/2 days in February  1980.  They addressed  the models and the
information required to  use  them  in six separate  task forces:

     •    Chemical Element Balance Receptor Models
     •    Multivariate Receptor Models

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      •    Microscopic Identification Receptor Models
      •    Field Study Design and  Data Management
      •    Source Characterization
      •    Analytical Methods

      The objectives  of these inter-related task forces were to:

      •    define the state-of-the-art via summaries of past and
           present research,
      •    outline future research required to make the models useful
           tools for  the scientific  community, regulators, and planners,
      •    suggest vehicles  for  carrying out that research within the
           context of ongoing projects.
      This  report presents  the results of this meeting with sufficient
 background material  and references  on receptor models to make the
 recommendations  meaningful  to uninitiated but potential receptor model
 users.
      This  introduction presents the general concept of a receptor
 model,  the input it  requires, and the output it produces.  Chapter Two
 will  describe  chemical mass  balance, multivariate, microscopic and
 hybrid model approaches,  the specific data they require, the
 recognized state-of-the-art, and  research directions for each model.
     Having specified  the data required in Chapter Two, Chapter Three
 will  summarize the state-of-the-art of the methods of obtaining those
 data  in terms  of  field study design, source characterization, and
 analytical methods.  Areas requiring exploration and refinement will
 be stated.
     Chapter Four makes  specific  recommendations for meeting the needs
 proposed in Chapters Two  and Three.
     The extensive bibliography following Chapter Four, and the
 liberal reference to it  thoughout the text, is intended to provide
 direction  to present and future researchers and users of receptor
modeling methods.

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                     CHAPTER 2:  THE RECEPTOR MODELS

     Receptor models  presently in  use  can  be  classified  into  one  of
four categories:   chemical mass  balance, multivariate, microscopic,
and  source/ receptor hybrids.   Each classification  will be  treated
individually, though  it will become apparent  that  they are  closely
related.
     The starting  point for the  receptor model  is  the source  model.
Though the source  model may not  deliver accurate results under many
conditions, its limitations are  primarily  due to its inability to
include every environmentally  relevant variable and inadequate
measurements for the  variables it  does include.  The general
mathematical formulations, however,  are representative of  the way in
which particulate  matter  travels from  source  to receptor.
     In general, the  source model  states that the  contribution of
source j to a receptor, S.  £s the product of an emissions  rate,
E;, and a dispersion  factor, D-,
     Various  forms  for D. have been proposed  (Pasquill,  1974,
Benarie, 1976, Seinfeld,  1975),  some  including provisions  for  chemical
reactions, removal,  and  specialized topography.  None  are  completely
adequate to describe the  complicated,  random  nature  of particulate
matter  travel  in  the atmosphere.   Similarly,  E.  is difficult to
quantify on an absolute basis  for  many sources.  The advantage of  the
receptor model is that exact knowledge of D.  and E-  is unnecessary.
     If a number  of  sources, p,  exists and  there is  no interaction
between their  aerosols to cause mass  removal, the total  aerosol mass
measured at the receptor, C, will  be  a linear sum of the contributions
of the individual sources.

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      Similarly, the mass concentration of aerosol property i,
 will  be
                    Ci  =   V  ai.S.
                            i-i
where a.. £s the mass fraction of source contribution j possessing
        1J
property  i  at the receptor.

2.1  The  Chemical Mass Balance Receptor Model

     Equation 3  looks similar to Friedlander's (1973) chemical element
balance which has been used in Pasadena (Miller et al. 1972, Hammerle
and Pierson, 1975), Chicago (Gatz, 1975), Fresno, Pomona, San Jose,
Riverside (Gartrell and Friedlander 1975), New York (Kneip et al 1972,
Daisey  et al., 1979), Portland (Henry, 1977, Watson, 1979),
Washington, B.C. (Kowalczyk et al. 1978),  Denver (Heisler
et al.  1980, Courtney et al., 1980), Miami (Hardy, 1979),
Smokey  Mountains (Stevens et al. 1980), and  St. Louis (Dzubay
et al 1980) to assess source contributions.  If the p sources are
considered  "source types",  that is, grouping sources with similar
properties  together, the set of equations like Equation 3 for all of
the elemental concentrations is_ the chemical element balance.
     A  better name for this model might be chemical mass balance.
Historically,  elemental measurements were most readily available.
Recent  analytical developments allow chemical compounds and ions to be
among the properties considered.
     If one measures n chemical properties of both source and
receptor, n equations of the form of Equation 3 exist.  If the number
of source types contributing those properties is less than or equal to
the number of equations, i.e., p< n, then the source contributions,
the S.   can be calculated.
     Four methods of performing this calculation have been proposed,
the tracer property,  linear programming, ordinary linear least squares
fitting, and effective variance least squares fitting.

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     The tracer element method  is  the simplest.   It assumes  that  each
aerosol  source type  possesses a unique  property which  is common to no
other source  type, Equation  3 then  reduces  to
                                                                  (4)
for each source  j with  its  tracer  t..   It works well when  the
tracers meet  the following  requirements:

          at.• perceived  at  the  receptor is well known  and
          • JJ  •
          invariant.
     2-   Ct  can be measured accurately and precisely  in  the
          ambient sample.
     3.   The concentration  of property t- at the receptor comes
          only from source  type  j.

     These conditions cannot be  completely met  in practice,  and  by
limiting the  model to only  one tracer  property  per  source  type,
valuable information contained in  the  other aerosol properties is
being discarded.  Thus, solutions  to the set of equations  like
Equation 3 have  been developed to make use of the additional
information provided by more than  one  unique chemical property of a
source type,  and even that  of properties which are not  so  unique.
     The linear  programming  and  weighted least squares  solutions deal
with the case of a number of constraints, n, greater than  the number
of unknowns,  p.
     Henry (1977) has applied a  linear  programming algorithm
(Hadley,  1962) which maximizes the sum  of the source contributions
subject to the following constraints:

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                  0 < S. 1C                                      (5)
               •'   fc    '+3*=
where CT  is the uncertainty in the  measurement  C^.
        c.
         i
This  solution has not developed further.
      In the ordinary weighted least  squares  method,  the most  probable
values  of S. when n>p are achieved  by minimizing  the  weighted  sum
of  squares of the difference between the  measured  values  of C^  and
those calculated from Equation 3 weighted by OU    the  analytical
uncertainty of the C^ measurement.
          2     Jl   ( C. -  V   a.,  S.  )2                      (8)
         X   =
                i= I
This solution provides the added benefit  of being able  to  propagate
the measured uncertainty of the C^ through the  calculations  to  come
up with a confidence interval around the  calculated  S..
     The ordinary weighted least squares  solution is incomplete,
however.  The ambient aerosol chemical properties,  the  C.   are  not
the only observables on which measurements are  made. The  chemical
properties of the source aerosol,  the a..  are  also  measured
observables, but the errors associated with those measurements  are not
included in the ordinary weighted  least squares fit.
                                   10

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     Dunker  (1979)  and Watson  (1979) have  applied  the  treatment of
Britt and Luecke  (1973)  to  the  solution of a  set of Equations 3.  The
maximum  likelihood  solution minimizes  the  function
                 n     ( C. -   V  a.. S.  )2                       (9)
                                       2      2
                                       T*     c
                                       d * •   o *
                                         ij    J
where Q^   £g  the uncertainty associated with the a- •
        ij                                         1J
measurement.
     This solution provides two benefits.  First, it propagates a
confidence interval around the calculated S- which reflects the
cumulative uncertainty of the input observables.  The more precise the
measurements of the ambient source property concentrations are, the
better the estimate of the source contributions will be.  The second
benefit provided by this "effective variance" weighting is to give
those chemical properties with larger uncertainties, or chemical
properties which are not as unique to a source type, less weight in
the fitting procedure than those properties having more precise
measurements or a truly unique source character.
     In a series of simulation studies on artifically generated,
randomly perturbed data sets, Watson (1979) shows that these benefits
are indeed realized in practice.
     Each least squares solution exhibits instabilities when source
compositions are similar, though not exact.  Very large or negative
source contributions result.  Other fitting methods  such as
constrained least squares (Twomey, 1977) and non-negative least
squares (Leggett, 1977) need to be explored with the addition of the
uncertainties in the source compositions.
     The input data required for the chemical mass balance consist of
the following:

     1.   The concentrations of the chemical components which comprise
          the total mass of the sample, the C^, and  their
          precisions,  the 0"-.
                            1      11

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      2.   The number,  p,  and identification of source types
           contributing to the receptor samples.
      3.   The source type compositions,  the a£ j ,  and  their
           variabilities 
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     If no other sources of chemical component i exist, E. = \t
F
 i greater than one  implies sources of component i other than
source b.  For example, King  et al. (1976) noticed a high Sb
enrichment at one  site in Cleveland, Ohio.  Further investigation
revealed  the existence of a nearby  chemical plant producing Sb
compounds.
     Ambient aerosol property measurements are quite sophisticated;
the state of source measurements  is atrocious.  Certain aerosol
property measurements have been made on emissions from geological
material  (Rahn, 1976), auto exhaust (Pierson and Brachaczek, 1974),
marine background  (Hidy et al. 1974), coal combustion (Gladney et
al. 1976), municipal incinerators (Greenberg, 1978), iron and steel
blast furnaces (Jacko, 1977), tire  dust (Pierson and
Brachaczek, 1974), copper smelters  (Zoller et al. 1978), vegetative
burning (Core and  Terraglio,  1978), kraft recovery boilers
(Watson,  1979) and cement plants.   The references cited are
representative rather than exhaustive.  These tests seldom provide a
full accounting of aerosol properties, have not taken samples similar
to the ambient samples, report no confidence intervals on the
measurements, and  do not fully describe the operating parameters of
the source at the  time of the test.
     Even if a methodology existed  for exactly quantifying the source
type compositions, it is unlikely that all individual emitters would
have the  same composition or  even that the composition would remain
the same  over the  period of time  during which ambient samples are
taken.
     The source contributions of aerosol formed from gaseous
emissions, such as sulfate, nitrate and certain organic species,
cannot be quantified by chemical mass balance methods.  Watson (1979)
proposes a unique  source type which will put an upper limit on the
contributions of secondary aerosol  sources, but it cannot attribute
those contributions  to specific emitters.
     Even given these limitations,  users of the chemical mass balance
feel that the method has been developed to the point where it can
frequently be used as a basis for state implementation plans for the
control of particulate matter pollution.  It is conceptually simple,
based on real data, and given the proper input data, it is able to
                                    13

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 quantitatively apportion  contributions  of  sources  to  ambient  air
 quality.   The  difference  between  the mass  concentration  at  the
 receptor  and the sum of  the  source  contributions offers  a consistency
 check;  if the  sum is much greater than  the total mass, one  or more  of
 the source contributions  have been  over-estimated;  if the sum is  much
 less than the  mass,  sources  have  been left out  or  some of those
 included  do not belong.   This same  check can be applied  to  chemical
 components not included  in the fitting  procedure.
      Major source contributions are quantified  with greater precision
 than minor contributions, but this  may  not be a limiting feature  for
 many purposes.  Watson  (1979) observed  that the industrial  source
 contributions  to the Portland airshed were subject to large
 uncertainties; if their exact determination was required, the results
 would have been inadequate.   However, for  the control-strategy-planning
 purposes  of that study,  they were sufficient for concluding that  the
 maximum possible industrial  contributions  were  not causing  standards
 violations.
      The  future development  of the  chemical mass balance receptor
 model must include:
          More  chemical  components measured  in  different  size  ranges
          at both  source and  receptor.
          Study of other mathematical methods of  solving  the chemical
          mass balance equations.
          Validated and  documented computer  routines  for  calculations
          and error estimates.
          Extension of the chemical mass balance  to an  "aerosol
          properties balance"  to apportion other  aerosol  indices  such
          as light extinction.
2.2  Multivariate Models

     The chemical mass balance uses the aerosol property of chemical
composition.  If source and ambient samples are taken in more  than  one
size range, the size property can be used to separate the contributions

                                     14

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of one source from another.  The mass balance presently has no way to
incorporate the variability of ambient concentrations and source
emissions.  The multivariate methods can do this.
     Linear regression  (Kleinman, 1977, 1980, Hammerle and Pierson,
1975, Neustadter  et al.,  1976), correlation (Moyers et al., 1977,
Cahill et al., 1977) and  factor analysis (Hopke et al., 1976,
Henry, 1977) are  the forms these models take.
     While the chemical mass balance receptor model was easily
derivable from the source model and the elements of its solution
system were fairly easy to present, this is not the case for
multivariate receptor models.
     Watson (1979) has carried through the calculations of the
source-receptor model relationship for the correlation and principal
components mpdels in forty-three equation-laden pages.  Only a few
highlights can be offered here.
     The mathematical obfuscation of these models must not remove the
requirement that  every receptor model must be representative of and
derivable from physical reality as represented by the source model.  A
statistical relationship between the variability of one observable and
another is insufficient to define cause and effect unless this
physical significance can be established.
     The multivariate models deal with a series of m measurements of
aerosol component i during sampling period or at sample site k.  From
Equation 3,
              C.    =    >     a. . S.,     k=l...m                (12)
               ik        L^      ij   jk
The multivariate models deal only with the C-, with the objective of
predicting the number of sources, p, and which a^. are associated
with which S.  or mOre ambitiously, estimating a— and Sj^.
                                    15

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      The linear  regression  model  sets
              C ,  =   a C  .  +  b                                   C13)
               vk       uk
 where
                         C  C    -   C  C
               a   =       v u	v u



                         —         2
 and
                         Cu    -   Cu                               (14)
               b   =   C     -    a  C                                 (15)
                      v          u
 with
                        m
            C  C    =  -  T]    C  ,C  ,                              (16)
            v u        *—*.    vk uk
                    m  k=l
                            C  ,                                    (17)
                            uk
            	           m


            C  2   =   -   Y,     C ,2                             (18)
            u            r—',      uk
                      m   k=l
     A

 and  C^k  is  the  value  calculated  from Equation 12 as  opposed to the


 measured  value,  C  ,
               '  vk-




 When  chemical components u  and v originate  uniquely  in source type j,


 cv and Cu can be replaced by  Equations  4  in Equations  14 and 15 to


 give


                      a  .







               b  =   0                                            (20)






The linear regression model yields  the  ratios of the source


compositions for chemical components  unique to one source.
                                    16

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     The correlation model  relies  on  the  correlation  coefficient,
                                 c   c    -     c   c
     rc c                         u  v        u  v
                     f ~2      - 2  \ 1/2  /	2     - 2  X  1/2
                     ( C  2   -   C 2  )     (  C  2   -  C 2  \       (21)
                     v  u       u  y     \v       v  /
to measure  the  extent  to which  ambient  concentrations  u  and  v vary in
the same way.   If u  and v  are from  the  same  source,  then Equation  4
holds and upon  incorporation into Equation 21
              rC C   =1                                         (22)
                u v
     The  traditional  factor  analysis model  transforms  equation  12  to
                       a£.   S.J  +   d.   Ui-                       (23)
where
                        c.. -  c.
       cik   =    	—-——~                            (24)
        jk          / —^-_   _ 2 x  1/2

and
                       S.,  -   S.
                                                                  (25)
             -   *ij  I    ^   "   V     V                         ^
                       ~   -   C.2
                          i        i
where  a^. is called the  factor  loading, and  is  related  to  the
source compositions through Equation  25, and  S?^ is  called  the
factor score, which is related to the  source  contributions  through
Equation 24.  The d- and  U- are  unique  factor loadings and  scores,
respectively, which are  often left out  of  the analysis.   The  resulting
is a principal components analysis
                                    17

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                             i-i

      The factor model treats  the  Cs.   as  components  of  a vector
 for each chemical component,  i, in an m-dimensional space.   If
 Equation 3 is true,  then only p vectors, where  p <_ m,  in a  less
 complex p-dimensional space are required to  produce the vectors  of
 C?.  This p-space is defined  by the  eigenvectors of the
 correlation matrix of the C?. These p eigenvectors merely  define
 the space, however,  and are not necessarily  representative  of the
 sources, the S? vectors.  They must  be linearly combined to form
 the new source vectors.
      Alpert and Hopke (1980)  have experimented  with an unstandardized
 correlation matrix with correlations between samples as opposed  to the
 standardized correlation between  chemical  species  of Equation 21.
 This approach retains more of the information in the data and allows
 the proportionality  among the chemical species  to  be maintained.
      The foregoing discussion can by no means initiate the  casual
 reader to the full power and  limitations of  the multivariate models;
 it  can only impress  on him the complexity  of the subject and the
 necessity to study it carefully before proceeding.
      Multivariate models have been successful in identifying source
 contributions  in urban areas. They  are not  independent of  source
 composition  knowledge since the chemical component  associations  they
 reveal must  be  verified by source emissions  analyses.   The  linear
 regression model  can  produce  the  typical ratio  of  chemical  components
 in  a  source,  but  only under fairly restrictive  conditions.   The  factor
 and  principal  components analysis models require source composition
 estimates  to  find the right set of S? vectors,  though  it seems
 that  these a^.  estimates can  be refined as a result of the  analysis
 (Henry,  1977, Alpert,  1980).
      The most  important  caveat to be  heeded  in  the  use of multivariate
models is that  though origination in  the same source will cause  two
 chemical  components  to  correlate,  the  converse,  that chemical

                                   18

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components which correlate must have originated in the same source, is

not true.  The substitution of Equation 1 into Equation 13 and its
propagation through the subsequent equations shows that the

correlation between elements u and v is a function of the non-source

related dispersion factor, Difc} as well as the source-dependent
emissions factor, E.,
                 '  ik«
     The only input data required of the multivariate receptor models
at their present state-of-the-art are the ambient concentrations, the

^ik-  This data  set must be large (just how large is yet undefined)
and must contain substantial variability.  With an estimate of the

ai j , the source compositions and contributions can be refined.  No
provision has yet been made for propagating the measurement

uncertainties, the CTC_ and aa_, through the model or of
evaluating their effect on model output as has been done for the
chemical mass balance.

     Future development of the multivariate models includes:
     •    Testing of other multivariate methods.  Suggestions include
          ridge regression (McDonald and Schwing, 1973) regression
          against principal components (Henry and Hidy, 1979),
          clustering techniques (Gaarenstroom et al., 1977), time
          series analysis (Box and Jenkins, 1976), and non-parametric
          (Bradley, 1968) approaches.  The formulation and testing of
          such models should draw statisticians and applied
          mathematicians into working with aerosol study specialists
          to become aware of the full range of multivariate methods
          available and to apply them appropriately to air quality
          problems.

     •    Creation of simulated ambient data sets from a simple source
          model with known source compositions and contributions
          perturbed by typical experimental error.  The multivariate
          models should be applied to these data sets, as did
          Watson (1979) for the chemical mass balance, to determine
          the extent to which the models can apportion source
          contributions under various conditions.


2.3  Microscopical Identification Models


     Microscopic identification and classification of individual
aerosol particles into source categories can be a valuable tool for
the study of settled and suspended atmospheric particles.
                                   19

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      Many different optical  and  chemical  properties  of  single aerosol
 particles can be measured, enough  to  distinguish  those  originating in
 one source type from those originating  in another.   The microscopic
 analysis receptor model  takes  the  form  of the  chemical  mass  balance
 equations presented in Equation  3.
               M.   =  Y   *••  S-                                   <28)
                i     ^-rf    ij   J
 where
        M.    =   %  mass  of  particle i  in  the receptor sample
        a—   =   fractional mass  of particle type i  in source  type  j
        S.    =   %  of  total mass  measured at the receptor due
                to source  j .
      The model  of Equations  3  and  28 might be better  termed an  aerosol
 properties mass  balance  to encompass both the chemical mass balance
 and microscopic  receptor models.
      The solutions  to  the set  of Equations 28 are the same as those
 described by  Equations 4, 5  to 7,  8, and 9,  though only the tracer
 method,  i.e., each  receptor  particle type is unique to one source
 type,  has been used in the past.
     The microscopic receptor  model can include many more aerosol
 property measurements than those used to date in the  chemical mass
 balance  and multivariate models.   It has not taken advantage of the
mathematical  framework developed in the other two models to deal with
 particle types which are not unique to a given source type or the
 ambient  and source measurement  uncertainties.
     The  data inputs required  for  this model are the  ambient
 properties measurements, the M^, and the source properties
measurements, the a^..   To estimate the confidence interval of  the
 calculated S.  the  uncertainties (TM  and a_   are also
                                   i       ii
 required.  Microscopists generally agree that a list  of likely  source
                                   20

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contributors,  their  location with  respect  to  the receptor, and
windflow during  sampling are helpful in confirming their source
assignments.
     The major limitation of microscopic receptor models is that the
analytical method, the classification of particles possessing a
defined set of properties, has not been separated from the source
apportionment of those particles.  Equations  28 have never been used
in this application.  The source identification takes place on
recognition of the particle by the microscopist.  The particle
properties he uses for this identification are his alone (or his
laboratory's) and are not subject  to interpretation by another.
     Source contributions assigned to the  same aerosol sample have
varied greatly in inter-comparison studies (Bradway and Record, 1976),
but without the  intermediate particle property classifications, it is
impossible to ascribe the differences to the  analytical portion or to
the source assignment portion of the process.
     Many times  the microscopist relies on his past knowledge of the
properties of aerosol sources without the  examination of local source
material.  For example, a coarse particle  sample taken in the vicinity
of a coal fired  power plant may show a 20% contribution due to flyash
and an 80% contribution due to minerals.   As  Brookman and Yocom (1980)
point out, the 20% flyash may not have come from the power plant
during the sampling period.  An examination of nearby soils could show
a 20% flyash concentration resulting from  long-term deposition.  Using
one of the least squares or linear programming approaches to the
solution of a set of Equations 28 with local  source compositions could
alleviate this problem.
     Though the  aerosol properties mass balance suggested by the
microscopic models shows promise,  it is limited by the lack of a
standardized, reproducible analytical method.  A few laboratories are
pursuing the establishment of such a method,  however, and the
state-of-the-art of their efforts will be  summarized in Chapter Three.
                                   21

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     Future development for this model include:
     •    Creation and acceptance of a standardized methodology.
     t    The definition of important optical criteria and their
          measurement/methods.
     •    A method of reporting and cataloging source properties by
          means of the chosen criteria.

2.4  Hybrid Source/Receptor Models
     Until now, the receptor models have been treated as if they were
 completely separate entities from the source models.  This need not be
 the case.  Three examples of source/receptor model hybridization show
 promise,  and many others are probably waiting to be developed.  A
 source model incorporates measured or estimated values for the
 emission  rate, E-  and the dispersion factor, D-  in Equation 1.
 Whenever  either of these enter the receptor model as observables,  it
 shall be  termed a hybrid model.  The three applications considered
 here are  emission inventory scaling, micro-inventories, and dispersion
 modeling  of specific sources within a source type.
     Emission inventory scaling, proposed by Gartrell and Friedlander
 (1975), uses the relative emission rates of two source types subject
 to approximately the same dispersion factor (e.g., residential heating
 by woodstoves and natural gas) to approximate the source contribution
 from the  source type not included in the chemical mass balance (e.g.,
 natural gas combustion).  The ratio of the emission rates is
multiplied by the contribution of the source type which was included
 in the balance.
     The micro-inventory approach developed by Pace (1979) has been
shown to be a good predictor of annual average TSP based on a detailed
assessment of emissions close to the sampling site.  Four types of
emissions are compiled using standard emission factors where
applicable.

     o    AREA emissions:  annual area source particulate matter
          emissions within one mile of the monitor.  This variable
          includes fugitive dust and the influence of the monitor
          height.
                                   22

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     •    POINT emissions:  annual point  source emissions within
          five miles of the receptor.
     •    LOCAL emissions:  annual emissions  from  traffic-related
          sources within 200 feet of the  receptor.
     •    VISPLUME emissions:   an indicator variable  for the presence
          or absence of traffic related/suspended dust plumes from
          nearby (200 ft.) streets.
     Pace investigated many other variables in multiple linear
regressions with TSP, but found these to  be the significant ones.
     Figure 2 shows the excellent relationship between predicted and
measured values for the 79 data sets from four cities used by Pace to
derive the following relationship:

     Annual Average TSP = 0.0045 (AREA) + 0.00096  (POINT) +      (29)
                          50.5  (LOCAL) +  18.6 (VISPLUME) +
                          CITY EFFECTS

     Pace emphasizes that Equation 29 is  not  applicable to other
cities in an absolute sense, but he does  show, with data from three
other cities, that it is effective in determining  the relative
contributions of AREA, POINT, LOCAL, and  VISPLUME  effects.  Large
contributions from LOCAL and VISPLUME indicate that the sampler
location is probably inadequate to represent  the airshed as a whole,
and that the best control measures are those  taken in the vicinity of
the monitor.
     A more specific equation than Equation 29 could be calculated by
adding new data sets to the 79 already in use and  recalculating the
coefficients, or by using the existing HIVOL  sites to create a new
equation.
     The micro-inventory should be a pre-requisite for aerosol mass
balance or microscopic model applications to  identify the most likely
sources for sampling, analysis and inclusion  in the balance.
     A major limitation of receptor models is their inability to
distinguish between specific sources within a source  type.
Resuspended road dust may be a major cause of standard violations, but
until the offending roadways can be pinpointed, a  control strategy
                                   23

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      180



      160



      140
      100




      ! 80
      I
      I


      I 60
    V)

    g 40
       20
         0    20    40    60    80   100   120   140   160   180

                 PREDICTED CONCENTRATION, MB/m3
Figure 2.       Plot  of predicted versus observed
                concentration for regression.
                From  Pace   (1979)
                           24

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cannot be implemented.  A major  limitation of  source models  is the
necessity to estimate emission rates  from the many, diverse  producers
of suspended particulate matter.  Figure 3 schematically illustrates a
possible combination of the two models.  The receptor model  quantifies
the source type  contributions.  Only  the major  contributors  need  to be
evaluated for the source model, so that resources which might have
been used to inventory an entire airshed can be concentrated on
determining emission rates from the specific emitters within a source
type.  This improved data with fewer  source inputs should increase the
accuracy with which the relative contribution  from each individual
source type can  be calculated.  An application of this hybridization
has never been attempted, but it merits exploration.
     Two more sets of observables are introduced into the hybrid
models, the emissions factors, the E-  and the dispersion factors,
the D.   it is the difficulty of quantifying these that led  to the
use of a receptor model over the source model  in the first place, so
it would seem there is little advantage in re-introducing them.   The
advantage of the hybridization is that the  number of E- and D.
can be considerably reduced and that  the relative values rather than
the absolute values are used.  These  relative values are more accurate
in most cases.
     Still the uncertainties CTg _ and o^ need to be evaluated
and incorporated into any source/receptor hybrid model.
     Future areas of development include:

     •    Theoretical formulation of  source/receptor models.
     0    Validation tests with real  and simulated data.
                                   25

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                     DATA INTERPRETATION USING DUAL "ODEL APPROACH
                 TYPICAL INTERACTION 0* SOURCE AND RECEPTOR '1QDELS TO
                 DETERMINE SOURCES Of TOTAL SUSPENOE D PARTICIPATES
                 THE DIAGRA*' SHOWS ONE OF SEVERAL POSSIBLE SOURCE DISTRIBUTIONS
Figure  3.  This source  receptor model  hybridization uses
            the receptor model  to calculate the contributions
            of  each source type and the source  model to quantify
            the contribution  of each  specific  source to its
            source type.  (From ERT,  1979)
                                 26

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                  CHAPTER 3.   RECEPTOR MODEL INPUT DATA

     It is evident  from  the previous  chapter  that  the  receptor models,
like all such simplified  representations of reality, can return
results no better than the input  data with which  they  are supplied.
     The measurements required  for  the present receptor model
state-of-the-art  include  particulate  matter composition, size and
variability of both source and  receptor.  Aerodynamic  diameter and
variability must  be distinguished at  the field sampling stage (though
microscopic sizing  can provide  an £ posteriori estimate of optical
diameters).  While  real  time measurements of  particle  composition
would be ideal, the state-of-the-art  requires laboratory analysis of
particulate matter  collected on appropriate substrates.
     In this chapter, the collection  of input data for receptor models
will be examined.

3.1  Field Study  Design  and Data  Management

     Few aerosol  characterization studies performed  in the past have
been designed with  the goal of  applying a receptor model.  The
receptor models have  traditionally  been developed  and  applied after
data collection as  a method of  interpreting large, complicated sets of
measurements.  This has  been a  productive development  mechanism, but
the present state-of-the-art demands  a more precise  definition of the
goals of a study,  the receptor  models to be used,  the  input data
required, and the measurement and quality assurance  program to obtain
that input data.  These  goals might include:

     •    studies to further validate the receptor models and
          measurement methods,
     •    evaluation of health  related particulate matter constituents,
     •    causes  of visibility  impairment,  and
     •    providing a detailed  breakdown of source contributions to
          different particle  size fractions in order to devise a
          control  strategy.
                                    27

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     Cost will be the primary controlling factor in the experimental
 design in essentially all cases.  The cost of obtaining the  entire
 population of possible measurements is prohibitive.  The  field  study
 design must select a subset which is representative of the  population
 within definable confidence limits and which can be obtained within
 the  constraints of existing resources.
     Several generalizations can be made about aerosol characterization
 study design based on past experience.
     Existing data should be used to obtain an understanding of  the
 area under study.  These data include historical HIVOL and  gas
 concentrations, meteorological data, emission inventories,  chemical
 and  optical analyses, and the results of dispersion modeling.
 Step-by-step procedures of how to use this information need  to be
 developed.
     Siting of monitoring stations should take advantage  of  existing
 sites with consideration to land use categories and transportation
 source influences.  Prevailing wind directions and the locations of
 important sources should be located prior to siting and used in  the
 siting process.  Source-oriented sites are often useful,  but both
 upwind and downwind, baseline or background sites are needed.   Simple
 source-oriented modeling can provide helpful guidance for the location
 of sites.  Hougland and Stephens (1976) describe an analytical
 technique for siting monitors while Stalker and Dickerson (1962) and
 Solomon et al. (1977) offer empirical evidence that a small  network
 can  represent an airshed as well as a larger one under certain
 conditions.  In many cases of current interest, sampling  for vertical
 stratification may be needed to distinguish between tall  stack  and
 ground level contributions.
     The frequency and duration of measurement are important factors;
 source contributions at a fixed station are often short-term and to
measure their variability requires sampling times of the  same order  as
 that variation.  Twenty-four hour sampling is considered  minimal,  and
 shorter term sampling is often desirable.  Less than 12-hr  samples  are
 usually required to relate samples to a constant wind direction.
                                    28

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Measuranents  are needed  to  extrapolate  to  annual  average  conditions;
however,  it  is  not  necessary  to  sample  daily  to achieve this.  It is
important to  obtain information  on  both intense pollution conditions
(episodes) and  relatively clean  conditions.   Thus, more samples than
needed  should be taken with a subset  chosen for detailed  analysis
based on  meteorological  or  other factors.  Samples should be taken
every day over  selected  seasonal periods rather than one  per third or
sixth day to  capture the progression  effect of multiday events.
     Aerosol  sampling devices must  be chosen  which can obtain an
adequate  amount of  particulate matter for  analysis within the sampling
duration.  The  samplers  must  separate the  ambient aerosol
concentrations  into the  desired  size ranges with a defined efficiency.
     The  particle size cuts of the  sampler and their variation with
respect to windspeed and wind direction (McFarland et al., 1979) must
be quantified if comparability of results  between one study and another
is to be  achieved.   Several of the  sampling devices available for aerosol
characterization studies were intercompared via the simultaneous sampling
of air during sixteen  consecutive twelve-hour periods (Camp et al.,
1978).  More  of  this  testing  and intercomparison work is  required of
existing  samplers.
     For  sampling in which  the variation of aerosol concentrations
with time  is  required, the sampler  should  be  able to switch filters
sequentially  without  operator attention.   Camp et al. (1978) report
three commercially  available  samplers,  the automated dichotomous
sampler,  the  sequential  filter sampler,  and the streaker  sampler,
capable of this.
     Because  of  the  re-entrainment  and  bounce-off problems associated
with cascade  impactors,  which cause large  particles to penetrate to
the small  particle  stages, virtual  impactors  (Loo et al., 1975) and
cyclone preseparators  (Mueller et al.,  1980)  are the most commonly
used size  separating devices  in  current  aerosol characterization
studies.
     In most  studies,  particularly  those in which regulatory issues
are addressed, a 24-hour  high  volume sample should accompany samples
taken with other devices; the  relationship of the aerosol study
samples to the historical total  suspended  particulate matter data base
can then be evaluated.
                                    29

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     Meteorological information which has been useful to receptor
model studies includes temperature, relative humidity, mixing height,
windspeed and wind direction.  For hybrid approaches using a source
model, stability class, sigma theta and vertical temperature profiles
may be needed.  The wind direction is particularly important for  the
verification of certain receptor model source contribution
predictions; definite differences should exist between samples on
which the source is upwind and downwind of the receptor.  Kleinman
(1977) incorporated a normalization factor, which is a function of
windspeed and mixing depth, to minimize dispersion related
correlations from his multivariate receptor model.  Existing
monitoring at airports, television stations and private facilities may
be sufficient for the aerosol study.  These networks, their ability to
meet the requirements of the study, and the data collection procedures
need to be defined as part of the field study design.
     Source characterization must be an integral part of any field
study design.  A microinventory (Pace, 1979) of each sampling site
should be conducted and specimens of nearby fugitive emissions sources
identified by it should be taken and analyzed.  Aerosol properties of
likely point source contributors identified in the emission inventory
must be measured during the course of ambient sampling.  Source
sampling and analysis techniques need to be compatible with ambient
techniques.  With limited resources, not all sources can be
characterized.
     Priority should be given to those sources which are expected to
be heavy contributors on the basis of calculated emissions
(EPA, 1973), and which have not been characterized in previous studies,
     The chemical components to be quantified in each sample and  the
analytical methods to be used should be specified before the first
sample is taken.  The experimental design must be reviewed to assure
that  the field samples will be amenable to the chosen techniques.
This  requires:
          Comparison of component concentrations likely to be  found  in
          samples to the lower quantifiable  limits of the analytical
          methods.  The sampling design or analytical method must be
          modified if the majority of the expected amounts are  less
          than these limits.
                                   30

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      •     Selection of filter  media which will  not  bias  the  aerosol
           measurement  because  of  variable blank concentrations  or
           artifact  formation of the chemical  species  to  be measured.
           If  x-ray  fluorescence is  to  be  used,  the  aerosol must be
           deposited on the  surface  rather than  inside of the filter  to
           prevent absorption of x-rays by the filter  material.
           Simultaneous sampling on  more than  one substrate may  be
           required.
      •     Transport and storage procedures must prevent  changes in the
           components  to be  quantified  between sampling and analysis.
      An overwhelming number of chemical compounds can be  found  in the
typical urban aerosol, and  some subset must be  selected  for
quantification.  Two general rules  can narrow the scope  of chemical
analysis  somewhat.   First,  the sum  of  the masses  of chemical
components measured should  equal, within  stated precision estimates,
the total mass concentration of the aerosol.  Without this equivalence
one cannot necessarily assign  the unaccounted for mass to a  source,
nor is it  possible  to  verify the  other component  quantities  via a mass
balance.  Thus the  first requirement of chemical  analysis is that the
major chemical components of total  aerosol mass in the sample are
quantified.
      The  second requirement  is that components  unique  to  specific
aerosol sources affecting the  ambient  sample  are measured.   The
precise chemical species will  depend on the sources in the airshed
under consideration.
     Most studies will  require measurement of certain "basic"
particulate matter  species  including ions, elements,  and  organic and
inorganic carbon.
     A quality assurance component  must be integral to the study to
verify the accuracy of  its measurements and to  estimate a precision
for each one.  This  component  should include  co-located sampling,
replicate analysis, station  audits, data  validation,  interlaboratory
comparisons and a full  set  of  standard  operating procedures.  The
quality of the data set generated should  be discussed and should
include the results of  validation,  analysis of  outliers and  overall
estimates of  accuracy  and precision.
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     Every data  item should be considered an  interval  rather  than  a
number and the precision of each measurement  determined  from  replicate
analysis  should  be propagated through all calculations
(Bevington,  1969).
     The  final important ingredient of experimental design  is data
management,  which is normally carried out by  computer.   The data must
be  organized and merged into uniform formats  accessible  by  the
receptor  models.  Provisions for the entry and processing of  quality
assurance data will greatly reduce the efforts required  for this often
neglected study  component.  All data from initial analyses  must be
retained  until the sorting of relevant and irrelevant information  can
be  achieved.  Economical accessibility, security and definition of
uncertainty  should be keynotes of data management systems for  this
work.  Organization techniques for "data dipping" subsets of  data  from
a number  of  large data bases to a microcomputer must be  developed  to
maximize  economic data handling and computation.
     Though  the  field study design task is presented here as  a
separate  entity, it requires a knowledge of all other aerosol  study
aspects and  dictates which subset of the array of tools  available  will
accomplish the goals of the study within the  resources available.  No
two field study  designs will be alike,  but studies with  similar goals
should be similar in design.
     Several generalized "ideal" or "template" designs to meet the
needs of users with a specific set of goals would be helpful  examples
to those designing a field study for the first time.
     Future  development efforts in field study design and data
management should include:
          Develop methodologies for choosing sampler location,
          sampling schedule, and sampling devices.
          Measure the collection efficiency of available samplers as a
          function of particle size, windspeed and wind direction.
          Create a series of "typical" design scenarios which can be
          specified for different aerosol study objectives.
          Develop standardized data bases from which ambient and
          source information can be "data dipped."
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      •    Develop standarized  receptor models  for  computer
          implementation  and standard interfaces to the relevant data
          bases.
      •    Create  quality  assurance  procedures  and methods of reducing
          the  data to  assign a confidence  interval to each measured
          quantity.
 3.2   Source Characterization

      All  receptor models, even the  source/receptor hybrids, require
 input data  about  the particulate matter  sources.  The multivariate
 models, which  can conceivably  be used to better estimate source
 compositions,  require  an  initial knowledge of  the  chemical species
 associations in sources.   The  lack  of knowledge of a. . and 0"a. . in
 Equations 3, 8, and 9  poses the greatest limitation to receptor
 modeling.
      Existing  data on  characteristics of particles from various types
 of sources  are inadequate for  general use, though  they have been used
 in specific studies with  some  success.   Most of the source tests have
 been  made for  purposes  other than receptor modeling and complete
 chemical and microscopical analyses have not been  completed.  Source
 operating parameters which might affect  the aerosol properties of
 emissions have not been identified nor measured.  Particle size
 separations are rarely the same as  those measured in ambient sampling
 and no provision  is made  for likely transformations of the source
material when  it  comes into equilibrium  under  ambient conditions.
     For receptor  modeling, the only source characteristics that are
 relevant are those perceived gt the receptor.  But if source
 components  could  be separated  from  each  other  at the receptor, there
would be no need  for a receptor model.
      Stack  sampling is not sufficient for  characterizing all sources
 and may not be the best method  even for  ducted point sources.  Because
of condensation of vapors, fallout of very large particles and the
neglect of  non-ducted emissions, the materials collected from stacks,
especially  those  at high  temperatures, will often not represent the
particles from the source  as observed at a receptor several kilometers
away.

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     Several source type categories, such as road dust, automobile
exhaust and home heating, contain many individual sources whose
emissions compositions may vary considerably.  A source sampling
program for these source types must consider the selection of a
representative subset as well as the sampling mechanics.
     At present, most source sampling groups measure elemental,
organic or microscopic components, each depending on its area of
expertise.  No complete set of measurements on a single sample exist.
     In spite of this criticism of existing source characterization
data, knowledge of several source types and testing methods  is
growing.  Certain aerosol property measurements have been made on
emissions from geological material (Rahn, 1976), auto exhaust (Pierson
and Brachaczek, 1974), marine background (Hidy et al., 1974), coal
combustion  (Gladney et al., 1976), municipal incinerators
(Greenberg, 1978), iron and steel blast furnaces (Jacko, 1977), tire
dust (Pierson and Brachaczek, 1974), copper smelters (Zoller
et al., 1978), vegetative burning (Oregon Department of Environmental
Quality, 1979), kraft recovery boilers (Watson, 1979) and cement
plants which, though semi-quantitative for the most part, have been
useful in applying receptor models.  These source characterization
experiences point out some of the considerations which are required of
receptor model source sampling.
     For use with receptor models, it is desirable to collect
particles far enough from the source to allow the emissions  to reach
equilibrium with the atmosphere, but not so far away that the source
material under test becomes contaminated with aerosol from other
sources .
     Armstrong et al. (1978) describe a unique approach of attaching
sampling equipment to tethered balloons which are maneuvered from  the
ground into the plume of smokestack emissions.  The payload  these
balloons can carry is presently low, but conceivably it could be
increased to allow the placement of size-selective sampling devices in
the plumes  of tall point sources.
     Aircraft sampling in plumes (Mroz, 1976) has long been used, but
it is expensive and difficult.  Sampling flowrates need to be
increased because of the short period of time an airplane can remain
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in  the  plume.   A real  time measurement device,  such as a nephelometor,
condensation nuclei counter or S02 monitor,  is  required to  inform
the sampler  when it enters and leaves the plume so that sampling can
be  started and stopped accordingly.  Flowrates  must be changed with
airspeed to  maintain isokinetic conditions  -  this makes
size-selective sampling difficult.  The high cost  and  trouble of
aircraft sampling do not encourage its widespread  use  for receptor
model source characterization.
     A  promising development is that reported by Rheingrover  and
Gordon   (1980).   Using ambient samplers located in "maximum effect"
areas for specific  sources and wind flow patterns,  they have
distinguished  the composition of a single point source at^ £ receptor.
They then use  these source characteristics to represent that  source in
areas less affected by that source, where its contribution  is not so
obvious.  This approach could be incorporated into field study designs
in  the  following way:

     1.   After identifying major point sources, determine  the
          "maximum  effect" areas via source  modeling.
     2.   Locate samplers  and windvanes at these sites and  sample
          simultaneously with the other receptor sites.
     3.   Analyze samples  for all days on which the sampler is
          downwind  of  the  source.
     4.   Determine which  components of the  sample are due  to the
          source in question.
     The last  point is  the hardest to accomplish and reverts  to  the
question of, "If that  can  be done,  who needs the receptor model?"  The
true advantage  of having a sampler in the "maximum effect"  area  may be
in eliminating  the  particular source it is intended to monitor from
consideration  in the receptor modeling at other sites;  if it  cannot be
detected where  it should hit hardest,  then there is  little  hope  of
finding it elsewhere.
     In-stack  testing  procedures  are still under development  with a
greater inclination on  the part  of  developers to produce  samples  of
use for receptor modeling.   In the  past,  few stack  samples  have
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obtained more than mass emission rates under stack conditions.  New
sampling methods include dilution with clean air to simulate ambient
conditions, filter media amenable to chemical analyses, and samples in
size ranges similar to those sampled in ambient air
(Bruce Harris, EPA/IERL, personal communication, 1980).
     Detailed studies of large point sources should be done in such a
way as to enhance the generality of the results.  The relevant
operating parameters affecting emission compositions need to be
identified, measured and reported with each source test.  It is only
with this information that the test results can be evaluated for use
in receptor model studies other than that for which the test was made.
     Studies of motor vehicle emissions are difficult now and will
become even more so as lead is phased out of gasoline.  Studies of
tailpipe emissions should be done with dilution and cooling of the
exhaust.  A serious drawback of individual automobile testing is the
variability of emissions compositon as a function of car and driving
cycle.  In his review of the automobile emissions literature,
Watson (1979) found the lead composition of auto exhaust varying from
12 to 70 percent, depending on the test.
     Studies in tunnels (Pierson and Bracheczek, 1976, Ondov
et al., 1979) and along highways (Feeney, et al., 1975), might offer
more representative compositions of the motor vehicle fleet affecting
receptors.  At present, no components unique to diesel exhaust have
been found, and with the phase-out of lead in gasoline, the major
tracer for conventional engines is being lost.  Much greater emphasis
on the characterization of this universal aerosol source category  is
required.
     The characterization of fugitive emissions, those originating
from roadways, storage piles, and rock crushers, is extremely
important for the source apportionment of the total and coarse
suspended particulate matter fractions of ambient concentrations.
Once likely sources are identified, ambient samples can be taken at
site or bulk material can be taken to the laboratory, resuspended  and
sampled on a filter substrate and analyzed.  Analysis of the bulk
material without resuspension may yield a biased characterization
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 since  the larger particles of the bulk sample which do not  remain
 resuspended often have compositions differing from the smaller
 particles which do remain suspended (Rahn,  1976).
      Source characterization results are not located in a centralized
 facility which is constantly updated,  and each researcher has  to
 assemble his own collection of results or use the  assemblage of
 someone else which may not be applicable to the case under  study.
 Fortunately, the Environmental Protection Agency has established  the
 Environmental Assessment Data System (EADS) (Larkin and Johnson,  1979)
 which  contains chemical compositions of particulate matter  emissions
 tests.   This existing computerized structure can provide the
 centralized location  for receptor model source characterization
 information.  Procedures such as  those described for ambient data  in
 the  previous section, need to be  developed  which will allow receptor
 model  users to access this data base over telephone lines.  The data
 required of receptor  model source tests should be  incorporated into
 the  EADS and source characterization results should report  this
 information in an EADS compatible format.
     Future development efforts in source characterization  should
 include:
           Develop  new source  sampling methods  including  tethered
           balloon  and ground  based  sampling.
           Standardize data  reporting  and management  procedures  and
           store  all  data  in a central data base.
           Create a chemical component analysis  protocol  to  obtain
           maximum  information from  each  source  test.
3.3  Analytical Methods

     Many chemical  and physical  analysis methods exist  to characterize
particulate matter  collected  on  a  substrate.  Though  several methods
are multi-species,  able to quantify a number of chemical components
simultaneously, no  single method is sufficient to both  quantify the
majority of the collected particulate matter mass and those components
which serve to identify and quantify source contributions.
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     After the composition measurements to be made have been selected,
each analytical method must be judged in terms of four necessary and
three desirable criteria.  These apply not only to the analytical
method, but to the laboratory performing the method.
     The necessary criteria are:
     1.   The analytical method must have been developed and tested
          specifically for the analysis of suspended particulate
          matter.
     2.   Lower quantifiable concentrations of the method must be less
          than the concentrations expected from the ambient samples
          taken.
     3.   The method must be free of biases for all components
          quantified.
     4.   The values achieved by the method must be reproducible
          within defined and reasonable confidence intervals.
          If an analytical method is successful for certain types of
environmental samples, it is convenient to assume that it is
appropriate for all samples.  Hard and bitter experience shows this
not to be the case for suspended particulate matter.  Before a
procedure can be accepted, one must have identified and corrected
likely interferences, defined amenable aerosol collection substrates
and sampling requirements, considered the effects of different aerosol
matrices, and verified its ability to meet the final three criteria.
     The amount of suspended particulate matter available for analysis
depends on the ambient concentration, the flowrate of air through the
substrate, the sampling duration, and the fraction of the sample
presented for analysis.  Cooper (1973) provides a useful tabulation of
typical concentrations and ranges of urban aerosol elemental
concentrations;  it would be helpful to update this summary, expand it
to certain chemical compounds, and stratify it by site types (urban,
rural,  etc.).  The expected amounts available for analysis should be a
factor of ten or more above the lower quantifiable concentrations of
the analytical method.
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     Measurement accuracy can only be established  through
 interlaboratory/intermethod comparisons  and  the analysis of standard
 reference  materials.   Intermethod comparisons  are  better for
 evaluating accuracy since interlaboratory analyses using the same
 method  will exhibit the  same types of biases.   Urban  Particulate
 Matter  Standard  Reference Material 1648  (Greenberg,  1979) provides  a
 means for  initial  and  routine verification of  accuracy.  The
 concentrations of  additional chemical components in this standard need
 to be quantified and  their constancy with time assessed.  NBS  16A8  was
 collected  in St. Louis and is representative of the eastern city
 aerosol matrix.  Other aerosol standards from  a variety of  locations
 would be helpful for  the evaluation of analytical  bias.
     Replicate analyses  of the same sample must return results with a
 standard deviation of  +_  10% or less at concentrations greater  than  ten
 times the  lower  quantifiable limit.  The data  from replicate analysis
 should  be  used to  define the precision of each value measured.
     The desirable criteria are:

     1.    The method  should measure a number of components  in  a single
           analysis.
     2.    The analysis should be  non-destructive.
     3.    The analysis should be  cost-effective.

     Many  analysis  techniques are capable of measuring more  than one
 chemical component  of  interest with adequate precision, accuracy and
 sensitivity.  Not  only do these methods  save the cost of many
 individual  analyses,  they minimize the amount  of sample required.
     A non-destructive method is  preferred since the  sample  can be
made available for  other analyses to verify  the non-destructive
 results or  to complement them with the measurement of additional
 chemical components.
     Given  the choice  of analytical methods  meeting the necessary and
desirable criteria, the  least expensive  analysis per sample  should  be
chosen.   This choice may vary with  the number  of samples to  be
processed.

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     The range of analytical methods available for particulate matter
analysis is large; many of the available methods are critically
reviewed by Katz (1980).  A complete review of all methods applied in
the past with a view toward their use for receptor modeling does not
exist, and its production would be a useful contribution to the
state-of-the-art.  Several analytical tools have been found to meet
the stated criteria, or are in the development stages of trying to
meet them, and are being used to supply the input measurements for
receptor models.  One means of classifying available and useful
analysis procedures for source and receptor studies consists of the
following categories:

     1.   Elements with atomic number greater than 11.
     2.   Carbon
     3.   Ions
     4.   Organic Compounds
     5.   Inorganic Compounds
     6.   Physical and Optical Properties

     Several specific methods belonging to each  category and the
extent to which they meet the stated criteria are discussed here
because of their widespread acceptance and use in the field of
receptor modeling.  Analytical methods not mentioned here  should not
be dismissed; they are also potentially useful.  As the extent to
which they meet the necessary and desirable criteria becomes known,
their use for obtaining receptor model input data will increase
accordingly.

Elements

     X-ray emission spectroscopy  (Giaque et al.,  1974, Cahill
et al., 1976) (photon or proton excited) has developed as  a reliable,
available, cost-effective and non-destructive elemental analysis
method.  More aerosol samples, numbering in the  hundreds of thousands,
have been analyzed by this method than by any other.  The  method
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requires  aerosol  samples  uniformly deposited on a  thin,  flat  organic
substrate  (Teflon,  nuclepore,  polycarbonate  and cellulose  acetate
membrane  filters  are commonly  used).   In typical urban  samples  from 10
to  20  elements  are  routinely measured.   Biases  exist  due to the
attenuation  of  light element (e.g., Al  and Si)  x-rays in coarse
(>2jLim) particles,  but  corrections (Dzubay and  Nelson,  1974)  have been
devised and  applied. HIVOL  samples on  fibrous  filters  are
inappropriate for this  method  because a portion of  the  aerosol
penetrates beyond the filter surface and is  collected within  the
volume of  the filter material;  the x-rays emitted by  these particles
are partially absorbed  by the  filter material.   Spectral interferences
of one element  x-ray with another  must  be accounted for  in the  data
reduction, but  this  is  usually handled  by the computer  based  spectrum
processing routine  (Bonner et  al,  1973).  Interlaboratory  and
intermethod  comparisons (Camp  et al.,  1974,  1975) verify its  accuracy
and precision.
     Instrumental neutron activation analysis (Zoller et al., 1970,
Dams et al., 1970)  is also reliable, available,  cost-effective  and
non-destructive (though substantial decay times  may be required before
the sample can  be submitted  to other analyses).  It equals or
surpasses x-ray emission  in  sensitivity for  many elements  and allows
the quantification  of a number of  rare-earth elements not  detectable
by other methods.   It is  more  labor intensive than  x-ray analysis and
therefore more  costly.  The  aerosol deposit  need not be  confined to
the substrate surface since  high energy gamma rays  experience no
absorption in the filter  material.  Suspended particulate  matter on
glass fiber  substrates  have  been analyzed by neutron activation
(Lambert and Wilshire,  1979) but due to the  high and variable blank
concentrations  of certain elanents  in these  filters their  use is not
recommended  (Gilbert and  Fornes, 1980).  Several fibrous filters
appropriate  for HIVOL sampling (Dams et al.,  1972)  have  been evaluated
and found satisfactory.   Most  spectral  interferences can be eliminated
by optimizing irradiation time, decay time and  counting  time.
Camp et al.  (1974,  1975,  1978)  have verified the accuracy  and
precision of the method in interlaboratory comparisons.
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     Atomic Absorption (AAS), Atomic Emission, (AES) and Inductively
Coupled Plasma/Atomic Emission Spectroscopy (ICP/AES)  (Ranweiler and
Moyers, 1972, Olson et al., 1978, Lynch et al., 1980)  are destructive
methods, requiring sample dissolution, with the requisite sensitivity
for suspended particulate matter analysis.  The AAS and AES analyses
are single element methods while ICP/AES  is multi-element.  The method
is applicable to aerosol collected on fibrous as well  as membrane
filters, though glass fiber  substrates with large  and  variable blank
concentrations bias analytical results.   The particulate matter must
be totally dissolved with a minimum loss  of elements through
volatilization; more than one extraction  procedure may be required,
depending on the elements sought.  McQuaker et al.  (1979) and
Ranweiler and Moyers (1972) describe extraction procedures and their
successful applications  to standard reference materials.  The variable
dissolution  of particulate matter might be used to  identify the
compounds in which elements  occur through a series  of  sequential
extractions  (Tessier et  al., 1979); this  approach has  not been tried
for suspended particulate matter.  Intel-method comparison results  of
particulate matter samples are available  for only  a few elements  (Camp
et al., 1975, Walling et al., 1978, Barbaray et al., 1979); the
results of these intercomparisons are variable, with some elemental
concentrations being reported factors of  five and  six  lower than  the
values reported by the other participating laboratories.  A systematic
intecomparison with the  standard urban aerosol for  a variety of
extraction procedures is needed.
     Other elemental analysis methods, including spark source mass
spectrometry are available and their appropriateness for suspended
particulate matter analysis needs to be evaluated.

Carbon

     Though carbon is indeed an element,  its quantification is not
amenable to the aforementioned methods.   Because of its large
contribution to both source and ambient suspended  particulate matter,
its concentration in samples is  important.  Combustion in oxygen
followed by C02 measurements, or conversion of COj  to  CHA and
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measurement with  a  flame  ionization  detector,  can  provide  reproducible
and quantitative  total  carbon  values.   Different atmospheres and
combustion  temperatures can provide  an  operational separation  of
elemental and  organic carbon (Johnson and  Huntzicker,  1978).   Nuclear
(Macias  et  al.,  1978),  solvent extractions (Appel  et al.,  1976, 1979),
and light absorption methods have  been  devised.  Macias et al.  (1978)
report some intermethod comparison results, but more interlaboratory
work is  needed.   Carbon values for the  NBS  1648 are not reported and
accepted values need to be  obtained.
     An  important development  in the measurement and classification of
carbon for  receptor models  is  the  quantification of the radioactive
C1* content of suspended  particulate matter by low-level counting,
(Currie  et  al.,  1978).   Carbon 14  is a  unique  tracer for carbon from
recently living material; it is nearly  non-existent in emissions from
fossil fuel sources.
     Carbon analyses should be performed on non-carbon containing
substrates, though  there  are possibilities of  subtracting  the  filter
blanks (R.K. Stevens, USEPA, personal communication, 1980).
Ions
     A wide variety  of  ion  analysis methods  exist with adequate  lower
quantifiable  concentrations.   All  are  destructive,  requiring
dissolution of  a  portion  of the  sample.  For receptor model studies,
the multi-element capabilities of  ion  chromatography  (Small,  1975) and
automated colorimetry (Technicon,  1972) have resulted in the  greatest
volume of suspended  particulate  matter  ion analyses being performed by
one of the two methods.   Practically all collection substrates are
amenable to these  analyses  though  sulfate and nitrate biases
(Coutant, 1977, Meserole  et al., 1979,  Spicer et al., 1978) have been
observed due  to adsorption  of  sulfur and nitrogen oxide containing
gases by the  filter medium  during  sampling;  the HIVOL glass fiber
filter material experiences this artifact formation.  Intermethod
comparisons for ion chromatography (Butler et al.,  1978) and  automated
colorimetry (Mueller et al., 1980) show them to be  accurate and
precise analytical methods  for a number of ions.

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Organic Compounds

     The number of organic compounds in suspended particulate matter
is high; it will probably be impractical to quantify  them all.  Those
species important to receptor modeling will be those which are unique
to certain source types and retain their chemical character between
source and receptor.  These compounds have not yet been identified,
but a number of methods are under development for that purpose. They
are all destructive and their sensitivities, accuracy and precision
are unknown at the current state-of-the-art.  Benzene extraction of
glass-fiber filters followed by weighing of the residue has been
widely used in the past to quantify the organic content of HIVOL
samples, but since Grosjean (1975) showed that this solvent does not
dissolve all organic materials, its use has decreased.  Appel et al.
(1979) propose a dual extraction on different sample sections with
cyclohexane and a benzene methanol-chloroform combination; they assert
that these extractions differentiate between organic material of
primary and secondary origins.  Daisey et al. (1979) have used ambient
polynuclear aromatic hydrocarbon concentrations in receptor models.
Cronn et al. (1977) have used high resolution mass spectrometry
(Schuetzle et al., 1973) to identify many organic compounds in ambient
aerosols.  Standardized procedures, the definition of lower
quantifiable limits, precision, accuracy and interlaboratory
comparisons are lacking for the organic compound analysis methods.

Inorganic Compounds

     X-ray diffraction analysis has been applied to suspended
particulate matter samples (Davis and Cho, 1977) and  can identify  the
types of minerals present (Davis et al., 1979).  This identification
is useful in distinguishing the sources of fugitive emissions.
Minerals can be identified very specifically by x-ray diffraction,
even to the extent of measuring crystallographic parameters and
subspecies composition (such as "iron rich chlorite", etc.).  Other
inorganic compound analysis methods, such as ESCA, Auger Electron
Spectroscopy,  SIMS, Laser Raman, and IR absorption have
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received  limited  study  for  aerosol  analysis  and  could develop  into
useful  techniques.   Standardized  procedures,  lower  quantifiable
1 units, precision, accuracy and interlaboratory  comparisons are
lacking.

Optical and Physical Properties

     Microscopy,  as  noted earlier,  can measure many properties of the
aerosol by examining a  number  of  the  individual  suspended  particles
which it  comprises.   Optical microscopy  (McCrone and Delly, 1973,
McCrone et al.,  1978) is best  suited  to  the  examination  of particles
in  the  coarse mode  ( >2 ym  optical  diameter).  Electron  microscopy
(Lee et al.,  1979)  can  examine fine as well  as coarse particles  and
can be  automated  to  reduce  subjectivity  and  analysis costs.  Electron
and optical microscopy standardized procedures for  preparing samples,
sizing  particles, assigning densities, and measuring particle
properties have  not  been  developed; Crutcher (1979) has  proposed
procedures for optical  microscopy which  merit evaluation and
development.  Crutcher  and  Nishimura  (1978)  have also identified the
sources of experimental error  in  microscopic  analysis results  as
sample  population statistics,  mensuration methods and human factors.
They propose ways to quantify  these uncertainties and propagate  them
through the final results.
     Bradway and Record (1976) and  Crutcher  (1978)  have  performed
interlaboratory  comparisons of optical microcopical  analysis;  the
results cast doubt on the accuracy  and precision of  the  method,  but
considering the  lack of standardization  among participating
laboratories, these  findings are  not  surprising. These
interlaboratory  tests should be undertaken again after a standard
method is developed.
     Development areas  for  analytical methods applied to receptor
models should include the following:
          Critically review all aerosol analysis methods for their
          practicality  to  receptor modeling.  Determine the extent to
          which they meet  the necessary and desirable criteria.
          Identify potentially useful methods for  development.
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•    Develop standard reference materials representing different
     ambient and source particulate matter matrices.
     Characterize them in terms of relevant aerosol properties.

•    Standardize and conduct intermethod comparison tests of
     organic compound, inorganic compound, carbon,  and
     microscopical analysis  methods.
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                    CHAPTER 4:  RECEPTOR MODEL NEEDS

     Receptor modeling is a new and growing  field.  Unlike many fields
of science which start with a  few key researchers and branch out to
include new ones, receptor modeling's roots  are spread over an array
of disciplines and organizations.  Nuclear spectroscopists, chemical
engineers, industrial plant managers, regulatory agency personnel —
each has approached the relationship of source to receptor by aerosol
properties from his own point of view.  It is not surprising that a
coherent theory of receptor modeling and standardized methodologies
have yet to emerge.
     Each of the study areas summarized in the previous sections has
ended with a list of research  recommendations.  These lists are not
exhaustive, but they do contain those issues which the most
experienced scientists in the  field of receptor modeling believe are
in need of resolution for the  specific study area.  For receptor
modeling in general, five major development  areas exist:
     The primary need of receptor modeling today is a general theory
within which to operate.  Each specific receptor model application
should be derivable from this  framework.  If not, either the
application of the theory is incorrect, or the theory must be
changed.  Throgmorton and Axetell (1978) have compiled the
applications.  Henry (1977) and Watson (1979) have outlined the theory
including some of those applications.  The theory must be expanded to
include them all.
     Next, the applications have to be validated and placed into
standardized forms.  Validation should consist of two steps.  First,
simulated data sets of aerosol properties should be generated from
pre-selected source contributions as did Watson (1979) in his
simulation studies of the chemical mass balance method.  These data
should be perturbed with the types of uncertainties expected under
field conditions.  The types of sources and  their contributions
predicted by the receptor model application  should be compared with
the known source model values  and the extent of perturbation tolerable
should be assessed.  This will define the precision required of the
input data for the application in question.

                                   47

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      The  next  step  in validation requires  a  real  data  set with  as many
 properties  of  source and  receptor as  can be  obtained in  an  area with
 well-known  sources.  All  receptor models should be  applied  and  the
 results should be examined for a self-consistent  picture of  source
 contributions.
      This consistency should  include  the following  elements:
      1.   Concentrations  of all measured species  should  be  predicted
          to within a specified tolerance.
      2.   Concentrations  of chemical  species which  originate in a
          source type should  be highly correlated.
      3.   Spatial source  contribution fluctuations  should be  extreme
          for  point source and smooth for homogeneously  distributed.
      4.   For  samples taken during periods of constant wind  direction
          source contributions should be higher when a source is
          upwind of a receptor than when it  is downwind.
      5.   Source contributions to different  particle size ranges
          should be consistent with the measured  size distribution of
          the  souce emissions.
 If  a  consistent picture does  not emerge, the inconsistent applications
 must  be reformulated or discarded.  A systematic  elimination  of
 measurements from the data set should then be made  to find the  most
 cost-effective sampling and analysis  scheme  to provide valid
 information within  a specified confidence interval.
     The  third need is standardization.  The receptor model
 applications need to be written as standard  computer routines,  common
 data  structures that can  accommodate  uncertainties  of the observables
 need  to be created, and sampling and  analysis equipment  and  procedures
 must  produce equivalent results.  Field study "scenarios" for typical
 situations should be proposed.
     The  fourth need is for aerosol property measurement methods.
 Cost-effective aerosol composition size and variability measurements
 at both source and receptor are required for receptor models  to work.
Their predictions will be only as good as the information presented to
 them.  Though  several sampling and analytical techniques have reached
 a high degree  of sophistication, many gaps remained to be filled.  The

                                   48

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most important of  these  is  adequate  source sampling and
characterization,  the  lack  of which  appears  to be  the major  factor  in
limiting  advances  in the state-of-the-art of receptor modeling.  A
systematic  development of source  and ambient sampling and analytical
techniques  must  be defined,  priorities must  be assigned, and the work
must be carried  out.
     The  fifth and final need is  for documentation and education.   The
validation  and standardization  will  go for naught  if the practice of
receptor modeling  cannot be  established  at the state implementation
plan level  where it is most  sorely needed.   Major  reviews of model
applications, analytical methods, source characterization and  field
study design need  to be  prepared  and communicated  to those most likely
to make use of them.
     The mechanisms for  carrying  out the research  required are not
clear.  These mechanisms must be  cost-effective while involving as
wide an array of talent  as  possible.  It is  evident from the meeting
of experts  which generated  this report that  cross-disciplinary and
inter-institutional approaches  to meeting these needs must be  fomented.
     Enough receptor modeling by  other names is going on today that,
with the proper coordination and  leadership,  the cost of pursuing
these developments should not be  prohibitive.  Most of the development
should take place  within the context of ongoing projects.  EPA,
however, needs to  provide the direction  and  small  amounts of financing
to get the  extra mileage out of these projects.
     An EPA task force on receptor models needs to be established.  It
should incorporate representatives of the suspended particulate matter
standards making and enforcing, ambient monitoring, and source
characterization entities.   This  task force  should keep itself
informed of the  status of non-attainment areas and the studies being
undertaken  to formulate  implementation plans; its members should also
keep abreast of regional  air quality  studies  funded by EPA and
industry.  The task force should  define the  needs  stated in  this
                                   49

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report in operational terms which can be economically incorporated
into the ongoing studies, arrange additional financing to cover the
additional scope of work, monitor the progress toward meeting the
needs, and document the results.  This has been done in the past for
source models.  Receptor models have shown enough potential that they
deserve similar treatment.
                                   50

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                                TECHNICAL REPORT DATA
                         (Please read Instructions on the reverse before completing!
 REPORT NO.
 EPA-600/2-81-039
2.
                           3. RECIPIENT'S ACCESSION- NO.
4. TITLE AND SUBTITLE
Receptor Models Relating Ambient Suspended
 Particulate Matter to Sources
                           5. REPORT DATE
                           March 1981
                           6. PERFORMING ORGANIZATION CODE
 AUTHORIS)
John G. Watson
                           8. PERFORMING ORGANIZATION REPORT NO
 . PERFORMING ORGANIZATION NAME AND ADDRESS
Environmental Research and Technology, Inc.
696 Virginia Road
Concord, Massachusetts 01742
                           10. PROGRAM ELEMENT NO,
                            CAAN1D
                           11. CONTRACT/GRANT NO.

                            68-02-2542,  Task 8
12. SPONSORING AGENCY NAME AND ADDRESS
 EPA, Office of Research and Development
 Industrial Environmental Research Laboratory
 Research Triangle Park, NC  27711
                                                      13. TYPE OF REPORT AND PERIOD COVERED
                                                       Task Final;  11/79-9/80
                           14. SPONSORING AGENCY CODE
                             EPA/600/13
15. SUPPLEMENTARY NOTES jERL-RTP project officer is John O. Milliken,  Mail Drop 61,  919/
541-4125.
  . ABSTRACT
              report describes the use of receptor models to determine the source
contributions to ambient particulate matter loadings at sampling sites, based on
common properties between sources and receptors. (This is in contrast to using
source models which start with emission rates and meteorological measurements to
predict ambient concentrations.) Three generic receptor models have been identified:
chemical mass balance, multivariate ,  and microscopial identification. Each has
certain requirements for input data to provide a specific output. An approach that
combined receptor and source models, source/receptor model hybridization, has
also been proposed, but it needs further study. The input to receptor models is ob-
tained from ambient sampling, source  sampling, and sample analysis. The design of
the experiment is  important in obtaining the most information for the least cost.
Sampling schedule, sample duration, and particle sizing are part of  the ambient sam-
pling design. Analysis for elements, ions, carbon, and organic and inorganic com-
pounds is included in the sample analysis design. Which sources to sample and how
:o sample them are part of the source  sampling design.
                             KEY WORDS AND DOCUMENT ANALYSIS
                DESCRIPTORS
                                          b.lDENTIFIERS/OPEN ENDED TERMS
                                                                  c. COSATl Field/Group
Pollution            Analyzing
Mathematical Models
Receivers           Sampling
Particle Density
Dust
Aerosols
               Pollution Control
               Stationary Sources
               Receptor Models
               Particulate
13 B
12A
17B
14G
11G
07D
14B
 3. DISTRIBUTION STATEMENT
 Release to Public
               19. SECURITY CLASS (i
               Unclassified
                                                                         89
               20. SECURITY CLASS (This page)
                Unclassified
                                                                  22. PRICE
EPA Form 2220-1 (9-73)
                                          89

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