NVIRONMEIMTAL.IST8, INC.


                      AND ITS IMPACT ON

                   Guy  B.  Oldaker,  Ph.D.
                        MAY 1980
 P.O. Box 12291. Resseanch "Triangle Park, North Carolina 27~7O9
                    Dhone SIS-TEH-355O


              AND ITS  IMPACT ON

                  May 1980
                Prepared by:

            Guy B. Oldaker, Ph.D.

       Entropy Environmentalists, Inc,
           Research Triangle Park
              . North Carolina
                Prepared for:

  Division of Stationary Source Enforcement
United States Environmental Protection Agency

        Project Officer:  Kirk Foster
        Contract Number:  68-01-4148
            Task Number:  69

This document has not been reviewed by the U. S. EPA, and is
not intended to reflect official policy or standards.  The
opinions, suggestions, and conclusions expressed herein are
those of the author, and do not necessarily represent those
of the United States Environmental Protection Agency.

                    TABLE OF CONTENTS


Introduction  	  	    1
  The Effects of Condensible Particulate
  on the Development of NSPS Particulate
  Sampling Methodology 	    5
Physicochemical Effects on the Condensible
  Particulate Loading  	   25

            Physical Changes  	   26
            Chemical Reactions 	   46
            Summary	64
Assumptions and Limitations of Reference
  Method 5 Sampling	66
Recommendations   	   73
                     IIMVIRONMEIMTAUBTB. INC.

     For sources subject to New  Source  Performance  Standards

 (NSPS), compliance  with  particulate standards is most often

determined  through  the use of EPA  Reference  Method 5.   Put

simply,  this method  entails  sampling  a metered  volume of

effluent  with  a   heated  probe  and   then   collecting   the

particulate  matter  on a  heated  filter.   The  particulate

catch  is currently  interpreted  by  the EPA as  being   the

material caught in  the probe and on the  filter.

     The  use  of  Reference   Method  5   produces  acceptable

particulate emissions  data  for  most NSPS source categories.

However, when  the  method  is  extended  to non-NSPS  or novel

source categories,  the particulate  emissions data  sometimes

suffer from imprecision and positive biases.  These problems

with the Reference  Method  5  data  arise from the  fact  that

some  particulate-forming  reactions occur  in  the  effluent

stream: before, during, and even after  sampling.

     The  positive  bias,  or  extra  particulate,  which  is

measured is  termed  "condensible  particulate," or sometimes,

"pseudoparticulate."  As  the  term  "condensible  particulate"

implies, the extra  particulate  originates  from condensation

processes.    Most  condensible  particulates   are  formed  by

gases  condensing   in  the  effluent,  and  the  particulate


control  equipment  has  no  effect  upon  gaseous  substances.

Since the  focus  of  particulate testing  for  many compliance

determinations  is  on  the  performance  of   the  particulats

control  equipment,  if  gaseous substances  form  condensible

particulate  in  the  effluent  downstream   of  the  control

equipment but upstream of  the  sampling probe,  the resultant

particulate measurements will  provide a  poor  indication of

control  equipment  performance.   Indeed, such  measurements

would be biased against the source.

     The  imprecision  observed  in  Reference  Method  5  data

results  from  the  fact  that   the  formation of  condensible

particulate  is  usually strongly dependent  on  temperature.

Thus, the  appearance  of condensible  particulate  depends on

the temperatures of the effluent and of  the  probe and filter

of the Reference Method 5 sampling system.   Depending on the

chemical properties  of  the condensible  particulate,  it  is

sometimes possible for a difference  in temperature  of  a few

degrees to determine whether or  not condensible particulate

is formed.

     The  subject  of condensible  particulate  is  important,

because  it  bears  directly  on  determinations  of  source

compliance.   In  fact,   condensible  particulate,  because  it

contributes   a   positive   bias   to   Reference   Method   5

measurements,  can  be  the  determinant  of  compliance  or

non-compliance.    In  addition,  the   issue  of  condensible

                   IIMVIRONMEIMTAUBTS, INC.

participate  raises  questions  regarding:  (1)   the  use   of

Reference Method  5 at sources  which  are  not  subject to  NSPS;

(2)  the  precision required  for  controlling  the  temperature

of  filtration  during Reference  Method 5  sampling;   (3)  the

interactions which occur between  particulate and  condensible

particulate  (is it always  possible to  distinguish the two?);

(4)  the  relation between  opacity measurements  obtained  by

transmissometry and  by  visual  methods (Reference  Method  9);

and  (5)  the  interpretation of  "particulate"  itself.

     This   paper   addresses   the   subject  of   condensible

particulate  from  several  directions.  The  first  section  of

the  paper views condensible  particulate  from the  historical

perspective.   The  impact  of   the   condensible   particulate

problem  was  recognized  when   the   New   Source   Performance

Standards   and   their  associated   testing   methods   first

appeared in  the Federal Register  in  1971.  Since  that  time,

numerous references  to the  condensibles  problem have been

made in  the  Federal  Register and also in EPA  documents  for

NSPS review  and development.

     The  section  which  follows  the  historical  discusses

those  physicochemical  factors  which determine  the  identity

and  loading  of  condensible  particulate.   Throughout  the

section,  general   principles  are stressed,  which  can   be

applied  to  interpreting  or   predicting  the   effects   of

condensibles   on    the   Reference   Method     particulate

measurements.  In a sense, this section can stand  alone,  and


is intended to serve as a  brief  guide  for understanding the

formation of condensible particulate.

     The following  section,  "Assumptions  and Limitations of

Reference   Method   5   Sampling,"   views   the   impact   of

condensible  particulate on  the  interpretation  of  current

Reference  Method   results.    This   section   leads  to  the

"Recommendations" section, which addresses solutions to the

problems created by condensible  particulate.

     The use and interpretation  of particulate data obtained

from  including  the   back-half   catch   (i.e.,  particulate

measured  in the  water filled  impingers  which  follow  the

heated  filter  in the  Reference  Method  5 train)  have been

controversial  issues,  because  the  impact  of  condensible

particulate appears to be greater in the  back-half.  Limited

data  exist  which correlate  back-half  particulate  data  to

front-half  (probe and filter)  data, mostly because back-half

data  are  not required  for  NSPS  sources.  In  addition,  few

state and local  agencies require the  inclusion of back-half

particulate results.   Because  the regulatory  status  of the

back-half particulate catch is variable,  and also because of

the limited amount of quality  data  from the  back-half, this

paper   will   not  specifically   address   the   effects   of

condensible    particulate     on    back-half    particulate



          The Effects of Condensible Particulate

                   on the Development of

           NSPS Particulate Sampling Methodology
     The subject of  condensible particulate  and  its effect

on particulate emissions measurements  is best approached by

reviewing   the   literature   pertaining   to  New   Source

Performance Standards (NSPS).  The following  discussion is a

chronological  review of  the  pertinent  material  from  the

Federal Register.  The reader  should note that the focus of

the  review  is  on  NSPS  sources  rather  than on  existing

sources subject to State  Implementation Plans (SIPs).  This

distinction must be made, since  the  statements which appear

in the  Federal  Register apply  to  NSPS  sources and  are not

always  extendable  to  SIP  sources,   which  represent  an

extremely varied population in terms  of process  operation,

control systems, and emissions.

     Several reoccurring themes, with  respect  to condensible

particulates, appear  in a  review, of the NSPS developments.

Among these are: the  importance  of defining  the particulate

state,  the  potential  for   the  formation of  particulate  by

physicochemical  mechanisms,  and  the   use   of  measurement

methodology for evaluating  control system performance.

     Sources  subject to  New  Source  Performance  Standards

(NSPS)  are   required  to  measure  emissions   of  particulate

matter  in  order  to  determine  compliance   with  emission


standards.   The methodology  used  in  measuring  particulate

emissions is stated within 40 CFR  60,  Appendix  B.   Currently

applicable   methods   are  Reference   Methods   5  and   17.

Illustrations   of  the   sampling   equipment   used  in   the

reference methods are presented  below.

     Reference  Method 5  requires that  a sample  be  withdrawn

from  the  effluent stream  via  a heated  sampling probe,  and

that  the  sample  stream  be  subsequently  filtered   at   an

elevated temperature.  The filter  is  located  outside  of  the

stack,  and   its  temperature   is controlled  by  locating   it

within a thermostated filter oven.

     As Reference Method 5 was  originally proposed  in  1971,

the impingers  following  the  filter were  considered part  of

the measurement system.   Material  which  passed through  the

filter  was   collected  in  the  impingers.   The  particulate

catch, using  the originally  proposed  methodology,  consisted

of the sum of the filter and  probe catches (front-half)  and

the  impingers1   catch  (back-half) .  At  this   time, "parti-

culate" was  defined  in  terms of the   state of  the material

which was collected, rather than in terms of the  measurement

methodology  used.   Thus,  particulate  was  defined  as "any

material except  uncombined water,  which exists  in a  finely

divided form as  a liquid or solid  at standard conditions."

     Including  the  back-half catch and  employing standard

conditions  in   the  definition  of  particulate   provide   a


                                  TEMPERATURE SENSOR

                                                                    IMPiNGER TRAIN OPTIONAL.MAY BE REPLACED
                                                                         BY AN EQUIVALENT CONDENSER
                                                      HEATED AREA

                          )   BY-PASS VALVE
                                                   DRY GAS METER



                                                                    IMPINGER TRAIN OPTIONAL. MAY BE REPLACED
                                                                          BY AM EQUIVALENT CONDENSER
                        ORIFICE MANOMETER
                                                           DRY GAS METER

reference  point  for particulate  measurements, and  make  it

possible to relate  particulate  measurements  to the state  of

the   particulate   near   ambient   conditions.    Thus,    in

principle,  it would  be  possible  to  relate   the  measured

particulate to the  nature  and  quantity of particulate which

would  exist  after  dilution  and  cooling of   the  effluent

stream to ambient temperature and pressure.

     The inclusion  of the impingers'  or back-half catch  into

the   determination   of   particulate  measurements   was  a

controversial  point.   Some  critics  maintained  that  the

back-half  catch  was  biased because  of  chemical  reactions

                                            r  C T Q Q
which  could  occur  within  the  impingers. '  ' ' '   Their

arguments  focused  on the  formation  of "pseudoparticulate,"

specifically,  particulate  sulfate  (SO.   )   formed  by  the

oxidation of dissolved gaseous  sulfur dioxide  (S02(aq)).


                    S02(aq)—>  S042~(aq)

For  this  case,  when  the  contents  of  the   impingers  are

evaporated, the sulfate will remain as a weighable residue.

     Put simply, their argument was  that  a  substance which

was  normally  a  gas  at   standard   conditions  was  being

converted  by  the test  method  to  a  substance which  would

ultimately be measured as  a solid.   Thus,  this particulate

was not  included within  the definition of 1971; it  was not

true particulate,  it  was  "pseudoparticulate.n It was  also

argued that other reactions could  occur  within the proposed

sampling  train  (including  the   impingers)  which  have  no

counterparts in the effluent stream.  Measuring the products

of these reactions gives results that are non-representative

of  the  source's  actual   emissions;   they  are,  instead,

artifacts created by the test method.

     The "pseudoparticulate" argument  led  ultimately to the

exclusion  of  the back-half catch  from  Reference  Method  5

measurements.    Introductory   statements   accompanied   the

promulgated method   ,  which addressed  the  omission  of the

back-half catch:

            Particulate matter performance testing
          procedures   have   been    revised    to
          eliminate the  requirement  for  impingers
          in the  sampling  train.  Compliance  will
          be based only  on the  material collected
          in   the   dry  filter   and   the   probe
          preceding  the  filter.   Emission  limits
          have  been   adjusted  as  appropriate  to
          reflect the  change  in  the test methods.
          The adjusted standards  require the  same
          degree  of   particulate  control  as  the
          originally proposed standards.

     Thus,   the  change  in the  test  methodology  and  the

revision   of   the   emission   standards   focused  on   the

evaluation/regulation of control equipment performance.  EPA

concluded its introductory remarks by  citing  Section  III of

the Clean  Air  Act,  which  requires  that  the  standards  of

performance "reflect the degree of  emission  reduction which

(taking into account  the cost  of achieving  such  reduction)

the   Administrator    determines    has   been    adequately



     In  1972  the  EPA  published   supplementary  statements

which  pertained  to the  final  promulgation of  the  sampling

methodology,  and  which  detailed   the  background  for  the

omission  of  the  back-half  particulate  catch.   The  EPA

responded  to suggestions that  particulate standards should

"be based  either  on  the 'front-half (probe  and  filter)  of

the  EPA  sampling  train or  on  the  American  Society  of

Mechanical Engineers'  test procedure.  Both of these methods

measure only those materials  that  are solids  or  liquids at

250 F  and  greater temperatures."     (One  of  the differences

between the  two methods  lies in the location  of the filter:

the  EPA method  employs  an  out-of-stack  filter;   the  ASME

method  uses  an  in-stack filter.)  The   EPA  opined  that,

"particulate standards based either on the front-half or the

full  EPA  sampling  train will  require  the  same degree  of

control  if  appropriate  limits  are applied."  They  stated

further  that   their   "analyses  show  that   the   material

collected in the  impingers of the sampling train is usually,

although not in  every  case,  a consistent fraction  of  the

total particulate loading." This statement was the apparent

basis  for  the  subsequent omission  of  the back-half  catch

from the sampling procedure  and the  concommitant  reduction

of  the some of  the   particulate   emission   standards  (see

Table I).   Thus,  the back-half  catch  was  apparently assumed

to contribute a consistent fraction of the total particulate


                            TABLE I

                     Proposed  and Promulgated
                      Particulate Standards
                         for NSPS Sources
                         Originally proposed
                        particulate standards
                            (full EPA train)
                 particulate standards
                 revised sample method
                    (front  half only)
Steam generators -
lbs/106 Btu heat input
Incinerators -
gr/scf at 12% C02
Cement Kilns -
Ibs/ton feed
Cement Coolers -
Ibs/ton feed
                         I IMVIROIMMENTAUSTS,IIMC.

catch, and  the standards  were  scaled down  accordingly.  An

obvious impetus for omitting the back-half was the resultant

simplification of sampling and analysis procedures.

     Table  I  shows  that  two  of the  four  source categories

were affected  by the omission  of the back-half  catch from

the  sampling  methodology.   The  values  of  the  affected

standards suggest that the back-half catch may contribute up

to 50% of  the mass of  particulate measured  at  fossil fuel

fired  steam  generators,  and  up  to  20%  of  the  measured

particulate mass at incinerators.   The standards for cement

kilns  and  cement  coolers   indicate  that   the  material

condensed  in   the  impingers  does  not make  a  significant

contribution to the total particulate catch.

     It is noteworthy that the  following  statement was also

included  within  the  EPA opinion:   "There  has  been  only

limited  sampling with  the  full  EPA train  such that  the

occasional  anomalies  cannot  be  explained   fully  at  this


     The change  in  the   particulate  measurement  methodology

was reflected  in the  revised  definition of "particulate"  in

40 CFR 60.2:
            "Particulate matter" means  any finely
          divided solid or  liquid  material,  other
          than  uncombined  water,  as measured  by
          method 5 of the appendix.

     This definition does  not  include  an explicit statement

regarding   the   important   physical   parameters   of   the

particulate, but instead defines particulate in terms of the

measurement methodology.  The essence of this change is that

the  methodology is  no  longer  directed  toward  measuring  a

sample which is directly  representative  of source emissions

on  a defined  absolute  basis.    Instead,  the  focus  is  on

evaluating  source  operation  and control  system performance.

Again,  this change  is  in  keeping  with  the  provisions  of

Section  III  of the  Clean  Air Act.  Thus,  the fate  of the

emitted  pollutants  is  not  the  primary  issue.  Of  greater

importance  is  the degree  to  which  the  affected  facilities

control their pollutant emissions, relative to  the magnitude

of emissions which would result if no control was present.

     Critics  , nevertheless,  maintained  that  the  revised

Method 5  sampling  train was still subject  to  biases caused

by the  condensation of gases  within the  probe and  on the

filter.   It was argued  that  condensible  particulate was not

restricted  to  the  back-half.    Emphasis  was  placed  on

condensation  processes   involving   sulfur  oxides:   sulfur

dioxide and sulfur trioxide.  Data were presented which were

interpreted as  indicating  the extent of  these condensation

effects.   (See Table   II.)   The  data  were  obtained  from

simultaneous sampling  of  the  effluent  from  a fossil-fuel

fired steam generator  with  a  Reference  Method  5  sampling

train and a train  incorporating  an  in-stack filter.   In


                             TABLE II

                Weights of  "Particulate" Matter
             Measured  During Simultaneous Sampling -
              EPA vs.  In-Stack Sampling Apparatus

                        EPA train                Alundum thimble
                      "front half,"            filter inside stack,
Sample No.                mg                          mg
                         INVIROIMMEIMTAUSTB, INC.

almost  all  cases, the  Reference Method  5 train  yielded  a

greater amount of measured particulate.

     In  October   1975  the  EPA   published  revisions  to  the

performance  test  procedures  for  fossil-fuel   fired   steam

generators. " These revisions addressed the biases caused by

condensation  reactions involving  sulfur  oxides.   With  the

filter  temperature  maintained  at   120  C,  gaseous  sulfur

oxides  were  condensing  within the probe and  on  the filter.
The  EPA stated  that,   "the   inclusion  of  this  condensible

matter  would  not  be  indicative  of  the  control  system

performance."   In  addition,   studies  were   cited    which
indicated that sampling  at 120  C produced  variable biases.
The  magnitudes   of  the   biases  caused  by  the  increased

particulate loading  from  the condensing  sulfur  oxides were
recognized  to  be  unpredictable because  of  their  apparent
dependence  on  "total   sulfur  oxide   concentration,  boiler

design  and  operation,  and  fuel  additives." The  EPA  stated

that  the  particulate   mass   contributed  by  the  condensed

sulfur  oxides was not  a serious problem,  since  studies  had

shown the contribution  to range from 0.001 to  0.008  grains
per standard cubic  foot,  which  is  relatively insignificant

when compared  to the  then current  standard  of  0.07  grains

per standard  cubic foot.   Nevertheless,  a higher  sampling
temperature of 160 C was accepted for testing at fossil-fuel

fired steam generators, "to insure that an unusual case will
not occur where a high  concentration  of  condensible matter,

not  controllable with  an ESP  felectrostatic precipitator]

would prevent attainment of the particulate standard."

     The  EPA  also discussed  the  temperature  dependence of

particulate  matter  within  the   comments  accompanying  the

revisions.  The  use of sampling methodology incorporating an

out of  stack  filter  — as opposed to  an  in-stack filter —

was  supported  because  of  the   necessity  to  control  and

measure   the   temperature   during   the   determination   of

particulate.  It was  stated  that "[temperature  control] is

needed  to define particulate matter on a common basis, since

it  is   a  function of  temperature and is  not  an  absolute

quantity."  Continuing along these lines, the EPA said:

            If   temperature   is   not  controlled,
          and/or if the effect of temperature upon
          particulate  formation   is  unknown,  the
          effect on an emission control limitation
          for particulate  matter  may  be  variable
          and unpredictable.

     This statement  contains the crux of  the  difficulties

which stem  from  condensible  particulate:  specifically,  that

the effects of  temperature upon  particulate  formation  must

be known before  one can  understand  the relationship between

the sampling methodology and what is actually measured.

     Also in  their comments  of  October 1975, the  EPA cited

the results of tests which indicated that S0_ does not react

to  a  significant degree  to  yield  condensed  particulate

within  the  front  half  of  the  Method  5  train.   The  EPA


emphasized again  that  Reference Method  5 was  intended  for

evaluating  the  control   system performance  of  stationary

sources. They  concluded  with  a  statement  pointing  out that

the   application   of  sampling  methodology   may   require

flexibility,  depending  on what  is  to  be measured.   As  an

example, they cited the  condensation  of sulfur  trioxide and

water to form sulfuric acid mist.  If control performance is

to be  evaluated,  particulate would  be  best  measured  at  a

temperature  of  160 C.   This  temperature would  prevent  the

condensation  of  the   SO-,,  the product  of  which  is  not

controlled.   If  the  "applicable  standards  are  based  upon

emission reduction to  achieve ambient air quality standards

rather  than   on   control  technology,   a   lower  sampling

temperature would  be  appropriate."   Put  simply,  what  is  to

be measured  determines  how  the measurement  will  be  made.

Implicit  within   this   argument   is  the  fact   that  the

applicability  of  Reference   Method   5   is  not  necessarily


     A  recent  addition  to  EPA  particulate  measurements

methodology  is  "Reference  Method  17:   Determination  of

Particulate  Emissions  from  Stationary  Sources   (In-Stack

Filtration Method)."14'15 The  difference between  Method  5

and  Method  17   involves  the   location  of   the   filter.

Reference Method 17 employs an  in-stack  filter and  is thus

similar to the ASME method.    It was this method  which  was

used  in the  arguments  discussed earlier,  which  showed that


the Reference Method 5 train, even  without  the inclusion of

the back-half, was  subject  to condensation  processes.   The

introduction to the method  bears on the problems  caused by

condensible material:

            Particulate  material  is  not  an  ab-
          solute quantity; rather it is a function
          of temperature and pressure.  Therefore,
          to  prevent  variability   in  particulate
          matter, emission regulations, and/or as-
          sociated  test  methods,  the  temperature
          and pressure at which particulate matter
          is to be measured  must be carefully de-
          fined.  Of the two variables (i.e., tem-
          perature and pressure),  temperature has
          the  greater  effect  upon  the  amount of
          particulate matter in  an effluent  gas
          stream; in most stationary  source  cate-
          gories, the  effect of  pressure  appears
          to be negligible.

     This paragraph is then  followed  by  the  criterion which

underlies the applicability of the method:

            Therefore,  where  particulate  matter
          concentrations (over the normal range of
          temperature associated  with  a  specified
          source category)  are  known to  be  inde-
          pendent of temperature,  it  is  desirable
          to eliminate the glass probe and heating
          systems,  and  sample  at  stack  tempera-

     Where particulate matter concentrations are independent

of temperature, Reference Method 5 and  Reference  Method 17

should give identical results.   Reference Method 17 would be

preferred   in   those   situations,   because   the   sampling

procedure is easier and requires less equipment.

     Again  the  issue  of  the  temperature  dependence  of

particulate matter  concentration is  stated,  and  again  the

                    INVIRONMEIMTAUBTS, INC.

focus is on the  filtration  temperature.   The application of

this  methodology is  important,  because  it shows  that the

problem of condensible material  is  not general, i.e.,  then-

are sources and situations where all filtration methods will

give  equivalent   results,   and   there   are   sources  and

situations   where   different   filtration   methods   will

significantly affect the results.

     More recently, the issue of condensible particulate was

raised during the review of performance standards  (NSPS) for

                      14  15
petroleum  refineries.   '    Performance  tests  of  fluidized

catalytic cracking (FCC)  units appeared  to  be  biased by the

condensation of sulfuric acid mist  in  the Reference Method 5

probe  and  filter.   Table  III  shows  the  results   of  a

performance test  cited within  the  background information.

It is significant that approximately 50% of the catch can be

ascribed to sulfur oxides,  e.g., sulfuric  acid (H-SO.) and
sulfate  (SO.  ).    (These   compounds   are  also  primarily

responsible for  the  condensibles1   interference  in tests at

fossil-fuel  fired steam generators.)  Currently,  neither  a

higher Reference Method 5 filter temperature nor an in-stack

filtration method  (Reference Method  17)  are  applicable to

fluidized  catalytic   cracking  units.    Thus,   the  bias

associated  with   condensible   sulfates   is   included  in

particulate sampling  results at petroleum refineries.

                        TABLE  III

                Results for Evaluation of
             Condensible Particulate Loading
                at FCC Unit Regenerators
ASME instack filter
NaOH titration of
  Method 5 catch for
89% less particulate matter
    than Method 5
50% H2S04
Thermal analysis of
  Method 5 catch
60% weight loss
Sulfate analysis of
  Method 5 catch
64% sulfate
X-ray spectrograph of
  Method 5 catch
          in probe wash

     In  summary,   when  the  literature  pertaining  to   NSPS

source sampling  is reviewed  with  regard to  the subject  of

interferences  from condensible particulate  matter,  several

ideas  and   concepts   are   repeatedly  emphasized.    These

include:  (1) the strong dependence  of the particulate  catch

on the  filtration  temperature,  (2)  the variability  of  the

particulate catch as a result  of  the condensation of sulfur

oxides, (3) the variability  of  the  particulate catch due  to

particulate forming reactions,  and  (4) the Reference Method

5  particulate  catch  as   an  indicator  of  control  system


        Standards £f Performance for New Stationary Sources.
A Compilation. November 1977.  EPA-340/1-77-015.
        Federal  Register,  Vol.  36,  p.   15704,  August  17,

      3 Ibid.
        "Response," J. Air  Pollut.  Control Assoc.,  22,  726

        W. S. Smith and R.  A. Estes, "Condensibles, Reactive
Compounds,  and  Effect of   Sampling  Train  Configuration,"
Source  Sampling  Reference Manual,  Part  III.   Supplemental
Training  Material  for  Technical  Workshop  on  Evaluating
Performance Tests.  U. S.  EPA, November 1977.

        D.  R.  Kendall,  "Recommendations  on  a  Preferred
Procedure  for  the Determination of Particulate  in  Gaseous
Emissions," J^ Air Pollut.  Control Assoc., 26, 871 (1976) .

        W.  C.  L.  Hemeon  and  A.  W.  Black,  "Stack  Dust
Sampling:  In-Stack Filter  or EPA  Train,"  J_._ Air  Pollut.
Control Assoc., 22, 516 (1972).
        L. J. Hillenbrand,  R. B.  Engdahl, and R. E. Barrett,
"Chemical  Composition of  Particulate  Air  Pollutants  from
Fossil-Fuel Combustion Sources,"  U. S.  EPA Report,  March 1,
        J.  Kowalczyk,  et al.,  "Source  Test  Procedure  for
Determination of  Particulate Emissions  from Veneer Driers,"
Publication of the Control  Agency Directors  -  8 Source Test
Committee,  Pacific  Northwest  International  Section,  Air
Pollution Control Association, September 1972.
        Federal  Register,   Vol.   36,  No.  247  -  Thursday,
December 23, 1971.

        Federal Register, Vol. 37,  No.  55 -  Tuesday,  March
21, 1972.

     12 Kendall.

        Federal Register,  Vol. 40,  No. 194 - Monday,  October
6, 1975.

     14 Federal  Register,  Vol.   41,   No.  187  -  Friday,
September 24, 1976.

     15 Federal  Register,  Vol.   43,  No.   37  -  Thursday,
February 23, 1978.

        "Determining  Dust Concentration  in a  Gas  Stream,"
Performance   Test   Code   27-1957.   American   Society  of
Mechanical Engineers, New York, New York.

        Federal Register, Vol. 44, No. 205  - Monday, October
22, 1979.
        K. Barrett  and  A.  Goldfarb,  "A  Review of Standards
of  Performance  for  New  Stationary  Sources  -  Petroleum
Refineries," March  1979, EPA-450/3-79-008.

                          ON THE
     The  loading  of   condensible   particulate  within  an

effluent stream depends  primarily on  the  chemical identity

of the condensible material.   The chemical  identity  of the

condensible material will  in  turn determine  the  importance

of chemical and physical  changes in affecting  the observed

loading of  condensible particulate.   When  viewed together,

chemical and physical  changes  may be termed physicochemical


     The  discussions  which  follow  briefly  describe  the

operation of physicochemical changes and attempt to show how

the  observed   loading   of   condensible  particulate  can  be

subsequently  rationalized.   These  discussions   are  quite

general, because the operation of physicochemical  changes is

not trivial.   Many of  the  arguments have  been simplified;

nevertheless,  the ideas presented  in  the  discussions  can be

applied to understanding and interpreting measurements which

suggest interferences from condensible particulate.


                     PHYSICAL CHANGES:

                  Definitions and Examples

     Physical  changes  are familiar  as "changes  of state."

For  example,  water  changing  from  liquid  to  gas  (evapora-

tion) , and dry ice changing from solid to gas  (sublimation),

are  examples  of physical  changes.   Those  physical changes

which  can  potentially  affect   the  amount  of  condensible

material  measured  are  condensation,  evaporation,  sublima-

tion, absorption, adsorption, and desorption.

     The  term  condensation  describes  the  process  during

which  material in  a gaseous  state  (or  phase)   changes   to

either the  liquid  or the solid phase. Familiar  examples  of

these condensation  processes  are the  formation  of  rain and

snow from water vapor.   Condensation processes increase the

particulate mass loading, and as a  result,  may contribute  a

positive bias to such measurement.

     Evaporation  and  sublimation   are  physical   processes

which  are  essentially  the  reverse  of  the  condensation

processes  described   above.    Evaporation   occurs  when   a

substance in  the  liquid  phase  changes to  a  gaseous phase,

and sublimation occurs  when  a substance in  the  solid phase

passes directly to  the gaseous  phase.  The  biases  of these

processes  operate  in  reverse  of  those  associated  with

condensation;   evaporation   and   sublimation    reduce   the

measured particulate mass loading.

                    IIWIRONMEIMTAUBTS, INC.

     Adsorption  and  absorption  are  special  condensation

processes  in  which  a  substance   in   the  gaseous  phase

associates  itself  with  the  surface of  a  solid  material

(adsorption), or  with  the  bulk (i.e., both  the  surface and

the  interior)  of a  liquid  or solid  material  (absorption) .

The  two  processes  are  easily  confused,  and  are  often

difficult to distinguish;  therefore, the two  processes are

often  jointly  termed   "sorption."   Because  sorption  is  a

condensation  process,  it  can contribute  a positive  bias.

However, in general, the  effects  of sorption  are  of lesser

magnitude than the other condensation processes.

     Gaseous sulfur dioxide dissolving in liquid water is an

example  of  absorption.    Sulfur   dioxide   can  adsorb  on

materials- used  for  sampling gases   (e.g.,  Tygon  tubing and

surgical tubing).   In  effect,  the  material  becomes coated

with   a  molecular  film   of  sulfur   dioxide.   (Adsorbed

substances   can   exist   in   layers  much    thicker   than

monomolecular films.)

     The exact  reverse  of   the  sorption  processes described

above  is  termed  desorption;  material  adsorbed  on  a  solid

surface or  absorbed in  liquids returns  to the  gas phase.

The biases contributed  by desorption  are  analogous to those

of evaporation and sublimation.

                    Physical Parameters

     At the  point  of  generation, the physical  state  of the

effluent  is  different  than it  is  at the  point of exhaust.

If all of the effluent components are  in  the gas phase, the

state  of  the  effluent   is   described   by  the  following

parameters:  (1) the  chemical  composition,  as  determined by

the   identities   and   associated   concentrations   of  all

components;  (2) the  pressure;  and   (3) the temperature.  If

non-gaseous components  (solids or liquids)  are  also present,

then the  ratio(s)  of the solid/liquid to gaseous phases must

be considered for each component.

     Of the  parameters above,  the  temperature  is  the most

important with respect  to  potential changes of state.  Many

of  the equations  which  are   used   in  describing  physical

changes have a logarithmic temperature  dependence.  This is

an  important  fact,  because it  predicts  that  phase  changes

will be very sensitive to  temperature changes.

     The  pressure of  the  effluent  is  ordinarily relatively

close to  ambient pressure, and as a result,  pressure changes

usually   have  a   lesser  effect   on  phase  changes  than

temperature  does.    The   effluent  composition   pressure

independence, however,  does not necessarily extend  to the

effluent  as defined   at  the  Reference   Method  5  filter.

Across the filter  there  often  exists  a  significant pressure


differential,   which   may  affect   the   concentrations  of

volatile compounds on the filter  and  the  rates of sorption,

desorption, condensation, and/or sublimation.  In general, a

decrease in pressure will push the equilibrium of gas-liquid

systems and gas-solid systems toward the vapor state.

     If  the  composition  of  the  effluent  is  known,  it  is

often  possible  to  predict  the  physical  states  of  the

components within  the  effluent.   For example, if  one knows

that the effluent  contains  sulfur trioxide  and  water vapor

in  certain  concentrations,  it is  possible to predict when

sulfuric   acid   mist   will   condense,   if    the   effluent

temperature  is   known.   The  ability  to   predict  the  acid

dewpoint  is  strictly  analogous  to determining  the  water

dewpoint; both  require  two  important pieces  of information:

(1) the  identity of  the substance  (e.g.,  sulfur  trioxide),

and  (2)  the  concentration  of  the  substance expressed  in

units of  mass  per unit volume  (e.g.,  g/L;   gr/ft  ,  mg/m ,

etc.) .

     For the majority of effluent  systems, most  of  the mass

can  be  chemically  identified.    Unfortunately,  the  small

amount of  mass  which  resists  complete characterization  is

often  that  same  mass   associated   with   the  condensible

particulate.   A complete  characterization  of some  source

effluents is often impossible,.

     The effluent stream  of  a  coal-fired  boiler  provides a

good  example  of  why  effluent   streams  resist  complete

characterization.  The identity of the effluent is dependent

on   the   particular   fuel   characteristics,   the   source

operation, the control equipment operation, and any chemical

reactions  occurring   within  the  effluent stream.   All  of

these parameters  may change with  time,  and  some of  these

parameters  are  interrelated.   Thus,  a   thorough  effluent

characterization  can  be  miserably compromised by  temporal


     If  the  chemical  identity  of  the  effluent  is  not

adequately   known,   it   may   be   difficult   to   interpret

particulate    measurements    obtained    using    standard

methodology.   Ignorance   of  effluent  composition may  even

further compromise any measurements  obtained  using  modified

sampling  procedures.   Put  simply,  the  prerequisite  for

meaningful  measurements  is  a  knowledge  of  what is  being

measured  and  an   understanding   of  the   effects   and/or

limitations  of the measurement technique  on  the  parameters

of interest.
                 I NVIRONMENTALJSTSt INC.

             The Operation of Physical Changes
                     Within an Effluent
     The  discussion which  follows  describes  the  physical

changes  that  can  occur  within  an  effluent  stream.   A

hypothetical  effluent   generated  by  the   combustion  of

fossil-fuel at a utility boiler is used as an example system

here, because the complexity of such  an  effluent provides a

most  general  case,   since   all  the   physical  processes

described   above   are   operating.    The   physical   changes

occurring in this effluent will be discussed  from generation

to  collection  on   the  reference   method   filter.   Where

necessary, digressions will be made in order  to elaborate on

the descriptions of the physical processes.

     In  this  section,  chemical  reaction  pathways  will  be

pointed  out,   but  will  not  be  discussed.   The  chemical

reactions that  accompany the physical  changes will  be the

subject of the following section.

Initial Conditions

     At the point  of  generation,  the effluent  is  quite hot

     O        o   2
[1000 C  (1800 F)]   and  still  chemically   reactive,  even

though  the  major  chemical  reaction, oxidation,  has  gone

essentially to completion.  The particulate can be described

as  a  mixture  of  unburned  fuel   and metal   and  non-metal

oxides.  At this  high  temperature, many  compounds  and some

elements will be in a vapor state.


     As  used  here,  the  word  "vapor"   implies  that  these

species may condense  by  the  time the effluent  reaches the

filter  of  the   sampling   train.   As  such,  all  of  these

elements   and   compounds   may   be   termed   condensible


     Recent   investigations   at   fossil   fuel  fired  steam

generators  have  dealt with  the  chemical  composition  of

particulate matter as a function of depth into the particles

(chemical depth  profiles),  and  as  a function  of  particle

size.  The results indicated that the more volatile elements

are  associated  with  the  particle  surfaces  and  those  same

volatile elements are preferentially adsorbed on the smaller

particles.    Complementary   investigations    focused    on

particulate  chemical  depth  profiles   as   a  function  of

distance traveled within  the  effluent  stream.   It was found

that  elements within  the effluent  were fractionated  with

respect to volatility, i.e., the more volatile elements were

found  associated  with   the  particulate  obtained  at  the

greater  distances  (and  cooler  temperatures)  within  the

effluent.   All  of   the   studies   indicate:   (1)   that

condensation   processes   are   in   continuous   operation

throughout  the  effluent  stream,  and  (2)  that  particulate

matter serve as nuclei for the condensation processes.

     It  is  difficult  to  quantify  the  contribution  these

particle-surface  condensations  make  to   the  condensible


particulate loadinq, because no  studies  have been conducted

which focus on such condensations  in  the Reference Method 5

train.  Because this particular  formation  mode  is a surface

phenomenon, and because it can be argued that the surface is

but a  small  part  of  the  entire particle,  it  can  also  be

argued that particle-surface condensations contribute little

to the condensible  particulate  loading.   Further study into

this particle formation mode is needed before truly accurate

rationalizations and/or predictions can be made.'

The Temperature Profile

     The extent  to which  condensation  processes —  and  by

extension, physical  changes —  occur,  is  dependent  on  the

effluent temperature and on the  amount of  time  the effluent

spends at that temperature.  This idea is illustrated by the

effluent temperature  profile.   The temperature  profile,  as

used  here,  is the  relation  between the change  in effluent

temperature with  time.   (See  Figure 3.)   (The  effluent  flow

rate  defines  the  relationship  between  the  effluent  stream

temperature  and  the distance  traveled  along  the  effluent


     In general, the extent of a chemical reaction increases

with  time.    Indeed,  this  is  also  true  when extended  to

physical changes, since the same  basic  principles apply;  at

least a  finite  amount  of  time  is  required  for a  system  to

reach an equilibrium state.   Thus, the  extent  of  a physical

change  is  dependent upon  the temperature and  the  time the

effluent spends within that temperature region.

     In  the   effluent  at   generation,   some  condensible

material exists which may  be  described  as condensible metal

oxides  [e.g.,  calcium  oxide  (CaO),  sodium   oxide   (Na-0),

etc.].   Only at  very  high  temperatures are these  metal

oxides  stable  as  vapors.   When   the  effluent  temperature

drops  as the  effluent leaves  the  boiler,  the  conditions

favorable  for  condensation  are   produced,  and  the  metal

oxides  quickly  condense.    The  condensations which  occur

within boilers produce scale.  Since the condensation of the

metal oxides occurs upstream  of the control equipment (e.g.,

an  electrostatic   precipitator   [ESP]),   the   condensation

products,  particulate,  can  be  collected  by the  control

equipment.   These condensible components will  have completed

condensation  well  ahead   of  the  sampling  and  filtration

points.  Therefore,  the measurement  of  these   metal  oxides

provides an accurate gauge of control equipment performance.

     Other  classes  of  condensible compounds still  exist  in

vapor  form  at  the  high  temperatures  at  the  exit  of  the

boiler.  If any of these compounds condenses before the ESP,


measuring that  compound  as particulate  would  contribute to

an  accurate  evaluation  of  control  equipment  performance.

Whether  these compounds  condense,  and  the extent  to which

they do  condense,  will be determined  to a  large  extent by

the remainder of the effluent temperature profile.

     In  addition  to the  effluent temperature  profile,  the

extent of physical changes is intimately associated with the

chemical  identity  of the  condensible substance  within  the

effluent  stream.   Each  substance is  characterized  by  its

boiling  point and  vapor  pressure.   The  concept  of vapor

pressure  is   fundamental   for    an   understanding   of  the

magnitude of  the condensible particulate loading.

     The  discussions of  vapor  pressure  which  follow will

assume equilibrium  conditions.   This assumption ignores the

fact that a temperature  gradient  exists  within the effluent

stream.   The   reader  should   understand   that  the  vapor

pressure  of a substance  will be  variable, and  will  show a

dependence on the effluent temperature and the time within a

temperature domain.

     The  vapor  pressure  of a substance  is a measure  of the

amount of material in the  gas phase  at  equilibrium with the

amount of material  in  the condensed  phase.   Water provides

an example of this physical property.  If water is placed in

a closed  container,  the  water  will evaporate  until   enough

water exists  in  the  gas  phase to provide  a  balance  between

                 IIMVIRONMENTAUSTB, INC.

the evaporation and condensation processes.  At equilibrium,

water vapor will  be condensing  at  the same  rate  as liquid

water will  be  evaporating.   All  condensed  phases  display

this behavior to varying  extents;  thus,  any condensed phase

will be associated with some vapor.

     The vapor  pressure  of a substance is  described by the

following equation:

-H i
R '
f 1

( T
             H   is  the heat  (enthalpy) of vaporization or

             P.   is  the vapor pressure of the substance
                     at its normal boiling point, usually
                     29.92 in. Hg  (760 mm Hg),

             P   is  the vapor pressure of the substance at
                     temperature T,

             R   is  the gas constant,

             T.   is  the substance's normal boiling  point
                     temperature,  in absolute units,

             T   is  the temperature of the substance when
                     its vapor pressure is P.
     The  significance  of   this   equation  lies  with   the

logarithmic dependence of vapor pressure on temperature.   In

simple terms, small changes  in temperature may produce large

changes  in   vapor  pressure.    Thus,   small   changes    in

temperature may produce large changes in the distribution  of


mass between the condensed phase and the vapor  (condensible)


     The  vapor  pressure  curve  for  water  is  presented   in

Figure 4.   (Vapor  pressure  curves for  other  substances are

similar.)  Two   features  of   the  curve   are   of  special

importance.  Firstly, as  the  system approaches the boiling

point, the vapor pressure increases  at  an exponential  rate,

and   secondly,   with  decreasing   temperature,  the   vapor

pressure  decreases  and  approaches  zero  asymptotically.

These  properties  of  vapor  pressure afford  the   following


      (1)  The  amount of mass  in  the vapor  phase   increases

          significantly   near   the   boiling   point.    The

          magnitude   of    the    effects    of   condensible

          particulates  will  be  of greatest  importance for

          those  substances  which  have  boiling  points near

          the  filtration  temperature.    In  addition,  the

          magnitude of the effect  will  be very sensitive  to


      (2)  Substances  with  boiling  points  well  removed from

          the filtration  temperature will not  interfere (as

          "condensible  particulate")   with   the   measured


         20   40    CO    gO   100
     YaporPressure Curve-for
           J^iqur-e v


     These   ideas   are  graphically  illustrated  with   the

hypothetical example  presented  in  Figure  5.   The  temperature

dependence  of  the  vapor pressure  has been  interpreted in  a

different  way.   Here,  the  percentage  of   mass  which   is

uncondensed  (i.e., in  the vapor  phase)   is  plotted  versus

temperature.    The   percentage   of  uncondensed   mass   is

proportional to the vapor  pressure; thus,  the curves  reflect

the logarithmic temperature dependence  of  vapor pressure.
                           -H a R~
     A  multicomponent  effluent  is  represented  here.   A

filtration  temperature  range  is shown  by  the  rectangular

region  within  the  graph.    Relative   to  the  filtration

temperature,  substance  C would  be  totally  in the  form of

particulate: i.e., substance  C  would  have totally condensed

before  collection  within  the   Reference  Method  5  train.

Substance A  represents  the  opposite case.   As indicated in

the figure,  substance  A  would  be totally in  the  gas/vapor

phase at the  specified  filtration temperature  range.  Thus,

substance A  would  either  condense in  the  back-half  or  pass


through the sampling system without condensing.

     Substance  B  displays  intermediate  behavior,  since it

condenses within the filtration temperature range.  The mass

of B collected on the filter will  depend  on the temperature

at the moment  of  filtration and on the variation  in filter

temperature  after  collection.   Thus,  substance  B can  be

collected on the  filter,  but may  subsequently evaporate off

if the temperature  of the filter  increases.  The collection

of substance B at the indicated filtration  temperature range

varies roughly from 10 to 60 percent.

     Each  substance,  A,  B,  or C,  will  contribute to  the

particulate catch in  proportion to its mass  loading  in the

effluent.   In  a  real  life  situation,  the  contribution of

substance B to the measurable particulate mass loading could

be insignificant.   Therefore,  the  variability caused by the

condensation of substance B would not impact on the measured

particulate, and no condensible particulate problem would be


     The essence of this graph  is that as the effluent moves

through the ductwork, a  potential  multitude of condensation

processes can ensue. As  the  effluent  cools, those compounds

with high  boiling points will  condense  first,  followed by

the compounds with lower boiling points.

     These phase  changes are not  strictly abrupt.   In  the

neighborhood of its phase change temperature, each component

will  be  partitioned  between the  condensed  phase and  the

vapor phase, Thus, when Reference Method 5 is applied, clear

demarcations   may  not   exist   between  particulate   and

condensible particulate  at  any  particular point  along  the

effluent pathway.

     Vapor  pressure  can  also  play  a  significant role  in

affecting  the measured  efficiency  of  particulate  control

equipment.     Most    control   equipment   operates    by

discriminating between condensed material  and gases/vapors.

Such is the case  for  electrostatic precipitators, cyclones,

and fabric  filtration  units.   Particulate material entering

these devices  can be  removed from the  effluent,  and thus,

can be  controlled.   Obviously,  particulate  material  which

results from  the condensation  of  vapors  after  the  control

device cannot be  affected.   The potential control, however,

is not necessarily a clear cut  issue.   In those cases where

vapors condense while passing through the  control equipment,

the degree of control is potentially variable.  This will be

true for those effluent components which have boiling points

within  the  temperature  profile of  the  control  equipment.

Figure 6 illustrates these concepts.

     The  graph  shows the   temperature  dependence  of  the

percent uncondensed mass of  three  components.  The behavior


of component C  in  this diagram indicates that  all  the mass

will be  in the condensed  phase at  the  temperature  of the

control equipment.  The curve  for  component  B passes wi';hin

the temperature  range of  the  control equipment.   For this

case,   the  collection  efficiency  of  the  component  will  be

variable.   Over  the   temperature   range   of  the  control

equipment, between 50% and 10% of the mass of this component

will be  in  the  gas  phase  and  wil]  not be  controlled.  The

behavior of component  A in this scenario will  be, even more

extreme.  Between 45%  and  100% of  the mass  of component  A

will be  uncontrollable.  The  magnitude of this effect will

be dependent mainly  upon  the  relative mass  loadings  of the

affected  components,   and  the  temperature   of  the  control

equipment. Again, in real  life  situations,  the  magnitude of

the effect may or may not be significant.


Physical Changes in the Sampling System
     In most  respects,  the physical  environment  inside the

sampling probe is quite  similar  to  the physical environment

the  particulate  matter  views  within  the  effluent  stream.

Indeed,  If  the   temperature  of  the  probe  is  maintained

identical  to  the effluent temperature,  and  if  isokinetic

sampling  is  conducted,  the  physical  properties  of  the

effluent  sample   should  differ  little  from  those  of  the

effluent  itself.   Particulate  matter will  collect   in  the

probe  as  a result of  gravitational settling  and  impaction

with the walls of the probe.

     The effect of  temperature  on  the  particulate measured

in  the  probe  can operate  in two  directions,  depending on

whether the probe temperature  is greater than  or  less  than

the temperature of the effluent.  In addition, this measured

particulate will reflect the relative temperature difference

which exists during the entire sampling operation.

     If  the  probe  temperature   is  less  than  the  effluent

temperature, condensation  reactions can  occur on the cooler

probe walls. Similarly, condensible substances may adsorb on

the  walls  of  the  probe.   On  the  other  hand,  if  the

temperature of the probe is greater  than the temperature of

the  effluent,  not  only  will   condensation  and  adsorption

reactions be prevented,  but material  already condensed and


adsorbed may  be  volatilized.   Particulate can  be  caught in

the  probe,   but   also   can  be   subsequently   removed  by

volatilization.    Thus,   if   condensible   particulate  is

sampled, a variable  probe  temperature can  cause  a variable

probe  particulate catch.   However,  the  operation   of the

Reference Method 5 sampling train  is  intended to account for

this  potential variability,  through the  provision  of the

heated filter  which follows the probe and  is maintained at a

known temperature.

     After the effluent  sample exits the probe,  it  passes

through the filter.  Particulate  matter  will be impacted on

the  filter and may accumulate to  form a  filter cake  if the

loading is sufficiently high.   The filter cake will  provide

an additional  site for physical  reactions, depending  on the

temperature of the filter relative to the  temperature of the

effluent  sample.  Indeed,  the  potential  physical   changes

will  parallel  those  which  were  associated  with  the  probe.

The  temperature  of the  filter  can affect the  state  of any

condensible particulate which  is  formed  or  is  collected on

the  filter.   However, if  particulate is  vaporized from the

filter, it  will pass on  to the  impingers,  and may  not be

quantified.  Therefore,  if  only the  front-half  of the  train

is  used  for  the  particulate  determination,  the  filter

temperature  is  the  last   major   physical   parameter   which

determines the measured  particulate.

     The  pressure  difference across  the filter  and filter

cake   makes   a   lesser   contribution   to   the   potential

variability of the filter particulate  catch.   If  the filter

cake contains  compounds  having  have vapor  pressures which

are  significant   at  the   filtration   temperature,  these

compounds  may  evaporate  as   a   result  of  the   pressure

difference.    The   evaporation  reflects   the   shift   in

equilibrium toward the gas phase, brought about by the lower

relative  pressure  on  the  other  side  of  the  filter.   The

evaporation  of  volatile compounds on  the  filter  during

sampling  is  analogous to the  lower boiling  point  of water

observed   at   higher  altitudes,   and   lower   atmospheric


     Since the  filter  marks  the final point  in sampling an

effluent,  it  is  extremely  important  that   any   material

passing through is physically well characterized;  otherwise,

the characterization of the material collected  on the filter

will be compromised.   If condensible particulate  is present

within an  effluent stream,  it  may pass  through the filter.

The  amount of  uncharacterized  and unmeasured condensible

particulate  which   passes   through  will  depend   on   the

temperature history of the filter.  The observed variability

in  the  measured particulate will  be strongly  dependent on

the variability of the filtration temperature.  Finally, the

effect  of  the   filtration  temperature  on   the   measured

particulate can be profound.

                      IIMV1RONMEMTAUSTB, INC.

                     Chemical Reactions
     The occurrence of chemical reactions within an effluent

can  greatly  affect   the  observed  loading  of  condensible

particulate.   The   reactions   that  may   occur   are   not

necessarily independent of physical  changes;  thus, chemical

reactions may lead to physical changes,  and  vice versa.   In

the discussions that follow,  the reader should be mindful of

the complicated interplay of chemical reactions and physical


Definitions and Examples

     The  operations  of chemical  reactions  within effluent

streams will be addressed from  three  general  subject areas.

The first area, chemical  reactivity,  is concerned  with  the

ability  of  substances  to  react  to  form  products.   The

reactivity  of  an  air-gasoline  mixture  serves  as  a  simple

example.  Experience  tells  us  that  this  mixture  is  quite

reactive, if the conditions are right.

     The second subject area,  chemical thermodynamics, deals

with  the  stabilities  of  the  products  and  reactants  of

chemical reactions. The reaction of ammonia, sulfur dioxide,

and water vapor  provides  an example.   Reactivity arguments

predict that the mixture is reactive, with the product being


ammonium bisulfite.  Thermodynamics, however, shows that the

                                                O       o
product of  the  reaction  is  unstable above  400  C  (750  F);

therefore, if ammonium  bisulfite  is formed above  400  C,  it

will   instantaneously   decompose   back   to   the   original

reactants, ammonia,  sulfur  dioxide,  and  water.    For  this

chemical  system,  thermodynamic   arguments   determine  the

reaction actually observed.

     Chemical kinetics, the  third subject area, deals with

how  fast  a  reaction occurs  and,  in  a  sense, how  far  a

reaction  goes  to  completion.   Time  is   the  parameter  of

interest  here.   An  example   which  shows  the interplay  of

thermodynamics  and   kinetics  involves   the   reaction   of

nitrogen, oxygen, and water to form nitric acid.
    nitrogen  +  oxygen  +    water   	>  nitric acid

     (gas)       (gas)       (liquid)         (liquid)
     Thermodynamics predicts that the  reaction  can occur at

ambient  temperatures.    Chemical  kinetics,  however,  shows

that the  reaction  is  infinitely slow.   Experience supports

this argument, for if the rate of reaction were significant,

the atmosphere would dissolve  in  the oceans to  form nitric


Reactivity and Reactions

     Most effluent streams  are  still  chemically reactive at

the  moment  of  generation.   This  is  especially  true  for

effluents  generated   by   combustion.   Thus,  even  though

oxidation, the  primary reaction,  has occurred, many other

reactions can still occur.

     The combustion of a  fossil-fuel,  coal,  can serve as an

example  of   how   reactivity  arguments  can   be   used   to

rationalize  the  formation  of   condensible   particulate  by


chemical reactions.  During combustion, the primary reaction

is  oxidation;  the  principle products  are  carbon  dioxide,

CO-, and  water, H?0.   Impurities associated with  the  coal

are  also  oxidized.  If the oxidized   impurities are  gases,

they  will  mix  with  the   excess air,  carbon  dioxide,  and

water.  On  the  other  hand, if   the oxidized  impurities  are

solids, they  will  either  be collected in the ash  pit or be

entrained in the effluent as fly ash  (particulate).

     Using simple  acid/base theory,  general  statements  can

be made regarding  the relative reactivities of the solid and

gaseous oxidized  impurities. According  to  simple  acid/base

theory, the  oxides of  metallic   elements  are  classified as

bases,   and   the   oxides   of    non-metallic  elements   are

classified as acids.   Using this classification scheme,  the

typical fly ash constituents,    sodium oxide  (Na_0), calcium

oxide (CaO),  iron  oxide (Fe203),  and  aluminum oxide  (A1-0-)



are classified as basic  substances.   The gaseous compounds,
sulfur dioxide (S0_) ,  sulfur  trioxide  (SO,) ,  carbon dioxide
(C02) ,   and   nitrogen   dioxide   (N02) •   are   consequently
classified   as   acidic  substances.   According   to  simple
acid/base theory, acids react with bases; thus, if a process
feedstock contains  metallic and  non-metallic  elements, and
if this feedstock is decomposed in an oxidizing environment,
potentially  reactive acidic  and  basic compounds  will  occur
together  in  the effluent.   An  example  of  an  acid/base
reaction that occurs in the effluent  of  a coal-fired boiler
is given by  the  reaction of sulfur trioxide and  iron  oxide
to yield iron sulfate, a component  of boiler scale.
   Sulfur trioxide      iron oxide             iron sulfate
      (gaseous)           (solid)                 (solid)
       "acid"             "base"
     In  the course  of  the  reaction,  a  solid  and  a  gas
combine to give more solid.   The  reaction  is rather general
with respect to the  physical  states  represented here; thus,
the acid is a gas, and the base and products are solids.

     Many  chemical  reactions  similar  to  the  example above
occur in the effluent stream.   These  reactions may continue
to  the  moment  when the  particulate  is  weighed   in  the
laboratory, or viewed from a  different  perspective, to when
the  particulate  becomes dispersed  in  the   atmosphere.   It
should  be  emphasized that  chemical  condensation   reactions


tend to produce positive biases to particulate measurements,

if such reactions occur within the sampling  probe or on the

heated  filter  of the  Reference  Method 5  train.   Using the

reaction above as an example of the  potential  impact of the

bias,  the  solid  phase  increases its relative  mass  by  a

factor of  2.5,  more than  doubling  the mass which  would be

termed particulate.

     The  effect  of chemical  condensation reactions  on the

measured  particulate  is  dependent on  where  these reactions

occur  within  the  effluent.   If a   condensation  reaction

occurred  before  a  control  device,   then  the   particulate

collected  in  the probe  and  on the  filter  during emissions

tests will reflect control equipment performance. Obviously,

reactions  occurring  after the control equipment  would not

reflect  control  equipment  performance.  Finally, reactions

occurring  on  the  reference  method   filter  may  lead  to

erroneous  interpretations  of  source  performance, especially

if these reactions have  no counterparts within the effluent

stream.   The  potential   occurrence  of particulate-forming

reactions   on   the   filter   has  been   the    subject  of

investigations  of   sampling   at   fossil-fuel   fired   steam


     The limited amount of data currently available suggests

that  chemical  reactions  occurring  at  the  filter   do not

contribute   significantly   to   particulate   measured  at


fossil-fuel  fired  steam  generators.   Further  studies  at

other source categories  are  needed  to assess the  importance

of particulate forming reactions at the  filter.

     For oil-fired boilers,  one  chemical reaction which  can

make   a   significant    contribution   to   the   condensible

particulate  loading   is  that  between  sulfur   trioxide   and

water vapor to form sulfuric acid mist.
      trioxide       water             sulfuric  acid
       (gas)         (gas)                (liquid)
     As  was  discussed  in  the  Historical   section,   this

reaction   was   responsible   for   the    higher    filtering

temperature which is permitted at affected  fossil  fuel  fired

steam   generators.    With   regard   to  the   formation   of

condensible particulate, the  result of the  reaction of  SO,

and H20 is essentially the same as  the one  presented  earlier

for S02 and  Fe203.   The difference is that  instead of  the

mass of the  solid  phase increasing,  particulate  matter  is,

in effect, appearing "spontaneously"  in the effluent.

     The  consequence  of the  reaction  between SO.,  and  H,,0

extends beyond the formation of the sulfuric acid mist.   The

sulfuric  acid  can  react with  additional  water to  form  an

aqueous (water) solution of sulfuric acid.

      sulfuric acid     water            sulfuric acid
         (liquid)         (gas)               (aqueous)
                                         [a  solution of
                                         sulfuric acid
                                         and  liquid water]
     Thus, the reaction of gases to yield particulate matter

can  ultimately  result in  further  condensations  which  will

increase the observed mass loading.

     The problem  here transcends  the  increased particulate

loading  contributed  by the  reaction.   The  fact  that water

contributes  to  the  condensation   reaction  is  of  greater

significance.  Water, unlike  the  sulfur  trioxide,  is  not

classified  as  a   pollutant;  thus,  condensation   reactions

which   involve   water   will  doubly   bias   the   observed

particulate loading.

     Water  can contribute   to  the condensible  particulate

loading  in yet another fashion.  Compounds can be chemically

associated  with  water  molecules.   These  associations  are

called  hydrates  and  are  often   in  the   form  of  solids.

Examples of  hydrates  and  their  formulations are  given by

iron  sulfite  trihydrate  (FeS03 •  3H?0),  magnesium  sulfate

heptahydrate   (MgS04 «  7Ho°^ »   and    magnesium   chloride

hexahydrate (MgCl2 * 6H20).

     The   formulations   presented   here   illustrate    two

important  points.    The   first  is  that   the   number  of

associated water molecules  depends on the chemical  identity

of  the  compound of  interest.   Secondly, the  mass  that  the

water contributes  to the  total compound is  also variable.

The  percentages  of  water  by weight   for   the  preceding

compounds are tabulated below.

          Compound               % Water  by Mass

         FeS03 • 3H20(s)                28%

         MgS04 • 7H20(s)                51%

         MgCl2 •6H20(s)                53%

     It is apparent  from  the  examples that  the contribution

made  to   the  particulate   mass'   by  the   water   can  be

significant.  As  a prelude to  discussions  which  appear in

the  section  dealing  with  the  stability  of  compounds, it

should  be   added   that  the    number  of  water  molecules

associated with a  specific compound  may be  variable.    For

example,   magnesium  chloride   hexahydrate   (MgCl2 •»  6H20)

represents the maximum hydration observed for  this compound.

A  lower formulation  exists:  magnesium   chloride dihydrate

(MgCl2 • 2H20),  which  is  the  more stable  hydrate  form at

higher temperatures.

     Not all  compounds  form hydrates; nevertheless,  because

moisture is  a common  effluent  component, the  potential  for

                • NVIRaNMENTAUSTS, INC.

hydrate  formation   should   be   recognized.   In  addition,

hydrates are often stable above  the  boiling point of water,

so that heated probes and filters will not  necessarily cause

their  decomposition  or  prevent  their, formation.  Finally,

data  showing   the  contribution  of  water   of  hydration  to

particulate measurements are  lacking;  thus, it is currently

not possible  to  assess  the  real  impact of  hydrates  on such


     The  discussions  above  treated  effluent   reactivity.

Only  two  simple  chemical  reaction  types  were  discussed:

reactions of acids and  bases, and  reactions involving water

vapor.   Many  other   reaction  types exist,  but it  would  be

beyond  the  scope   of  this  paper  to  discuss  them  all.

Finally, it must  be  emphasized  again  that  a  limited amount

of data exists for combustion processes —  even  on a simple


Stability Considerations/Chemical Thermodynamics

     Many reactions can be postulated as occurring within an

effluent stream.   Whether the  reactions  actually  occur  is

dependent   in   part   on   thermodynamic   considerations.

Thermodynamics  involves  the  stability of  chemical systems,

either  pure  compounds  or  elements,  or  mixtures  thereof.

Within the scope of  thermodynamics  the  important parameters

are:  the  chemical  identity  and  concentrations  of  all  the

substances in  the  system, the  pressure  of  the  system,  and

the temperature  of the  system.   The  examples which follow

illustrate how  thermodynamic  concepts  can be  applied  to

reactions within effluent streams.

     The  results   of  recent   investigations     into   the

anomalous behavior of a cement kiln plume have suggested the

occurrence of the following condensation reaction:


    ammonia      sulfur       water         ammonium
      (gas)       dioxide       (gas)           sulfite
                 (gas)                       (solid)

     Ammonia, sulfur dioxide, and water are all stable up to

very high temperatures.  This is  not  the  case, however,  for
                                             o         013
the product,  ammonium  sulfite.   Between  60 C and  70 C,

ammonium sulfite decomposes to  the  reactants,  NH.., SO,,,  and

H-0.  This fact  dictates  that  if the reaction occurs above

this temperature range, the  product  will  immediately revert

to  reactants.   Thus,  the reaction  is  observable only  at

lower temperatures.

     Indeed,  the  plume  from  the  cement  kiln displayed  a

temperature dependence which was associated with the time of

day.   The  plume  was  most  visible  "during   early  morning

hours, but diminished rapidly  as the day progressed"  and as

the ambient temperature consequently rose.  Thus, it appears

that  the   reaction   is  dependent  on   the  thermodynamic

stability of the product ammonium sulfite in the effluent.

     The  authors  of  the  report on  the  cement  kiln  plume

suggested yet  another reaction pathway  to account for  the

anomalous   plume.    In   this  alternative  pathway,   sulfur

dioxide  dissolves  in  water  droplets  and   is  subsequently

oxidized  by dissolved  oxygen.  Dissolved  ammonia  promotes

the  reaction  by  increasing   the  solubility  of  the  sulfur

dioxide  in  the water,  and  also reacts  with  the  dissolved,

oxidized  sulfur  to form  ammonium  bisulfate  (NH.HSCK).   If

this scheme is correct, then the daily variation may reflect

the  fact  that the necessary water  droplets will  form more

readily  when  the  plume  contacts  the  cooler  morning  air.

Here, the thermodynamic  stability  of  liquid  water droplets

determines the outcome of the condensation reaction.

     Another  example  of  how  thermodynamics  affects  the

outcome of condensation reactions involves hydrates.  As was

discussed earlier,  some substances can associate  with water

                   I NVIRONMEIMTAUBTa,INC.

molecules  to  varying  degrees.    (For  the  purposes  of  the

following  argument,  it is assumed  that  temperature  is  the

controlling factor in determining the degree of hydration.) >

     Water   molecules   involved   in  hydration   are   not

necessarily  weakly held.  Heating  a hydrated  compound  to

100 C does not necessarily boil off the water molecules.  In

addition,  the extent  to  which increased  temperature  causes

water  to  leave  a  hydrated  substance  is dependent  on  the

chemical identity of the  substance.   The  compound  magnesium

sulfate can be used as an  example.   Heating  solid  magnesium

sulfate heptahydrate to 150 C results in loss of six  of the

waters of  hydration.

     StpSOff*) -^ AljSQf '

     Increasing the temperature to 200 C  results in the loss

of  the  remaining   water  molecule  and  produces   anhydrous

magnesium  sulfate.
(Heating  the  anhydrous compound  to 1124  C decomposes  the

substance  into  magnesium oxide  (MgO)   and  sulfur  trioxide

(S03) , "base"  and "acid,"  respectively.)

     Hydrates  formed  in  the  effluent,  on the  filter,  or

during  the laboratory phase  of  the  method   may  display

similar patterns of stability.  In  this  regard,  hygroscopic

particulate  matter,  i.e.,  particulate  which  will  take  up

moisture,  collected  at  the  filtration  temperature,  may

acquire  additional  water  when   it  is  exposed   to  cooler

ambient air.

     One  must  recognize   the   impact   of  stabilities  of

condensible substances in the effluent, if one is  to predict

condensation  reactions.   This recognition  presupposes  that

the  identity  of  the   condensible   material   is  known.

Stability  arguments,  however,  do  not  always  dictate  the

observed particulate mass variability.  Kinetic factors, the

subject of the following section, must be considered also.
Rates of Reactions - Chemical Kinetics

     The presence  of a  reactive  system and  the  conditions

necessary for  stable  products  do  not necessarily  lead  to a

measurable  reaction  within  the  effluent.   It is  the  time

dependence of a reaction which determines  the extent of the

reaction.   Reactions  may occur quickly or slowly;  thus,  a

reaction that  is  slow relative  to  the  time scale  of the

particulate measurement may not be observed  at all, because

insufficient products will exist at the time of measurement.

In   addition,   reactions   which  can   produce   condensed

particulate may  not  make  significant  contributions  to the

measured particulate because of time  constraints  imposed by
reaction rates.

     The rates of chemical  reactions  are  determined by: (1)

the  chemical   identities  of  the  reacting  substances,  (2)

temperature, and (3) the concentrations of these substances.

It  is  important  to   understand   that  reaction  rates  are

measured  by  experimentation.   As  a  result,  it  is  not

possible  to  predict   the   rates   of  chemical  reactions  £

priori.  Instead, the  identity  of the  reactive  system must

first  be  determined;  then,   the  reaction   rate   may  be

determined experimentally.   Sometimes,  rate  predictions can

be made by  referring  to earlier experimental  data,  if such

data  exist.  Obviously, prediction will  be  compromised  by

insufficient data.  Unfortunately,  chemical  kinetic  data for

effluent  systems are  either lacking  or  are  difficult  to

apply, because of the enormous complexity of such systems.
Chemical Identity

     Identifying  all  the  components   of   even  a  simple

reactive system can be a difficult (and often an impossible)

task.  The complexity of most  effluent  streams explains why

chemical  kinetic  data  for  such  systems  are  few.   The

combustion of coal  can  serve  as an example again.  Not  only

is the  elemental  composition  of  coal  a  variable,  but its

chemical  composition is  poorly  defined  and   is  also  the

subject of current study.  As a starting point for obtaining


kinetic  data,   the   identities   of   the   reactants   are

determined.  The reactants are identified first, because the

problem gets horrendously complex  when  the reaction starts,

and  most  of  the   kinetic  data  are  obtained  during  the

reactions.   With coal,  identification is  a  complex problem

to start with.

     The  question  of   reactant   identity   is   made  more

difficult when  catalytic processes  are  operative,  and  the

chemical complexity of effluent  streams in  general argues

strongly for  the  presence  of  catalytic reactions.   As  a

result, extra scrutiny  is often necessary to  establish  the

roles  of  catalysts in  reactions.  Moreover,   catalysts  may

exert  their effects in relatively low  concentrations,  with

the  result  that  the  task  of  identification becomes  more

difficult,  because the catalysts are difficult to detect.

     Identifying all the reactants  that  determine the rates

of reactions occurring  in effluent  streams is presently not

possible, and  represents a  formidable  task.   Most  of  the

major species, however, can be identified, so that it may be

possible  to  make  predictions   regarding  some  potential

condensation reactions.


     Most  chemical  reactions display  increasing  rates with

increasing temperature.  This generality predicts a decrease

in reaction rates as an effluent cools.  Thus, with cooling,

chemical  reactions, leading to condensation  products should

contribute  less  to  the   particulate  loading,  because  of

slower  rates.   This  argument,  however,  is  difficult  to

aPPly» because of the interplay of numerous other processes.

The  effect of  effluent  temperature  on  chemical  reaction

rates   must   be   viewed   within   the   constraints   of

thermodynamics  and   with  regard  to physical  states.   For

example,  reactions  generally  occur faster in  solution than

in the gas phase (when all  the  reactants  are gases).  Lower

temperatures  predict  slower  reaction  rates,  but  in  this

case,  lower  temperatures  favor  the formation of  condensed

phases,  which  in  turn  provide  reaction  conditions  which

favor  accelerated  reaction rates.    The  reaction  of  oxygen

with sulfur dioxide  to form  (ultimately)  condensed  sulfate

occurs slowly at stack temperatures, when  the  reactants are

all gases. If the reactants are dissolved in water, however,

the reaction  proceeds  much faster.  Condensed water,  which

would  be  present  only  at  relatively  low  temperatures,

provides an alternate  reaction  pathway,  with a  faster rate

of reaction.


     In  general,   the  role  of  temperature   in  influencing

rates of  chemical  reactions is overshadowed by  the  role of

temperature with  regard  to providing  condensed  phases that

promote reactions with faster rates.

     The  preceding  paragraphs  touched upon  the  effect  of

concentration  on  reaction rates.   Generally,  reaction rate

is   proportional    to   concentration,    i.e.,    if   the

concentrations  of  reactants  are   increased,  the  rate  of

reaction  is  increased.   Condensed  phases  promote  greater

reactant  concentrations  relative  to   the  gas phase;  thus,

reactions occurring  in a  liquid medium  ordinarily  proceed

faster than similar reactions in which the reactants are all

gases.. The  impact  of  this  fact  is   that  the  presence  of

condensed   material   may   accelerate   the   formation   of

additional condensed material  - condensible particulate.  A

good example  of  the  potential  effect  can  be  found  with  the

impingers (back-half)  of  the EPA Reference  Method  5  train.

A  condensed  phase,  the  water,  dissolves   (concentrates)

sulfur dioxide, which  may  oxidize  to  ultimately  form solid

sulfate.  This reaction occurs  much  faster in the impingers

than in an effluent stream.

     The  filter  of  the  Reference  Method 5  train provides

another  example.  Particulate  matter   in the  effluent   is

concentrated  on  the  filter  during  sampling.   This,   of

course,  is  a necessary  step  in measuring  the  particulate.

Nevertheless,  this  concentrating  will  result  in increased

rates  of reactions  if  reactants  exist  within  the   filter

cake.  If  such  condensation   reactions   make  a  measurable

impact,  the  biases  will be  positive.    An  obvious  dilemma

exists: the method of  measuring particulate may potentially

result in a measurement which has an unknown relation  to the

particulate which actually exists within  the effluent.

     Understanding  the   origin  of  condensible  participate

both  within  effluent  streams  and  within  the  Reference

Method 5 train requires  knowledge of the  chemical identity

of  the  effluent  at generation  and  all  the  physicochemical

reactions  that  can  occur  after  that  point.   For  most

effluents such an  understanding is presently  not  possible,

because  of  their  chemical complexity  and  because  of  the

inherent  difficulty  of  analyzing  chemical  and  physical

changes  which   operate   concurrently.    Nevertheless,   the

observation of condensible particulate can be rationalized.

     The temperature is  the single  most important  parameter

affecting  the  condensible  particulate  which  is  ultimately

measured.  The formation  of condensible  particulate  can be

extremely  sensitive  to  temperature,  and  consequently,  the

relation of particulate formation to the temperature profile

of the effluent should be known, if accurate interpretations

of the particulate catch are expected.  Finally, because the

filter ultimately  provides  the  measure  of  particulate,  its

temperature  is  crucial  when  an  effluent   with  a  high

condensible particulate loading is sampled.

     Reference  Method  5  is  applicable  to  those  effluent

streams where  physicochemical  changes are  relatively small.

In  effect,   the   method   assumes  that   the  effluent   is

physicochemically  static  once  it has  been generated   or

controlled,  (i.e., the  mass  loading,  size distribution, and

chemical  identity  of  the  particulate  matter  are constant).

When    physicochemical    changes   producing   condensible

particulate  occur  within  the  filtration  temperature range,

and  when  significant mass  is  involved   in   such  changes,

Method  5  gives  a  biased  measure of the  performance   of

particulate  control devices.

     In situations where the evaluation of  control equipment

performance  is not the  important issue, a  physicochemically

reactive  system may require  extra  attention to the sampling

procedure  in order to ensure reproducible data.  For extreme

conditions,  the sampling  location  temperature and the  probe

and filter temperature control may be very  important factors

affecting  particulate measurement  results.

     Because  the  occurrence  of  condensible  particulate   is

sensitive   to  temperature   changes,  precise   filtration

temperature  control is  a  prerequisite for obtaining precise

particulate measurements when condensibles  are present.  The

filtration  temperature  control  of  Reference Method   5   is

ordinarily sufficient for measuring particulate in effluents

where the particulate loading is independent of temperature.


                                1 2
However, the  results  of studies '   comparing  the Reference

Method 5 filtration temperatures to  the temperatures of the

thermostated   box   (the  temperature   actually  monitored)

indicate that  significant disparities  may exist between the

two.  Thus,  the  assumption  that the temperature  control of

the Reference  Mehod  5 train is sufficient may  not  be valid

for sources with high loadings of condensible particulate.

     No  data  exist which show the   relation  between source

operation - control equipment  performance and the resulting

loading  of condensible  particulate   in  the  effluent stream.

Nevertheless,  it  can  be  anticipated   that  the   relative

contribution  of  condensible  particulate to   the   measured

particulate will  increase  as  the efficiency  of particulate

control devices increase.  Again, if condensible particulate

makes  up a  significant fraction of the  total particulate

loading,   precise    measurements    will    demand   precise

temperature control. Thus, the extension  of Reference Method

5 sampling to  sources with  low particulate loadings may be

limited  by   the   precision  of  the   method's  filtration

temperature control.

     Reference Method 5 is often used to  measure particulate

at sources not  subject  to NSPS.  These sources  represent a

more varied and extensive source population, and, therefore,

the potential occurrence of  effluents  with high condensible

loadings  is   correspondingly  greater.    As  a  result,  the

reference method is often unintentionally applied to sources


with    high    loadings    of    condensible    particulate.

Consequently,   either   the   quality   of   the   particulate

emissions data  is poor,  or  the condensible  loading  is  so

great that sampling is aborted.

     Reference  Method  5  was  developed  in  conjunction with

NSPS, and,  as  such,  it was never  intended  to be  used  as a

general  method  for  measuring  particulate.   The  general

applicability of  Reference Method  5 may not  be  assumed.   A

flexible  approach is  required when  particulate  tests  are

conducted at source  categories which  cannot  be  compared  to

those covered by NSPS.  Any particulate sampling methodology

should be chosen so that it not only  is  compatible with the

source operating conditions,  but,  of  greater  importance,  it

should also provide data with a known relation to the system

being evaluated.

     As   a    criterion    pollutant   for   NSPS   sources,

"particulate" differs from the other criterion pollutants —

sulfur dioxide, nitrogen  oxides,  hydrogen  sulfide,  etc.  —

in that  particulate  is defined in  terms  of  physical  state,

rather  than in terms  of  chemical  identity.   Sampling  and

quantification  are  greatly   simplified   when the  chemical

identity of  the substance  of  interest is known,  because  if

the chemical identity  is  known,  the  physical properties  of

the  substance  can  be  easily  obtained.  Thus,  when  the

chemical  identity of  a  substance  is  known, sampling  and


quantification  take   advantage   of  both  the  substance's

chemical  and  physical  properties.   As   a  consequence  of

particulate   being   defined  on   a   physical   basis,  the

methodology   for   its   sampling   and  quantification  lacks

specificity and precision  relative to the methods used for

determining  emissions  of  other  NSPS  criterion pollutants.

In addition,  the physical state of  particulate  is  defined in

terms of  only one  physical parameter  —  the  temperature of

filtration;  the pressure  drop  across  the   filter   is  not

considered.   "Particulate"  can therefore  be  interpreted as

"any   substance  which   condenses  above   the   filtration

temperature   and  which  has   a   vapor  pressure  which  is

negligible relative to the pressure drop across  the filter."

     The  definition  (as  interpreted  by  the  procedures  of

Reference Method 5)  makes  only one  distinction of chemical

identity:  the  filtration  temperature  is held  above  the

boiling point of water to prevent  it  from being measured as

particulate.   A similar  situation exists  for  fossil fuel

fired steam generators where  high  loadings of sulfuric acid

mist exist.   A higher filtration temperature is  permitted to

prevent   the    measurement   of   sulfuric  acid  mist   as

particulate.   Both choices  of  filtration temperature  are

based  on the same  idea:  the  temperature  is  selected  to

exclude a known compound  which is  not functionally related

to  the  system  being  measured.    This idea  points  to  the

fundamental problem with the definition of particulate; this


problem   is   manifested   by  the   issue  of   condensible


     The   presence   of    condensible   particulate   during

particulate   measurements   for   compliance   determinations

compromises  the  results  of  such  determinations,  because

condensible particulate has an undefined relation to control

system  performance.   The   relation   is  undefined   as  a

consequence of  the fact that  the chemical identity  of the

condensible   particulate   is   generally   unknown.    Without

knowledge  of  the chemical  identity  of a  substance,  it is

difficult  to  understand  the physicochemical history  of the

substance within an effluent stream.

     One recurring theme throughout this paper has been that

condensible  particulate  does   not  reflect  control  system

performance if  it forms  in the  effluent  stream  after the

control system.  If the chemical  identity of the condensible

particulate were known, it  would  be possible  to resolve the

problem of the  relation  between condensible  particulate and

control system performance, because it would  be possible to

determine  at  what  point  the condensible  particulate formed

in the effluent stream.

     The  fact  that  the  chemical identity  of  particulate

matter is  undefined  (and  its physicochemical  history within

the effluent stream is unknown) leads to yet another problem

with interpreting particulate  emissions data:  at what point


in  an   effluent   stream   is   particulate   classified   as

condensible? Answering  this  question  is impossible, because

as particulate  is  currently defined, a  distinction between

"true"  particulate and  condensible  particulate  cannot  be

made without some knowledge of the  chemical  identity of the

entire effluent.

     The issues discussed above all point  to the same basic

limitation of  Reference Method 5.   The limitation  has  its

origin in the current definition  of particulate matter.  If

an  effluent   stream   is  physicochemically  reactive  and

condensible particulate is forming,  it  becomes difficult to

determine what is being measured, because the parameter used

in  the  measurement has a  poorly defined  relation  to  the

effluent stream.

        R.  F.  Vollaro,  "An  Evaluation of  the  Current  EPA
Method  5  Filtration  Temperature  Control  Procedure,"  in
"Stack  Sampling  Technical  Information,  A  Collection  of
Monographs and  Papers," Vol.  IV,  EPA-450/2-78-042d, October

        E.  T.  Peters  and  J.  W.  Adams,  "Evaluation  of
Stationary Source  Particulate  Measurement Methods,  Volume
III.  Gas  Temperature  Control  During  Method   5 Sampling,"
EPA-600/2-79-115, June 1979.

1.    Because  the  formation  of  condensible  particulate  is

     extremely sensitive to  temperature,  precise  control  of

     the  Reference  Method  5   filtration   temperature  is

     imperative,  if  precise  particulate  measurements  are

     desired for effluents with high condensible particulate

     loadings.   Preliminary   investigations   should    be

     conducted  to   assess   the  feasibility   of  directly

     monitoring the  filtration temperature during Reference

     Method 5 sampling.

2.    The  chemical  identities  of  condensible  particulates

     should  be  determined,  and   their   contributions  to

     particulate  measurements  should  be  quantified.    In

     addition,  investigations   should   be   made   of   the

     functional dependence   of  condensible  particulate  on

     source performance, control equipment performance,  etc.

     With  knowledge  of  the  chemical  identity,   the  mass

     loading, and the  functional dependence  on performance,

     it may  then  be  possible  either  to  adjust  particulate

     measurements  to  account for the presence of condensible

     particulate,  or  to  modify  the sampling methodology  to

     remove the condensible particulate contribution.

3.    Future  investigations  should   focus   on   identifying

     chemical   indicators   of   system   performance.    The

     specificity of an indicator of  known  chemical identity

     would remove  the ambiguity  associated  with  the  term

     "particulate"  and would, in all  probability,  result in

     correspondingly  specific   (and  precise)   methods  of

     sampling and quantification.

          As  a hypothetical example,  iron may be a specific

     indicator  of  the  performance  of   an  electrostatic

     precipitator.   Thus,  sampling  for  iron would  be  the

     basis   for   evaluating   the   performance   of   the