United States
          Environmental
          Protection
          Agency
            Office of Air Quality
            Planning and Standards
            Research Triangle Park, NC 27711
EPA-450/4-91-015
May 1991
&EPA
          AIR
CRITERIA FOR ASSESSING THE ROLE
OF TRANSPORTED OZONE/PRECURSORS
IN OZONE NONATTAINMENT AREAS

-------

-------
                                          PROTECT***
                                            AGENCY

                                         •ALLAS, TBIAf
CRITERIA FOR ASSESSING THE ROLE OF TRANSPORTED
OZONE/PRECURSORS  IN  OZONE  NONATTAINMENT  AREAS
                   MAY 1991
    U. S. Environmental Protection Agency
 Office of Air Quality Planning and Standards
          Technical Support Division
      Research Triangle Park, NC  27711

-------

-------
                        TABLE OF CONTENTS


                                                             Page

LIST OF FIGURES	iii

LIST OF TABLES	iv

1.0  INTRODUCTION 	   1

2.0  ROLE OF TRANSPORT DETERMINATIONS IN IMPLEMENTING CLEAN
     AIR ACT REQUIREMENTS	   3

     2.1  Implications for Modeling and Monitoring  	   3
     2.2  CAA Modeling Requirements and Implications for
          Determining Transport 	 . 	   4

3.0   CONSIDERATION OF TRANSPORT IN THE DESIGN OF CONTROL
      STRATEGIES  	   9

     3.1  Determining Whether an Exceedance is Primarily Due
          to Local Emissions  	   9
     3.2  Determining Likely Contributing  Areas  in Cases of
          Overwhelming Transport  	  15

          3.2.1  A Predominant Source Area is Identified  . .  16
          3.2.2  No Predominant Source Area is Identified . .  17

     3.3  Consideration of Transport in Attainment
          Demonstrations  	  18

          3.3.1  Use of Regional Scale Models	19
          3.3.2  Use of Monitored Data to Estimate Model
                 Boundary Conditions  	  23
          3.3.3  Use of Modeling Procedures to Diminish
                 Importance of Transport   	  26

4.0  MONITORING DATA FOR CHARACTERIZING TRANSPORT IN
     RECOMMENDED MODELS 	  31

     4.1  Data Needed to Support Characterization of
          Transport in Models	31

          4.1.1  Trajectory Models  	  31
          4.1.2  Urban Airshed Model  	  33
          4.1.3  Empirical Kinetics Modeling Approach ....  36
          4.1.4  Regional Oxidant Model 	  37

-------
     4.2  Instrumentation/Deployment  	  38

          4.2.1  Winds, Other Meteorological Data	38
          4.2.2  Ozone	38
          4.2.3  NOX  	38
          4.2.4  CO	39
          4.2.5  NMOC	39

     4.3  Quality Assurance of Monitored Data	40

5.0  SUMMARY	43

REFERENCES CITED  	  49
                                11

-------
                    LIST OF FIGURES
                                                        Page

Multiperiod Back Trajectory With Area Most Likely  ...  12
Contributing to Observed Ozone Identified

Portion of United States Covered By Potential ROM  ...  21
Applications

Future Ozone Transport as a Function of Present  ....  27
Transport

Minimal Ozone Monitoring Network 	  34
                          111

-------
                         LIST OF TABLES

                                                             Page

1    Default Recommendations for Present Transported  ....  30
     Boundary Conditions
                                IV

-------
1.0  INTRODUCTION

     The  intent of  this  document  is  to  present means  (i.e.,

criteria) for assessing  the effect of transported ozone  (O3) and

its  precursors  on  O3  concentrations observed  in  locations not

attaining the National  Ambient Air Quality Standard (NAAQS) for 03.

The  primary  purpose for making  such an assessment is  to foster

design  of  control  strategies  which  are  most  responsive  to

environmental  conditions  prevailing in  a  nonattainment  area.

Therefore, the  criteria discussed  herein address not only current

conditions  but  future periods    (after  control  strategies  are

implemented) as  well.   This  is necessary in order to assess whether

a proposed control strategy is likely to be successful in meeting

prescribed deadlines for attaining the NAAQS for O3.

     This document is prepared in response to Section 184(d) of the

Clean Air Act (CAA)  as  amended in 1990.  Section 184(d) states the

following:

     "For purposes of this section, not later than 6 months after
     the date of the enactment of the Clean Air Act Amendments of
     1990, the Administrator shall promulgate criteria for purposes
     of  determining  contribution   of  sources  in one  area  to
     concentrations of ozone  in another  area which  is  a  non-
     attainment area for ozone.  Such criteria shall require that
     the  best  available  air quality  monitoring and  modeling
     techniques   be   used   for   purposes   of   making   such
     determinations."

     The remainder of  the document  is organized in the following

manner.   Section  2  discusses why  it is important to be  able to

characterize transport.   This is  done  by  identifying  pertinent

requirements  in the  amended Clean  Air Act and  by  noting  how

consideration of  transport is a  prerequisite for meeting these

-------
requirements.  Because  Section 184(d), as well as other portions
of the CAA,  imply the need for quantitative estimates of transport,
modeling  is  recommended as  the  prime  means  for  making  this
determination.    Monitoring  is needed  to  support and  estimate
performance  of  the recommended modeling procedures.   Section 3
describes  the  appropriate   sequence  of modeling  analyses  for
considering transport in the  design  of control strategies.   This
sequence  proceeds  by   first  noting   the   role  of  transport
determinations in  selecting locations in which to apply controls to
most  effectively  reduce O3  during an  observed episode.   Next,
procedures  for  considering  transport  in order to quantify  the
controls  needed  in identified  areas  to  reduce O3  to the  level
specified  in the  NAAQS (0.12  ppm) are described.   Section  4
presents  monitoring  recommendations  (criteria)  for  estimating
transported ozone and precursors needed in  the modeling analyses
recommended in Section 3.  Section 5 summarizes identified modeling
and monitoring criteria  for determining contributions of transport
in downwind nonattainment areas.

-------
2 .0  ROLE OF TRANSPORT DETERMINATIONS IN IMPLEMENTING CLEAN AIR ACT
     REQUIREMENTS.

     2.1  Implications for Modeling and Monitoring

          The  1990  Clean  Air Act  amendments  reflect  a mix of

prescribed  reductions of  volatile  organic  compound  (VOC)  and

nitrogen   oxides   (NOX)    precursors   of   O3  (technology-based

requirements).    The  Act  also  requires  States  to  ensure   that

prescribed emission reductions are sufficient to meet the O3 NAAQS

(air quality management requirements)  in many  nonattainment areas.

It is in meeting  the Act's air quality management requirements  that

proper consideration of transport is important.  This consideration

fulfills several roles:

          (1)  to help identify the primary reason  (i.e., transport

or local emissions)  for an observed "exceedance "* of the NAAQS in

a nonattainment area,

          (2)  to identify an upwind  location(s) most  likely to

contribute  to  (and therefore  the  most appropriate  locations to

apply a set of strategies for reducing) an observed "exceedance",

          (3)  to allow quantitative estimates to be made regarding

reductions in VOC and/or NOX emissions needed in areas identified

as likely  to contribute  to an  observed  exceedance in  order to

remedy the exceedance,

          (4)  to ensure  and track effectiveness of promulgated

control strategies,  and
     *In this^ document, the term "exceedance" is used to denote any
observed daily maximum ozone concentration greater than the level
specified in the NAAQS (0.12 ppm).

-------
          (5)  to  assess  the  extent  of  interstate  transport

throughout designated Transport Regions and assess strategies for

mitigating interstate transport.

     Use of photochemical air quality dispersion models is the only

practical way to meet the third and fifth roles  identified above —

that of assessing  whether contemplated emission control strategies

will be sufficient to reduce O3 to <0.12  ppm and whether interstate

transport  has  been  reduced  sufficiently  to  make  the  goal  a

realizable one.

     The roles  of meteorological and air quality monitoring are

threefold:

          (1)  to provide  information concerning  which areas and

episodes to model;

          (2)  to  provide  input information to models  so that they

might be used to  make  estimates of needed emission reductions in

modeled areas; and

          (3)   to aid  in evaluating the performance  of selected

models.

     2.2  CAA   Modeling   Requirements    and   Implications   for
          Determining Transport

          The CAA amendments categorize ozone nonattainment areas

into five  groups.  These  are,  in descending  order of severity,

extreme,  severe,  serious,  moderate,  and marginal.   Air quality

management-related requirements  are  imposed  in the first four of

these categories.   In addition, rural transport areas, as defined

in ^ection 182(h),  are subject  to the  same  restrictions  as  a

marginal nonattainment area, regardless of the severity of measured

                                4

-------
ozone levels, if it can be shown  that  failure to attain in such an



area is attributable to transport.  Finally, certain small areas,



as defined in Section  185(e),  may be  exempted from sanctions for



failure to attain the NAAQS by a  prescribed  date, if attainment is



prevented by transport  after  all local State Implementation Plan



(SIP) provisions are implemented.



     In extreme, severe, and serious areas,  use of a photochemical



grid  model  is  required  to  demonstrate that  proposed  control



measures will be sufficient to attain the NAAQS by specified dates.



The Urban'Airshed Model (UAM)  is  the grid model recommended by the



EPA for this  purpose, and  is expected to be widely used (Morris, et



al. 1990 a,b; Douglas et al. 1990; Causley 1990; Tang et al. 1990).



     In  moderate  nonattainment  areas,  use of  grid modeling  is



required if  the area  includes territory in more than  one State.



Otherwise, grid modeling is preferred, but the Empirical Kinetics



Modeling Approach  (EKMA)  is also an  acceptable  procedure (USEPA



1989 a-c;  Systems  Applications,  Inc., 1988; Meyer et  al.  1989).



Both the UAM and EKMA are regarded as "urban scale" models.  That



is, the modeling domain ordinarily addressed is sufficiently large



to consider movement of pollutants over 12 daylight hours (e.g., 8



a.m. - 6 p.m.).  Generally, this  has resulted in applications over



domains on the order of a couple hundred kilometers on an upwind/



downwind axis at most.   However,  it is possible to consider larger



domains for urban grid models.  Domain size is usually limited by



data  base management  considerations  and   computer  limitations.

-------
Criteria  for  considering  transport must  address  the  following

issues relating to use of the UAM and EKMA models.

            (1)   Is  use of  one  of these models  appropriate for

modeling the nonattainment area containing the ozone exceedance in

question?  If not, what should be done?

          (2)   What  area/modeling domain  should be modeled to

adequately consider the effects of a proposed control strategy on

an observed exceedance?

          (3)  What inputs are needed to these models in order to

reflect effects of transport?

             (4)  How can the inputs needed for  the  urban scale

models be derived?

     The EPA has published guidance describing suitable procedures

for using the  UAM and EKMA in  attainment  demonstrations (USEPA

1991a, USEPA  1989c).   Much  of the ensuing discussion  regarding

criteria  for considering transport is drawn from these guidance

documents and from Meyer, et al.  1989.  Each model application is

likely to have to respond to  some area-specific characteristics

which  cannot  be  anticipated in  general  guidance.    Thus,  model

application guidance  has  recommended  formation  of working groups

consisting  of  representatives  from  each  State affected  in  a

particular   modeling   demonstration,    appropriate    US   EPA

representatives and other interested parties (USEPA  1991a).   It is

expected that criteria for assessing the role of transported ozone

and  precursors  identified  in  this  document  will  be  treated
                               «r
similarly.  That  is,  a group of general procedures are identified


                                6

-------
herein.   It  will  be  up to  the working  group  responsible  for



developing and implementing a modeling protocol for a specific area



to adapt this general guidance  for  use  in  specific areas.  It is



also  conceivable  that  special circumstances  prevailing  in  a



particular area for which a modeling protocol is being developed



may warrant use  of procedures which differ  from those described



herein.  In such  cases,  the rationale  for  a different procedure



must  be  documented  and  submitted  to  the  appropriate U.S.  EPA



Regional Office for consideration on a case-by-case basis.

-------
This page intentionally left blank
                 8

-------
3.0  CONSIDERATION OF TRANSPORT IN THE DESIGN OF CONTROL STRATEGIES

     In order to quantify effects of transport and to ensure that

transport is  appropriately  considered in the  design  of  a SIP to

demonstrate attainment of the NAAQS for ozone, it is necessary to

use sophisticated, resource  intensive modeling tools.  To conserve

resources, it is useful to focus modeling analysis on locations and

incidents  which,   if  remedied,  would  most  likely  result  in

attainment of the NAAQS.  The discussion in Section 3.0 begins by

describing  several  relatively  simple tools  (trajectory  models)

which may be useful in focusing analyses with complex models (e.g.,

UAM, Regional Oxidant Model (ROM)) needed  to consider transport

quantitatively.   Section 3.0 concludes with a discussion of urban

and  regional  scale  photochemical  dispersion models needed  to

quantify effects of transport in SIP attainment demonstrations.

     3.1  Determining Whether  an Exceedance  is  Primarily Due to
          Local Emissions

     The  first  step  in  assessing  the role  of  transport is  to

determine   whether   transport   is   so  overwhelming  that   the

contribution  of  local  emissions  to   an  observed exceedance  is

relatively  minor.   Such a  case  is referred  to  as  "overwhelming

transport".    Procedures  described in this  step  are useful  in

selecting episodes  to test whether  local  control measures  are

sufficient to eliminate  exceedances which are  largely attributable

to local emissions.  In many cases,  there may be an upwind/downwind

gradient in observed 03 concentrations and/or man-made VOC and NOX

emission density is much greater in the Consolidated Metropolitan

Statistical Area  (CMSA)  or  Metropolitan  Statistical Area  (MSA)

                                9

-------
under consideration than in surrounding locations.  In such cases



it is the prerogative of  those responsible for the area's modeling



protocol   whether   to   perform   an  "overwhelming   transport"



determination using more rigorous procedures described below.  If



it is decided that a  rigorous overwhelming transport determination



is unnecessary,  the analyst should proceed to Section 3.3.  Failure



to perform  an adequate "overwhelming transport"  analysis  when a



detailed  analysis is warranted  could  lead to  very  stringent



prescriptions   for   control   of  local  emissions.   While  such



prescriptions might possibly work, they may not be a particularly



efficient way to eliminate an exceedance which is largely a result



of transport from external sources.



     If an assessment of overwhelming transport is performed, the



approach generally recommended is to perform trajectory analyses to



assess  the  likelihood  of  overwhelming  transport.    The  model



ordinarily recommended for this purpose  is  the  US EPA TRAJECTORY



model (Meyer, et al.  1989).  However, as described shortly, other



trajectory  models may be  used  if  it can  be  shown  that  use of



surface wind measurements alone inadequately describes transport.



The EPA TRAJECTORY model  uses surface wind data to  construct a back



trajectory from the site of the observed exceedance, beginning at



the time of the daily maximum O3 concentration observed on the day



of the exceedance.



     There is usually considerable uncertainty regarding the exact



position  of  an   air  parcel   nominally  following  a  computed



trajectory.  The TRAJECTORY model  incorporates this by considering





                                10

-------
variability in wind data noted at nearby stations.  The further one
progresses from  the back trajectory's starting  point  (i.e., the
ozone monitoring site  recording  the exceedance)  the greater this
uncertainty becomes.  As  a result,  one obtains a  cone-like figure,
emanating from the  monitoring  site,  which describes the. probable
position  of   pollutant-laden  air  during  periods  preceding the
observed  exceedance.   This  is shown  conceptually in  Figure  1.
Figure 1 depicts a back trajectory from a monitoring site with an
observed  daily maximum O3 concentration  at  2:00 p.m.   The  "Vit"
represent distance traveled during  each hour.  The 6± are measures
of  uncertainty whose  derivation  is  described  in Meyer et al.
(1989).  Significance of the shaded area will be described shortly.
     The trajectory is computed  using  surface  wind data from all
National  Weather Service  and other suitably sited wind monitors
(see  USEPA,   1987)  within  160  km  of  the  most  likely  computed
position  of an air parcel following the  trajectory at  any  hour.
Because the nighttime surface layer may be very  shallow and winds
aloft may differ  significantly  from surface observations at night,
TRAJECTORY may only be  applied  for  daytime hours  (e.g., 8 a.m. - 8
p.m.).
     An  underlying  assumption  in the  USEPA   TRAJECTORY  model
application for identifying overwhelming  transport is that  if  an
air parcel corresponding with an observed  exceedance is within the
nonattainment  area  during 8 a.m.  - 12  noon on the day of the
exceedance, there  is  a good chance  that local  emissions play  a
significant role in causing the exceedance.   This assumption is

                               11

-------

-------
supported  by diurnal  meteorological  conditions  as  well  as  by



typical  diurnal  emission  patterns  for  many  important  source



categories of VOC and NOX precursors for O3.  Thus, if all or part



of the local CMSA/MSA containing or in close proximity to the site



with the observed exceedance falls within the shaded area in Figure



1, it can be assumed that its  emissions play a significant role in



leading  to  the  observed exceedance.    As noted  in Meyer et al.



1989, if the average resultant wind velocity is low,  it should be



assumed  the  local area  contributes  to the exceedance.   If such a



finding  is made, the analyst can skip Step 2 in the procedure for



considering  transport  (i.e.,  Section 3.2) and proceed to Step 3



(Section 3.3).   If a finding of overwhelming transport is made, the



episode  in question can be ignored in the local area's attainment



demonstration unless  it  is  not possible  to identify an upwind



CMSA/MSA(s)  likely  contributing to the observed  exceedance.   In



this case, see the discussion in Section 3.2.2.



     It  should  be noted that  it is possible for the  TRAJECTORY



model to yield misleading  results  under some circumstances.  For



example,  if  an  exceedance  occurs as  the result of  mid-morning



fumigation  of   ozone   which   remains  aloft  overnight,   it  is



conceivable  that this   is  a  result  of  transport  rather  than



recirculated  locally   generated  pollution.     For   exceedances



occurring  at 11  a.m.,   local  civil  time (LCT), or  earlier,  a



trajectory model such as the Atmospheric Transport and Dispersion



Model (ATAD) or  the Branching Atmospheric Trajectory  model (BAT)



(Heffter 1980,  1983)  is recommended to assess the likelihood  of





                                13

-------
overwhelming  transport.    These  models  utilize  upper  air data.
Prior to applying such a  trajectory model,  the modeling protocol
working group should consider whether  the  exceedance  is  due to
fumigation.  Review of available diurnal  mixing height information
and time series  analysis of air.  quality data may  be  helpful in
distinguishing a  fumigation-induced problem from one  resulting from
photochemistry  relatively  early  in  the  day.   If  a  multiday
trajectory model  is used to assess likely sources of  a morning
exceedance, attention should be given to  MSA/CMSA's  traversed by a
swath  surrounding the trajectory from  8  a.m. -  6 p.m.  on  the
preceding day.   Width of the swath  is a function of  uncertainty
associated with  the  trajectory  estimates.    Uncertainty  can be
determined by a  climatological  review  of  trajectories computed
under similar synoptic conditions and wind patterns.
     The TRAJECTORY model  generally remains the model of  choice for
addressing exceedances occurring after 11 a.m., because it utilizes
more  dense surface  monitoring networks  and  its application is
confined to  periods of  the day when wind shear  is likely to be
minimized.    Thus,  surface winds would be more representative of
flow  in the mixed  layer  in  most  locations.   Choice  of  the
trajectory model and its underlying rationale must be documented by
the working group preparing a modeling protocol and is subject to
review by the U.S. EPA.
     It is next appropriate to consider  rural transport areas, as
described  in  CAA  Section  182(h),  more  explicitly.     Use  of
trajectory models,  as described  in the previous  paragraphs, is

                                14

-------
generally the preferred approach for confirming that an area, which

otherwise qualifies,  may be treated  as a rural  transport area.

However,  it  may happen  that the wind  data available  near such

locations are too sparse  to  be  reliable,  or available trajectory

models are otherwise unsuitable.   If the working group responsible

for a modeling protocol determines that available trajectory models

are  inappropriate  for  the  purpose  of  identifying overwhelming

transport into  a proposed rural transport area,  the  reasons for

this determination should be documented and are subject to review

by the  U.S.  EPA.   If the EPA agrees  with  this assessment, other

methods  may  be  used  to   justify   treatment  of  a  candidate

geographical location as  a rural  transport area.   An  area may be

treated as a  rural  transport area if justified by the  weight of

supporting evidence of two or more of the  following types  (l) NOX

and VOC inventories  are much  less  than those in locations where it

is plausible to believe pollution may be  originating,  (2)  a past

photochemical grid  modeling  analysis supports the hypothesis of

overwhelming transport, (3) a field study supports the likelihood

of overwhelming transport, or (4) other pertinent guidance can be

presented.  If an area is  determined to be  a rural transport area,

exceedances occurring  therein  should be considered in  selecting

episodes to model and in the  choice of modeling domains for nearby

CMSA's/MSA's.

     3.2  Determining  Likely  Contributing  Areas  in  Cases  of
          Overwhelming Transport

          Once it is  determined that  "overwhelming transport" is

likely, the  next  step  is to  try to establish  the most  likely

                               15

-------
predominant  source(s)  of  an  observed   "exceedance".    If  the



TRAJECTORY model  is  used,  this is done by  noting any CMSA/MSA's



located completely or partially within the shaded area in Figure 1.



If a model using upper air data is  used to estimate the cause of a



morning exceedance, CMSA's/MSA's located within a swath surrounding



the trajectory during 8 a.m. - 6 p.m. of the preceding day should



be identified.  As noted in Section 3.1, the width of the swath is



a function of uncertainty in the trajectory path as estimated from



climatology of the area with the observed exceedance.  Results of



applying  any  of the  trajectory models  may yield any of several



outcomes:



          (a)  One of the  identified CMSA/MSA's has  many more NOX



or VOC emissions than any of the other identified CMSA/MSA's.



          (b)   Several  CMSA/MSA's  are identified, but  it  is not



obvious   which   one(s)   exerts  the  predominant  influence  on



transported ozone/precursors;



          (c)  No CMSA/MSA's are identified.



     3.2.1  A Predominant Source Area is Identified



          If the emissions of NOX  or VOC in one of the identified



CMSA/MSA's  greatly exceed those in the others,  it may be assumed



to be the predominant cause  of the observed exceedance.  In this



case, the episode in question should  be among those considered for



modeling  for this upwind  CMSA/MSA.    Procedures for  selecting



episodes to model with UAM or EKMA are described in USEPA 1991a and



in USEPA  1989c, respectively.  If the UAM is used and the episode



in question  is  one of those  selected for modeling,  the downwind





                                16

-------
boundary of  the  modeling domain for this  upwind CMSA/MSA should



extend beyond the monitoring site, as described in USEPA 1991a.



     3.2.2  No Predominant Source Area is Identified



          Outcomes (b) or (c) above are possible if an exceedance



is the.composite effect of emissions in many areas or is a result



of multiday transport.  Several approaches are possible if one of



these outcomes  occurs.   First, if  there are  a number  of  such



incidents,  this  might  serve  as  one  consideration  in  deciding



whether to petition the EPA Administrator to establish a Transport



Region in  accordance with Section  176A  of the  CAA.   Cumulative



effects  of  SIP's  in  several   CMSA's/MSA's  or  States  are  best



simulated with regional scale models, such as the EPA ROM, (Lamb,



1983) used in concert with urban scale models.  Regional models are



also the  recommended  approach for quantifying interstate transport,



as required in Transport Regions.  Application of ROM and its role



in assessing effects of transport will be described more fully in



Section 3.3.



     If there is  a limited number of  "unattributed" exceedances, it



may  be  possible to  address  the  problem without establishing  a



Transport Region.  A  second approach could be  use of an urban scale



photochemical  grid model, like the  UAM,  and  a large  modeling



domain.   The  domain  would encompass monitoring  site(s)  observing



unattributed  exceedances  as  well  as  the  several  CMSA/MSA's



identified  through  use  of   trajectory   methods   as  potential



contributors to  those  exceedances.   The  episode(s)  including the



unattributed  exceedances would be  among those considered  for





                                17

-------
simulating over the large modeling domain  (USEPA, 1991a).  In such
cases, the effect of emissions in  one or several CMSA/MSA's on air
quality downwind can be assessed through model sensitivity tests.
     If it is not feasible to  exercise either of the preceding two
approaches, it would be necessary  to focus once again on the local
area's attainment demonstration.   As noted  previously,  it is not
necessary to simulate  effects  of  local  controls  on an exceedance
which is a product of overwhelming transport.  Instead, it should
be treated as an "irreducible exceedance".
     If EKMA is used for the local  area's attainment demonstration,
guidance with respect to irreducible exceedances presented  in Meyer
et al. 1989 should be followed.  In essence,  this requires reducing
the number  of  incidents in which  an exceedance  is allowed after
simulation  of   proposed   controls.     A   similar  procedure  is
recommended if a photochemical  grid model (e.g., UAM)  is used.  For
example, suppose guidance in USEPA 1991a  permitted one post-control
modeled  exceedance.   In  this case,  presence  of  one   or  more
irreducible exceedances would mean that a proposed control strategy
would  no  longer be acceptable  if it  resulted  in any  modeled
exceedances.
     3.3  Consideration of Transport in Attainment Demonstrations
          The   preceding  two  sections   addressed  qualitative
procedures  for  identifying  location(s)  most  likely  to  be  the
primary  cause   of  an  observed  exceedance.    Once  these  are
identified, an urban scale modeling analysis should be focused on
the  identified  area(s)  using guidance in  USEPA  199la  or USEPA

                                18

-------
1989c.  An  identified area is, by  definition,  one whose control



strategies may significantly affect whether  an observed exceedance



is eliminated.   Effectiveness of  controls  in such  an  area may,



nevertheless, be  influenced by transport.   The purpose  of this



Section is,to present recommendations for considering transported



ozone and precursors  in  urban  scale modeling used for attainment



demonstrations.    In  attainment  demonstrations,  transport  is



considered  by  specifying  boundary  conditions  for urban  scale



models.  Approaches for doing this are enumerated below.



     3.3.1  Use of Regional Scale Models



          The preferred approach for generating boundary conditions



for urban scale modeling applications is to  "nest" the urban scale



modeling  domain  within  a  regional  modeling  domain.    Typical



regional modeling applications consider domains on  the  order of



1000 km or more  on a side.  Regional scale modeling simulations are



begun two or more  days prior to the period to be  simulated by using



a  gridded  photochemical model  such  as  the US  EPA's  ROM.   The



regional model is  used to simulate base case  boundary conditions as



well as regional impact of  control  strategies likely to be applied



in  and between  the  various  CMSA's/MSA's   within  the  regional



modeling domain.   The  procedure   followed  in the  regional (and



urban) modeling analysis is to  assume past meteorological episodes



corresponding with high ozone are characteristic  of future episodes



with ozone-conducive conditions, and apply a control strategy for



some future  year.   Generally, the year chosen would be the year in



which the CAA specifies  attainment  of the NAAQS should be reached.





                                19

-------
As  noted in  CAA Section  181(a),  this  varies  according  to how
serious the present ozone problem is for a CMSA/MSA.
     Use of a gridded regional model requires  a  large amount of
computer  capacity.     Further,  the  domain  is  often  likely  to
encompass many political jurisdictions, making it difficult  to have
access  to the  requisite  emission  information  over  the  entire
domain.  This latter problem can only be  overcome if States submit
point, area and mobile source information to some centralized data
system which can be  accessed by the regional model.   Because of the
difficulties  listed in this paragraph, it is recommended that the
US EPA ROM model be  used as the  model of  choice whenever feasible.
     States should submit emissions data to the US EPA's Aerometric
Information Retrieval  System (AIRS)  data base  (USEPA,  1989d) by
November 1992, so that regional modeling  efforts might make use of
these estimates within the  limited time  allotted by the Clean Air
Act.  The US EPA will run ROM for as many  episodes and locations as
resources permit.   Figure  2  depicts  that portion  of  the  United
States for which it  will be  possible to run ROM within the next 3-4
years.   Clearly,  the task  of ensuring consistent  data bases and
strategy assumptions in regional and urban scale modeling analyses
requires  extensive  coordination.     For this  reason,  whenever
regional  models are used,  the  EPA should be represented  on the
technical or  policy work group responsible  for conducting urban
scale attainment demonstrations.
     An  infrastructure exists  to  enable  States  to readily access
and use the results of ROM  simulations as input to their urban

                                20

-------
                                                 PQ

                                                 •a
                                                 
                                                  3

                                                  CX)
21

-------
scale modeling  analyses.    States  may access  ROM-generated data
using  the  Gridded  Model  Information  Support  System  (GMISS)
(Computer Sciences Corporation,  1991).   The US  EPA archives air
quality  predictions   as   well  as   certain   input  information
corresponding with each application  of  ROM into GMISS.   Groups
using the UAM can  readily make use of data retrieved from GMISS
using the ROM/UAM  Interface Program  System (Tang  et  al.  1990).
Similar means exist for using data  retrieved from GMISS if EKMA is
used (USEPA, 1991b).
     As implied by  Figure  2, there  are locations  within the United
States where it will  not be feasible to use  ROM in the foreseeable
future.   Further,  ROM results  may  not be available for  every
episode which is of interest in every nonattainment area.  Use of
alternative regional scale models to generate boundary conditions
for  urban  scale models   is  acceptable.   Such use  should  be
specifically addressed in modeling protocols  developed  for each
urban modeling  application, and  coordinated with the appropriate
U. S. EPA Regional  Office(s) for  approval on a case-by-case basis.
     Use  of regional  scale  models is  the preferred  method for
considering  transport  into a  nonattainment  area for  several
reasons.  First,  it is  the most  defensible means  for estimating
boundary  conditions   (i.e.,  transport)  after  implementation  of
regional  and  urban  strategies   in   upwind areas.    As  noted,
attainment demonstrations  must  focus on future periods specified in
the  Clean Air Act.   Therefore,  credibility of  estimated future
transport is  a  key consideration.   A second  advantage  of using

                               22

-------
regional models is that they provide a far more comprehensive set

of present  boundary  conditions than is  feasible  using any other

method.  This,  in turn, replaces much of the subjectivity necessary

in specifying present boundary conditions using other means.  For

example, the Urban Airshed Model generally considers five or more

vertical layers  in the atmosphere.   It is  necessary  to specify

boundary conditions  for each grid  cell  in each  of  these layers

along a domain's upwind boundary for each hour simulated.  As noted

in Section 3.3.2, it is impractical to collect monitored data for

each  of these  grid squares.    If  monitoring  data rather  than

regional models  are  used  to  specify  boundary  conditions,  the

specifications  must be based  on  a  limited  number  of  direct

observations and interpolation or some other, subjective procedure.

    3.3.2 Use  of  Monitored  Data  to  Estimate  Model  Boundary
          Conditions

          If it is not possible to  use a regional scale model to

generate boundary conditions for urban scale models, an alternative

approach is  to derive  estimates of boundary. conditions  based on

available air quality monitoring data.  If the UAM  is used, Section

4.2.6 in Morris et al.  1990b shows grid cells in the UAM modeling

domain  for  which boundary conditions must be  specified  for each

hour of the simulation.  As described in Morris et  al. 1990b, it is

possible to divide the modeling grid's boundaries into subsegments.

This may be useful  if monitored data suggest a distinct horizontal

concentration gradient along the modeling grid's boundaries.  The

UAM software permits use of two  procedures for estimating hourly

boundary concentrations  in surface level grid  cells comprising each

                               23

-------
segment of the domain's boundaries.  The first of these assumes a
constant concentration (of O3,  precursors)  for each segment.  The
second   approach  performs   a   linear  interpolation   between
concentrations specified at each segment's end points to estimate
boundary  conditions  in  each  surface  grid  cell  included in  a
boundary segment.   Morris et  al.  1990b note that  the procedure
generally  followed is  to assume  a  spatially  invariant   (i.e.,
constant) concentration for cells in each segment.
         The UAM software also contains provisions for specifying
hour-by-hour boundary conditions in grid cells  aloft.   These are
described in Section 4.1.7 of Morris et  al. 1990b.  Two procedures
have been most commonly used in past applications of UAM:
          (1)   Assume  a  concentration which  is  constant with
height;
          (2)   Specify a vertical concentration profile pattern
which  varies  between  a  concentration estimated,  as  described
previously, in a surface grid square and a concentration specified
or  calculated  previously  in  a grid  cell  just  above  the  mixing
height (i.e., DIFFBREAK).
     The  first method  is the simpler of  the two  and  may  be
justified, particularly during times of  day with vigorous vertical
mixing.  The second method is seemingly  more  sophisticated but, if
used,  a  rationale for  the  selected  vertical  profile  should  be
included in  the protocol describing the technical  basis for the
attainment demonstration.   In the second  method, concentrations
                                24

-------
above DIFFBREAK are usually initially assumed to be at background



levels (see Section 3.3.3).



     It may often  happen that monitored data  for  ozone exist to



enable specification of boundary conditions,  but there are no data



for the NO, NO2, CO, and  VOC species which must also be specified.



In this case,  information in Table  1  (see Section 3.3.3) will have



to suffice for specifying values for unmonitored species.



     Boundary conditions are  considered somewhat  differently if



EKMA is  used.   In the  OZIPM4 model underlying EKMA,  one models



concentrations within  a moving column  of  air.  As  described in



USEPA  1989c,  the  simulation  begins  at 8 a.m.  on  the  day  of an



observed exceedance,  with the  column  located  over the central city



in  the modeled  CMSA/MSA.    The  column  follows   a  straightline



trajectory which places  it at the monitoring  site recording the



exceedance at the time of the exceedance.  During the simulation,



the column grows in height to reflect the typical diurnal rise in



mixing height.  As the column height grows, air is entrained from



aloft.   Boundary conditions are  considered by specifying ozone and



precursor concentrations  in this layer aloft at the beginning of



the simulation.  These specified  concentrations  aloft are invariant



with time.



     As  noted  previously,  for  attainment  demonstrations,  an



estimate of future transported ozone  and precursors is needed.  In



the absence of regional models,  Figure  3 has  been used to estimate



future transported O3, given  an observed  level of transported O3



(USEPA 1989c).  To illustrate use of the Figure,  suppose a boundary





                                25

-------
03 concentration for an isolated urban area is estimated to be 0.10



ppm.  The corresponding future boundary condition for O3 would be



0.09 ppm.  Figure 3 is based on application of OZIPM4/EKMA with a



20 percent reduction in VOC, no  change  in VOC speciation,  and no



change in  NOX.   Thus,  for consistency, these latter assumptions



should be  used in  conjunction  with Figure 3.   In  the absence of



better information, this methodology  may  be  applied for use with



UAM  as  well  as  with EKMA.   Use  of  alternative  procedures  for



estimating future  transport  in the absence  of regional modeling



must be  justified, and is  subject  to  approval by the US EPA on a



case-by-case basis.



     3.3.3  Use of Modeling Procedures to Diminish Importance of



            Transport



         Barring an intensive field study, it is clear from Section



3.3.2 that specification of  present  boundary conditions based on



monitoring data requires a number  of  arbitrary procedures and/or



subjective judgment.  Unfortunately, even when intensive field data



are  available, the period of  an intensive  study  often  will  not



coincide with O3 episodes of greatest interest.  Further, the basis



for  estimating   future   boundary  conditions   is   not  strong.



Therefore,  it  is  appropriate  to  consider  ways   in  which  the



sensitivity of model predictions to assumed boundary conditions can



be diminished.



     Sensitivity of  UAM predictions  to  boundary  conditions  can



likely be diminished by increasing the size of the modeling domain
                                26

-------
                                                o
                                                 cc.
                                                 UJ
                                                 e:
                                                 a.
                                                 o

                                                 o
                                                 o
                                              CO  «
                                                 <

                                                 to
                                                 c;
                                                 o
                                                 Q.
                                                 LLj

                                                 o

                                                 o

                                                 LLJ
                                                 c;
                                         O
                                         a\
                                         CO
3N020 3yninj

-------
on the upwind side of the CMSA/MSA which is the focus of attention.

There are, of  course,  practical limits to this  in  terms of data

base management and computer constraints.  Further, a tradeoff must

be made against the desirability of  extending the domain downwind

beyond the location of  monitors observing exceedances attributable

to the CMSA/MSA being modeled.

     Table 1 contains  recommended default  inputs for  boundary

conditions contained in USEPA 1989c.  Defaults may be used if the

UAM modeling domain is  enlarged,  as described  above.   The recom-

mendations   for  nonmethane  organic   compounds*   (NMOC),   NMOC

speciation, and O3 are  based on a review of aircraft observations

in an  unpublished report by  Baugues  (1987).   Subsequent  to the

Baugues  (1987)  review,  doubt was cast  on the  observed NOX data.

Hence the NOX defaults  are based on  earlier recommendations (USEPA

1978).   Recommendations for  CO  are  based on a review  of  data

produced from sampling aboard aircraft during the 1980 PEPE/NEROS

study.  The CO recommendation differs   from that in USEPA (1989c).

The recommendations made herein are believed more representative of

available  data  and   should   supersede  the   CO  default  value

recommended  in  USEPA  (1989c).   In the absence  of  better,  area-

specific information,  these defaults may be assumed to be constant

vertically and  horizontally.   In USEPA 1989c,  it  is  noted that

future levels  of  NMOC  and CO may be  reduced  20  percent, and NOX

kept constant.  NMOC composition  is kept constant.
     "The term "nonmethane organic  compounds"  applies to ambient
measurements of organic compounds.

                                28

-------
     Recommendations  in  Table  1  differ  from  some  published



elsewhere for use with the UAM (Morris et al. 1990c).  The Morris



et al. (1990c) recommendations are  based on observations in more



remote areas, whereas those  in Table  1  are based on observations



upwind and aloft of several  cities.   Unless the upwind bounds of



the  UAM  modeling  domain  are  reflective  of  a  remote  area,



information  in  Table  1  would appear more  appropriate.    If  the



Morris et al. (1990c)  recommendations  are considered more suitable



in specific  cases,  future boundary conditions  should  be assumed



identical to present  boundary conditions.   This  is appropriate



since the  Morris et  al. (1990c)  suggestions  are  believed more



reflective of natural background.



     As described in USEPA 1989c, the values in  Table 1 may be used



as defaults  for the  layer  aloft  considered in  the OZIPM4/EKMA



procedure.  As with the  UAM,  the defaults  for  NMOC and CO may be



reduced by 20 percent for future boundary conditions.
                               29

-------
                              Table 1








DEFAULT RECOMMENDATIONS FOR PRESENT TRANSPORTED BOUNDARY CONDITIONS








           NMOC                   30 ppbc



             CBIV Speciation



             (Carbon Fractions)
             03
             NOX




             NO




             CO
 *Source:  PEPE/NEROS Study









40 ppb
2 ppb
0 ppb
350 ppb*
PAR
ETH
OLE
ALD2 =
FORM =
TOL
XYL
I SOP =
NR




0.498
0.034
0.020
0.037
0.070
0.042
0.026
0
0.273




                                 30

-------
4.0  MONITORING DATA FOR  CHARACTERIZING TRANSPORT IN RECOMMENDED
     MODELS

     An obvious question to ask upon  reading  Section  3.0 is, "What

monitoring data are needed  to  drive  the methods used to estimate

boundary conditions for use with  UAM and EKMA?"  This subject is

addressed in Section 4.   For serious, severe, and extreme  O3 non-

attainment areas,  recommendations contained herein must be regarded

as interim.   Monitoring  for these  locations will be subject to

regulations for  enhanced  monitoring networks in accordance with

Section 182 (c)(l) of  the  Clean Air Act.  These  regulations are to

be promulgated by June 1992.  Recommendations in  this  Section which

are inconsistent with  those future regulations will be superseded.

The discussion  below  proceeds  by noting meteorological  and  air

quality data needed to support each modeling procedure described in

Section 3.   Next,  suggestions are made for sampling and analysis to

obtain  the data identified as necessary.  Section 4 concludes with

recommendations regarding quality assurance of collected data.

     4.1  Data Needed to Support Characterization of Transport in
          Models

          4.1.1  Trajectory Models

               As described in Sections 3.1 and 3.2, the trajectory

models are  used to establish which CMSA/MSA(s) is (are) most likely

contributing to an observed exceedance.   The key data required by

the U.S. EPA TRAJECTORY model are hourly National Weather Service

(NWS)  surface  wind data measured within 160 km of the most probable

location of an air parcel  during each hour from  8 a.m., LCT to the

time of  the  observed  daily maximum O3  concentration at  the 03


                                31

-------
monitor  recording  an exceedance.   Because  of concern  over the



representativeness of surface data at night,  only  8 a.m.  - 8 p.m.,



LCT,  surface  wind  data  recorded  on  the  day(s)  of  an  observed



exceedance are needed.  Table B-l in Meyer  et al.  (1989)  lists NWS



sites for which data may be ordered.



     It is desirable to use as many wind observations as possible



to construct trajectories with TRAJECTORY.  However, prior to using



additional observations, a note  about NWS  wind data  is in order.



These data  reflect  observations  taken over  a  few minutes during



each hour rather than continuous  hourly averages.  Allowances have



been made in the TRAJECTORY model for this.   It  is  recommended that



data used  to  supplement the NWS  observations  be  compatible with



this characteristic.



     Two kinds  of  ancillary data are  useful with the TRAJECTORY



model.   These  are   surface  O3  measurements and  upper  air wind



observations.    Upper air wind data are useful  as  a guide to test



whether  adjustments  made  to surface  data  by  TRAJECTORY  are



appropriate.     These  adjustments   are  made   to  make  surface



observations more representative of mean  hourly winds  in  the mixed



layer.   Clearly,  if a trajectory model, like  BAT or ATAD,  which



requires use of upper air  data is used, upper air  wind information



is not ancillary, but essential.   In ATAD and BAT, upper air data



are used directly to estimate mean mixed layer winds or to estimate



winds in discrete layers.



     Ozone  data  are  useful for  testing  the  plausibility  of



conclusions drawn  from trajectory models  about  whether or not





                               32

-------
overwhelming transport is  likely.   Time  sequences for ozone data



observed along  the  track of an  estimated  trajectory may provide



additional support for conclusions reached using the wind data.



          4.1.2  Urban Airshed Model



               The Urban Airshed Model makes  use of a wide variety



of meteorological and  air quality data.   These  are  described in



Morris et al.  (1990b) and in USEPA  (1991a).  The discussion herein



dwells solely on data useful to characterize boundary conditions.



It is desirable to have air quality data collected at the surface



and aloft (especially during periods of atmospheric stratification



like nighttime).  However, collection of data aloft is a resource



intensive operation which  needs  to  be designed on a case-by-case



basis.   The  following  discussion addresses  minimum  surface data



needed to avoid having to rely entirely on the large domain/default



assumption methodology described in Section 3.3.3.



          Figure  4  is  a conceptual  picture  of  a minimal  ozone



monitoring network  suitable for use  with  UAM.   For  purposes of



illustration, conditions conducive to high ozone most frequently



occur with winds from Ux.  Second most conducive conditions occur



with winds from U2.



     The  following  presents  rough guidance for  the siting  of



monitors in the network shown in Figure 4.



     Site 1:    15-50 km in the predominantly  upwind direction from



               the city limits.   Minimum distance upwind



               should be determined on a case-by-case basis,
                                33

-------
   U2
              0)
     U1
                                             (4)
                                    (3)
                           (2)
                                       (5)
CENTRAL CITY
   LIMITS
FIGURE 4.  MINIMAL OZONE MONITORING NETWORK
                      34

-------
               depending on city size and surroundings.  Data from



               this monitor are to be used primarily to estimate O3



               transported  to   the   model   domain  from  upwind



               sources.



     Site 2:   Near the  predominantly downwind edge  of  the city



               limits.



     Site 3:   15-35 km from the city limits in the predominantly



               downwind direction.



     Site 4:   30+ km  from the city  limits  in the predominantly



               downwind direction.



     Site 5:   15-50  km  in  the second  most  prominent  downwind



               direction.



     Under the first set  of meteorological conditions  (UJ , Site 1



is useful for estimating boundary conditions.  Data from Site 5 may



also be  useful  if,  like  Site 1, it measures  ozone on a regional



scale as defined in 40 CFR 58,  Appendix  D.   Data  from Site 4 may



supplement those from Site  1 in  establishing boundary values under



the  set  of  conditions depicted by U2,   providing the data  are



regional in scale (40 CFR,  Part 58,  Appendix D) .  Data from sites



not used for specifying boundary conditions may be used to assess



model performance in predicting observed ozone concentrations.



     Care must  be  taken in interpreting surface  ozone  data  for



establishing transport during periods of high atmospheric stability



(e.g., night).  During such periods, surface data are unlikely to



be representative of concentrations  aloft.  In  the  absence of more
                                35

-------
direct measurements  or  indicators of ozone  aloft,  the following



approximation of ozone aloft may be used:



     Use the higher value of the observed surface concentration for



the hour in question, or the surface ozone concentration averaged



over 9-11 a.m. LCT on the following morning.



Precursors



     For purposes of characterizing boundary conditions for NMOC,



NOX,  and  CO,  sampling may be performed at sites (1),  (5) and  (4) in



that order of preference.   Care should be taken to ensure that the



sampling  sites  are  well-exposed.   Sampling for  NMOC  within  a



vegetative canopy  is unacceptable for  purposes  of characterizing



regional boundary conditions.



     As  with 03,  there  is  a  concern that nighttime  surface



precursor data are unrepresentative of precursors aloft.  Unlike 03



however, the concern  is that surface observations will overestimate



concentrations aloft.  In  the  absence  of more direct information



regarding concentrations aloft, during  nighttime, the lower  of the



observed hourly  surface  measurement and the surface measurement



averaged over 9-11 a.m.,  LCT, on the  following morning may be used



to approximate nighttime NMOC,  NOX and CO aloft at regional sites



intended to  measure  transport.   During daylight  hours, ozone and



precursor data should be used as described in



Section 3.3.2.



          4.1.3  Empirical Kinetics Modeling Approach



               Unlike UAM,  EKMA only requires one  assessment of



boundary values for O3, NMOC, NOX, and CO per day.  As described in





                                36

-------
USEPA 1989c,  the  period chosen is the  first  full hour occurring



after breakup of the nocturnal inversion.   If  this is not known, a



10 a.m.  -  12 noon LCT  average  surface  concentration observed at



upwind,  regional  sites  may  be  used.    For  ozone,  a  minimal



monitoring network similar to that in Figure  4 is suggested.  The



discussion in Section 4.1.2 also applies.   Sampling of transported



NMOC, analysis  of speciated  NMOC data and  sampling/analysis of



transported NOX  and CO, though desirable, has  a lower priority with



EKMA than with UAM applications.



          4.1.4  Regional Oxidant Model



               Because  of  the spatial  scales involved  with this



model, specification  of its boundary conditions  is  likely to be



less  critical  than   is  the  case for  urban  models.    However,



measurements of  regional ozone/precursors concentrations within the



regional domain may be useful for evaluating ROM model performance.



Monitored ozone data may be used to establish boundary values for



ozone in ROM using applicable  guidance described in Sections 3.3.2



and 4.1.2 for UAM.  Use of a natural background default value for



ozone (Morris,  et al. 1990c)  is an acceptable alternative in the



absence  of  suitable  monitored  data.    Once   boundary values  are



specified for ozone,  a routine in the ROM  establishes  chemical



equilibration with  the  specified ozone concentrations  to derive



concentrations  for   other  chemical  species.     Hence,   it  is



unnecessary for the user to specify these values.
                                37

-------
     4.2  Instrumentation/Deployment



          4.2.1  Winds, Other Meteorological Data



               Guidance provided in USEPA (1987) should be followed



with respect  to instrumentation  and deployment at  surface wind



monitoring sites.  Meteorological data aloft will be derived from



sounding information collected twice daily at sites approximately



500 km apart.   These data  are  archived  and may be obtained from



the National Climatic Data  Center in Asheville, NC.  Data collected



in special field studies such as the  Lake Michigan Ozone Study and



the Southern  Oxidant Study should also be  used if available for



periods of interest.



          4.2.2  Ozone



               Ozone should be  measured as described in Appendix D



to  40 CFR,  Part 50.   For  characterizing transport with  UAM and



EKMA, these measurements should be on a regional  scale (40 CFR,



Part 58, Appendix D).



          4.2.3  NOX



               UAM  and  EKMA require  measurement of  both nitric



oxide (NO) and nitrogen  dioxide  (NO2).  Transported  NO, NOX, and NO2



should  be measured using  alternative A  (gas  phase titration)



described in Appendix F  to  40 CFR, Part 50.   Measurements should be



collocated  with the regional  scale  ozone  measurements  used to



characterize ozone  boundary conditions.
                                38

-------
          4.2.4  CO



               Carbon monoxide should be measured as described in



Appendix C to 40 CFR, Part 50.  Measurements should be collocated



with regional scale ozone measurements.



          4.2.5  NMOC



                  Procedures  for  sampling and  analyzing ambient



organic compounds are rapidly  evolving.  It is no longer sufficient



to  use  procedures outlined  in Appendix  E to  40 CFR,  Part 50.



Instead, it  is  recommended that sampling  be done remotely using



canisters.   Contents  of the canisters  may be analyzed in a central



laboratory.   Sampling  procedures  and care  of the  canisters is



described by McAllister et al. (1990).   Collection  of canister data



to provide hourly boundary conditions  for use in UAM would present



very difficult logistical problems.  Therefore,  if  it  is decided to



sample boundary conditions  for NMOC using canisters, this will most



likely have to be done on a discontinuous,  sporadic basis.  Three-



hour samples collected mid-morning  (9-12),  early afternoon (12-3),



late afternoon (3-6),  and at night (8-11)  at 6-day  intervals during



the ozone season, may provide a sufficient basis for establishing



representative boundary conditions  and diurnal patterns needed for



the  UAM.    Whether  an  NMOC  sampling program  for. UAM  boundary



conditions should be  undertaken is  a  decision  most appropriately



made by those responsible for  deriving the  modeling protocol for a



CMSA/MSA7s attainment demonstration (USEPA I991a).  If performed,



sampling should be done at  regional  scale monitoring locations (40



CFR, Part 58, Appendix  D).  Due to large concentration gradients





                               39

-------
likely near vegetation,  sampling should be out  in  the  open,  not
within a canopy of vegetation.
     Sampling needs for estimating boundary NMOC  for use with EKMA
are-somewhat  less  demanding.   Consistent  with the  discussion in
Section 4.1.3, sampling needs  to  be performed over a single 3-hour
period from 10-12 LCT as frequently as feasible.  As with UAM, one
of the issues  addressed by those constructing the modeling protocol
should be whether such sampling is necessary.
     Two approaches are possible for analyzing NMOC samples.  The
first approach is through use of gas chromatography and analysis of
peaks  on resulting  chromatograms.   Appropriate procedures  for
analyzing NMOC samples are described  in  Seila, et al. (1989).  The
principal advantage of this approach is that it enables retention
of  data  which  allow one  to  develop NMOC species profiles  for
boundary  conditions.    The major  drawback is  that it  requires
availability  of  a highly  trained  analyst  and is,  therefore,
expensive.  The  second  analytical  approach is  the cryogenic pre-
concentration approach  (often  abbreviated  PDFID) (McElroy et al.
1985).   This approach  is considerably  less  expensive  than  the
first, but it does  not allow one to examine  speciated data.  Choice
of analytical approach  is  dictated by priorities in a particular
study area and by available resources.
     4.3  Quality Assurance of Monitored Data
          The  same scrutiny  given  all monitored  data  used  to
support UAM and EKMA  analyses applies to data being considered to
                                40

-------
derive boundary conditions.  Appendix A to 40 CFR, Part 58 outlines



a series of mandatory features  for an acceptable quality assurance



program.  These are listed below.



          (1)  Documented   selection   procedures   for   methods,



               analyzers or samplers.



          (2)  Provisions for training of personnel.



          (3)  Installation of equipment.



          (4)  Selection and control of calibration standards.



          (5)  Adherence to calibration procedures.



          (6)  Procedures for zero/span checks and adjustments



               of automated analyzers.



          (7)  Procedures for control checks and their frequency.



          (8)  Control  limits  for zero,  span and  other  control



               checks  and  commitment to  respective  corrective



               actions when such limits are surpassed.



          (9)  Calibration procedures and zero/span checks for



               any multiple range analyzers.



         (10)  Provisions for preventive  and remedial maintenance.



         (11)  Quality  control  procedures   for   air   pollution



               episode monitoring.



         (12)  Recording and validating data.



         (13)  Data quality assessment (precision and accuracy).



         (14)  Documentation of quality control information.
                                41

-------
This page intentionally left blank
                42

-------
5.0  SUMMARY



     A  series  of  modeling  analyses  has  been  identified  for



characterizing transport into nonattainment  areas.  These analyses



enable one to:



          (a)   determine the most  likely principal cause  of an



observed exceedance (transport or local emissions);



          (b)  identify upwind CMSA/MSA's most likely to contribute



to an exceedance if overwhelming  transport is determined likely in



(a);



          (c)  quantify transport into CMSA/MSA's identified in (b)



so  that  such transport  may be  considered  in  estimating whether



contemplated control strategies will be sufficient to eliminate an



exceedance observed downwind.



          (d)   estimate  the cumulative  effect of emissions  in



several CMSA/MSA's on interstate transport.



     The discussion next focused  on  meteorological and air quality



monitoring data needed to support the analyses noted above.  Needed



measurements,   considerations   in  monitoring   network   design,



instrumentation,  operating  procedures   and  quality  assurance



provisions were identified.



     To implement the procedure for characterizing transport into



nonattainment areas, use of the following modeling and monitoring



criteria are suggested.



          (1)  Use of  trajectory models is ordinarily recommended:



                (a)  to establish whether an exceedance is primarily



due to local emissions or overwhelming transport (Section 3.1);





                               43

-------
               (b)  to identify contributing CMSA/MSA(s) if



overwhelming transport is identified in (a) (Section 3.2);



          (2)   The US  EPA TRAJECTORY  model  is  appropriate  for



qualitatively  estimating  the  prime  cause  (transport or  local



emissions) of most exceedances.



          To support use of the TRAJECTORY model, the



following monitoring data are needed or desirable:



     %         (a)  Surface wind data  at  NWS  sites within 160 km



(Sections 3.1 and 4.1.1);



               (b)  other surface wind data, as appropriate



(Section 4.1.1);



               (c)  surface ozone data (desirable)  (Section 4.1.1);



               (d)  upper air wind data  (desirable for TRAJECTORY,



required for other trajectory models)(Section 4.1.1).



          (3)  Trajectory models may also be used to identify rural



transport areas.  Several additional procedures are suggested for



this purpose if it is  determined that available data or models are



inadequate for use in a particular application (Section 3.1).



          (4)  For extreme, severe, serious, and  some  moderate 03



nonattainment areas,  the Urban Airshed Model  (or other approved



urban scale photochemical grid models) should be used to estimate



controls  needed  in  upwind CMSA/MSA's to  eliminate  a  downwind



exceedance.   Transport  into a modeled CMSA/MSA  (i.e.,  boundary



conditions) may be considered using one of several approaches.



               (a)  The  preferred approach  is  use of the EPA ROM



(Section 3.3.1).





                                44

-------
               (b)  Use of other regional models is encouraged when



it is not feasible to use ROM.  Modeling procedures are subject to



US EPA approval on a case-by-case basis (Section 3.3.1).



               (c)  In the absence of regional modeling data,



boundary conditions  may  be derived from  monitored  data (Section



3.3.2).



               (d)  In the absence of regional modeling results and



sufficient monitoring data,  expand the upwind dimension of the UAM



modeling  domain  and  use   recommended  default  assumptions  for



boundary conditions (Section 3.3.3).



          (5)  For some moderate 03 nonattainment areas,  the



Empirical Kinetic Modeling  Approach (EKMA) may be used to estimate



controls needed in a contributing CMSA/MSA to eliminate a downwind



exceedance.   Consider transport  into  a modeled  CMSA/MSA   (i.e.,



boundary conditions) using one of several approaches.



               (a)  The  preferred  approach  is use of the EPA ROM



(Section 3.3.1).



               (b)  Use of other regional models is encouraged when



it is not feasible to use ROM.  Modeling procedures are subject to



US EPA approval on a case-by-case basis (Section 3.3.1).



               (c)   In  the absence of  regional modeling  data,



boundary conditions  may  be derived from  monitored  data (Section



3.3.2).



               (d)  In the  absence of regional modeling data and



sufficient monitoring  data, use  recommended  default values  for



boundary conditions (Section 3.3.3).





                               45

-------
          (6)  Regional ozone models, such as ROM, are recommended,



when available, as the most appropriate procedures for estimating



cumulative effects of emissions from many CMSA/MSA's on interstate



transport of ozone.  (Sections 3.2.2, 3.3.1)



          (7)  To  estimate  boundary conditions for UAM  based on



monitored   data,    the   following   measurements   are   minimal



requirements:



               (a)   surface ozone at regional  site(s)  (Sections



4.1.2, 4.2.2);



               (b)    surface  NO,  NO2,  CO,  at  regional  sites



(Sections 4.1.2, 4.2.3, 4.2.4);



               (c)   NMOC may  be  sampled using  canisters during



several  3-hour periods  at  intervals of  no  more  than  six  days



(desirable) (Sections 4.1.2, 4.2.5);



               (d)   NMOC may  be  analyzed  from  chromatographs



(desirable) or using the  PDFID approach.   The former approach is



necessary to obtain speciated data (Section 4.2.5).



          (8)  To  estimate  boundary  conditions  for EKMA based on



monitored   data,    the   following   measurements   are   minimal



requirements:



               (a)   use  of  late morning  surface  ozone  data at



regional sites (Sections  4.1.3, 4.2.2);



               (b)  surface NO, NO2, and CO observed late morning



at regional sites  (Sections 4.1.3, 4.2.3, 4.2.4).
                                46

-------
               (c)  NMOC may be sampled during a 3-hour period in



late morning using canisters at intervals  of no more than six days



(desirable) (Sections 4.1.3, 4.2.5);



               (d)   NMOC  may be  analyzed from  chromatographs.



However, use of the PDFID approach and default recommendations for



NMOC speciation is recommended (Sections 3.3.3, 4.2.5).



          (9)    Monitored  ozone data  are  ordinarily  used  to



establish  boundary conditions for  regional   scale  models,  but



default  natural  background  levels  can  also  suffice.   In  ROM,



boundary  values  for  other  chemical  species are  derived  from



specified  ozone  values.    Data  collected  at  regional  scale



monitoring sites for urban scale modeling analyses  may be useful in



evaluating performance of regional models (Section 4.1.4).



          (10)  To be used  as  suggested  herein,  air  quality data



should  be  collected  and  analyzed  consistently  with  mandatory



quality assurance procedures (Section 4.3).
                                47

-------
This page intentionally left blank
                48

-------
                         REFERENCES CITED
BAUGUES, K. A., (1987), Support Document for Selection of Default
     Upper Air Parameters for EKMA. Unpublished report.

CAUSLEY, M.  C.,  1990,  User's Guide for the  Urban Airshed Model.
     Volume  IV;   User's  Manual  for  the  Emissions  Preprocessor
     System. EPA-450/4-90-007D.

COMPUTER SCIENCES CORPORATION,  (1991),  Gridded Model Information
     Support System  (GMISS^f  UAM  Subsystem,  User's Guide. Volume
     II: fUAM Subsystem. EPA-450/4-91-009.

DOUGLAS, S. G., R. C. KESSLER and E. L. CARR (1990), User's Guide
     for the Urban Airshed  Model.  Volume  III;   User/s Manual for
     the Diagnostic Wind Model. EPA- 450/4-90-007C.

HEFFTER, J. L., (1980), Air Resources Laboratories Atmospheric
     Transport  and   Dispersion  Model  CARL-ATAD)   NOAA  Technical
     Memorandum  ERL  ARL-81,  Air  Resources  Laboratories,  Silver
     Spring, MD.

HEFFTER, J. L., (1983), Branching Atmospheric Trajectory (BAT1
     Model. NOAA  Technical  Memorandum ERL ARL-121, Air Resources
     Laboratory, Rockvilie, MD.

LAMB,  R.  G.,   (1983),  A   Regional   Scale   (1000km)  Model  of
     Photochemical Air Pollution, Part 1 - Theoretical Formulation,
     EPA -600/3-03-035.

MEYER,  E.  L.  and  K.  A.  BAUGUES,  (1989),  Consideration  of
     Transported  Ozone and  Precursors and  Their  Use in  EKMA,
     EPA-450-4-89-010.

MORRIS, R. E. and T.  C. MYERS,  (1990),  User's Guide for the Urban
     Airshed Model.  Volume I;  User's Manual for UAM (CB-IV1.
     EPA-450/4-90-007A.

MORRIS, R. E., T. C.  MYERS,  E.  L. CARR, M.  C.  CAUSLEY  and  S. G.
     DOUGLAS, (1990b), User's Guide for the  Urban Airshed Model.
     Volume II:  User's Manual for the UAM  fCB-IVl Modeling System.
     EPA-450/4-90-007B.

MORRIS, R. E., T. C.  MYERS,  H. HOGO, L. R. CHINKIN, L. A.  GARDNER
     and R. G. JOHNSON, (1990), Urban Airshed Model Study of Five
     Cities, a Low-Cost Application for the Urban Airshed Model to
     the New York Metropolitan Area and the City of  St. Louis, EPA-
     450/4-90-006E.
                                49

-------
REFERENCES (CONTINUED)


MCELROY,  F.  F.,  v.  L.  THOMPSON and  H. G.  RICHTER,  (1935),  A
     Cryogenic  Preconcentration  - Direct FID  (PDFID)  Method for
     Measurement of NMOC  in  Ambient Air. NTIS Publication Number
     PB-120631.

MCALLISTER, R. A., p. L. O'HARA, D. DAYTON, j. E. ROBBINS,
     R. F. JONGLEUX,  R.  G. MERRILL,  JR.,  JO RICE  and E. G. BOWLES,
     (1990), 1990 Nonmethane  Organic Compound and Three-Hour Air
     Toxics Monitoring  Program,,  Draft  Final   Report,  N. F. Berg,
     USEPA Project Manager.

SEILA, R. L.,  W. A. LONNEMAN and S. A. MEEKS,  (1989), Determination
     of C, to  C,2 Ambient Hydrocarbons in 39 U.S. Cities from 1984
     to 1986.  EPA/600/3-89/058 (Appendix B).

SYSTEMS APPLICATIONS, INC.,  (1988), A PC Based System for
     Generating EKMA Input Files. EPA-450/4-88-016.

TANG, R. T., S. C. GERRY, J. S. NEWSOME, A. R. VAN METER,
     R.  A.  WAYLAND,  J.  M.  GODOWITCH  and  K. L.  SCHERE,  (1990),
     User/s  Guide  for  the  Urban  Airshed  Model,   Volume  V:
     Description and  Operation of  the  ROM—UAM  Interface Program
     System. EPA-450/4-90-007E.

USEPA, (1978), Ozone Isopleth Plotting Package fOZIPP),
     EPA-600/8-78-014b.

USEPA, (1987), On-site Meteorological Program Guidance for
     Regulatory Modeling Applications, EPA-450/4-87-013.

USEPA, (1989a), User's Manual for OZIPM4 (Ozone  Isopleth Plotting
     With Optional Mechanisms^ Volume lf EPA 450/4-89-009a.

USEPA, (1989b), User's Manual for OZIPM4 (Ozone  Isopleth Plotting
     With and Optional Mechanisms^.  Volume  2  - Computer Code, EPA-
     450/4-89-009b.

USEPA, (1989c), Procedures for Applying City-Specific EKMAf
     EPA-450/4-89-012.

USEPA, (1989d), Aerometric Information Retrieval System (AIRS),
     Volume  I; Office  of  Air  Quality  Planning  and Standards,
     Research Triangle Park, NC  27711.
                                50

-------
                                    TECHNICAL REPORT DATA
                             (Please read Instructions on the reverse before completing)
1. REPORT NO.
 EPA-450/4-91-015
                              2.
                                                             3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
 Criteria  for Assessing  the Role of Transported Ozone/
 Precursors in Ozone Nonattainment Areas
              5. REPORT DATE
               May 1991 Date of  Issue
              6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
 E. L. Meyer
                                                             8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
 U.S. Environmental Protection Agency  (MD-14)
 Office  of Air Quality  Planning and  Standards
 Technical  Support Division
 Research  Triangle Park,  NC   27711
              10. PROGRAM ELEMENT NO.
                A24A2F
              11. CONTRACT/GRANT NO.
                 None
12. SPONSORING AGENCY NAME AND ADDRESS
     Same
                                                             13. TYPE OF REPORT AND PERIOD COVERED
                                                                Final
                                                             14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
  A series  of  modeling analyses appropriate  for characterizing transport of  ozone and
  its precursors into nonattainment areas  is  discussed.  Air  quality and meteorological
  measurements needed to characterize transport in identified modeling techniques are
  also identified.  The report fulfills requirements in Section 184(d) of the Clean
  Air Act Amendments of 1990,  in which the U.S.  Environmental  Protection Agency is
  directed  to  identify criteria for estimating  transport of pollutants into  ozone
  nonattainment areas.
17.
                                 KEY WORDS AND DOCUMENT ANALYSIS
                  DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS  c. COSATI Field/Group
  ozone
  ozone models
  ozone/precursor  monitoring
  pollutant transport
18. DISTRIBUTION STATEMENT

  Unlimited
19. SECURITY CLASS (Tins Report)
                                                                           21. NO. OF PAGES
                                 51
                                               20. SECURITY CLASS (Tills page/
                                                                           22. PRICE
EPA Form 2220-1 (Per. 4-77)   PREVIOUS EDITION is OBSOLETE

-------