&ER&
United States
Environmental Protection
Agewv
Office of Air Quality
Planning and Standards
Research Triangle Park NC 27711
EPA-450/4-80-027
March 1981
Guideline For Use
Of City-specific EKMA
In Preparing Ozone SIPs
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EPA-450/4-80-027
Guideline For Use Of City-specific EKMA
In Preparing Ozone SIPs
Air Management Technology Branch
Monitoring and Data Analysis Division
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office Of Air, Noise, and Radiation
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
March 1981
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This report 1s Issued by the Environmental Protection Agency to report
technical data of Interest to a limited number of readers. Copies are
available free of charge to Federal employees, current contractors and
grantees, and nonprofit organizations - in limited quantities - from the
Library Services Office (MD-35), Research Triangle Park, North Carolina
27711; or, for a fee, from the National Technical Information Service,
5285 Port Royal Road, Springfield, Virginia 22161.
Publication No. EPA-450/4-80-027
11
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TABLE OF CONTENTS
Page
Summary v
List of Figures x
List of Tables xi
1.0 Introduction 1
2.0 Estimating Control Requirements for 1982 Ozone SIP s 7
2.1 Selection of Days to Model 10
2.2 Day-Specific Control Estimates 10
2.3 SIP Control Requirement 11
3.0 Generation of Day-Specific Isopleth Diagrams 16
3.1 OZIPP Modeling Data 17
3.1.1 Light Intensity 19
3.1.2 Dilution 19
3.1.3 Transport of Ozone 20
3.1.4 Precursor Transport 24
3.1.5 Post-8:00 a.m. Emissions 26
3.1.6 Reactivity 38
3.2 Empirical Data 39
3.2.1 Dally Ozone Design Value 40
3.2.2 NMOC/NO¥ Ratios 40
rt
3.3 Use of OZIPP to Generate Isopleth Diagrams 43
4.0 Calculation of Control Estimates 47
4.1 Use of Single Day-Specific Diagrams 48
4.2 Concurrent Changes in Emissions and Other Factors 49
4.2.1 Concurrent Reductions 1n Local Precursors and
Transported Ozone 52
4.2.2 Concurrent Reductions 1n Local Precursors and
Transported Precursors 58
4.2.3 Concurrent Changes In Local Precursors and
Diurnal Emission Patterns 59
4.2.4 Consideration of Multiple Changes 60
5.0 Acknowledgment 62
Appendix A. Estimation of Mixing Heights for Use 1n OZIPP A-l
Appendix B. Consideration of Transported Precursors B-l
References R-l
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SUMMARY
This summary outlines the procedure used 1n applying city-specific EKMA 1n
State Implementation Plans (.SIPs) for ozone. City-specific EKMA consists of two
components: the OZIPP model and the EKMA procedure (I.e., OZIPP/EKMA).
OZIPP (Ozone Isopleth Plotting Package) is a computer program which allows
the user to plot maximum hourly ozone concentrations as an explicit function of
initial (e.g., 8 a.m.) ambient concentrations of the precursors non-methane
organic compounds (NMOC) and oxides of nitrogen (NO ). The resulting output 1s
^
an ozone isopleth diagram. Because the OZIPP model allows consideration of
meteorological inputs, pollutants transported from upwind and precursor emissions
which are appropriate for each city under review, the Isopleths are also implicit
functions of these variables.
EKMA (Empirical Kinetic Modeling Approach) is a procedure for applying the
ozone isopleth diagram obtained with OZIPP to estimate the Impact of controlling
urban volatile organic compound (VOC) and/or NO emissions on peak hourly ozone
A
concentrations. Ambient 6-9 a.m. NMOC/NO ratios measured 1n the urban core and
J\
peak hourly ozone measured within or downwind of the city are needed to apply an
Isopleth diagram in the EKMA, procedure.
Because urban VOC and/or NO emission reductions are likely to be more
^
effective under some conditions than others, there is not necessarily a simple
1:1 correspondence between high observed ozone concentrations and emission controls
estimated as necessary to attain the National Ambient A1r Quality Standard (NAAQS)
for ozone. Thus, in order to ensure that the standard 1s attained, 1t 1s neces-
sary to perform city-specific EKMA modeling for several days. This provides more
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complete assurance that the standard will be met 1f a control target 1s achieved.
Consideration of the five days with the highest observed dally maximum ozone
concentrations at each site affected by the urban area 1s believed to be sufficient.
The procedure for applying city-specific EKMA is outlined in the following
seven steps. Each step is discussed 1n greater depth 1n the indicated section(s)
of this report.
1. Select the five days with highest maximum hourly ozone concentra-
tions observed at each site affected by the urban area over the past three years
(Section 2.1).
2. For each of these days, estimate the 6-9 a.m. NMOC/NO ratio
^
prevailing in the urban core (Section 3.2.2).
3. Using the input data summarized 1n Table SI, apply the OZIPP
computer program to generate ozone isopleth diagrams for each day. The exact
procedure 1s described in User's Manual for Kinetics Model and Ozone Isopleth
Plotting Package. EPA-600/8-78-014a. The resulting diagrams denote sensitivity
of peak hourly ozone concentrations to locally generated precursors, given a set
of "current" accompanying conditions (e.g., a specified concentration of trans-
ported ozone from upwind sources).
4. Using the ozone concentrations obtained in Step 1 and the NMOC/NO
J\
ratios derived in Step 2, establish a "starting point" on each of the ozone
isopleth diagrams obtained 1n Step 3 (Section 4.1).
5. If there 1s a change(s) in the base case conditions assumed to
prevail in generating Isopleth diagrams obtained in Step 3, it is necessary to
VI
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Table SI. Inputs Needed to Generate an Ozone Isopleth Diagram
Input
(1) Light Intensity
Atmospheric
Dilution
(3) Present Transport
of Ozone
(4) Present Transport
of Precursors
(5) Post 8 a.m. Emissions
Mow Used and Obtained
Enter the datn and a city's latitude, longitude and time
zone to the OZIPP program.
Use National Weather Servlre (NWS) or Urban Radiosonde data
and urban surface temperatures to estimate R a.m. mixing
height, maximum (tally mixing height and the Mmr> which the
maximum daily mlxim) height occurs. In the event NWS or
urban data arc unavailable, use values compiled In Table A-l.
The model assumes that ozone Is transported In two layers:
at the surface and aloft. Ozone transported at the earth's
surface Is generally assumed to be zero. Ozone transported
aloft can be estimated using mid-morning ozone concentrations
observed at a continuously operated surface monitor located
upwind of the city on each day considered.
Measurements and past model applications have indicated the
Impact of transported precursors is generally negligible.
Hence, these are ordinarily assumed to be zero. In cases
where thorn Is reason to believe precursor transport is high,
special procedures nro needed. Those procedures roqiiire fi-9 a.m.
measurements of precursor concentrations upwind of the city
obtained by simulation of organic species.
Derived using 6-9 a.m. ambient NMOC and NO measurements In the
urban core on each day modeled, seasonal countywlde VOC and NO
emir.-.Ion inventories anil I nforin.it I on concerning the location of
the maximum observed ozone concentration on each day modeled.
Sectlon(s) of Report
Describing Process
In Detail
Section 3.1.1
Section 3.1.2
Appendix A
Section 3.1.3
Section 3.1.4
Appendix 0
Section 3.1.5
(6) Reactivity
Recommended default values should he used.
Section 3.1.6
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generate a second set of Isopleth diagrams. This second set of diagrams reflects
the Impact of changing the set of "current" accompanying conditions described 1n
Step 3. For example, a second set of diagrams is most frequently used to allow
the user to consider changes in ozone transported Into a city. In such an appli-
cation, the second set of diagrams is obtained using an assumed future concentra-
tion of transported ozone. Suggested procedures for estimating future transported
ozone are described in Section 4.2.1.
6. VOC and/or NO controls needed to reach 0.12 ppm 0« on each day at
X «3
each site are estimated using the starting point on each diagram representing the
current conditions (Step 4} and calculating controls needed to reach the 0.12 ppm
ozone Isopleth on the corresponding diagram obtained in Step 5. This procedure
enables the user to consider concurrent changes 1n local precursor emissions and
in such variables as transported ozone from upwind sources.
7. As a result of Step 6, there is one estimate of VOC controls
needed to reach a peak hourly ozone value of 0.12 ppm at each site for each day.
Each of these estimates 1s valid only for the best estimate of changes in NO
/\
between the base year* and 1987. The site specific VOC emission reduction is the
fourth highest control estimate, assuming a three-year data base. If there were
only one year of data at a site, the control requirement would be the second
highest control estimate; two years of data, the third highest control estimate,
etc. Because of possible significant changes in emissions or emission patterns
over longer periods, a three-year sampling period 1s the maximum which should
* Normally the base year is 1980.
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normally be considered. The SIP VOC emission reduction for the urban area is the
highest site-specific control estimate. Selection of the target control goal for
a SIP is illustrated 1n Table 2.2.
ix
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LIST OF FIGURES Page
3-1 Example Isopleth Diagram 18
3-2 Examples of Acceptable Monitoring Locations for Estimating
Transported Ozone 25
3-3 Example Formulation of Post-8:00 a.m. Emission Density Scheme . 30
3-4 Illustration of Emission Fractions Calculated Using
Initial Conditions 35
3-5 Example Calculation of Emission Fractions 37
3-6 Example Calculation of the Design NMOC/NO Ratio 44
A
4-1 Example Emission Reduction Calculation Using a Single
Ozone Isopleth Diagram 51
4-2 Future Ozone Transport as a Function of Present Transport ... 54
4-3 Example Emission Reduction Calculation Considering Changes
in Transported Ozone 57
A-l Flow Chart for Table A-3 A-9
B-l Vertical Pollutant Profile Illustrating a Shallow Layer of
Elevated NOV Concentrations Aloft B-5
% /\
B-2 Example Emission Reduction Calculation with the Explicit
Consideration of Precursor Transport in the Surface Layer ... B-10
B-3 Illustration of the Treatment of Contiguous Urban Areas .... B-l6
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LIST OF TABLES Page
S-1 Inputs Needed to Generate an Ozone Isopleth Diagram vii
1-1 Data Requirements for Use of City-Specific EKMA 3
2-1 Tabular Estimation of Site-Specific Control Requirements 12
2-2 Selecting the SIP Control Requirement: An Example 14
3-1 Data Requirements for Calculating Mixing Heights According
to the Recommended Procedure 21
3-2 Recommended Procedure for Calculating Emission Fractions 36
3-3 OZIPP Options for Model Input Data 45
4-1 Control Calculations Using a Single Isopleth Diagram 50
4-2 Control Calculations Using Two Isopleth Diagrams 53
A-l NWS Radiosonde Stations and Climatologlcal Mixing Heights for
Selected Cities A-3
A-2 Preferential Order of Data Selection A-4
A-3 Procedures for Estimating Mixing Heights A-7
A-4 Worksheet for Computing Mixing Heights A-8
A-5 Surface and Sounding Data A-10
A-6 Morning Mixing Height Determination A-13
A-6A Example A-14
A-7 Maximum Mixing Height Determination A-l5
A-7A Example A-l7
B-l Typical Effects of NMOC Transport Aloft on Control Estimates. . . B-2
B-2 Typical Effects of NMOC Surface Layer Transport on Control
Estimates B-7
B-3 Explicit Treatment of Surface Layer Precursor Transport B-9
XI
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1.0 INTRODUCTION
This document is intended to fulfill several purposes:
1) to describe application of a relatively simple modeling procedure,
city-specific EKMA, which is useful for estimating the effectiveness of reducing
emissions of volatile organic compounds (VOC) and/or oxides of nitrogen (NOX) in
reducing peak ozone values downwind or within a city;
2) to indicate how available emissions, air quality and meteorological
data are used in the modeling procedure;
3) to provide one means for Air Pollution Control Agencies to check
the completeness and suitability of analyses performed with the model to support
the need for urban VOC and/or NOV emission controls.
y\
The city-specific EKKA modeling procedure has also been referred to as
"Level III analysis." These terms are synonymous. City-specific EKKA consists
of two components: the CZIPP model and the EKMA procedure (i.e., OZIPP/EKMA).1 >2'3
"OZIPP" (Ozone Isopleth Plotting Package) is a computer program which allows the
user to plot maximum hourly ozone concentrations as an explicit function of
initial (8 a.m.) ambient concentrations of non-methane organic compounds (NMOC)
and NO within the urban area. The resulting output is an ozone isopleth diagram.
A
Although the ozone isopleths are explicitly plotted as a function of initial NMOC
and NO , they are also implicit functions of numerous other variables. For
/\
example, the role of subsequent VOC and NO emissions, meteorology and pollutants
A
transported from areas upwind of the modeled city are also considered in OZIPP.
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"EKMA" (Empirical Kinetic Modeling Approach) is a procedure for applying the
ozone isopleth diagram generated with the OZIPP to estimate the impact of changing
urban VOC and/or NOV emissions on peak hourly ozone concentrations. Two pieces
/\
of information must be available to apply EKMA: the 6-9 a.m. ambient NMOC/NO
/\
ratio prevailing in the urban area, and the peak hourly ozone concentration
measured within or downwind of the city. These two pieces of information provide
a starting point on the isopleth diagram from which to estimate control requirements.
The conceptual basis for the Isopleth diagram is a Lagrangian model (OZIPP)
which follows the evolution of ozone from precursors within a migrating column of
air. The column of air extends from the earth's surface throughout the mixed
layer. All pollutants are uniformly mixed within the column. From early morning
to mid-afternoon, the height of the column Increases due to the diurnal rise in
mixing height. This results in simultaneous dilution of pollutants within the
column and entrainment of additional pollutants from above the mixed layer.
Concurrently with the foregoing dilution and entrainment, fresh precursor emis-
sions encountered as the column is transported by the wind are injected into it.
All resulting pollutants within the column of air are assumed to react chemically
in accordance with the chemical kinetic mechanism in OZIPP.
The data base needed to develop isopleth diagrams in accordance with the
model formulation described in the previous paragraph is summarized in Table 1-1.
Such a data base is consistent with what has been described on pages 65669-65670
in the November 14, 1979, Federal Register as a "Level III" analysis. The data
are adequate for insuring that the observed peak ozone value has, indeed, occurred
within or downwind of the city being reviewed. However, the data are not adequate
for tracing the exact trajectory leading to the peak ozone value, nor for precisely
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Table 1-1. Data Requirements for Use of City-Specific EKMA
Data Item
Requirements
1. Air Quality Data
A. Ozone Monitors
- Minimum of 3 sites; one upwind
the second on downwind edge of
city and the third 15-40 km
downwind. (See EPA-450/2-77-C21a
and Section 3.1.3)
B. Precursor Data
- Minimum of 1 site with collocated
NMOC and NO monitors, with two
sites deslrSble. (See
EPA-450/4-80-011 and Section 3.2.2)
2. Meteorological Data
A. Upper Air Data
- National Weather Service Rawlnsonde
data 1f available. (See Section 3.1.2
and Appendix A)
Surface Temperature and
Pressure Data
- Hourly surface temperature and
pressure data at one site in the
urban area. (See Section 3.1.2)
Surface Wind Data
-Minimum of two sites; one in high
precursor area and one additional
site. (See Section 3.2.1)
3. Emission Data
A. VOC Emissions
B. NO. Emissions
- A seasonally adjusted, countywide,
annual emission rate for each
broad source category. (See
Section 3.1.5)
- A seasonally adjusted, countywide,
annual emission rate for each
broad source category. (See
Section 3.1.5)
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estimating emissions injected into a particular column of air. The procedures
described 1n this document therefore make assumptions about the trajectory of the
modeled column of air. The column is assumed to be within the urban area at
8 a.m. and to migrate downwind in a straight Hne to the site observing the peak
ozone concentration by the time the peak is observed.* Although use of city-
specific input data should improve model accuracy., the limited data base and the
resulting assumptions made in applying the city-specific EKMA (i.e.,, Level III
analysis) still make it uncertain that the model will always perform well in an
absolute sense. That is, one would not necessarily expect to be able to measure
NMOC and NO downtown and then use the isopleth diagram to predict peak ozone
/\
concentrations. However, sensitivity studies have shown that differences
resulting from incomplete input data or gross assumptions employed by the model
tend to exhibit proportional impacts on the positions of various ozone isopleths
on an isopleth diagram. Thus, the model should perform satisfactorily when
applied in a relative sense (e.g., to estimate a change in peak ozone accom-
panying changes in local precursor levels).
City-specific EKMA is expected to be widely used in preparing State
Implementation Plans (SIPs) submitted to attain the National Ambient Air Quality
Standard (NAAQS) for ozone. The NAAQS for ozone is now in a statistical form
(i.e., daily maximum ozone concentrations are not expected to exceed 0.12 ppm
more than once per year). Because urban VOC and/or NO emission reductions are
* Because a review of St. Louis RAPS data has suggested that ordinarily the
diurnal variation in urban NMOC/NO ratio is small, it is not regarded as
critical that the column of air bexwith1n the urban area at precisely 8 a.m.
It should be sufficient if the air is within the urban area by mid-morning.
If extensive wind data suggest that the column of air is still upwind of the
urban area at noon or later, problems of this nature need to be addressed
on a case by case basis 1n consultation with the EPA.
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likely to be more effective under some conditions than others, there 1s not
necessarily a simple 1:1 correspondence between high observed ozone concentrations
and estimated emission controls needed to attain the ozone NAAQS. Thus, 1n order
to ensure that daily maximum ozone concentrations are not expected to exceed
0.12 ppm more than once per year, 1t 1s necessary to apply city-specific EKMA to
several different days observing high ozone concentrations. This differs from
common past practices in which a single ozone design value was selected and
control requirements were calculated based solely on this value. Chapter 2.0
describes the procedure, underlying rationale, and key issues which arise 1n
applying city-specific EKMA on several days.
Data needs for applying city-specific EKMA on each day selected pursuant to
guidance in Chapter 2.0 have been summarized in Table 1-1. Chapter 3.0 discusses
how these data are transformed Into input to city-specific EKMA. The discussion
concerning each input variable follows a consistent format. First, 1t 1s assumed
that valid data have been collected as specified in the Federal Register. The
most appropriate procedure for transforming these data into each input variable
is identified. However, it is also recognized that the available data will not
always conform exactly to the Federal Register specifications. For example, in a
few cases, the data base may be more detailed than what is specified in the
Federal Register. Procedures are described for utilizing such a data base if so
desired. More often, some data may be missing or subsequently determined to be
invalid. Procedures for deriving model inputs under such circumstances are also
identified. In the event that quality assured NMOC and NO data cannot be obtained
/\
for a sufficient number of days to provide a reliable estimate of the prevailing
NMOC/NOX ratio, city-specific EKMA cannot be used.
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Once all of the input has been prepared consistently with guidance in
Chapter 3.0, the OZIPP model is used to generate ozone Isopleths for each of the
days identified as necessary. The EKMA procedure is then applied to each set of
isopleths to estimate the amount of VOC and/or NO controls needed to reduce the
/\
peak hourly ozone concentration to 0.12 ppm on each day. From these estimates,
the amount of VOC and/or N0v control 1s selected such that a peak hourly 0,
X 0
concentration of 0.12 ppm will not be expected to be exceeded on more than one
day per year. Chapter 4,0 illustrates the application of city-specific EKMA to
estimate controls for each day. The determination of the SIP control requirement
is described in Section 2.3.
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2.0 ESTIMATING CONTROL REQUIREMENTS FOR 1982 OZONE SIPs
Prior to discussing procedures for estimating control requirements with
city-specific EKMA, 1t is appropriate to address the National Ambient Air Quality
Standard (NAAQS) for ozone. The NAAQS affects the choice of ozone values Input
to EKMA, as well as the stringency of a city's calculated control requirements.
The National Ambient Air Quality Standard for ozone 1s attained when the
expected number of days per calendar year, with maximum hourly average concen-
trations above 0.12 ppm, 1s less than or equal to one. This differs from the
previous photochemical oxidant standard which specified a concentration "not to
be exceeded more than once per year." As with the previous standard, air quality
data are examined on a site by site basis and each site must meet the standard.
The Guideline for the Interpretation of Ozone A1r Quality Standards recommends
that a period of three successive years of air quality data be used as the basis
o
for determining attainment of the standard. As more years of data are included,
a greater chance exists for minimizing the effects of an extreme year caused by
unusual meteorology. However, extending the number of successive years too far
increases the risk of averaging data during a period 1n which a real shift in
emissions and air quality has occurred.
Two important differences with past practices occur as a result of the new
standard. First, only one hourly value is considered for each site on each day.
This can affect the set of candidate "ozone design values" used to estimate the
amount of controls needed to reach 0.12 ppm ozone. Formerly, extremely rare
episode days with a number of very high ozone values at any given site were
weighted disproportionately. The new standard inherently recognizes this problem
by allowing only one concentration (and therefore one control estimate) to be
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considered per site per day.
Second, the phrase, "... expected number of days per calendar year..."
alleviates a concern with the former standard that those States which have main-
tained conscientious monitoring programs over the years are penalized. Since the
expected or "average" number of days per year with daily maximum ozone concentra-
tions greater than 0.12 ppm is of concern, this means that there can be more than
one day observing ozone concentrations in excess of 0.12 ppm if the data base is
two or more ozone seasons in length.
Another implication of the NAAQS is that the frequency distribution of ozone
concentrations at each monitoring site which occurs after the implementation of
controls is the key consideration in demonstrating attainment. This has always
been the case. In the past, however, very simplistic models (e.g., rollback,
envelope curves) were used to demonstrate attainment. Minimal use was made of
meteorological or air quality data. Under such circumstances, choosing the ozone
value to input into a model in order to calculate control requirements was very
straightforward. The design value was simply the second highest value observed.
The degree of control needed to attain the NAAQS, however, is a function of many
things in addition to observed ozone concentrations during the base period. For
example, controls needed to attain the NAAQS are a function of pollution trans-
ported from upwind sources, prevailing NMOC/NOV ratios and atmospheric dilution.
A
Therefore, it is conceivable that the second highest ozone design value would not
require the second highest control requirement to attain the NAAQS if one uses
city-specific EKMA or more sophisticated models. Of paramount interest is the
frequency distribution of control estimates calculated with such models. Depend-
ing on the length of the period of record at any given monitoring station, one
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would choose the control estimates which would Insure that, on average, the dally
maximum hourly ozone concentration would not exceed 0.12 ppm more than once per
year at any monitoring site. For example, if the period of record at one site
were three years, the fourth highest calculated control estimate would be chosen
as demonstrating attainment at that site. The control requirement needed to
demonstrate attainment for the city as a whole 1s whatever 1s necessary to demon-
strate attainment at all ozone monitoring sites. Therefore, 1t is necessary to
model a number of high ozone days to determine the degree of control required to
attain the ozone standard. This need, while always present, can now be adequa-
tely addressed due to increased data availability. Given this situation, demon-
stration of attainment could entail generating isopleths for (1) each site and
each day above 0.12 ppm ozone, or (2) for each set of meteorological conditions,
with associated probabilities of occurrence, that may result 1n violations of the
NAAQS. Depending on the nature of the ozone problem for a given city, either
approach would require generating several isopleth diagrams. Because 1t is
relatively easy to generate these diagrams and apply EKMA, procedures described
in the next Section recommend examining several days and monitoring sites without
very elaborate procedures to eliminate a number of candidate days prior to the
modeling. Persons using more sophisticated modeling procedures would most likely
find 1t preferable to develop screening procedures to eliminate a number of
candidate days prior to the modeling exercise.
Even for city-specific EKMA, given the size of monitoring networks and the
expected number of observed ozone concentrations greater than 0.12 ppm in many
urban areas, the computer costs and manpower requirements for the two approaches
mentioned above might exceed the resources available to many State and local
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agencies. Therefore, 1n developing a procedure for estimating urban area control
requirements, consideration has been given to resource requirements, model com-
plexity and model input requirements, as well as to the form of the ozone standard.
2.1 SELECTION OF DAYS TO MODEL
Control estimates obtained with city-specific EKMA can be sensitive to such
2
factors as the level of ozone transported into an urban area. Thus, control
estimates based on the "classical design day" could understate the degree of
control required for the city to attain the NAAQS. As a result, several days
should be selected for modeling.
Recommended Procedure: For each ozone monitoring site, the five (5) days
with the highest daily maximum ozone concentrations should be selected as candi-
dates for modeling. In selecting the days for each site, only those days on
which ozone values are observed downwind or within the urban area should be
considered. Determination of what is "downwind" on a given day requires the
review of prevailing wind data for that day. Such a review may, in fact, reveal
that a nominally "downwind" site is in actuality upwind of the city on a parti-
cular day (see Figure 3-2 for an example of "upwind" versus downwind areas). If
this is the case, the ozone value observed at that site should not be modeled.
The days should be chosen from the most recent three (3) years for which meas-
urements were made at the site. By limiting the number of days to model, this
approach represents a compromise between a strict interpretation of the ozone
standard and consideration of model complexity and local agency resources.
However, the control estimates obtained with this procedure should not differ
significantly from those obtained by modeling each site and day above the ozone
standard. EKMA, when used in this manner, serves as a "screening procedure" for
identifying the control strategy design day. With more sophisticated models,
other (e.g., statistical) techniques may prove to be more viable for selecting
days to model for control strategy evaluations.
Alternate Procedure: Alternative attainment demonstrations might include
modeling each day in which the NAAQS was exceeded during the past three years, or
modeling a statistically determined design day or set of meteorological classes.
Probabilistic approaches, however, may be more difficult to develop and implement
than simply using EKMA itself as the screening procedure.
2.2 DAY SPECIFIC CONTROL ESTIMATES
Once the days to be modeled ere selected, control estimates must be calculated
10
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for each of these days. Considerable duplication 1n high ozone days 1s likely
for many of the sites 1n the monitoring network. When this occurs, the same
isopleth diagram can usually be used to make control estimates for a number of
sites.
Recommended Procedure: The OZIPP should be used to generate an Isopleth
diagram for each day Identified as described in Section 2.1. Preparation of the
model input data 1s described in Section 3.1. Development of a second Isopleth
diagram may be necessary if different control measures are implemented concur-
rently, e.g., reductions In future levels of ozone transported aloft. Procedures
for handling this situation are presented in Chapter 4.
Two additional pieces of information are needed to calculate control
estimates for each day and site: the dally maximum ozone value at each site and
the urban 6-9 a.m. NMOC/NO ratio. Section 3.2.2 provides procedures for deter-
mining the appropriate ratto for use in city-specific EKMA.
Having assembled the necessary data and generated an ozone Isopleth
diagram for each selected day and (if necessary) each site,* the VOC reduction
necessary to lower the peak ozone selected value to 0.12 ppm 1s calculated for
each day at each appropriate site. The procedures for calculating control esti-
mates using the isopleth diagrams are described 1n Chapter 4.
2.3 SIP CONTROL REQUIREMENT
The control requirement for use in the 1982 ozone SIPs 1s determined from
the control requirements estimated for each site.
Recommended Procedure: Given the form of the ozone standard, the SIP control
requirement Is that control estimate with frequency of occurrence of 1/365 for
the controlling site. Thus, having modeled the five highest days at each site,
it is assumed that the upper portion cf the control requirement distribution has
been defined. Table 2-1 indicates which control estimate would be selected as
the control requirement for each site. The SIP control requirement is the highest
of the site-specific control requirements.
Often, it will not be necessary to generate as many diagrams as implied by
this procedure. For example, if high ozone values occur at two or more
sites on the same day, with rare exceptions, the same diagram can be used.
One exception to this generalization is discussed in Section 3.1.5.
11
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Table 2-1. Tabular Estimation of Site-Specific Control Requirements
Number of Complete Data Point Used
Ozone Seasons for Site-Specific
Monitored* Control Requirements .
1 Second highest control estimate
2 Third highest
3 Fourth highest
* Monitoring data at a site is considered to be complete if valid daily
maximum hourly concentrations exist for at least 60 days during the
ozone season. If a site does not meet this criterion during any of the
last three ozone seasons, the second highest control estimate calculated at a
site is the site-specific control requirement. In order for a season's daily
maximum ozone values to be valid, there can be no systematic pattern of
missing potential peak hours in the data base.
12
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Table 2-2 contains an example of the procedure for selecting SIP control
requirements for urban areas. In constructing this example, it is assumed that
the urban area has three ozone monitoring sites: Site A within the city, Site B
in the predominantly downwind direction from the city, and Site C in the
predominantly upwind direction of the city. Site A has two (2) years of ozone
data, Site B has three (3) years of data, and Site C has only one (1) year of
ozone data.
The first step in calculating the SIP control requirement is to list the
ozone maxima and dates of the five highest ozone days at each site. A site 1s
only Included for a specific day if the wind data indicate that the site is
actually downwind of the urban area.
An examination of the high days at each site reveals some duplication in the
dates of high ozone days among sites. For example, in Table 2.2, June 8 appears
for both Site A and Site B. For this case, the same isopleth diagram can usually
be used at each site. Control estimates are then made for each site/day combi-
nation using the appropriate ozone isopleth diagram.
Experience with the model, and an examination of the differences in such
factors as transported ozone levels between the day to be modeled and other days
with higher ozone maxima, may provide a means for limiting the number of sites or
the number of isopleth diagrams to be generated for each site. In the example in
Table 2-2, because of the duplication of days among the sites, only two isopleth
diagrams were generated for the Site A, and only one for Site C. Then, using the
selection criteria presented in Table 2-1, the site-specific control requirements
were obtained (the control estimates enclosed in boxes in Table 2-2). In Table 2-2
13
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Table 2-2. Selecting the SIP Control Requirement: An Example
Site A
P/
.24
.18
.16
.15
.14
Date
10/1/80
6/8/81
10/2/80
8/13/81
8/21/80
% R
60
57
(45)
39
*
Site B
%+
.22
.19
.19
.18
.17
Date % R
6/8/81 58
8/25/80 54
10/2/80 55
8/26/80 (51)
7/26/79 49
Site C**
ik+ Date % R
.16 77/31/81 45
.15 9/17/81 (38)
.15 6/1/81 *
SIP Control Requirement = 51% obtained from Site B.
* Isopleth diagrams were not generated for these days since transport and
mixing heights were similar to days with significantly higher ozone
values; thus, the control requirements would be less.
** On these days, the Site C was actually downwind of the city as indicated
by local wind data.
+ The daily maximum Q3 at each site.
Assumptions:
(1) Urban Area has three monitoring sites, Site A, Site B
and Site C.
(2) Site A has two years of ozone data, Site B has three
years of data, and Site C has only one year of ozone
data.
(3) Control requirements (%R) may not decrease monotonically
due to daily variations in transported ozone levels,
mixing heights, NMOC/NOV ratios, etc.
X
14
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the SIP control requirement 1s the maximum of the site specific control require-
ments, I.e., the 51 percent estimate Site B for this example.
In summary, the method for estimating urban area control requirements for
1982 SIPs involves (1) the repeated application of the OZIPP model to generate
Isopleth diagrams for each of the five highest ozone days from the past three
years at each site, (2) the use of the EKKA procedure to provide a control esti-
mate for each site-day, and (3) the selection of the SIP control requirement as
the control estimate needed to demonstrate attainment at all monitoring sites for
the urban area as a whole.
15
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3.0 GENERATION OF DAY-SPECIFIC ISQPLETH DIAGRAMS
As described in Section 2.1, a number of days with elevated ozone concen-
trations are selected for modeling. An ozone isopleth diagram 1s generated for
each day using the OZIPP computer model. Each model application requires the
use of day-specific modeling Inputs. Day-specific empirical data (or suitable
surrogates} are then used in conjunction with each diagram to calculate the VOC
and/or NO controls necessary to reduce the peak hourly ozone concentrations
^
observed on each day to 0.12 ppm. The empirical data are used to locate a
starting point on each diagram, from which control calculations are made.
Because the scales of the diagram axes can be varied 1n OZIPP, the empirical
data must be developed prior to generation of a diagram to Insure that the
starting point 1s located in an appropriate position on the d1agra». This
Chapter describes the methodologies appropriate for deriving the day-specific
•edeling da£t. the day-spec If ft empirical data, and the procedures for generatta?
the diagrams. The control calculations are described in Chapter 4.
In describing the techniques for developing modeling Inputs, more than one
procedure is usually presented. The first method listed is generally preferable,
given the level of detail of information normally available. However, 1t 1s
recognized that 1n some Instances more detailed information may be available and
could be Included 1n the analysis, 1f desired. On the other hand, Information
may not always be available, or reliable. Consequently, optional methods of
developing Input data are also presented. If no information at all 1s available,
default values, or methods, are sometimes included. In practice, the methods
used to derive Input to the model Involve a trade-off between the resources
required to collect and process data, and the enhanced credibility of the analysis
16
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by more completely representing physical processes. The preferred approaches
are designed to provide a fairly complete representation, given data assumed to
be commonly available. To insure specificity to a particular city under review,
city-specific determinations of Input data are strongly recommended, with default
measures recommended only as a last resort.
3.1 OZIPP MODELING DATA
The conceptual basis for the OZIPP/EKMA model has been described References 1,
2 and 3. The following discussion focuses on the procedures for deriving the
input data for using OZIPP to generate isopleth diagrams for each day investigated.
As shown in Figure 3.1, ozone isopleths are expressed as explicit functions
of initial NMOC and NO concentrations. However, the positioning of the ozone
j\
isopleths on the diagram is also an implicit function of meteorology, pollutant
transport, emissions, and chemistry. In the OZIPP model, several variables can
be input to the model to.tailor the diagram to a specific situation, I.e., the
atmospheric conditions occurring on that day. The OZIPP input variables for
developing day specific diagrams can be grouped according to the following
categories:
1) light intensity
2) dilution
3) 0., transport
4) precursor transport
5) emissions
6) reactivity
In the discussion that follows, procedures for deriving the input variables in
each group are described.
17
-------
1.2 1.4 1.5 1.9
2.0
Figure 3-1. Example Ozone Isopleth Diagram
18
-------
3.1.1 Light Intensity
The OZIPP program utilizes latitude, longitude, day of the year, and
time zone to calculate the appropriate variation of photolytic rate constants.
The model does not provide for adjusting the attenuation of light Intensity due
to cloud cover. Hence, conditions without significant cloud cover are assumed,
corresponding to the types of conditions normally found on days with high ozone
concentrations. Studies have shown that control requirements are relatively
insensitive to variations in light intensity, so this assumption is not perceived
as critical.
Recommended Procedure: The recommended approach for specifying light
intensity is straightforward.The local latitude and longitude for the center
of the city should be used. The day of the year and the appropriate time zone
should be specified, as described in EPA 600/8-78-014a.3
3.1.2 Dilution
In OZIPP, dilution 1s assumed to occur as a result of the rise in
atmospheric mixing height which normally occurs between early morning and mid-
afternoon. The mixing height is the top of a surface-based layer of air which
is well-mixed due to mechanical and thermal turbulence. The mixing height rise
is governed by the specification of four variables Input to OZIPP: the 0800
local civil time (LCT)* mixing height, the maximum mixing height, the time at
which the rise begins in the model (e.g., 0800 LCT), and the time at which the
mixing height reaches its maximum.
* In most areas 1n the United States, local civil time is Identical to local
daylight time during the ozone season. In areas which do not switch to
daylight savings time, local civil time is the same as local standard time.
The OZIPP program was designed to operate on the basis of Local Daylight
Savings Time. For those areas which do not switch to daylight savings time,
the model may be made to operate on standard time by adding one (1) hour to
the time zone described in Section 3.1.1. See also page 39 of Reference 3.
19
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Recommended Procedure: The recommended approach for estimating the
0800 LCT mixing height and the maximum mixing height uses temperature sounding
data routinely compiled by the National Weather Service. Supplemental surface
temperature and pressure data are also needed. Table 3-1 contains guidelines
for selecting the required data, while the detailed procedures for calculating
the morning and maximum mixing heights are contained 1n Appendix A. A minimum
0800 LCT mixing height of 250 meters above ground level (AGL) is recommended.
This value is based on studies of the St. Louis and Philadelphia early morning
urban mixed-layer,11 and is recommended even 1f the morning mixing height com-
puted using the NWS sounding 1s lower. The 250 m minimum is due to mechanical
turbulence caused by Increased surface roughness in the urban area. Also, any
maximum mixing height greater than twice the cllmatological value contained in
Table A-l of Appendix A or Reference 12 should be checked as described in
Appendix A. If no alternate data are available in this case, twice the clima-
tological value is recommended 1n place of the computed value.
Alternate Procedure: Direct measurements of the urban vertical tem-
perature profile may be used in place of the NWS data if they are available.
Mixing heights can be found from local urban radiosonde measurements, helicopter
soundings, or by sodar (I.e., acoustic radar). Identical computational pro-
cedures as those described in Section A-2 of Appendix A should be employed. As
for the recommended procedure, a minimum value of 250 meters should be used if
the computed morning mixing height is less than 250 meters.
Default Procedure: If none of the information needed for the first
two procedures is available, then the climatological values listed in Table A-l,
or obtained from Reference 12 may be used. If the latter is used, the average
summertime maximum mixing height on non-precipitation days should be used. For
the default procedure, the mixing height rise may be assumed to continue from
250 meters at 0800 LCT until the time of the cllmatological maximum daily surface
temperature. If the latter is unknown, then a climatological value of 1500 LOT
(i.e., 1400 LST) can be assumed.
3.1.3 Transport of Ozone
The transport of ozone and its precursors into and from urban areas
has been reported by numerous investigators. ' The discussion in this
section is limited to the transport of ozone; precursor transport is discussed
in the following section.
The two primary mechanisms by which ozone 1s transported into an urban
area are:
20
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Table 3-1. Data Requirements For Calculating Mixing Heights According
to the Recommended Procedure
Surface Temperature Measurements - For each day modeled, the urban
surface temperature at 0800 LCT and the maximum temperature occurring
between 0800 and 1800 LCT are required. The most suitable data are those
taken from a well ventilated shelter at a site near the center of the urban
area.
Surface Atmospheric Pressure Data - For each day modeled, the urban
surface barometric pressures for the same time and location of the
temperature measurements are needed. If these are not available, local
National Weather Service (NWS) or Federal Aviation Administration (FAA)
pressure data may be used.
NWS Radiosonde Data - For each day modeled, mixing heights are
calculated from vertical temperature profiles obtained from radiosondes
taken by the NWS at several sites throughout the United States. Appendix A
contains information on selecting an appropriate site and obtaining the
necessary data.
21
-------
1) advection of ozone along the earth's surface, and
2) advection of ozone aloft, typically at night and during early
morning hours above the ground-based mixed layer, with downward mixing when the
mixing layer increases later in the day.
Ozone transported at the surface is subject to surface reactions and scavenging
by other species (e.g., NO) emitted during the night. As a result of nighttime
atmospheric stability, ozone transported aloft does not come into contact with
scavengers emitted during the night. Thus, overnight advection of ozone aloft
appears to be the more significant mechanism of transport from one urban area to
another.1'13
Control strategies designed to attain and/or maintain the ozone standard
in individual urban areas must take into consideration the impact of transported
ozone on peak afternoon concentrations. The procedure of using OZIPP with the
EKMA technique for the case where future transported ozone concentrations might
be significantly different from current levels is explained fully in References T
and 3, and described in Chapter 4 of this report.
A. Present Transport of Ozone at the Surface
The chief Impact of ozone transport near the surface is expected
to be the more rapid conversion of NO to N02« When Incoming ozone near, the
ground was varied using OZIPP, the impact on maximum ozone concentrations was
generally found to be negligible. This finding held true for incoming concen-
trations as high as 0.12 ppm ozone. In addition, several field studies have
shown that ozone transported along the surface tends to be minimal. '*
22
-------
Recommended Procedure: Based on the previous discussion, 1t 1s
recommended that, for most situations, the value for present ozone transported at
the surface be set equal to zero for each day modeled.
Alternate Procedure: If the situation arises, as a result of the
geographical location of the city under study, that consideration of surface
ozone transport is desirable, then dally estimates of ozone surface transport may
be obtained from urban monitoring sites. It is suggested that the 6-9 a.m. LCT
average ozone concentration at an urban site(s) be used as the estimate of the
concentration of ozone transported Into the urban area along the surface for the
given day.*
B. Present Transport of Ozone Aloft
As noted above, 1t appears that unscavenged ozone transported
aloft is likely to be the component of transport having the greatest Impact on
maximum afternoon ozone levels observed within or downwind from cities. Thus,
daily estimates of ozone aloft are needed for control strategy development with
OZIPP/EKMA. Techniques for estimating the level of ozone transported aloft have
been the subject of two studies.13'18 Five different techniques, which were
considered to be feasible were field tested in Philadelphia during the summer of
1978. The five methods are: 1) use of fixed ground based stations; 2) use of
airborne measurements in a dedicated aircraft; 3) use of airborne measurements
with a portable instrument package; 4) use of free 11ft balloon soundings; and 5)
use of soundings by tethered balloon. Reference 13 contains a detailed description
of each of these techniques as well as a discussion of the findings of the study.
Of the five measurement techniques evaluated, surface measurements at fixed
sites, airborne measurements by dedicated instrumented aircraft and soundings by
ozonesonde beneath a free balloon were judged to be practical means of providing
information on ozone transported aloft.
* See related footnote on page 39
23
-------
Recoimiended Procedure: In selecting the technique to use, consid-
eration was given to such factors as technical capability and available funding,
and the intended use of the data. Ozone measurements taken on the day being
modeled are recoil-mended as the best estimate of ozone aloft. These measurements
should be obtained at surface monitoring sites upwind of the city during the
first hour after breakup of the nocturnal inversion. An acoustic radar (sodar)
can be used to determine the time of inversion breakup for the day. If the time
of the breakup of the nocturnal radiative Inversion is not known, the 1000-1200
Local Standard Time average ozone concentration recorded at the upwind monitor
should be used as the transport estimate. A major advantage of surface measure-
ments is that 1t is the only method which allows continuous measurements, and
thus assurance that measurements exist for days or for times of day which are
later determined to be of Interest. The s1te(s) should be located in as rural a
location as possible so as not to be appreciably affected by local sources of
precursors. The distance such upwind sites should be located from a city depends
on the extent of urban development. Because it is desirable not to measure
pollutants which are redrculated from the city under review, a distance of
40 km or more upwind from the urban core should be sufficient. This distance
perhaps could be reduced for smaller cities. Figure 3-2 depicts orientations
for acceptable upwind sites.
Alternate Procedure; Information on the vertical distribution of
ozone transported above the surface layer in the early morning may be used
directly if it is available. Such information might include aircraft or free-
lift ozonesonde measurements. The reader is referred to Reference 13 for a
detailed discussion of these techniques.
Missing Data: In the event that an estimate of transport is not
available for a given day being modeled, the median transport value from the
remaining days being modeled should be used as a default value. This procedure
applies to all the data gathering techniques described above; fixed site, air-
craft and ozonesonde observations.
3.1.4 Precursor Transport
Just as for ozone, precursor pollutants could be transported in both
the surface layer and aloft. However, consideration of precursor transport is
usually not considered essential for several reasons. First, transported pre-
cursor concentrations tend to be substantially less than concentrations within
2
urban areas. Secondly, in most areas transported organic species are likely to
be less reactive than urban species because of the rapid reactions of the more
reactive species.
24
-------
(B)
STAGNATION
Denotes upwind area
Figure 3-2. Examples of acceptable monitoring locations for estimating
transported ozone.
25
-------
Reconmended Procedure; Several studies have suggested that signifi-
cant transport of precursors Into an urban area 1s not an Important consideration
in most cases.2,13,18 Consequently, transported concentrations of NMOC and NOX,
in both the surface layer and aloft, are recommended to be set to zero.
2
Sensitivity studies presented 1n Appendix B and elsewhere Indicate
that, for a wide range of assumed levels of transported NMOC, there 1s not an
appreciable impact on estimated VOC control requirements using city-specific
EKMA. Further, consideration of transported precursors requires collection of
additional data. However, if 1t is still desired to include consideration of
transported precursors in the analysis, the following alternative procedure may
be used.
Alternate Procedure: Utilize the methodology presented in Appendix B
to estimate local emission control requirements for a city subject to significant
and pervasive precursor transport from upwind sources.
3.1.5 Post 8 a.m. Emissions
As was previously described, the OZIPP/EKMA model is similar in concept
to a Lagrangian photochemical dispersion model in that ozone and precursor
concentrations within a well mixed column of air are modeled as the column
traverses the city. The column of well-mixed air is assumed to originate 1n the
urban core, and begin moving at 0800 LCT toward the site of the peak ozone
concentration. Thus, the emissions occurring subsequent to 0800 LCT are deter-
mined by the space-time track of the column. Within OZIPP, emissions data are
input to the model for each hour after 0800 LCT, and are expressed relative to
the initial concentrations. Thus, there are two basic, and separate, problems
in deriving the necessary emissions Information:
1) determining emissions along the space-time track of the theo-
retical column^
26
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2) expressing the emissions derived in 1) relative to the initial
concentrations. These initial concentrations are assumed to be the result of
local urban emissions occurring prior to 8 a.m.
The first of these involves the use of an emissions inventory to estimate the
emissions occurring along the assumed path. The second involves the calculation
of relative emission fractions that are directly input to the OZIPP model. Each
of these is discussed separately below.
A. Preparation of Emissions Data
The first step in preparing the available emissions data for use
in OZIPP/EKMA is to specify the space-time track of the column trajectory. The
column is assumed to begin moving from the urban core at 0800 LCT directly
towards the site of the peak ozone concentration. The rate of movement is
estimated using the time and location of the peak ozone concentration. The
column is assumed to move at uniform speed (throughout the day) to the site of
the peak ozone value such that it arrives at that site at the time of the
observed peak.* For example, assume the observed peak one-hour-average ozone
concentration on a particular day was measured between 1400-1500 LCT at a site
35 kilometers downwind of the urban core. The column speed would be calculated
* Recall from Chapter 2 that some duplication in high ozone days is likely for
many of the sites in the monitoring network. A rigorous modeling approach
would involve specifying trajectories for each site/day combination, and
generating the corresponding diagrams. However, in most instances, the
trajectory leading to the peak ozone observed on that day should be a suf-
ficient approximation of the other trajectories. Hence, only one diagram can
be developed for the day and be used for all sites. The exception would be
cases in which significantly different post 8 a.m. emissions occur along the
different trajectories between the urban core and the different monitoring
sites. For this situation, separate site/day diagrams need to be developed.
27
-------
by dividing 35 kilometers by seven hours (i.e., the elapsed time between Q800 LCT
and 1500 LCT). The location of the column at any particular hour would be
determined by assuming the column -moved in a straight line between the urban
core and the site of the peak at the uniform speed. (For the example, the speed
would be 5 km/hour.) The assumed trajectory may not be identical to the actual
trajectory corresponding to highest observed ozone concentrations. However, the
wind data should be checked to assure the modeler that the peak ozone concentra-
tion observed at a monitor station is, in fact, downwind from the city. Observa-
tion of urban NMOC/NO ratios made during the St. Louis RAPS do not suggest the
.A
prevailing urban ratio varies greatly during the morning. Further, several
hours are required for ozone to reach its peak. Hence, the trajectory described
above should be an acceptable approximation, provided the column of air passes
over the city by mid-morning (e.g., 1000-1100 LCT).
With the trajectory path identified, the next step in preparing
the emissions data is to use the emission inventory to calculate the hourly
emissions. The procedure depends to some degree on the spatial and temporal
resolution of the emission inventory. In the recommended methodology that
follows, a seasonally adjusted, annual county-wide emissions inventory of
reactive VOC* and NOV is assumed to be available. This level of detail will
J\
result using procedures presented in Reference 19. An alternate method addresses
procedures that can be used with inventories of greater temporal and/or spatial
* In the discussion of post 8 a.m. emissions in Section 3.1.5, the term "VOC,"
volatile organic compounds, refers to the sum of reactive organic emissions
included in emission inventories. The term "NMOC," non-methane organic .
compounds, refers to ambient measurements of all organic compounds other than
methane.
28
-------
resolution. Regardless of the resolution of the inventoryt the goal of this
step is to develop emission densities representative of the area over which the
column 1s assumed to pass each hour. Thus, the emission density represents the
average emission density "as seen by the column" for each hour between the
simulation start and the time of the measured peak.
Recommended Procedure: For this approach, a county-wide emissions
inventory 1s assumed; I.e., total reactive VOC and NO emissions on a seasonally
adjusted annual basis are available at the county level only. The simplest
method of deriving the necessary Information 1s to compute the county-wide
emission density by summing total emissions (point plus area source) and dividing
by the area of the county. Hourly resolution of the Inventory can be estimated
by assuming emissions occur uniformly throughout the year. For example, one
would divide the seasonally adjusted annual emissions by 8760 hrs/yr. The
emission density at any hour 1s thus determined by the county in which the
trajectory path is located for that hour. For those hours 1n which the trajec-
tory path crosses a county boundary(s), the county emission densities may simply
be averaged.
The procedure just described can best be illustrated by example
(see Figure 3-3). Part A of the figure shows the information typically available.
Here it assumed that the peak ozone concentration measured on the example day
occurred at a site 35 kilometers downwind of the urban area between 1400 and
1500 LCT. The first step is to depict the trajectory path on an appropriate map
by marking off hourly segments (see Part B). Step 2 Involves deriving the
county-wide emission densities on an hourly basis (Part C). Finally, in Step 3,
the sequence of emissions is determined by using the emissions for the county in
which each hourly segment lies. For those cases 1n which a segment lies in two
counties, the emission densities of the two counties were averaged. Part D
shows the results of Step 3.
The approach just described 1s a relatively simple one which 1s
consistent with the amount of information typically available. However, as
29
-------
A) Information Available
Peak ozone measured
between 1400-1500 LCT.
Site is 35km downwind
of center-city (cc).
County Emissions Data
Adjusted Adjusted
VOC NOX
Emissions Emissions
Area,km2 kg/yr kg/yr
5.45x1O7 2.96x1O7
3.93x1O7 3.38x1O7
1.68xl06 1.17xl06
B) STEP 1: Determine Trajectory Segments
A straight line is drawn between the center-city and the downwind
site. The line is divided into seven equal segments, representing
the number of hours between 800 and 1500 LCT.
C) STEP 2: Calculate, hourly, county-wide emission densities
Area, km2
150
500
300
Adjusted
VOC Emissions
kg/yr
5.45x1O7
3.93x1O7
1.68xl06
Adjusted
VOC Emission*
density, kg/hr km2
41.5
9.0
.6
Adjusted
NO Emissions
xkg/yr
2.96x1O7
3.38x1O7
l.UxlO6
Adjusted
NOV Emission*
defisity. kg/hr km2
22.5
7.7
.4
*Emission density = emissions/(8760 x area)
D) STEP 3: Specify Sequence of Emission Densities
Hour
1
2
3
4
5
6
7
Time. LCT
8-9
9-10
10-11
11-12
12-13
13-14
14-15
Trajectory Segment
Location (County)
A
A/B
B
B
B/C
C
Adjusted
VOC Emission
density, kg/km2 hr
41.5
25.3
9.0
9.0
9.0
4.8
.6
Adjusted
NO Emission
density, kg/km2 hr
22.5
15.1
7.7
7.7
7.7
4.1
.4
Figure 3-3. Example Formulation of Post 8 a.m. Emission Densities Scheme
30
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described below, more sophisticated techniques may sometimes be desired. It
should be remembered, however, that city-specific EKMA (Level III analysis) does
not require a precise definition of an air parcel trajectory. Use of spatially
and temporally detailed inventories implies a need for greater efforts to define
trajectories. Such efforts are more consistent with the use of more sophisticated
models. Although the use of very detailed emission Inventories 1s inconsistent
with the degree of sophistication inherent in city-specific EKMA, methods for
improving spatial and temporal resolution are possible. These are described 1n
the following paragraphs.
Alternate Procedure; In the recommended approach, emission
densities were determined on a county-wide basis. In some Instances, a finer
spatial resolution may be desired. For example, suppose total emissions are
available for the county, but the county encompasses a very large land area, of
which the urban area is a relatively small part. In this case, one may wish to
suballocate the emissions to areas smaller than the county"levels. For example,
the very large county might be divided into a rural portion and an urban portion,
with emissions apportioned to each area. The methodology for apportioning will
usually depend on available data and the particular situation encountered.
Consequently, no specific guidance can be given here, but the concepts contained
in References 19 and 20 may be adopted. If an allocation 1s performed to a sub-
county level, the sub-county areas should not be resolved to less than 100 square
kilometers. Resolution to smaller areas is not recommended because of the
inability of the model to consider horizontal gradients in pollutant concentra-
tions.
Alternate Procedure; A second way in which the recommended
approach could be made more precise is more detailed consideration of the temporal
distribution of emissions. In the recommended approach, hour by hour differences
in emissions are not considered. If more detailed information is available,
these data could be employed to derive more precise temporal resolution of
emissions as described in Reference 20. In the absence of geographically specific
data, a city-wide average may generally be used for distributing temporal emission
patterns. For example, the distribution could be calculated as the average of
the temporal distribution of mobile and stationary sources.
Alternate Procedure: In some cases, emissions inventory data
will be available that Is of a finer resolution than a county-wlde/annual basis.
For example, an hourly gridded emissions inventory may be available. This
procedure addresses the problem of using an hourly emissions inventory with
grids finer than 10x10 kilometers on a side. However, the development of a
gridded inventory specifically for use with the OZIPP/EKMA technique is not
recommended.
31
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Recall that the model underlying the OZIPP/EKMA procedure does
not consider the existence of horizontal concentration gradients. The emission
density "seen by the column" during any hour should represent an average. Con-
sequently, 1t is recommended that emissions inventory data resolved to grids
smaller than 10x10 kilometers Ci.e., 100 km2) be aggregated to a minimum size of
100 square kilometer grids. The larger grid squares conform more readily to the
assumptions underlying the model. The larger grid cells should be located such
that the average emission density is representative of the area it covers.
Thus, for example, a 10x10 km grid square might be centered on the center city,
and the new grid network for OZIPP/EKMA developed from there.
The procedure for determining the emissions encountered by the
column of air simulated with OZ1PP is similar to the one described for the
recommended methodology. However, in this case the network with the larger grid
squares is used 1n place of the county-wide data. The resulting emissions
schedule 1s established by the location of the trajectory segments with respect
to the grid cells. If a trajectory segment crosses a grid boundary, the emission
densities of the adjacent grids may be averaged.
B. Derivation of Emission Fractions
In Section A, the procedure for estimating the sequence of emis-
sions was described. The emission sequence represents emissions injected into
the modeled column of air each hour subsequent to the 0800 LCT simulation starting
time. As indicated in the example problem (see Figure 3-3), the emission densities
comprising the sequence of emissions are expressed 1n terms of mass per unit
area (e.g., kg/km2). In OZIPP, however, the emissions must be expressed relative
to initial concentrations. Thus, it is necessary to translate the sequence of
emissions (in mass units) to fractions of initial concentrations. This is
accomplished by first deriving an initial emission density which is tied to the
initial concentration. The emission fractions are then computed by dividing the
hourly post 8 a.m. emission densities (i.e., from the sequence of emissions) by
the initial emission density. In essence, this procedure is the same as calcu-
lating the concentrations that would be generated by the emissions within the
imaginary column of air after one hour, and then dividing those computed
32
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concentrations by the initial concentration to obtain the appropriate fractions.
The approach recommended for computing emission fractions 1s one
in which an initial emission density 1s computed from Initial conditions. The
initial emission density is calculated as the emission density necessary to
generate in one hour the initial concentrations observed within the column. So,
if an initially empty column were "exposed" to the calculated initial emission
density for one hour, the concentrations of precursors in the column at the end
of the hour would equal the observed Initial level. The emission density for
any hour after 0800 LCT can then be related to the Initial concentrations by
means of the initial emission density. For example, 1f the emission density for
hour 1 (i.e., 0800-0900 LCT) is one-third that of the initial emission density,
then one-third of the initial concentration would be generated by the emissions
for that hour. The emission fraction can therefore be calculated using the
following equations:
Q0=aC0Ho (3-1)
and
Qi
E1 = ui (3-2)
where
QQ = calculated initial eirisslon density (kg/km2)
CQ = initial precursor concentration (ppm)
Hp = initial mixing height (kilometers)
Q.J = emission density for hour i from the sequence of emissions
(kg/km2)
E.J = emission fraction for hour i
33
-------
a = conversion factor for converting from volumetric to
mass units
The methodology 1s further Illustrated 1n Figure 3-4, and the procedures for
deriving the necessary data are described below.
Recommended Procedure: The first step in calculating the emission
fractions is to compute an initial emission density for MO and VOC. This
requires the specification of an initial concentration for each precursor and the
initial mixing height. The initial concentrations can be obtained from ambient
6-9 a.m. measurements of NMOC and NO on the specific day being modeled. If NMOC
or NO ambient data for the specific day being modeled are unavailable, then the
median 6-9 a.m. NMOC and NO concentration for all days being modeled should be
used for each precursor.
The computational steps necessary to calculate the emission
fractions are outlined in Table 3-2 and illustrated in Figure 3-5. A brief
explanation of each step follows:
Step 1: The initial concentration to be used in the emission
fraction calculations is the 6-9 a.m. average pre-
cursor concentration 1n the urban area. (Average
concentrations are calculated for both NMOC and
NO .) The procedures for calculating the 6-9 a.m.
average concentrations at individual monitors are
described in Section 3.2.2, and should be followed
here. If more than one monitor 1s located in the
urban area, the 6-9 a.m. concentrations at each
monitor should be averaged to obtain an the overall
urban average 6-9 a.m. concentration.
Step 2: An Initial emission density 1s calculated for VOC
and NO , individually. The recommended conversion
factors (a) for VOC and NO are 595 kg HC/ppmC km3
and 1890 kg NO /ppm km3, respectively. The deri-
vation of the conversion factors is described in
Table 3-2. For converting NMOC to VOC, it is
assumed that one ppmC represents a molecular
weight equivalent to CHa-s9. For NO , a molecular
weight of 46 is assumed because inventories list
NOY as equivalent N02.
A
Step 3: The hourly emission fractions are calculated by
dividing the emission densities for each hour by
the initial emission density. This 1s done sepa-
rately for each pollutant.
34
-------
Urban Area
Time: 0800
C = Column concentration at
0 0800 LCT
H = Mixing Height at 0800 LCT
Assume the precursor concentration in the
column is CQ. Therefore, QQ " C H
Time: 0800 - 0900
Urban Area
Assume the emission density for the hour 0800-0900 equals 1/4
of the emission density calculated from the initial concen-
tration-
The concentration generated by the emissions occurring between
0800 and 0900 would be 1/4 of the initial concentration-
Therefore, the emission fraction for Hour 1 would be
1/4, or .25:
'
- -
Figure 3-4. Illusiration of Emission Fractions Calculated
Using Initial Conditions.
35
-------
Table 3-2. Recommended Procedure For Calculating Emission Fractions
Step 1: Calculate the 6-9 a.m. urban average NMOC and NO concentrations for
the day being modeled. If data from more than one urban monitoring
site are available, average the Individual 6-9 a.m. levels. If data
for the specific day being modeled are not available, then use the
median of the 6-9 a.m. averages for all days being modeled.
Step 2: Calculate the initial emission density for VOC and for NO :
Co Ho
where
Q = Initial emission density, kg/km2
HQ = Day-Specific mixing height at 0800 LCT (kilometers)
« = Conversion factor*
Step 3: Calculate individual hourly emission fractions:
where
E.J = Hourly emission fraction for hour i
Q.. = Emission density for hour 1, kg/km2
QQ = Initial emission density calculated in Step 2 above,
kg/ km2
* Conversion factors: « For NMOC to VOC = 595 kg/km3 ppmC
« For NOV = 1890 kg/km3 ppm
A
These conversion factors were calculated assuming a molar density of dry air at
25°C (i.e., 1 mole/24.4 liters). For NMOC to VOC conversion, the molecular
equivalent to one ppmC is assumed to be CH2>5 (i.e., a molecular weight of 14.5
is assumed).9 For NO, a molecular weight of 46 1s assumed since NO emission
inventories are complied as equivalent N02)-
36
-------
A) Available Information
• Air Quality Data
NMOC [=] ppmC-
NOX L=J Ppm
Urban
Monitor
1
2
Pollutant
NMOC
NOX
NMOC
NOV
6-7
2.3
.250
1.7
.190
7-8
2.0
.200
1.7
.210
8-9
1.5
.180
1.6
.170
6-9 AVR.
1.9
.210
1.7
.190
• Emissions Schedule Shown
In Figure 3-3
• 0800 LCT Mixing Height = .25km
B) Step 1: Calculate Urban Average 6-9 LCT Concentration
NOV
1.9 + 1.7
= 1.8
.210+.190
.200
C) Step 2: Calculate Initial Emission Densities
For VOC
Qo - a Co Ho • (595 k9/km3 ppraC) (1.8 ppmC) (.25 km) = 268 k9/km2
For NOX
Qo = «Co Ho = (1890 kg/km3 ppm) (.200 ppm) (.25 km) = 95kg/km2
D) Step 3: Calculate Hourly Emission Fractions
VOC Hourly
NQX Hourly
Hour
1
2
3
4
5
6
7
Time, LCT
8-9
9-10
10-11
11-12
12-13
13-14
14-15
Emission Density,*
kg/ km2
. 41.5
25.3
9.0
9.0
9.0
4.8
.6
NMOC Emission
Fraction**
.15
.09
.03
.03
.03
.02
.00
Emission Density* NOX Emission
kg/km2
22.5
15.1
7.7
7.7
7.7
4.1
.4
Fraction**
.24
.16
.08
.08
.08
.04
.00
* Hourly Emission Densities From Figure 3-3
** Emission Fraction = (Emission Density)/(Initial Density)
Figure 3-5. Example Calculation of Emission factions
37
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3.1.6 Reactivity
The OZIPP model incorporates a chemical kinetic mechanism to describe
the reactions taking place among pollutants. The kinetics model used 1n OZIPP
represents a detailed sequence of chemical reactions which has been proposed for
a mixture of propylene, n-butane and NO . The chemical mechanism used 1n the
J\
kinetics model is based on information obtained in smog chamber experiments with
22 23
propylene and n-butane separately. The kinetics model predictions were
matched against Bureau of Mines (BOM) smog chamber data obtained by irradiating
automobile exhaust. Initial proportions of propylene and n-butane were then
adjusted so that consistently close agreement was obtained with observations in
the BOM chamber. Of the available smog chamber studies, the ones using auto-
motive exhaust are thought to use a mix of reactants most representative of the
mixes found in urban atmospheres.
In OZIPP, total NMOC is represented by the sum of propylene and
n-butane, with aldehydes related to the total "NMOC" concentration. The reactivity
is determined by specification of three variables: 1) the fraction of NMOC that
is propylene; 2) the fraction of NMOC that is to be added as aldehydes; and 3)
the fraction of initial total NO that is N0?. The proportional mix of propylene
A £
and n-butane for which OZIPP yields peak ozone predictions comparable to that
observed with automobile exhaust in the BOM chamber is 25 percent and 75 percent,
respectively, with an additional 5 percent of the initial NMOC added as aldehydes.
Propylene-butane mixes have not been established for any atmospheric mix other
than the automotive mix used in the BOM chamber. Unless satisfactory corre-
spondence between other atmospheric mixes and other propylene-butane mixes can be
established, the 25 percent propylene, 75 percent butane, plus 5 percent aldehydes,
should be used.
38
-------
The third variable to consider Is the fraction of the Initial N02 that
is NOX. Sensitivity studies have suggested that the effect of the Initial N02/N0>
mix on peak ozone concentrations is small. Consequently, specification of this
variable is not deemed critical.
Recommended Procedure: The 25 percent propylene-75 percent butane mix,
with 5 percent of the initial NMOC added as aldehydes, should be assumed for the
model simulations. This mixture corresponds to the reactivity of automotive
exhaust irradiated in a smog chamber. Unless satisfactory correspondence can be
established between other propylene-butane mixes and other atmospheric mixtures
which differ appreciably from automotive exhaust, the 75 percent/25 percent mix
should be used.
A default value of 25 percent for the initial N02 to NO ratio is
recommended. Sensitivity studies have shown that peak ozone concentrations (and
hence control estimates) are relatively insensitive to any particular assumption.
However, day-specific information may be used if desired. For this case, the 6-
9 a.m. average N02 should be divided by 6-9 a.m. average NO to obtain an N02/N0
ratio at each monitor located in the central core of the uroan area. If more
than one monitor is located in the urban area, then an average ratio may be
obtained by averaging the individual ratios.*
3.2 EMPIRICAL DATA
Two pieces of empirical data are needed to establish a starting point on the
ozone isopleth diagram for calculating control requirements. The first is the
maximum one-hour average ozone concentration observed at the site of interest.
The degree of emission control necessary to reduce this "peak" to 0.12 ppm is to
be calculated; hence, the peak level will be termed the daily design value.
Strictly speaking, this latter procedure is more consistent with the use of
measured 6-9 a.m. urban ozone concentrations to estimate ozone transported
into the city within the morning mixed layer Csee page 23). Howevei; use
of the default value makes little difference 1n the resulting control estimates.
39
-------
The second piece of information needed is the NMOC/NO^ ratio. This ratio is
derived from the 6-9 a.m. concentrations of NMOC and NOV within the urban area.
y\
These measurements correspond conceptually to the NMOC and NO concentrations on
j\
the axes of the isopleth diagrams. The ratio will be termed the design ratio.
The procedures for deriving both the design ozone values and the design ratios
are described below.
3.2.1 Dally Ozone Design Value
The dally ozone design value is used 1n conjunction with the NMOC/NOX
ratio to establish a starting point on the Isopleth diagram for calculating
control estimates. The "dally design value" 1s used to refer to the measured
maximum hourly ozone value for the day being modeled.* For use with the isopleth
diagram, the design value should be expressed 1n ppm units rounded to two decimal
places.
Recommended Procedure: A daily maximum 1 hour value is obtained for
each site which is downwind of the city, and/or within the city in the case of
light and variable winds on the day for which the isopleth diagram is to be
developed. Surface wind data should be examined to assure that the site is not
"upwind" of the city. Based on the results of field studies and reviews in which
ozone gradients downwind from urban areas were examined, peak ozone concentrations
should generally be observed within 15-45 km downwind of the central business
district.2,25~2* Specific siting criteria for the monitoring of photochemical
pollutants are discussed elsewhere.2,26"27
3.2.2 NMOC/NOX Ratios
The prevailing 6-9 a.m. LCT NMOC/NOV ratio measured in the urban core
/\
of the city 1s the second piece of empirical data required to define the starting
point on the Isopleth diagram. The design ratio is viewed as a characteristic of
* Note that an ozone design value exists for each site for which the day being
modeled 1s among the five highest ozone days.
40
-------
the city which would prevail during the remainder of the morning and early after-
noon in the absence of chemical reactions. The ozone isopleth diagram expresses
peak ozone concentrations as a function of the initial concentration of NMOC and
NOV. Thus, the 6-9 a.m. LCT NMCC/NOV ratio 1s considered to be the appropriate
A ./»
ratio for use with the Isopleth diagram since this ratio 1s consistent with the
28
conceptual basis of the model. To ensure that representative ratios are obtained,
the NMOC and NOV instruments should be collocated in the central core of the
A
urban area. The slteCs) should be located in an area of relatively uniform
emission density and not significantly influenced by any individual source. More
detailed guidance on siting NMOC instruments is contained 1n Reference 29.
Guidance on the operation of NMOC Instruments 1s available in Reference 30.
Significant discrepancies have been found between NMOC/NO ratios
A
calculated on the basis of ambient measurements and those obtained from emission
31
inventory data. Reasons for the lack of correlation between the two ratio
calculation procedures have not been resolved. As a result, only ambient NMOC/NO
A
ratios should be used with EKMA since these ratios are consistent with the con-
ceptual basis of the model and the emission ratios have been shown to be poor
surrogates for these ambient ratios. To ensure maximum usefulness of the contin-
uous NMOC data, careful attention to calibration, operational procedures, and
quality assurance 1s necessary. Presently available instruments are capable of
yielding acceptable data at concentrations above about O.S.ppmC 1f they are care-
fully maintained and calibrated.''
The NMOC data are to be collected during the season of peak ozone
concentrations Csummerl. Because NMOC concentrations are apt to be relatively
high in central urban locations at those times of the day (early morning) when
41
-------
these measurements are required for use in EKMA more confidence can be placed in.
the estimate. Data from a recent study of continuous NMOC Instruments suggest
that relative standard deviations of 30 percent are likely for well operated and
maintained instruments when concentrations are above 0.5 - 1.0 ppmC. However,
because of the uncertainties in individual NMOC readings, the NMOC/NO¥ ratio
J\
calculated at a single site for a single day is not recommended for use 1n city-
specific EKMA. Considering FID Instrument reliability and model sensitivity, the
following procedure is recommended for calculating NMOC/NO ratios.
/\
Recommended Procedure:
1. Individual NMOC/NO ratios at a site are calculated as the ratio of
the 6-9 a.m. LCT average NMOC ana NO concentrations, i.e., the average of the
hourly concent-rations for hours 6-7, 7-8, and 8-9 LCT, respectively. Ratios
should not be calculated for any day with less than two valid hours for either
NMOC or NOV.
y\
2. If precursor measurements from more than one urban site are avail-
able for the same day as the ozone design value, and the individual ratios at
each site do not differ by more than 30 percent from the average ratio, then the
design ratio (DR) is the average of the individual 6-9 a.m. NMOC/NO ratios. If
data from only one site are available for a specific day, the design ratio for
that day should be calculated using the procedure described in (3) below.
n
DR = z (R.) = E
=1
n
where
R, = 6-9 a.m. (NMOC/NOJ ratio at Site 1
I f\
ff = the average ratio
n = the number of sites
3. If only one site measuring both NMOC and NO is available, or if
the values from different sites are missing or not comparable (I.e., some ratios
differ by more than 30% from the mean ratio), the following procedure is recom-
mended. The ratio for use with the isopleth diagram should be calculated as the
median of the ratios observed on all those days being modeled vdth accompanying
NMOC and NO data.
42
-------
DR = median IR--}, for a single site
j
or
DR = median" IK.}, for multiple sites
where
j = a high ozone day, and j = 1,2»...,N
When the monitor fs located In a relatively high and uniform emission density
area, good agreement has been found between ratios calculated on Individual high
ozone days and more robust measures..-1,2,^8 Thus, use of the tnedlan ratio 1s
viewed as providing a robust estimate of the dally design ratio which 1s consist-
ent with the conceptual basis of the model.
4. If no collocated pairs of NMOC and NO monitors were operated 1n
the urban area during one or two of the years 1n the suggested three year period,
1t 1s recommended that the procedure tn (3) above be followed using the available
NMOC/NO data to choose a median NMOC/NO ratio. In this case, the median ratio
would be used with ozone data from all years without the appropriate precursor
concentration data.
Two examples of calculating NMOC/NO¥ ratios for use with EKMA/OZIPP are
A
contained 1n Figure 3-6.
3.3 USE OF OZIPP TO GENERATE ISOPLETH DIAGRAMS
An ozone Isopleth diagram 1s to be generated for each day Investigated.
Section 3.1 described the procedures for deriving the day-specific modeling data,
and Section 3.2 described the formulation of the empirical data. This section
briefly addresses the procedures for producing a day-specific diagram using these
data. The details are described in Reference 3, the OZIPP User's Manual.
The modeling data are input to OZIPP by means of option cards. Table 3-3
shows the appropriate option card to be used with each category of model vari-
ables described in Section 3.1. There are only two other important considerations.
First, the diagram must contain the starting point defined by the intersection of
the design NMOC/NOV ratio and the daily design ozone level. This is accomplished
A
by selecting appropriate NMOC and NQ.. scales on the abscissa and ordinate,
n
43
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Example 1.
Given: Ratios at five urban core sites on the day being
modeled are respectively 9.1, 6.2, 6.4, 6.5 and 9.8
Find: The NMOC/NO ratio for use in EKMA
Solution: First calculate the average ratio
F 9.1 + 6.2 + 6.4 + 6.5 + 9.8
R = -. g
R = 7.6
Note that all the ratios are within +_ 305- of R", i.e., all
the ratios are.between 5.3 and 9.9. Then, the design ratio
is
DR = R = 7.6
Example 2.
Given: Assume that only one site is available for the study.
Assume also that the NMOC/NOX ratios are available for
five of the design days. These ratios are 8.8, 8.6,
15.5, 9.7, and 14.3, respectively.
Find: The design ratio for use with all the design days.
Solution: Since only one site is available, the design ratio
is
DR = median {8.8, 8.6, 15.5, 9.7, 14.3}
DR = 9. 7
FIGURE 3-6. Example Calculations of the Design NMOC/NC Ratio
A
44
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Table 3-3. OZIPP Options For Model Input Data
Input Data Section OZIPP Option
Light Intensity 3.1.1 PLACE
Dilution 3.1.2 DILUTION
03 Transport 3.1.3 TRANSPORT
Precursor Transport 3.1.4 TRANSPORT
Post-8:00 a.m. Emissions 3.1.5 EMISSIONS
Reactivity 3.1.6 REACTIVITY*
* Since OZIPP default values are recommended, this option may be omitted.
45
-------
respectively, Reference. 3 provides guidance for choosing the proper scales using
the ISOPLETH option. Secondly, tsopleths corresponding to the ozone dally design
value and to 0.12 ppm should &e Incorporated In the diagram to facilitate control
calculations. This 1s also accomplished by using the ISOPLETH option. Conse-
quently, a day-specific Isopleth diagram can be generated by proper specification
of the ISOPLETH option 1n addition to those listed 1n Table 3-3.
46
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4.0 CALCULATION OF CONTROL ESTIMATES
The previous Chapter described procedures for deriving day-specific ozone
isopleth diagrams. These diagrams are used to calculate VOC emission controls
necessary to reduce the peak ozone level observed at a particular site on an
individual day to 0.12 pom. The SIP requirement 1s determined from those results
according to the method described 1n Section 2.3. This Chapter describes the
techniques that are used to calculate the VOC emission reduction estimates for
each site-day 1n order to determine the SIP control requirement.
In estimating the degree of VOC control necessary to reduce peak ozone
levels to 0.12 ppm, the role of NOX should be accounted for. This is accomr
pi 1 shed by estimating the change 1n NO between the base period and the future
A
period which is of Interest. For the 1982 SIPs, the most straight-forward
procedure for estimating this change 1s to project the expected percent change
in total region-wide NOV emissions between the base period and 1987. -Factors to
A
consider include growth, anticipated effects of various control programs, and
technological advancements.
The first step in calculating controls using a diagram is to establish a
starting point on the diagram. This point is defined by the intersection of the
design NMOC/NO¥ ratio line with the isopleth corresponding to the ozone dally
^
design value, and represents the base case conditions (i.e., base emissions,
base transport, etc.). All other points on the diagram represent the effects of
changing precursor emissions relative to the base case assuming that everything
else remains constant. Thus, control requirements may be calculated for a given
day using a single diagram if:
47
-------
11 Initial precursor concentrations and post 8;OQ a.m. emissions are-
reduced proportionally, and
2} All other non-emission factors (e.g., transported ozone} remain
constant.
A second situation arises tf there 1s a concurrent change 1n emissions and
some other factor, or If post 8:00 a.m. emissions are not reduced proportionally
with Initial concentrations. However, meteorological conditions must be assumed
to be the same 1n the future case as 1n the base case, e.g., mixing heights will
be the same for both diagrams. In this case, two Isopleth diagrams are required:
(1) a diagram applicable for base case conditions, and (2) a diagram applicable
for the future (i.e., the post-control period 1n 1987), which reflects the con-
current changes described above. This situation 1s discussed in Section 4.2.
4.1 USE OF SINGLE DAY-SPECIFIC DIAGRAMS
An isopleth diagram derived for a specific day corresponds to the base
period. If non-emission conditions corresponding to the base period are expected
to remain unchanged, then the single day-specific diagram can be used to estimate
the VOC control requirements. The single diagram cannot be used if one of the
following situations is expected to occur between the base period and the future
period of interest (e.g., 1987):
1) ozone transported into the area changes
2) precursors transported into the area change
3) the diurnal emission pattern changes grossly (.I.e., hourly emissions
change independently of one another}.
48
-------
If one or more of these situations 1s anticipated, the procedures described 1n
Section 4.2 must be followed.
The procedure for arriving at the necessary VOC emission reduction 1s out-
lined 1n Table 4-1 and an example 1s shown 1n Figure 4-1. The starting point on
the diagram 1s located by the Intersection of the design NMOC/NCL ratio line
A
with the Isopleth corresponding to the dally ozone design value. The NMOC and
N0¥ coordinates of this point correspond to the base case conditions to which
A
all changes 1n NOY and/or NHOC must be referenced. The next step 1s to estimate
^
the change 1n NO between the base state and the future period. The base NOV
A X
level 1s adjusted by the percent change 1n total NOX emissions anticipated
between the two periods. A post-control point 1s then located on the 0.12 ppm
isopleth at the point reflecting the projected change In NOV. The final step 1n
J\
the calculation Is to compute the percent change 1n NMOC required to reduce NMOC
from the base point to the post-control point. This percent reduction Is the
degree of VOC emission control necessary to reduce the peak ozone level to
0.12 ppm.
4.2 CONCURRENT CHANGES IN EMISSIONS AND OTHER FACTORS
Consideration of different control measures that are implemented concur-
rently necessitates using a different procedure than that described 1n Section 4.1.
The major examples of concurrent implementation of control measures include:
1) reduction in local precursors and reduction of ozone transported
into a city;
2) reduction in local precursors and reduction of precursors trans-
ported into a city;
49
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Table 4-1. Control Calculations Using A Single Isopleth Diagram
Step 1 : Locate the base-case point on the diagram by finding the Intersection
of the design NMOC/NO ratio line with the Isopleth for the ozone
dally design value. Cet the NMOC and NO coordinates of this point
be signified by (NMOC)i and (NOYh, respectively.
A
Step 2: Calculate the post-control NO coordinate by adjusting the base
NO level by the expected percent change 1n NO emissions between the
base and post-control periods. Let the post-control NO coordinate be
signified by (NOJ2. Thus, *
A
ANO
(NOX)2 = (N0xh X (1 -H
where
(NOV)2 = post-control NOV coordinate
X A
(N0v)i = base case NOV coordinate
X X
ANOV = expected change in NOV, percent
A A
Step 3: Locate the post-control point on the diagram by finding the post-
control HOY coordinate, (N0¥)2» on the 0.12 ppm ozone Isopleth. Let
the NMOC coordinate of thisxpo1nt be (NMOC)2.
Step 4: Compute the percent reduction necessary to lower (NMOC)i to (NMOC)2.
Thus,
% Reduction in VOC = [1 - (NMOC)? ] x 100
"
50
-------
GIVEN: 03 Dally Design Value = .24
Design NMOC/NOX =8:1
Anticipated Change in N0¥ = -20%
J\
Base case diagram shown below
FIND: Percent reduction in VOC emissions needed to reduce ozone from .24
to 0.12 ppm
SOLUTION:
BflSt ^PSf DlflGRP.f. 03 «!'.CrT L .12
STEP 1: The base case point is found by the intersection of the 8:1 NMOC/NO
ratio line with the .24 ozone isopleth (Point 1) on the diagram. At
Point 1, (NMOCh = 1.64 and (N0vh = .205
/\
STEP 2: The post-control NO coordinate is calcualted as follows:
y\
(NO)2 = (.205) x (1 - = .164
STEP 3: The post-control point is located at the intersection of the .164 NOX
coordinate and the 0.12 ppm ozone isopleth (Point 2). At Point 2,
(NMOC)2 = 0.46
STEP 4: The VOC emission reduction is calculated as
% reduction = (1 - 6) x 100 = 72%
Figure 4-1. Example emission reduction calculation using a single ozone
isopleth diagram
51
-------
31 reduction 1n local precursors and gross changes 1n diurnal emission
patterns;
4} combinations of the above.
In each case, the procedure for calculating YOC emission reductions requires the
development of an additional Isopleth diagram. The VOC emission reduction is
then calculated using both the base case and the additional diagram. Each of
the above four situations are considered below.
4.2.1 Concurrent Reductions in Local Precursors and Transported Ozone
When calculating emission reductions, consideration should ordinarily
be given to the situation when future transported ozone concentrations may be
different from the base period levels as a result of the imposition of control
measures upwind of the city of interest. Before calculating VOC emission reduc-
tions, an isopleth diagram must be generated for the post-control case, i.e.,
the case in which the ozone transported into the area is reduced. It must be
recognized that it is difficult to generalize about what should be assumed
concerning future levels of transported ozone. One source of this difficulty
arises as a result of the differing characteristics of "upwind areas." For
example, 1n the Northeastern United States, one could expect greater reductions
in "future transported ozone" than in many other areas. The greater reductions
would occur because of large designated nonattainment areas for ozone which are
upwind of northeastern cities. Nonattainment areas are subject, at a minimum,
to emission controls arising from the Federal Motor Vehicle Control Program
(FMVCP), application of Best Available Control Technology (BACT) on new sources
of VOC, phasing out of old, poorly controlled stationary sources and application
of Reasonable Available Control Technology (RACT) on existing sources. In many
52
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other areas of the country however, upwind areas are predominantly unclassified
or attainment areas. These areas are subject only to the FMVCR and emission
reduction which might occur as the result of existing, poorly controlled sources
being retired and replaced with new sources having BACT. The procedures described
below require case by case judgments as to whether areas upwind of a city being
modeled are primarily nonattalnment areas or otherwise. Once this judgment 1s
made, these procedures may be used to estimate the degree of reduction expected
due to control programs Implemented upwind of the city. Following this discus-
sion 1s a description of the quantitative techniques for estimating VOC emission
reductions.
A. Estimating Future Transport of Ozone
Recall from Section 3.1.3 that ozone may be transported 1n both
the surface layer and aloft. As was described 1n that section, several studies
have shown that advectlon of ozone aloft appears to be the more significant
mechanism of transport from one area to another. If control programs are imple-
mented in upwind areas, ozone transported into the city is likely to be reduced.
However, in most cases, the source area and the level of future controls are not
likely to be known to any degree of certainty.
Recommended Procedure: Because of the considerable uncertainty
in the location and future control levels of the source area(s) for ozone trans-
ported into the urban area, the relationship depicted in Figure 4-2 is recommended
for estimating the future ozone transport level given the level of present
transport. The solid curve in Figure 4-2 was derived on the basis of changes in
VOC emissions which are projected assuming a national mix of source categories;
national estimates of projected growth in stationary source emissions and vehicle
miles traveled (VKT); anticipated impact of applying reasonably available control
technology CRACT) to stationary sources and the impact of the Federal Motor
Vehicle Control Program on mobile sources; and consideration of natural back-
ground levels.2,32'35 It was assumed that future ozone levels would not exceed
the NAAQS. The solid curve is most appropriate for use by cities subject to
impacts from large upwind nonattainment areas. The dashed curve in Figure 4-2
53
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Q.
Q.
S-
o
Q.
c/J
£1
o
N
C
d)
S-
Present Ozone Transport, ppm
Figure 4-2 Future Ozone Transport as a Function of Present Transport
-------
differs from the solid curye only 1n that the Impact of FACT 1s ignored. The
dashed curve is most appropriate for use when a city 1s Isolated and not Impacted
by large designated nonattainment areas.
Without Information to the contrary, future transport along
the surface should be assumed equal to zero. If significant non-zero concen-
trations were found for present ozone transport along the surface, then future
ozone transport levels should be obtained using the relationships shown in
Figure 4-2.
B. Calculation of 1/OC Emission Reductions
The computational procedure for determining the required VOC
emission reductions is outlined in Table 4-2, and an example problem is shown in
Figure 4-3. The procedure is similar to that described in Section 4.1. The
starting point for the calculation is found in exactly the same manner as
described in Section 4.1, I.e.» by the intersection of the design NMOC/NO ratio
A
line and the ozone isopleth corresponding to daily ozone design value on the
base case diagram. Again, the NMOC and NO coordinates of this point correspond
J\
to the base case conditions to which any changes in NMOC and/or NO must be
A
referenced. The post-control point is found exactly as was previously described,
except that a diagram corresponding to future transported ozone level is used.
Changes expected 1n NOY are first calculated by adjusting the base NOV level
A A
(i.e., the NO coordinate of the starting point) by the assumed percent change
A
in NO expected between the base period and the post-control period. The post-
A
control point 1s found on the 0.12 ppm isopleth of the future case diagram at
the post-control NO level. The NMOC reduction is then determined by calculating
A
the percent reduction necessary to reduce NMOC from the base point to the post-
control point. This percent reduction is the VOC emission reduction necessary
to reduce the peak ozone concentration to 0.12 ppm, assuming that ozone trans-
ported aloft changes in the future.
55
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Table 4-2. Control Calculations Using Two Isopleth Diagrams
Step 1 : After developing a Base case diagram, generate a future-case diagram
for the post-control period. For example, 1f transported ozone Is
expected to be reduced, a diagram reflecting that reduction should be
generated.
Step 2: Locate the base-case point ph_the base-case diagram by finding the
intersection of the design NMOC/NO ratio line with the isopleth for
the ozone dally design value. Let the NMOC and NO coordinates of
this point be signified by (NMOCh and (NO h, respectively.
A
Step 3 : Calculate the post-control NO coordinate by adjusting the base NO
level by the expected percentrchange in NO emissions between the Base
and post-control periods. Let the post-control NOV coordinate be
signified by the CNOj2. Thus, x
ANO
CNOX)2 = (N0xh x (1 +
where
(NO )2 = post-control NOV coordinate
A X
(NO h = base case NO coordinate
A X
ANOV = expected change in NOV, percent
X X
Step 4: Locate the post-control point on the future-case diagram by finding
the post-control NOV coordinate, (NOV)2, on the 0. 12 ppm ozone Isopleth.
Let the NMOC coordinate of this point be (NMOC)2.
Step 5: Compute the percent reduction necessary to lower (NMOC)i to (NMOC)2-
Thus,
% Reduction in VOC = [1 - z ] x 100
56
-------
= .24
= 8:1
GIVEN: 03 Design Value
Design NMOC/NOX
Present Transport of 03 Aloft = .12
Future Transport of 03 Aloft = .09 (from Figure 4-2)
Anticipated change in NO = -202
Base case and future diagrams shown below.
FIND: Percent reduction in VOC needed to reduce ozone from .24 to .12 ppm
SOLUTION:
NIIMC.P'TC
STEP 1: The future case diagram shown above was generated by using the OZIPP input data for the base
case diagram, except that ozone transported aloft was changed from 0.12 to 0.09 ppm.
STEP 2: The base case point is found by the intersection of the 8:1 NMOC/NO ratio line with the .24
ozone isopleth (Point 1) on the base case diagram. At Point 1, (NMOCh = 1.64 and (NO h = .205
STEP 3: The post-control NOX coordinate is calculated as follows:
(NOX)2 = (.205) x (1 - ^) = .164
4: The post-control point is located on the future case diagram at the intersection of the .164
NOX coordinate and the 0.12 ppm ozone isopleth (Point 2). At Point 2 (NMOC)2 = .61
STEP
STEP 5: The VOC emission reduction is calculated as:
% reduction = (1 - ) = 63%
Figure 4-3. Example emission reduction calculation considering changes in transported ozone.
57
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4.2.2 Concurrent Reductions In local Precursors and Transported Precursors
As was described In Section 3,1.4, the transport of precursors 1s not
considered essential Inmost Instances, especially If upwind reductions parallel
local reductions. However, If precursor transport Is deemed critical, procedures
that may be employed are addressed 1n detail 1n Appendix B. The conceptual
framework for considering precursor transport 1s discussed below, along with
procedures for estimating changes 1n future levels of precursors transported
into an area.
Conceptually, the procedures for considering precursor transport are
exactly the same as those described for ozone transport. The major problem 1s
estimating the precursor concentrations transported Into the area. This in part
depends on the geographical location of the city, and is addressed 1n detail in
Appendix B. Because control programs are likely to be implemented upwind, the
concentrations of precursors transported into an area are likely to change.
Described below are procedures that may be used to estimate the changes in pre-
cur^sor levels transported into an area. These may be applied to both surface
layer transport and transport aloft where applicable.
Recommended Procedure: Because of the considerable uncertainty in
future control levels for the source area(s) for precursors transported into an
urban area, the following reductions are recommended: NMOC transported concen-
trations may be reduced up to 40% in cities being impacted by upwind nonattain-
ment areas and up to 20% in other cities. NO levels are not projected to
change significantly, so no change should be assumed. The basis for these
recommendations is the projection of VOC and NO emissions that was described in
Section 4.2.1 on estimating future transported ozone levels.
Alternate Procedure; If specific information concerning the primary
source of precursors transported into the urban area, and the scheduled controls
for that area are available, then estimates of future transport may be developed
using a proportional model. However, the source area should be clearly identified
through the use of trajectory analysis and the assumptions concerning the imple-
mentation of future controls should be fully documented.
58
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The procedures for considering precursor transport aloft are exactly
the same as those described for ozone transport. A base case diagram is used in
conjunction with a diagram representing the post-control state. The first repre-
sents the base case with existing transported levels, while the second diagram
corresponds to the situation in which changes 1n precursor transport are expected.
The procedures outlined 1n Table 4-2 are also applicable to this case. The
procedure for considering precursor transport 1n the surface layer 1s more complex,
and is discussed in Appendix B.
4.2.3 Concurrent Changes 1n Local Precursors and Diurnal Emission Patterns
Gross changes in the diurnal emission pattern expected between the base
period and the post-control period can be Incorporated into an analysis. It must
be emphasized that these changes must be significant and on a scale as large as,
or larger than, the spatial and temporal resolution of the emissions Inventory
used 1n the analysis (see Section 3.1.5). Because of the assumptions inherent 1n
the model, evaluation of small scale changes cannot be made using EKMA. Thus,
for example, the OZIPP/EKMA approach could not be used to evaluate the effects of
constructing a new highway. However, it could be used to assess the effects of
large scale changes, such as a suburban county substantially increasing emissions
relative to an urban county as a result of rapid growth.
The procedures for incorporating changes in diurnal emission patterns
are similar to those for treating changes 1n transported pollutants. A base case
diagram is developed using the existing emission information, and a diagram
representative of future emissions is developed incorporating the expected changes
in the diurnal emission pattern. The expected changes must be derived from
locally applicable projections. For example, an increase in emissions in one or
59
-------
more counties might be anticipated due to population growth or industrial expan-
sion. This expected increase would be incorporated in the analysis by developing
a future case diagram using the emission fractions corresponding to the projected
emissions increase. Thus, if a two-fold increase in county-wide emissions (in
the absence of controls) is assumed for a county, the emission fractions for the
affected county would be doubled for generating the future case diagram. Control
calculations are performed exactly 1n the manner described in Table 4-2.
Normally, consideration of changes in diurnal emission patterns will
not be necessary. The modeler will have to decide whether or not any anticipated
changes are significant enough to warrant special consideration.
4.2.4 Consideration of Multiple Changes
The previous three sections summarized the procedures for calculating
control estimates for cases in which local precursors are reduced and one other
significant change is expected to occur. If more than one additional change is
anticipated, the same procedures can be used. In addition to the base case
diagram, one diagram reflecting all future changes is developed. For example,
assume transported ozone, transported precursors, and gross changes in the
diurnal emission pattern are all expected. The base case diagram would be devel-
oped using the base case transported ozone, transported precursors, and diurnal
emission fractions. The second diagram would be developed using the future
transported ozone levels, future transported precursor levels, and the emission
fractions corresponding to the projected diurnal emission pattern. This new
diagram would incorporate all changes simultaneously, and any calculated VOC
emission reductions would reflect these assumptions. However, the future case
diagram would still use the same meteorological conditions, e.g., parcel path and
60
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mixing heights, as the base case. The calculations themselves would be carried
out just as outlined in Table 4-2.
61
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5.0 ACKNOWLEDGEMENT
The principal authors of this document are Gerald L. Gipson, Warren P. Freas,
Robert F. Kelly, and Edwin L. Meyer, Jr. The authors are indebted to members of
the EPA Working Group on Ozone Modeling for their many helpful written and verbal
comments. The excellent typing and general clerical support from Mrs. Carole Mask
is also gratefully acknowledged.
62
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APPENDIX A
ESTIMATION OF MIXING HEIGHTS FOR USE IN OZIPP
-------
In OZIPP, the rate of dilution of atmospheric pollutants 1s governed by the
diurnal change 1n mixing height. The mixing height Is the top of a surface-based
layer of air which is well-mixed due to mechanical and thermal turbulence. As
described in Section 3.1.2, the input variables required for OZIPP include: the
mixing height at 0800 LCT, the maximum mixing height, the time at which the
mixing height begins to rise If it starts to rise after 0800 LCT, and the time at
which the mixing height reaches its maximum. The rate of rise 1s computed
internally by OZIPP.
Three different procedures for determining daily morning and afternoon
mixing heights were outlined 1n Section 3.1.2. The recommended procedure entails
the use of temperature soundings taken routinely by the National Weather Service
at various locations throughout the United States. If more direct measurements
are available (e.g., radiosondes taken in the urban area or sodar data), they may
be used instead of NWS data. If neither of the above two sets of measurements
can be used, then the use of 250 m for the 0800 LCT mixing height and the climato-
logical mean value for the maximum mixing height is recommended. The procedures
to be followed for each approach are described below.
A.I RECOMMENDED PROCEDURE USING NWS RADIOSONDES
Temperature soundings are taken by the NWS at sites throughout the United
States. Soundings are usually taken every 12 hours at 1200 and 0000 Greenwich
Mean Time (GMT), corresponding to 0800 and 2000 Eastern Daylight Time, respec-
tively. Therefore, to estimate daily mixing heights, (1) a NWS site must be
selected which is representative of the city of Interest, (2) appropriate
sounding data and urban surface data must be obtained, and (3) these data must be
used to compute the morning and maximum mixing heights. Each of these steps is
discussed below.
A-l
-------
A.T.I- Site Selection
In selecting a NWS site as the basis for mixing height estimation,
care should be taken to Insure that the site 1s meteorologically representative
of the city of Interest. Table A-l contains recommended sites for a number of
cities. Backup sites are listed for those cases In which radiosonde data may
not be available for a given day, or 1f the site has significantly different
meteorological conditions. Examples of the latter are the case 1n which a
surface front lies between the sounding site and the city or the city 1s clear
but cloudiness or precipitation occurs at the sounding site.
A.1.2 Selection of Day Specific Data
The dally morning mixing height for the model 1s normally estimated
using the 1200 GMT (0800 EOT) sounding, while the maximum mixing height is esti-
mated using the 0000 GMT (2000 EOT) sounding. In some cases, these soundings
may not be available or appropriate and alternate approaches will be necessary.
Table A-2 summarizes the order of preference in selecting the radiosondes for
estimating the daily mixing heights. The actual data may be obtained from the
National Climatic Center (NCC).*
In addition to the sounding data, surface temperature and pressure
data are also needed for each day modeled. The urban surface temperature at
0800 LCT (or the average temperature between 0800-0900 LCT) and the maximum
*National Climatic Center, Federal Building, Asheville, NC 28801
Telephone: (704) 258-2850, x203
Please allow about four weeks for NCC to fill an order.
A-2
-------
Table A-!.
City
Allentown, PA
Baltimore. MD
Boston, MA
Bridgeport, CT
Chicago, IL/IN
Cincinnati. OH/KY
Cleveland, OH
Dayton, OH
Denver, CO
Detroit, MI
Fresno, CA
Hartford. CT
Houston, TX
Indianapolis, IN
Los Angeles. CA
Louisville, KY/IN
Milwaukee, WI
Nashville, TN
New Haven, CT
New York. NY/NJ
Philadelphia. PA/NO
Phoenix, AZ
Pittsburgh, PA
Portland, OR
Providence, RI
Richmond, VA
Sacramento, CA
St. Louis, MO/IL
Salt Lake City. UT
San Bernardino, CA
San Diego, CA
San Fransdso, CA
Scranton, PA
Seattle. WA
Springfield, MA
Trenton, NO
Ventura-Oxnard, CA
Washington DC/MD/VA
Wilmington, DE
Worcester, MA
Youngstown, OH
NWS Radiosonde Stations
PRIMARY BACKUP(S)
Cllnatologlcal
Mixing Heights
(m AGO
MAX
NYC. NY; At! City, NO
Dulles AP, VA
Portland, ME
NYC, NY; At! City, NJ
PeoHa, IL
Dayton, OH
Dayton, OH
•Dayton, OH
•Denver, CO
Flint, MI
Oakland, CA
Albany, NY
Victoria. TX
Dayton, OH
Vandenberg AFB, CA
Dayton, OH
Green Bay. MI
*Nashv1lle, TN
NYC. NY; Atl City, NJ
•NYC, NY; Atl City, NJ
NYC. NY; Atl City. NJ
Tucson, AZ
•Pittsburgh, PA
Salem. OR
New York. NY
Dulles AP. VA
Oakland. CA
Salem. IL
•Salt Lake City, UT
San Diego, CA
•San Diego, CA
Oakland. CA
NYC, NY; Atl City, NJ
Oullayute. WA
Albany, NY
NYC, NY; Atl City, NJ
Vandenberg AFB.'CA
•Dulles AP, VA
Dulles AP, VA;
Atl City, NJ
Albany. NY
Pittsburgh, PA
Albany, NY; Dulles AP, VA 1825
Wallops Is., VA; Atl City, NJ 1825
Albany, NY; Chatham, MA 1375
Albany. NY 1500
Green Bay. WI 1575
Huntlngton, WV 1650
Buffalo. NY 1650
Huntlngton. WV 1661
Grand Junction, CO 3358
Dayton, OH 1700
Vandenberg AFB. CA 2000
NYC, NY; Atl City, NJ 1500
Lake Charles. LA 1525
PeoHa, IL; Salem; IL 1600
San Diego, CA 603
Nashville. TN 1700
PeoHa, IL 1575
Jackson. AL 1845
Albany, NY 1450
Albany, NY 1512
Dulles AP. VA 1700
Wlnslow. AZ; 3250
Dayton, OH; Dulles AP, VA 1794
Kedford, OR; Qullavute, WA 1575
Albany, NY; Chatham, MA; 1350
Atl City, NJ
Greensboro. NC; Wallops Is., VA 1725
Vandenberg AFB. CA 1600
PeoHa. IL; Monett, MO 1625
Grand Junction, CO 3673
Vandenberg AFB, CA 1200
Vandenberg AFB, CA 564
Vandenberg AFB, CA 625
Albany, NY; Atl City, NJ 1850
Dulles AP, VA
Salem, OR 1398
NYC, NY; Atl City, NJ 1600
Dulles AP, VA 1700
San Diego, CA 610
Wallops Is., VA 1884
Wallops Is., VA; New York, NY 1700
Portland, ME; Chatham, MA 1500
Buffalo, NY; Dayton, OH 1700
• This station should be used unless the data 1s missing for all the times
listed 1n Table A-2. However, 1f a frontal passage occurs between the time of
maximum ozone and the time of the launch of the 0000 GMT sounding (normally
about 2300 GMT), the 1200 GMT sounding from th?t site should be used.
NOTE: The NYC. NY radiosonde station was replaced by Atlantic City. NJ on
September 2, 1980.
A-3
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Table A-2. Preferential Order of Data Selection
Morning Mixing Height Estimate
1. 1200 GMT Sounding at Primary Site
2. 0600 GMT Sounding at Primary Site*
3. 1200 GMT Sounding at Backup Site
4. 0600 GMT Sounding at Backup Site*
Maximum Mixing Height Estimate
1. 0000 GMT Sounding at Primary Site
2. 1800 GMT Sounding at Primary Site*
3. 1200 GMT Sounding at Primary Site
4. 0000 GMT Sounding at Backup Site
5. 1800 GMT Sounding at Backup Site*
6. 1200 GMT Sounding at Backup Site
* Soundings are not normally taken at these times, but may be available 1n some
instances.
A-4
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temperature occurring prior to 1800 LCT are needed to estimate the morning and
maximum mixing height, respectively. The surface temperature data should be
measured to the nearest 0.1 °C at a well ventilated site. The site should be
located near the center of the urban area. Surface atmospheric pressure measure-
ments are needed at the same time and location of the urban surface temperature
measurements, if at all possible. If these measurements are not available, a
local NWS or Federal Aviation Administration weather reporting station's barometer
reading may be used.
If the elevation of the pressure reading and the urban temperature
site are different, an adjustment should be made to the pressure measurement
using equation (3).
where
Z . = the elevation, in meters above sea level (mASL), of the
pressure measurement
Zsfc = t'ie e^evatl'on (mASL) of the urban temperature measurement
Pobs = ^e Pressure» in millibars, at Z -
Psfc = the pressure, in millibars, at the urban temperature site
NOTE: ZQks will be equal to zero meters ASL when a pressure reduced to sea
level is used.
The value of P - from equation (3) is an approximate value and can be rounded
to the nearest whole millibar.
A-5
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A. 1.3- Nixing Height Esttetfon
The procedures for estimating the 0600 LCT mixing height and the
maximum mixing height are outlined In Table A-3. These procedures have been
automated. Appropriate computer listings and a User's Guide can be obtained
from the authors. The procedures 1n Table A-3 are designed for use with the
worksheet displayed In Table Ar4. Figure A-T contains a flow diagram of the
process. The procedures use the mandatory and significant pressure levels
reported for each sounding (Table A-5). The steps lead to determination of the
height at which the adlabatic lapse rate (extended from the surface temperature
and pressure) intersects the vertical temperature profile. (For background
information, the reader Is referred to References 21, 36-37.) An example
problem is presented 1n Section A.4.
In some instances, the mixing heights estimated by this procedure way
not be representative. If the 0800 LCT morning mixing height is estimated to be
less than 250 meters, then a value of 250 meters should be used. This assumed
minimum value for the 0800 LCT mixing height accounts for the effects of mixing
due to mechanical turbulence caused by Increased surface roughness in the urban
11 38
area. ' Similarly, if the city's maximum mixing height 1s greater than twice
the cHmatological maximum value (e.g., see Table A-l), the surface temperature
and pressure used and the choice of sounding site should be checked for repre-
sentativeness using the guidelines 1n A.1.1 and A.1.2 above. If no backup data
are available, twice the cHmatological value should be used as the maximum.
Also, a maximum mixing height less than or equal to the morning mixing height,
or less than one-third the cUmatological maximum mixing height value is suspect.
Using data from a backup site may provide a more realistic value. However, if
A-6
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Table A-3. Procedures for Estimating K1x1ng Heights
Step 1 — For reference, the Information at the top of Table A-4 should be listed
(e.g., date, city, etc.). If the naming mixing height 1s to be calculated, the 0800 LCT
surface data are used. If the maximum mixing height Is to be calculated, the data cor-
responding to the time of maximum temperature (I.e., between 800-1800 LCT) are used. In
the row labeled URBAN SURFACE DATA, enter the following Information: 1) the elevation of
the urban temperature site In meters above sea level; 2) the surface pressure In millibars
(this value 1s P,fc)> and 3) th& surface temperature In degrees Celsus (°C).
Convert the surface temperature In column four to degrees Kelvin (°K) by adding
273.2, and enter the result In column five. This value Is T f (CK).
Use Equation 1 below and the values Just entered to calculate the potential
temperature at the surface (0C. In eK to the nearest 0.1 °K) and enter this value under
column six ue(cK)". sfc
G fin °IO - T
e un K; '
(In mb)°-286
sfc vm *' • 'sfc V1" *'\—1000 mb
Step 2 — Using the temperature sounding data, find the highest pressure level other
than the sounding's surface value that Is less than the pressure at the urban surface.*
From this pressure level on the sounding, enter the height (If listed), pressure and
temperature (1n °C) Into the row marked "(2)" on Table A-4.
Step 3 — Convert the temperature at this le*vel to the Kelvin scale and enter 1n
column 5. Compute the potential temperature (6 ) to the nearest 0.1"K using the pressure
(P, In mb) and temperature (T 1n °K) at this level 1n Equation 2 below:
/ . . \.Q 286
0 /<„ OK\ _ T /, o|/\ f (in mb) I /.x
«p nn K; ip un KJ ^ jA.^ mD' / IO
Enter the value of 9. found from Equation (2) Into the same row under the column labeled
Step 4 -- If the potential temperature, "9," of the last row that was entered 1s
greater than the potential temperature 9 - , and this Is the first level above the surface,
then 250 meters should be used as the mixing height. Otherwise, go to Step 5. If It 1s
less than or equal to 8 . , then enter the height (1f given), pressure and temperature of
the next lowest pressure level found on the sounding Into the next row of Table A-4 and
return to Step 3.
Step 5 — The mixing height 1s between the last two levels entered Into Table A-4. If
height values are given for both of these levels, the elevation of the mixing height can be
found using Step 6. If one of the levels does not have a height value, use linear Inter-
polation to find the pressure value for the potential temperature value of 8 - + 0.1 "K.
Enter this pressure value Into the row marked "MIXING HEIGHT" at the bottom 8fcTable A-4
under the column "PRESSURE In mb." Proceed to Step 7.
Step 6 — From the two levels where height 1s given on the sounding surrounding the
mixing height level, use linear Interpolation to find the height (1n meters ASL) at the
value 6 - + O.TK (I.e.. the potential temperature 0 at the mixing height). Enter the
value found by linear Interpolation Into the row labeled "MIXING HEIGHT" under the column
"HEIGHT (mASL)" and proceed to Step 8.
Step 7 -- Use linear Interpolation to find the height above sea level of the mixing
height using the pressure at the mixing height (found 1n Step 5) and the pressure levels on
the sounding above and below the mixing height pressure that have both pressure and height
values. Enter the height value found Into the row "MIXING HEIGHT" under the column marked
"HEIGHT, (mASL)" and proceed to Step 8.
Step 8 — Subtract the elevation of the urban site (mASL) from the height (mASL) of
the mixing height. The result 1s the height of the mixing height 1n meters above the
surface of the dty (mA.GL). Enter this value Into Table A-4.
NOTE; Despite the fact that pressure and height, and potential temperature and
height, are not linearly related, linear Interpolation does not produce
significant errors over the limited ranges used above.
* For example, 1f the urban surface pressure 1s 985 mb, and the sounding pressures are:
1005, 1000, 963, 850 mb, etc., 963 mb 1s the "highest pressure level that 1s less than
the pressure at the urban surface." 850 mb 1s the "next lowest pressure level" needed
In Step 4.
A-7
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Table A-4. Worksheet for Computing Mixing Heights
Date: Time Of Mixing Height For Input Into Model:
Sounding Method:
LCT. Surface elevation:
City:
Time of Sounding:
Location of Sounding:
LOCATION OF URBAN SURFACE DATA (IF DIFFERENT THAN ABOVE) -
tiiASL
LEVEL
Urban
Surface
Data (1)
(2)
MIXING
HEIGHT
HEIGHT
(mASL)
PRESSURE
(mb)
TEMP.
(°C)
0 + 0.1 °K PRESSURE HEIGHT
(°K) (mb) (mASL)
TEMP.
(°K)
9
(°K)
REMARKS
Kfc
•
HEIGHT HEIGHT USED IN
(mAGL) MODEL (mAGL)
/
A-8
-------
- ENTER URBAN SURFACE DATA
INTO TABLE A-If,
- CONVERT SURFACE TEMPERATURE
TO "X
-mro egf USING EQUATION (i).
3}- ON TABLE A-tf LIST DATA FROM
*^ SOUNDING FROM THE FIRST PRESSURE
LEVEL ABOVE THE URBAN SURFACE LEVEL.
i - CONVERT TEMPERATURE TO °K AND
USE EQUATION (2) TO COMPUTE PO-
TENTIAL TEMPERATURE (9_) FOR
THE LEVEL JUST ENTERED.
- ENTER NEXT PRESSURE
LEVEL INTO TABLE A-f
TES
- MIXING HEIGHT IS
AT esfc + 0.11.
- ARE THE
'HEIGHT VALUES GIVEN
THE LAST TWO ROWS
ENTERED INTO
JABLE A-4,
NO
TES
- USE LINEAR INTERPOLATION
TO FIND THE PRESSURE AT
OF
- FIND THE HEIGHT (mASL)
OF THE MIXING HEIGHT BY
LINEAR INTERPOLATION FROM
THE PRESSURE AT THE MIXING
HEIGHT.
USE LINEAR INTER-
POLATION TO FIND THE
HEIGHT (mASL) AT
mijcing height.
fl/- FIND THE HEIGHT ABOVE THE
URBAN AREA (mAGL) OF THE MIX-
ING HEIGHT (THIS GIVES THE
ANSWER).
Figure A-1. How Chart for Table A-3. Numbers in circles are step numbers in Table A-3.
A-9
-------
Table A-5. Surface and Sounding Data
Hour Starting at. LCT
8
9
10
11
12
13
H
15
16
17
18
Surface Data
Temperature °C
23.2
23.9
25.8
27.3
28.7
29.3
30.1
30.4
30.8
31.4
31.2
Pressure, mb
1010.3
1010.7
1010.8
1010.
1010.
1010.0
1009.6
1009.2
1008.8
1008.6
1008.5
Sounding Data
1200 GMT Sounding
0000 GMT Sounding
Pressure (mb) Height (m ASL) Temp. (°C) Pressure (mb) Height (m ASL) Temp. (°C)
S 1015
M 1000
S 967
M 850
827
817
M 700
680
661
608
M 500
491
453
438
M 400
388
349
324
M 300
S 267
M 250
M 200
M 150
S 148
8*
139
1550
3168
5860
7560
9640
10890
12370
14190
23.0
23.0
24.4
16.2
14.2
13.6
4.6
5.6
5.6
0.4
-8.3
-9.3
-12.7
-13.9
-18.7
-20.1
-26.3
-29.7
-33.7
-39.5
-47.7
-51.7
-60.9
-61.5
S 1012
M 1000
M 850
S 831
S 791
S 778
S 760
M 700
S 628
S 560
M 500
M 400
S 371
M 300
S 265
M 250
S 205
M 200
M 150
S 127
S 120
M 100
M 70
50
30
20
15
8*
114
1537
3164
5860
7560
9650
10900
12370
14190
16690
18900
21040
24350
27030
31.0
30.6
16.4
15.4
13,
11,
11,
7.0
1.6
-1.5
-7.3
-18.9
-21.7
-33.1
-39.9
-42.9
-52.9
-53.3
-61.1
-64.9
-61.7
-63.3
-58.5
-54.5
-49.9
-44.7
-42.1
Note: M = Mandatory Levels and S = Significant Levels
If NWS Data are used, both the mandatory and significant levels
are needed.
The 0000 GMT Sounding 1s the following day in GMT.
* The lowest level of the sounding should not be used 1n the mixing height calculations.
A-10
-------
the low afternoon mixing height 1s due to the existence of a surface-based
stable layer, an adjustment to the procedures outlined In Table A-3 can be
employed. Replace the "Urban Surface Data" with the following data from the
sounding site: 1) the maximum temperature, 2) the estimated or observed surface
pressure at the time of maximum temperature, and 3) the height of the sounding
surface level. Then compute the mixing height according to the procedure 1n
Table A-3. If this problem occurs on a majority of modeling days, then an
alternative, more representative site should be used for all the modeling days.
A.2 USE OF ALTERNATE DATA
Other, more direct measurements of mixing height may be used to Increase
the representativeness of the estimated values. These methods Include direct
urban temperature sounding and sodar data. The measurements should be taken
over the urban area near the center of the city at 0800 LCT, and close to the
time of the climatological maximum surface temperature. It 1s not recommended
that these measurements be taken specifically for the OZIPP/EKMA techniques;
however, they may be employed 1f available. Examples are discussed below.
1) Local Urban Radiosonde — the methods described in Section A. 1.3
can be used to find the mixing height from radiosondes taken within the urban
area as opposed to NWS sites. The radiosonde surface temperature and pressure
should be used in place of the URBAN SURFACE DATA.
2) Urban Helicopter Soundings — Similarly, vertical temperature
profiles obtained from helicopter soundings can be used in place of the NWS
soundings. The urban site surface temperature and pressure should be used as
the URBAN SURFACE DATA.
A-ll
-------
3) Sodar ~ (also known as Acoustic Radar) the mixing height found by
sodar (1n mAGL) can be used directly 1n the model.
NOTE: Regardless of the procedure applied, the limitations concerning the
morning and maximum mixing heights that were described in Section A.1.3 should
be observed.
A.3 USE OF CLIMATOLOGICAL MEANS
If radiosonde data are not available, 250 m should be used for the 0800 LCT
mixing height and the city-specific cllmatological mean value may be used for
the maximum mixing height. Table A-l lists representative values for several
cities, and Reference 12 contains information for the contiguous United States.
If Reference 12 is used, values for summer, non-precipitation days should be
used. The appropriate starting and ending times of the mixing height rise in
the model are 0800 LCT and the time of the maximum temperature. If the latter
is unknown,.1400 1ST (1500 LOT) may be assumed.
A.4 EXAMPLE PROBLEM
To illustrate the procedure described 1n Section A.1.3, an example problem
is included for reference. Table A-5 shows relevant data typically available.
Note that both the 1200 GMT and the 0000 GMT soundings are used 1n the calcula-
tions, the former for the morning mixing height and the latter for the maximum
mixing height. Table A-6 shows the individual computational steps for the
morning mixing height calculation, while Table A-7 shows the same for the maximum
mixing height.
A-l 2
-------
Table A-6. Morning Mixing Height Determination —
Example from Table A-5:
08 LCT Temperature = 23.2°C
Maximum Temperature after 08 LCT = 31.4°C at 17 LCT
08 LCT Pressure = 1010.3 mb
Pressure at time of maximum temperature (1700 LCT) = 1008.6 mb
Time of morning mixing height = 0800 LCT
Time of maximum mixing height = 1700 LCT
Problem:
Find the 0800 LCT mixing height using data from the sounding shown in
Table A-5 (i.e., the 1200 GMT sounding). A worksheet is shown as Table A-6A.
The elevation of the urban surface site 1s 62 mASL.
Solution:
STEP 1
Enter 62., 1010.3 and 23.2 into row (1) of Table A-6A (URBAN SURFACE DATA)
TEMP (°C) = 23.2
Converted to °K = 23.2 + 273.2 = 296. 4°K
Enter 296.4 into row (1) of Table A-6A under "TEMP(°K)"
Using Equation (1) on the Urban Surface Data:
0 = ?Qfi 4°K /'3 mb\
ysfc ^6-4 K MOOO. mbj
Gsfc = 295>5°K
STEP 2 - Enter 139., 1000. and 23.0 into row (2) of Table A-6A.
STEP 3 - 23.0 + 273.2 = 296. 2°K
Using Equation (2):
Q - ?Qfi 7°K /J99.P. m^\
6p ' Z96'Z K C1000 mb}
0 = 296. 2°K (Enter this value into Table A-6A)
STEP 4 - Op (296. 2°K) is greater than Qsfc (295. 5°K).
Since 9 is from the first level above the surface, the 250 m default value
should Be used for the 0800 LCT mixing height.
A-13
-------
Table Example (Hypothetical Data)
Date: PATE OF MoOE-tiNfr Time of Mixing Height For Input Into Model: 080O EPT
City: CITY TO BE M»oeLCP Sounding Method:
Time of Sounding: 0$OO LCT. Surface Elevatio
Location of Sounding: fl/AME OF SotirtO/Nfr SITE
LOCATION OF URBAN SURFACE DATA (IF DIFFERENT THAN ABOVE) - Sr«rrr
, URBAN KAPIOSO/V0E
mASL
1
LEVEL
Urban
Surface
Data (1)
(2)
MIXING
HEIGHT
__ ~ 2
HEIGHT
(mASL)
U
13?
3
PRESSURE
(mb)
/ 0/0.3
1000.
Osfc+ 0.1 °K PRESSURE
(°K) (mb)
2 95. D ^~"
4 1
TEMP.
33.^
W.o
5
TEMP.
a*.*
W6.^
HEIGHT
(mASL)
O
f 6
oO
*i ^^ £"
(A IO.O
3iu.a
7
REMARKS
^
9 AT TMIS LtVtl
IS Hlt-HtfTHAtl
^SFC+aiV.
HEIGHT HEIGHT USED IN
(mAGL) MODEL (mAGL)
O 2£"O
A-14
-------
Table A-7. Maximum Mixing Height Determination
Example from Table A-5:
08 LCT Temperature = 23.2°C
Maximum Temperature = 31.4°C at 17 LCT
08 LCT Pressure = 1010.3 mb
17 LCT Pressure = 1008.6 mb
Time of morning mixing height = 0800 LCT
Time of maximum mixing height = 1700 LCT
Problem:
Find the maximum afternoon mixing height using data from the sounding shown In
Table A-5 (I.e., the 0000 GMT sounding). A worksheet 1s shown as Table A-7A. The
elevation of the urban site 1s 62 mASL.
Solution:
STEP 1 - »
Enter 62, 1008.6 and 31.4 Into row (1) of Table A-7A (Urban Surface Data)
TEMP (°C) = 31.4CC
Converted to °K = 31.4 + 273.2 = 304.6°K
Enter 304.6°K Into row (1) of Table A-7A under "TEMP (°K)
Using Equation (1) on the Urban Surface Data
lftnfi , mh -0.286
0 - 304 6CK f]zz°' Pi
sfc •""•" * Mooo mo
Osfc = 303.9
STEP 2 -
Enter 114., 1000., and 30.6 Into Table A-7A.
STEP 3 -
30.6°C + 273.2 = 303.8°K
Using Equation (2):
0 = 303.8CK
6 = 303.88K
STEP 4 - 303.8°K 1s less than 303.9°K
Therefore, enter 1537., 850. and 16.4 Into Table A-7A.
and return to STEP 3.
STEP 3 - 16.4°C + 273.2 = 289.6°K
Using Equation (2)
850 mb •°'286
0 = 303.4°K
STEP 4 - 303.4°K 1s less than 303.9°K
Therefore, enter 831. and 15.4 into Table A-7A (note that there 1s no
height value for this pressure level) and return to STEP 3.
A-15
-------
Table A-7 (Continued)
STEP 3 - 15.4°C -f 273.2 = 288.6°K
Using Equation (2):
a,, mk - 0.286
°p ' 288-6°K (TOT*
0 = 304.3CK
STEP 4 - 304.3°K Is greater than 303.98K
STEP 5 -
°sfc + °*10|< " 303-9°K * 0<1°K = 3M.08K
Using linear Interpolation from potential temperature (0) to pressure since a
highest value 1s not given for the 831 mb pressure level
0 (°K) Pressure (mb)
303.4 850
304.0 P mixing height
304.3 831
P mixing height = 831 mb - (850 mb jff1Bmb){3M.O;K - 304.3°K)
. 831 . 09 mbH-0 3°K)
= 837.3 mb
The pressure at the mixing height (rounded to the nearest whole
millibar) 1s 837 mb.
STEP 7 -
Use linear Interpolation to find the height above sea level of the
mixing height. Enter 3164. and 700. Into Table A-7A.
PRESSURE (mb) HEIGHT (mASL)
850 1537.
837 Z mixing height
700 3164.
Z mixing height - 1537 . * ("64 . O537 m^mb - 850 mb)
- 1537 n, + 062? m)M3 mb)
- 1&3/ m + -ISO mb
Z mixing height = 1678 m
STEP 8 -
1678 mASL - Height of mixing height
-62 mASL - Elevation of urban surface site
1616 mAGL = Mixing height 1n meters above the urban area.
1616 m 1s the height of the maximum mixing height to be used In the model
with the time of 1700 LCT.
A-16
-------
Table Example (Hypothetical Data)
Date: Time of Mixing Height For Input Into Model: I~]OO£PT
City: Sounding Method: NWS.
o f} r\f*\ o
Time of Sounding: A\J\J\J LCT. Surface Elevation: o. mASL
Location of Sounding:
LOCATION OF URBAN SURFACE DATA (IF DIFFERENT THAN ABOVE) -
1
LEVEL
Urban
Surface
Data (1)
(2)
MIXING
HEIGHT
" 2
HEIGHT
(mASL)
U
//f
ISY7
—
3W
9sfC(°°)10K
3o*o
3
PRESSURE
(mb)
/oo8.£>
IOOQ.
ISO.
%3/.
100.
PRESSURE
(mb)
03.tA1
HEIGHT USED IN
MODEL (mAGL)
/6/6.
A-17
-------
APPENDIX B
CONSIDERATION OF PRECURSOR TRANSPORT
-------
Transport of pervasive, high precursor concentrations into a city as a
result of emissions from upwind sources presents difficulties 1n applying city-
specific EKMA. One difficulty is estimating the concentrations of precursors
transported into the urban area. Such estimates generally require special
monitoring programs to detect transported pollutant levels. Often, data may not
be available for a specific day being investigated. This is further complicated
by the fact that transported pollutant concentrations are strongly affected by
the meteorological conditions on a given day, making any generalizations regarding
treatment of transport difficult. In spite of these difficulties, general quanti-
tative techniques have been developed to account explicitly for the role of
precursor transport. As will be described, some sensitivity analyses have been
performed using these techniques. The results indicate that consideration of
precursor transport 1s not normally necessary, and is not recommended. However,
the techniques are presented for those cases in which explicit treatment of pre-
cursors is perceived by a user as an Important consideration in the overall
modeling analysis.
Three topics are discussed below: 1) the transport of precursors aloft; 2)
the transport of precursors in the surface layer; and 3) the case in which the
nonattainment area consists of more than one high-emission density area.
B.I PRECURSOR TRANSPORT ALOFT
Most evidence suggests that concentrations of precursors transported aloft
are usually very low.13,11*,17,18 Generally, concentrations of NMOC measured
above the morning mixing height have been found to be less than 0.1 ppmC. NO
levels transported from upwind areas above the morning mixed layer are usually
much less than concentrations attributable to the urban area. Table B-l summarizes
B-l
-------
Table B-1. -Typical Effects of NMOC Transport Aloft on Control Estimates*
Base Case NMOC Transported Aloft, ppm
03 Design Value
.18
.18
.18
.24
.24
.24
.30
.30
.30
NMOC/NOY
t\
8:1
12:1
16:1
8:1
12:1
16:1
8:1
12:1
16:1
.05
+4
+3
+1
+3
+2
+3
+2
+2
+2
.10
+8
+5
+3
+5
+4
+5
+3
+4
+3
.15
+12
+8
+4
+8
+7
+7
+5
+5
+4
Entries in the table represent the typical difference between considering
precursor transport aloft versus neglecting Its effect. For example, if
the control estimate obtained by considering transported NMOC were 50%,
and that computed using the normal OZIPP/EKMA technique (I.e., neglecting
transport) were 45%, a difference of 5% in control level would be recorded
in the table.
B-2
-------
the results of a sensitivity analysis that was performed to assess the effects of
considering NMOC transport. These tests were conducted using conditions likely
to be associated with what 1s believed to be unusually high concentrations of
precursor transport. Since areas experiencing significant precursor transport
would likely be subject to relatively high ozone concentrations transported
aloft, the concentration of ozone transported aloft was assumed equal to 0.12 ppm.
However, control estimates were made assuming that both ozone and precursors
transported aloft would be reduced according to the recommended approach described
in Sections 4.2.2 and 4.2.3. The table shows the difference in control estimates
obtained by explicit consideration of precursor transport aloft versus using the
OZIPP/EKMA technique in the normal manner. For example, if the control estimate
obtained by considering precursor transport explicitly were 50%, and that obtained
using the normal method were 45%, the difference of +5% would be reported in the
table. The results reveal that differences in control estimates are small for
concentrations of NMOC transported aloft which are less than about 0.1 ppmC. As
a result of these findings, and the uncertainties and difficulties associated
with measuring precursors aloft, explicit consideration of precursor transport
aloft is np_t normally recommended. If, however, conditions are such that explicit
treatment 1s perceived by the user as essential, the required additional measur-
ements and the manner in which these measurements can be employed 1n an OZIPP/
EKMA application are described below.
The only appropriate method for estimating precursor concentrations aloft 1s
by direct measurement, such as airborne measurements or those taken on tall
towers. Surface measurements of precursors may not be good indications of
precursor transport aloft because of possible influences of surface layer
B-3
-------
transport and local generation. Thus, precursor transport aloft can only be
considered 1f direct measurements are available. These measurements should be
made 1n the early morning, upwind of the city, at a height above the morning
mixed layer but below the anticipated maximum daily mixing height. Enough
samples should be taken to Insure that five measurements are available on days
for which precursor transport is likely to be important (i.e., on which the
prevailing wind flow may be from highly industrialized or urbanized areas upwind
and conditions are conducive to ozone formation). Normally, this requires a five
to six week sampling program. Reference 13 contains guidance on obtaining direct
measurements.
Explicit Consideration of Precursors Transported Aloft: If direct measure-
ments of precursors aloft are available on the day being investigated, they may
be used directly in the modeling analysis. If no measurements were taken on the
day being modeled, but are available for days with somewhat similar meteoro-
logical conditions (e.g., wind is from the same general direction), then the
median value of these measurements may be used. At least five measurements taken
on days conducive to high ozone formation are necessary for estimating the median
value. In either of the above cases, care should be taken to insure that the
measurements used are truly representative of the vertical concentration profile
above the mixed layer. For example, a measurement of high concentration above
the mixed layer may reflect the presence of a plume within that layer, but may
not be representative of concentrations extending throughout the layer found
above the mixed layer. Figure B-l illustrates the problem.
The quantitative treatment of precursors transported aloft is analogous
to that of ozone transported aloft (see Section 4.2.1). A base case diagram is
first developed with the precursor concentrations transported aloft estimated
according to the procedure described 1n the preceding paragraph. A post-control
diagram Is then generated using precursor concentrations aloft which reflect the
effects of upwind control programs. Section 4.2.2 describes the methodologies
for estimating future concentrations of precursors transported aloft. The compu-
tational procedures necessary to estimate the necessary VOC reductions are also
described in Section 4.2.2, and summarized 1n Table 4-2.
B-4
-------
I—I—I—I i—I—i—i——i—i—i—i
0.00 0.25 0.50 0.75 1.00 1.35
1
1 1 1
1
1 I 1
2
i •
1
i
•4
I i i
1
6
|
i i i i
IS
i i i
c
OZOME,HO,riO.-.,ritlD TEHFEPHTIJPE 'S nLTITUDE
Figure B-l. Vertical Pollutant Profile Illustrating a Shallow Layer of
Elevated NO^ Concentrations Aloft.
B-5
-------
B.2 PRECURSOR TRANSPORT IN THE SURFACE LAYER
Similar to transport of precursors aloft, most evidence suggests that urban
concentrations resulting from precursors being transported within the surface
layer are usually negligible.13,11*,17,18 Furthermore, the contribution of pre-
cursors transported in the surface layer to urban levels 1s accounted for to some
degree by using the normal OZIPP/EKMA technique. For example, the design NMOC/NOX
ratio determined from urban measurements reflects contributions from both the
urban area and the upwind area. To the extent that precursor reductions in both
areas parallel one another, consideration of precursor transport will have little,
if any, effect on local emission reductions. Table B-2 summarizes the results of
some sensitivity tests designed to assess the effect of incorporating the trans-
port of NMOC within the surface. These tests were similar to those conducted for
the transport of NMOC aloft. In addition to surface layer transport of NMOC, the
concentration of ozone aloft was assumed to be relatively high, I.e., 0.12 ppm.
However, control estimates were made assuming that both ozone aloft and precursors
transported in the surface layer would be reduced by 40%, as described in
Sections 4.2.2 and 4.2.3. The table shows the difference in control estimates
obtained by explicitly considering surface layer transport versus using the
OZIPP/EKMA in the normal manner (I.e., surface layer transport is not explicitly
considered). The differences are generally small, especially for contributions
from upwind areas less than 30%. Thus, because of the 1nsens1tivity, and because
of the approximations and assumptions that must be made in order to evaluate
surface layer transport explicitly, consideration of precursor transport within
the surface layer 1s not generally recommended. However, if consideration of
precursor transport is perceived as a critical Issue 1n the modeling analysis,
the additional measurements which are necessary and the manner in which they are
B-6
-------
Table B-2. Typical Effects of NMOC Surface Layer Transport on Control Estimates*
Contribution of Surface Transport
to Urban Levels, percent**
03 Design Value NMOC/NO¥ 5-10 10-20 20-30 30-40
/\ _____^_^_^_^__^_^_^^__^__^__
.18 8:1 +1 +2 . +3 +3
.18 12:1 +2 +1 +2 +3
.18 16:1 +1+1 +1 +2
.24 8:1
.24 12:1
.24 16:1
.30 8:1
.30 12:1
.30 16:1
* Entries 1n the table represent the typical difference between considering NMOC
transport in the surface layer versus neglecting Its effect. For example,
if the control estimate obtained by considering transported NMOC were 50%,
and the estimate derived using the normal OZIPP/EKMA technique (I.e.,
neglecting transport) were 45%, a difference of +5% would be entered in the
table.
** A 10% contribution implies that 90% of the urban, 6-9 a.m. concentration
is due to local generation and 10% is due to transport from upwind.
+3
+2
+2
+1
+3
+4
+1
+4
+5
-3
+4
+8
+1
+2
+2
+1
+2
+2
0
+3
+4
+1
+6
+7
B-7
-------
used in the analysis are described below.
The determination of surface layer transport 1s accomplished by means of
surface based measurements taken at the upwind edge of an urban area. It 1s
recognized, however, that upwind measurements will not always be available for
the days of interest. The technique described below makes use of the available
upwind measurements. References 13 and 29 contain guidance on monitor siting and
sampling. However, deployment of a continuous NMOC analyzer for the sole purpose
of estimating precursor transport is not recommended. Rather, collection of a
limited number of discrete samples, analyzed chromatographically with the species
summed to yield total NMOC, is preferable for estimating upwind NMOC. These
upwind samples should be collected between 6-9 a.m. LCT. In order to adequately
characterize precursor transport, samples for a minimum of five days on which
meteorological conditions favor significant transport (I.e., days on which the
prevailing wind flow may be from highly industrialized on urbanized areas upwind
and conditions are conducive to ozone formation) should be available. Normally,
a five to six week sampling program will be adequate.
Explicit Treatment of Surface Layer Transport: Table B-3 summarizes the
computational procedures for considering surface layer transport of precursors.
The concepts employed to account for surface layer transport are 1) to estimate
the contribution of transported precursors to urban levels using available upwind
measurements and corresponding urban area measurements, and 2) to incorporate
these relative contributions in the OZIPP/EKMA technique. The first two steps
involve estimating typical relative contribution of precursor transport to urban
levels. Thus, for example, a median contribution factor of .5 implies that 50%
of the precursor concentrations measured in the urban area are due to precursor
transport. Contribution factors should be computed separately for NMOC and/or
NO Steps 3 through 5 entail quantifying precursor transport relative to the
normal OZlPP/EKMA base case point. The precursor concentration to be entered in
OZIPP as surface layer transport is calculated in Step 4, and the design NMOC/NO
ratio is adjusted to remove the relative contribution of precursor transport
(Step 5). In Step 6, a new base case diagram is generated to reflect the effects
of precursor transport in the surface layer. As Indicated In Step 7, the esti-
mation of future transport, development of a post-control diagram, and subsequent
B-8
-------
Table B-3. Explicit Treatment of Surface Layer Precursor Transport
1. Compute the ratio of upwind measurements to urban average levels for each
day on which upwind measurements are available.
(CF). = j^upwlndJi
lSirbanM
where
(CF). = fractional contribution of transported levels to urban
levels for day i
upwind 6-9 a.m. precursor measurement for day i
(C . )i = 6-9 a.m. urban average concentration (if data from more
uroan than Qne „„,„.,• tor are available, the 6-9 levels for each
monitor are averaged).
2. Determine the typical transport level by taking the median of the contn's,
bution factors calculated in Step 1. Let this factor be represented by CF.
3. Generate a base case isopleth diagram neglecting the contribution of surface
layer transport. Determine the base case point by finding the intersection
of the design NMOC/NO ratio with the isopleth corresponding to the daily
design value. Let the coordinates of this point be represented by (NMOC)j
and (NO )j. (Note that this is identical to what is done when precursor
transport is not considered.)
4. Estimate the relative contributions of transported precursors by multiplying
the contribution factor(s) by the corresponding base coordinate(s) found in
Step 3. Thus,
x (NMOCh
x (NOJ,
(CTRAN}NO
X
where x
= Relative Transported Concentration
(CF) = Contribution Factor calculated in Step 2
(NMOC)lt (N0x)j = Base case coordinates found in Step 3
5. Compute an adjusted NMOC/NO ratio to remove the contribution of transported
precursors.
Radj = C
where
R = normal NMOC/NOX ratio calculated according to Section 3.2.2
R j. = an NMOC/NO ratio adjusted to remove the contribution of
aaj transported
Develop a new base case diagram. The relative precursor concentrations
calculated in Step 4 are entered in the OZIPP model as the concentrations of
precursors transported in the surface layer. [If post 8 a.m. emissions are
considered, the emission,fractions calculated according to Section 3.1.5 must
also be divided by l.-(CF).]
Follow the procedures described in Section 4.2.2 for calculating VOC
emission reductions. The diagram developed in Step 6 serves as the base
case diagram, and the adjusted NMOC/NO ratio calculated in Step 5 should be
used as the design ratio.
B-9
-------
GIVEN: 03 Design Value = -24
Design NMOC/NOX = 8:1
Present Transport of 03 Aloft = .12
Future Transport of 03 Aloft = .09
Anticipated change in NOX = -30%
Median contribution factor for NMOC = .25
Median contribution factor for NOX = 0.0
FIND: Percent reduction in VOC needed to reduce ozone from .24 to 0-12 ppm, assuming that future surface
transport of NMOC will be reduced by 40%.
SOLUTION:
STEPS 1 and 2: The median contribution factors are 0.25 for NMOC and 0.0 for NOX- Therefore, only
the transport of NMOC will be considered.
STEP 3: The base case diagram (neglecting transport) is shown below. The base case point is found
in the normal fashion, i.e., the intersection of the .24 isopleth with the 8:1 NMOC/NOX<
The coordinates of this point are (NMOC)! = 1.85 and (NO h = .231
STEP 4: The relative contribution of NMOC transported in the surface layer is calculated as follows:
^RAN^MOC = (-25) x 1<85 = <46
n = 0.0
STEP 5: The adjusted NMOC/NOX ratio is computed as follows:
ADJ
Figure B-2. Example emission reduction calculation with the explicit consideration of precursor transport
in the surface layer.
B-10
-------
STEP 6: The new base case diagram is shown below. The following modifications were made to the input data
that was used to generate the original base diagram (Step 3): 1) surface layer NMOC transport was
set to .46 as opposed to zero for the original diagram; and 2) the emission fractions for NMOC were
each divided by 1.0 - .25 = .75.
" ~~ V* ~"s"~ ' * "*': ^
• Jr V" ' "" " 'l* ' 11 • ' ' *-*
a
The starting point (Point 1) on this diagram is found by finding the intersection of the adjusted
NMOC/NOV ratio line (6:1 in this case) with the .24 ozone isopleth. The coordinates of this point
are (NM6c)i = 1.52 and (N0xh = .253.
STEP 7: A future case diagram is developed to reflect the expected changes in transported pollutants. Thus,
the input data used to generate the base diagram (Step 6) is modified as follows: 1) ozone transported
aloft is set to .09 rather than .12 (see Section 4.2.2); and 2) NMOC transported in the surface layer
is reduced from ,46 to .28 (see Section 4.2.3). The resultant diagram is shown below.
,='.J
". '.' ••.--:~i'
...... . ., .
-i.'--:'-.r.:---::-
-L: -.-.:•::: T. •:: .
i::--:::.:.:.::...::: ;:-!qjll4-ir-rqqL'.
:---:;::tr.-:HF!:;:.::iitiH^.;rH!;
-" •- ljp*"r - : '
i—
•? •
Figure B-2. Example emission reduction calculation with the explicit consideration of precursor transport
in the surface layer, (continued)
B-ll
-------
The post-control point is found in the normal fashion. First, the post-control NOX point is calculated:
(NOX)2 = (.253) x (1 - yjg) = .202
The post-control point is then located on the future case diagram at the inter-section of the
.202 NO coordinate and the 0.12 ppm ozone isopleth (Point 2). At Point 2, (NMOC)2 = .40.
The VOC emission reduction is calcualted as
% reduction = (1 - y^) = 74%
Note that the base point used in this calculation was that found in Step 6, not that in Step 3.
Figure B-2. Example emission reduction calculation with the explicit consideration of precursor transport
in the surface layer, (continued)
B-12
-------
calculation of the VOC emission reduction 1s carried out according to the pro-
cedure described in Section 4.2.2. An example 1s presented 1n Figure B-2.
The above procedure represents an Idealized situation, so extreme care
should be taken in Its application. First, the procedure should only be applied
to days with similar meteorological conditions (I.e., the wind 1s out of same
general direction). Second, only days with meteorological conditions conducive
to high ozone formation should be considered. Third, siting of upwind monitors
is critical. Any upwind measurements that are affected by local sources will
invalidate the approach. Also, the upwind measurements must be taken close
enough to the urban area so that further significant dilution of the tranported
precursor concentrations does not occur. Consequently, the approach can only be
used for contribution factors less than one. A contribution factor greater than
one indicates the assumptions underlying the approach have been violated, and the
normal OZIPP/EKMA application (i.e., precursor transport 1s not explicitly incor-
porated) must be employed.
B.3 MORE THAN ONE HIGH EMISSION DENSITY AREA
In some instances, more than one high emission density area may be found
within the region for which a control program(s) is being developed. Examples
include the following:
1) An urban core and a second separate, clearly defined industrallzed
area with high emission density;
2) One urbanized area located in two different States, for which a
separate control program must be devloped for each area due to jurlsdictional
considerations;
B-13
-------
3} Urbanized areas which consist of two separate, clearly defined,
urban cores (e.g., twin cities).
Such geographies may present special problems in applying the OZIPP/EKMA technique.
Ideally, the OZIPP/EKMA technique should be applied 1n exactly the same
manner as described in Chapter 3, I.e., the column should be assumed to originate
in the urban core and move directly towards the site of peak ozone concentration.
The urban core should always be used as the origin of column movement because the
chemical kinetic mechanism is based upon reactions of NMOC/NO mixtures representa-
J\
tive of .automotive exhaust. Surface wind measurements should be analyzed to
insure that the peak ozone level is located 1n the general downwind direction of
the urban core of Interest. However, an exact trajectory cannot usually be
determined due to uncertainties in deriving the spatial and temporal variations
in wind fields. Consequently, some assumptions in estimating trajectories must
\
'be made.
First, consider the case of an Industrialized area located near an urban
area. In most instances, the routine OZIPP/EKMA application will provide the
best estimate of overall regional control targets. However, in some cases the
industrial area may be quite removed from the urban core. If the two areas are
separated by a region of little or no source activity, the procedures outlined in
the previous subsection on precursor transport could be employed in those instances
on which the industrial area contributes to the urban area (i.e., the urban area
•is downwind of the industrial region). However, estimates of control of the
industrial area must be arrived at independently of the OZIPP/EKMA technique.
Using the industrial area as the origin for the column movement would be inappro-
priate considering the chemistry is more representative of automotive exhaust
mixtures.
B-14
-------
For the case in which an urban area is divided by a jurisdictional boundary
(e.g., a State), the ideal method is to develop one control estimate for the
entire urban area (i.e., treat the urban area as one entity). If this cannot be
done because of jurisdictional considerations, each area should be treated as an
entity, and the same procedure followed for each area. Figure B-3 illustrates
the types of assumptions that could be made for trajectories under two different
situations.
The case of two separate urban cores in a region may be treated in one of
three ways. An independent analysis could be performed for each urban core.
Alternatively, the major city could be chosen as the design case, and the results
of that^ analysis applied to each city. A third alternative is to use the pro-
cedures described in B.2 of this appendix when appropriate. However, for this
procedure to be applicable, the cities must be separated by a region of little or
no precursor source activity.
B-15
-------
7
Figure E-3, Illustration of the Treatment of Contiguous Urban Areas,
B-16
-------
REFERENCES
1. Uses, Limitations and Technical Basis of Procedures for Quantifying
RelationshipsJtetween Photochemical Oxldants and Precursors,
EPA-450/2-7/-021a, U.S. Environmental Protection Agency, Research Triangle
Park, North Carolina, November 1977.
2. Procedures for Quantifying Relationships Between Photochemical Oxldants
and"^Precursors: Supportlhg Documentation. EPA-450/2-77-021bt U.S.
Environmental Protection Agency, Research Triangle Park, North Carolina,
November 1978.
3. G. Z. Whltten and H. Hugo, User's Manual for Kinetics Model and Ozone
Isopleth Plotting Package, EPA-600/8-78-014a, U.S. Environmental Protection
Agency, Research Triangle Park, North Carolina, July 1978.
4. Ozone Isopleth Plotting Package (OZIPP). EPA-600/8-78-014b, U.S.
Environmental Protection Agency, Research Triangle Park, North Carolina,
July 1978.
5. Federal Register. 44 (221) 65669-65670 (November 14, 1979).
6. 40 CFR 50.9
7. Federal Register, 36(84) 8186 (April 30, 1971).
8. T. C. Curran, Gu1del1ne_f6r the Interpretation of Ozone Air Quality Standards,
EPA-450/4-79-003, U.S. Environmental Protection Agency, Research Triangle
Park, North Carolina, January 1979.
9. J. Trljonls, Verf1catl6n_orthe Isopleth Method for Relating Photochemical
Oxldant to Precursors. EPA-600/3-78-019, U.S. Environmental Protection
Agency, Research Triangle Park, North Carolina, February 1978.
10. M. C. Dodge, Effect or Selected Parameters on Predictions of a Photochemical
Model, EPA-600/3-77-048, U.S. Environmental Protection Agency, Research
Triangle Park, North Carolina, June 1977.
11. J. M. Godowitch, J. K. Chlng and J. F. Clarke, "Dissipation of the Nocturnal
Inversion Layer at an Urban and Rural Site In St. Louis," Fourth Symposium
on Turbulence, Diffusion and A1r Pollution, Reno, Nevada, 1979.
12. G. C. Holzworth, Mixing Heights, Wind Speeds, and Potential for Urban Air
Pollution Throughout tne Contiguous United States, AP-101, U.S. Environmental
Protection Agency, Research Triangle Park, North Carolina, January 1972.
13. M. W. Chan, D. W. Allard and I. Tombach, Ozone and Precursor Transport
Into an Urban Area - Evaluation of Approaches, EPA-450/4-79-039, U.S.
Environmental Protection Agency, Research TrTangle Park, North Carolina,
December 1979.
R-l
-------
14. C. E. Decker, et. a "I, Ambient Monitoring Aloft of Ozone and Precursors
Near and Downwind of St. Louis. EPA-450/3-77-009. U.S. Environmental
Protection Agency, Research Triangle Park, North Carolina, January 1977.
15. G. T. Wolff, et. a!, "Transport of Ozone Associated with A1r Mass," paper
presented at the 70th Annual Meeting of the A1r Pollution Control Association
In Toronto, Canada, June 20-24, 1977.
16. W. S. Cleveland, et. al , "Photochemical A1r Pollution: Transport From the
New York City Area Into Connecticut and Massachusetts," Science. 191,
pp 179-181, 1976.
17. F. L. Ludwig, Assessment of Vertical Distributions of Photochemical
Pollutants and Meteorological Variables in the Vicinity of Urban ATeas.
EPA-450/4-79-017, U.S. Environmental Protection Agency, Research Triangle
Park, North Carolina, August 1979.
18. W. C. Eaton, M. L. Saeger, W. D. Bach, J. E. Sickles, II, and C. E. Decker,
Study of the Nature of Ozone. Oxides of Nitrogen and Non-methane Hydrocarbons
In Tulsa, Oklahoma - Volume III: Data Analysis and Interpretation,
EPA-450/4-79-008c, U.S. Environmental Protection Agency, Research Tri angl e
Park, North Carolina, September 1979.
19. Procedures for the Preparation of Emission Inventories for Volatile Organic
Compounds. Volume I. EPA-450/2-77-028, U.S. Environmental Protection Agency,
Research Triangle Park, North Carolina, December 1977. (Second Edition)
20. Procedures for the Preparation of Emission Inventories for Volatile Organic
Compounds, Volume II: Emission Inventory Requirements for PhotocfiemicaT
TTTr Quality Models, EPA-450/4-79-018. U.S. Environmental Protection Agency.
Research Triangle Park, North Carolina, September 1979.
21. R. C. Wanta and W. P. Lowry, "The Meteorological Setting for Dispersal of
Air Pollutants," Air Pollution. Volume U 3rd edition, A. C. Stern, ed.,
Academic Press, 1976, pp 337-352.
22. G. Z. Whitten and H. Hogo, Mathematical Modeling of Simulated Photochemical
Smog. EPA-600/3-77-011, -U.S. Environmental Protection Agency, Research
Triangle Park, North Carolina, January 1977.
23. M. C. Dodge, "Combined Use of Modeling Techniques and Smog Chamber Data
to Derive Ozone-Precursor Relationships." EPA-600/3-77-001b, ibid., p. 881.
24. B. Dimitriades, "Effects of Hydrocarbon and Nitrogen Oxides on Photochemical
Smog Formation." Environmental Sciences and Technology 6, 253 (1972).
25. E. L. Martinez and E. L. Meyer, Jr., "Urban-Nonurban Gradients and Their
Significance," Proceedings. Ozone/Oxidant Interaction with the Total
Environment Specialty Conference. Air Pollution Control AssociationT March
T57F; - -
R-2
-------
26. Report of the Air Monitoring Siting Workshop, U.S. Environmental Protection
Report of the Air Monitoring siting K
Agency, Las Vegas, Nevada, July 19/6.
27. F. L. Ludwig and E. Shelar, Site Selection for the Monitoring of
Photochemical A1r Pollutants. EPA-450/3-78-013, U.S. Environmental
Protection Agency, Research Triangle Park, North Carolina, April 1978.
28. B. Dimitriades, "An Alternative to the Appendix J Method for Calculating
Oxidant and NOa Related Control Requirements," International Conference
on Photochemical Ox1dant_P6llution and Its Control: Proceedings, Volume II,
EPA-600/3-77-0016, U.S. Environmental Protection Agency, Research Triangle
Park, North Carolina, January 1977.
29. Guidance for Collection of Ambient Non-Methane Organic Compound (NMOC)
Data for Use in 1982 Ozone SIP Development, and Network Design and Siting
Criteria for the NMOC and NO Monitors, EPA-450/4-80-011, U.S. Environmental
Protection Agency, Research Triangle Park, North Carolina, June 1980.
30. Technical Assistance Document for the Calibration and Operation of
Automated Ambient Non-Methane Organic Compound Analyzers, EPA-600/4-81-015,
U.S. Environmental Protection Agency, Research Triangle Park, North Carolina,
in preparation.
31. P. J. Drives, Comparison of Ambient NMHC/NO Ratios Calculated From
Emissions Inventories, EPA-450/3-78-026, U.S. Environmental Protection
Agency, Research Triangle Park, North Carolina, June 1978.
32. Mobile Source Emission Factors, EPA-400/9-78-005, U.S. Environmental
Protection Agency, Washington, D.C., March 1978.
33. User's Guide to MOBILE!: Mobile Source Emissions Model. EPA-400/9-78-007,
U.S. Environmental Protection Agency, Washington, D.C., August 1978.
34. K. H. Lloyd, Cost and Economic Impact Assessment for Alternative Levels
of the National Ambient Air Quality Standard for Ozone. EPA-450/5-79-002,
U.S. Environmental Protection Agency, Research Triangle Park, North Carolina,
February 1979.
35. W. F. Hunt, Jr., et. al, National Air Quality and Emission Trends Report,
1977. EPA-450/2-78-052, U.S. Environmental Protection Agency, Research
Triangle Park, North Carolina, December 1978.
36. E. W. Hewson, "Meteorological Measurements," Air Pollution. Volume I,
3rd edition, A. C. Stern, ed., Academic Press, l9?6, pp 59l::S37":
37. D. H. Slade, Meteorology and Atomic Energy. NTIS No. TID-24190, NTIS U.S.
Department of Commerce, Springfield, Virginia 22161, July 1968, pp 33-39.
38. C. W. Benkley and L. L. Schulman, "Estimating Hourly Mixing Depths from
Historical Meteorological Data," Journal of Applied Meteorology. 18, pp 772-
780, June 1979. ~
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-450/4-80-027
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Guideline for Use of City-specific EKMA in
Preparing Ozone SIPs
5. REPORT DATE
. .... March 1981
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
G. L. Gipson, W. P. Freas, R. F. Kelly, E. L. Meyer
8. PERFORMING ORGANIZATION REPORT NO
9. PERFORMING ORGANIZATION NAME AND ADDRESS
10. PROGRAM ELEMENT NO.
U.S. Environmental Protection Agency
Office of Air Quality Planning and Standards
MDAD, AMTB, MD-14
Research Triangle Park, North Carolina 27711
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Same
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
Report describes how to use the city-specific EKMA model as a means for
estimating .emission control requirements needed to demonstrate attainment of
the ozone NAAQS in 1982 SIP's. Topics addressed include (a) use of air quality,
meteorological and emissions measurements or estimates for generating ozone,
isopleth diagrams; (b) application of the ozone isopleth diagrams in estimating
controls needed to attain the ozone NAAQS at each monitoring site; and (c) esti-
mation of the city-wide control requirement for use in the SIP.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COS AT I Field/Group
ozone
control strategies
photochemical pollutants
models
SIPs
§»»
IPP
18. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (This Report!
20. SECURITY CLASS (This page}
21. NO. OF PAGES
116
22. PRICE
•m 2220-1 (Rev. 4-77) PREVIOUS EDITION °s OBSOLETE
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ADDENDUM TO EKMA GUIDELINE DOCUMENT
EPA-450/4-80-027
March 1981
SECTION A.1.2 (page A-2)
The phone number for the National Climatic Center listed in the EKMA
Guideline document is for users who want a whole year's radiosonde data on a
computer tape. If radiosonde data for selected days are needed, they can be
obtained on hard copy by calling (704) 258-2850, extension 683.
The cost for computer tapes with a year (or any part of a year) of radio-
sonde data from one station is as follows (each tape has one year's data for one
station):
--$85 for the first tape
--S45 for each additional tape
The cost for hard copy (from the new number above) is $0.60 per sounding.
At stations with the usual two soundings per day, the cost is $1.20 a day per
station. Orders for hard copy must total at least $5.00.
-------
United States
Environmental Protection
Agency
Office of Air. Noise, and Radiation
Office of Air Quality Planning and Standards
Research Triangle Park NC 27711
Official Business
Penalty for Private Use
8300
Publication No. EPA-450/4-80-027
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
If your address is incorrect, please change on the above label:
tear off; and return to the above address.
If you do not desire to continue receiving this technical report
series. CHECK HERE D ; tear off label; and return it to the
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