vvEPA
United States
Environmental Protection
Agency
Office of Air Quality
Planning and Standards
Research Triangle Park NC 27711
EPA-450/4-81-031b
September 1981
Air
The Sensitivity Of
Complex Photochemical
Model Estimates To Detail
In Input Information
Appendix A -
A Compilation Of
Simulation Results
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This report was furnished to the U.S. Environmental Protection
Agency by Systems Applications, Incorporated in fulfillment of
Contract 68-02-2870. The contents of this report are reproduced
as received from Systems Applications, Incorporated. The opinions,
findings and conclusions expressed are those of the author and not
necessarily those of the Environmental Protection Agency. Mention
of company or product names is not to be considered as an endorsement
by the Environmental Protection Agency.
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EPA-450/4-81-031b
The Sensitivity Of
Complex Photochemical
Model Estimates To Detail
In Input Information
Appendix A -
A Compilation Of
Simulation Results
EPA Project Officer: Edwin L. Meyer, Jr.
Prepared for
U.S. Environmental Protection Agency
Office of Air, Noise and Radiation
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
September 1981
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CONTENTS
LIST OF ILLUSTRATIONS v
LIST OF TABLES ix
1. Overview A-l
2. Generic Description of Sensitivity Runs A-l
3. Measures for Ascertaining Model Sensitivity A-2
a. Signed Deviation. A-2
b. Absolute Deviation A-6
c. Temporal Correlation A-6
d. Spatial Correlation A-7
e. Overall Maximum Ozone Level A-7
f. Maximum Ozone Statistics A-8
g. Dosage A-8
h. Isopleths of Maximum Ozone Deviation A-9
i. Ozone Profiles at Air Quality Monitoring Stations A-9
j. Summary of Sensitivity Measures A-10
4. Simulation Results A-ll
a. Model Sensitivity to Upper Air Meteorological Data--
Simulation of 26 June 1974 A-ll
b. Model Sensitivity to Upper Air Meteorological Data--
Simulation of 4 August 1975 A-32
c. Model Sensitivity to Surface Meteorological Data--
Simulation of 26 June 1974 A-53
d. Model Sensitivity to Surface Meteorological Data-
Simulation of 4 August 1975 A-69
e. Model Sensitivity to Surface Air Quality Data--
Simulation of 26 June 1974 A-86
f. Model Sensitivity to Upper Air Quality Data--
Simulation of 26 June 1974 A-103
g. Model Sensitivity to Upper Air Quality Data--
Simulation of 4 August 1975 A-110
iii
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h. Model Sensitivity to RHC and NOX Boundary Conditions--
Simulation of 26 June 1974 A-116
i. Model Sensitivity to Hydrocarbon Initial Concentrations-
Simulation of 26 June 1974 A-123
j. Model Sensitivity to Hydrocarbon Initial Concentrations-
Simulation of 4 August 1975 A-130
k. Model Sensitivity to Hydrocarbon Speciation—
Simulation of 26 June 1974 : A-142
1. Model Sensitivity to Hydrocarbon Speciation—
Simulation of 4 August 1975 A-152
m. Model Sensitivity to Mobile Source Emissions: Older
Inventory—Simulation of 26 June 1974 A-158
n. Model Sensitivity to Mobile Source Emissions: Estimate
Based on Gas Sales—Simulation of 26 June 1974 A-165
o. Model Sensitivity to Mobile Source Emissions: Estimate
Based on Gas Sales—Simulation of 4 August 1975 A-178
p. Model Sensitivity to Point Source Temporal Resolution-
Simulation of 26 June 1974 A-184
q. Model Sensitivity to Area Source Spatial Resolution--
Simulation of 26 June 1974 A-187
r. Model Sensitivity to Area Source Spatial Resolution--
Simulation of 4 August 1975 A-201
s. Model Sensitivity to Temporal Resolution of Area
Emission Sources—Simulation of 26 June 1974 A-207
t. Model Sensitivity to Grid Size—Simulation of
26 June 1974. A-213
u. Model Sensitivity to Grid Vertical Resolution
(Two Grid Layers)—Simulation of 26 June 1974 A-216
v. Model Sensitivity to Grid Vertical Resolution
(One Grid Layer)—Simulation of 26 June 1974 A-221
References A-234
iv
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ILLUSTRATIONS
A-l Mixing Height Difference (m:) Case l--Base Case A-14
A-2 Wind Field at Ground Level, 26 June 1974 A-18
A-3 Air Parcel Trajectories: Case l--Base Case A-26
A-4 Deviation of Maximum Ozone Concentrations (ppb):
Case I—Base Case Between the Hours of 4 and 19 LSI A-29
A-5 Comparison of Predicted Ozone Concentrations: Case 1... A-30
A-6 Mixing Height Difference (m): Case 2--Base Case A-35
A-7 Comparison of Predicted NO Concentrations: Case 2 A-39
A-8 Wind Field at Ground Level, 4 August 1975 A-40
A-9 Air Parcel Trajectories: Case 2--Base Case A-48
A-10 Deviation of Maximum Ozone Concentrations (ppb):
Case 2—Base Case between the Hours of 4 and 19 LST A-49
A-ll Comparison of Predicted Ozone Concentrations: Case 2... A-50
A-12 Mixing Height Difference (m): Case 3—-Case 1 A-59
A-13 Wind Field at Ground Level, 26 June 1974 A-62
A-14 Air Parcel Trajectories in Case 3—Case 1 A-66
A-15 Deviation of Maximum Ozone Concentrations (ppb):
Case 3—Base Case between the Hours of 4 and 19 LST A-67
A-16 Deviation of Maximum Ozone Concentrations (ppb):
Case 3—Case 1 between the Hours of 4 and 19 LST A-68
A-17 Comparison of Predicted Ozone Concentrations: Case 3... A-70
A-18 Mixing Height Difference (m): Case 4—Base Case A-78
A-19 Wind Field at Ground Level, 4 August 1975 A-81
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A-20 Air Parcel Trajectories: Case 4—Case 2 A-85
A-21 Deviation of Maximum Ozone Concentrations (ppb):
Case 4--Base Case between the Hours of 4 and 19 LSI A-87
A-22 Deviation of Maximum Ozone Concentrations (ppb):
Case 4—Case 2... A-88
A-23 Comparison of Predicted Ozone Concentrations: Case 4... A-89
A-24 Deviation of Maximum Ozone Concentrations (ppb):
Case 5.I—Base Case between the Hours of 4 and 19 LSI... A-96
A-25 Deviation of Maximum Ozone Concentrations (ppb):
Case 5.2--Base Case between the Hours of 4 and 19 LSI... A-97
A-26 Comparison of Predicted Ozone Concentrations:
Case 5.1 A-99
A-27 Comparison of Predicted Ozone Concentrations:
Case 5.2 A-101
A-28 Deviation of Maximum Ozone (ppb): Concentrations
Case 6—Base Case between the Hours of 3 and 19 LSI A-107
A-29 Comparison of Predicted Ozone Concentrations: Case 6...A-108
A-30 Deviation of Maximum Ozone Concentrations (ppb):
Case 7--Base Case between the Hours of 4 and 19 LSI A-113
A-31 Comparison of Predicted Ozone Concentrations: Case 7...A-114
A-32 Deviation of Maximum Ozone Concentrations (PPB):
Case 8—Base Case between the Hours of 4 and 19 LSI A-120
A-33 Comparison of Predicted Ozone Concentrations: Case 8...A-121
A-34 Initial Conditions for 26 June 1974 A-124
A-35 Deviation of Maximum Ozone Concentrations (ppb): Case 9—
Base Case between the Hours of 4 and 19 LSI A-131
A-36 Comparison of Predicted Ozone Concentrations: Case 9...A-132
A-37 Initial Conditions for 4 August 1975 A-135
A-38 Deviation of Maximum Ozone Concentrations (ppb):
Case 10—Base Case between the Hours of 4 and 19 1ST A-141
vi
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A-39 Comparison of Predicted Ozone Concentrations: Case 10..A-143
A-40 Deviation of Maximum Ozone Concentrations (ppb):
Case ll--Base Case between the Hours of 4 and 19 LSI A-149
A-41 Comparison of Predicted Ozone Concentrations: Case 11..A-150
A-42 Deviation of Maximum Ozone Concentrations (ppb):
Case 12—Base Case between the Hours of 4 and 19 LSI A-155
A-43 Comparison of Predicted Ozone Concentrations: Case 12..A-156
A-44 Total Daily Emissions for Ground-Level Sources A-161
A-45 Deviation of Maximum Ozone Concentrations (ppb):
Case 13--Base Case between the Hours of 4 and 19 LSI A-166
A-46 Comparison of Predicted Ozone Concentrations: Case 13..A-167
A-47 Total Daily Emissions for Ground Level Sources A-172
A-48 Deviation of Maximum Ozone Concentrations (ppb):
Case 14--Base Case between the Hours of 4 and 19 LST A-175
A-49 Comparison of Predicted Ozone Concentrations: Case 14..A-176
A-50 Deviation of Maximum Ozone Concentrations: Case 15—
Base Case between the Hours of 4 and 19 LST A-181
A-51 Comparison of Predicted Ozone Concentrations: Case 15..A-182
A-52 Deviation of Maximum Ozone Concentrations (ppb):
Case 16--Base Case between the Hours of 4 and 19 LST A-188
A-53 Comparison of Predicted Ozone Concentrations: Case 16..A-189
A-54 Total Daily Emissions for Area Sources A-194
A-55 Deviation of Maximum Ozone Concentrations (ppb): Case 17—
Base Case between the Hours of 4 and 19 LST A-198
A-56 Comparison of Predicted Ozone Concentrations: Case 17..A-199
A-57 Deviation of Maximum Ozone Concentrations: Case 18—
Base Case between the Hours of 4 and 19 LST A-204
A-58 Comparison of Predicted Ozone Concentrations: Case 18..A-205
A-59 Deviation of Maximum Ozone Concentrations (ppb):
Case 19—Base Case between the Hours of 4 and 19 LST A-210
vi i
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A-60 Comparison of Predicted Ozone Concentrations: Case 19..A-211
A-61 Deviation of Maximum Ozone Concentrations (ppb):
Case 20--Base Case between the Hours of 4 and 19 LSI A-217
A-62 Comparison of Predicted Ozone Concentrations: Case 20..A-218
A-63 Comparison of Predicted and Observed Ozone
Concentrations: Case 20 A-220
A-64 Deviation of Maximum Ozone Concentrations (ppb):
Case 21--Base Case between the Hours of 4 and 19 LSI A-224
A-65 Comparison of Predicted Ozone Concentrations: Case 21..A-225
A-66 Comparison of Predicted Ozone Concentrations: Case 22..A-230
viii
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TABLES
A-l Description of the Airshed Model Sensitivity Simulations A-3
A-2 General Sensitivity Measures—Case 1 A-12
A-3 General Sensitivity Measures—Case 2 A-33
A-4 General Sensitivity Measures—Case 3 vs. Base Case A-54
A-5 General Sensitivity Measures—Case 3 vs. Case 1 A-56
A-6 General Sensitivity Measures—Case 4 vs. Base Case A-74
A-7 General Sensitivity Measures—Case 4 vs. Case 2 A-76
A-8 General Sensitivity Measures—Case 5 vs. Case 3 A-92
A-9 General Sensitivity Measures—Case 5 vs. Base Case A-94
A-10 General Sensitivity Measures—Case 6 A-104
A-ll General Sensitivity Measures—Case 7 A-lll
A-12 General Sensitivity Measures--Case 8 A-117
A-13 General Sensitivity Measures--Case 9 A-128
A-14 General Sensitivity Measures--Case 10 A-139
A-15 General Sensitivity Measures—Case 11 A-145
A-16 Hydrocarbon Speciation of Some Source Categories A-148
A-17 General Sensitivity Measures—Case 12 A-153
A-18 General Sensitivity Measures—Case 13 A-159
A-19 General Sensitivity Measures—Case 14 A-169
A-20 Total Daily Emissions from Mobile Sources A-174
A-21 General Sensitivity Measures—Case 15 A-179
1x
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A-22 General Sensitivity Measures—Case 16 A-185
A-23 General Sensitivity Measures—Case 17 A-191
A-24 General Sensitivity Measures—Case 18 A-202
A-25 General Sensitivity Measures--Case 19... A-208
A-26 General Sensitivity Measures—Case 20 A-214
A-27 General Sensitivity Measures—Case 21 A-222
A-28 General Sensitivity Measures--Case 22 A-228
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Appendix A
COMPILATION OF SIMULATION RESULTS
1. OVERVIEW
This appendix presents and discusses the results of twenty-two SAI
Airshed Model sensitivity simulations. A general description of the
sensitivity simulations is presented in section 2. Various measures,
presented in section 3, are used to quantify the sensitivity of model
ozone calculations to variations in input parameters and data. These
measures include ozone concentration level deviations, temporal and
spatial correlations, comparison of maximum ozone levels, dosage, and so
on. In Section 4, the most significant changes in model predictions for
each simulation (compared with the base cases) are discussed under the
heading General Sensitivity Measures.
Section 5 discusses how a reduction in available data is manifested
in perturbations to one or several input variables to the simulation
model. For example, the perturbation in hourly average mixing depths
resulting from the use of a single upper air sounding station is
analyzed. Altered mixing depths lead, in turn, to changes (from the base
case) in the temporal and spatial distributions of model ozone
calculations.
2. GENERIC DESCRIPTION OF SENSITIVITY RUNS
The 22 sensitivity runs performed in this study may be grouped into
the following general categories:
> Meteorology
> Air Quality
> Emissions
> Model Structure.
A-l
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Table A-l describes each simulation briefly. A more detailed descript.on
of each sensitivity case is given in the main report "Sensitivity of
Complex Photochemical Model Estimates to the Detail in Input Information,"
Chapter III. The sensitivity runs are discussed in section 4 in the order
shown in table A-l.
3. MEASURES FOR ASCERTAINING MODEL SENSITIVITY
An important step in quantifying model sensitivity is the definition
of specific measures. Several useful measures include the following:
> Signed deviation.
> Absolute deviation.
> Temporal correlation.
> Spatial correlation.
> Overall maximum ozone level.
> Maximum ozone statistics (peak level difference, peak time
lag).
> Dosage.
In addition, isopleths of maximum ozone deviation and ozone profiles at
air quality monitoring stations are developed to provide information on
the spatial and temporal perturbations in the model predictions.
Note that these measures, to be defined more precisely in the
following subsections, are quite similar to those used to evaluate model
performance in simulating the June and August oxidant episodes.
a. Signed Deviation
The signed deviation is calculated as follows:
- E *
N f
S-
where CSjl- j and C^j j are the ozone concentrations for the sensitivity
case and'tfie base case, respectively, at station (or grid cell) i and for
A-2
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Run
Number
TABLE A-l
Description
74 upper air
DESCRIPTIONS OF THE AIRSHED MODEL SENSITIVITY SIMULATIONS
Characteristics of the Base Case
Upper level
vlnd
Mixing
depths
Radiosondes at Riverside (0600 PST).
El Monte (0700, 1330). LAX (0630,1230),
Pt. Mugu (0400. 1000. 1600 PST) and San
Nicholas Island (1400 PST)
Acoustic sounder at El Monte
Aircraft spiral at Riverside (0600 PST)
Characteristics of the Sensitivity Run
26 June 1974 wind fields and mixing depths based on
0700 and 1330 El Monte radiosondes
75 upper air
Meteorological data
Upper level
winds
l
CO
Mixing
depths
74 surface and upper
air meteorological
data
Surface
Minds
Radiosondes at LAX (0630. 1230 PST).
El Monte (0700. 1300 PST), Pt. Mugu
(0400. 1000. 1600 PST). and San
Nicholas Island (1400 PST)
Radiosondes at LAX (1130 PST). El Monte
(0610.1230 PST), Pt. Mugu (0350, 1004,
and 1615 PST). and San Nicholas Island
(1405 PST)
Plbals at Burbank (1940 PST) and San
Bernardino (0345 and 1030 PST)
Aircraft spiral at Riverside (0300 PST)
Radiosondes at LAX (0630. 1030 PST).
El Monte (0610. 1230 PST), Pt. Mugu
(0360. 1004. 1615 PST). and San
Nicholas Island. (1405 PST)
60 surface wind monitoring stations
4 August 1975 Mind fields and mixing depths based on
0610 and 1230 El Monte radiosondes
?6 June 1974 wind fields and mixing depths based on
0700 and 1330 El Monte radiosondes and surface winds
and temperatures at ten monitoring stations
Upper level
winds
Mixing
depths
Surface
temperatures
Radiosondes at Riverside (0600 PST).
El Monte (0700. 1330), LAX (0630. 1230).
Pt. Mugu (0400. 1000. 1600 PST) and San
Nicholas Island (1400 PST)
Acoustic sounder at £1 Monte
aircraft spiral at Riverside
Radiosondes at LAX (0630. 1230 PST).
El Monte (0700, 1300 PST), Pt. Mugu
(0400. 1000. 1600 PST). and San
Nicholas Island (1400 PST)
Temperatures at several stations
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J*
i
75 surface and upper
air meteorological
data
5.1 Ground level initial
and boundary
conditions
5.2 74 reduced meteor-
logical and air
quality data
Upper air quality
data
75 clean air
boundary conditions
74 clean air
boundary conditions
74 assumed RHC/NO.
ratio
10 75 assumed RHC/NO
ratio
11 74 hydrocarbon
emissions spec tat Ion
Surface
winds
TABLE A-l (Continued)
56 surface wind Monitoring stations
Upper level Radiosondes at LAX (1130 PST). El Monte
Minds (0610. 1230 PST), Pt. Nugu (0350. 1004.
and 1615 PST). and San Nicholas Island
(1405 PST)
PlbiH at Burbank (1940 PST) and San
Bernardino (034S and 1030 PST)
Nixing
depths
Aircraft spiral *t Riverside (0300 PST)
Radiosondes at LAX (0630. 1030 PST).
El Monte (0610. 1230 PST). Pt. Mugu
(0350, 1004. 1615 PST) and San Nicholas
Island (1405 PST)
Surface Temperatures at 15 stations
temperatures
Initial and boundary conditions based on synthesis of
data froa 39 air quality monitoring stations
See descriptions of runs 3 and 5.1 above
Upper air concentration profiles assumed to decrease
with height to assumed background values
Boundary conditions based on synthesis of data from
48 air quality Monitoring stations
Boundary conditions based on synthesis of data from
39 air quality Monitoring stations
Reactive Hydrocarbon concentrations based on
empirical relationship derived from a*lent RHC Measure-
ments by Nayersohn et al. (1975) in 1974
Reactive hydrocarbon concentrations based on
empirical relationship derived from ambient RHC measure-
ments by Hayersohn et al. (1976) in 1975
Volatile organic compound speclation based on research
by KV8 Engineering, Incorporated, under EPA Contract
Ho. 68-02-3209
4 August 1975 Hind fields and Mining depths based on
0610 and 1230 U Monte radiosondes and surface winds
and temperatures at ten monitoring stations
26 June 1974 Initial and boundary conditions based on
10 surface Monitoring stations
26 June 1974 wind fields, mixing depths. Initial
conditions, and boundary conditions based on 0700 and
1300 El Itonte radiosondes and surface winds.
temperatures, and pollutant concentration measure-
ments at ten monitoring stations
26 June 1974 simulation with layer of precursor
Material aloft, estimated from 3-0 gradient study
profiles
4 August 1975 slnulatlon with less precursor material
aloft; clean air boundary conditions
26 June 1974 simulation with less precursor material
aloft; clean air boundary conditions
26 June 1974 simulation with Initial hydrocarbon
concentrations based on an assumed terometrlc hydro-
carbon/Ho, ratio of 7; clean air boundary conditions
4 August 1975 simulation with Initial hydrocarbon
concentrations based on an assumed aercmetrlc hydro-
carbon/NOx ratio of 7; clean air boundary conditions
26 June 1974 reactive hydrocarbon emissions split
according to an assumed composite urban mix
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TABLE A-l (Concluded)
tn
M 75 hydrocarbon
emission speclit I on
13 74 mbile source
14 74 gas sales
IS 75 gas sales
16 Point source
17 74 area source
IB 75 area source
19 Temporal resolution
20 10 km
21 two-layer model
22 one-layer model
Volatile organic compound special Ion based on research
by KVB Engineering, Incorporated, under EPA Contract
No. 68-02-3209
Emission estimates derived from the LASTS transportation
rwirlol »nrt thp ARR nTIM emission model
Emission estimates derived from the LARTS transportation
nodel and the ARB OTIM emission model
Emission estimates derived from the LARTS transportation
model and the ARB DTIM emission model
Day-specific, hourly-average emission rates for power
plants obtained directly from the utilities
Detailed, distributed area source Inventory developed
by the South Coast Air Quality Management District
(SCAQHD, 1978)
Detailed, distributed area source inventory developed
by the South Coast Air Quality Management District
(SCAQHD, 1978)
Detailed, distributed area source inventory developed
by the South Coast Air Quality Management District
(SCAQMO. 1978)
Horizontal grid resolution of 5 km
Four levels of grid cells
Four levels of grid cells
4 August 1975 reactive hydrocarbon emissions split
according to an assumed composite urban mix
26 June 1974 mobile source emissions based on outdated
transportation model and emission simulator
26 June 1974 mobile source emissions based on estimated
vehicle fuel economy, aremide fuel sales, ensemble
emission factors, and composite urban vehicle mix
4 August 1975 mobile source emissions based on
estimated vehicle fuel economy, areawide fuel sales,
ensemble emission factors, and composite urban vehicle
mix
26 June 1974 power plant emissions based on annual
average emission rates and average diurnal generating
profile
26 June 1974 distributed area sources spatially
allocated according to the demographic distribution
4 August 1975 distributed area sources spatially
allocated according to the demographic distribution
26 June 1974 area sources temporally resolved according
to assumed generic diurnal profiles
26 June 1974 simulation based on a 10-km horizontal
grid mesh
26 June 1974 simulation with one layer below the
inversion and one above
26 June 1974 simulation with one layer below the
inversion
* The ten stations are: downtown Los Angeles. Atusa. Burbank. Long Beach. Anaheim. San Bernardino, Reseda. Lennox. Prado Park, and Upland.
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the hour j; N Is the number of stations (or grid cells), and N1 the number
of simulation hours.
Two signed deviations are calculated. The signed deviation is com-
puted for the ozone levels at the air quality monitoring stations and for
the ozone levels in all ground-level grid cells (grid cells in mountainous
areas and over the Pacific ocean are not included).
b. Absolute Deviation
The absolute deviation in ozone levels is computed as follows:
N' N ,r r I
¥ ' «- " M J'
Absolute deviation in ozone concentration levels ( i.e., base case vs.
simulation) is computed for the air quality monitoring stations and for
the ground-level grid cells.
c. Temporal Correlation
The temporal correlation refers to the "timing" of the ozone concen-
tration levels computed by both the sensitivity case and the base case at
a specified station or in a specified grid cell. The temporal correlation
at a given location is determined from the hourly concentrations predicted
by the sensitivity case and the base case at a given location j. A
correlation coefficient is then calculated for each station according to
routine statistics. These correlation coefficients are normalized with
respect to the "perfect correlation line" (Hoel, 1962) by performing the
following change of variable:
1 1 + ri
*j = 7 £n T^r: ' (A'3)
J
where r* is the computed correlation coefficient for the station or grid
cell j. The mean value of the i's is computed for all locations:
-i E
(A-4)
A-6
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where N is the number of stations or grid cells. Because the values of 4>.
are approximately normally distributed (Hayes, 1978), the average temporal
correlation coefficient p is evaluated from the following formula:
(A-5)
Thus, the average temporal correlation coefficient is:
P - - . (A-6)
exp (2 4) + 1
The temporal correlation is computed both from station and grid
statistics. Perfect correlations exists when p = 1.0.
d. Spatial Correlation
The spatial correlation between the concentration fields calculated
in a sensitivity run and those calculated in the base case is another
useful measure. Hourly correlation coefficients can be computed by consi-
dering the values of concentrations predicted by the sensitivity case and
by the corresponding base case for each station or grid cell. Then, the
estimation of the average spatial correlation coefficient follows the pro-
cedure described above for the temporal correlation coefficient. Two
spatial correlation coefficients are computed from station statistics and
from grid statistics, respectively.
These sensitivity measures (signed deviation, absolute deviation,
temporal correlation, and spatial correlation) may be evaluated as a func-
tion of concentration level. They are computed in this study for ozone
levels > 12 pphm (the National Ambient Air Quality Standard) and for ozone
levels > 20 pphm.
e. Overall Maximum Ozone Level
The maximum ground level ozone concentration in the basin is computed
for the sensitivity case and the base case from station and grid statis-
tics. The overall maximum ozone level and the corresponding location
(station or grid) provide an additional measure of model sensitivity.
A-7
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f. Maximum Ozone Statistics
The maximum ozone levels occurring at each monitoring station may be
computed for both the sensitivity and the base case. The peak level
normalized difference is defined as follows:
1
IT
N
z
1=1
*
Cs,i-Cb,
i
*
cb,1
(A-7)
n t*m^ f
i=l b,i
where C . and C . . are the maximum ozone concentrations for the sensi-
tivity caie and the'base case, respectively, at Station i. This measure
is computed for the 23 air quality monitoring stations within the computa-
tional grid. Coastal stations are principally affected by boundary condi-
tions and local emissions since the wind flow in both base cases is wes-
terly for the majority of the simulation time. Accordingly, these
stations are removed from calculation of the maximum ozone statistics.
Peak level normalized differences are computed for the remaining 16
downwind stations.
The average peak time lag for maximum ozone level occurrence is eval-
uated as follows:
N
IX) TC - TK I . (A-8)
s-b
1=1
T and J. are the time of the maximum ozone level in the sensitivity
and in the base case, respectively. This measure is evaluated for
where
case anc
the 23 stations and for the 16 downwind stations.
g. Dosage
Dosage measures were based on the gridded area with simulated ozone
levels above 20 pphm. Dosage is obtained by adding the number of grid
cells with ozone levels above 20 pphm over the entire 19-hour simulation
period. This measure is computed for both the base cases and sensitivity
cases. The normalized difference of dosages provides an additional
measure of the model sensitivity:
The coastal stations that are not included in this analysis are
Costa Mesa, El Toro, Laguna Beach, Long Beach, Los Alamitos, Redondo
Beach, and West Los Angeles.
A-8
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orma ize ^ Dosage of sensitivity case - Dosage of base case
difference Dosage of base case
h. Isopleths of Maximum Ozone Deviation
Quantification of the spatial changes in predicted ozone levels aids
in the interpretation of the sensitivity results. Isopleths of the devia-
tions in maximum ozone concentrations are presented. It should be noted
that maximum ozone concentrations may occur at the same location at dif-
ferent times. This isopleth presentation provides useful information
about the magnitude and location of changes in ozone concentrations.
i. Ozone Profiles at Air Quality Monitoring Stations
Comparison of calculated and observed ozone concentrations at various
air quality monitoring stations is another useful measure of model sensi-
tivity; accordingly, the time-varying ozone concentrations at the monitor-
ing stations are compared for the sensitivity and base cases. This
provides information on the temporal variation and magnitude of the
perturbations in ozone concentrations at various locations throughout the
basin.
To keep the display of simulation results to a manageable level, 6
stations were selected from the 23 monitoring sites for detailed
discussion of the sensitivity results. The six monitoring locations are:
> Anaheim > Pasadena
> La Habra > San Bernardino
> Lynwood > Upland.
These stations were chosen because they typically present discernible
deviations in ozone concentration levels between the sensitivity and base
cases. Moreover, the stations are aligned with the windflow trajectory
that carries the photochemical plume eastward across the basin. Where
indicated, additional monitoring stations that present interesting fea-
tures in the diurnal ozone profiles will be discussed in some sensitivity
studies.
A-9
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j. Summary of Sensitivity Measures^
These sensitivity measures are considered in the following discus-
sion:
> Signed deviation, absolute deviation, temporal correla-
tion, and spatial correlation of ozone levels for the
following selected station locations and grid cells.
- Stations with ozone levels above 12 pphm.
- Stations with ozone levels above 20 pphm.
- Grids with ozone levels above 12 pphm.
- Grids with ozone levels above 20 pphm.
> Overall maximum ozone level predicted by the sensitivity
case and the base case and the corresponding location of
occurrence for:
- Station statistics
- Grid statistics
> Ozone peak level normalized differences and peak time lag
for:
- All 23 stations
- 16 downwind stations.
> Dosages of the sensitivity case and of the base case, and
the corresponding normalized difference.
> Isopleths of maximum ozone deviations between the sensi-
tivity case and the base case.
> Ozone concentration profiles predicted by the sensitivity
case and the corresponding base case at some monitoring
stations.
A-10
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4. SIMULATION RESULTS
a. Model Sensitivity to Upper Air Meteorological Pat a--Simulation of 26
June 1974
In this sensitivity study, the number of upper air meteorological
stations has been reduced. This reduction affects the estimation of the
mixing heights computation of the wind field, and estimates of eddy
diffusivity coefficients and upper air thermal structure.
1) General Sensitivity Measures
Some measures of the general sensitivity of the model are presented
in table A-2. There is a strong effect on the predicted ozone levels from
reduction in upper air meteorological data. Overall, lower ozone levels
are predicted and the deviation from the base case is larger for higher
ozone levels. The values of the temporal and spatial correlation coeffi-
cients are low (less than 0.622), which suggests that the temporal and
spatial features of the model have been notably perturbed. No major
discrepancy appears between the station and grid statistics.
For the maximum ozone-level comparisons, similar results are obtained
with all stations and with the downwind stations. This finding suggests
that ozone predictions have been affected throughout the basin. An
important reduction of the area with ozone levels above 20 pphm has
occurred; this reduction corresponds to the important reduction in ozone
levels that appears in the signed deviation sensitivity measure.
2) Sensitivity of Model Input Variables to Input Data
The model input variables affected by changes in the upper air
meteorological data are the mixing height, the wind field (wind velocity
and wind direction in the three-dimensional grid model), and the eddy
diffusivities.
The differences in mixing heights between the sensitivity case and
the base case between the hours of 4 and 5, 11 and 12, and 15 and 16,
L.S.T. are shown in figure A-l. The mixing height is higher in the center
of the basin, from Lynwood to Riverside, in the early morning. This
pattern moves eastward, and by 10 a.m. the mixing height is lower in the
sensitivity case than in the base case, throughout the basin. This
situation persists until 15 L.S.T. At about 15 L.S.T., the mixing height
A-ll
-------
ro
Sensitivity Measure
Signed deviation
Absolute deviation
Temporal correlation
Spatial correlation
TABLE A-2. GENERAL SENSITIVITY MEASURES—CASE 1
(a) General Ozone Level Deviations
Station Statistics
03
> 12 pphm
-0.177
0.300
0.023
0.622
03 > 20 pphm
-0.342
0.366
-0.009
-0.133
Grid Statistics
03 > 12 pphm 03 > 20 pphm
-0.229 -0.366
0.329
0.134
0.376
0.378
0.012
0.403
(b) Overall Maximum Ozone Level
Station Statistics
Sensitivity case/
base case ratio
Peak level (pphm):
* Sensitivity case
Base case
Corresponding locations:
Sensitivity case
Base case
0.718
25.5
35.5
Upland
Azusa
Grid Statistics
0.814
31.6
38.9
30 - 16
33 - 14
-------
:>
CO
TABLE A-2 (Concluded)
(c) Maximum Ozone Statistics
All Stations Downwind Stations
Peak level 0.253 0.258
normalized difference
Peak time lag (hrs) 1.77 1.87
(d) Dosage
Sensitivity Case Base Case
Normalized Difference (km2) (km2)
-0.402 5,975 10,000
-------
MIRTH
10
20
-
10
•
10
1 t
S0UTH
(a) Between the Hours of 4 and 5 LSI
FIGURE A-l. MIXING HEIGHT DIFFERENCE (m): CASE 1--BASE CASE
-------
NBRTH
20
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(b) Between the Hours of 11 and 12 LSI
FIGURE A-l (Continued)
-------
CTl
•iv.y Jr.:.;.:!!:
10
NBRTN
10 20
:lv:.:Jv:.:vk/.ix.:o|:^^^
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(c) Between the Hours of 15 and 16 LSI
FIGURE A-l (Concluded)
-------
is higher around Upland and Chino for the sensitivity case. This pattern
extends to the whole basin in two hours.
From these results, one would expect higher ozone concentrations in
most of the basin because of lower mixing heights, except in the eastern
part of the basin where the morning pattern of higher mixing height
persists until 10 L.S.T. The opposite effect is predicted, however.
Higher mixing depths in the early morning will lead to greater dispersion
of the primary pollutants. However, higher mixing heights do not occur in
the western part of the basin (where upwind emission sources are located)
long enough to account totally for the lower ozone levels, therefore some
other factor must be considered.
The ground-level wind field is shown in figure A-2 for the base case
(26 June 1974) and for the sensitivity case, between the hours of 4 and 5,
8 and 9, 11 and 12, and 18 and 19 L.S.T. The wind field is very sensitive
to upper air meteorological data. In the base case, one observes
southerly winds at 8 L.S.T. that evolve to southwesterly winds around 11
L.S.T. In the sensitivity case, winds are southwesterly at 8 L.S.T.
(about 45° difference from the base case) and become more southerly around
11 L.S.T.
In the southeastern part of the basin, between the Santa Ana
mountains and the San Jacinto mountains, the wind field is quite
different: in the base case there is a wind flow in the valley towards
the southeast, whereas in the sensitivity case southerly winds dominate
the whole wind field. This should lead to higher pollution levels in the
downwind regions for the sensitivity case.
Wind velocities appear slightly higher in the sensitivity case in the
morning (e.g., 8 to 9 L.S.T.); however, the difference seems insufficient
to account for the large deviations in ozone levels.
The air parcels that reach Pasadena, Azuza, and Prado around noon
differ between the base case and the sensitivity case. Different
emissions of primary pollutants will have been injected into the air
parcel reaching the source monitoring site in both the sensitivity case
and the base ca.se. Air parcel trajectories arriving at Pasadena, Azuza,
and Prado at 12 L.S.T. are shown in figure A-3 for the base case and the
sensivitity case. A deviation of one or two grid cells may occur at
certain hours along the path of these air parcels. This results in
different levels of precursors. For instance, concentrations of NO, N02
This corresponds approximately to the ozone peak time, except for the
base case at Prado.
A-17
-------
1 INCH = 4.5 M/SEC
00
J*y.3::\:-*:y.-;\.W^
\N\\\
iii&ii&'i'i&jft^^
(a) Base Case Between the Hours of 4 and 5 LSI
FIGURE A-2. WIND FIELD AT GROUND LEVEL, 26 JUNE 1974
-------
1 INCH = 4.5 M/SEC
i i i
20™
io
20
30
,.,..... ii..........i L|. ......................mi".. .1....II i. ..I. .11 .l7Q
(:::::>>£>:-::::fc:X::3::^
m\ \ \ t f f tv*
II t M \ t / / v
IK \ \ \ \ ft*
ll\ M t t / / /
^ik f /• / / / / /
10
i:*::::!:;::?:-::::::*:::::*^
— ^^ *>
^*>-^-^
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S
^^>y^7"7 \Tj^ \ v
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lllllili / / / ss
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\ 4 / t
\ \ \ j
ii;xj:;:r;:;x:^:i:;:;::ii>x;:;:iiiii:i:^
10 20 30
0
(b) Sensitivity Case 1 Between the Hours of 4 and 5 LST
FIGURE A-2 (Continued)
-------
1 INCH = 4.5 H/5EC
ro
o
20
.0
10 20 30
wffttmiai;^
20
10
r
F
* * * t t * t t f t *
0
'"l :-:':vl :.::v.l:
0
10
!i\
7 v\ \ * '
\mH;ii
\nw*J
'IMM^
10 20 30
<:':-.V:V:v:'.
0
(c) Base Case Between the Hours of 8 and 9 LSI
FIGURE A-2 (Continued)
-------
ro
1 INCH =4.5 M/SEC
I I I
10
20
30
f;;g';'!;';gi;';';';'!|;';';;;4
\ \ 4 \
'//mi:;',
20
10
:::::: ::: f / / / 4
-------
1 INCH = 4,5 M/SEC
i
ro
ro
20
30
*:::S:3:>#:tt::v#!:::^
20
10
rO::':|:':O;^;J:-i::v:l::£:::i:^
0
10
20
30
0
(e) Base Case Between the Hours of 11 and 12 LSI
FIGURE A-2 (Continued)
-------
ro
CJ
1 INCH = 4.5 M/SEC
i i I
30
:;:;5:;:::;:::£:::;:::;£:::;^^
::::::::££:&::::::&:::::::£::::::::£
10
20
30
(f) Sensitivity Case 1 Between the Hours of 11 and 12 LSI
FIGURE A-2 (Continued)
-------
1 INCH =4.5 M/SEC
I L
3»
ro
0,
LO
(g) Base Case Between the Hours of 18 and 19 LSI
FIGURE A-2 (Continued)
-------
1 INCH = 4.5 H/SEC
I I
ro
en
10
20
30
^
,i
20
10
£%;:if;£i5^
10
20
30
(h) Sensitivity Case 1 Between the Hours of 18 and 19 LSI
FIGURE A-2 (Concluded)
-------
20r—r—r
10
3>
ro
0
i—i—i—r
T—i—i—r
T
T « T
-BASE CASE, 26 JUNE 1974
-SENSITIVITY CASE 1; REDUCED UPPER
AIR METEOROLOGICAL DATA
10
20
30
FIGURE A-3. AIR PARCEL TRAJECTORIES: CASE 1--BASE CASE
-------
and olefins for the air parcels reaching Azusa and Pasadena are as
follows, between the hours of 4 and 5 L.S.T.:
Sensitivity Case Base Case
Azusa Air Parcel
Pasadena Air Parcel
Prado Air Parcel
Grid
NO
N02
Olefins
Grid
NO
N02
Olefins
Grid
NO
N02
Olefins
[11-8]
35 ppb
44 ppb
10 ppb
[9.9]
77 ppb
49 ppb
13 ppb
[18-3^
0 ppb
33 ppb
6 ppb
[13-8]
15 ppb
43 ppb
7 ppb
[10-9]
57 ppb
46 ppb
11 ppb
[17-9]
14 ppb
57 ppb
9 ppb
Note that the major difference is for NO concentrations. Higher
nitric oxide concentrations are observed in the sensitivity case for the
Azusa and Pasadena parcels, and lower concentrations are observed for the
Prado parcel. For the hydrocabron/nitrogen oxides ratio observed in the
Los Angles basin, this would lead to lower ozone levels for higher NO
concentrations and to higher ozone levels for lower NO concentrations.
Since only three air parcels and the initial concentrations {neglecting
subsequent emissions) were considered, this example is too limited to
explain totally the dynamics of an urban airshed. However, it is in
agreement with the lower ozone levels observed in mid-basin and the higher
ozone levels observed at Prado. This suggests that the wind field
perturbation is an important factor in the deviations observed in the
predicted ozone levels.
The eddy diffusivity coefficients have not been considered here.
These values are affected by the reduction of meteorological input data
since they depend on wind velocities. However, Liu et al. (1976) have
shown that the lirban airshed model is only mildly sensitive to vertical
diffusivity.
In conclusion, it appears that the wind field Is the most important
model input variable in this sensitivity study. The large perturbations
in wind direction seem to account for most variations in predicted ozone
levels.
A-27
-------
3) Sensitivity of Ozone Levels to Upper Air Meteorological Data
Isopleths of maximum ozone levels with time are shown in figure A-
4. Ozone profiles are shown in figure A-5 for both the sensitivity case
and the base case at the following stations: Anaheim, Fontana, La Habra,
Pasadena, Lynwood, Riverside, San Bernardino, Redlands, and Upland. The
ozone peak levels are lower at all of these stations except San
Bernardino. Higher ozone levels at San Bernardino and Prado may be
explained by the absence in the sensitivity case of back flow in the
southeastern basin (See the Prado air parcel trajectory in figure A-3).
More pollutants are thus transported from the southwest toward Prado,
Fontana and Riverside.
Lower ozone levels in the rest of the basin occur despite the
occurrence of lower mixing heights. This appears to result from the
important perturbations undergone by the wind field, which leads to
variations in the precursor levels between the sensitivity case and the
base case.
At Riverside and Upland, the peak occurs 2 or 3 hours earlier in the
sensitivity case than in the base case. This results from the faster
transport of pollutants in the sensitivity case (note the larger air
parcel trajectories for the sensitivity case in figure A-3).
Consequently, the peak time should be observed farther downwind in the
sensitivity case. This may be observed roughly when comparing the
following stations:
La Habra Upland Riverside
Peak time (LST): Base Case 1300 1500 1600
Peak time (LST): Sensitivity Case 1100 1300 1400
The peak occurs earlier in the sensitivity case, and there is better
agreement between the peak hour at the station upwind in the base case
than at the same station in the sensitivity case.
4) Conclusions
In this sensitivity study, the model input variables that have been
perturbed are the wind field, the mixing heights and the eddy diffusivi-
ties. From the results of the model simulations, it appears that the
change in wind field has the largest effect on the predicted ozone
A-28
-------
2 10
--
.
NlftTH
10
x^T^x^xl-lx^liwx^
:V
J
'\
\
m
\
20
•:-f:v:v:l-:-.:.'::l::::'-.-.t::
.' ' >. -.. .. - '•.'
' '• * " - -Kft '••"' f • \
*« _.-- ou ». •• • »
-.-...... _r;;..,o-- ,.,•... .-
L0NG
. .t f :{•• )
J I
f
10
S0UTH
FIGURE A-4. DEVIATION OF MAXIMUM OZONE CONCENTRATIONS (ppb). CASE 1—
BASE CASE BETWEEN THE HOURS OF 4 AND 19 1ST
-------
12
16
60
50
| | | | I | 1 I I Mj| I I I I I | I I I I I ,|
FiNTflNfl
i 30
20
10
6 12 18
TIME (HfURS)
so
30
20
10
50
40
J:30
20
10
6 12
i i i i i | i i i i i I
- RNflHEIH
- BflSE CfiSE —
r SEMS1TWTY RUN —
18
2\o
50
40
30
20
10
til
6
12
TIME (HfURS)
18
60
12
18
12
TIME (HfURS)
16
60
50
40
30
20
10
Ut
i i i i i 1 i i i i i I i i i i i | < i i i i _
- LYNMiBD
- BflSE CHSE —
- SENSITIVITY RUN — j;
I -
- -
I -
" y^^ J
I 6 12 18 2
50
40
30
20
n
4°
TIME (HfURS)
FIGURE A-5. COMPARISON OF PREDICTED OZONE CONCENTRATIONS: CASE 1
A-30
-------
•0
so
16
ao
10
i i i i i i i
- RIVERSIDE
- BRSE CflSE
- SENSITIVITY RUN
i i i
iiiiliiiiiiii
50
40
30
6.°n
6
12
18
50
40
i 30
20
10
I I | I I I 7 -IT
- SRN BERNftD
- BRSE CRSE —
- SENSITIVITY RUN —
i |
50
40
30
20
10
6 12 18
TIHE (MURS)
w
60
50
40
t 30
s
20
10
12
18
rftc
. LRND
- BHSE CRSE —
- SENSITIVITY RUN —
till
I I
50
40
30
20
10
6 12 18
THE CHfUftSI
60
50
40
t 30
20
10
12
- Lfl HRBRE
- BASE CRSE —
SEKSITIVITT KM —
18 24
TT|T"T™TTTT™£
6 12 18
TINE IHIURS1
50
40
30
20
10
24°
FIGURE A-5 (Concluded)
A-31
-------
levels. Though the mixing heights are affected by the reduction in upper
air meteorological data, there is no evident pattern to the effect of the
mixing heights on pollutant concentrations.
b. Model Sensitivity to Upper Air Meteorological Pat a--Simulation of
4 August 1975
The number of upper air meteorological stations has been reduced as
in the previous case. The wind field, mixing height, and eddy diffusivity
coefficients are affected.
1) jeneral Sensitivity Measures
Some general sensitivity measures are listed in table A-3. In
general, lower ozone levels are observed in the sensitivity case. When
comparing ozone concentrations at the monitoring stations, a larger
maximum ozone level is observed in the sensitivity case. However, the
actual maximum occurs in grid [11-16] for the sensitivity case, and it is
lower than the base-case maximum.
When all the grids are considered, larger deviations from the base
case are observed for higher ozone levels. In general, these deviations
are not as important as those that occurred for the 26 June 1974 case.
Values of the temporal and spatial correlation coefficients are higher
than for the previous case (e.g., spatial correlation = 0.974 for stations
with Oj > 20 pphm).
Maximum ozone statistics are comparable with all stations and
downwind stations. Finally, the reduction in dosage rsulting from the
perturbation is less than for the 26 June 1974 meteorological conditions.
2) Sensitivity of Model Input Variables to Input Data
The mixing height, wind field, and eddy diffusivities have been
perturbed by the reduction in upper air meteorological data. The
differences in mixing depths between the sensitivity case and the base
case are shown in figure A-6, for the hours of 0400 to 0500, 1100 to 1200,
and 1800 to 1900 L.S.T. In the morning, mixing depths are lower in most
of the basin except for higher depths around Riverside and Fontana.
Higher mixing depths are observed for the sensitivity case over an
increasing part of the basin, and at 1100 most of the basin presents
higher depths in the sensitivity case. This pattern persists until 1700
L.S.T., when lower mixing heights are observed in the eastern and western
A-32
-------
TABLE A-3. GENERAL SENSITIVITY MEASURES—CASE 2
(a) General Ozone Level Deviations
Station Statistics
Grid Statistics
GO
CO
Sensitivity Measure
Signed deviation
Absolute deviation
Temporal correlation
Spatial correlation
03 > 12 pphm
-0.094
0.164
0.912
0.638
03 > 20 pphm
-0.034
0.082
0.768
0.974
03 > 12 pphm 03 > 20 pphm
-0.046 -0.108
0.168
0.878
0.396
0.171
0.321
0.439
(b) Overall Maximum Ozone Level
Station Statistics
Sensitivity case/ 01.038
base case ratio
Peak level (pphm):
Sensitivity case 27.3
Base case 26.3
Corresponding locations:
Sensitivity case Upland
Base case Pomona
Grid Statistics
00.839
31.1
37.0
11 - 16
30 - 16
-------
TABLE A-3 (Concluded)
(c) Maximum Ozone Statistics
All Stations Downwind Stations
Peak level 0.128 0.132
normalized difference
Peak time lag (hrs) 0.56 0.5
(d) Dosage
Sensitivity Case Base Case
Normalized Di-fference _ (km^) _ (km^)
-0.017 8,600 8,750
-------
10
NIRTH
DflbU
10
.-
">H Lfl '
^^
PflSfi
:rjgr_""v—mr £m?;"-~''^j$"":;Jvv
.
'-. O
10
20
S0UTH
(a) Between the Hours of 4 and 5 LSI
FIGURE A-6. MIXING HEIGHT DIFFERENCE (ffl): CASE 2--BASE CASE
10
-------
N8RTH
•
10
1
Jj
a
REDB
H Lfl
10
20
:••<-:•:•:-:•»:•:•::-:*•:
10
SBUTH
(b) Between the Hours of 11 and 12 UST
10 g
FIGURE A-6 (Continued)
-------
MMTH
10
I
--.
21
t >
DdLR
REtJB
U LR ''
:x-x-:»X'X-»x-x-:txx-»x-xJ-x-x->x-xT:
I:YKO M imrrtnw
L0NG .
,-rt'NT ,&•'
&'
r^o
,&Vf •$»•'''.••" "»•*
10
: t- I ...)
SOUTH
(c) Between the Hours of 18 and 19 LSI
FIGURE A-6 (Concluded)
-------
parts of the basin. Lower mixing heights in the morning hours lead to
higher precursor levels, as shown by the NO concentration profiles at Long
Beach and Anaheim in figure A-7; the higher mixing depths that occur in
the late morning and afternoon tend to lower atmospheric concentrations
because of the larger mixing volume available.
The wind fields obtained for the base case and the sensitivity case
for different hours are shown in figure A-8. It appears that the wind
fields are very similar and that no major perturbation in,the model
prediction should result from changes in this input variable, as indicated
by the two air trajectories for the sensitivity case and the base case
shown in figure A-9. The wind field is, in general, more homogeneous
under the 4 August 1975 conditions than under the 26 June 1974 conditions;
for instance, in the former case there is no wind flow toward the
southeast between the Santa Ana Mountains and the San Jacinto Mountains.
Because the governing equators of the wind represent a three-dimensional
boundary value problem, resultant wind fields are sensitive to perturba-
tions near the boundaries. In a complex region, a computed wind field
will be more sensitive than a homogeneous wind field to input data.
Eddy diffusivities should not undergo important perturbations because
the wind field has remained almost unchanged and the airshed model has
been shown to be rather insensitive to the eddy diffusivities.
It appears in this simulation that the mixing height is the most
perturbed model input variable. This result is quite different from that
of the 26 June 1974 simulation in which the wind field was the most
perturbed variable under the same perturbation of input data.
3) Sensitivity of Ozone Levels to Upper Air Meteorological Data
Maximum ozone deviations are shown in figure A-10. Lower ozone
concentrations occur in the eastern part of the basin, whereas other
regions present slightly higher ozone levels. This pattern appears in
figure A-ll which presents ozone profiles at nine air monitoring
stations. This may be explained by considering the variations in mixing
depth.
In the western part of the basin, precursor levels are higher in the
sensitivity case because of lower mixing depths. Therefore, one may
expect higher ozone levels downwind at such locations as Anaheim, downtown
Los Angeles, La Habra, Los Alamitos, Pasadena, and Lynwood. Higher mixing
depths, which occur in most of the basin in late morning and afternoon,
provide a larger mixing volume and lead to a decrease of atmospheric
pollutant concentrations. This effect appears as the pollutants are
A-38
-------
50
-30
20
10
6 12
i I i i | i i i i "I |
_ RNflHEIM
BR5E CRSE ——
SENSITIVITY CASE --•
18
I'M
1 1
10
20
10
6 12 18
TIME CHiURS)
12
18
o.
0.
20
10
1 I I I | I 1 1 1 I |
LBNG BEflCH
BflSE CRSE -
SENSITIVITY CASE —
40
30
20
10
i i i t i
6 12 18
TIHE (H0URS)
2f
FIGURE A-7. COMPARISON OF PREDICTED NO CONCENTRATIONS: CASE 2
A-39
-------
1 INCH =4.5 M/SEC
i
-f*
O
I t I
20
10
10
.:
\\\\ \\
20
30
20
•:•:•:•:•:>•:•:•:•:•;
f / t t / //
t / / / / / / / / S S
/ / / ////////
r / s ss/ / / / / *
*. m. X
v *. V V
: ::::::x ::: f *' *' ' ' s
illll /,/////
* ^1
K
\\ N \ V V
*+• *+, ^
^ X X V
'.' JN
OH
10
iag&t:&:f^
10
20
30
(a) Base Case Between the Hours of 4 and 5 LSI
FIGURE A-8. WIND FIELD AT GROUND LEVEL, 4 AUGUST 1975
-------
1 INCH =4.5 M/5EC
I I
30
ISfriJwi&S-k^
t M \ \
10
\\\ \ ^ ^ ^
\-** j x x
1//XXXX/////X
" ////////
_» x*
^
f
f
^ / //
" * * M / i
^ * i i $y|
I M 1
^
v
:J:::^i;iiS:SJ:::S>ii^:::Oif:^:S^S^ii:>::^it::^
0
10
20
30
(b) Sensitivity Case 2 Between the Hours of 4 and 5 LSI
FIGURE A-8 (Continued)
-------
1 INCH =4.5 M/5EC
\\ \ H 1 i
1. 1 ft f /
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////
20
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10
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to
20
30
(c) Base Case Between the Hours of 8 and 9 LSI
FIGURE A-8 (Continued)
-------
1 INCH = 4.5 M/SEC
J I
20
30
///
1 f t f //
s///// / t.t /
xS^^iii^i^^^iiiSi:^
30
(d) Sensitivity Case 2 Between the Hours of 8 and 9 LSI
FIGURE A-8 (Continued)
-------
1 INCH = 4.5 M/5EC
1 i i
20
30
\\ i\ \
yMmmmmmMMimmXj:m&
(e) Base Case Between the Hours of 11 and 12 LSI
FIGURE A-8 (Continued)
-------
i
-P»
cn
1 INCH = 4.5 M/5EC
I I I
30
SSfc^^
30
(f) Sensitivity Case 2 Between the Hours of 11 and 12 LSI
FIGURE A-8 (Continued)
-------
1 INCH = 4.5 M/5EC
I i I
30
EwSSxRH:!:^
rr/rm.
20
30
(g) Base Case Between the Hours of 18 and 19 LSI
FIGURE A-8 (Continued)
-------
1 INCH = 4.5 M/5EC
1 I i
30
:•:•:*:•:•:•:•»»:•:•:<•:•:•:•: •»:•:-: •:•:<•: •:•:•:•>:•:•:•:•:«•:•:•:•:•»:•:•:•:•:<• :•:•:•;•»:•:•:•: :$•:•:•:•:>
7/7 T
v^
g 10
(h) Sensitivity Case 2 Between the Hours of 18 and 19 LSI
FIGURE A-8 (Concluded)
-------
3>
CO
20
T 1 1 1 1 1 r
10
01 I i I I I I I L
i — i — i — i
i — i — I — i — i — i — i — i — i — i — i — i —
BASE CASE: 4 AUGUST 1975
5.5
SENSITIVITY CASE 2: REDUCED UPPER
AIR METEOROLOGICAL DATA
456?
J 1 1 1 1 1 1 1 I I I I 1 I I I I I I I I 1 I
10
20
30
FIGURE A-9. AIR PARCEL TRAJECTORIES: CASE 2—BASE CASE
-------
N8RTH
LI
V-
*>
c
|x;x:*;X:x:J:;::x:*-
10
FIGURE A-10. DEVIATION OF MAXIMUM OZONE CONCENTRATIONS (ppb): CASE 2-
BASE CASE BETWEEN THE HOURS OF 4 AND 19 LSI
-------
0
60
50
40
|
t 30
S
20
10
rn(
60
50
40
X
o.
m
20
10
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6 12 18 24
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BflSE CflSE —
- HI PP EH1SSI0NS — ^
1 _
— -
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-
1 . •
L , .-wfi^rrrr-T^ , , , j
> 6 12 18 2
TIME (HIURS)
3 6 12 18 2
.~rrr i \ \ \ \ \ i i | i i i i i i i i i i i_
- Lfl HRBRE
• BflSE CflSE —
- HI PP EHISSI0NS --•
-
— —
-
- -
\ ^/x_ i
0 6 12 16 2
TIME (HIURS)
bO 60°
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30 St 30
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- -
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TIME (HIURS)
1 8 12 18 2
- L0S RLRMIT -
- BRSE CRSE —
^ HI PP EMISSIBMS —
—
—
-
-
L^^-r-^, \
] 6 12 18 2
TIME (HIURS)
•o
so
40
30
20
10
4°
so
40
30
20
10
'
FIGURE A-11. COMPARISON OF PREDICTED OZONE CONCENTRATIONS: CASE 2
A-50
-------
12
18
24
60
SO
40
X
i 30
en
20
10
n
_ i i i i i | i i i i I | I i i i i | i i 1 i i _
- PRSROENR
- BflSE CflSE
- HI PP EKISSI0NS --•
—
-
-
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_ t
— * » —
" 1 I 1 I I rVi I I 1 1 t i I I l^S*J i i l l l ""
6 12
TIHE (H0URS)
60
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40
30
20
10
60
50
40
i 30
20
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i i i i 1 i i i i f
- LYNW00D
- BflSE CflSE
- HI PP EHISSI8NS -
12
I i
18
24
12
TIHE (H0URS)
18
60
50
40
30
20
10
24
60
50
40
a.
t 30
20
10
12
18
24
i n if i i i i
r RIVERSIDE
- BflSE CflSE
u HI PP EMISSI0NS
I i i i i
60
50
40
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20
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TIHE IHfURS)
18
24°
60
50
40
x
0_
5; 30
in
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- SRN BERNflD
- BflSE CflSE
- HI PP EHISSI0NS
60
50
40
30
20
10
12
TIHE (H0URS)
18
FIGURE A-11 (Continued)
A-51
-------
60
SO
40
i 30
20
10
6
12
18
I n i i
ii i ^ i it * i
- UPLflNO
- BflSE CflSE -
I- HI PP EM1SSIBNS —
till
12
TIKE (HfURSI
18
50
30
20
10
FIGURE A-11 (Concluded)
A-52
-------
transported further downwind, e.g., at San Bernardino and Riverside. It
is apparent also in the ozone profiles at mid-basin stations, such as
Pasadena. The ozone peak is higher because of higher precursor levels,
but the increasing mixing volume leads to rapidly decreasing ozone
concentrations; at 1400 L.S.T., ozone levels are lower than in the base
case.
4) Conclusions
It appears that reduction of upper air meteorological data strongly
affects model predictions. With the 26 June 1974 meteorology, wind field
variations created the largest changes from the base case, whereas mixing
depth variations were most influential with the 4 August 1975 meteorology.
c. Model Sensitivity to Surface Meteorological Data—Simulation of
26 June 1974
The number of upper air meteorological stations has been reduced as
in the previous cases. The number of surface meteorological stations has
also been reduced. By comparing the results of this simulation with (1)
the corresponding base case and (2) the sensitivity case with reduced
upper air meteorological data, one can evaluate the impact of reduced
surface meteorological data on model predictions.
1) General Sensitivity Measures
Some measures of the general sensitivity of the model are presented
in tables A-4 and A-5, for comparisons with the base case and the former
sensitivity case (case 1: reduced upper air meteorological data),
respectively. Deviations in ozone levels from the June base case are
similar to those in case 1. Notice that the overall maximum level in grid
cell [30-16] is much higher for this case (53.1 pphm, compared with 31.6
pphm in case 1). The deviations in peak levels from the base case at the
air monitoring stations are of the same order as in case 1 (table A-4 and
A-5), but there^ is some discrepancy between this case and case 1 (table A-
2). (This is possible since absolute values are considered in this
measure.) The peak time lag has increased slightly also.
It appears that the dosage is the most sensitive measure in this
study. The percent deviation in dosage between this case and case 1 is
23.9. The effect of surface meteorological data on model predictions is
not negligible. This fact would not be apparent if only ozone level
A-53
-------
TABLE A-4. GENERAL SENSITIVITY MEASURES—CASE 3 VS. BASE CASE
(a) General Ozone Level Deviations
Station Statistics
3*
l
cn
Sensitivity Measure
Signed deviation
Absolute deviation
Temporal correlation
Spatial correlation
03 > 12 pphm 03 > 20 pphm
-0.172 -0.367
0.320
0.389
-0.183
0.310
-0.455
-0.185
Grid Statistics
03 > 12 pphm 03 > 20 pphm
-0.225 -0.392
0.347
-0.034
0.247
0.443
-0.293
0.331
(b) Overall Maximum Ozone Level
Sensitivity case/
base case ratio
Peak level (pphm):
Sensitivity case
Base case
Station Statistics
0.710
25.2
35.5
Corresponding locations:
Sensitivity case San Bernardino
case
Grid Statistics
1.366
53.1
38.9
30 - 16
33 - 14
-------
TABLE A-4 (Concluded)
(c) Maximum Ozone Statistics
All Stations Downwind Stations
Peak level 0.249 0.260
normalized difference
Peak time lag (hrs) 2.17 2.37
3»
ui (d) Dosage
Sensitivity Case Base Case
Normalized Difference (km2) (km2)
-0.260 7,400 10,000
-------
TABLE A-5. GENERAL SENSITIVITY MEASURES—CASE 3 VS. CASE 1
(a) General Ozone Level Deviations
Station Statistics
Grid Statistics
in
Sensitivity Measure
Signed deviation
Absolute deviation
Temporal correlation
Spatial correlation
°3
> 12 pphm
-0.018
0.259
0.947
0.810
03 > 20 pphm
-0.058
0.097
0.519
0.272
03 > 12 pphm 03 > 20 pphm
-0.007 -0.050
0.171
0.826
0.656
0.167
0.521
0.632
(b) Overall Maximum Ozone Level
Station Statistics
Sensitivity case/
case 1 ratio
Peak level (pphm):
Sensitivity case
Case 1
Corresponding locations:
Sensitivity case
Case 1
0.989
25.2
25.5
San Bernardino
Upland
Grid Statistics
1.690
53.1
31.6
30 - 16
30 - 16
-------
TABLE A-5 (Concluded)
(c) Maximum Ozone Statistics
All Stations Downwind Stations
Peak level 0.104 0.108
normalized difference
Peak time lag (hrs) 1.25 1.25
(d) Dosage
Sensitivity Case Case 1
Normalized Difference (km2) (km2)
0.239 7,400 5,975
-------
deviations between this sensitivity case and the base case were
considered; the comparison with case 1 therefore, is useful to assess the
importance of surface meteorological data.
2) Sensitivity of Model Input Variables to Input Data
Meteorological data affect the mixing height, wind field, and eddy
diffusivities. The eddy diffusivities are not considered, here, since
their effect on model predictions is negligible compared to that of the
other meteorological variables.
Mixing height differences between this sensitivity case and the base
case are shown in figure A-12; the perturbations are similar to those
obtained in case 1. The mixing depths are slightly lower in mid basin
around 1100 L.S.T. but slightly higher in the afternoon around 1500.
The wind field at ground level, shown in figure A-13 for the hours of
0400 to 0500, 0800 to 0900, 1100 to 1200, and 1800 to 1900 L.S.T.,
presents a pattern similar to the sensitivity of case 1. The differences,
however, are not negligible. Some air parcel trajectories are shown in
figure A-14 for this case and case 1. The differences at Azusa and Prado
are not as large as those resulting from the reduction in upper air
data. In the eastern part of the basin, however, the wind flow is much
affected, as shown by the air parcel trajectories that reach Redland at
1200 L.S.T. The strong perturbations on the eastern boundary of the
airshed may be a result of the reduction of meteorological boundary values
for the wind model.
In mid basin, wind velocities are larger for this sensitivity case
than for case 1, as shown in figure A-13. This will result in more
atmospheric dispersion and lower the species concentrations (Liu et al.,
1976).
It seems that the reduction in surface meteorological data is not as
perturbing as the reduction of upper air meteorological data. The mixing
depth and wind field are not affected as much as in case 1. However, one
should expect some variations in ozone levels as a result of those non-
negligible perturbations in the meteorological variables
3) Sensitivity of Ozone Levels to Surface Meteorological Data
Isopleths of maximum ozone deviations are shown in figures A-15 and
A-16 for the comparisons with the base case and case 1, respectively. The
largest deviations occur along the eastern boundary of the airshed. It
A-58
-------
MIRTH
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S0UTH
(a) Between the Hours of 4 and 5 LSI
FIGURE A-12. MIXING HEIGHT DIFFERENCE (to): CASE 3--BASE CASE
-------
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(b) Between the Hours of 11 and 12 LSI
10
FIGURE A-12 (Continued)
-------
NIRTH
10
20
10
\ \ '«-.. L
\ X.
10 £
10
20
S0UTH
(c) Between the Hours of 15 and 16 LSI
FIGURE A-12 (Concluded)
-------
1 INCH =4.5 M/SEC
ro
10
I
ZiflaH^^^
mmmmm^m
^ / t
A i
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t t f f / M t t -|
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Si
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(a) Sensitivity Case 3 Between the Hours of 4 and 5 LSI
FIGURE A-13. WIND FIELD AT GROUND LEVEL, 26 JUNE 1974
-------
1 INCH = 4.5 M/SEC
I t I
Ci
CO
^i^&m&mbx-M.
20 ......... 30
SftteSfe^
I t / s s s
^nmimn
/ /
\ \ jgslia
(b) Between the Hours of 8 and 9 LSI
FIGURE A-13 (Continued)
-------
1 INCH =4.5 M/SEC
3>
i
O>
/ t
/ / / m
^^mmmmrn\n
(c) Between the Hours of 11 and 12 LSI
FIGURE A-13 (Continued)
-------
i
cn
01
1 INCH = 4.5 M/SEC
I I J
20
10 g
(d) Between the Hours of 18 and 19 LSI
FIGURE A-13 (Concluded)
-------
llllllI I
I I
I I
SENSITIVITY CASE 1
SENSITIVITY CASE 3
10
0
AZUSA
J I
REDLAND
_
0
10
20
30
FIGURE A-14. AIR PARCEL TRAJECTORIES: CASE 3—CASE 1
-------
NfRTH
10
20
S 10
.rHwi»Vr«*«*i*U«
\ LiNG
20
S0UTH
FIGURE A-15. DEVIATION OF MAXIMUM OZONE CONCENTRATIONS (ppb): CASE 3—
BASE CASE BETWEEN THE HOURS OF 4 AND 19 1ST
-------
NflRTH
I < . .>.. ':< > : j:::::::j
S0UTH
FIGURE A-16. DEVIATION OF MAXIMUM OZONE CONCENTRATIONS (ppb): CASE 3-
CASE 1 BETWEEN THE HOURS OF 4 and 19 1ST
-------
was shown in figure A-13 that the wind flow is strongly perturbed in this
part of the basin, and this may explain the large ozone variations. Ozone
profiles at nine air quality monitoring stations are presented in figure
A-17 for this sensitivity case and for the base case. Profiles for the
sensitivity case are similar to those of case 1 at most stations. A
higher ozone peak at Pasadena may result from lower mixing depths, though
a different air trajectory may also be a possible factor. The profile at
Redlands is very different from the profile of case 1 (see figure A-5)
owing to the strong perturbation in the wind field in this part of the
basin. Higher wind velocities probably constitute one of the factors
leading to lower ozone levels in mid basin (e.g., Azusa and Pomona).
4) Conclusions
It appears that surface meteorological data affect mixing depths,
wind direction (especially at the airshed boundaries), and wind speeds.
These perturbations lead to some deviations in the ozone levels, but the
overall effect is not as large as that caused by the reduction of upper
air meteorological data.
These results depend on the nature of the wind model. The wind field
is obtained by solving a boundary value problem for a potential
function. Therefore, the results should be more sensitive to meteorologi-
cal data located at the boundaries of the airshed than to the intensity of
data in mid basin, for example. Upper air meteorological data have a
strong effect on the wind field with those meteorological conditions, and
it has been shown that perturbations in the wind field caused by a
reduction in surface data were larger near the airshed boundaries.
Notable perturbations are observed in the mixing depths, and their
effects may be larger than in case 1, though the relative importance of
perturbations in the mixing height and wind field is difficult to
evaluate.
d. Model Sensitivity to Surface Meteorological Data—Simulation of
4 August 1975
In this sensitivity simulation, surface and upper air meteorological
data have been reduced. . To evaluate the effect of a reduction in surface
meteorological data, comparisons will be made with case 2 (reduced upper
air meteorological data) and the August base case.
A-69
-------
•0
50
«0
x
I 30
S
20
10
12
1 I
18
- RIVERSIDE
- BflSE CflSE ——
L SENSITIVITY RUN —
6 12 18
TINE (HfURS)
50 so
40 40
30
10
i
£30
20 20
10
B 12
iiiijiiiii |
- SflN BERNflO
- BflSE CflSE —
- SENSITIVITY RUN —
18
40
30
20
10
i I i i i t
6 12 18
TINE CHiURS)
60
50
12
18
I so
20
10
- UPLflNO
i i I i I
RUN —
60
50 50
40 40
30 t 30
20 20
10 10
12
18
12
TINE (MURS1
IB
24°
i i~n T^ ' ' ' ' I
- LYNH000
- BflSE CRSE
- SENSITIVITY RUN —
i i i i i
I I I I
50
40
30
20
10
I I I I I
6 12 18
TINE (HIURS)
FIGURE A-17. COMPARISON OF PREDICTED OZONE CONCENTRATIONS: CASE 3
A-70
-------
to
50
40
I
130
S
20
10
6 12
I i i i I i rTTT"T"
FBKTBNA
- BflSE CASE
- SENSITIVITY RUN —
16
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6 12 IB
TINE IHiURS)
24°
60
50
10 40
£30
20 20
10 to
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18
i i i i
- RNRHEIM
- fiflSE CASE -
- SENSITIVITY RUN —
6 12 16
TIME (HfURS)
50
40
30
20
10
60
SO
i 30
8
10
12
18
n i i i i | \ i u i j| i i i i i i i i t i i.j
- LR HRBRE
- BRSE CflSE
- SENSITIVITY RUN —
J. I I I I I
) BO
50 SO
40 40
30 £30
20 20
10 10
12
16
6 12
TIME (HfURS)
TTT] I I I I i
- PRSflDENfl
- BftSE CHSE —
- SENSITIVITY RUN —
50
30
20
10
' ' '
12
TIME (HILIR5)
16
FIGURE A-17 (Continued)
A-71
-------
60
50
40
In
20
10
12
16
I I I I I I I I I I I I
REDLRNDS
- BRSE CflSE
- SENSITIVITY RUN —
6 12 16
TIME (H1URS)
50
30
20
10
FIGURE A-17 (Concluded)
A-72
-------
1) General Sensitivity Measures
Some measures of the general sensitivity of the model are listed in
tables A-6 and A-7 for comparisons with the base case and case 2.
The absolute deviations are of the same order as those obtained in
case 2. However, the signed deviations are larger (see table A-3). In
general, ozone levels are lower in this case than in case 2 and,
therefore, than in the 4 August 1975 base case. This effect appears
clearly in the dosage, which is much lower than in case 2 or the base
case. The dosage-normalized difference is comparable to that obtained
with the 26 June 1974 meteorological conditions.
Ozone peak levels are also affected by a reduction in surface
meteorological data, and the overall maximum ozone level and the station
maximum ozone statistics show a decrease in ozone concentrations.
Although spatial and temporal correlations depend on the statistics
considered (ozone level, grids or stations), they are closer to case 1
with these meteorological conditions than with the 26 June 1974 conditions
(see table A-3).
2) Sensitivity of Model Input Variables to Input Data
The mixing height and wind field are the only variables considered
here, since estimation of eddy diffusivities is not heavily data
dependent.
Mixing depths for the hours of 0400 to 0500, 1100 to 1200, and 1800
to 1900 L.S.T are shown in figure A-18. When compared with the mixing
depths of case 2 (see figure A-6), it appears that the mixing height is
slightly higher in this case around Pasadena and Whittier (20 to 40 m),
lower around Anaheim (20 to 40 m), and similar to case 2 in the eastern
part of the basin (e.g., Prado).
The wind field is shown in figure A-19 for various hours of
simulation. There are no important perturbations between this wind field
and the wind fields of case 2 or the base case (see figure A-8), as shown
by the comparison of air parcel trajectories shown in figure A-20. There
is a slight deviation for the Prado air parcel in the early morning hours,
but it is minor when compared to the deviations observed with the
26 June 1974 meteorological conditions (see figures A-3 and A-14).
A-73
-------
TABLE A-6. GENERAL SENSITIVITY MEASURES--CASE 4 VS. BASE CASE
(a) General Ozone Level Deviations
Station Statistics
Grid Statistics
Sensitivity Measure
Signed deviation
Absolute deviation
Temporal correlation
Spatial correlation
03 > 12 pphm 03 > 20 pphm
-0.146 -0.073
0.189
0.104
0.799
0.648
0.682
0.937
03
> 12 pphm
-0.107
0.198
0.737
0.450
03 > 20 pphm
-0.165
0.187
0.263
0.608
(b) Overall Maximum Ozone Level
Sensitivity case/
base case ratio
Peak level (pphm):
Sensitivity case
base case
Corresponding locations:
Sensitivity case
base case
Station Statistics
0.988
26.0
26.3
Upland
Pomona
Grid Statistics
0.755
28.0
37.0
27 - 15
30 - 16
-------
TABLE A-6 (Concluded)
(c) Maximum Ozone Statistics
Peak level
normalized difference
Peak time lag (hrs)
All Stations
0.143
0.825
Downwind Stations
0.121
0.812
01
Normalized Difference
-0.244
(d) Dosage
Sensitivity Case
(tan2)
6,625
Base Case
(km2)
8,750
-------
TABLE A-7. GENERAL SENSITIVITY MEASURES—CASE 4 VS. CASE 2
(a) General Ozone Level Deviations
Station Statistics
Grid Statistics
Sensitivity Measure
Signed deviation
Absolute deviation
Temporal correlation
Spatial correlation
°3
> 12 pphm
-0.061
0.098
0.907
0.894
03 > 20 pphm
-0.076
0.084
0.986
0.572
03 > 12 pphm 03 > 20 pphm
-0.061 -0.093
0.110
0.922
0.835
0.110
0.923
0.697
(b) Overall Maximum Ozone Level
Sensitivity case/
case 2 ratio
Peak level (pphm):
Sensitivity case
Case 2
Corresponding locations:
Sensitivity case
Case 2
Station Statistics
0.953
26.0
27.3
Upland
Upland
Grid Statistics
0.900
28.0
31.1
27 - 15
11 - 16
-------
TABLE A-7 (Concluded)
(c) Maximum Ozone Statistics
Peak level
normalized difference
Peak time lag (hrs)
All Stations
0.09
0.30
Downwind Stations
0.069
0.310
(d) Dosane
Normalized Difference
-0.230
Sensitivity Case
(km2)
6,625
Case 2
(km2)
8,600
-------
MIRTH
ft
S0UTH
(a) Between the Hours of 4 and 5 LSI
FIGURE A-18. MIXING HEIGHT DIFFERENCE (m): CASE 4—BASE CASE
-------
NiRTM
10
20
UJ
>
D
FBNT
j :_: : t:- : : f '. : t .j x j.jy ! i'j.:.: xt . ;>> -t
tvS^xKt:;:::;:^:::;^:::^^:-:: :-.! x:::><:>>v: xt ::
S0UTH
(b) Between the Hours of 11 and 12 LSI
FIGURE A-18 (Continued)
-------
MIRTH
>
•LING--—-•
J I i . I ) I t : I.. t .
.:::.:. I:.;..-.».'.- J.::.::':»':.'.'.:l.V.:.':l:.:.:..T.'.:..r.:. : J I i I.I
S0UTH
(c) Between the Hours of 18 and 19 LSI
FIGURE A-18 (Concluded)
-------
1 INCH s 4.5 M/SEC
I j :
,JO 10
zOb&^&i^mjiti-imsMimsimm
20
IN \ \
Ik f f
10
//////// / .
«/////// H
l^jfM
wwnim
I/////// M f
'^ -*•-»
s s s
/ S S
' ' 1 \ \ *.' x x x "
•'^it<«***1'*
f f / / /
t f / /
n f f
t t t
\ \ i
\ i 1
llmmnHmni ^
Illlllllillllillfc t t
1
^ x
/ *
f /
t 1
V *.
-*• •*
t t
\ t
npKii^imi^ffl^iifit
•mmmmmmmm.
X X
' / i
' / / ^
/ /y a:
^ \4i
10
10
20
30
(a) Sensitivity Case 14 Between the Hours of 4 and 5 LSI
FIGURE A-19. WIND FIELD AT GROUND LEVEL, 4 AUGUST 1975
-------
CO
r>o
1 INCH = 4.5 M/5EC
I
>. cVvvvvv WOC- > \ \x^»-•>-•»>• 4 . »»»•>•>• *m
'f\\\ N t \ V v v vN^/ * / / M \ * » ,;;»»4» < * ,11
//Mlt\\\ t / /S^'' "<•<•* f M \ t > <.||
' >• / / / a 111IIIL/fcZCZIZL.'* \\\\\l I
777
////
20
10
M /////// M
0
10
20
wmmmmsmm
30
0
(b) Between the Hours of 8 and 9 1ST
FICURE A-19 (Continued)
-------
CO
CO
1 INCH = 4.5 M/SEC
I i i
30
(c) Between the Hours of 11 and 12 LSI
FIGURE A-19 (Continued)
-------
1 INCH = 4.5 M/SEC
00
I I
;:":'^^
(d) Between the Hours of 18 and 19 LSI
FIGURE A-19 (Concluded)
-------
I
CO
cn
20
0
0
i j _ j_ i i
' i I I i i I I i I i i iI I I r
SENSITIVITY CASE 2
SENSITIVITY CASE 4
AZUSA
i i I i I i I 1 I 1 1 L
10
20
30
FIGURE A-20. AIR PARCEL TRAJECTORIES: CASE A--CASE 2
-------
3) Sensitivity of Ozone Levels to Surface Meteorological Data
Comparisons of maximum ozone concentrations with the base case and
case 2 are shown in figures A-21 and A-22, respectively. The comparison
with the base case shows pattern similar to the isopleths of case 2
compared with the base case. There are, however., some variations between
this sensitivity case and case 2, that appear in figure A-22. Ozone
levels are lower in northern midbasin and higher in the eastern part for
this case than for case 2. By considering the wind flowland the
variations in mixing depth, one may relate the higher mixing depth around
Whittier to lower ozone levels downwind (Azusa, Pomona, Upland) and the
lower mixing depth around Anaheim to higher pollutant levels in the
eastern part of the basin.
Ozone profiles are presented at six stations in figure A-23.
Profiles are similar to those obtained in case 2, except for a lower ozone
peak at Pasadena and a slightly higher peak level at San Bernardino, both
of which have been discussed earlier.
4) Conclusions
Under the 4 August 1975 meteorological conditions, surface meteoro-
logical data affect mainly the mixing height, whereas the wind field is
not notably perturbed. The same effect was observed with the reduction of
upper air meteorological data for the same simulation day. This is an
important difference from the 26 June 1974 simulations, in which the wind
field was strongly perturbed and seemed to be the major factor affecting
the model predictions.
In conclusion, it appears that the influence of meteorological data
on the model depends on the nature of the meteorological conditions and
that the mixing height and the wind field may both affect the model
predictions strongly according to the existing atmospheric conditions.
e. Model Sensitivity to Surface Air Quality Data—Simulation of
26 June 1974
The effect on the model predictions of a reduction in the number of
air quality stations is considered in this section. The sensitivity of
the model to surface air quality data (case 5-1) is considered first.
This is followed by consideration of sensitivity of the model (case 5-2)
to a reduction in surface air quality data (as in case 5-1) and to a
reduction in upper air and surface meteorological data (as in case 3).
A-86
-------
NflRTH
10
'•-
.
10
10
'__ __( • 1 '... '
FIGURE A-21. DEVIATION OF MAXIMUM OZONE CONCENTRATIONS (ppb): CASE 4—
BASE CASE BETWEEN THE HOURS OF 4 AND 19 1ST
-------
MIRTH
2 10
•3.
:» ..t......I...
1C
20
• If 11 « : f :::l
10 £
':':•:-: ::T::-:':'::X'X-X:::::-X ,
<:•: .•,•.«:: -.-<:..: :>•:•:•:.-!.•:•.-: :t '•:•:-. I:-.-.-. .<-:': .-.-I...-..1,-... I..-. ,-.t-.•.•.•.!.•,•.•. .t-,.,. I .
"
SBUTH
Between the Hours of 4 and 19 LSI
FIGURE A-22. DEVIATION OF MAXIMUM OZONE CONCENTRATIONS (ppb): CASE 4—CASE 2
-------
12
18
60
50
40
1
t 30
£
20
10
°(
fr A
60
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20 20
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60 bu
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-------
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12
16
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40
i 30
20
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SRN BERNflD
BflSE CflSE —
HI PP EMISSIBNS —
12
TIME (H0URS)
18
50
40
30
20
10
24°
60
50
40
x
a.
Jb 30
CO
20
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12
.1 I I I I | I I II I
- UPLflNO
- BflSE CflSE ——
- HI PP EMISSIBNS —
IB
6 12 18
TIME (HiURS)
50
40
30
20
10
FIGURE A-23 (Concluded)
A-90
-------
1) General Sensitivity Measures
Some measures of the general sensitivity of the model to a reduction
in air quality data and to a reduction in both meteorological and air
quality data are presented in tables A-8 and A-9, respectively.
The results presented in table A-8 show that the model is not very
sensitive to the reduction in surface air quality data. The ozone
deviations, peak level difference, and dosage difference are small. There
is, however, a large difference between the maximum ozone statistic for
all stations and that for downwind stations. This fact suggests that
coastal stations are more sensitive to air quality data reduction than are
downwind stations. The temporal and spatial correlations are high {above
0.965).
The results presented in table A-9 (reduction in meteorological and
surface air quality data) are similar to the results presented in table A-
8 (reduction in meteorological data only). This is consistent with the
results of table A-8, which indicate that the model is not very sensitive
to surface air quality data. Ozone predictions of sensitivity case 5-2
are systematically lower than those of case 3. The combination of
meteorological and air quality data reduction is, therefore, not additive,
since no overall decrease in ozone levels is observed in case 5-1. This
is particularly apparent when comparing the dosages. Finally, the pattern
observed in case 5-1 for the maximum ozone statistics of all stations and
downwind stations also appears in case 5-2.
2) Sensitivity of Model Input Variables to Input Data
The reduction in surface air quality data affects the initial and
boundary conditions for ozone, carbon monoxide, nitrogen oxides, and
hydrocarbons. The perturbation in the model equations will depend in part
on the spatial distribution of the air monitoring stations in the base
case and in the sensitivity case. The locations of the stations have been
presented in chapter three.
3) Sensitivity of Ozone Levels to Surface Air Quality Data
Isopleths of maximum ozone deviations are presented in figures A-24
and A-25 for the sensitivity cases 5-1 and 5-2, respectively. It appears
in figure A-24 that the southwestern part of the basin presents lower
ozone levels in case 5-1 than in the base case. Higher ozone levels occur
west of Pasadena, and the two effects compensate each other in most of the
A-91
-------
TABLE A-8. GENERAL SENSITIVITY MEASURES—CASE 5 VS. CASE 3
(a) General Ozone Level Deviations
Station Statistics
Grid Statistics
<£>
ro
Sensitivity Measure
Signed deviation
Absolute deviation
Temporal correlation
Spatial correlation
03
> 12 pphm
0.000
0.028
0.990
0.986
03 > 20 pphm
0.003
0.022
0.990
0.986
> 12 pphm 03 > 20 pphm
0.006 0.010
0.032
0.988
0.980
0.032
0.984
0.965
(b) Overall Maximum Ozone Level
Sensitivity case/
base case ratio
Peak level (pphm):
Sensitivity case
Base case
Corresponding locations:
Sensitivity case
Base case
Station Statistics
0.997
35.4
35.5
Azusa
Azusa
Grid Statistics
0.982
38.2
38.9
19 - 15
33 - 14
-------
u>
TABLE A-8 (Concluded)
(c) Maximum Ozone Statistics
All Stations Downwind Stations
Peak level 0.061 0.031
normalized difference
Peak time lag (hrs) 0.52 0.0
(d) Dosage
Sensitivity Case Base Case
Normalized Difference _ (km^) _ (km^)
0.048 10,475 10,000
-------
TABLE A-9. GENERAL SENSITIVITY MEASURES—CASE 5 VS. BASE CASE
(a) General Ozone Level Deviations
Station Statistics
Grid Statistics
Sensitivity Measure 03 > 12 pphm 03 > 20 pphm 03 > 12 pphm 03 > 20 pphm
Signed deviation
Absolute deviation
Temporal correlation
Spatial correlation
-0.208
0.329
-0.390
0.402
-0.183
0.313
-0.402
-0.184
-0.253
0,355
-0.067
0.265
-0.416
0.459
-0.253
0.348
(b) Overall Maximum Ozone Level
Sensitivity case/
base case ratio
Peak level {pphm):
Sensitivity case
Base case
Corresponding locations:
Sensitivity case
Base case
Station Statistics
0.683
24.2
35.5
San Bernardino
Azusa
Grid Statistics
1.251
48.6
38.9
30 - 16
33 - 14
-------
en
TABLE A-9 (Concluded)
(c) Maximum Ozone Statistics
All Stations Downwind Stations
Peak level 0.293 0.266
normalized difference
Peak time lag (hrs) 2.25 1.93
? (d) Dosage
Sensitivity Case Base Case
Normalized Difference (km2) _
-0.288 7,125 10,000
-------
NfKTH
10
$
•M«4<<««'<44+4*44<:Mi.»v.'"*"**"*'t.'€fHt"""*'
3BUTH
FIGURE A-24. DEVIATION OF MAXIMUM OZONE CONCENTRATIONS (ppb): CASE 5.1—
BASE CASE BETWEEN THE HOURS OF 4 ar.d 19 1ST
-------
MIRTH
c
• .
10
20
.->.•.-.v.Cv.-.v
^
S 10
I
H
rtytf^^
."r^^'^rllv
,*»«.**" QMtrtT ™" "**. • *.. *
20- *
' Oi;
(o:,1
• ••!••*••
/JP
::S;S:f:iS
!-'X-."-
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*\ T o \!\^ /J -^
I >% ' i^; ^ \ w , / ,
S'i v I '**«. \ \ "' •'••'••'•
;;|||:.:,.,." "-...^" ..1"L^ ^ wftjlll
:;:ji::;:;x;^:;x^;:;s:;:;tx;:::;:i|gx;:;ii:ox;:ij;xxJ:^^
10
20
SBUTH
FIGURE A-25. DEVIATION OF MAXIMUM OZONE CONCENTRATIONS (ppb): CASE 5.2— BASE CASE
BETWEEN THE HOURS OF 4 AND 19 LST
-------
general sensitivity measures except in the maximum ozone statistics for
all stations and for downwind stations, which showed the perturbation at
the coastal air quality stations. Figure A-25 may be compared with figure
A-24. The major difference is also in the southwestern part of the basin.
Ozone profiles at eight air quality monitoring stations are
presented in figures A-26 and A-27 for the sensitivity cases 5-1 and 5-2,
respectively. The coastal stations Costa Mesa and Laguna present lower
ozone levels; other ozone profiles are not much affected when compared
with the base case and case 3, respectively.
In the southwestern part of the basin, the air quality data are
scarce in the sensitivity case, since winds are southerly (that is, there
is an inflow into the airshed) and the only stations considered in the
sensitivity case in this area are Long Beach and Anaheim. The same
phenomenon occurs around Pasadena, where there is an inflow with westerly
winds and no monitoring stations upwind of Pasadena or downtown
Los Angeles. These perturbations, however, are located near the
boundaries of the airshed where there is an inflow, and the overall model
performance is not very much affected by the reduction of the number of
air quality monitoring stations.
In the sensitivity case 5-2, the deviation in the model prediction J
is caused by perturbations in the meterological input data M and in the
surface air quality data A. The relationship between the deviation AJ and
the perturbations AM and AA may be expressed to second order as follows:
0 (AA3, AM3, AA2AM, AAAM2) . (A-l)
As shown in the general sensitivity measures that the reductions in air
quality data and meteorological data were not additive (see, for instance,
the dosages for cases 3, 5-1 and 5-2), which suggests that the factors are
interrelated and that the coupling between AA and AM is non-negligible.
The importance of the coupled sensitivity coefficient 32J/3A3M reflects
the coupling of chemical and physical processes in the atmosphere and the
importance of including in a mathematical model all atmospheric phenomena
without dissociating them.
A-98
-------
12
16
24.
SO
40
i 30
20
10
- ANAHEIM
- BflSE CflSE — —
- SENSITIVITY RUN —
-
-
-
9 6 12
-
-
—
18 2
SO
40
30
20
10
o
f
30 tg0
S
TIME (HfURS)
60
50
40
30
20
10
°C
3 6 12 18
,i i i i i i i i i i i | i i i i i | i r
- CiSTA HESfl
- BflSE CASE —
- SENSITIVITY RUN --•
-
-
-
\ X^^^s.
:, , , &*\\ , , t . ,%?r^j ,
6 12 16
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TT-n
^
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—
-
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*60
50
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30
20
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f
TINE (HiURS)
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SO
40
^30
S
20
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ie
24
J I I I I | I I M I | I 1 M I [
- LA HflBRE
- BflSE CflSE —
- SENSITIVITY RUN —
TTT
' *
50
40
30
20
10
6 12s 1«
TIME tHiURS1
- PflSADENfl
- BASE CASE
- SENSITIVITY RUN
12 18
TINE (HiURSt
FIGURE A-26. COMPARISON OF PREDICTED OZONE CONCENTRATIONS: CASE 5-1
A-99
-------
60
50
40
••^
i 30
20
10
1218
I i i i | I I i I I |
- LYNM8BD
*- BBSE CRSE
- SENSITIVITY RUN
6 12
TIME (HIURS)
50
30
20
10
* I I I I I In
18 2f
60
50
40
x
t 30
•it
20
10
12
IB
i i i i i | i i i i i
- SON BERNflD
- BRSE CRSE
- SENSITIVITY RUN --
6 12 18
TIME CH0URS)
50
40
30
20
10
60
50
40
**
x
i 30
m
20
10
12
18
- UPUflND
- BflSE CflSE
- SENSITIVITY RUM
i i i i i
50
40
30
20
10
6 12 18
TIME CHfURS)
60
50
40
t 30
20
10
12
16
- LflGUNR
- BPSE CflSE —
- SENSITIVITY RUN —
i I
12
TIME (MiURS)
18
i i i.
•^9
FIGURE A-26 (Concluded)
A-100
-------
RnC
60
SO
40
£ao
s
20
10
°0
•J
BO
so
40
5:30
S
20
10
n
1
TT
-
M
-
-
-
a
ri
-
_.
-
-
li
6 12 18 2
1 1 1 1 | 1 I 1 I 1 | 1 1 1 ! 1 | I 1 1 1 1.
HNRHEIM
BfiSE CRSE — —
SENSITIVITY RUN — J
-
-
-
«•
y\r\ J
6 12 18 *
TINE (HfURS)
8 12 »B 2
1 1 II | 1 1 II 1 j || 1 1 1 1 I 1 1 ' ' '-
LRGUNfl I
BflSE CflSE — "
SENSITIVITY RUN — ^
-
-
-
^S****^ ~
' i «*TVT ti i i i i i * * '"i
en gn
DU WU
50 SO
40 40
JC
30 £ 30
s
20 20
10 10
0 0
r °c
^0 60
50 50
40 40
JC
X
30 - 30
S
20 20
10 10
D °,
0 6 12 10
_'»«»' 1 •' i i 1 | 1 1 1 I I | | I I 1 1"
- C0STA MESfl I
- BBSE CflSE I
- SENSITIVITY RUN - —
-
"™ ...
-
—
\ .^r^X \
•iii g^ti i ii ij . i , , . i . , , . ,-i
B 12 16 2
TINE (HIURS)
- Lfi HHBRE I
- BRSE CfiSE
-_ SENSITIVITY RUN —
" -
~ -
\ A \
• yC\ ^
"1 i i \-*>Tt i i i i 1 i i i .Xi ....,-
!4
60
50
40
30
20
10
4°
50
40
30
20
10
0
TINE IHfURS)
12
TINE CHCURS)
18
FIGURE A-27. COMPARISON OF PREDICTED OZONE CONCENTRATIONS: CASE 5.2
A-101
-------
SO
40
i 30
20
10
6
- PflSflOENfl
- BRSE CBSE
- SENSITIVITY RUN
12
16
i i i i
6 12 18
TIME (HBURS)
50
40
30
20
10
60
50
40
i 30
20
10
12
16
T
- LTNNB00
- ensE COSE —
u SENSITIVITY RUN —
l l l i I.
50
20
ID
6 12 18
TINE (HfURS)
60
50
6
12
18
£: 30
20
10
1 I T I | I I I I I I
- SON BERNRD
- BflSE CflSE —
- SENSITIVITY RUN —-
i i i i i i i i i i
AV
6 12 18
TIME (HiURS)
SO
40
30
20
10
60
50
40
t 30
20
10
12
18
- UPLfiND
- BBSE CflSE —
- SENSITIVITY RUN —
]
so
40
30
20
10
6 12
TIME (HIURS)
18
FIGURE A-27 (Concluded)
A-102
-------
4) Conclusion^
The reduction of the number of air quality monitoring stations does
not greatly affect the model predictions. Obviously, the choice of the
location of the monitoring stations is important. The locations appear to
have been appropriate in these sensitivity studies, since the perturba-
tions are limited to small areas along the airshed boundaries. It should
be noted, however, that the Los Angeles basin monitoring network is rather
dense, and it is not surprising that the model is relatively insensitive
to the intensity of surface air quality data. It would be interesting to
determine the minimum set of air quality monitoring stations that could be
used without affecting the model predictions notably.
Once the minimum number of air quality stations has been determined,
the optimal spatial distribution of these stations should be considered.
This optimization problem could be solved once an appropriate performance
measure has been determined (e.g., maximum hourly averaged ozone levels,
number of days on which air quality standards are exceeded).
Finally, the complexity of atmospheric dynamics appears clearly in
these sensitivity studies, where the coupling of meteorological and
chemical processes is apparent.
f. Model Sensitivity to Upper Air Quality Pata--Simulation of
26 June 1974
In this sensitivity study, the initial concentrations of nitrogen
oxides and reactive hydrocarbons in the third layer of the grid model
(i.e., above the inversion) were taken to be half their value in the
second cell. In the base case, precursor levels were assumed to be
representative of "clean air background".
1) General Sensitivity Measures
Some general sensitivity measures of the model to upper air quality
data are listed- in table A-10; generally higher ozone levels are
observed. The largest deviations are obtained for the ozone peak levels
(16.2 percent for all stations). The temporal and spatial correlations
are relatively high (above 0.94) for all ozone levels. Overall, higher
precursor levels above the inversion layer in the morning lead to higher
ozone levels, without notably perturbing the spatial and temporal features
of the model predictions.
A-103
-------
TABLE A-10. GENERAL SENSITIVITY MEASURES—CASE 6
(a) General Ozone Level Deviations
Station Statistics
Grid Statistics
o
Sensitivity Measure
Signed deviation
Absolute deviation
Temporal correlation
Spatial correlation
03>
12 pphm
0.105
0.106
0.981
0.975
03 > 20 pphm
0.110
0.110
0.983
0.959
03 >
12 pphm
0.103
0.108
0.977
0.961
03 > 20 pphm
0.110
0.113
0.972
0.941
(b) Overall Maximum Ozone Level
Station Statistics
Sensitivity case/ 1.109
base case ratio
Peak level (pphm):
Sensitivity case 39.3
Base case 35.5
Corresponding locations:
Sensitivity case Upland
Base case Azusa
Grid Statistics
1.122
43.6
38.9
33 - 14
33 - 14
N>
•yo
-------
70
to
o
CJ1
TABLE A-10 (Concluded)
(c) Maximum Ozone Statistics
All Stations Downwind Stations
Peak level 0.162 0.144
normalized difference
Peak time lag (hrs) 0.57 0.13
(d) Dosage
Sensitivity Case Base Case
Normalized Difference (km2) (km2)
0.4525 14,525 10,000
-------
2) Sensitivity of Model Input Variables to Input Data
In this sensitivity study, the upper level initial conditions have
been modified for nitrogen oxides and hydrocarbons. The importance of
this initial condition on the system of continuity equations will
determine the sensitivity of the model to upper air quality data.
3) Sensitivity of Ozone Levels to Precursor Initial Upper Boundary
Conditions
Isopleths of variations in maximum ozone levels are shown in figure
A-28. Higher ozone levels on the order of 20 to 40 ppb are observed
throughout the basin, except in the southwestern part where lower ozone
levels appear. In general, an inflow of precursors from aloft leads to
overall higher ozone levels. In the southwestern part of the basin,
photochemical smog formation is in its initial stage, since the wind flow
is from the southwest. Therefore, an increase of precursor levels may
lead to an inhibiting effect of nitric oxide on ozone formation and to
lower ozone levels.
Ozone profiles at eight air monitoring stations are shown in figure
A-29 for this sensitivity case and the corresponding base case. Higher
ozone levels are observed, except at the coastal Laguna station where
nitric oxide probably inhibits ozone formation. This effect, however,
does not appear at the nearby Costa Mesa station. The deviation in the
time of the peak at the inland stations is small, and inland ozone level
predictions are perturbed only in magnitude.
4) Conclusions
The upper air initial conditions for nitrogen oxides and hydrocarbons
have some effect on the magnitude of the ozone levels but do not perturb
the spatial and temporal features of the model. In model applications,
the importance of these initial conditions will depend on the meteoro-
logical characteristics of the area considered. It is probable that in a
well ventilated area the mapping of pollutants above the inversion layer
will not be important. It has been shown, however, that under suitable
meteorological conditions (such as in the rear part of an anticyclone)
pollutants are easily trapped above an inversion layer.
Meteorological considerations and upper air experimental data should
provide the information necessary for the definition of the initial upper
air pollutant concentrations.
12&
A-106
-------
NiRTH
>
:
S0UTH
FIGURE A-28. DEVIATION MAXIMUM OZONE (ppb): CASE 6--BASE CASE
BETWEEN THE HOURS OF 3 AND 19 1ST
-------
BO
SO
40
I
i 30
s
20
10
12
16
I I I I I I T I
- LflGUNR
- BflSE CflSE —
- SENSITIVITY RUN —
50
30
20
10
6 12 18
TINE (HfURS)
BO
50
12
i 30
20
10
16
I ' ' ' < ' I '
- Lfl HfiBRE
- BflSE CflSE
- SENSITIVITY RUN
6 12 18
TIME (HIURS)
'-
a
80
12
i i i I i
- PfiSRDENfl
- BRSE CflSE
- SENSITIVITY RUN
6 12
TINE (HIURS)
60*
W V
50
40
X
a.
5: 30
ID
20
10
Q
°c
6 12 1R
.» " i i i i 1 I 1 1 I j 1 I | | | |
- flNRHEIH
- BASE CflSE —
- SENSITIVITY RUN —
-
-
•
-
f y^\
:, , , ^^, , , , M \^,
1 6 12 IB
2'
TTTI r
~
~
Z
~
~
— ' j '"^
TINE (HBURS)
FIGURE A-29. COMPARISON OF PREDICTED OZONE CONCENTRATIONS-
CASE 6
A-108
-------
60
50
40
£b30
20
10
12
18
24
J I I I I | I I I I I | I I I I I I
- CBSTfl MESfl
- BflSE CflSE —
- SENSITIVITY RUN —
60
50
40
30
20
10
6 12 18
TIME (H0URS)
60
50
40
O-
Jb 30
20
10
12
16
II II i
- LYNH00D
- BflSE CRSE — —
u SENSITIVITY RUN --•
12
TIME tHiURS]
18
60
SO
6
12
18
Sb 30
20
10
_ i i i i i | i i i i
- SflK BERNflD
- BRSE CflSE
- SENSITIVITY RUN
i i i I
6 12 18
TIME (HBURS)
50
40
30
20
10
60
50
40
a.
i 30
20
10
12
18
24
i t I I I I I I I I ]
- UPLflND
- BfiSE CRSE
- SENSITIVITY RUN --•
I '
I I I I t I I I t t I I I I I J
6 12 16
TIME (HBURS)
FIGURE A-29 (Concluded)
A-109
-------
g. Model Sensitivity to Upper Air Quality Data—Simulation of 4 August
1975
In this sensitivity case, upper air quality data have been modified
in the third layer of the grid model. Precursor concentrations of RHC and
NOX in the third layer are lower in the sensitivity case than in the the
base case. Boundary conditions at ground level also involve lower
precursor concentrations.
1) general Sensitivity Measures
Some measures of the general sensitivity of the model are presented
in table A-ll. In general, lower ozone levels are observed, resulting
from precursor levels above the inversion. This is consistent with case
6, in which higher precursor levels aloft increased photochemical forma-
tion. It appears that ozone formation is slightly sensitive to the
initial amount of precursors in the third grid layer.
In case 6, the temporal and spatial correlations are relatively high
(above 0.95), and the time lag of the ozone peaks is fairly short (an
average of 4 minutes for the downwind stations). The dosage is the most
sensitive measure.
2) Sensitivity of Model Input Variables to Input Data
The upper air initial conditions have been modified for nitrogen
oxides and hydrocarbons. Precursor concentrations in level 3 are lower in
the sensitivity case than in the base case.
3) Sensitivity of Ozone Levels to Precursor Upper Air Initial
Conditions
The maximum ozone perturbation isopleths are shown in figure A-30.
Deviations in ozone levels occur in the northern part of the basin around
Pasadena and Pomona. Other areas do not show any major perturbations in
ozone-level predictions.
In figure A-31 ozone profiles for this sensitivity case and the base
case are shown for six air quality monitoring stations. Slightly lower
ozone levels are observed, but the timing and shapes of the ozone profiles
are not much perturbed.
12R 2
A-110
-------
TABLE A-ll. GENERAL SENSITIVITY MEASURES—CASE 7
(a) General Ozone Level Deviations
Station Statistics
Grid Statistics
Sensitivity Measure
Signed deviation
Absolute deviation
Temporal correlation
Spatial correlation
°3
> 12 pphm
-0.073
0.073
0.980
0.953
Oj > 20 pphm
-0.048
0.049
0.982
0.996
03 > 12 pphm 03 > 20 pphm
-0.071 -0.053
0.073
0.981
0.965
0.057
0.950
0.970
(b) Overall Maximum Ozone Level
Sensitivity case/
base case ratio
Peak level (pphm):
Sensitivity case
Base case
Corresponding locations:
Sensitivity case
Base case
Station Statistics
0.927
24.4
26.3
Pomona
Pomona
Grid Statistics
1.019
37.7
37.0
30 - 16
30 - 16
-------
TABLE A-11 (Concluded)
(c) Maximum Ozone Statistics
All Stations
Downwind Stations
Peak level 0.0570
normalized difference
Peak time lag (hrs) 0.04
0.0694
0.06
(d) Dosage
Normalized Difference
-0.504
Sensitivity Case
(km2)
4,350
Base Case
(km2)
8,750
M
5O
-------
N0RTH
.
10
20
-wnrtHH-
LBSL
flMRH
flZUS P0HF
UPLD
oix^ifcx'^x^&ff:^
;
Si? H:
FBNT
10
I
I
L
10
20
S0UTH
FIGURE A-30. DEVIATION OF MAXIMUM OZONE CONCENTRATIONS (ppb): CASE 7—
BASE CASE BETWEEN THE HOURS OF 4 AND 19 LCT
-------
fin
60
50
40
X
i 30
m
20
10
f\
°0
60
50
40
X
0.
i 30
«n
20
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-
-
-
-
-
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-
-
-
-
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i i i i | i i i i i | I 1 i i I | I i I I i _
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—
-
-
«•
-
-
^S\t. •Vrr-s^. ~-
6 12 18 2'
TIHE (HBURS)
6 12 16 2
flNflHEIH
BflSE CflSE —
SENSITIVITY RUN -— ^
—
—
-
Ill) m\^t 1 1 1 1 1 1 1 | |^4»wJ I 1 1 1 1
1
c n RO
60 "U
50 50
,0 <0
X.
30 t 30
•n
OB
20 20
10 10
n f\
P °c
\o Rnc
60 60
50 50
40 40
X
30 ^ 30
20 20
10 10
n n
D 6 12 18 2
. I I I i i | i i I I I | t I I 1 i | i i i i _
- PRSflDENfl "
- BflSE CflSE — •
- SENSITIVITY RUN —
-
-
—
—
-
/\ \
) 6 12 18 2
TIHE (HBURS)
) 6 12 18 2
_ i i i i i | i i i i ( | i i i i i | i i i i i_
- LYNW000
- BflSE CflSE —
- SENSITIVITY RUN -— j;
1 -
I -
1 -
i ^~^.,,,J
4
50
40
30
20
10
4
*60
50
40
30
20
10
f
6 12 18
TIHE (HIURS)
TIHE (H0URS)
FIGURE A-31. COMPARISON OF PREDICTED OZONE CONCENTRATIONS: CASE 7
A-114
-------
60
50
IB
o.
2:30
IT n T 1 I I I r I
- SON BERNflD
- BflSE CfiSE —
- SENSITIVITY RUN -•
60
50
60
50
30 i 30
20
10
I ' '
12
I I 1 I I I
18
L UPLflND
- BflSE CflSE —•
- SENSITIVITY RUN - —
t \ I "ISO
50
TIME (H«URS)
12
TIME (H0URS)
18
30
FIGURE A-31 (Concluded)
A-115
-------
4) Conclusions
For the 4 August 1975 conditions lower ozone levels are predicted,
with lower precursors aloft in the early morning. This is consistent with
the results of case 6. The model appears to be slightly less sensitive
for the 4 August 1975 conditions.
h. Model Sensitivity to RHC and NOX Boundary Conditions—Simulation
of 26 June 1974
In this simulation, the boundary conditions were reduced to back-
ground levels at the western and southern boundaries of the airshed.
1) General Sensitivity Measures
Some measures of the general sensitivity of the model are presented
in table A-12. Lower ozone levels are predicted when boundary concentra-
tions of nitrogen oxides and RHC are lower. This is consistent with case
6, where higher precursor levels at the upper boundary induced higher
ozone levels. The temporal correlation is high (above 0.9), and the
overall ozone maximum occurs at the same location {Azusa, or grid
[33-14]); however, the spatial correlation is rather low (about 0.6) for
ozone levels above 20 pphm.
2) Sensitivity of Model Input Variables to Input Data
The nitrogen oxides concentrations have been reduced at the western
and southern boundaries. The wind flow is westerly, and this boundary
condition is important, since it is given by the following equation:
v. V C^ - V £ V C^ = I V c{ - V £ 7 c{ A_2
where V is the wind vector, K the eddy diffusivity tensor, and C^ and c|
the concentrations of species i outside and inside the domain,
respectively. In the case of an outflow (e.g., at the northern and
eastern boundaries) the boundary condition does not depend on the species
concentrations outside of the domain and is simply given by the follow ng
equation:
A-116
-------
TABLE A-12. GENERAL SENSITIVITY MEASURES—CASE 8
(a) General Ozone Level Deviations
Station Statistics
Grid Statistics
Sensitivity Measure
Signed deviation
Absolute deviation
Temporal correlation
Spatial correlation
03 > 12 pphtn 03 > 20 pphm
-0.141 -0.177
0.145
0.181
0.914
0.927
0.933
0.613
°3
> 12 pphm
-0.130
0.139
0.925
0.896
03 > 20 pphm
-0.165
0.169
0.928
0.794
(b) Overall Maximum Ozone Level
Sensitivity case/
base case ratio
Peak level (pphm):
Sensitivity case
Base case
Corresponding locations:
Sensitivity case
Base case
Station Statistics
0.804
28.5
35.5
Azusa
Azusa
Grid Statistics
1.002
38.9
38.9
33 - 14
33 - 14
-------
I
00
TABLE A-12 (Concluded)
(c) Maximum Ozone Statistics
All Stations Downwind Stations
Peak level 0.188 0.187
normalized difference
Peak time lag (hrs) 0.870 0.750
(d) Dosage
Sensitivity Case Base Case
Normalized Difference (km*-) (km*-)
-0.38 6,200 10,000
-------
Ci • ° (A-3)
Where there Is inflow, the boundary condition affects the dynamic behavior
of the continuity equations. The sensitivity results will provide some
estimate of the importance of the boundary condition on the model.
3) Sensitivity of Ozone Levels to Nitrogen Oxides Boundary
Conditions
Isopleths of maximum o.zone deviation are shown in figure A-32. The
largest ozone deviations occur in the northern part of the basin, from
Pasadena to Riverside. As mentioned in the discussion of the general
sensitivity results, lower nitrogen oxides boundary concentrations result
in lower ozone levels. This appears clearly in figure A-33, where ozone
profiles for the base case and the sensitivity case are shown at six air
monitoring stations.
The effect of the western boundary condition increases as the
chemical reactions proceed in time during the eastward transport of the
polluted air masses, then decreases farther downwind as new injections of
nitrogen oxides from emission sources modify the system's kinetics
(compare, for instance, the ozone profiles at Anaheim, Upland, and San
Bernardino). The boundary condition of the urban airshed model can be
interpreted as the initial condition of a Lagrangian trajectory model.
The effect of the initial conditions is small when little ozone has been
formed (e.g., at Anaheim) and increases when ozone builds up (e.g., at
Pasadena or Upland).
Finally, when more emissions are introduced into the air mass, the
initial conditions are "forgotten," and the perturbation in the ozone
level decreases again.
4) Conclusions
This sensitivity study shows that the chemical kinetic behavior of
the urban airshed is sensitive to the upwind boundary condition (for
nitrogen oxides). This condition should, therefore, be presented appro-
priately. In this case, lower nitrogen oxides concentrations at the
upwind boundary induced lower ozone levels downwind; this effect depends
on the relative concentrations of atmospheric pollutants however (nitrogen
oxides, hydrocarbons, ozone). The opposite effect could be obtained under
different conditions (e.g., with a different hydrocarbon/nitrogen oxide
ratio), and it cannot be predicted a priori.
A-119
-------
NIRTH
10
20
PO
c
10
$£;;;£;; i^
£:£K^^
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10
S0UTH
.-'.' \
10
FIGURE A-32. DEVIATION OF MAXIMUM OZONE CONCENTRATIONS (ppb): CASE 8—
BASE CASE BETWEEN THE HOURS OF 4 AND 19 1ST
-------
(
60
50
40
3C
Q.
i 30
o>
n
20
10
°1
r
60
SO
40
X
x
t 30
«n
CD
20
10
°0
J 6
.11 n i TT
- RNRHEIM
- BBSE CflSE
- SENSITIVITY
-
•P
-
-
-
^
1 6
I 6
JIM ITT
- PflSRDENR
- 8RSE CflSE
- SENSITIVITY
-
-
-
"
—
^
•
m
.
-
—
: , , ,^S
6
12 18 2
M 1 1 1 1 1 II 1 | 1 1 1 ' '-
RUN --* 2
-
-
—
-
-
/?>tt± --
12 18 *
TINE (HIURS)
i? 18 2
I i i i | I 1 I I I I i I M L
RUN — I
-
_
—
/A\ -
/ ' V \ -
/ * \\ •
ft \\
/' *\ -
/* V.
/ \ :
/ Vi.
~ ^\
. ... i |i i i i T « i i i i
12 IB Z'
TIME (HIURS)
Rfi ftn
ou w
50 SO
40 40
a.
30 t30
^
) 6 12
TIME (HiURS)
18 2
i | 1 i 1 f f_
—
—
—
_
-
-
•™
j^J i i i i l~
ie 2
ie 2
1 j i i i i i_
—
-
-
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—
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-
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S.J i i i i i~
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\0
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40
30
20
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4°
1
50
40
30
20
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f
FIGURE A-33. COMPARISON OF PREDICTED OZONE CONCENTRATIONS: CASE 8
A-121
-------
60
50
40
x
a.
i 30
m
m
20
10
12
IB
24.
~ n r \ T
- UPLAND
- BRSE CflSE
- SENSITIVITY RUN
i i tn i T
60 60
50 SO
40 40
x
30 | 30
en
m
20 20
10 10
12
12
TIME (HiURS)
18
24°
- SRN BERNflD
- BflSE CflSE
- SENSITIVITY RUN
12
TIME (HIURS)
IB
FIGURE A-33 (Concluded)
A-122
-------
i. Model Sensitivity to Hydrocarbon Initial Concentrations—Simulation
of 26 June 1974
In this sensitivity study, non-methane hydrocarbon initial concentra-
tions were determined from nitrogen oxides initial concentrations accord-
ing to the relationship [NMHC]/[NOX] = 7. In the base case, nonmethane
hydrocarbon initial concentrations were computed from total hydrocarbon
concentrations, according to the following formula [NMHC] = 0.7 ([THC] -
1.3), which was obtained from atmospheric data by regression. The initial
concentrations of nitrogen oxides are also slightly different. Initial
concentrations of nonmethane hydrocarbons and nitrogen oxides are shown in
figure A-34.
1) General Sensitivity Measures
The overall sensitivity of the model to the definition of hydrocarbon
initial concentrations is presented in table A-13. Lower ozone levels are
obtained with the relationship [NMHC]/[NOX] = 7. The deviation due to the
change in initial concentrations is on the order of 30 to 40 percent.
This is a large perturbation, and it suggests that the definition of the
initial concentrations of reactive hydrocarbons is an important component
of the urban airshed model.
The temporal correlation is relatively high (above 0.8) and the time
lag is less than an hour. The spatial correlation is, however, low for
ozone levels above 20 pphm. The dosage is more sensitive to the pertur-
bation than the other measures.
2) Sensitivity of Model Input Variables to Input Data
Initial concentrations of nitrogen oxides and nonmethane hydrocarbons
have been modified, as shown in figure A-34. The perturbation in the
nitrogen oxides concentrations is not as important as the change in the
reactive hydrocarbon concentrations. Reactive hydrocarbon concentrations
are on the order of 0.4 ppm in the sensitivity case; they are as high as
1.8 ppm at Fontana and Riverside in the base case.
According to the relative concentrations of nitrogen oxides and
hydrocarbons in the Los Angeles basin, an increase in hydrocarbon concen-
trations should lead to an increase in ozone levels.
A-123
-------
NBRTH
2 10
i
PO
ID
20
n
v.v.>;.;.;.
f:x::#i::
•
iiiiiiiiiii
iiiiiii
10
10
20
SflUTH
(a) Base Case NOX (pphm)
FIGURE A-34. INITIAL CONDITIONS FOR 26 JUNE 1974
-------
N§RTH
X
I
10
20
S 10
^i : :j g::
10
20
S0UTH
(b) Sensitivity Case 9 NOX (pph)n)
:
FIGURE A-34 (Continued)
-------
NIRTH
•
-,•
D
:<;:'::::::ii:;:;:;:':f I J I f
J:::xl } I J :l 1: I . J I .1
S0UTH
(c) Base Case RHC (pptm)
FIGURE A-34 (Continued)
-------
N0RTH
*»
* *::.:::::k:^^
CH.P*- -^_^/
rm vwnrrtHN
jr
S0UTH
(d) Sensitivity Case 9 RHC (pptm)
FIGURE A-34 (Concluded)
-------
TABLE A-13. GENERAL SENSITIVITY MEASURES—CASE 9
(a) General Ozone Level Deviations
Station Statistics
Grid Statistics
i
l\3
00
Sensitivity Measure 03 > 12 pphm 03 > 20 pphm
Signed deviation
Absolute deviation
Temporal correlation
Spatial correlation
-0.344
0.344
0.869
0.800
-0.384
03 > 12 pphm 03 > 20 pphm
-0.317 -0.357
0.384
0.984
0.433
0.318
0.807
0.800
0.357
0.893
0.735
(b) Overall Maximum Ozone Level
Station Statistics
Sensitivity case/
base case ratio
Peak level (pphm):
Sensitivity case
Base case
Corresponding locations:
Sensitivity case
Base case
0.632
22.4
35.5
Upland
Azusa
Grid Statistics
0.832
32.4
38.9
33 - 14
33 - 14
-------
ro
UD
TABLE A-13 (Concluded)
(c) Maximum Ozone Statistics
All Stations Downwind Stations
Peak level 0.320 0.354
normalized difference
Peak time lag (hrs) 0.96 0.56
(d) Dosage
Sensitivity Case Base Case
Normalized Difference (km2) _ (km2)
-0.7575 2,425 10,000
-------
3) Sensitivity of Ozone Levels to Hydrocarbon Initial Concentrations
Isopleths of deviations in maximum ozone levels are shown in figure
A-35. Lower ozone levels are observed throughout the basin. The largest
deviations from the base case occur in the northern central part of the
basin around Pasadena, Azusa, and Pomona, where air pollution is the most
important. This appears also in figure A-36, which presents ozone
profiles at six air quality monitoring stations for this sensitivity case
and for the base case. Ozone peak levels are lower at all stations, but
the shape of the peak is usually conserved. The ozone profile at Laguna
differs, however, since the ozone peak is reduced at 0800 L.S.T. in the
sensitivity case and at 1400 L.S.T. in the base case. The perturbations
in the shape of the ozone peaks are larger at the coastal stations and
this appears also in the averaged peak time lag (table A-13), which is
shorter for downwind stations.
4) Conclusions
Ozone levels are very sensitive to initial concentrations of precur-
sors and are determined by more than pollutant emissions during the
simulation day. Thus, the specification of the initial conditions of the
species continuity equations is an important component of the urban
airshed model.
Atmospheric measurements of reactive hydrocarbons are usually not
very accurate, since they are often observed by subtracting methane
concentration from total hydrocarbon concentration—that is, by the
difference of two close numbers. More reliable measurements may be
obtained by gas chromatography, but these are not always available.
Consequently, hydrocarbon initial concentrations are usually defined by
means of a formula relating reactive hydrocarbon concentrations to some
other species concentration that is easily measured (nitrogen oxides,
total hydrocarbons).
It appears from this sensitivity study that the choice of this
relationship for the estimation of initial reactive hydrocarbon concen-
trations is a major input of the urban airshed model and that it should be
selected carefully.
j. Model Sensitivity to Hydrocarbon Initial Concentrations--Simulation
of 4 August 1975
As in case 9, nonmethane hydrocarbon initial concentrations were
determined from nitrogen oxides initial concentrations according to the
A-130
-------
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FIGURE A-35. DEVIATION OF MAXIMUM OZONE CONCENTRATIONS (ppb): CASE 9--
BASE CASE BETWEEN THE HOURS OF 4 AND 19 LST
-------
60
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FIGURE A-36. COMPARISON OF PREDICTED OZONE CONCENTRATIONS: CASE 9
A-132
-------
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6
12
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LYNH00D ___
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FIGURE A-36 (Concluded)
A-133
-------
formula [NMHC]/[NOX] » 7. In the corresponding base case, nonmethane
hydrocarbon initial concentrations were computed from total hydrocarbon
concentrations according to the following regression formula [NMHC] *
1.034 ([THC] - 1.4). Nitrogen oxides Initial concentrations were not
modified in this study. Initial concentrations are shown in figure A-37
for this sensitivity case and the 4 August 1975 base case.
1) General Sensitivity Measures
Some measures of the general sensitivity of the model to hydrocarbon
initial concentrations are shown in table A-14. As in case 9, lower ozone
levels are obtained in the sensitivity case. The deviation is larger than
with the 26 June 1974 conditions; here it is on the order of 40 to 50
percent. The overall ozone maximum occurs in the same grid, but it is
notably perturbed (about 33 percent).
The value of the temporal correlation coefficient is relatively low,
especially for ozone levels above 20 pphm; the average ozone peak time
lag, however, is on the order of an hour. The dosage is the most sensi-
tive measure (a perturbation of about 95 percent.)
2) Sensitivity of Model Input Variables to Input Data
The choice of the formula to define nonmethane hydrocarbon initial
concentrations affects the hydrocarbon concentration field, as shown in
figure A-37. The perturbation is not as large as in case 9, and it is
mainly located in the northern central part of the basin. Lower hydrocar-
bon initial concentrations are obtained in the sensitivity case, i.e.,
with [NMHC]/[NOX] = 7, than in the base case. For instance, at Pomona,
the reactive hydrocarbon concentration is 1.6 ppm in the base case and 1.2
ppm in the sensitivity case.
3) Sensitivity of Ozone Levels to Hydrocarbon Initial Concentrations
Isopleths of maximum ozone deviations are shown in figure A-38.
Lower ozone levels are observed throughout the basin, with the largest
deviations occurring in the upper central part of the basin, from Pasadena
to Riverside. This area corresponds to the largest perturbation in the
initial hydrocarbon concentrations. As in the previous case, lower
hydrocarbon concentrations lead to lower ozone levels in the Los Angeles
basin.
A-134
-------
NflRTH
B
L
S8UTH
(a) Base Case NOX (pphm)
FIGURE A-37. INITIAL CONDITIONS FOR 4 AUGUST 1975
-------
MRTH
.
10
1
'
I
-
j i >
i .1 if . I 1 , J t J
1 .) ( _ 1 .t 1 I
. t !:?/!.
:
20
SBUTH
(b) Sensitivity Case 10 NO (pphm)
FIGURE A-37 (Continued)
-------
NfRTH
--
.-
- .
S0UTH
(c) Base Case RHC (pptm)
FIGURE A-37 (Continued)
-------
MIRTH
S
u
5
U Lfl
M«4<<"
HEM
< i i i t i < i i If i f
20
FMT
R1VR
j: f ':'.': I •': 1
:
]
SiUTH
(d) Sensitivity Case 10 RHC (pptm)
10
FIGURE A-37 (Concluded)
-------
U)
to
TABLE A-14. GENERAL SENSITIVITY MEASURES--CASE 10
(a) General Ozone Level Deviations
Sensitivity Measure
Signed deviation
Absolute deviation
Temporal correlation
Spatial correlation
Station Statistics
03 > 12 pphm 03 > 20 pphm
-0.450 -0.486
0.450
0.486
0.680
0.578
0.280
0.990
Grid Statistics
03 > 12 pphm 03 > 20 pphm
-0.443 -0.463
0.443
0.722
0.806
(b) Overall Maximum Ozone Level
0.463
0.336
0.872
Sensitivity case/
base case ratio
Peak level {pphm):
Sensitivity case
Base case
Corresponding locations:
Sensitivity case
Base case
Station Statistics
0.523
13.8
26.3
Upland
Pomona
Grid Statistics
0.670
24.8
37.0
30 - 16
30 - 16
-------
TABLE A-14 (Concluded)
(c) Maximum Ozone Statistics
All Stations Downwind Stations
Peak level 0.394 0.476
normalized difference
Peak time lag (hrs) 1.0 0.81
.L (d) Dosage
-t»
o
Sensitivity Case Base Case
Normalized Difference (km2) (km2)
0.95 450 8,750
-------
NfltTH
S 10
-
S0UTH
FIGURE A-38. DEVIATION OF MAXIMUM OZONE CONCENTRATIONS(ppb): CASE TO--
BASE CASE BETWEEN THE HOURS OF 4 AND 19 LST
-------
Ozone profiles at six air monitoring stations are shown in figure A-
39. The large deviations in ozone levels appear clearly in these
profiles. The shape of the ozone peak is well conserved for the downwind
stations. This, however, is not the case for the stations located in the
western basin (Anaheim and Lynwood). A similar effect was observed in
case 9 with the coastal stations (e.g., Laguna). This is probably because
the initial concentrations are more important in determining the ozone
profiles for upwind stations, since there are fewer pollutant emissions
affecting the area.
It is interesting to note that, though the reactive hydrocarbon
initial concentrations do not differ from the base case as much in case 10
as in case 9, the meteorological conditions enhance the effect of this
perturbation. In the 4 August 1975 simulation, the mixing depths are
lower than in the 26 June 1974 simulation. This creates a smaller volume
of mixing for the pollutants, and the effect of a perturbation in pol-
lutant concentrations is more important in the case of a smaller volume
(i.e., for the 4 August 1975 case).
4) Conclusions
It appears from sensitivity studies 9 and 10 that, under different
meteorological conditions, the definition of the reactive hydrocarbon
initial concentrations is an important component of the model. This
suggests the need for an accurate procedure to determine atmospheric
nonmethane hydrocarbon concentrations for input into urban airshed models.
k. Model Sensitivity to Hydrocarbon Speciation—Simulation of 26 June
1974
In the base case, hydrocarbon speciation was considered for various
source categories (e.g., motor vehicle, boilers distillate oil, crude oil
evaporation, dry cleaning, etc.). In this sensitivity case, a common
average hydrocarbon speciation was considered for all sources.
1) General Sensitivity Measures
Some general measures of the sensitivity of the model to hydrocarbon
speciation are listed in table A-15. The averaging of hydrocarbon
speciation among source categories leads to slightly higher ozone
levels. The overall maximum ozone level and the temporal and spatial
A-142
-------
60
50
40
£ 30
12
18
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20
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2460
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BflSE CflSE
SENSITIVITY RUN
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18
50
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60
50
40
6
30 i 30
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20 20
10
12
1 ' I '
18
24
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60
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6o0rrr
50
40
^*
£ 30
S
20
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40 40
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- BASE CflSE
- SENSITIVITY RUN
12
TINE (HfURS)
I '
16
50
40
30
20
10
24°
FIGURE A-39. COMPARISON OF PREDICTED OZONE CONCENTRATIONS; CASE 10
A-143
-------
BO
50
40
n
20
10
6 12
I i I I i I i i I i i I i i
- SAN BERNAD
BflSE CflSE ——
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18
6 12 16
TINE (HiURS)
60 60
50 50
40 40
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30 £ 30
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10 10
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i i i i i i i i i i i r i i i i j i i
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- SENSITIVITY RUN —
60
50
30
20
10
I i i LI i
6 12 16
TINE (HiURS)
24°
FIGURE A-39 (Concluded)
A-144
-------
l
-P»
tn
TABLE A-15. GENERAL SENSITIVITY MEASURES—CASE 11
(a) General Ozone Level Deviations
Sensitivity Measure
Signed deviation
Absolute deviation
Temporal correlation
Spatial correlation
Station Statistics
03
> 12 pphm
0.046
0.046
0.989
0.985
03 > 20 pphm
0.035
0.035
0.990
0.979
Grid Statistics
03 > 12 pphm 03 > 20 pphm
0.022 0.041
0.039
0.984
0.983
0.041
0.985
0.982
(b) Overall Maximum Ozone Level
Sensitivity case/
base case ratio
Peak level (pphm):
Sensitivity case
Base case
Corresponding locations;
Sensitivity case
Base case
Station Statistics
1.023
36.3
35.5
Azusa
Azusa
Grid Statistics
1.018
39.6
38.9
19 - 15
33 - 14
-------
TABLE A-15 (Concluded)
(c) Maximum Ozone Statistics
All Stations Downwind Stations
Peak level 0.114 0.092
normalized difference
Peak time lag (hrs) 0.30 0.44
1, (d) Dosage
cn
Sensitivity Case Base Case
Normalized Difference (km2) _ (km2)
0.138 11,375 10,000
-------
correlations are the least affected measures in this sensitivity study.
The dosage appears to be the most sensitive measure (about 14 percent
deviation).
2) Sensitivity of Model Input Variables to Input Data
Two important sources of hydrocarbons in the Los Angeles basin are
automobile exhausts and refineries. The averaged hydrocarbon speciation
is similar to the speciation of automobile exhausts; refineries speciation
differs from the former. Some hydrocarbon speciations are listed in
table A-16.
In the sensitivity case, refinery emissions will have higher levels
of olefins, aromatics, aldehydes and ethylene (except for aldehydes in
boilers distillate oil); motor vehicle exhaust will present only a small
decrease in aromatics emissions. Olefins, aromatics and aldehydes are
oxidized in the atmosphere faster than paraffins; consequently, they are
better precursors of photochemical smog. Therefore, one should expect
higher ozone levels in the area downwind of the refineries and negligible
changes in the areas where automotive exhausts predominate.
3) Sensitivity of Ozone Levels to Hydrocarbon Speciation
Isopleths of maximum ozone deviation are shown in figure A-40. There
is an area of higher ozone levels for the sensitivity case. This area
centers around Whittier and La Habra, downwind of the refineries that are
located around Long Beach. Therefore, this effect results directly from
the increase of reactive hydrocarbons such as olefins, aromatics and
aldehydes in the refinery emissions.
The northern part of the basin is affected most by motor vehicle
exhausts from downtown Los Angeles and the surrounding freeways. Accord-
ingly, little perturbation occurs in the model predictions.
Ozone profiles for six air quality monitoring stations, which are
presented in figure A-41, confirm these results. Higher ozone levels are
observed for the sensitivity case at Anaheim, La Habra, and Lynwood;
negligible changes occur at Pasadena, Upland, and San Bernardino.
4) Conclusions
The use of a common hydrocarbon speciation for all source categories
does not affect strongly the overall predictions of the model. However,
A-147
-------
I
-S*
00
TABLE A-16. HYDROCARBON SPECIATION OF SOME SOURCE CATEGORIES
(mole/g)
Source Category
Olefins
(except Ethylene)
Paraffins Aromatics Aldehydes^ Ethylene
Boilers distillate oil
Crude oil evaporation
(fixed roof)
Motor vehicles
Sensitivity case
0.0
0.0
0.00123
0.0016
0.0352
0.0531
0.0435
0.044
0.0
0.000152
0.00280
0.0018
0.0162
0.0
0.00184
0.0017
0.0
0.0
0.00123
0.00097
-------
NfftTH
3
•
i
S 10
lii
F0NT
R1VR
. :t.:. t
10
20
S0UTH
FIGURE A-40. DEVIATION OF MAXIMUM OZONE CONCENTRATIONS (ppb): CASE 11-
BASE CASE BETWEEN THE HOURS OF 4 AND 19 LST
-------
.0
50
40
2: 30
20
10
6
12
18
_| I I I I | I I
- RNRHEIM
I I I | I I I I I | I I I I l_
6 12 18
TINE (HfURS)
50
40
10
60
50
40
12
18
30 t 30
«r>
20 20
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_l I I I I | I I I I I I I I I I I | I I ' I l_
- UPLflND
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- SENSITIVITY RUN --•
12
TIME (HiURS)
18
50
40
30
20
10
24°
60
50
40
t 30
20
10
12
18
- Lfl HRBRE
- BflSE CflSE
- SENSITIVITY RUN
12
TIHE (HIURS)
18
50
40
10
60
50
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12
18
30 £30
m
20 20
10
I i i
PRSRDENR
BflSE CflSE —
SENSITIVITY RUN —
50
40
20
10
6 12
TINE (HfURS)
I I I I I I In
18 2f
FIGURE A-41. COMPARISON OF PREDICTED OZONE CONCENTRATIONS: CASE 11
A-150
-------
60
50
«0
a.
i 30
I
£ec
- LYNH00D
- BHSE CflSE —
• SENSITIVITY RUN —
I i i i
t \
50
40
30
20
10
6 12 18
TIME (HiURS)
24°
FIGURE A-41 (Concluded)
A-151
-------
areas concerned with precursor speciations that have been modified in the
averaging procedure, e.g., refineries, present notable deviations in air
quality levels.
The sensitivity of the model to the chemical composition of emission
sources depends on the nature and spatial distribution of these sources.
Clearly, a detailed hydrocarbon speciation will be desirable for urban
areas involving various types of hydrocarbon emission sources; an averaged
hydrocarbon speciation may give good results if one source category is the
primary source of precursors in the area.
1. Model Sensitivity to Hydrocarbon _Speci_ati on—Simulation of
4 August 1975
As in case 11, a common averaged hydrocarbon speciation was defined
for all source categories.
1) General Sensitivity Measures
As with the 26 June 1974 conditions, higher ozone levels are observed
with the common hydrocarbon speciation (see table A-17). In general,
larger deviations are observed. The dosage is the most sensitive measure
(about 60 percent larger in the sensitivity case). The overall maximum
ozone level is not much affected in this study, since it is located in an
area that is only slightly perturbed by the hydrocarbon speciation (see
figure A-42). The temporal correlation is high (above 0.950), but the
spatial correlation is slightly lower (0.8 for the station statistics).
2) Sensitivity of Model Input Variables to Input Data
The modification in the source emissions resulting from the averaging
of hydrocarbon speciation has been presented for case 11.
3) Sensitivity of Ozone Levels to Hydrocarbon Speciation
Deviations of maximum ozone between the sensitivity case and the base
case are shown in figure A-43. A wider area is affected than in the 26
June 1974 case. Also, higher ozone deviations are observed. The fact
that mixing depths are lower for the 4 August 1975 case than for the 26
June 1974 case (e.g., 324.6 m at Azusa between 12 and 13 L.S.T. for this
case and 594.2 m for case 11), increases the effect of the perturbation,
since the mixing volume is reduced.
A-152
-------
cn
to
TABLE A-17. GENERAL SENSITIVITY MEASURES—CASE 12
(a) General Ozone Level Deviations
Sensitivity Measure
Signed deviation
Absolute deviation
Temporal correlation
Spatial correlation
Station Statistics
°3
> 12 pphm
0.121
0.125
0.969
0.818
03 > 20 pphm
0.085
0.085
0.961
0.940
Grid Statistics
03 > 12 pphm 03 > 20 pphm
0.138 0.090
0.142
0.966
0.923
0.091
0.958
0.856
(b) Overall Maximum Ozone Level
Station Statistics
Sensitivity case/ 1.128
base case ratio
Peak level (pphm):
Sensitivity case 29.7
Base case 26.3
Corresponding locations:
Sensitivity case Pomona
Base case Pomona
Grid Statistics
1.003
37.2
37.0
30 - 16
30 - 16
-------
TABLE A-17 (Concluded)
(c) Maximum Ozone Statistics
All Stations Downwind Stations
Peak level 0.303 0.313
normalized difference
Peak time lag (hrs) 0.25 0.39
3>
(d) Dosage
en
Sensitivity Case Base Case
Normalized Difference (km2) _ (km2)
0.597 13,975 8,750
-------
NffRTH
-
--
S0UTH
FIGURE A-42. DEVIATION OF MAXIMUM OZONE CONCENTRATIONS (ppb): CASE 12—
BASE CASE BETWEEN THE HOURS OF 4 AND 19 1ST
-------
60
50 -
40 -
t 30 -
20 -
10 -
12
18
24
12
18
24
- LTNN00D
- BflSE CflSE — —
- SENSITIVITY RUN —
-
-
_
•
t \
-
—
—
™
-
60 60
50 50
40 40
X
30 t 30
en
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n n
_ i i i i i | i i i i i | i i i i i |
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- BftSE CRSE —
- SENSITIVITY RUN —
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*'s
j I/ \
[,,,^^/L,,,,,,
* 1 1 1
-
-
—
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bU
50
40
30
20
10
6 12 18
TIME (HIURS)
6 12 18
TINE (HIURS)
6
12
18
16
50
40
i 30
20
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_l II I I j I (
- UPLflND
- 8BSE CflSE —
- SENSITIVITY RUN -••
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TINE (HIURS)
50
40
30
20
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6U
50
40
t 30
*r>
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.1 1 ! 1 1 | 1 1 1 1 1 | 1 1
- RNRHE1H
- BflSE CBSE — •
- SENSITIVITY RUN •-•
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1 6 12
i i i | i ) i i i _ bu
- 50
- 40
- 30
™
- 20
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"i***^ i i i i t" _
18 24°
TIME (HiURS)
FIGURE A-43. COMPARISON OF PREDICTED OZONE CONCENTRATIONS: CASE 12
A-156
-------
60
50
40
t 30
20
10
12
16
6
_Tl II I | I I I I I |
- LR HRBRE
- BRSE CRSE —
- SENSITIVITY RUN —
12
TIME (HfURS)
IB
50 50
40 40
tL.
30 ± 30
tn
20 20
10 10
12
"T"
18
II 11(111
- PflSRDENfl
- BflSE CflSE —
SENSITIVITY RUN —
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TIME (HIURS)
w
50
40
30
20
10
24°
FIGURE A-43 (Concluded)
A-157
-------
Profiles of ozone concentrations at six monitoring stations are shown
in figure A-43. When these are compared with figure A-41, it appears that
the perturbations are more important in this case. The effect of the
hydrocarbon speciation is transported far downwind from the refineries,
and the ozone profile at San Bernardino presents some perturbation.
Lower mixing depths and slightly higher wind speeds cause the effect
of the emission perturbation to be transported farther downwind and to be
more pronounced.
4) Conclusions^
It was shown in the previous sensitivity study (case 11} that
averaging hydrocarbon speciation among source categories affects the areas
downwind of refineries. It appears in this study that this effect may be
important and extended to a large part of the basin when the perturbation
is combined with appropriate meteorological conditions (lower mixing
depths and higher wind speeds).
m. Model Sensitivity to Mobile Source Emissions: Older Inventory--
Simulation of 26 June 1974
In this sensitivity study an older mobile source inventory was
used. This will affect nitrogen oxides, hydrocarbons and carbon monoxide
emissions from mobile sources.
1) General Sensitivity Measures
Some measures of the general sensitivity of the model are listed in
table A-18. The overall sensitivity of the urban airshed is not much
affected in this sensitivity study. The most sensitive measure is the
dosage (11 percent higher). In general, higher ozone levels are obtained,
but the deviations from the base case remain below 4 percent. The overall
maximum ozone level occurs at the same location, and it is not perturbed
notably. The values of the spatial and temporal correlation coefficients
are high (above 0.969).
2) Sensitivity of Model Input Variables to Input Data
Mobile source emissions have been slightly perturbed by the use of an
older inventory. Isopleths of daily ground level emissions of nitrogen
oxides and hydrocarbons are presented in figure A-44 for this case and the
A-158
-------
TABLE A-18. GENERAL SENSITIVITY MEASURES—CASE 13
(a) General Ozone Level Deviations
Station Statistics
Grid Statistics
tn
<£>
Sensitivity Measure
Signed deviation
Absolute deviation
Temporal correlation
Spatial correlation
03 > 12 pphm 03 > 20 pphm
0.027 0.022
0.037
0.029
0.988
0.983
0.987
0.969
03 > 12 pphm 03 > 20 pphm
0.022 0.018
0.039
0.984
0.983
0.034
0.977
0.975
(b) Overall Maximum Ozone Level
Sensitivity case/
base case ratio
Peak level (pphm):
Sensitivity case
Base case
Corresponding locations:
Sensitivity case
Base case
Station Statistics
1.020
36.2
35.5
Azusa
Azusa
Grid Statistics
1.027
39.9
38.9
33 - 14
33 - 14
-------
TABLE A-18 (Concluded)
(c) Maximum Ozone Statistics
All Stations Downwind Stations
Peak level 0.028 0.029
normalized difference
Peak time lag (hrs) 0.350 0.440
o (d) Dosage
Sensitivity Case Base Case
Normalized Difference _ (km2) _
0.113 11,125 10,000
-------
N0RTH
207 | | | |
10
20
30
(3'°
0.
i i i i i i i i i i—i—i—i—i—I—i—i—i—i—i—i—i—i
20
10
20
30
50UTH
IDg
(a) Base Case NOX (Tons of N02)
FIGURE A-44. TOTAL DAILY EMISSIONS FOR GROUND-LEVEL SOURCES
-------
N0RTH
i
i i i i i 11
30
50UTH
(b) NO (Tons of N02) Sensitivity Case 13
FIGURE A-44 (Continued)
-------
N0RTH
:
...
i I I I l I 1—I—I—I—I—I—I—I—I
50UTH
(c) Hydrocarbons (Tons) Base Case
FIGURE A-44 (Continued)
-------
i
. •
01
N0RTH
20
10
20
30
I I I
a
20
I I I
20
30
50UTH
(d) ) Hydrocarbons (Tons) Sensitivity Case 13
FIGURE A-44 (Concluded)
-------
corresponding base case. The major difference appears near the coast
around Lennox. In general, the older emission estimate is not as detailed
and results in smoother emission patterns.
3) Sensitivity of Ozone Levels to Mobile Source Emissions
Isopleths of maximum ozone deviations are shown in figure A-45. The
predictions have been perturbed by less than 10 ppb. Ozone profiles at
six air quality monitoring stations are shown in figure A-46. The largest
deviation occurs at San Bernardino. The air parcel which reaches this
station has traveled across the center part of the basin, and slight
changes in the emission patterns have probably accumulated to create this
perturbation in the ozone peak level. Other areas show little perturba-
tion in ozone levels.
The emission inventories presented in figure A-44 are averaged by
grid in the model simulation. It is probable that the grid averaged
emissions show deviations which are too small to induce any large pertur-
bation in the urban airshed dynamics.
4) Conclusions
The use of an older emission inventory for mobile sources has a
negligible effect on the air quality predictions. The model appears to be
rather insensitive to small perturbations in the mobile source emissions.
n. Model Sensitivity to Mobile Source Emissions: Estimate Based on Gas
Sales—Simulation of 26 June 1974
In this sensitivity study, the mobile source inventory has been
obtained by considering averaged gas sale estimates, assuming a reasonable
temporal distribution and resolving the spatial distribution according to
population estimates.
1) General Sensitivity Measures
The general effects of the perturbation in the mobile source inven-
tory are presented in table A-19. The deviations in ozone levels are
more important than in case 13 (older inventory), however, they do not
exceed 8.5 percent (signed and absolute deviations and maximum ozone
statistics). The dosage is the most sensitive measure with an increase of
24.5 percent.
A-165
-------
NBRTH
i
Ol
cr\
FIGURE A-45. DEVIATION OF MAXIMUM OZONE CONCENTRATIONS (ppb): CASE
BASE CASE BETWEEN THE HOURS OF 4 AND 19 1ST
-------
60
50
40
ac
t 30
12
18
en
20
10
_nn TI n i i
- RNRHEIM
: HiiHffTY RUN
1 1 1
6 12 16
TIME (HfURS)
24
60 60
50 50
40 40
30 i 30
20 20
10 10
12
18
24°
2
I i i i f | I i i i i |
LR HRBRE
BRSE CRSE ——
SENSITIVITY RUN —
6 12 18
TIME (HiURS)
40
30
20
10
4°
1 ' I
- PflSRDENR
- BRSE CRSE —
- SENSITIVITY RUN —
8
12
18
24
12 16
TINE (HIURS)
FT
I | I I I I I | I I i I I | I I I I l_
LYNH00D
BRSE CRSE
SENSITIVITY RUN —
60
12
TINE IHfURS)
18
50
40
30
20
10
FIGURE A-46. COMPARISON OF PREDICTED OZONE CONCENTRATIONS: CASE 13
A-167
-------
60
SO
40
**
a.
i 30
en
OB
20
10
6
12
18
iiii rj i i
- SRN BERNftD
- BflSE CflSE -
- SENSITIVITY RUN —
ll | II r
6 12 18
TINE (HIURS)
i i
60
50 50
40
30 S: 30
tn
Ok
20 20
10
24°
10
6 12
i i i i i I i I I I i |
L UPLfiND
r BflSE CflSE
" SENSITIVITY RUN —
18
• 1 ' '
12
TIME (HIURS)
18
50
30
20
10
FIGURE A-46 (Concluded)
A-168
-------
TABLE A-19. GENERAL SENSITIVITY MEASURES—CASE 14
(a) General Ozone Level Deviations
Station Statistics
Grid Statistics
CT>
UD
Sensitivity Measure
Signed deviation
Absolute deviation
Temporal correlation
Spatial correlation
°3
> 12 pphm
0.064
0.067
0.988
0.983
03 > 20 pphm
0.075
0.075
0.989
0.973
03 > 12 pphm 03 > 20 pphm
0.070 0.085
0.073
0.986
0.980
0.085
0.982
0.967
(b) Overall Maximum Ozone Level
Station Statistics
Sensitivity case/ 1.101
base case ratio
Peak level (pphm):
Sensitivity case 39.1
Base case 35.5
Corresponding locations:
Sensitivity case Azusa
Base case Azusa
Grid Statistics
1.056
41.1
38.9
19 - 15
33 - 14
-------
TABLE A-19 (Concluded)
(c) Maximum Ozone Statistics
All Stations Downwind Stations
Peak level 0.070 0.082
normalized difference
Peak time lag (hrs) 0.130 0.190
f»
(d) Dosaqe
o
Sensitivity Case Base Case
Normalized Difference _ (km^) _ (km^)
0.245 12,450 10,000
-------
The temporal and spatial correlations are high (above 0.967) and the
peak time lag is short (an average 12 minutes for downwind stations).
In general, higher ozone levels are predicted in the sensitivity
case, but the perturbations remain under 10 percent (except for the
dosage).
2) Sensitivity of Model Input Variables to Input Data
The spatial and temporal distributions of the mobile source inventory
have been modified. The spatial distributions of the total daily
emissions of nitrogen oxides and hydrocarbons from ground level sources
are shown in figure A-47 and can be compared with the base case emissions
presented in figure A-43. Total daily emissions from mobile sources are
presented in table A-20 for this sensitivity case and the 26 June 1974
base case. Emissions of reactive hydrocarbons and carbon monoxide are
higher by about 50 percent in the sensitivity case; the perturbation in
nitrogen oxides is only 6 percent. This increase of hydrocarbon emissions
leads to overall higher ozone levels shown in table A-19.
3) Sensitivity of Ozone Levels to Mobile Source Emissions
The deviations in maximum ozone concentrations between the sensi-
tivity case and the base case are shown in figure A-48. The largest
deviations occur in upper mid-basin. This appears also in figure A-49,
where ozone profiles at six air quality monitoring stations are shown.
Higher ozone levels result from higher primary pollutant emissions
(especially hydrocarbons) from mobile sources. Since most of the mobile
sources are located in the western part of the basin around downtown Los
Angeles, the areas that are most affected by this new emission pattern are
downwind of the heavy traffic region. Hence, the major deviations in
ozone levels are predicted to occur at Pasadena and Anaheim. As
atmospheric dispersion occurs the differences decrease, as ozone profiles
at stations further downwind, such as Upland and San Bernardino, indicate.
4) Conclusions
The use of gas sale estimates and population distributions to derive
a mobile source inventory leads to higher emission levels and consequently
to higher ozone levels, particularly in the area downwind of the heavy
traffic region. However, the general perturbations do not exceed 10
percent, except for the dosage, which is 25 percent higher. This effect
A-171
-------
N0RTH
-
20
~I 1" —T 1
I I I I I I I I I I 111
3D
50I..ITH
(a) NOX (Tons of N02) Sensitivity Case 14
FIGURE A-47. TOTAL DAILY EMISSIONS FOR GROUND LEVEL SOURCES
-------
N0RTH
Js
10
20
30
20
i i i i ' i i I—I—I—In
50UTH
(b) Hydrocarbons (Tons)
FIGURE A-47 (Concluded)
-------
TABLE A-20. TOTAL DAILY EMISSIONS FROM MOBILE SOURCES
Nitrogen Oxides Reactive Hydrocarbons Carbon Monoxide
Species (tons of NO?) (tons) (tons)
Sensitivity Case
Base case
760.0
719.0
1,256
845
11,885
8,250
Ratio = sensitivity case ^ l ^
base case
-------
NBRTH
-
-
FIGURE A-48. DEVIATION OF MAXIMUM OZONE CONCENTRATIONS (ppb): CASE 14—
BASE CASE BETWEEN THE HOURS OF 4 AND 19 LST
-------
12
18
60
50
40
x
A.
i 30
en
B
20
10
°I
_ i i i i i | i i i i i | ' iii
- RNflHEIM
- BflSE CflSE
- SENSITIVITY RUN —
-
-
-
_
-
I /*^
" s \
"ill \—*#f\\ 1 1 1 1 1 1 1 1 1
) 6 12
' 1 ' ' ' ' '.
-
—
—
-
—
-
—
_
-
TM i i i i r
18 2
ou
50
40
30
20
10
f
60
50
12
a.
£ 30
r>
20
10
i i i i i I i i i i
- SON BERNRD
- BflSE CflSE
- SENSITIVITY RUN
18
i i i i i |
24
60
50
40
30
20
10
TIME (HiURS)
6 12 18
TINE (HIURS)
on
60
50
40
x
o.
i 30
en
m
20
10
°C
) 6 12
- LYNM800
- BflSE CRSE — '
- SENSITIVITY RUN —
-
-
-
—
*i
) 6 12
1 1 Ml 1 1 1 1^0
-
- 50
- 40
- 30
M
_
- 20
- 10
|S1SwJ ' ' ' ' '" n
16 2f
60
50
40
x:
t 30
-------
60
50
40
£• 30
20
10
12
I ' i ' I ' > ' '
- PRSRDENR
- BflSE CRSE
- SENSITIVITY RUN
IB
1 ' I i
12
TIME (HBURS)
18
50
10
24°
60
50
6
12
16
24
40 40
^-»
ac
30 fc 30
CO
m
20 20
10
I I I I i | I I I I I | I I 1 I
- UPLftND
- BflSE CflSE —
- SENSITIVITY RUN —
6 12 18
TIME (H8URS)
60
50
30
20
10
FIGURE A-49 (Concluded)
A-177
-------
is more important than what was obtained in case 13 with the use of an
older emission inventory (about 4 percent deviation is for ozone levels;
11 percent is for the dosage).
o. Model Sensitivity to Mobile Source Emissions: Estimate Based on Gas
Sales—Simulation of 4 August 1975
This sensitivity study involves the same modification in mobile
source emissions as that involved in case 14, with the 4 August 1975
meteorological conditions.
1) General Sensitivity Measures
Some measures of the general sensitivity of the model to mobile
source emissions are presented in table A-21. As for the 26 June 1974
conditions, higher ozone levels are predicted with the sensitivity case.
The deviations are as high as 16 percent for the grid statistics, 24
percent for the maximum ozone statistics, and 59 percent for the dosage,
which is the most sensitive measure. The overall maximum ozone peak is
not much perturbed, though it occurs at a different location (grid [11-16]
instead of grid [30-16]).
The temporal correlation is high, but the spatial correlation is
slightly lower (0.74 for stations with ozone levels above 12 pphm).
Compared with case 14, wind velocities are larger and mixing depths are
lower, which probably enhances the spatial spreading of the perturbations
in the model predictions.
2) Sensitivity of Model Input Variables to Injjut Data
The mobile source emissions have been modified in this sensitivity
case as in case 14. Thus, higher emission levels from mobile sources are
considered in the sensitivity case.
3) Sensitivity of Ozone Levels to Mobile Source Emissions
Isopleths of maximum ozone deviation are shown in figure A-50. As in
case 14, larger deviations in ozone levels occur in mid basin; however,
the deviations are higher than in case 14 (80 ppb near Azusa and
Pasadena). The perturbations affect a much larger area than was affected
by the 26 June 1974 conditions. This appears clearly in the ozone
profiles shown in figure A-51. For instance, the perturbations in ozone
A-178
-------
3>
l
to
TABLE A-21. GENERAL SENSITIVITY MEASURES—CASE 15
(a) General Ozone Level Deviations
Sensitivity Measure
Signed deviation
Absolute deviation
Temporal correlation
Spatial correlation
Station Statistics
03
> 12 pphm
0.115
0.127
0.977
0.738
03 > 20 pphm
0.082
0.084
0.955
0.922
Grid Statistics
03 > 12 pphm 03 * 20 pphm
0.146 0.095
0.160
0.963
0.905
0.108
0.945
0.840
(b) Overall Maximum Ozone Level
Station Statistics
Sensitivity case/ 1.139
base case ratio
Peak level (pphm):
Sensitivity case 30.0
Base case 26.3
Corresponding locations:
Sensitivity case Pomona
Base case Pomona
Grid Statistics
1.033
38.3
37.0
11 - 16
30 - 16
-------
TABLE A-21 (Concluded)
(c) Maximum Ozone Statistics
AIT Stations Downwind Stations
Peak level 0.243 0.214
normalized difference
Peak time lag (hrs) 0.130 0.260
l
& (d) Dosage
o
Sensitivity Case Base Case
Normalized Difference (krn^) (km^)
0.59 13,900 8,750
-------
NMTH
Iv£^y &
m^^J
S0UTH
FIGURE A-50. DEVIATION OF MAXIMUM OZONE CONCENTRATIONS: CASE 15
BASE CASE BETWEEN THE HOURS OF 4 AND 19 1ST
-------
60
50
40
I
|ao
«n
^B
20
10
60
50
40
£
a.
2; 30
y -
^/ ( § j
6 12 18 2
TINE (HIURS)
6 12 18 2
i i i i 1 i i i i i | i i i i i I i i i i i _
Lfl HflBRE
BflSE CflSE —
SENSITIVITY RUN --• ^
-
-
-
-"
_
-
^ z
/ "*» ""
^^^^0 -
1 1 1 l^^^l 1 1 1 1 1 1 1 l^^^fcj III 1 l~
6 12 16 2
\50
DU
50
40
30
20
10
4°
\0
bU
50
40
30
20
10
P
t
50
40
3E
CL
t 30
i i 1 i _
- flNflHEIM
- BflSE CflSE —
- SENSITIVITY RUN — ^
—
-
•• —
•• ••
m _
— —
-
*™ *"
I x\ -
f \
i ^^^rr?^ :
I 6 12 18 2
TINE (HfURS)
) 6 12 18 2
_ i I i i i I i i i i i | i i i i i | i i i i i_
- PflSflDENfl
- BftSE CflSE
- SENSITIVITY RUN —
- -
-
I I
!
* »
~ y » *"
!/\\ ;
*/ V *». —
V V »
J ^o ~
I 6 12 18 2
60
50
40
30
20
10
A
4°
4
50
40
30
20
10
4°
TINE (HIURS)
TINE (HfURS)
FIGURE A-51. COMPARISON OF PREDICTED OZONE CONCENTRATIONS: CASE 15
A-182
-------
12
18
12
16
BO
50
40
i 30
en
20
10
°<
_ I i i I I | I I I I i | I I I I i | I i I I i_
LYNHB0D
BflSE CflSE —
SENSITIVITY RUN —
—
-
— —
" ""'X :
) 6 12 18 2
60 60
50 50
40 40
ac
30 i 30
m
CD
20 20
10 10
4° °
_ I I I I I | I i I i i | i i
- UPLfiND
- BflSE CflSE
- SENSITIVITY RUN --•
-
-
1 r
) 6 12
1 ' ' 1 _
-
-
^ —
\ 1
18 2
50
40
30
20
10
4°
TIME (HfURS)
TIME (HfURS)
FIGURE A-51 (Concluded)
A-183
-------
levels observed at San Bernardino are larger than those obtained in case
14 (See figure A-49).
Larger perturbations in the model predictions with the 4 August 1975
conditions result from slightly higher wind velocities and lower mixing
depths. Therefore, perturbations in the emission levels have a larger
effect, since the mixing volume affected is smaller and the propagation of
the perturbation is slightly faster.
4) Conclusions
The results obtained with the 4 August 1975 meteorological conditions
are consistent with those obtained with the 26 June 1974 conditions.
Higher ozone levels are predicted as a result of higher emission levels
from mobile sources. The perturbations are more important in this case,
as a result of lower mixing depths.
p. Model Sensitivity to Point Source Temporal Resolution—Simulation of
26 June 1974
In this sensitivity study, temporal profiles of point source
emissions have been modified. A yearly averaged emission pattern was
chosen instead of the more detailed daily emission data. As a result,
lower nitrogen oxides emissions were obtained for the sensitivity case.
1) General Sensitivity Measures
The overall sensitivity of the model to point source emissions is
presented in table A-22. The perturbations on the ozone level predictions
are small. The largest perturbation occurs with the peak level normalized
difference (2.9 percent for all stations). The overall maximum ozone
levels occur at the same locations and are not much perturbed (0.4 percent
for the grids). The values of the temporal and spatial correlation
coefficients are very high for both station and grid statistics (above
0.988).
In general, slightly higher ozone levels are obtained in the
sensitivity case.
A-184
-------
TABLE A-22. GENERAL SENSITIVITY MEASURES—CASE 16
(a) General Ozone Level Deviations
Station Statistics
Grid Statistics
00
in
Sensitivity Measure
Signed deviation
Absolute deviation
Temporal correlation
Spatial correlation
°3
> 12 pphm
0.010
0.011
0.990
0.990
03 > 20 pphm
0.006
0.006
0.990
0.989
03 =
> 12 pphm
0.009
0.010
0.990
0.990
03 > 20 pphm
0.007
0.008
0.988
0.990
(b) Overall Maximum Ozone Level
Stat i on St at i s t i c s
Sensitivity case/ 1.000
base case ratio
Peak level {pphm):
Sensitivity case 35.5
Base case 35.5
Corresponding locations:
Sensitivity case Azusa
Base case Azusa
Grid Statistics
0.996
38.7
38.9
33 - 14
33 - 14
-------
TABLE A-22 (Concluded)
(c) Maximum Ozone Statistics
All Stations Downwind Stations
Peak level 0.029 0.020
normalized difference
Peak time lag (hrs) 0.13 0.19
I
oo (d) Dosage
Sensitivity Case Base Case
Normalized Difference (km2) (km2)
0.013 10.125 10,000
-------
2) Sensitivity of Model Input Variables to Input Data
Emission levels of point sources have been perturbed by averaging
emissions over the year. Point sources release nitrogen oxides, sulfur
dioxide, and particulates, primarily. In the present simulation, nitrogen
oxides are the pollutant of interest. The averaging procedure resulted in
lower nitrogen oxides emissions.
3) Sensitivity of Ozone Levels to Point Source Emissions
Isopleths of maximum ozone deviation are shown in figure A-52.
Deviations are less than 10 ppb throughout the basin. Ozone profiles at
seven air quality monitoring stations are presented in figure A-53. The
agreement between the sensitivity case and the base case is good except at
La Habra, Anaheim, and Los Alamitos. These three stations are located in
areas downwind of point sources. Lower nitrogen oxides emissions lead to
higher ozone levels; in the Los Angeles basin the hydrocarbon/nitrogen
oxides ratio is such that decreasing nitrogen oxides concentrations
increase ozone concentrations 1n the near downwind area.
4) Conclusions
The temporal resolution of point source emissions does not appear to
be an important factor in the dynamics of the urban airshed model since
the effects are small and limited to areas immediately downwind of the
point sources.
q. Model Sensitivity to Area Source Spatial Resolution—Simulation of
26 June 1974
In this sensitivity case, the spatial resolution of area sources has
been simplified. Area sources have been allocated according to
demographic distribution.
1) General Sensitivity Measures
The effect of a simpler spatial resolution of area sources on the
overall sensitivity of the model is presented in table A-23. There is a
general trend toward higher ozone levels. The deviations are on the order
of 6 percent. The dosage is the most sensitive measure and increases by
19 percent. Both temporal and spatial correlations are high (above
0.979).
A-187
-------
NIRTH
-••
-
S0UTH
FIGURE A-52. DEVIATION OF MAXIMUM OZONE CONCENTRATIONS (ppb): CASE 16—
BASE CASE BETWEEN THE HOURS OF 4 AND 19 1ST
-------
- UPLflND
- BRSE CflSE
- SENSITIVITY RUN
6 12 IB
TIME IMiURS)
60
50
40
i 30
20
10
12
_l I I I I | I I I I I |
ANAHEIM
BRSE CflSE -
SENSITIVITY RUN —
16
I I i i I
24
60
50
40
30
20
10
6 12 18
TIME (HIURS)
24°
80
50
40
30
20
10
12
18
12
18
I I I I I I I I
- LH HflBRE
BRSE CRSE
SENSITIVITY RUN
12
TIME I HIURS)
18
50
40
SO S: 30
in
20
10
74°
SO
40
30
20
10
us
.1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
- L0S RLRHIT
• BRSE CRSE —
- SENSITIVITY RUN —
-
-
-
\ ^rv,
i 6 12 18
I I I i_
-
-
-
-
2
bu
50
40
30
20
10
4°
TIME (HIURS)
FIGURE A-53. COMPARISON OF PREDICTED OZONE CONCENTRATIONS: CASE 16
A-189
-------
60
50
40
i 90
20
10
12
16
^I!ijr i i i i i ii i ir|i i
- PflSflOENR
- BflSE CflSE —
- SENSITIVITY RUN —
6 12 16
TINE (HIURS)
SO
40
30
20
10
eo
so
40
i 30
20
10
6
12
18
I 1 I | 1 i
iiiiji
- LYNMI00
- BRSE CflSE —
- SENSITIVITY RUN —
1 I I i I I "_
6 12 18
TINE (HIURS)
2<6C
50
40
30
20
10
24°
12
16
24.
50
40
lao
S
20
10
- SflN BERNflD
- BflSE CflSE
- SENSITIVITY RUN
60
50
40
30
20
10
12
TIME (HIURS)
16
FIGURE A-53 (Concluded)
A-190
-------
TABLE A-23. GENERAL SENSITIVITY MEASURES—CASE 17
(a) General Ozone Level Deviations
Sensitivity Measure
Signed deviation
Absolute deviation
Temporal correlation
Spatial correlation
Station Statistics
03 > 12 pphm 03 > 20 pphm
0.054 0.057
0.055
0.057
Grid Statistics
03 > 12 pphm 03 > 20 pphm
0.053 0.060
0.055
0.060
0.990
0.982
0.990
0.979
0.988
0.984
0.986
0.981
(b) Overall Maximum Ozone Level
Sensitivity case/
base case ratio
Peak level (pphm):
Sensitivity case
Base case
Corresponding locations:
Sensitivity case
Base case
Station Statistics
1.067
37.8
35.5
Azusa
Azusa
Grid Statistics
1.046
40.7
38.9
19 - 15
33 - 14
-------
TABLE A-23 (Concluded)
(c) Maximum Ozone Statistics
All Stations Downwind Stations
Peak level 0.063 0.063
normalized difference
Peak time lag (hrs) 0.13 0.19
(d) Dosage
Sensitivity Case Base Case
Normalized Difference (krn^) (km2)
0.193 11,925 10,000
-------
The overall maximum ozone level occurs in a different grid, but the
peak level deviation is only 4.6 percent.
2) Sensitivity of Model Input Variables to Input Data
The area source emissions have been modified. Total daily emissions
of nitrogen oxides and hydrocarbons from area sources are shown in figure
A-54 for this sensitivity case and the corresponding base case. The
emissions of nitrogen oxides and reactive hydrocarbons are more smoothly
distributed in the sensitivity case. This results from the less spatially
detailed inventory procedure used in the sensitivity case.
3) Sensitivity of Ozone Levels to Area Source Spatial Resolution
Isopleths of maximum ozone deviation are shown in figure A-55.
Higher ozone levels (about 20 ppb increase) are observed in upper mid
basin around Pasadena, La Habra, and Azusa.
Ozone profiles at eight air quality monitoring stations are presented
in figure A-56. Ozone levels predicted by the sensitivity case are higher
than those calculated in the base case. The largest deviations occur in
areas downwind of important emission sources, for instance, at Azusa,
Fontana, La Habra, Pasadena, and Lynwood. Further downwind the deviation
in ozone predictions starts to decrease as atmospheric dispersion
overcomes the initial effect of the smoother spatial distribution of the
sensitivity case emissions. This effect appears at Upland and San
Bernardino.
The areas along the coast are not much affected by the area source
emission perturbation, since air quality predictions at those stations
depend more on the initial and boundary conditions than on the emission
levels (e.g., the ozone profiles at Laguna).
4) Conclusions
The redistribution of the area source emissions has the most affect
on the areas immediately downwind of the large area sources. The
perturbations in ozone levels are on the order of about 6 percent for this
redistribution of emissions based on demographic distribution.
A-193
-------
20
10
N0RTH
20
30
I
20
: i
-
i
10
O -
o
i i i i i i
10
20
30
50UTH
(a) NO Emissions—Base Case
(tons of N02 per day)
FIGURE A-54. TOTAL DAILY EMISSIONS FOR AREA SOURCES
-------
i
c
j
N0RTH
20
10
20
30
ii—i—i—i—i—i—i—i—I—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—120
(
i i i j i
10
20
30
S0UTH
(b) NO Emissions—Sensitivity Case 17
A
(tons of NC>2 per day)
FIGURE A-54 (Continued)
-------
i
1C
T—|20
2DT i i i
i—i—i—i—i—i—i—i——i—i—i—i—i—i—i—i—i
I I I I I I
10
20
30
50UTH
(c) Hydrocarbon Emissions—Base Case
(tons per day)
FIGURE A-54 (Continued)
-------
N0RTH
--
•-.
10
30UTH
(d) Hydrocarbon Emissions—Sensitivity Case 17
(tons per day)
FIGURE A-54 (Concluded)
-------
NBRTH
<« 1Q
yj *u
-
> ;::*::;::»< ) I • » ' I ' i 1 ' ( If
•
S0UTH
FIGURE A-55. DEVIATION OF MAXIMUM OZONE CONCENTRATIONS (ppb): CASE 17-
BASE CASE BETWEEN THE HOURS OF 4 AND 19 LST
-------
12
Id
60
50
40
20
10
I I 1 I I I I I I I I I M M I I I M I I I
60
RNRHEIM
50
40
30
20
10
6 12 IB
TINE (H0URS)
60
50
40
t 30
m
20
10
6
18
i i i i I i i i i i I
- FBNTRNR
- BRSE CRSE ——
- SENSITIVITY RUN —
i I i i i
op4-
6 12 18
TINE (H8URS)
60
50
30
20
10
24°
60
50
12
18
20
10
- LflGUNB
- BflSE CRSE
- SENSITIVITY RUN
i i i I i
12
TIKE (H8URS)
IB
50
40
30
20
10
60
50
40
20
10
12
I ' »
- Lfi HflBRE
- BRSE CRSE
- SENSITIVITY RUN
18
I '
24
6 12 18
TINE (HIURS1
60
50
40
30
20
10
24°
FIGURE A-56. COMPARISON OF PREDICTED OZONE CONCENTRATIONS; CASE 17
A-199
-------
60
- PflSflDENR
- BflSE CRSE
- SENSITIVITY RUN --•
6 12 16
TIME (H0URS)
60
50
40
£ 30
20
10
6
1 ' ' ' I ' ' ' '
- LYNH00D
- BflSE CfiSE
- SENSITIVITY RUN
12
18
24
60
50
30
6 12 18
TIME (HIURSI
Ml \ I I I I I I 1 I
12
18
24
50
40
x
t 30
(O
20
10
|
- SRN BERNRD
- BflSE CRSE
- SENSITIVITY RUM
60
50
40
20
10
6 12 18
TIME (HIURS)
60
50
40
x
a.
t 30
en
20
10
12
16
I 1 T I t\ I I IT |J TT
- UPLRND
- BfiSE CflSE
- SENSITIVITY RUN --•
I '
6 12 16
TIME (H0URS)
460
50
FIGURE A-56 (Concluded)
A-200
-------
r. Model Sensitivity to Area Source Spatial Resolution—Simulation of
4 August 1975
The spatial resolution of area sources has been modified in case 18
as it was in sensitivity case 17.
1) General Sensitivity Measures
Some measures of the general sensitivity of the model are presented
in table A-24. As was the case with the 26 June 1974 conditions, higher
ozone levels are predicted in the sensitivity case for the 4 August 1975
conditions. Deviations from the base case are larger for this case than
for case 17. This appears in the maximum ozone statistics and in the
dosage, particularly.
The temporal correlation is higher than the spatial correlation. In
general, deviations are on the order of 10 to 17 percent (station, grid
and maximum ozone statistics).
2) Sensitivity of Model Input Variables to Input Data
The area source emissions have been modified as they were in case 17,
and the total daily emissions of nitrogen oxides and hydrocarbons have
been presented in figure A-54.
3) Sensitivity of Ozone Levels to Area Source Spatial Resolution
Deviations of maximum ozone levels are shown in figure A-57.
Deviations as high as 70 ppb and 100 ppb occur near Azusa and Pasadena,
respectively. For comparison, deviations on the order of 20 ppb in
mid-basin were observed in case 17.
Ozone profiles at seven air quality monitoring stations are shown in
figure A-58. A wider part of the basin is affected by the perturbation
than was affected in case 17. Slightly higher wind velocities and lower
mixing depths cause the enhancement of the perturbation in ozone levels.
A good example of this effect is the ozone profile at Fontana, which is
strongly affected in this case.
A-201
-------
TABLE A-24. GENERAL SENSITIVITY MEASURES-CASE 18
(a) General Ozone Level Deviations
Station Statistics
Grid Statistics
ro
O
ro
Sensitivity Measure
Signed deviation
Absolute deviation
Temporal correlation
Spatial correlation
03
> 12 pphm
0.118
0.127
0.977
0.789
03 > 20 pphm
0.103
0.103
0.963
0.946
03 > 12 pphm 03 > 20 pphm
0.141 0.103
0.149
0.969
0.919
0.107
0.960
0.836
(b) Overall Maximum Ozone Level
Sensitivity case/
base case ratio
Peak level (pphm):
Sensitivity case
Base case
Corresponding locations:
Sensitivity case
Base case
Station Statistics
1.171
30.8
26.3
Pomona
Pomona
Grid Statistics
0.997
36.9
37.0
11 - 16
30 - 16
-------
TABLE A-24 (Concluded)
(c) Maximum Ozone Statistics
All Stations Downwind Stations
Peak level 0.254 0.241
normalized difference
Peak time lag (hrs) 0.13 0.26
r!j (d) Dosage
o
CO
Sensitivity Case Base Case
Normalized Difference (km?) (km^)
0.571 13,750 8,750
-------
NflRTH
10
•:-:€-:•:•:-:->:•:•:•:-:«-:•.-.•.•>.•:•.•:•.<•:•:
2 »o
•
PO
c
x $::*::£:::•:•:£::•:
lill
•:•: :|:;:;:T:v:;.;:v:;:;X:
20
w
10
10
S0UTH
FIGURE A-57.
DEVIATION OF MAXIMUM OZONE CONCENTRATIONS: CASE 18
BASE CASE BETWEEN THE HOURS OF 4 AND 19 1ST
-------
UOi
DV
so
40
fcso
S
20
10
n
°
en
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40
i
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*>
20
JO
"<
1 D It Id £•
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- FBNTflNfl
- BRSE CRSE —
- SENSITIVITY RUN —
—
-
-
I /s^ -
''/ ^^
" ' f ^^ ""
" $ * Vk "
// v ~
™ ^ '^r \ ™
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) 6 12 18 2
TINE (HIURS)
) 6 12 18 2
_ i i i i i | i i i i i | i i i i i i i i i i i _
PRSRDENR
BRSE CRSE — -
SENSITIVITY RUN —
—
I I
~ "^ —
/ \
: \ —
. •
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7 t y»^ » 1
i j ^v %
™ ' * m ^ ~
™ 1 m ^t % ""
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t • 19 tO t
60
6U 60
50 50
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30 |30
2
20 20
10 10
n
4° 0
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50 50
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fe
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m
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20 20
10 10
J> n
3 6 12 18 2
_ i i i i i | i l l l i | l l i l l | i i i i i
- Lfl HRBRE -
- BRSE CRSE —
- SENSITIVITY RUN —
-
—
-
_ _
• ••
^ ^
^
- /^\ -
J^r "^L\
- f ^^ ~
_t-J^1 l^*****>»»«^l
0 6 12 18 2
TINE (HIURS)
6 12 16 2'
_ ' i l i i ) l i i i i | l i i i i | i i l i i_
- RNRHEIH -
- BRSE CASE —
- SENSITIVITY RUN —
—
_
— _
-
"™ ~
" «
•w ^
•• w
^
™
: A '-.
: ^/\^T^>>^., '-
4
60
SO
40
30
20
10
f
60
50
40
30
20
10
n
TINE (HiURS)
6 12 18
TIHE (HIURS)
FIGURE A-58. COMPARISON OF PREDICTED OZONE CONCENTRATIONS: CASE 18
A-205
-------
60
50
12
18
£: 30
20
10
.1 i i ' ' I ' ' ' '
- LYNM00D
>- BfiSE CflSE
<- SENSITIVITY RUN
I I I I
50
20
6 12 18
TIME (HiURSJ
60
50
12
16
24.
30 &• 30
20
10
T
- SflN BERNflD
- BflSE CflSE —
SENSITIVITY RUN —
12
TINE (HIURS)
16
60
50
40
30
20
10
2*°
60
50
12
16
a.
i 30
20
10
n n
i i
I > ' ' ' LJ
- UPLflND
- BflSE CflSE —
- SENSITIVITY RUN —
I I I I
lilt
50
40
30
20
10
6 12 18
TIME (H1URS)
FIGURE A-58 (Concluded)
A-206
-------
4) Conclusions
The perturbation in model predictions that results from the redistri-
bution of the area source emissions depends on the meteorological condi-
tions (wind velocity and mixing depth) and may be relatively high, as
shown in table A-24. In general, the spatial and temporal characteristics
of the model are not strongly affected, and the largest perturbation
occurs in the magnitude of the ozone levels.
s. Model Sensitivity to Temporal Resolution of Area Emission
Sources—Simulation of 26 June 1974
The temporal resolution of area emission sources has been simplified
for this sensitivity study.
1) General Sensitivity Measures
Some measures of the overall sensitivity of the model to this
perturbation in stationary sources are presented in table A-25. The
temporal resolution of stationary sources does not affect the model
predictions very much. In general, lower ozone levels are obtained in the
sensitivity case. The deviations are on the order of 0.5 percent (station
statistics) to 3 percent (dosage). The temporal and spatial correlations
are high (above 0.985), and the ozone peaks occur at the same hour at all
stations. The overall maximum ozone peak occurs at the same location
(Azusa or grid [33-14]), and the deviation from the base case in ozone
level is only 0.2 percent.
2) Sensitivity of Model Input Variables to Input Data
The only perturbation in this sensitivity case is the modification of
the temporal variations of the emission term (for stationary sources) in
the continuity equations.
3) Sensitivity of Ozone Levels to Temporal Resolution of Stationary
Emission Sources
Isopleths of maximum ozone deviation are shown in figure A-59. Ozone
profiles at six air quality monitoring stations are shown in figure
A-60. No large perturbations are observed in either case.
A-207
-------
TABLE A-25. GENERAL SENSITIVITY MEASURES—CASE 19
(a) General Ozone Level Deviations
Station Statistics
Grid Statistics
ro
o
00
Sensitivity Measure
Signed deviation
Absolute deviation
Temporal correlation
Spatial correlation
03 > 12 pphm 03 > 20 pphm
-0.005 -0.006
0.007
0.010
0.990
0.990
0.990
0.985
> 12 pphm 03 > 20 pphm
-0.008 -0.009
0.010
0.990
0.990
0.012
0.989
0.990
(b) Overall Maximum Ozone Level
Station Statistics
Sensitivity case/
base case ratio
Peak level (pphm):
Sensitivity case
Base case
Corresponding locations:
Sensitivity case
Base case
0.988
35.0
35.5
Azusa
Azusa
Grid Statistics
1.002
38.9
38.9
33 - 14
33 - 14
-------
o
vo
TABLE A-25 (Concluded)
(c) Maximum Ozone Statistics
All Stations Downwind Stations
Peak level 0.008 0.011
normalized difference
Peak time lag (hrs) 0.0 0.0
(d) Dosage
Sensitivity Case Base Case
Normalized Difference (km^) (km^)
-0.03 9,700 10,000
-------
N0RTH
10
-:
•
:
t * :» I I * * < * V > ; f :•>:•:•:•: \
10
FIGURE A-59. DEVIATION OF MAXIMUM OZONE CONCENTRATIONS (ppb): CASE 19—
BASE CASE BETWEEN THE HOURS OF 4 AND 19 1ST
-------
60
50
12
18
30
20
10
i i i I i (^1 i i I
BNflHEIH
- BflSE CRSE
- SENSITIVITY RUN
6 12
TIME (H0URSI
16
60
50
40
30
10
60
50
Q.
5:30
20
10
6 12 35
11 II I | J J II l | J J I l l | i I I ' f l_
Lfl HflBRE
BrtSE CHSE
SENSITIVITY RUN --•
60
50
30
20
10
12
TIME (HOURS1
16
12
- BflSE CRSE —
- SENSITIVITY RUN —
tf>
& 12
TIME (KBUR5J
eo
so
tk.
t 30
20
10
12
' * ' ' > I i i i i
^ LYNH00D
- BflSE CfiSE
- SENSITIVITY RJN --
i i i i i
6 12 18
TIME IH8URS)
50
30
20
10
24°
FIGURE A-60. COMPARISON OF PREDICTED OZONE CONCENTRATIONS: CASE 19
A-211
-------
60
50
40
x
a.
t 30
m
20
10
12
.''"•'I11 ' ' M
- SHN BERNflD
L BfiSE CflSE ——
- SENSITIVITY RUN - —
18
1 I
60
50
30
12
TIME (HBURS)
- UPLRND
- BflSE CHSE
- SENSITIVITY RUN - —
12
TIME (HBURS)
18
FIGURE A-60 (Concluded)
A-212
-------
4) Conclusions
The temporal resolution of emission sources does not appear to be a
parameter of major importance for the urban airshed model, since the
sensitivity measures do not show any large perturbation.
t. Model Sensitivity to Grid Size—Simulation of 26 June 1974
In this sensitivity study the structure of the urban airshed model
was modified. A grid size of (10 x 10) km2 was used instead of the
(5 x 5) km2 grid of the base case.
1) General Sensitivity Measures
Some measures of the general sensitivity of the model to the grid
size are presented in table A-26. The deviations in ozone levels are
larger for lower ozone concentrations. There is an increase of low ozone
levels (e.g., statistics for ozone levels above 12 pphm) and a decrease of
high ozone levels (e.g., statistics for ozone levels above 20 pphm). This
is clearly the result of averaging over a larger grid size.
The temporal correlation is high (above 0.848), since the temporal
properties of the model input variables have not been perturbed. However,
the spatial structure of the model has been modified, and this appears in
the lower spatial correlation.
The dosage is very much affected by this perturbation, because this
measure is based on the number of grids with ozone levels above 20 pphm,
and a larger area 1s computed for the sensitivity case as a result of the
larger grid size.
2) Sensitivity of Model Input Variables to Input Data
A larger grid size affects the model input and output variables
(meteorological variables, emissions, and concentrations), since they are
averaged over a larger area. The spatial resolution of pollutant emis-
sions, for instance, will be less accurate, and this will affect the model
predictions.
A-213
-------
TABLE A-26. GENERAL SENSITIVITY MEASURES—CASE 20
(a) General Ozone Level Deviations
Station Statistics
Grid Statistics
ro
Sensitivity Measure
Signed deviation
Absolute deviation
Temporal correlation
Spatial correlation
03 > 12 pphm 03 > 20 pphm
0.148 -0.037
0.193
0.087
0.848
0.634
0.982
0.721
03 > 12 pphm 03 > 20 pphm
0.100 -0.053
0.200
0.831
0.397
0.150
0.889
0.115
(b) Overall Maximum Ozone Level
Station Statistics
Sensitivity case/
base case ratio
Peak level (pphm):
Sensitivity case
Base case
Corresponding locations;
Sensitivity case
Base case
0.909
32.2
35.5
Pomona
Azusa
Grid Statistics
0.854
33.2
38.9
20 - 14
33 - 14
-------
TABLE A-26 (Concluded)
(c) Maximum Ozone Statistics
Peak level
normalized difference
Peak time lag (hrs)
All Stations
0.155
0.545
Downwind Stations
0.112
0.750
IV3
cn
(d) Dosage
Normalized Difference
0.60
Sensitivity Case
(km2)
16,000
Base Case
(km2)
10,000
-------
3) Sensitivity of Ozone Levels to Grid Size
Isopleths of maximum ozone deviations are shown in figure A-61, and
ozone profiles at eight air quality monitoring stations are presented in
figure A-62.
In general, ozone profiles are smoother in the sensitivity case as a
result of averaging of the variables and parameters over larger grid
cells. The timing of the ozone peak is not much perturbed, except for
cases where the smoothing process affects the ozone profiles notably, as
at Fontana and Riverside.
The averaging of model features induces a trend toward averaging of
ozone concentrations. Higher ozone levels are lower in the sensitivity
case (e.g., Upland); stations with low ozone levels show higher concentra-
tions in the sensitivity case (e.g., Anaheim). Ultimately, a box model
would give an average common concentration at all stations.
In the base case, there was a systematic bias toward underestimation
of ozone levels. Since a larger grid cell leads to higher ozone levels in
most areas of the basin, the model performance appears to be better with a
larger grid cell. This appears in figure A-63, where ozone predictions at
4 stations are compared with atmospheric data. A similar result was
obtained in an earlier study where the grid size was increased from
(2 x 2) miles2 to (4 x 4) miles2 (S. D. Reynolds et al., 1979). However,
the better prediction that is obtained with a larger grid size is coinci-
dental, and one must consider the sensitivity of the model with respect to
the base case.
4) Conclusions
The Los Angeles airshed model appears to be fairly sensitive to the
grid size. The nature of the emission field and atmospheric dynamics
affects the sensitivity of the model. For instance, one would expect the
model to be less sensitive with a smoother emission field and important
atmospheric mixing. It would be of interest to study the sensitivity of
the model to the grid size for different grid sizes and urban airsheds.
u. Model Sensitivity to Grid Vertical Resolution (Two Grid Layers)--
Simulation of 26 June 1974
The number of grid cell layers has been reduced in this study from
four to two. The mixing depth is located between the first and second
layers.
A-216
-------
NBRTH
i
FIGURE A-61 DEVIATION OF MAXIMUM OZONE CONCENTRATIONS (ppb): CASE 20—
BASE CASE BETWEEN THE HOURS OF 4 AND 19 1ST
-------
60
50
40
i 30
20
10
12
i r
16
- SRN BERHRD
- BBSE CRSE —
- SENSITIVITY RUN "•
i I
6 12 IB
TIME (HIURS)
50
30
20
10
24°
60
50
40
a.
«b30
-------
0
BO
50
40
a.
tso
20
10
12
16
j i i M | M i i i i M i M | i i i i r
V,
12
18
Lfl HRBRE
BflSE CflSE —
- SENSITIVITY RUN —
50
40
30
20
10
6 12
TIHE (HiURS)
50
40
o.
i 30
20
10
flNRHEIH
BflSE CflSE
SENSITIVITY RUN --•
I < i i i i | I i i I i_
*-•-••»•
6 12 IB
TINE (HIURS)
50
40
30
20
10
FIGURE A-62 (Concluded)
A-219
-------
60
50
40
1
*: 30
20
10
6
' ' ' ' I ' ' '
- LBS RLAHIT
- 8BSERVED •
- PREDICTED —
12
16
1 ' I
6 12 16
TINE IHtURS)
i i i i i I i—rrr
- flZUSfl
- iBSERVED
- PREDICTED
I i i i . . [ in m n m ti
6 12 18
TIME tHiURS)
60
SO
12
18
i 30
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I I I I
I :,i
- CHINB
- BBSERVED
- PREDICTED
1 ' I
T*
6 12 18
TINE CHfURS)
60
SO 50
40 40
30 !b 30
20 20
10 10
12
16
24°
- UPLflND
- BBSERVED
|- PREDICTED
.' • ' ' ; " -: : ' , I 9 • • . ,-
6 12 18
TINE (HfURS)
r^c
50
40
30
20
10
24°
FIGURE A-63. COMPARISON OF PREDICTED AND OBSERVED OZONE CONCENTRATIONS: CASE 20
A-220
-------
1) General Sensitivity Measures
Some measures of the general sensitivity of the model are listed in
table A-27. General deviations in ozone levels are less than 6 percent.
Both temporal and spatial correlations are high. There is no trend toward
higher or lower concentrations because the signed deviations are much
lower than the absolute deviations.
2) Sensitivity of Model Input Variables to Input Data
The structure of the model has been modified in its vertical resolu-
tion. This affects the model input variables, such as the three-dimen-
sional wind field and elevated emissions, as well as the solution of the
continuity equations for chemical species.
3) Sensitivity of Ozone Levels to Grid Vertical Resolution
Isopleths of maximum ozone deviation are shown in figure A-64, and
ozone profiles at eight air quality monitoring stations are presented in
figure A-65. Deviations from the base case are the largest in mid basin
(e.g., La Habra and Lynwood) and at Pasadena.
As a result of the vertical averaging of chemical species concentra-
tion, the concentrations field is smoother, and this appears in the ground
level ozone concentrations. It appears in figure A-65, for the stations
at Chino and Riverside.
4) Conclusions
The model is not very sensitive to the reduction of the number of
grid cell layers from four to two. The computational cost is reduced
since only half the number of continuity equations has to be solved. This
may be an interesting simplification of the model.
v. Model Sensitivity to Grid Vertical Resolution (One Grid Layer) —
Simulation of 26 June 1974
The number of grid cell layers has been reduced in this study from
four to one. The single grid cell layer is located below the base of the
inversion layer.
A-221
-------
TABLE A-27. GENERAL SENSITIVITY MEASURES—CASE 21
(a) General Ozone Level Deviations
Station Statistics
Grid Statistics
ro
ro
Sensitivity Measure
Signed deviation
Absolute deviation
Tempor al corre1 at i on
Spatial correlation
03
> 12 pphm
-0.007
0.053
0.975
0.972
03 > 20 pphm
0.006
0.033
0.989
0.982
03 > 12 pphm 03 > 20 pphm
-0.011 -0.000
0.055
0.975
0.965
0.041
0.981
0.949
(b) Overall Maximum Ozone Level
Station Statistics
Sensitivity case/
base case ratio
Peak level (pphm):
Sensitivity case
Base case
Corresponding locations:
Sensitivity case
Base case
1.019
36.1
35.5
Azusa
Azusa
Grid Statistics
1.020
39.6
38.9
19 - 15
33 - 14
-------
TABLE A-27 (Concluded)
(c) Maximum Ozone Statistics
All Stations Downwind Stations
Peak level 0.055 0.043
normalized difference
Peak time lag (hrs) 0.22 0.25
ro (d) Dosage
CO
Sensitivity Case Base Case
Normalized Difference (km2) (kmz)
0.0425 10,425 10,000
-------
NBRTH
10
-.
10
> < "> :.t:::-v':t':::-:';>':":''>''::V I ''.'.I i :> t
FIGURE A-64. DEVIATION OF MAXIMUM OZONE CONCENTRATIONS (ppb): CASE 21—
BASE CASE BETWEEN THE HOURS OF 4 AND 19 1ST
-------
• n
60
50
40
£ 30
£
W
20
10
0
K 12 18 21
J 1 1 1 1 | 1 1 1 1 1 1 1 1 M 1 1 ' ' ' ' '-
- RNRHEIH I
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bU
50
,0
30
20
10
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TIME (H0URS)
TIME (H0URS)
60
50
40
30
20
10
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6
12
18
I 1 I I I | 1 1 I
- LB.HRBRE
RUN
I I I M I I I | I I I I II
50
40
30
20
10
6 12 18
TIME (HtURS)
24°
- PRSflDENR
- BRSE CRSE
- SENSITIVITY RUN
6 12 16
TIME IH1URS)
FIGURE A-65. COMPARISON OF PREDICTED OZONE CONCENTRATIONS: CASE 21
A-225
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60
50
40
a.
i 30
12
16
24
i i i i j i i
- UPLflND
- BflSE CflSE —
- SENSITIVITY RUN —
- 10
12
TIME (HIURS)
18
FIGURE A-65 (Concluded)
A-226
-------
1) General Sensitivity Measures
Some measures of the general sensitivity of the model are listed in
table A-28. General deviations in ozone levels are fairly high, ranging
from 16 to 38 percent. There is a slight trend towards lower predicted
ozone levels when compared with the base case. The two-layer model showed
much less deviation from the base case, with a general deviation in ozone
levels of less than 6 percent.
The temporal and spatial ozone concentration profiles appear to be
fairly perturbed according to the low value of the temporal and spatial
correlations.
The overall maximum ozone level is not notably affected. The dosage
is a more sensitive measure, since it is increased by about 15 percent.
This is in agreement with the ozone level deviation for grid statistics,
which is on the order of 20 percent for ozone levels above 12 pphm.
2) Sensitivity of Model Input Variables to Input Data
The gridded structure of the model has been modified in its vertical
resolution. This affects some model input variables such as the three-
dimensional wind field, elevated emissions, and boundary conditions aloft.
3) Sensitivity of Ozone Levels to Grid Vertical Resolution
Ozone profiles at ten air quality monitoring stations are presented
in figure A-66. Larger deviations are observed at stations near the coast
(e.g., La Habra, Long Beach, Los Alamitos, and Anaheim). Very large
deviations in the ozone peak levels are observed at these stations, e.g.,
28 pphm in the sensitivity case versus 12 pphm in the base case at
Anaheim, and 24 pphm in the sensitivity case versus 8 pphm in the base
case at Long Beach. These deviations explain the higher value of the
dosage 1n the sensitivity case when compared with the base case value.
Use of a single-layer model affects the treatment of elevated
emissions and this may partially explain the higher ozone levels observed
in the sensitivity case. In a multiple-layer model, nitrogen oxide
emissions that are injected above the mixing layer in the morning may be
entrained into this layer as the mixing height increases with time during
the day. The re-entrained nitric oxide may then reduce the ozone concen-
trations. In a one-layer model, however, these emissions are transported
A-227
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TABLE A-28. GENERAL SENSITIVITY MEASURES—CASE 22*
(a) General Ozone Level Deviations
Station Statistics
Grid Statistics
ro
INS
00
Sensitivity Measure
Signed deviation
Absolute deviation
Temporal correlation
Spatial correlation
03 > 12 pphm 03 > 20 pphm
-0.250 -0.235
0.377
0.332
0.787
0.347
0.790
0.526
°3
> 12 pphm
-0.067
0.207
0.766
0.701
03 > 20 pphm
-0.086
0.162
0.834
0.678
(b) Overall Maximum Ozone Level
Sensitivity case/
base case ratio
Peak level (pphm):
Sensitivity case
Base case
Corresponding locations:
Sensitivity case
Base case
Station Statistics
1.054
35.5
33.6
Azusa
Azusa
Grid Statistics
0.947
36.8
38.9
14-15
33-14
-------
TABLE A-28 (Concluded)
(c) Dosage
Sensitivity Case Base Case
Normalized Difference (km2) (km2)
0.1525 11525 10000
Maximum ozone statistics, such as peak-level normalized difference and peak time lag
averaged over several stations, were not available.
i
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TIME (HOUR?)
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50
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(c) La Habra (d) Pasadena
FIGURE A-66. COMPARISON OF PREDICTED OZONE CONCENTRATIONS: CASE 22
A-230
-------
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50
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FIGURE A-66 (Continued)
A-231
-------
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FIGURE A-66 (Concluded)
A-232
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out of the airshed and cannot be re-entrained in the mixing layer. Thu-j,
the nitric oxide emissions entrained above the mixing layer are not
available for later scavenging of ambient ozone.
4) Conclusions
The model is sensitive to the use of a single grid cell layer. The
temporal variation of the mixing height affects the chemical composition
of the mixing layer through the entrainment of species from aloft into the
mixing layer. This dynamic behavior of the mixing height may have some
notable effect on ozone formation; therefore, from this sensitivity study,
it appears important to consider at least two grid cell layers in an
airshed model--one for the mixing layer and one for the inversion layer.
A-233
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REFERENCES
Hayes, S. R, (1978), "Performance Meaasures and Standards for Air Quality
Simulation Models," EF78-93R, Systems Applications, Incorporated, San
Rafael, California.
Hoel, P. G. (1962), Introduction to Mathematical Statistics (John Wiley &
Sons, Inc., New York, New York).
Liu, M. K., et al. (1976), "The Chemistry, Dispersion, and Transport of
Air Pollutants Emitted from Fossil Fuel Power Plants in California:
Data Analysis and Emission Impact Model," EF76-18R, Systems
Applications, Incorporated, San Rafael, California.
Reynolds, S. D., et al. (1979), "Photochemical Modeling of Transportation
Control Strategies. Vol. I—Model Development, Performance Evaluation
and Strategy Assessment," EF79-37, Systems Applications, Incorporated,
San Rafael, California.
A-234
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
REPORT NO.
EPA-450/4-81-031b
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
5. REPORT DATE
The Sensitivity of Complex Photochemical Model
to Detail in Input Information -- Appendix A:
Compilation of Simulation Results
Estimates
A
6. PERFORMING ORGANIZATION CODE
7, AUTHOR(S)
C. Seigneur, T. W. Tesche, L. E. Reid, P. M. Roth,
W. R. Oliver, and J. C. Cassmassi
8. PERFORMING ORGANIZATION REPORT NO.
SAI No. 12R-EF81-6
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Systems Applications, Incorporated
950 Northgate Drive
San Rafael, California 94903
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
68-02-2870
12. SPONSORING AGENCY NAME AND ADDRESS
13. TYPE OF REPORT AND PERIOD COVERED
U.S. Environmental Protection Agency
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This report summarizes results of 22 sensitivity tests in which the impact of degrading
the data base in the Los Angeles area on predictions of a photochemical grid model
(Urban Airshed Model) is tested. Input tested includes upper air and surface meteoro-
logical and air quality data, initial and boundary conditions, speciation of organic
pollutants, temporal and areal resolution of emissions, model grid square size, and
vertical resolution available in the model.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Photochemical grid models
Urban Airshed Model
Sensitivity tests
Model inputs
Ozone
b.IDENTIFIERS/OPEN ENDED TERMS
. COSATI Held/Croup
18. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (This Report)
21. NO. OF PAGES
20. SECURITY CLASS (TMs page)
22. PRICE
_245_
EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDIT.ON is OBSOLETE
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