United States
Environmental Protection
Agency
Office of Air Quality
Planning and Standards
Research Triangle Park NC 27711
E^A-450/4-87-003
February 1987
Air
Technical Discussion
Related To The Choice
Of Photolytic Rates
For Carbon Bond
Mechanisms In
OZIPM4/EKMA
-------
Technical Discussion
Related to the Choice of
Photolytic Rates for
Carbon Bond Mechanisms
in OZIPM4/EKMA
H.E. Jeffries
Kenneth G. Sexton
Department of Environmental
Sciences and Engineering
University of North Carolina
Chapel Hill, NC 27514
Prepared For
Monitoring and Data Analysis Division.
Office of Air Quality Planning and Standards
U.S. Environmental Protection Agency
Office of Air and Radiation
Office of Air Quality Planning and Standards
Research Triangle Park, NC
„...„-„.»'»:??"""""
-------
This report has been reviewed by the Office of Air Quality Planning and Standards, U.S. Environ-
mental Protection Agency and approved for publication as received from the Principle Investigator.
Approval does not signify that the contents necessarily reflect the views and policies of the Agency,
neither does mention of trade names or commercial products constitute endorsement or recommen-
dation for use.
ii
-------
Contents
1 Introduction l
Purpose 1
The Photolysis Process . 1
Photon Flux or Radiant Energy Flux 2
Radiation Models 9
Kinetics Parameters 10
Example Calculation 12
OZIPM Methods 12
Spectral Distribution of Rates 15
2 Review of Calculated Rates 18
Effects of Changes hi Cross Section and Quantum Yield 18
Values Calculated For Carbon Bond m hi OZIPM2 25
Nitrogen Dioxide Photolysis in CB3/OZIPM2 29
Carbonyl Photolysis in CB3/OZIPM2 29
Osone Photolysis in CB3/OZIPM2 31
How CB3/OZIPM2 Rates Influenced CB4/OZIPM3/4 Rates 32
Affect of Altitude on Photolysis Rates 32
3 Atmospheric Rates 34
Measurements of Nitrogen Dioxide Photolysis Rates . 34
Comparison of Theory and Measurement for Irradianee 34
UV Albedo 36
Adjustment of Calculated Actinic Flux for Albedo 41
iii
-------
4 Recommended Rates 45
Rates for Carbon Bond IV in OZIPMS/4 ................. 45
Surface Rates '45
Mixed Layer Rates 45
Recommended CB4 Photolytic Rates 46
Rates for Carbon Bond m in OZIPM3 ................... 46
Example Predictions Using New Rates 47
Simulation Conditions 48
Simulation Results 49
IV
-------
Figures
1. Extraterrestrial and Surface Solar Spectrum 4
2. Schematic Illustration of Gas and Aerosol Light Scattering Processes 5
3. Example of Spectral Irradiance Components 7
4. Sun's Position in Central NC For Five Months 8
5. Actinic or Spherical Irradiance 11
6. Calculation of Nitrogen Dioxide Photolysis Rate for Zenith Angle = 0° 14
7. Relative Spectral Photolysis Rates 16
8. Photolysis Rates Calculated From Peterson 1976 Actinic Flux 27
9. Quantum Yields For Nitrogen Dioxide Photolysis , , 28
10. Examples of Measured Atmospheric Rates of Nitrogen Dioxide Photolysis 35
11. Comparison of Radiation Model Predictions With Spectroradiometer Measure-
ments. 37
12. Comparison of Horisontal and Spherical Irradiance 38
IS. Comparisons of Theory with Measurements for Atmospheric NO2 Actinometry 44
14. Example Simulation Using CB4: Comparison of Surface and Mixed Layer Pho-
tolytic Rates 52
15. Example Simulation Using CBS: Comparison of Mixed Layer and 1984 Pho-
tolytic Rates 53
16. Comparison of CBS and CB4 Using Mixed Layer Photolytic Rates 54
17. Comparison of CARB (CBS) and HCHO (CB4) Using Mixed Layer Photolytic
Rates 55
18. Example Simulation Using CB4: 40% HC Control Using Mixed Layer Pho-
tolytic Rates 57
19. Example Simulation Using CBS: 40% HC Control Using 1984 Photolytic Rates .... 58
20. Comparison of Oione-Hydrocarbon Relationships for CBS and CB4 59
-------
Tables
1. Calculation of Nitrogen Dioxide Photolysis Rate for Zenith Angle = 0° 13
2. Definitions of Headings used in Photolytic Rate Tables 19
8. Theoretical Rates Used in EPA Models 20
4. Cross Sections and Quantum Yields Used : 26
5. Nitrogen Dioxide Photolysis Rate as a Function of Altitude 33
6. Albedo Values Assumed by Peterson. 40
7. Albedo Values Measured by Dickerson, et al. . 40
8. UV Albedo Values Measured by Doda and Green 41
9. Comparison of Higher Albedo Calculated Photolysis Rates with Atmospheric
Measurements 43
10. Recommended CB4 Surface Photolytic Rates 47
11. Altitude Adjustments Corrected For Albedo 47
12. Recommended CB4 Mixed Layer Photolytic Rates 48
IS. Recommended CBS Surface Photolytic Rates 49
14. Recommended CBS Mixed Layer Photolytic Rates 49
15. Initial Conditions and Emissions Fractions 50
VI
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1
Introduction
Purpose
The purpose of this report is to explain the methods and identify the sources of
information used to calculate photolytic rates for the System Applications, Inc.
(SAI) chemical models Carbon Bond III (CB3) and Carbon Bond IV (CB4) for
use in SAI's OZIPM3 and OZIPM4 oxidant modeling programs.1 Both OZIPM3
and OZIPM4 programs are very similar; the former allows larger mechanisms to
be used and has the Carbon Bond X mechanism built-in, while OZIPM4 is smaller
and has CB4 as the default mechanism. The mixed layer photolytic rates described
in Chapter 4 are also the default photolysis rates for CB4 in the OZIPM4 program.
OZIPM4 is expected to be used in new State Implementation Plan calculations.
This report will also review previous recommendations for photolytic rates that
were used in the original program, OZIPP*, and in the revised program, OZIPM2.3
In the last nine years these rates have undergone significant change. In addition,
new measurements and analysis of irradiances in the UNC outdoor chamber suggest
some major changes may be needed in the photolytic rates of the SAI developed
models when these models are used in atmospheric simulations.
The Photolysis Process
Three factors determine the photolysis rate of a chemical species, S, in the atmo-
sphere.
The first factor is the number of photons of a given wavelength (energy) moving
through an area of space as a function of time, that is, the photons-cm~2-sec~1-
nm"1. This is often called the actinic flux and will be designated here by the script
letter A\. Actinic flux is a function of wavelength, A, the solar zenith angle, x> the
altitude above the earth's surface, y, and the ground reflectivity or albedo, A.
-------
Introduction Photon Flux or Radiant Energy Flux
The second factor is the ability of the species molecule to absorb photons, that
is, the species absorption cross section (cm2-molecule~1) in the wavelength interval,
designated here as o^(S).
The third factor is the fate of the molecule after it has absorbed a photon.
That is, the number of species molecules that follow a particular reaction path
after absorbing a photon, divided by the number of-species molecules that absorbed
photons in the wavelength interval. This fraction is called the quantum yield (a
dimensionless number between 0 and 1) for a given process, and is designated here
as $A(S).
The photolysis rate of species S at a given zenith angle x> at an altitude y, and
at an albedo A, will be designated as J(x,y, A;S), and is calculated by:
(1)
that is, the photolysis rate is the area under the product curve of photon flux,
absorption cross section, and quantum yield as a function of wavelength. This area
has units of time"1. The radiant energy, or photon flux, A\, is common to all
species; the kinetics parameters, a\ and $*, are unique for each species.
The lowest wavelength at which a species will photolyze (Ai) is often determined
by the lower limit of photon flux reaching the earth's surface (290-300 nm), while
the highest wavelength (A]) is often determined by the cross section or quantum
yield approaching zero at that wavelength.
Photon Flux or Radiant Energy Flux
R&diometric Quantities and Units
Radiant energy, Q\, is normally measured in joules. The relationship between
wavelength, A, and energy is given by Planck's law. The energy of a single photon
is given by
o -hc
fiA~T
where h is Planck's constant. Because 1 watt = 1 joule/sec,
h = 6.626176 x I0~u joule-sec
= 6.626176 x lO"34 watt-sec2
The speed of light, c, is
c = 2.99792458 x 108 meters-sec"1
= 2.99792458 x 1017 nm-sec'1
-------
Photon Flux or Radiant Energy Flux Introduction
Thus the energy of a single photon of wavelength A is given by^
" fl>-1.9864775 xlO-»(i) Joule-secnm-sec^
\X/ photon
= 1.9864775 x 10~16(y) joule-photon-1
Broadband, or spectrally integrated radiant energy is
/
i,
and is measured in joules.
Spectral radiant flux is dQ\/dt and is measured in watts-nm l. Broadband
radiant flux, or just radiant flux, would be measured in watts.
Spectral radiant flux density, £>, is radiant flux per area (a) or
* = dQ>
X dadt
and the units are usually watts-m~2-nm-1 or photons-cm-'-sec^-nm"1.
Radiant flux density incident on a surface is called irradiance.
Components of Radiation at the Surface
The radiant flux density outside the earth's atmosphere is called the extraterrestrial
solar irradiance (#*)• One of the most recent estimates of M\ was produced by the
World Radiation Center, Davos, Switzerland, and was reported in Iqbal.4 This
spectrum is shown as the top line of Figure 1.
On their way to the earth's surface, many of the photons incident on the atmo-
sphere undergo multiple scattering and absorption processes (see Figure 2). This
not only partially depletes the radiant energy before it reaches the surface, it also
affects the directional distribution of the photons. Notice that in Figure 2, the shape
of the scattering intensity around aerosol particles is different from that around gas
particles. This shape is a complex function of the aerosol optical properties. The
component of the surface flux that is not scattered or absorbed is called the direct
normal spectral irradiance (that is, the amount of energy, or photons of a given
wavelength, per unit time incident on a unit surface that is perpendicular to the
direct solar beam and coming only from «5° view of sky containing the sun).
-------
Introduction
Photon Flux or Radiant Energy Flux
g
I
«J
2.60
2.40 -
2J20-
2.00-
L80-
L60-
L40
L20-
LOO-
0.80 -
0.60-
0.40-
OJ20-
0.00
World Radiation Center and LICOR 1800
0.3
0* . 0.7 ^ .
_ (Thousands)
Wavelenatn. nm
0.9
1.1
Figure 1. Extraterrestrial and Surface Solar Spectral Irradiance.
Top: World Radiation Center recommended extraterrestrial solar
irradiance, 2-nm resolution 300-700 nm, 10-20 nm resolution 700-
1100 nm; Bottom: Measured surface global irradiance with LiCor
1800 spectroradiometer using 2-nm intervals and 4-n.m resolution.
-------
Photon Flux or Radiant Energy Flux
Introduction
RAYLEIGH - SCATTERED DIFFUSE
AEROSOL-SCATTERED DIFFUSE
CIRCUMSOLAR
RADIATION
Figure 2. Schematic Illustration of Gas and Aerosol Light Scatter-
ing Processes (top). Bottom: Resulting direct and diffuse solar
radiation components. (From Iqbal.4)
-------
Introduction Photon Flux or Radiant Energy Flux
Because many of the photons that are scattered from the direct beam undergo
multiple scattering from gas molecules and aerosol particles, the component that
is scattered can arrive at the surface from a full hemisphere (2?r steradians). This
sky light is called the diffuse spectral spherical irradiance (that is, the amount
of energy per unit time incident on a unit sphere with no view restrictions). The
diffuse spherical irradiance is often divided into downward and upward components.
The combination of direct normal and diffuse spectral spherical irradiance is
called global spectral spherical irradiance (£A)> When the units of $\ are
photons-cm~2-sec~l-nm~1, then the term "actinic flux" is often used. Some re-
searchers have also used "actinic irradiance," "sealer irradiance," or "spherical irra-
diance." Without these qualifiers, the term irradiance generally means radiant flux
on a horizontal, or flat, surface.
The spectral irradiance measured on a cosine response instrument, a so called
"flat" receiver, at solar noon in central North Carolina on a clear day is shown as
the bottom line in Figure 1. Figure 3 shows, in the ultraviolet range (300-400 nm),
an example of the various spectral spherical irradiance quantities described above.
Notice that, at wavelengths less than 370 nm, the diffuse component is larger than
the direct component. This is because Rayleigh scattering is a strong function
(w A~4) of wavelength.
As shown in Figures 2 and 3, not all of the radiant flux is downward. Part of
the diffuse spherical irradiance is caused by the reflection of some of the incident
radiation from surfaces, When the source of the incident radiation is the sun, the
term "albedo" is commonly used instead of reflectance. In the meteorological lit-
erature, reflectance of the earth's atmosphere, as by clouds and air, is also called
albedo.4 In very general simple terms, the albedo (A) may be defined thus:
Radiation reflected from a surface
J\ *^~' •j-ujTuir -...
Radiation incident on a surface
This definition includes the surfaces of aerosols and gas molecules so that, for exam-
ple, if one looks down from a location well above the ground, most of the reflected
radiation is actually from the gas and aerosol below the viewpoint and only partly
from the generally low reflection from the ground below. Of course, the reflected
radiation is itself reflected, and thus multiple scattering produces additional flux
in all directions. Albedo is usually wavelength dependent (spectral albedo, A\),
and the integral, over wavelength, of the flux-weighted spectral albedo is called the
integral albedo or just albedo (shown here without A subscript), that is,
= # A,A, dX
-------
Photon Flux or Radiant Energy Flux
Introduction
Zenith Angle»0
6
a
a
«*
*
0.00
300
320
340 360 380
Wavelength, nm
400
420
Figure 3. Example of Spectral Irradiance Components. Calculated
from Schippnick and Green Fit to Dave Irradiance Model using
World Radiation Center extraterrestial solar irradiance.
-------
Introduction
Photon Flux or Radiant Energy Flux
300
60
W 270
90 E
240'
120
210
150
180
S
Figure 4. Sun's Position in the sky at a location in central North
Carolina For Five Months: a) June 22; b) August 24; c) Sept. 23;
d) October 24, e) Dec. 22. Numbers along top arc are Eastern
Daylight Time.
Because of the sun's apparent motion through the sky, the path length traversed
by photons reaching the surface varies as a function of time of day and location
on the earth's surface. Longer atmospheric paths provide more opportunity for
scattering and absorption. Thus, the relative contributions of diffuse and direct
radiation to global radiation varies as a function of local solar coordinates (zenith
angle). In addition, each "place" has a unique set of daily solar coordinates for each
day of each year. Figure 4 illustrates the approximate solar coordinates for central
NC for selected days in five months.
-------
Radiation Models Introduction
Radiation Models
Radiative transfer models have been developed to predict the global spectral irra-
diance using measured values of M\ and descriptions of the atmospheric absorption
and scattering processes. One such complex model developed by Dave5 was used
by Peterson6 to predict the actinic irradiance at the earth's surface, and at sev-
eral altitudes. This model assumed a cloudless, plane parallel, non-homogeneous
atmosphere. The model atmosphere was divided into 40 layers, and each layer had
unique properties: concentrations of air molecules, water vapor, carbon dioxide, and
ozone; number density of aerosols; and temperature. A monochromatic unidirec-
tional solar flux was incident at the top of the layers, and the surface at the bottom
of the layers was an ideal diffuse reflector with a variable albedo. In each layer, the
attenuated direct solar flux and upward and downward diffuse components were
calculated.
The primary output of the Peterson model was presented as the actinic flux
(units of photons-cm'^sec"1) over 5-nm and 10-nm intervals from 295 nm to 700
nm at 10 zenith angles (x =0°, 10°, 20°, ... 86°) for albedos of 0.0 and 0.05. In
addition, the changes in flux with altitude and albedo of 0.10 were also described.
The actinic flux was predicted to increase with distance above the surface. This
is due not so much to increased absorption of the downward component as it is
to a decrease in the upward component when approaching the ground. That is,
when well above the surface there is a downward directed component, as well as a
significant upward directed component (about 1/3 of total flux) caused by reflection
from the air molecules and aerosols below. At or near the surface the downward
component is about the same at higher up, but the upward component is much
less (about 1/9 of the total flux) because the ground is not as reflective as several
kilometers of air. Near the surface, then, the total spherical flux is lower than
further away from the surface mostly because the upward component is lower near
the surface. Later we will show albedos measured at different altitudes. The higher
altitude albedos were much larger than the surface albedos as would be expected
based on the above description.
Schippnick and Green7 have fitted a series of analytical functions to all five of
the Dave irradiance models and to Peterson's actinic flux model. These functions
use as input: extraterrestrial flux, solar zenith angle, altitude (0 to 5 km), and
surface albedo (0-0.3). They approximate, to a high accuracy, the original computer
simulation outputs allowing for the simultaneous calculation of global irradiance on
a horizontal surface (what meteorological instruments measure) and the actinic
flux, or global spherical irradiance (what a molecule absorbs). This Schippnick and
Green model is used throughout this chapter to produce the various irradiances
-------
Introduction _ Kinetics Parameters
shown. An updating of the actinic flux calculation methods are needed, however,
because the World Radiation Center values for H\ are lower than the values used
by Peterson and newer information is available on aerosol properties which will
affect the calculated actinic fluxes. Because there is no need to compute and match
global irradiance measurements in OZIPM model applications, the original Peterson
fluxes, with their older assumptions of H\ and other gas and aerosol distributions
were used in Chapters 3 and 4 photolytic rate calculations so as to be consistent
with other workers.
Albedo
In his 1976 calculations, Peterson assumed that 0.05 was the "best" albedo in the
UV region. It is important to distinguish between the "regional" albedo, which will
affect the area wide amount of light reflected upward to be scattered back downward,
and the "local" albedo such as the surface under a spherical sensor. The present
literature is not conclusive as to what are reasonable values for albedos in the UV
region, and some satellite data suggests values as high as 0.15. Figure 5 illustrates
the calculated actinic irradiance in the ultraviolet region (295-400 nm) at 0° zenith
angle, at sea level for regional albedos of 0.05 and 0.15. These values probably
represent the range of available photon flux for a primary photolysis reaction at the
earth's surface in this wavelength region.
Kinetics Parameters
In effect, the absorption cross section is "how big an area" the molecule presents
to the photon flux at each wavelength. At a given wavelength, a large cross section
means that the molecule is more likely to absorb a photon, and therefore react.
Depending upon the energy in the absorbed photon, some molecules photo-
disassociate in more than one way. For example, formaldehyde (HCHO) photolysis
can produce different products:
HCHO -**-* H2 + CO (2)
HCHO -^ H + HCO (3)
The quantum yield for a process is the ratio of the number of molecules that react
by a given path to the number of molecules absorbing photons in the wavelength
interval. For HCHO there would be two quantum yields, one for process (2) and one
for process (3). Of course, the quantum yield for a given process or the combined
quantum yields for all processes for a particular species cannot be greater than 1.0.
A quantum yield of zero means that, although the molecule may absorb photons at
10
-------
Kinetic* Pmmtten
Introduction
8
a
7
d
CM
6
o
s
.8
0.30
OJ28
OJ86
024
0.22-
OJ80-
0.18 -
046-
WRC ET, ZA-0, Ait-0. Albgdo=0.05i 045
OJ2-
040-
0.08-
0.06 -
0.04-
0.02 -
0.00
300 320 340 360 380 400
Wavelength, nm
420
Figure 5. Theoretical Actinic or Spherical Irradiance at the Surface
for Two Albedos.
11
-------
Introduction Example Calculation
the given wavelength, it does not undergo the given process. The quantum yield is
dimensioftless.
The absorption cross sections and quantum yields for a species must be mea-
sured in carefully controlled laboratory situations; they cannot be calculated theo-
retically. Newer measurements using better instruments have improved the accuracy
and precision for these data and have resulted in a series of changes in calculated
rates over the last 10 years. Evaluations of the experimental measurements have
been published by various groups, such as NASA,* which recommend values for use
primarily in stratospheric modeling. Sometimes, where there is some uncertainty,
the absolute values of absorption cross sections have been estimated by "fits" to
smog chamber experiments. That is, the measured values are used to define the
relative spectral response, but the absolute magnitudes are scaled up or down as
needed to fit model predictions to data.
Example Calculation
In this example, the actinic flux values are based on the WRC M\ with a wavelength
interval of 2 nm, centered at 300, 302, 304, .... Thus the a\ and $* values for
each species must be averaged over the same 2 nm interval so that the area under
the product curve will be correctly approximated. When this averaging is done,
the integration operation in Equation 1 can be replaced by a summation over all
the 2 nm intervals in which the product of the three components is not zero. For
nitrogen dioxide (NO]), for example:
420 _
J(x,y,^;No2)= £ XA(x,y,A)AA y = 0, A = 0.05. Figure 6 shows the same process
in graphical form.
Some type of solar location program (astronomical almanac) is used to predict
the zenith angle of the sun as a function of time for the particular location and
day of the year. These predicted zenith angles are used to interpolate the species
photolytic rates.
OZIPM Methods
Tables of Peterson's surface "actinic flux" as a function of wavelength and zenith
angle for an albedo of 0.05 were incorporated as built-in data in the original OZIPP
12
-------
OZIPM Methods Introduction
Table 1. Calculation of Nitrogen Dioxide Photolysis Rate for Zenith
^-Angle = 0°, altitude = 0 m, and albedo = 0.05.
dJ/dX*
300
302
304
306
308
310
312
314
316
318
320
322
324
402
404
406
408
410
412
414
416
418
420
0.0016
0.0035
0.0063
0.0110
0.0162
0.0227
0.0315
0.0390
0.0459
0.0510
0.0575
0.0597
0.0590
0.2277
0.2182
0.2160
0.2213
0.2293
0.2351
0.2366
0.2394
0.2363
0.2415
2i
1.0685
1.1700
1.1700
1.4150
1.6600
1.7100
1.7600
1.7600
2.0050
2.2500
2.3950
2.5400
2.5400
6.7600
6.7600
6.5400
6.3200
6.0450
5.7700
5.7700
5.5850
5.4000
5.4500
imxl
* dJ/dX column has been
dj
dX
/ 1017 photon
1.0000
0.9976
0.9953
0.9929
0.9906
0.9882
0.9859
0.9835
0.9812
0.9788
0.9765
0.9741
0.9718
0.5650
0.4050
0.2875
0.1900
0.1375
0.0914
0.0743
0.0572
0.0401
0.0230
3&dJ/dX =
multiplied by
>\ /10-19cm2\ _.
0.0171
0.0409
0.0734
0.1546
0.2664
0.3836
0.5466
0.6751
0.9030
1.1232
1.3447
1.4771
1.4563
8.6968
5.9739
4.0613
2.6574
1.9059
1.2404
1.0146
0.7648
0.5114
0.3027
0.4419
min
1000
Vcm2-min-nmy V molecule ) """ ""*
13
-------
Introduction
OZIPM M.thodi
CM
O
55
C
O
O
w
1 S 5 1
I—•«•
§ § i
«—01
'!
S 1 52 S S S I § I
*
I!
ill
n*v( *M«*IM
Figure 6. Calculation of Nitrogen Dioxide Photolysis Rate Using
World Radiation Center 2-nm Extraterrestrial Spectrum, Albedo
of 0.05, and Zenith Angle = 0°.
14
-------
Spectral Distribution of Rates Introduction
and OZIPM2 computer code. Similarly, species cross sections and quantum yields
were alscrincluded as built-in data in OZIPP and OZIPM2. At the beginning
of a simulation, these programs would calculate the species photolytic rates as a
function of zenith angle and subsequently would interpolate these for the particular
zenith angle needed at the time in the simulation. In the OZIPM3/4 code, the first
step—calculation of species photolysis rate as a function of zenith angle—has been
eliminated along with the built-in data for actinic flux and species cross sections and
quantum yields. Instead, each species photolysis rate as a function of zenith angle
is stored as built-in data. These were computed external to OZIPM3/4 using the
method that was in OZIPM2, that is, using Peterson's actinic flux and up-to-date
species cross sections and quantum yields. In OZIPM3/4, the user can also supply
species photolysis rates as a function of zenith angle as part of his input, and thus
override the built-in information.
Spectral Distribution of Rates
In the Carbon Bond Mechanisms, the most important photoacceptor species are:
nitrogen dioxide (NO}), formaldehyde (HCHO), ozone (0$) photolyzing to atomic
oxygen (Olr>), and acetaldehyde (RCHO). As described above, HCHO has two path
ways: one to radicals (HCHO,R) and one to stable products (HCHO,S).
Using the actinic flux of Figure 5 (zenith angle of 0°) and currently recom-
mended species cross sections and quantum yields, the relative, spectral photolysis
rates (averaged over 10 nm intervals) of the four most important processes are
shown in Figure 7 (the area under each species curve is scaled to unity). Acetalde-
hyde's rate is much less than HCHO, but its wavelength dependency is very similar
to HCHO,R. In addition, the relative spectral response of the Eppley UV sensor is
included. This sensor is commonly used in field measurements and is used by the
University of North Carolina (UNC), SAI, and University of California at Riverside
(UCR) modeling groups to derive or adjust theoretical photolysis rates for simulat-
ing experiments in the UNC and outdoor UCR chambers. The figure shows that
the sensor only covers a part of the total actinic spectrum. The sensor's response
is especially low at the short wavelengths where most of the photolysis of O3 and
HCHO,R occurs.
As shown in Figure 7, NOj has a broad photolysis spectrum, extending into the
visible range (410 nm). O3 has a very sharp photolysis spectrum, with more than
half of the photolysis occurring in the interval 305-315 nm. This shorter end of the
spectrum is more affected by path length (more scattering) and thus the photolysis
rate of O3 will decrease faster with increasing zenith angle than will that of NO2.
15
-------
Introduction
Sp«ctr«l Distribution of R«t««
CO
o
c
"o
o
Figure 7. Relative Spectral Photolysis Rates.
16
-------
Spectral Distribution of Rates Introduction
HCHO shows a broader photolysis spectrum than O3, and the rate is split between
the two processes that produce stable and radical products. The radical process for
HCHO is a very important source of radicals in all mechanisms.
17
-------
2
Review of Calculated Rates
In this discussion, the photolytic rate data are presented as tables of rates vs. solar
zenith angle. Because Whitten also used the ratio of each rate to the NO} rate, these
ratio values are included (across the bottom of the tables) for comparison, but only
at a zenith angle of zero. Table 2 explains the headings used in these tables. All
of the rates used in all EPA models discussed in this report appear in Table 3,
including the values recommended in this report. A few of these tables will appear
again in later chapters as their method of calculation is explained.
Effects of Changes in Cross Section and Quantum Yield
The first set of theoretical rates used in EPA models were those of Schere and
Demerjian, 1977* (See Table 3, heading Schere77). These rates were based upon the
radiation model results of Peterson and the absorption cross sections and quantum
yields as they were known at the time. The absorption cross section for NOj changed
just as the report was being finished. An addendum was included giving the new
rates calculated with the new absorption cross sections. The old rates compared to
the new rates are shown to the right of the Schere77 table. This change subsequently
caused problems in the photolytic rates incorporated into the OZIPP program code,
and these will be discussed below.
The Demerjian, Schere, and Peterson 1980 report,10 was a major revision of the
1977 work. In addition to using revised cross sections and quantum yield values,
this work examined the effect of altitude and albedo on rates. The sea level rates
are given in the Table 3, under the heading DemerSO. The rates at various altitudes
will be discussed later.
Carter's tt a/, final 1986 report11 on the new surrogate species mechanism used
reviewed information on cross sections and quantum yields as of February, 1986,
18
-------
Effects of Changes in Cross Section and Quantum Yield
Review of Calculated Rates
Table 2 Definitions of Headings used in Photolytic Rate Tables.
Sch«r«77 The rates calculated by Schere and Demerjian in "Calculation of
Selected Photolytic Rate Constants over a Diurnal Range," EPA-
600/4-77-015, 1977.
DcaerSO The rates calculated by Demerjian, Schere, and Peterson in "The-
oretical Estimates of Actinic Flux and Photolytic Rate Constants
for Atmospheric Species in the Lower Troposphere," Adv. Environ.
Sci. TechnoL, 29, 1980.
CBS.84 The rates calculated by Killus and Whitten in "Technical Discus-
sions Relating To the Use of Carbon Bond Mechanism in OZIPM/
EKMA," EPA-450/4-84-009,1984.
Cart«r86,8urf The rates calculated by Carter, Lurmann, Atkinson, and Lloyd in
"Development and Testing of a Surrogate Species Chemical Reac^
tion Mechanism," Final Report, EPA Contract 68-02-4104, 1986.
VhittmiM.sur* The rates calculated by Whitten in "Using CBM-X in EKMA with
Computer Code OZIPM-3"; these surface rates were not explicitly
described in the report but were determined by back calculating
from the altitude corrected values that were used in the final re-
port.
Vhitttn86,600B The rates calculated by Whitten in "Using CBM-X in EKMA with
Computer Code OZIPM-3" after altitude corrections were applied
to the surface rates.
CB4.8urf .A-0.08 The rates recommended in this document.
CB4.640a.A-0.08 The rates recommended in this document.
ZA Zenith angle.
J(N02) Photolysis rate for NOj in units of min"1.
J(FR) Photolysis rate for HCHO to radicals in units of 1 x 10~s min"1.
Photolysis rate for HCHO to stable products in units of 1 x 10~3 min"1.
Photolysis rate for CARB to radicals in units of 1 x 10~3 min"1. See text for
CARB composition.
J(C8) Photolysis rate for CARB to stable products in units of 1 x 10~3 min"1.
J(01D) Photolysis rate for Os to OlD in units of 1 x 10~3 min"1.
J(CCHO) Photolysis rate for acetaldehyde to radicals in units of 1 x 10~3 min"1.
J(FS)
J(CR)
19
-------
Review of Calculated Rates
Effects of Changes in Cross Section and Quantum Yield
Table 3. Theoretical Rates. Used in EPA Models.
"(all rates and ratios except NO2 have been mul
(all rates used A = 0.05 except those mark<
ZA
0
10
20
30
40
SO
60
70
78
86
ZA
0
10
20
30
40
BO
60
70
78
86
J(N02)
0.5129
0.5087
0.4963
0.4741
0.4395
0.3880
0.3168
0.2058
0.1014
0.0221
1.00
JCN02)
0.5326
0.5282
0.5159
0.4922
0.4562
0.4026
0.3287
0.2132
0.1050
0.0229
J(FR) J(FS)
2.14
2.11
2.01
1.85
1.61
1.30
0.92
0.49
0.20
0.04
5.60
5.53
5.33
4.98
4.45
3.73
2.84
1.62
0.72
0.15
4.17 10.92
J(Pt) J(F8)
2.23
2.20
2.09
1.90
1.62
1.27
0.86
0.43
0.16
0.03
2.96
2.92
2.81
2.61
2.32
1.92
1.41
0.80
0.34
0.07
J(010)
4.210
4.110
3.730
3.160
2.420
1.610
0.840
0.280
0.060
0.007
8.21
J(OID)
2.710
2.630
2.360
1.960
1.460
0.930
0.470
0.150
0.030
0.003
Itiplied by 1000)
;d otherwise)
Old
J(N02)
0.5784
0.5736
0.5595
0.5343
0.4950
0.4367
0.3562
0.2309
0.1109
0.0244
1.00 4.19 5.66 5.09
20
-------
Effects of Changes in Cross Section and Quantum Yield
Review of Calculated Rates
Table 3, cont. Theoretical
"•(all rates and ratios except NO
ZA
0
10
20
30
40
50
60
70
T8
86
ZA
0
10
20
30
40
SO
60
70
78
86
J(N02)
0.4505
0.4559
0.4445
0.4245
0.3034
0.3472
0.2708
0.1840
0.0007
0.0104
1.00
J(N02)
0.5120
0.5087
0.4073
0.4741
0.4305
0.3880
0.3168
0.2058
0.1014
0.0221
J(FR)
1.81
1.70
1.70
1.54
1.32
1.04
0.71
0.36
0.14
0.02
3.05
1 Rates
2 have b
rter86 . £
J(FS)
2.78
2.75
2.65
2.47
2.21
1.84
1.37
0.70
0.35
0.07
6.05
-Vhitt«n86,8urf-
J(PR)
1.30
1.37
1.30
1.18
1.00
0.78
0.52
0.26
0.10
0.02
J(FS)
1.03
1.91
1.84
1.71
1.52
1.27
0.05
0.53
0.23
0.05
Used in EPA Models.
>een multiplied by 1000)
> ILEX
J(01D)
2.267
2.107
1.970
1.634
1.217
0.775
0.380
0.110
0.028
0.003
4.03
J(01D)
2.390
2.310
2.060
1.670
1.220
0.745
0.352
0.098
0.021
0.002
J(CCHO)
0.292
0.286
0.265
0.230
0.186
0.133
0.078
0.032
0.010
0.002
0.63
1.00 2.71
3.76
4.66
21
-------
Review of Calculated Rates
Effects of Changes in Cross Section and Quantum Yield
Table 3, cont. Theoretical Rates Used in EPA Models.
"(all rates and ratios except NOj have been multiplied by 1000)
ZA
0
10
20
30
40
SO
60
70
80
86
ZA
0
10
20
30
40
50
60
70
80
86
J(N02)
O.S129
0.5087
0.4073
0.4741
0.4395
0.3880
0.3168
0.2058
0.1014
0.0221
1.00
J(N02)
0.6000
0.5952
0.5856
0.5642
0.5318
0.4851
0.4087
0.2882
0.1552
0.0348
J(FR)
1.74
1.71
1.64
1.49
1.30
1.05
0.74
0.40
0.16
0.03
3.39
,ot
J(FS)
2.06
2.05
1.97
1.83
1.65
1.38
1.05
0.60
0.26
0.06
4.02
-Vhitt«n86,600B-
J(FE)
1.79
1.79
1.68
1.54
1.33
1.07
0.74
0.40
0.16
0.03
J(FS)
2.39
2.39
2.29
2.15
1.95
1.68
1.30
0.79
0.38
0.08
J(01D)
2.390
2.310
2.060
1.670
1.220
0.745
0.352
0.098
0.021
0.002
4.66
J(01D)
3.240
3.150
2.820
2.310
1.710
1.080
0.530
0.160
0.040
0.005
1.00 2.98
3.98
5.40
22
-------
Effects of Changes in Cro»« Section and Quantum Yield
Review of Calculated Rates
Table 3, cont. Theoretical
"(all rates and ratios except NO
ZA
0
10
20
30
40
50
60
70
78
86
ZA
0
10
20
30
40
50
60
70
78
86
J(N02)
0.5358
0.5312
0.5166
0.4911
0.4524
0.3960
0.3184
0.2094
0.1025
0.0196
1.00
J0102)
0.5893
0.5851
0.5713
0.5470
0.5093
0.4537
0.3740
0.2578
0.1341
0.0242
J(FR)
1.89
1.85
1.76
1.59
1.36
1.06
0.71
0.36
0.14
0.04
3.53
J(FR)
2.18
2.14
2.04
1.86
1.60
1.27
0.87
0.45
0.17
0.04
1 Rate
2 have
.Surf.
J(FS)
2.98
2.94
2.83
2.63
2.34
1.95
1.44
0.83
0.37
0.10
5.56
.640m.
J(FS)
3.39
3.35
3.24
3.03
2.72
2.30
1.73
1.03
0.47
0.13
s Used in EPA Models.
j been multiplied by 1000)
»
A^U • UO
J(01D)
2.310
2.232
2.003
1.650
1.216
0.764
0.371
0.113
0.024
0.003
4.31
J(01D)
2.715
2.620
2.362
1.962
1.463
0.944
0.462
0.140
0.030
0.003
J(CCHO)
0.301
0.294
0.272
0.236
0.189
0.134
0.079
0.032
0.010
0.002
0.56
J(CCHO)
0.347
0.338
0.314
0.275
0.222
0.161
0.096
0.041
0.012
0.002
1.00 3.70 6.75 4.61
0.59
23
-------
Review of Calculated Ratea Effects of Changes in Cross Section and Quantum Yield
including corrections for errors that occurred in the printing of some previous re-
views of photolysis rates (personal communication from Carter, 1986). Photolytic
rates calculated from the cross sections and quantum yields used by Carter et al.
and the Peterson 1976 actinic fluxes are shown in the Table 3, under the heading
Carter86. These rates were calculated by his program which assumes that all input
values were points connected by straight lines, even though HCHO data, for example,
were given as IQ-nm interval averages centered at the wavelength. The NO2 cross
sections and quantum yields used by Carter are the same as those recommended
by Atkinson and Lloyd in their 1984 review.12 The NC>2 absorption cross sections
were the same as those used in the Schere77 addendum (Bass et al. data), and these
are still the recommended values in the latest NASA review.8 The quantum yields
used in the 1977 work, the 1980 work, and in Carter's work were different, however.
The CB3.84 values were described in Killus and Whit ten's 1984 technical discus-
sion document" on the OZIPM2 program. The values in Table 3, however, were
extracted from the computer code and the CARB rates have been converted back to
HCHO rates. This rates will be described in detail in the next section.
The Whitten86.Surf values in Table 3 were calculated by us using information in
the final report* "Using CBM-X in EKMA with Computer Code OZIPM-3" and
in the computer code. These values do not actually appear in the final report, but
are the basis of the altitude adjusted values that were recommended. The altitude
adjusted rates are given in the table headed Whitten86.600m in Table 3. The latter
two tables should be compared with the table headed CB3.84 in Table 3.
A recent (November 1986) intercomparison of photolytic rates was conducted
by Jeffries (UNC) among Schere (EPA), Carter (UCR), Lunnann (ERT), Whitten
and Gery (SAI) to establish a uniform treatment and to agree on sources of cross
sections and quantum yields for use in model testing. NASA8 was the source for
NO}, HCHO, and Os. Carter et al.11 was the source for CH3CHO. These cross sections
and quantum yields were integrated (depending upon whether the original values
were point values or interval averages) and re-interpolated to 5-nm interval averaged
values for use with Peterson's surface actinic flux data. The 5-nm interval averaged
cross sections and quantum yields are given in Table 4.
The data in Table 4 were used with Peterson's surface flux, an albedo correc-
tion, and ratios of 640 meter photolysis rates to surface photolysis rates from the
Demerjian et al. 1980 report to calculate the rates recommended in this report.
The exact process will be described in Chapter 4. The resulting rates are given in
Table 3 with the headings CB4.Surf.A=0.08 and CB4.640m.A=0.08.
24
-------
Values Calculated For Carbon Bond III in OZIPM2 Review of Calculated Rates
Figure 8 compares four species rates from these studies. Figure 9 compares the
quantum yields for NOj used in the OemerSO calculation and in the Carter86 calculation.
The different $> assumptions were responsible for the differences in the NO2 rates
shown in Figured.
Values Calculated For Carbon Bond III in OZIPM2
In the previous "Technical Discussions Relating To the Use of Carbon Bond Mech-
anism in OZIPM/EKMA,"13 Killus and Whitten describe the calculation of photol-
ysis rates for CBS in the OZIPM2 model. The method differed somewhat from the
procedure described in the introduction above.
Because OZIPM2 still had the Dodge Mechanism as the built-in default mech-
anism, the built-in photolysis data had to be applicable to that mechanism. Thus
the photolytic data stored in OZIPM2 were the Peterson 1976 actinic flux and the
Schere and Demerjian 1977 cross sections and quantum yields. In effect the values
shown in Table 3, heading Schere77 were the rate constants built into the program.
At the time Carbon Bond III was implemented in OZIPM2, significant changes
had occurred in the cross sections and quantum yield values compared to the ones
used in the Dodge mechanism, and thus the program calculated photolysis rates
had to be corrected. In addition, the Demerjian, et a/., 1980 study had shown
that photolysis rates should increase with altitude. Because the mixing height in
OZIPM2 often extended to 1500 m in typical applications, Killus and Whitten also
wanted to increase the calculated photolytic rates to account for this altitude effect.
Finally, in the CBS mechanism, carbonyls are combined into a single species
CARB. The characteristics of CARB were based on its approximating a mixture in
photochemical equilibrium with a constant composition:
Species Carbon Fraction
Formaldehyde
Higher Aldehydes
Glyoxal
Ketones
0.55
0.35
0.05
0.05
Thus, another correction factor had to be used to account for the CARB composition.
In Table 12 of the 1984 technical discussion report, the ratio of CARB photolysis to
HCHO photolysis was estimated to be 0.696 for radical product photolysis processes
and 0.65 for stable product photolysis processes. Thus the "true" HCHO radical
25
-------
Review of Calculated Rate*
Value* Calculated For Carbon Bond III in OZIPM2
Table 4. Absorption Cross Sections and Quantum Yields
(erou sections are 10~ cm -molecule~ , ba»« e)
NO2
nm
295-300
300-305
305-310
310-315
315-320
320-325
325-330
330-335
335-340
340-345
345-350
350-355
355-360
360-365
365-370
370-375
375-380
380-385
385-390
390-395
395-400
400-405
405-410
410-415
415-420
420-425
a
10.7
14.1
17.1
20.1
24.0
26.7
28.9
32.2
36.7
39.8
40.9
46.2
48.2
5L5
56.0
53.9
56.7
59.7
59.7
59.5
63.3
65.4
60.5
55.9
54.5
55.0
*
0.982
0.978
0.974
0.970
0.966
0.962
0.958
0.954
0.950
0.946
0.942
0.938
0.934
0.930
0.926
0.922
0.845
0.745
0.793
0.867
0.795
0.552
0.241
0.092
0.045
0.012
HCHO.R'
a
2.62
2.62
2.45
2.45
1.85
1.85
1.76
1.76
1.18
1.18
0.42
0.42
0.06
0.06
*
0.78
0.78
0.77
0.77
0.62
0.62
0.31
0.31
0
0
0
0
0
0
HCHO.S* CH3CHO
a
2.62
2.62
2.45
2.45
1.85
1.85
1.76
1.76
1.18
1.18
0.42
0.42
0.06
0.06
a $
0.22 4.24 0.453
0.22 3.73 0.370
0.23 3.07 0.280
0.23 2.41 0.193
0.38 1.85 0.113
0.38 1.37 0.053
0.69 0.91 0.015
0.69 0.34 0
0.69
0.69
0.40
0.40
0.12
0.12
QlD
a $
55.81 0.900
28.84 0.898
14.98 0.753
7.56 0.311
3.87 0.043
2.02 0
All a and <£ values were averaged over 5-nm intervals except those marked with *, which were
averaged over 10-nm interval* (e.g., 295-305, 305-315), and therefore each of these values appears
twice for the 5-nm averaged actinic flux data (e.g., once for 295-300, once for 300-305).
26
-------
Value* Calculated For Carbon Bond III in OZIPM2
Review of Calculated Rates
<0
OS,
m
"m
51
cu «
09
8s
3^
«d
OS
O
K 5
3 S 3 I 3 § 3 J I 1
-------
Review of Calculated Ratea
Values Calculated For Carbon Bond III in OZIPM2
no
290
~310 ' 330 ' 350 370 ' "'
Wavelength, nxn
390 410 ' 430
Figure 9. Quantum Yields For Nitrogen Dioxide Photolysis.
28
-------
Nitrogen Dioxide Photolysis in CB3/OZ1PM2 Review of Calculated Rates
photolysis rate would be multiplied by 0.696 to account for the composition of
CARB. _
So many corrections increased the likelihood of errors, and some were made in
the final specification of the photolysis rates for CBS used in OZIPM2.
The table headed CB3.84 in Table 3 gives the photolysis rates used by CBS
in OZIPM2. These were computed by using built-in data in the OZIPM2 code.
For discussion purposes, the CBS CARB rate has been converted back into HCHO
radical and stable rates in this table by "un-doing" the CARB composition correction
described above. For example the CARB to radicals rate at x = 0° was 1.21 min"1
in the OZIPM2 program. The rate given in the table headed CBS.84 in Table 3
is 1.74 = 1.21/0.696, which would be the true HCHO,R photolysis rate assumed
by Killus and Whitten. Likewise, the HCHO,S rate in Table 3 was calculated as
2.06 = 1.34/0.65.
Nitrogen Dioxide Photolysis in CB3/OZIPM2
Killus and Whitten consulted the Demerjian tt a/., 1980 report to determine what
the J(NOj) values should be for CBS when used in OZIPM2. The rates listed in the
1980 report at a zenith angle of zero were
y, meters J(0°, y, 0.05; NO2)
0 0.5328
150 0.5652
640 0.6216
In Table 9 of the Technical Discussion report,15 Killus and Whitten indicated that
OZIPM2 computed J(x, 0,0.05; NO]) according to the older cross section data in
the Schere and Demerjian 1977 report which would give a value at x = 0° of 0.5784
min"1. Thus Killus and Whitten assumed that, with no changes, OZIPM2 would
calculate J(NOz) values that were comparable to those for an altitude somewhere
inbetween 150 and 640 meters using the newer data (which would have been about
a 9% increase compared to the ground value). Therefore, no changes were made to
the 1977 NO2 photolysis rates calculated by OZIPM2 for use with CBS.
•
Inspection of the OZIPM2 computer code, however, shows that Killus and Whit-
ten were mistaken about the values built-in to OZIPM2; the values from the adden-
dum for the Schere and Demerjian report were the ones actually used in OZIPM2.
These gave a «7(NO2) value at x = 0° of 0.5129 min~x, less than the ground level
rate in the Demerjian et al., 1980 data and only 89% of the value that SAI thought
they were using.
29
-------
Review of Calculated Rates _ Carbonyl Photolysis in CB3/OZIPM2
Carbonyl Photolysis in CB3/OZIPM2
Comparison of rates in Table 3 and Figure 8 shows that, compared to the rates
stored in the OZIPM2 program, the HCHO rates had decreased significantly by the
time Killus and Whitten were putting CBS into OZIPM2. They showed, in Table 10
of their Technical Discussion/5 that using what they thought was the Schere and
Demerjian 1977 data stored in OZIPM2, gives the ratios
J(0°, 0,0.05; HCHO, R)
J(0°,0,0.05;N02)
J(0°, 0,0.05; HCHO, S)
J(0°,0,0.05;N02)
,
= 9.68 x 10'
Based on their modeling of smog chamber experiments, however, Killus and Whitten
had to use lower rates to obtain good fits, and thus they concluded that better ratios
would be
J(0°,0,0.05; HCHO, R) .
.7(0°, 0,0.05; N02) *''*x™
J(0% 0,0.05; HCHO, S) .
J(0°,0,0.05;N02) = 3'76 X 10
Thus, Killus and Whitten stated that the built-in HCHO photolysis rates in OZIPM2
should be corrected by 2.71/3.7 = 0.73 for radicals and by 3.76/9.68 = 0.37 for sta-
ble products. Although the 0.37 "quantum yield update correction factor" appears
in Table 12 of the Killus and Whitten report," the 0.73 factor appears in the Ta-
ble 12 as 0.78. The actual "quantum yield update correction factor" used, however,
was 0.81 (shown by the final total correction factor being 0.564 which is 0.81 x 0.696,
the CARB to HCHO correction factor from above). Killus and Whitten argue (on page
42 of reference 13) that the difference between the 0.73 and the 0.81 accounts for
the increase in HCHO photolysis rate with height (which would have been about an
11% increase).
The wrong assumption about which set of NO2 rates were built-in to OZIPM2,
however, caused these ratios to be wrong. The actual Schere and Demerjian 1977
data stored in OZIPM2 had the following ratios:
7(0°, 0,0.05; HCHO, R)
J(0°,0,0.05;NO2)
= 4.17 x 10~s
J(0°, 0,0.05; HCHO, 5)
J(0°,0,0.05;N02)
30
X 10
,
-------
Ozone Photolysis in CB3/OZIPM2 Review of Calculated Rates
and the correct "correction factors" would have been 2.71/4.17 = 0.65 for radicals
and 3.76/10.92 = 0.35 for stable products.. Even using 0.81 as the correction factor
instead of the 0.65, however, did not compensate for the difference in the NC>2
photolysis rates, and thus the actual rates used were not at all what was intended.
Comparison of the HCHO photolysis rates plots in Figure 8 shows that, m at-
mospheric applications, CBS in OZIPM2 had what are now known to be low values
of HCHO photolysis rates, and therefore most likely would have a lower atmospheric
reactivity than it should have. It would thus be quite sensitive to 'external' radical
sources, such as NMOC aloft as has been determined in several SIP-like cases.14 This
large sensitivity is probably not correct, because it is most likely an artifact of the
anomalously low HCHO photolysis rates.
A major reason for Killus and Whitten having chosen low ratios for
J(HC«O)/J(NO2) was that these values produced the best fits to a large number of
UNC outdoor smog chamber experiments. Recent measurements of the irradiance
inside and outside the UNC chamber has shown, however, that the Teflon chamber
walls are not 100% transparent in the 300-400 nm region. Further, the interac-
tion between the film transmission and the reflective floor of the chamber results in
the NO] photolysis rate being slightly higher inside the chamber than outside the
chamber, while the HCHO photolysis is lower inside than outside. The best fits are
produced by using the CB4.Surf.A=0.08 values for the atmospheric (outside chamber)
and using a chamber light model that accounts for both the film transmission and
the floor albedo. This model has been described by Jeffries and Sexton.15 Thus,
while the lower HCHO photolysis rates chosen by Killus and Whitten are appro-
priate when simulating the chamber, they are inappropriate when modeling the
atmosphere.
Ozone Photolysis in CB3/OZIPM2
Killus and Whitten applied a large correction factor to the O3 photolysis rate built-
in to OZIPM2. Part of the correction was due to changes in the cross section data
reported by Demerjian et a/., 1980, but a further correction was made to reduce the
photolysis rate based on some atmospheric measurements. The final correction was
0.53 times the Schere and Demerjian 1977 rates. This resulted in rates that were
slightly higher (6%) than the surface rates calculated by Carter et a/., in 1986.
31
-------
Review of Calculated Ratea How CB3/OZIPM2 Rates Influenced CB4/OZIPM3/4 Rates
How CB3/OZIPM2 Rates Influenced CB4/OZIPM3/4 Rates
The base set of values used to calculate the CB4 photolytic rates recommended by
Whitten in his final report1 are listed under the heading Whitten86.Surf in Table 3. By
comparing these'with the CB3.84 rates and with the values of J(HCHO)/ J(NO2) (e.g.,
2.71 and 3.76) described by Killus and Whitten in their Technical Discussion report,
you can see that the errors made in the earlier work were carried forward. Thus
the values recommended by Whitten in his 1986 report depended upon the Schere77
NO; rates, upon the empirically determined value of HCHO-to-NO; photolysis rates
for inside the UNC chamber, and upon the ratio-adjusted Schere77 ozone photolytic
rates. Because the ultimate recommendations, the values listed under Whitten86.600m
in Table 3, incorporated a new altitude correct not used in CB3/OZIPM2, the
actual sources of the recommended rates were hard to determine. The final report
recommendations were simply the values listed under Whitten86.Surf corrected to a
higher altitude. So while the final recommended values were similar to the values
recommended in this report, the technical support for the recommendations were
lacking..
Affect of Altitude on Photolysis Rates
As indicated above, the Demerjian it al. 1980 study computed rates as a function
of altitude and showed large increases (factors up to 1.5 times the surface rate).
Because the mixing height often extends to 1500 meters in OZIPM3/4 applications,
the photolytic rates should be increased above the surface values. We will assume
that the rates at 640 meters can- serve as approximate average rates for a 0-1500
meter mixing depth. Table 5 gives the NO} rates computed by Demerjian et al.
1980 for 0, 640, and 1380 meters. We will assume that the relative ratios of these
values reflect the altitude effect and that these ratios can be used to adjust surface
computed rates using somewhat different assumptions of o\, and $>. Thus Table 5
includes, at the bottom, the ratio of the 640 m rate to the surface (0 m) rate when
the ground albedo is 0.05. Whitten used these ratios and the values in Whitten86.Surf
to compute Whitten86,600m, e.g., 0.5129 x 1.17 = 0.6001. We will perform a similar
adjustment for our recommended rates later in Chapter 4.
32
-------
Affect of Altitude on Photolysis Rates Review of Calculated Rates
Table 5 Nitrogen Dioxide I
ZA
0
10
20
30
40
so
60
70
78
86
J(N02)0
0.5326
0.5282
0.5159
0.4922
0.4562
0.4026
0.3287
0.2132
0.1050
0.0229
'hotolysis ]
Demer80-Al1
J(N02)640
0.6216
0.6180
0.6072
0.5868
0.5538
0.5028
0.4236
0.3000
0.1602
0.0312
Elate as a Function of Altitude.
L j 4»«dlA«i _«»_ _
b IbUaG* "" " ~~
J(N02)1380
0.6834
0.6678
0.6576
0.6384
0.6072
0.5568
0.4770
0.3486
0.1962
0.0372
1.00 1.17 1.28
—Ratio 640 to 0 a. A-0.06-
ZA N02 HCHOR HCH08 010
0
10
20
30
40
50
60
70
78
86
1.17
1.17
1.20
1.20
1.21
1.25
1.29
1.40
1.53
1.37
1.28
1.28
1.29
1.31
1.33
1.37
1.42
1.49
1.52
1.50
1.24
1.24
1.25.
1.27
1.29
1.32
1.37
1.44
1.49
1.45
1.36
1.35
1.38
1.39
1.42
1.46
1.51
1.58
1.67
1.00
33
-------
3
Atmospheric Rates
Measurements of Nitrogen Dioxide Photolysis Rates
A number of measurements of the atmospheric photolysis rate of NOj have been con-
ducted.16'17'18'19'20 Two sets of measurements, for example, are shown in Figure 10
from the Harvey, Steadman, Chameides work in 1977. The j\ refers to the mea-
sured NO] photolysis rates using a quartz flow reactor, and the Eppley UV values
were measured with the same type instrument as used at UNC. The points are the
measured values, the line were computed by Harvey et al. using 1977 theory and are
not relevant here. You should notice that the maximum measured ./(NO?) photolysis
rates are greater than the theoretically calculated maximum NOj photolysis rate at a
zenith angle of (f given the presently accepted cross sections and quantum yields of
Table 4 and the Peterson actinic flux at A = 0.05. That is, using the "best" values
of ^(NOj) and $A(NOJ) and the Peterson actinic irradiances for "best case" albedo,
the predicted maximum value is 0.503 min""1, compared with a measured value of
about 0.54-0.55 min"1. Thus measurements are about 1,1 times larger than theory.
Parrish et al. conducted an NO} actinometry study in Colorado19 in 1983. They
could fit their clear sky values with an equation of the form
j(NOz)= 0.7830 e-OS60"ex min-1 (5)
and all clear sky measurements fell within ±7% of this equation. This equation
predicts a x = 0° value of 0.5463 min"1, in close agreement with that shown in
Figure 10 for Michigan, but also larger than values predicted by present theory.
Comparison of Theory and Measurement for Trradiance
There are only three items that can be adjusted in the theory to improve its agree-
ment with NO} actinometry measurements: actinic flux, absorption cross sections,
and quantum yields.
34
-------
Companion of Theory and Measurement for Irradiance
Atmospheric Rates
E
o
s: 4
UJ
0.2
0.4
[mirr1]
UJ
•r 0
s
+ 30
f 455
UJ
M
.. so,
0.6
90
l corr*l«t<«« MMM Ewl«r U»
Jf for i elxr t«y. Oiu
•r* ft«m ««ui uw M>f*» nolui 41151« MISI»K far cut
• SUNRISE TO 8<30 AJvL clear
• 8>30 AM. TO II-3O AM, portly doudy
A ll<30 AM. TO 1-30 RM. ovwccnt
I 3
t£
5 2
a.
o.
UJ I
at 0.2
O.3 0.4 O.5
jt [min-i]
0.6
Figure 10. Examples of Measured Atmospheric Rates of Nitrogen
Dioxide Photolysis.
35
-------
Atmospheric Ratea _ UV Albedo
The NOj cross section values in current use were obtained by JBass et al.,21 with a
resolution-of 0.125 nm and an estimated absolute accuracy of ±10%. These values
were generally confirmed in the range 375-420 nm by Harkner et al.,22 who also
established the quantum yield with a resolution of 1 nm in this same range. The
low $> values reported by Harkner et al. for A > 375 nm have been confirmed by
Davenport.23 Thus, while these factors may yet change with new measurements,
there is no evidence for making ad hoc adjustments in these kinetic values, and we
will continue to use the values as recommended by the NASA review.8
We have recently compared calculated global irradiance (300-420 nm region)
with computerized spectroradiometer global irradiance measurements. The calcu-
lated values were produced by the Schippnick and Green7 fits to the Dave spectral
irradiance model and to the Peterson actinic flux model. We updated the ex-
traterrestrial flux to the World Radiation Center 2-nm flux. We found excellent
agreement over a zenith angle range of 14-80°. Examples of model predictions and
measurements from shortly after sunrise to solar noon are shown in Figure 11.
As was shown in Figure 3, however, actinic flux, or spherical irradiance, has
a significant upward component that is not sensed by an upward looking, cosine
response (flat) receiver such as the spectroradiometer or Eppley UV meter. The
downward scattering of this upward component has little effect on the flat, upward
looking sensor, but as shown in Figure 12, an increase in surface albedo from 0.05
to 0.15 can have a large effect (22% increase) on global actinic irradiance while it
only effects the global horizontal irradiance a small amount (< 2% increase). So the
fact that the horizontal irradiance model can fit horizontal irradiance measurements
still leaves the possibility that the regional albedo, or its impact on actinic flux may
not be correctly represented in the Peterson "best estimate surface albedo" actinic
flux data set.
UV Albedo
The present literature on ultraviolet albedo is not conclusive as to what are reason-
able values for the "regional" albedo that should be used in the radiation transfer
model calculations. Few spectrally resolved albedo values are available. Peterson
used measured data from Coulson and Reynolds74 to arrive at the spectral albe-
dos shown in Table 6. Much of the literature only discusses the integral albedo,
that is, the spectrally-weighted or "broadband" values. Using the solar spectrum
in Figure 1, and the equation
36
-------
UV Albedo
Atmospheric Rate*
33
332333
532233333-33533333:
ssgssssssssss
s
?
Figure H. Comparison of Schippnick and Green Fit to Dave Radi-
ation Model With LiCor 1800 Spectroradiometer Measurements,
2-nm intervals, 4-nm resolution.
37
-------
Atmospheric Rate*
UV Albedo
a
a
a
8
2.40
Zenith Angle«0
340 360 380
Wavelength, nxn
400
420
Figure 12. Comparison of Horizontal and Spherical Irradiance at
Two Albedos.
38
-------
UV Albedo Atmospheric Rates
we can calculate the integral albedo that matches Peterson's assumptions. By
keeping Peterson's distribution assumptions as given in Table 6, but increasing the
magnitudes uniformly, we can estimate both "broadband" or spectrally averaged
albedo(A) and UV albedo (e.g., A^o)- For example,
increase A A&Q
1.0 0.11 0.05
1.4 0.15 0.07
1.6 0.17 0.08
2.0 0.22 0.10
Dickerson et al.18 reported albedos measured with the Eppley UV radiometer
for various surfaces and from aircraft flights equipped with an upward and down-
ward looking Eppley UV radiometer system. These are reported in Table 7. Doda
and Green25'26 also measured UV reflectances from airplanes. These researchers
extrapolated their altitude data to the surface and estimated surface reflectivity.
Some of their measurements are presented in Table 8. The Doda and Green values
for pine forest are a factor of three lower than Dickerson's values for rain forest at
the same altitude.
King and Herman27 and King28 calculated ground albedo from a statistical
fit using empirically determined ratios of direct to diffuse light at a number of
wavelengths. They determined a mean ground albedo of 0.279 at wavelengths of
521 and 670 nm for an area near the center of the city of Tucson AZ. This is
significantly higher than the 0.10 value at 520 nm and the 0.15 value at 670 nm
assumed in the Demerjian et al. 1980 study (see Table 6) suggesting that the values
should be increased by nearly a factor of two.
Satellite data29 indicate that the minimum integral albedo (200-4000 nm) over
the U.S. is about 1.4 times higher than the 0.11 calculated from Demerjian et
al. assumed values. The whole U.S. (except for the Western deserts which have
minimum albedos of > 0.20) has a minimum measured integral albedo of 0.15-0.20.
Otterman and Fraser*0 used models of the scattering properties of the atmospheric
aerosols and LANDSAT data for the southwest U.S. to calculate surface albedos of
0.264 in the region 500-600 nm with little sensitivity to the aerosol model assumed.
This value is consistent with the values found by King, and reported by the NIMBUS
3 data29 again suggesting that larger albedo values should be used in the photolytic
rate calculations.
Using data from another satellite, the Atmosphere Explorer-E, Frederick and
Abfams31 also used a numerical model of radiative transfer, including multiple
39
-------
Atmospheric Rate« UV Albedo
Table 6. Albedo Values Assumed by Peterson.
A albedo
290-400
400-450
450-500
500-550
550-600
600-640
640-660
660-700
0.05
0.06
0.08
0.10
0.11
0.12
0.13
0.15
Table 7, a. Surface Albedo Values Measured by
Dickerson et a/., using Eppley UV Radiometer.
surface
grass
black cloth
white plywood
road surface
cement
albedo
0.01
0.02
0.07
0.07-0.09
0.17
Table 7, b. Near Surface Albedo Values Measured
by Dickerson et al. Using Modified Eppley UV Radiome-
ter.
surface altitude, km. albedo
rain forest 0.05-0.30 0.06-0.18
high plains 0.3 0.12
2.9 0.33
40
-------
Adjustment of Calculated Actinic Flux for Albedo Atmospheric Rates
Table 8. UV Albedo Values Measured by Doda and Green.
surface altitude, km. albedo
- pine forest
desert sand,
w. Texas
gypsum sand,
White Sands NM
0.0-0.33
0.0-0.33
0.0-0.33
0.02-0.04
0.05-0.07
0.16-0.19 (300 nm)
0.53-0.60 (400 nm)
scattering and surface reflection to calculate the distribution of albedo at two wave-
lengths, 331.2 and 339.8 nm. There were 7421 measurements; 69% produced albedo
values less than 0.30 and higher values were interpreted to include reflection from
clouds. Eleven percent of the albedo values were between 0.0 and 0.10, 29% were
between 0.10 and 0.20, and 20% were between 0.20 and 0.30. As expected, there
was no systematic variation of albedo with zenith angle.
Based on such recent evidence, other newer radiation models have used regional
UV albedos of » 0.15 (see for example Logan et al.32).
We will therefore multiply the values in Table 6 by 1.6 to obtain integral or
"broadband" albedo of 0.17 and a UV albedo of 0.08. The value 0.08 will be used
to adjust the actinic flux before photolytic rate calculations are performed in the
rest of this report.
Adjustment of Calculated Actinic Flux for Albedo
Information is supplied in the Demerjian et al. 1980 study to estimate the effect of
albedo changes up to 0.20. Demerjian et al. give a table of increases in actinic flux
as a function of wavelength and zenith angle as albedo was increased from 0 to 0.10.
They state that the changes were approximately linear with albedo. We have used
this table to produce an albedo enhancement factor as a function of A and \. These
factors are used to adjust the spectral actinic irradiance when computing rates.
If we apply a "regional" albedo correction to the Peterson actinic flux (that is,
increase the albedo from 0.05 to 0.08), then surface NO2 photolysis rates computed
from a\ and $\ in Table 4 are in much better agreement with Parrish et al. at-
mospheric measurements. Computed values are given in Table 9 and are shown in
Figure 13. The values in Table 9 that are under the heading 'Fit to Observations'
are predicted from Equation 5. The bottom line in Figure 13 shows (and the first
column of Table 9 gives) the values predicted from theory using the Peterson actinic
41
-------
Atmospheric Rates Adjustment of Calculated Actinic Flux for Albedo
fluxes and current cross sections and quantum yields. The second column (and the
next higher line in Figure 13) is the result of assuming a "regional albedo" of 0.08
rather than 0.05 in the standard flux calculations. The third column is the result
of applying the "site specific" corrections calculated by Parrish for his particular
location (e.g., elevation, aerosols, and total column 0$). The last column shows that
the fitted observations and the theory agree to within about 2% for small zenith
angles and within about 5% for large zenith angle where the site corrections are
quite large.
42
-------
Adjustment of Calculated Actinic Flux for Albedo
Atmospheric Rates
Table 9. Comparison of Higher Albedo Calculated Photolysis Rates
^_with Atmospheric Measurements. .
Effect of Albedo on J(N02) —
ZA
0
10
20
30
40
50
60
70
78
86
A-0.05 A-0.15
0.5031 0.5358
0.4991 0.5312
0.4866 0.5166
0.4643 0.4911
0.4300 0.4524
0.3794 0.3969
0.3062 0.3184
0.2023 0.2094
0.0990 0.1025
0.0188 0.0196
SiteAdj FitObs Obs/Theory
0.5498
0.5461
0.5342
0.5127
0.4802
0.4326
0.3629
0.2584
0.1383
0.0240
0.5463 0.99
0.5433 0.99
0.5338 1.00
0.5167 1.01
0.4894 1.02
0.4472 1.03
0.3811 1.05
0.2733 1.06
0.1386 1.00
0.0045
Adjustment Factors
ZA
0
10
20
. 30
40
50
60
70
78
86
Albedo
1.06
1.06
1.06
1.06
1.05
1.05
1.04
1.03
1.04
1.04
Site
1.03
1.03
1.03
1.04
1.06
1.09
1.14
1.23
1.35
1.23
Total
1.09
1.09
1.10
1.10
1.12
1.14
1.19
1.28
1.40
1.28
43
-------
Atmospheric Rate*
Adjustment of Calculated Actinic Flux for Albedo
I
T
*
1
0.60
0.50
0.40 -
050 -
0.20 -
0.10 -
0.00
Comparison of Theory with Measurement
Figure 13. Comparisons of Adjusted Theory with Parrish et al.
Measurements of Atmospheric NOj Photolysis Rates.19
44
-------
4
Recommended Rates
In this chapter, the actinic flux, kinetics parameters, and altitude effects from Chap-
ter 2 will be combined with the re-estimated best albedo value of 0.08 from Chapter 3
to estimate atmospheric rates at the surface and at 640 meters for use in OZIPM3/4
model program.
Rates for Carbon Bond IV in OZIPM3/4
Surface Rates
To compute surface rates, the actinic flux of Peterson, the albedo effect adjustment,
and the cross sections and quantum yields given in Table 4 were used.
The resulting rates, which would be the values to use for CB4 in a ground level
application, are shown in Table 10.
Mixed Layer Rates
As described near the end of Chapter 2, there is a strong effect of altitude on
photolytic rates. This is because, as stated in Chapter 1, the air below a given
altitude well above the ground has a greater reflectivity upward than the absorbing,
low albedo ground. Therefore, the spherical flux at an altitude is higher than at
the surface. Table 5 gave the ratio of photolysis rate at 640 m to that at 0 m for
the "best, albedo" assumptions of Demerjian et al. (0.05). If the albedo assumption
of 0.05 is too low, then the ratios in Table 5 are too high because the surface values
are too low. Thus the ratios in Table 5 are not appropriate to adjust the rates of
Table 10.
As an approximation to the correct ratios for an albedo of 0.08, we will use the
ratio of photolysis rates at 640 m to those at 150 m for an albedo of 0.05. That is,
45
-------
Recommended Rates Recommended CB4 Photolytic Rates
we assume that
J(0°, 640,0.05; S) ^ J(0°, 640,0.08; S)
J(0°, 150,0.05;S) * J(0°,0,0.08;S)
since at the higher albedo, there will be less difference between the higher altitude
rates and the surface rates because the surface is more reflective. These ratios are
shown in Table 11.
Applying the ratios of Table 11 to the surface values of Table 10, gives the
recommended values for the mixed layer. These are shown in Table 12.
Recommended CB4 Photolytic Rates
The values in Table 12 are the photolytic rates that should be used in OZIPM3/4
with the Carbon Bond Four Mechanism when performing control strategy calcula-
tions.
Rates for Carbon Bond III in OZIPM3
Because of previous use of CBS in making SIP calculations and because there were
a number of errors made in calculating the photolytic rates in OZIPM2, we have
made new recommendations for photolytic rates for use with CBS in OZIPM3/4.
The calculation of these new CBS rates follows the same procedure as that for
CB4 except that the carbonyl weighting factor for radical processes and for stable
process (see discussion in Chapter 2) has been recalculated and applied to the HCHO
photolysis rates to produce the CARB photolysis rates. The original weighting factor
for production of radicals (wr) was
wr = (0.55 + 0.005 + 0.0175) J(HCHO, R) + 0.35(J(CH3CHO)/J(HCHO))
where the numerical coefficients reflect the CARB composition as described in Chap-
ter 2. The coefficient of the last term, J(CH3CHO)/J(HCHO), changed from 0.35 to
0.16 for the new photolytic rates, thus lowering wr to 0.602 compared to its old
value of 0.695. The factor relating HCHO,S rates to CARB,S rates remains the same
as before, 0.65.
The recommended rates for CBS in OZIPM3/4 are given in Table 13 and Ta-
ble 14.
46
-------
Rates for Carbon Bond III in OZIPM3 Recommended Rates
Table 10.
Recommended CB4 Surface Photolytic Jlates.
(all rates and ratios except NO2 have been multiplied by 1000)
n-o A o._ ^ A f\ r\a
ZA
0
10
20
30
40
50
60
70
78
86
J(M02)
0.
0.
0.
0,
0.
0.
0.
0,
0.
0.
5358
5312
5166
4911
4524
3969
3184
2094
1025
0196
J(FR) J(FS)
1.
1.
1.
1.
1.
1.
0.
0.
0.
0.
891
859
759
593
359
062
714
360
138
036
2
2
2
2
2
1
1
0
0
0
.980
.943
.828
.631
.341
.947
.436
.830
.367
.103
. \JQ
J(03)
2
2
2
1
1
0
0
0
0
0
.310
.232
.003
.650
.216
.764
.371
.113
.024
.003
J(CCHO)
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
301
294
2?2
236
189
134
079
032
010
002
1.00 3.53 5.56 4.31 0.56
Table 11. Altitude Adjustments Corrected For Albedo.
Ratio 640 to 150m, to approx A-0.08
ZA N02 HCHOR HCHOS 010 CCHO
0
10
20
30
40
50
60
70
78
86
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
10
10
11
11
13
14
17
23
31
24
1
1
1
1
1
1
1
1
1
1
.15
.15
.16
.17
.18
.20
.22
.24
.24
.20
1
1
1
1
1
1
1
1
1
1
.14
.14
.14
.15
.16
.18
.21
.25
.27
.23
1
1
1
1
1
1
1
1
1
1
.17
.17
.18
.19
.20
.24
.25
.24
.25
.00
1
1
1
1
1
1
1
1
1
1
.15
.15
.16
.17
.17
.20
.22
.26
.26
.17
47
-------
Recommended Rates Example Predictions Using New Rates
Table 12 Recommended CB4 Mixed Layer Photolytic Rates.
(all rates except N02 have been multiplied by 1000)
--CB4,640m,A=0.08
ZA J(N02) J(FR) J(FS) J(03) J(CCHO)
0
10
20
30
40
50
60
70
78
86
0 . 5893
0.5851
0.5713
0.5470
0.5093
0.4537
0.3740
0.2578
0.1341
0.0242
2.179
2.141
2.036
1.858
1.599
1.272
0.873
0.448
0.172
0.043
3.391
3.353
3.237
3.032
2.724
2.304
1.732
1.034
0.466
0.127
2". 715
2.620
2.362
1.962
1.463
0.944
0.462
0.140
0.030
0.003
0.347
0.338
0.314
0.275
0.222
0.161
0.096
0.041
0.012
0.002
1.00 3.70 5.75 4.61 0.59
Example Predictions Using New Rates
Simulation Conditions
To illustrate the effect of the new recommendations, some example simulations will
be compared. Example 1 (CB4) and Example 2 (CBS), which were used in the
OZIPM3 guidance document1, were used as sources of conditions. The only differ-
ence between Example 1 and Example 2 was the change in mechanisms. Table 15
gives the simulation conditions. In all examples, the Characteristic Curve for Mixing
Height was used. All simulations began at 0800 LDT and ran for 10 hours.
In the control cases, the initial HC was reduced by various amounts and no
reduction occurred for NOX.
48
-------
Simulation Conditions Recommended Rates
Table 13. Recommended CBS Surface Photolytic Rates.
(all rates except NO2 have been multiplied by 1000)
ZA
0
10
20
30
40
50
60
70
78
86
J(N02)
0.5358
0.5312
0.5166
0.4911
0.4524
0 . 3969
0.3184
0.2094
0 . 1025
0.0196
I/DO , Ol
J(CR)
1.139 .
1.119
1.061
0.964
0.827
0.653
0.447
0.237
0.104
0.040
in , A=U . i
J(CS)
1.937
1.913
1.838
1.710
1.522
1.265
0.933
0.539
0.239
0.067
JO
J(03)
2". 3 10
2.232
2.003
1.650
1.216
0.764
0.371
0.113
0.024
0.003
1.00 2.13 3.62 4.31
Table 14. Recommended CB3 Mixed Layer Photoly tic Rates.
(all rates except NO2 have been multiplied by 1000)
. ZA
0
10
20
30
40
50
60
70
78
86
J(N02)
0.5893
0.5851
0.5713
0.5470
0.5093
0.4537
0.3740
0.2578
0.1341
0.0242
UDG ,*>
J(CR)
1.312
1.289
1.228
1.124
0.972
0.781
0.547
0.295
0.129
0.048
*um , A~W . i
J(CS)
2.204
2.180
2.104
1.971
1.770
1.498
1.126
0.672
0.303
0.083
JO
J(03)
2.715
2.620
2.362
1.962
1.463
0.944
0.462
0.140
0.030
0.003
1.00 2.23 3.74 4.61
49
-------
Recommended Rates
Simulation Conditions
Table 15, a.
Item
Latitude
Longitude
Date
Initial Mixing Ht.
Final Mixing Ht.
Initial NMOC
Initial NOX
Surface NMOC
Surface Os
Aloft NMOC
Aloft 03
Temperature
Water Vapor
Initial Conditions.
Value Units
39.93
75.10
6/24/80
250
1235
1.100
0.120
0.038
0.010
0.040
0.070
303
25000
degrees
degrees
mm/dd/yy
.. meter
meter
ppmC
ppm
ppmC
ppm
ppmC
ppm
K
ppm
Table 15, b. NMOC Fractions.
Source PAR ETH OLE TOL XYL RCHO HCHO NR
Emissions
Surface
Aloft
0.51
0.53
0.61
0.04
0.05
0.06
Table
Hour
NMOC
NOX
1
0.17
0.35
2
0.17
0.35
0.03
0.03
0.03
15, c.
3
0.17
0.35
0.12
0.07
0.08
0.10
0.06
0.07
0.03
0.16
0.09
0.02
0.10
0.06
0.16
0.00
0.00
Emissions Fractions.
4
0.10
0.19
5
0.02 0
0.03 0
6 7
.02 0.02
.03 0.03
8
0.02
0.07
50
-------
Simulation Results Recommended Rates
Simulation Results
Figure 14 shows the NO, NO2, and O3 profiles for CB4 using the surface photolytic
and 640 m photolytic rates from Tables 10 and 12 for the Example 1 case. The higher
photolytic rates (mixed layer rates) resulted in about a 5% increase in predicted
maximum O3 for these conditions.
Figure 15 shows the NO, NO2, and O3 profiles for CBS using the 640 m photolytic
rates from Table 14 and the older 1984 photolytic rates from Table 3 for the Example
2 case. The-higher photolytic rates (new rates) also resulted in a 5% increase in
predicted maximum O3 in this N0x-limited situation. That the increase was not
greater was caused by the fact that the much larger increase in CARB,S rates offset
the increase in CARB,R rates and less CARB photolyzed to radicals in the simulation
using the higher 640 m rates than did in the simulation using the 1984 rates. That
is, the total CARB consumption by photolysis to stable products was 181% of the
amount consumed with the 1984 rates, while the consumption by photolysis to
radical products was 97% of the amount consumed by this process with the 1984
rates. Therefore, most of the increase using the new rates was due to the increased
NO2 photolytic rates as opposed to the higher CARB rates.
Figure 16 shows the NO, NO2, and O3 profiles for both CBS and CB4 using
the mixed layer photolytic rates. CBS was initially more reactive than CB4 when
using the same basic photolytic data. This was in part because of the constant
composition CARB in CBS. Figure 17 shows the CARB profile from CBS and the
"calculated CARB" profile from CB4 (i.e., HCHO+ 2 RCHO). CBS maintained a high
level of CARB in the middle of the simulation compared to CB4. This higher CARB
level occured at the maximum photolysis rate and produced many more radicals
in CBS than in CB4, thus increasing its overall reactivity. The larger amount of
radicals also resulted in a more rapid removal of the NOX causing the 03 profile
to show a sharp decrease in rate at about 400 minutes. CB4 clearly has a more
realistic treatment of the carbonyl chemistry than CBS.
Figure 18 shows the NO, NO2, and O3 profiles for CB4 using the mixed layer
photolytic rates for: a) the Example 1 case, and b) the same conditions with a 40%
HC reduction. The 40% HC reduction (i.e., 1.10 to 0.66 ppmC) resulted in a 32% O3
reduction (i.e., 0.260 to 0.178 ppm).
Figure 19 shows the NO, NO2, and 03 profiles for CBS using the new mixed layer
photolytic rates for a) the Example 1 case, and b) the same conditions with a 40%
HC reduction. The 40% HC reduction (i.e., 1.10 to 0.66 ppmC) resulted in a 25% 03
reduction, that is, less reduction than occurred with CB4. A partial explanation for
51
-------
Recommended Rates
Simulation Results
0.30
Carbon Bond Four. Two Photolytic Rate Sets
a
a
o"
0
U
600
Figure 14. Example Simulation Using CB4: Comparison of Surface
and Mixed Layer Photolytic Rates. (Example 1 from Guidelines
for OZIPM31).
52
-------
Simulation Results
Recommended Rates
Carbon Bond III Two Photolytic Rate Seia
a
a
o
d
200 400
time, mins
600
Figure 15. Example Simulation Using CB3: Comparison of Mixed
Layer and 1984 Photolytic Rates. (Example 2 from Guidelines for
OZIPM31).
53
-------
Recommended Rates
Simulation Results
0.26
Carbon Bond HI and IV. 64O Meters
c_
o"
3
6OO
Figure 16. Comparison of CBS and CB4 Using Mixed Layer Pho-
tolytic Rates.
54
-------
Simulation Results
Recommended Rates
u
E
a
o"
3
0.080
CB3 CARB vs CB4 HCHO-i-RCHO
0.070 -
0.060-
0.050 -
0.040-
0.030 -
0.020 -
0.010-
O.OOO-
,CARB,CB3
HCHO +
2*RCHO, CB4
2OO 4OO
time, mins after O8OOIIDT
6OO
Figure 17. Comparison of CARB (CBS) and HCHO + RCHO (CB4) Using
Mixed Layer Photolvtic Rates.
55
-------
Recommended Rates Simulation Results
the difference between the two mechanisms can be obtained from Figure 20. This
figure shows the O3-HC relationship for CB4, CBS with older 1984 rates, and CBS
with the new mixed layer rates. All three profiles show a limiting of O3 production
with increasing HC, however, the CB4 profile shows a slightly "steeper" dependence
of O3 on HC. That is, CB4 made slightly more O3 at higher HC and less O3 at lower
HC than did CBS. In these simulations, it is the relative difference in the CARB vs.
HCHO profiles during the middle of the simulations"that is the primary cause of the
differences between CBS and CB4 in this case.
Figure 20 also shows a typical control calculation. The base case O3 is as-
sumed to be 0.18 ppm. Each mechanism predicts a different HC level would be
needed to produce this amount of O3: 0.667 ppmC for CB4; 0.648 ppmC for CBS,
1984 rates; and 0.591 ppmC for CBS, new rates. The slopes of the three curves
are similar between the 0.12 and 0.18 ppm O3 lines; that is AO3/AHC values are:
0.335 ppm/ppmC for CB4; 0.320 ppm/ppmC for CBS, 1984; and 0.357 ppm/ppmC
for CB3, new rates. Since the absolute reactivity of the three mechanisms is very
close at the 0.18 ppm O3 level, very similar control requirements are predicted for
the different mechanisms:
/O
= 100(a
0.179\
6687
0.187\
forCB4
(0 187\
^-—) for CB3,84
0.649 /
28% = 100^ for CB3,new
Although the three mechanisms gave similar results in this example, the im-
proved treatment of carbonyl chemistry in the Carbon Bond Four mechanism makes
it a superior mechanism compared to Carbon Bond Three and its predictions should
more accurately reflect the effects of emissions and photolytic rate changes than
those of Carbon Bond Three.
56
-------
References
I
u"
J
0.30
Carbon Bond Four, 64O Meters
200
40O
6(X)
time, mins
Figure 18. Example Simulation Using CB4: 40% HC Control Using
Mixed Layer Photolytic Rates.
57
-------
Reference*
Carbon Bond III, 640m Rates
o.
a
o
o
u
200 400
time, mina
600
Figure 19. Example Simulation Using CB3: 40% HC Control Using
1984 Photolytic Rates.
58
-------
Refe
Examples 1 and 2, Guide-lines Doc.
|
s
o
^
a
o
._-_< 0.59| (28%)
]«-A°iLv! 0.667 (27%)
1 20
Figure 20. Comparison of Ozone-Hydrocarbon Relationships for
CB3 and C134.
59
-------
References
References
1 H. Hogo, G.Z. Whitten,"Guidelines for using OZIPM3 with CBM-X or Optional Mecha-
nisms," EPA/600/3-86/004, U.S. Environmental Protection Agency, Research Triangle Park,
North Carolina, Jan 1986.
2 Whitten, G.Z., H. Hogo, "User's Manual for Kinetics Model and Ozone Isopleth Plotting Pack-
age," EPA-600/8-78-014a, U.S. Environmental Protection Agency, Research Triangle Park,
NC, 1978.
3 Gipson, G.L. "User's Manual for OZIPM-2: Ozone Isopleth Plotting With Optional Mecha-
nisms/Version 2," Office of Air Quality Planning and Standards, U.S. Environmental Protec-
tion Agency, Research Triangle Park, NC, 1984
4 Iqbal, M., "An Introduction to Solar Radiation," Academic Press, NY, 1983.
5 Dave, J.V.,"Development of Programs for Computing Characteristics of Ultraviolet Radia-
tion," Final Report, NAS5-21680, NASA Report CR-139134, National Aeronautics and Space
Administration, Goddard Space Fit. Ctr., Greenbelt, MD, 1971.
6 Peterson, J.T., "Calculated Actinic Fluxes for Air Pollution Photochemistry Applications,"
EPA-600/4-76-002, U.S. Environmental Protection Agency, Research Triangle Park, NC,
1976.
7 Schippnick, P.F., A.E.S. Green, "Analytical Characterization of Spectral Actinic Flux and
Spectral Irradiance in the Middle Ultraviolet," Photochemistry and Photobiology, 35, pp 89-
101, 1982.
8 "Chemical Kinetics and Photochemical Data for Use in Stratospheric Modeling," Evaluation
#7, Jet Propulsion Laboratory Publication 85-37, 1985.
9 Schere, K.L. and K.L. Demerjian, "Calculation of Selected Photolytic Rate Constants over a
Diurnal Range," EPA-600/4-77-015, U.S. Environmental Protection Agency, Research Trian-
gle Park, NC, 1977.
10 Demerjian, K.L., K.L. Schere, and J.T. Peterson, "Theoretical Estimates of Actinic Flux and
Photolytic Rate Constants for Atmospheric Species in the Lower Troposphere," Adv. Environ.
Set. TechnoL, 29, 1980.
11 Carter, William P.L., F.W. Lurmann, R. Atkinson, and A. Lloyd, "Development and Testing
of a Surrogate Species Chemical Reaction Mechanism," Final Report, EPA Contract 68-02-
4104, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, 1986
12 Atkinson, R. and Allen C. Lloyd, "Evaluation of Kinetic and Mechanistic Data for Modeling
Photochemical Smog," J. Chem. Ref. Data. 13, No. 2, p315-444, 1984.
13 Killus, J. and G.Z. Whitten, "Technical Discussions Relating To the Use of Carbon Bond
60
-------
References
Mechanism in OZIPM/EKMA," EPA-450/4-84-009, U.S. Environmental Protection Agency,
Research Triangle Park, NC, 1984.
14 Jeffries, H.E., K.G. Sexton, "Sensitivity of Carbon Bond Mechanism to NMOC aloft." Progress
Report, Sensitivity of EKMA-type Control Estimates to Model Inputs, EPA Co-operative
agreement CR812315, 1986
15 Jeffries, H.E. and K.G. Sexton, "UNC Chamber Photolytic Rate Calculation Procedure,"
Technical Guidance Report, Department of Environmental Science, UNC, Chapel Hill, NC,
1986.
16 Zafonte, L., P.L, Rieger, J.R. Holmes, "Nitrogen Dioxide Photolysis in the Los Angeles At-
mosphere," Envir. Sci. Techno. 11 5, pp 483-487, 1977.
17 Harvey R.B., D.H. Stedman, W. Chameides, "Determination of the Absolute Rate of Solar
Photolysis of NO2," J.A.P.C.A. 27, 7 pp 663-665, 1977
18 Dickerson R.R., D.H. Steadman, A.C. Delany, "Direct Measurements of Ozone and Nitrogen
Dioxide Photolysis Rates in the Troposphere," J, Geo. Res. 87, pp 4933-4966, 1982.
19 Parrish, D.D., P.C. Murphy, D.L. Albritton, F.C. Fehsenfeld, "The Measurement of the Pho-
todissociation Rate of N02 in the Atmosphere," Atmos. Environ. 17 pp 1365-1378, 1983.
20 Madronich S., D.R. Hastie, B.A. Ridley, H.I. Schiff, "Measurements of the Photodissociation
Coefficient of NO2 in the Atmosphere: I. Method and Surface Measurements," Journal Aim.
Chem. 1 pp 3-25, 1983
21 Bass, A.M, A.E. Ledford, A.H. Laufer, "Extinction Coefficients of NO2 and N204" J. Res.
NBS, 80A, No. 2, pp 143-166, 1976.
22 Harkner, A.B., W. Ho, J.J. Ratto, "Photodissociation Quantum Yield of NO2 in the Region
375 to 420 nm," Chem. Phy. Lettr. 50, No. 3, pp 394-397, 1977.
23 Davenport, J.E., "Determination of NO2 Photolysis Parameters of Stratospheric Modeling,"
Report No. FAA-EQ-78-14, 1978.
24 Coulson, K.L. and D.W. Reynolds, J. Appl. Meteorol.,10, pp 1285, 1971.
25 Doda, D.D., A.E.S. Green, "Surface Reflectance Measurements in the UV from an Airborn
Platform, Part 1," Applied Optics 19 pp 2140- 2145, 1980.
26 Doda, D.D., A.E.S. Green, "Surface Reflectance Measurements in the UV from an Airborn
Platform, Part 2," Applied Optics 20 pp 636-642, 1981.
27 King, M.D., B.M. Herman, "Determination of the Ground Albedo and the Index of Absorption
of Atmospheric Particnlates by Remote Sensing. Part I: Theory.," J. Atmos. Sciences 56 pp
163-173, 1979.
28 King, M.D., "Determination of the Ground Albedo and the Index of Absorption of Atmo-
spheric Particulates by Remote Sensing. Part II: Application," J. Atmos. Sciences 86 pp
61
-------
References
1072-1083, 1979.
29 Raschke, E., T.H. Vander Hair, W.R. Bande«n, M. Pasternak, "The Annual Radiation Bal-
ance of the Earth-Atmosphere System During 1969-70 from Nimbus 3 Measurements," J.
Atmoa. Sciences SO, pp 341-364, 1973.
SO Otterman, J., R.S. Fraser, "Earth-atmosphere System and Surface Reflectivities in Arid Re-
gions from LANDSAT Data," Remote Sena. Environ. 5, pp 247-266, 1976.
SI Frederick, I.E., R.B. Abrams, "The Surface Albedo of the Earth in the Near Ultraviolet
(330-340 nm)," Remote Sens. Environ. 11, pp 337-347, 1981.
82 Logan, J.A, M.J. Prather, S.C. Wofsy, M.B. McElory, "TVopospheric Chemistry: A Global
Perspective," J. Geo. Res. 86 pp 7210-7254, 1981.
S3 Jeffries, H.E., K.G. Sexton, C.N. Salmi, "The Effect of Chemistry and Meteorology on Ocone
Control Calculations Using Simple Trajectory Models and the EKMA Procedure," EPA-
450/4-81-034, U.S. Environmental Protection Agency, Research Triangle Park, NC, 1981.
62
-------
TECHNICAL REPORT DATA
/Please read Instructions on the re\ ersc before completing
1 REPORT NO.
EPA-450/4-87-003
3. RECIPIENT'S ACCESSION NO. .
4. TITLE AND SUBTITLE
Technical Discussion Related To The Choice Of Photolyti
Rates For Carbon Bond Mechanisms In OZIPM4/EKMA
5. REPORT DATE
c February 1987
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
H. E. Jeffries and Kenneth G. Sexton
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Dept. Of Environmental Sciences And Engineering
University Of North Carolina
Chapel Hill, NC
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Air Management Technology Branch (MD 14)
Monitoring And Data Analysis Division
Office Of Air Quality Planning And Standards
U. S. Environmental Protection Agency
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
EPA Project Officer: Edwin L. Meyer, Jr.
16. ABSTRACT
This report proposes to explain the methods, and to identify the sources of
information used to calculate photolytic rates, for the chemical models Carbon
Bond III (CB3) and Carbon Bond IV (CB4) for use in the OZIPM3 and OZIPM4 oxidant
modeling programs. The mixed layer photolytic rates described in Chapter 4 are alsc
the default rates for CB4 in the OZIPM4 program, expected to be used in new State
Implementation Plan calculations.
This report also reviews previous recommendations for photolytic rates used in
the original OZIPP program and in the revised program OZIPM2.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATl Field/Group
Photolytic Rates
Chemical Bond
Photochemical Model
OZIPM
Carbon Bond Model
Oxidant Model
State Implementat
Plan
ion
18. DISTRIBUTION STATEMENT
19. SECURITY CLASS (This Report)
21. NO. OF PAGES
70
20 SECURITY CLASS (This page)
22. PRICE
EP'A Form 2220-1 (Rev. 4-77) PREVIOUS EDITION is OBSOLETE
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