DETERMINATION OF RATES OF REACTION IN THE
GAS-PHASE IN THE TROPOSPHERE
THEORY AND PRACTICE
2. Rate of Direct Photoreaction: Screening-Level Test
Guideline § 796.3800. Laboratory Spectroscopic
Determination of the Cross Section and the Maximum
Rate of Direct Photoreaction in Sunlight
by
Asa Leifer
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF TOXIC SUBSTANCES
WASHINGTON, DC 20460
560/5-89-007
-------
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
OFFICE OF
PESTICIDES AND TOXIC SUBSTANCES
JAN I 6 1990
MEMORANDUM
SUBJECT: Corrected Copies of "Determination of Rates of Reaction
in the Gas-Phase in the Troposphere. Theory and
Practice. 2. Rate of Direct Photoreaction: Screening-
Level Test Guideline - Spectroscopic Determination of
the Cross Section and the Maximum Rate of Direct
Photoreaction in Sunlight. EPA 560/5-89-007 (1989)"
for NTIS
FROM: Asa Leifer, Senior Scientist
Exposure Assessment Branch (TS-798)
TO: Hattie Sykes, Librarian
OTS Chemical Library (TS-793)
Typographical errors have been found on the report
"Determination of Rates of Reaction in the
Gas-Phase in the Troposphere. Theory and
Practice. 2. Rate of Direct Photoreaction:
Screening-Level Test Guideline-Spectroscopic
Determination of the Cross Section and the
Maximum Rate of Direct Photoreaction in
Sunlight. EPA 560/5-89-007 (1989)".
Corrections have been made. Therefore, I am submitting 10
copies of the corrected report which should be sent to NTIS.
Attachments
Printed on Recycled Paper
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DISCLAIMER
Certain commercial equipment, instruments, and materials are
identified in this test guideline in order to specify adequately
the experimental procedure. In no case does the identification
of a manufacturer imply endorsement by the U.S. Environmental
Protection Agency.
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Contents
Page
Abstract v
PART I. THEORY AND DEVELOPMENT OF THE SCREENING TEST 1
I. A. Introduction 1
I.E. Development of the Screening Test:
Laboratory Determination of the Gas-Phase
Cross Section and the Maximum Rate of Direct
Photoreaction 2
I.B.I. Theoretical Aspects 2
I.E. 2. Screening Test Method 7
I.E. 2.a. Solar Irradiance 7
I.B.2.b. Determination of the Cross Section of a
Chemical in the Gas-Phase 11
I.B.3. Applicability and Specificity 12
PART II. TEST PROCEDURES AND DATA REPORTING 14
11. A. Procedures 14
II.A.I Experimental Conditions 14
II.A.I.a. Ultraviolet-Visible Spectrophotometer 14
II.A.l.b. Vapor and Liquid Absorption Cells....... 15
II.A.I.e. Vacuum Gas Handling System 17
II.A.l.c.i. Vacuum Pumping System 17
II.A.l.c.ii. Vacuum Rack 19
II .A. I.e. iii. Pressure Gauges 19
II.A. 2. Operation of the Gas Handling System 20
II.A.3. Preparation of Samples... 20
II.A.3.a. Preparation of the Gas-Phase Test Chemical
Sample: Preliminary Steps 20
II.A.S.b. Introduction of the Test Chemical into the
Gas Absorption Cell 21
II.A.3.C. Preparation of Solution-Phase Test Chemical
Sample 23
II.A. 4. Procedure for Obtaining the Spectrum 24
II.A.4.a. Determination of the Cell Path Length 24
II.A.4.b. Gas-Phase Spectrum 25
II.A.4.C. Solution-Phase Spectrum 25
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II.B.
II.B.I.
II.B.2.
II.B.3.
II.B.4.
II.B.5.
Pac
, >, • •"•• •!"—•
Data and Reporting 26
Treatment of Results 26
Determination of the Cross Section from ,the
Gas-Phase Spectrum. 26
Determination of the Cross.-Sectionfrom the
Solution-Phase Spectrum..'.".". .'.V ."•'..• • • ^7
Estimation of the Maximum Direct Photoreaction
Rate Constant and Minimum Half-Life .in the
Gas-phase ^. r..'..:*.'.'. .j 27
Test Data Report .••.•• •.../.,,'.,.". 27
Appendices
PART in. ILLUSTRATIVE";EXAMPLE.. 29
:• '-. "-.V -.V,- "
r...:. se
Appendix A. Tables 3-10 37
Appendix B. Operation of the Gas Handling System 45
References,
46
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Abstract
This report describes a simple and cost-effective screening
test for estimating an environmentally relevant maximum rate
constant for direct photoreaction of a chemical in the gas-phase
in sunlight and the corresponding minimum half-life.
Based on the theory of direct photoreaction of a gaseous
chemical in sunlight in the troposphere, it has been shown that
fkjrJ = 2.303 Z^o( J, where a' is the cross section of a
Q LJ luaX , A A A
A
gaseous chemical in the decadic logarithm system and J is the
A
actinic flux, or solar irradiance, in the troposphere. Using the
Beer-Lambert law and spectroscopic techniques, a detailed
experimental procedure is described for determining 0' , the
decadic cross section of a chemical in the gas-phase. Tables of
J, are given for the latitudes 0 to 70° N. in 10° increments as
a function of season of the year to cover the continental United
States and other parts of the U.S. such as Alaska, Hawaii, etc.
The maximum direct photoreaction rate constant [kjr,]m = v is
Q!J UtaX
obtained by calculating the products cr' J. and summing these
A A
results over A where the chemical absorbs light (i.e., where
a' is nonzero) . The minimum half-life is given by
A
An example is given to illustrate how all the experimental
cross section data is used to estimate t^^E^max an(^ ^fc ( l/2)E^min*
-v-
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PART I. THEORY AND DEVELOPMENT OF THE SCREENING TEST
I. A. Introduction
Numerous chemicals, both natural and anthropogenic, are
emitted into the troposphere from a variety of sources and may be
removed by wet or dry deposition or they may be transformed by
several reaction pathways. These reaction pathways are:
(1) direct photoreaction which involves the absorption of
sunlight, followed by transformation; (2) indirect photoreaction
which involves the reaction of a chemical with hydroxyl radicals
(OH); and (3) oxidation, which involves the reaction of a
chemical with ozone (0^). A quantitative measure of these three
processes is given by the rate constants k,E , kQH , and
kQ . The rate constant k^£ represents the first-order rate
constant for direct photoreaction while k.~u and k~ represent
Un U~
second-order rate constants for indirect photoreaction with OH
radicals and oxidation with 03 , respectively.
A two-tiered hierarchal test scheme has been developed for
determining the rate constants k,E , kOf, , and kQ and half-
lives ^t\^ *n t'ie Qas~Phase in th® troposphere JLeifer
[USEPA (1989)]} . This report describes a cost-effective
screening test to estimate the maximum direct photoreaction rate
constant [k,.,) „„ and the minimum half-life tt .,/-»„]„•_ in
at* max . \ i / f. i LJ nun
the troposphere.
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I.E. Development of the Screening Test: Laboratory
Determination of the Gas-Phase Cross Section and the
Maximum Rate of Direct Photoreaction
I.B.I. Theoretical Aspects
Radiation from the sun is the driving force for
tropospheric photochemistry. In a polluted urban troposphere,
chemical species are produced and destroyed by a complex process
that involves numerous specific kinetic reactions. The primary
pollutants NO (i.e., NO, N02, etc.) react with organic
X
chemicals and sunlight to form a number of intermediates (e.g.,
the hydroxy radical and the hydroperoxy radical). These
intermediates generate a host of secondary pollutants such as
ozone/ formaldehyde, nitric acid, nitrous acid, etc. (Finlayson-
Pitts and Pitts (1986)]. These pollutants absorb sunlight and
enter into a wide range of photochemical processes. Clearly, the
absorption of sunlight by chemicals in the troposphere and the
resultant chemical products are strongly dependent on the
incident solar radiation in the troposphere.
The troposphere receives ultraviolet and visible radiation
during the day directly from the sun, by scattered light from the
sky, and by reflection from the earth's surface. The quantity of
radiation received in the troposphere is dependent on the solar
irradiance outside the earth's atmosphere, the solar zenith
angle, scattering, diffusion, absorption by the earth's
atmosphere, and the reflection of sunlight from the surface of
the earth. Furthermore, the amount of radiation absorbed by
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chemical species within the polluted layer in the troposphere
depends on the radiation received, the absorption coefficient and
the concentration of the chemical species/ and on the path
length. Leiqhton carried out extensive research in the 1950's on
the photochemical processes that occur 'in the atmosphere, many of
his computational results were first reported in 1956 [Leighton
and Perkins (1956)], and much of this work was published in a
book in 1961 [Leiqhton (1961)]. His work describes in detail a •
simple, yet effective, radiative transfer model to calculate the
actinic flux (i.e., solar irradiance) at the earth's surface.
Leighton (1961) has shown that for weak absorbance of a
chemical in the atmosphere, the average rate of absorption of
sunlight per unit volume by a chemical is
Ia x = 2.303aAJ~1C [Idx secant(z) + ilg x ] (1)
where I is the average rate of absorption of sunlight in
a A
photons cm"3 s~ , I, ^ and I are the direct and sky solar
_ p _ i
irradiance in photons cm s , z is the solar zenith angle, C is
the concentration of chemical, a. is the decadic absorption
A
coefficient of the chemical, j is a constant which converts the
intensity units .into units that are compatible with o and C, and
A
i is a constant (i.e., L = ih, where L is the average path
s s
length of sky radiation traversing a surface layer of the
atmosphere of height h). Leighton indicated that to a good
approximation i = 2. Leighton called the term in the brackets of
-3-
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equation 1 J. , the actinic flux or irradiance (i.e., solar
irradiance), and equation 1 becomes
IaX=2.303a^jCJ^ (2)
where
X ~ d X s X
Letting a' = a. j , equation 2 becomes
A A
I = 2.303 a' C J (4)
a A A A
where af is the cross section of a chemical in cm^ molecule" , C
is the concentration of chemical in molecules cm"-*, and J is in
A
photons cm" ^ s"*.
Using the first and second laws of photochemistry (i.e, the
Grotthus-Draper and the Stark-Einstein laws, respectively), the
average rate of disappearance of a chemical undergoing direct
photoreaction (d) in the gas-phase in the troposphere at a fixed
wavelength is given by the expression
Average rate = -(dC/dt) , . = !?., (5)
Q A d A A
where I . is the average rate of light absorption of sunlight
c* A
by the chemical at wavelength X in photons per unit volume (cm^)
per unit time t (s) [the Grotthus-Draper law]; $. is the
A
reaction quantum yield of the chemical at X , the efficiency with
which the absorbed light transforms the chemical [the Stark-
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Einstein law]; and C is the concentration of the chemical in the
units molecules cm .
Substituting equation 4 in 5 yields
Average rate = -(dC/dt),. = 2.3.03C $. o. J. . (6)
Q A A A A
and summing equation 6 over all wavelengths of sunlight absorbed
by the chemical yields
Average rate = -J^(dC/dt)ax = 2*303C ^ *XaX JA (7)
A A
By defining the relationships
Average rate = 2^(dC/dt)dx = (dC/dt)dE (8)
A
and
k = 2.303
A
equation 7 becomes
-
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The half-life t/i/2)E *n the environ^ent is defined as the
time required for the chemical to reach one-half its initial
concentration. Therefore, under this boundary condition Cfc = CQ/2
and t = t.,/0. ; and equation 11 yields
(*•/ *• 1t-
t(l/2)E = ln 2/KdE = °'693/kdE (12)
Leiqhton's model and solar irradiance (J ) have been a
A
cornerstone in the development of atmospheric chemistry [Leighton
and Perkins (1956), Leighton (1961)]. His solar irradiance data
have been used to determine photodissociation rate constants of
several species, especially NC^, as a function of time of day or
zenith angle. These rate constants have been used in mathematical
diffusion modeling of photochemical pollution (Reynolds (1973)]
and in the computer simulation of mixtures of reactive chemical
species to evaluate various mechanisms for photochemical smog
formulation [Demerjian (1974)]. Peterson updated the work of
Leighton by using an improved radiative transfer model and
tabulated the improved solar irradiance data [Peterson (1976);
Demerjian et al. (1980)]. Rate constants have been calculated for
N02, O3, HONO, HON02, CH20, CH3CHO, and H20 using the updated Jx
values of Peterson [Schere and Demerjian (1977)].
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I.B.2. Screening Test Method
A simple first-tier screening test has been developed using
equation 9. As an approximation, it is assumed that the reaction
quantum yield
-------
(i.e., Mie scattering), and surface reflection. Leighton
originally estimated J^ based on limited information [Leighton and
Perkins (1956), Leighton (1961)].
Since the research work of Leighton became outdated,
Peterson (1976) carried out research (1) to update the radiative
transfer model of Leighton; (2) to develop a computer program to
calculate solar irradiance ( ^ ) from 290 to 700 nm as a
function of the solar zenith angle (z) from 0° to 86°; and (3) to
input into the computer program the best available atmospheric
data on molecular scattering, ozone absorption, aerosol scattering
and absorption, absorption by water vapor, oxygen, and carbon
dioxide, and the earth's surface albedo as a function of
wavelength.
For all the calculations, Peterson used the radiative
transfer model first developed by Dave (1972) and improved by
Braslau and Dave (1973a,b). This model was used to calculate the
optical properties of aerosols.
The Dave model (1972) was designed to calculate radiative
fluxes from a flat, horizontal, surface ( F ). However, for
A
photochemical applications, the irradiance ( J. ) is spherical
A
since the incident radiation enters the polluted layer from all
directions. Peterson showed that J = 2F. so that the
spherical irradiance is composed of the sum of the upward and
downward components. Thus, Peterson modified the Dave model to
include the upward and downward components of the flux F .
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The ozone absorption coefficients used by Peterson were
similar to those used by Leighton (1961). However, Peterson used
the value of (03) = 0.295 cm, based on the latest ozone measure-
ments, rather than the value of 0.22 cm used by Leighton (1961).
The atmospheric aerosols were assumed (1) to be spherical
and homogeneous; (2) to have a given size distribution and known
refractive index, both of which were assumed to be independent of
the height and wavelength; (3) to have density (i.e., the number
of aerosols per unit vo.lume) that could be varied with the
height; and (4) to be partly absorbing.
Peterson used the best available data on molecular (i.e.,
Raleigh) scattering and included absorption by water vapor,
oxygen, and carbon dioxide. Finally, the best available surface
albedo factors were used to account for reflection from the
earth's surface as a function of wavelength.
All of the above data were used in the computer program to
— 2 1
calculate the solar irradiance, { J ), in photons cm s for
clear sky conditions, for 10 solar zenith angles (0, 10,
20, , 70, 78, and 86°), and for 48 spectral wavelength
intervals from 290 to 700 nm to give the best values of J^ •
Schere and Demerjian (1977) improved the work of Peterson
by calculating J. over 10 nm intervals from 290 to 700 nm and
A
expanded the wavelength region from 700 to 800 nm.
The J. data obtained by Peterson are instantaneous values
A
in photons cm"2 s"1. Because many chemicals require more than
one day to photoreact, Hendry [Hendry and Kenle.y (1979) and in
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Mill et al. (1982)] modified J as follows. The J data from
the computer program of Schere and Demerjian (1977) were
integrated over a 24-hour day to obtain values in photons
—2 1
cm d~ . Hendry prepared tables of J as a function of X in
the spectral region 290 to 800 nm in 31 intervals at 10°, 30°,
and 50° North latitude for the winter and summer solstices and
the equinox. In addition, these tables included J for
A
averaged spring/summer and fall/winter. These tables have been
incorporated into a screening test method for determining direct
photoreaction rate constants and half-lives for the qas-phase
photoreaction of chemicals in sunlight in the environment in the
continental United States. The method was updated in 1983 to
include tables of J from 20° to 50°N. latitude in 10°
A
increments { Leifer [USEPA (1983)]|.
Recently, Mill et al. (1985) and Davenport (1985) updated
the J data of Hendry [Hendry and Kenley (1979) and in Mill et
A
al. (1982)] for the wavelength region 290 to 800 nm in 10-nm
intervals. Tables of J were prepared for 0 to 70° North
A
latitude in 10° increments for the winter and summer solstices,
the equinox, and the spring/summer and fall/winter averages. The
tables corresponding to 20°, 30°, 40°, and 50° N. latitude have
been incorporated into a screening test for determining rate
constants and half-lives for the gas-phase photoreaction of
chemicals in sunlight in the environment ILeifer [USEPA
(1985)]}. To make the solar irradiance data complete, Tables of
J for 0°, 10°, 60°, and 70° N. latitude have been incorporated
A
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in this report so that the screening test method is applicable to
other parts of the United States (e.g., Alaska, Hawaii, etc).
IoB.2.b. Determination of the Cross Section of a Chemical
in the Gas-Phase
The cross section of a test chemical can be obtained from
the Beer-Lambert law and the ultraviolet-visible absorption
spectrum. The Beer-Lambert law states that for an absorbing
chemical present in the gas-phase, the decrease in intensity of
light with thickness (-dl/d £ ) , at a fixed wavelength X , is
A
— 2 — 1
proportional to the intensity I in photons cm s and the
concentration of the chemical C in the gas-phase [Prutton and
Maron (1951)]. Therefore,
-(dl/d £ )x = ox CI x (15)
where 0.. is the proportionality constant.
A
Eguation 15 can be easily integrated to give the Beer-
Lambert equation
where l is the thickness of the gas absorption cell in cm; IQ
is the intensity of the light at X and SL = 0; I is the
intensity of light at X and at thickness £ ; C is the
_0
concentration of the gas in molecules cm ? and a^ is the
2 —1
Naperian cross section in the units cm molecule (the symbol
conventionally used by most atmospheric chemists). Conversion of
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equation 16 to the decadic logarithm system yields
where a' =o /2.303. Since A , the absorbance (which is
measured directly on most double beam UV-visible absorption
spectrophotometers) is equal to log-,0(I /I) , equation 17
becomes
A A = o'x C a . (18)
The absorbance A over the wavelength interval
AX , centered at X , can be obtained from the ultraviolet-
visible absorption spectrum of the test chemical in the gas-phase
as described by Hendry [Mill et al. (1982)] and improved by Pitts
et al. (1981). These data will be used in equation 18 to
calculate the cross section for 10 nm wavelength intervals,
centered at X , where the test chemical absorbs light. The
method outlined in PART II. of this report is a typical standard
spectroscopic procedure for determining the cross section of
chemicals in the gas-phase.
I.E.3. Applicability and Specificity
This test method is applicable to all chemicals which have
UV-visible absorptions in the range 290-800 nm. Solar radiation
reaching the earth's surface has a sharp cutoff at a wavelength
of approximately 290 nm due to the absorption by ozone [Leighton
(1961), Peterson (1976), Zepp and Cline (1977), Demerjian
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(1980)]. The long wavelength limit is set by thermochemistry
since light of wavelength greater than 800 nm is not of
sufficient energy to break chemical bonds of ground state
molecules [Calvert and Pitts (1966), Benson (1976)]. Direct
photoreaction does not occur unless there is absorption of
radiant energy. This is a direct consequence of the Grottus-
Draper law, the first law of photochemistry. If a chemical in
the qas-phase only absorbs light at wavelengths below 290 nm it
will not undergo direct photoreaction in sunlight. A few
examples of chemicals that only absorb light below 290 nm and
need not be tested in this test guideline are alkanes, alkenes,
alkynes, dienes, and f luoroalkanes.
This test guideline is only applicable to pure chemicals
and not to the technical grade. Overestimates of cross sections
usually occur when technical grade substances are tested because
the impurities frequently absorb in the same spectral region as
the pure chemical.
This first-tier screening test can be employed to estimate
[k,.,] and [t/1/oxcj • as a function of latitude and season
at, max (i/^)L mm
of the year in the United States including Alaska, Hawaii, etc.
under clear sky conditions. These data are in a form suitable
for mathematical modeling for the environmental fate of a test
chemical. Since o' can be determined relatively easily and
cheaply by spectroscopic techniques and tables of J. are
readily available, tkdEl and ^t(l/2)E^min can be obtained
easily and cheaply.
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If the data obtained from this test guideline indicate that
gas-phase photoreaction is an important process relative to other
gas-phase transformation processes such as oxidation with OH and
0^ , then it is recommended that an upper-tier photoreaction test
be carried out to determine the reaction quantum yield $. and
A
thus obtain more precise environmentally relevant rate constants
and half-lives.
PART II. TEST PROCEDURES AND DATA REPORTING
II.A. Procedures
The procedures outlined in this test guideline are based on
the method proposed by Hendry [Hendry and Kenley (1979) and in
Mill et al. (1982)] and developed by Pitts et al. (1981). It is
also recommended that Test Guideline CG-1050, Absorption in
Aqueous Solution: Ultraviolet/Visible Spectra [USEPA (1985)] be
consulted for additional guidance.
II.A.I. Experimental Conditions
II.A.I.a. Ultraviolet-Visible Spectrophotometer
Although single-beam spectrophotometers may be used,
recording double-beam spectrophotometers are highly recommended.
It is extremely important that the spectrophotometer be able to
scan over the wavelength region 270 to 800 nm and have an absor-
i
bance sensitivity, at a signal/noise ratio of 1, of approximately
0.001. It is important that the spectrophotometer be able to
attain a 90 percent separation of two monochromatic spectral
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features approximately 4 nra apart, peak to peak (i.e., the
resolution should be at least 4 nm). It is also desirable to
have a spectrophotometer that can accomodate absorption cells of
length > 10 cm. A Gary 219 UV-Visible Spectrophotometer, or an
equivalent model, is highly recommended.
II.A.l.b. Vapor and Liguid Absorption Cells
Long path length cells are preferable; however, many
commercial spectrophotometers will only accept absorption cells
of 10 cm or less. A suitable vapor cell is depicted in Figure 1
[which was reproduced from the report by Pitts et al. (1981)] and
can be contructed as follows. The vapor cell should be construc-
ted of Pyrex, 1 cm o.d. and 10 cm in length, and be fitted with
plane parallel quartz windows at each end. The quartz windows
can be conveniently attached to the Pyrex cell with vacuum tight
epoxy resin (e.g., Torr-Seal, Varian Associates) only applied to
the outside surface. A Teflon stopcock (or a Pyrex "o" ring
stopcock) should be connected to the cell and contain an "o"-ring
joint. The "o"-ring joint (e.g., #7 or 19, Kontes or Ace Glass)
must match the one on the vacuum rack. Viton "o"-rings are
highly recommended and should be frequently inspected for signs
of deterioration which would result in vacuum leaks. A matched
reference cell is extremely useful but not essential. However,
the sample and reference cells should be very similar. Small
spectral differences between the cells can be compensated for by
running a blank with the sample and reference cells in the
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#7 OR 9 0-RING JOINT
TEFLON STOPCOCK
(KONTES K-826500-004
0-4 mm OR EQUIVALENT)
QUARTZ WINDOWS
Figure 1. Gas Absorption Cell [Reproduced from
Pitts et al. (1981).]
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spectrophotometer. The use of stopcock grease is not required
with these cells and should be avoided.
A matched pair of liquid absorption cells is very desirable
but is not essential. A pair of quartz ultraviolet absorption
cells, 10 cm in length, and containing'ground glass or Teflon
stoppers are recommended. These liquid absorption cells are
readily available commercially.
II.A.I.e. Vacuum Gas Handling System
A suitable gas handling system is shown diagrammatically in
Figure 2 [which was reproduced from the report by Pitts et al.
(1981) and was modified slightly] and should be constructed
completely with Pyrex glass. The components of the gas handling
system are discussed below. The use of stopcock grease is not
required and should be avoided.
II.A.l.c.i. Vacuum Pumping System
In order to achieve a good vacuum, i.e., pressures <10~5
torr «1.3 x 10~6 kPa), two pumps are required. The forepump (A)
must be capable of achieving a pressure <0.05 torr «0.0065 kPa).
A rotary pump (e.g., a Welch Model 1402 Duo-Seal or an equivalent
model) is recommended. The forepump can be attached to the
vacuum system by means of heavy-walled rubber vacuum tubing (B),
or any flexible vacuum tubing. The exhaust from this pump should
be vented into a hood.
The second pump, a high vacuum model, should be a multi-
stage oil diffusion pump (C) [e.g., a Consolidated Vacuum Corp.
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0-RING
PINCH CLAMP
A
B
C
0
E
F
6
H
I
J
K
ULTRA-HIGH
PURITY AIR
CYLINDER
VENTED EXHAUST
ROTARY PUMP
RUBBER TUBING (THICK WALLED)
DIFFUSION PUMP
TRAP AT LIQUID NJTROGEN
TEMPERATURE
*7 OR 9 0-RING JOINTS
MOLECULAR SIEVE 4A TRAP
CAPACITANCE MANOMETER
THERMOCOUPLE GAUGE
IONIZATION GAUGE
LIQUID RESERVOIR
GAS ABSORPTION CELL
0-4 OR 0-5 mm
STOPCOCKS
0-8 OR 0-10 mm
STOPCOCKS
Figure 2. Schematic of Gas Handling Vacuum Rack [Reproduced
from Pitts et al. (1981) and modified slightly.]
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VMF-10 or VMF-20 or an equivalent model]. The pump fluid should
be a silicone oil with a room temperature vapor pressure of
10" torr ( 1.3 x 10~7 kPa) [e.g., Dow-Corning D.C. 702 or
703, or an equivalent grade].
It is extremely important that the pumping system contain a
trap (D) cooled with liquid nitrogen. The cone and socket joint
on this trap can be conveniently sealed with Apiezon W wax, or an
equivalent grade. This wax only requires gentle heating to apply
and makes an effective vacuum seal. It is possible that a few
test chemicals could dissolve Apiezon W wax. In this case, an
inert silicone grease may be used to seal the trap.
II.A.l.c.ii. Vacuum Rack
The recommended vacuum rack assembly is depicted in Figure
2. All stopcocks should be of Teflon with Viton "o"-rings
[Kontes K-826500 or K-826510 series or equivalent grades (or
Pyrex "o" ring stopcocks)]. The "o"-ring joints (E) [#7 or #9]
must be compatible with those on the gas absorption cell (K) or
on the liquid reservoir (J). These "o"-ring joints should be
clamped by pinch clamps with a screw lock device (e.g., Thomas
#18A, or an equivalent grade).
II.A.I.e.ill. Pressure Gauges
Three pressure gauges are required:
(_1_) An ionization gauge to measure high vacuum [<10~ torr
«1.3 x 10"4 kPa)];
(_2_) a thermocouple gauge to monitor the pressure in the
range 10~3 to 1 torr (1.3 x 10 to 0.13 kPa). A convenient
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pressure monitoring system which contains ionization and
thermocouple gauges is a Consolidated Vacuum Corp. Model GIC-300A
or an eguivalent model; and
(_3_) a pressure gauge to monitor the pressure of the test
chemical and diluent in the range 0.01 to 760 torr (0.0013 to
101.3 kPa); for example, an MKS Baratron 310 BHS-1000 with the
associated 170-6C electronics unit and a digital readout or an
eguivalent model. While this vacuum gauge exhibits a slow zero
drift, it can be readily rezeroed using the ionization gauge when
the pressure is approximately 10~3 torr (0.00013 kPa) or less.
II.A.2. Operation of the Gas Handling System
Since there are a wide variety of procedures available for
operating a gas handling system, the method used is left to the
discretion of the tester. For those testers who do not have
experience in handling a vacuum system, the detailed procedure
described in Appendix B is highly recommended.
II.A.3. Preparation of Samples
II.A.3.a. Preparation of the Gas-Phase Test Chemical Sample:
Preliminary Steps
If the test chemical is a gas at room temperature, then
attach the gas container to the no"-ring at the point where the
liguid reservoir (J) is placed. Close stopcocks 2 and 3 and open
— 2 —3
4. Pump until the pressure is less than 10 torr «1.3 x 10
kPa) as read on thermocouple gauge (^K Then open stopcocks 2
and 3 and close 4 and pump until the pressure is less than 10"
torr «1.3 x 10~6 kPa) as read on the ionization gauge (I).
-20-
-------
If the test chemical is a liquid at room temperature, add a
few cubic centimeters of liquid to a reservior tube (J), sealed
at one end and containing an "o"-ring at the other end, and
connect the tube via the "o"-ring to stopcock 6. Freeze the
sample with a Dewar containing liquid nitrogen, close stopcocks 2
and 3 and open 4 and 6. Degas the test chemical by allowing it
to warm up to the liquid state, briefly degas, and refreeze the
liquid. Repeat this process three or more times until the
evolution of gas bubbles ceases upon thawing. Freeze the liquid,
open stopcocks 2 and 3 and close 4. Pump until the pressure is
less than 10~5 torr (<1.3 x 10~6 kPa) as indicated by the
ionization gauge (I). Close stopcock 6.
II.A.3.b. Introduction of the Test Chemical into the Gas
Absorption Cell
For introduction of the test chemical into the gas
absorption cell, close stopcocks 5, 7, and 10, with 9 and 11
open. If the test chemical is a gas, then stopcock 6 should be
opened and the gas container valve gradually opened to admit the
gas into the gas handling manifold and gas absorption cell until
the desired pressure is attained, as read on the capacitance
manometer (G). Close the gas container.valve and stopcock 6 and
allow approximately 5 minutes before the final pressure at (G) is
read. If the pressure has not stabilized in approximately 5
minutes, allow the cell to condition for several hours before the
final pressure at (G) is read.
-21-
-------
For a liquid chemical in the reservoir (J), which has been
degassed and is at liquid nitrogen temperature, the liquid
nitrogen Dewar should be removed and stopcock 6 opened. The cold
liquid in the reservoir (J) is allowed to warm up until the
required pressure is attained/ as read by the capacitance
manometer (G). Close stopcock 6 and cool the reservoir again
with liquid nitrogen and allow approximately 5 minutes before the
final pressure at (G) is read. If the pressure has not
stabilized in approximately 5 minutes, allow the cell to
condition for several hours before the final pressure at (G) is
read.
With stopcocks 6, 8, and 11 closed and 5, 7, 9, and 10
open, the gas handling manifold is evacuated as described
previously to a pressure less than 10~5 torr «1.3 x 10~^ kPa).
Stopcocks 5 and 10 are then closed and ultrahigh purity air from
a cylinder is admitted into the qas handling manifold via stop-
cock 8 and through the trap (F) containing Molecular Sieve 4A.
When the manifold is at 1 atmosphere pressure, as measured by
pressure gauge (G), stopcock 11 is briefly opened to pressure the
gas absorption cell to 1 atmosphere, and then closed. Stopcocks
8 and 9 are closed and the gas handling system is evacuated as
described previously. The gas absorption cell can then be removed
from (E) and covered to avoid photoreaction.
Based on the pressure P of the test chemical, as measured
by gauge (G), the concentration of the qas sample is
-22-
-------
C (molecules cm"3) = 9.657 x 1018 P(torr)/T(K) (19)
C (molecules cm"3) = 1.287 x 1018 P(kPa)/T(K) (20)
where T is the room temperature in K, which should be routinely
monitored with a thermometer.
The recommended pressure of the test chemical should be in
the range 1-5 torr (0.13-0.65 kPa) where the Beer-Lambert law is
obeyed. A final check on whether the test chemical obeys the
Beer-Lambert law can be accomplished by demonstrating the
constancy of the cross section at three partial pressures
differing by a factor of 10.
II.A.3.C. Preparation of Solution-Phase Test Chemical Sample
If the properties of the test chemical (i.e., small cross
sections, low vapor pressure) are such that the maximum
absorbance obtainable is one-tenth of the most sensitive
spectrophotometer scale or less (i.e., 0.001 absorbance), a
solution-phase study should be undertaken. The most sensitive
scale may be limited by inherent spectrophotometer noise. For
example, a given spectrophotometer*s most sensitive scale is 0.00
to 0.10 absorbance units. Therefore, a test chemical for which
the product of its maximum cross section and its concentration is
less than 0.001 (in a 10 cm cell) could not be analyzed in the
vapor phase with this particular spectrophotometer.
The following spectroscopic grade chemicals are recommended
to prepare solutions: jv-hexane, and cyclohexane. Solutions of
-23-
-------
up to 10 percent by volume of test chemical can be prepared in
one of these solvents in the standard manner.
The concentration of the test chemical is given by the
equations
C (molecules cm"3) = 6.022 x 1023 mass (g)/FW (Vd) (21)
C (molecules cm"3) = 6.022 x 1023 V0 p/FW (V,) (22)
s o
where Vs is the volume of test chemical delivered into a volume V
of solvent in cm3, FW is the formula weight of the test chemical
in g, and p is the density of the test chemical in g cm~^ at the
room temperature the solution was prepared.
II.A.4. Procedure for Obtaining the Spectrum
As a general guide to obtaining UV-visible absorption
spectra, the procedures outlined in Test Guideline CG-1050,
Absorption in Aqueous Solution: Ultraviolet/Visible Spectra, are
highly recommended. Since the method presented in this procedure
was developed by Pitts et al. (1981), it is highly recommended
that this report be consulted for further details.
II.A.4.a. Determination of the Cell Path Length
The method for determining the cell path length of gas or
liquid cells is left to the discretion of the tester. However,
the method listed in Test Guideline CG-1050 | Leifer [USEPA
(1985)]}, using one of their reference compounds, is highly
recommended.
-24-
-------
II.A.4.b. Gas-Phase Spectrum
Measure the absorbance of the test chemical in duplicate
relative to a matched cell filled with ultrahigh purity air from
the same cylinder similarly passed through trap (F) containing
the molecular sieve. The absorbance should be measured at
wavelengths X > 280 nm using minimum slit widths. Record, in
duplicate, the baseline when both the sample and reference cells
are only filled with high purity air dried through the molecular
sieve and at the same settings as used for the test chemical
sample. These data will be used to calculate the cross
section, o' , at the appropriate wavelength intervals, centered
at wavelength X , listed in Tables 3-10, Appendix A.
II.A.4.C. Solution-Phase Spectrum
Measure the absorbance of the test chemical in duplicate
relative to a matched cell containing the solvent. The absor-
bance should be measured for wavelengths X > 280 nm using the
minimum slit widths. Record, in duplicate, the baseline when
both the sample and reference cells are filled with the solvents.
These data will be used to calculate the cross sections, a' , for
the appropriate wavelength intervals, centered at X , listed in
Tables 3-10, Section A.
The concentration of the test chemical should be in the
range where the Beer-Lambert law is obeyed. A check on whether
the test chemical obeys this law can be accomplished by
demonstrating the constancy of the cross section at three
concentrations differing by a factor of 10.
-25-
-------
II.B. Data and Reporting
II.B.I. Treatment of Results
II.B.2. Determination of the Cross Section from the Gas-Phase
Spectrum
The cross section, a' , can be determined from the gas-phase
absorption spectrum and the Beer-Lambert law in the form
o{ = A X/C£ (23)
where A is the absorbance at wavelength X , centered in the
A
wavelength interval AX , C is the concentration of test chemical
in molecules cm" , and £ is the cell path length in cm. The
cross section of the test chemical should be determined for the
wavelength intervals listed in Tables 3-10, Appendix A.
There are at least three nondestructive methods of deter-
mining the absorbance over a specified wavelength interval:
estimation, square counting, and planimetry. For many spectra,
estimating an average absorbance over a small wavelength interval
is sufficient to yield accurate results. However, for spectra
containing rapidly changing absorptions and complex fine
structure, square counting or planimetry should be used. These
two methods require the integration of a definite region (in
A x nm) followed by division by the width of the region in nm
A
to obtain the absorbance. The method using a compensating polar
planimeter is the most accurate and is highly recommended. The
absorbance should be obtained from the average of three tracings.
-26-
-------
II.B.3. Determination of the Cross Section from the Solution-
Phase Spectrum
The cross section, a' , can be determined from the
solution-phase spectrum using equation 23 for the wavelength
intervals listed in Tables 3-10, Appendix A. For solution
spectra, estimating an average absorbance over the wavelength
intervals is sufficient to yield accurate results.
II.B.4. Estimation of the Maximum Direct Photoreaction Rate
Constant and Minimum Half-Life in the Gas-Phase
Using the cross sections obtained from the spectra and the
values of J. from Tables 3-10, Appendix A, the maximum direct
A
photoreaction rate constant [k,P] can be calculated at a
Q£* IU3.X
specific latitude and season of the year using equation 13. The
minimum half-life ^t(i/2)E^min can be calculate<3 using this
(k^rJ , in equation 14.
Q tii Iu3 X
An example is presented in PART III. to illustrate how the
test data obtained in this test guideline is used.
II.B.5. Test Data Report
(a) Submit the original chart, or photocopy, containing a
plot of absorbance vs. wavelength plus the baseline. Spectra
should include a readable wavelength scale, preferably marked at
10 nm intervals. Each spectrum should be clearly marked.
(b) Gas-Phase Spectra
(i) Report the pressure of the test chemical in torr
{or kPa), the concentration in molecules cm"3, and the path
length of the sample cell in cm. Describe the method used to
determine the path length and report the experimental data.
-27-
-------
(ii) Report the wavelength X , the wavelength
interval for each 10 nm over the region of absorption, the value
of the absorbance ( A ) for each replicate, the mean
A
2 1
absorbance, and the mean cross section in cm molecule .
(iii) Report the site (or sites) where the chemical is
manufactured.
(iv) Report the estimated maximum direct photoreaction
rate constant in d and the corresponding minimum half-life in
days at the site (or sites) where the chemical is manufactured
for the summer and winter solstices.
(c) Solution-Phase Spectra
(i) Report the concentration of the test chemical in
molecules cm" , the type of cell used (quartz or borosilicate),
and the path length in cm. Describe the method used to determine
the path length and report the experimental results.
(ii) Report the identity of the solvent.
(iii) Report the wavelength A , the wavelength
interval over the region of absorption, the value of the
absorbance ( A ) of each replicate, the mean absorbance, and
A
") — i
the mean cross section ( a' ) in cm molecule .
A
(iv) Report the estimated maximum direct photoreaction
rate constant in d"1 and the corresponding minimum half-life in
days at the site (or sites) where the chemical is produced for
the summer and winter solstices.
(d) Report the name, structure, and purity of the test
chemical.
-28-
-------
(e) Submit a recent spectrum on appropriate reference
chemicals for photometric and wavelength accuracy.
(f) Report the name and model of the spectrophotometer used'
(g) Report the various control settings employed with the
spectrophotometer. These might include scan speed, slit width,
given, etc.
(h) Report anything unusual about the test; e.g., if the
Beer-Lambert law is not obeyed at a pressure of 1-5 torr (0.13 to
0.65 kPa), report the pressure at which the deviation was overcome
and the experimental data. If the Beer-Lambert law is not obeyed
in solution at high concentrations, report the concentration at
which the deviation was overcome and the experimental data.
(i) Report any other relevant information.
PART III. ILLUSTRATIVE EXAMPLE
Consider a chemical plant located in Freeport, TX which
produces acrolein [CH2=CHCHO] continuously every day of the year.
Despite the fact that all acrolein wastes, including vented
vapors, are treated in a waste treatment plant, some acrolein
escapes into the atmosphere. The chemical plant is located at
29° N. latitude. Estimate the maximum sunlight direct photore-
action rate constant and the corresponding minimum half-life in
the troposphere in the vicinity of the plant for the winter and
summer solstices under clear sky conditions.
The vapor phase spectrum of acrolein was obtained by the
procedure outlined in this test guideline and is depicted in
-29-
-------
Figure 3. The path length of the sample gas absorption cell was
measured according to the recommended procedure and was found to
be 9.98 cm. The gas absorption cell contained 6.52 x 1016
molecules cm" of acrolein. A compensating polar planimeter was
used to integrate each 10 nm interval throughout the region of
absorption from 285 nm to 425 nm in both the sample and blank
spectra. Based on triplicate measurements/ one square,
corresponding to 0.001 absorbance units (A), was found to be
0.148 vernier units (v.u.). The mean absorbance ( A ) was
A
obtained from these spectra and the mean cross section ( a' ) was
A
obtained using equation 23 for each wavelength interval, centered
at X . All the results are summarized in Table 1.
A sample calculation is given for the wavelength
A = 350 nm centered over the wavelength interval 345-355 nm. For
convenience, the area A, corresponding to 100 squares was blocked
off in this absorption area (Figure 3) and was not integrated
with the planimeter. The average vernier reading of the
remaining absorption area was 7.2 v.u. Hence,
7. 2 v.u. tn
= 49 squares
0.148 v.u./square
and the total area in the spectrum in the wavelength interval
345-355, centered at X = 350 nm, is 149 squares. This number of
squares corresponds to 0.0149 absorbance units:
(149 squares)(0.001 A/square) _ Q.0149-A
The spectral data were taken from the work of Pitts et al.
(1981).
-30-
-------
I
U)
350 370
X (nm)
390
410
430
Figure 3. Gas Phase Absorption Spectrum of Acrolein [Reproduced from
Pitts et al. (1981).]
-------
TABLE 1. ABSORBANCE AND CROSS SECTION FOR ACROLEIN VAPOR1
Wavelength
X
(nm)
290
300
310
320
330
340
350
360
370
380
390
400
410
420
Wavelength
Interval
(nm)
285-295
295-305
305-315
315-325
325-335
335-345
345-355
355-365
365-375
375-385
385-395
395-405
405-415
415-425
Mean
Absorbance
0.0037
0.0066
0.0104
0.0137
0.0156
0.0156
0.0151
0.0096
0.0073
0.0031
0.0016
0.0004
0.0003
0.0000
Mean Cross
Section [ a' ]
2 -1
(cm molecule )
5.69 x
1.01 x
1.60 x
2.11 x
2.40 x
2.40 x
2.32 x
1.48 x
1.12 x
4.76 x
2.46 x
6.15 x
4.61 x
0.00
io-21
10-20
IO-20
10-20
10-20
IO-20
10-20
10-20
ID'20
10"21
10-21
ID'22
10-22
6.52 x 1Q ® molecules cm in a 9.98 cm gas absorption cell.
The data was taken from the report by Pitts et al. (1981).
-32-
-------
From the blank spectrum, the baseline absorbance
(A blank) over this interval was -0.0001. The sample trace lay
at -0.0001 absorbance units relative to a zero point at 450 nm.
The observed samole absorbance is then equal to 0.0150 (0.0149 +
0.0001). The absolute corrected absorbance for the sample is
given by
Acorr = Aobs _
X sample X sample X blank
= 0'0150 ' (-°-001) = °'0151 A
Using equation 23 and the values for the corrected sample
absorbance, I , and C, the mean cross section for the
wavelength X = 350 nm, centered over the wavelength interval
345-355 nm, is
, = 0.0151
6.52 x 1016 molecules cm"3 (9.98 cm)
= 2.32 x 10~20 cm2 molecule"1.
Since the plant is located at 29° N. latitude, the closest
J values are at 30° N. latitude. These values are obtained
A
from Table 6 and are summarized in Table 2 for the summer and
winter solstices. Using the data in Tables 1 and 2, the products
o( J are calculated for each wavelength interval, centered at
A A
X , and the results are summarized in Table 2 for each of the
-33-
-------
TABLE 2. CALCULATION OF [k,_] = FOR ACROLEIN VAPOR:
QJc* luaX
RATE AT 30° N. ON WINTER AND SUMMER SOLSTICES
Wavelength
X
(nm)
290
300
310
320
330
340
350
360
370
380
390
400
410
420
Wavelength
Interval
(nm)
285-295
295-305
305-315
315-325
325-335
335-345
345-355
355-365
365-375
375-385
385-395
395-405
405-415.
415-425
Summer
Jx
Lcm-V°]
1 .0 x
8.31 x
1.14 x
2.84 x
5.02 x
5.49 x
6.28 x
6.49 x
8.09 x
7.93 x
8.12 x
1.11 x
1.41 x
1.47 x
1015
1017
1019
1019
1019
101'9
1019
1019
1019
1019
1019
1020
1020
1020
Solstice
°xjx
Id'1]
0.000
0.008
0.182
0.599
1.205
1.318
1.457
0.961
0.906
0.378
0.200
0.068
0.065
0.000
Winter Solstice
Jx
[photons'!
-2 ,-1
cm d J
2.1 x 1
8.35 x
3.00 x
1.06 x
2.13 x
2.48 x
2.89 x
3.10 x
3.95 x
3.95 x
4.12 x
5.73 x
7.37 x
7.81 x
O12
1016
1018
1019
1019
1019
1019
1019
1019
1019
1019
1019
1019
1019
-------
solstices. The terms /v a' J are also listed for each
A
solstice at the bottom of Table 2. Using these data in equations
13 and 14 yields:
Summer . Winter
[k,Fl v = 16.9 d"1 lkr,F)m*v = 7.60 d"1
at max Qt, max
[t(l/2)E]min = °'091
Thus, under the assumption that <|> = 1 , acrolein transforms
rapidly under clear sky conditions in the vicinity of the plant
at Freeport, TX on the summer and winter solstices. To define
the rate of direct photoreaction more precisely, <)> must be
determined in the laboratory using the procedure outlined in the
report by Mill (1983) and in the Test Guideline § 796.3810, to be
published shortly.
-35-
-------
APPENDICES
Appendix A. Tables 3-10 [from Mill et al. (1985) and Davenport
(1985)].
-36-
-------
Table 3
VALUES AT 0°N. LATITUDE
Wavelength
Center*1
290
300
310
320
330
340
350
360
370
380
390
400
410
420
430
440
450
460
470
480
490
500
510
520
530
540
550
560
570
580
590
600
610
620
630
640
650
660
670
680
690
700
710
720
730
740
750
760
770
780
790
800
Suomer
Solstice8
0.00000129
0.0557
0.873
2.28
4.09
4.51
5.11
5.37
6.71
6.60
6.77
9.28
11.8
12.3
12.5
13.9
16.0
17.3
17.8
18.1
18.1
18.4
18.6
18.6
18.8
18.7
18.6
18.8
19.0
19.4
19.7
19-8
20.0
19.9
19.8
20.3
20.9
21.2
21.5
21.5
21. 5
21.4
21.3
21.2
21.0
20.9
20.8
20.7
20.5
20.4
20.3
20.2
Equinox3
0.0000768
0.0754
1.017
2.52
4.44
4.85
5.46
5.72
7.13
6.98
7.14
9.77
12.4
12.9
13.1
14.5
16.7
18.0
18.6
18.8
18.9
19.2
19.3
19.4
19.6
19.4
19.3
19.5
19.8
20.2
20.4
20.6
20.7
20.7
20.7
21.2
21.7
22.0
22.2
22.2
22.2
22.2
22.0
21.9
21.8
21.5
21.5
21.4
21.2
21.1
21.0
20.8
Winter
Solstice3
0.00000124
0.0557
0.873
2.28
4.09
4.51
5.11
5.37
6.71
6.60
6.77
9.28
11.8
12.3
12.5
13.9
16.0
17.3
17.8
18.1
18.1
18.4
18.6
18.6
18.6
18.8
18.7
18.8
19.0
19.4
19.7
19.8
20.0
19.9
19.8
20.4
20.9
21.2
21.5
21.5
21.5
21.4
21.3
21.2
21.0
20.9
20.8
20.7
20.5
20.4
20.3
20.2
Wavelength
Center*
290
300
310
320
330
340
350
360
370
380
390
400
410
420
430
440
450
460
470
480
490
500
510
520
530
540
550
560
570
580
590
600
610
620
630
640
650
660
. 670
680
690
700
710
720
730
740
750
760
770
780
790
800
Fall or
Winter Avg.3
0.0000281
0.0654
0.945
2.40
4.27
4.68
5.29
5.55
6.92
6.79
6.96
9.53
12.1
12.6
12.8
14.2
16.3
17.7
18.2
18.5
18.5
18.8
19.0
1S.O
19.2
19.0
19.0
19.2
19.4
19.8
20.1
20.2
20.4
20.3
20.3
20.8
21.3
21.6
21.9
21.9
21.9
21.8
21.7
21.5
21.4
21.3
21.2
21.0
20.9
20.8
20.6
20.5
Sprinb or
Summer Avg.3
0.0000278
0.0654
0.945
2.40
4.27
4.68
5.29
5.55
6.92
6.79
6.96
9.53
12.1
12.6
12.8
14.2
16.3
17.7
18.2
18.5
18.5
18.8
19.0
19.0
19.2
19.0
19.0
19.2
19.4
19.8
20.1
20.2
20.4
20.3
20.3
20.8
21.3
21.6
21.9
21.9
21.9
21.8
21.7
21.5
21.4
21.3
21.2
21.0
20.9
20.8
20.6
20.5
Wavelength
Center0
29U
30u
310
320
330
340
350
360
370
3bO
390
400
410
420
430
440
450
460
470
480
490
500
510
520
530
540
550
56i)
570
580
590
600
610
620
630
640
050
660
670
680
690
70U
710
720
730
740
750
760
770
780
790
800
Bj values are in units of
A
1019 photons cm"2 day"1.
''wavelength intervals are uniforoly 10 nm wide, extending from 5 nm lower
than the center wavelength to 5 nm higher. Thus, the first interval
centered on 290 extends froo 285-295 no.
-37-
-------
Table 4
VALUES AT 10°N. LATITUDE
Wavelength
Center1*
290
300
310
320
330
340
350
360
370
380
390
400
410
420
430
440
450
460
470
480
490
500
510
520
530
540
550
560
570
580
590
600
610
620
630
640
650
660
670
680
690
700
710
720
730
740
750
760
770
780
790
600
Summer
Solstice8
0.0000316
0.0713
1. 01
2.55
4.52
4.95
5.58
5.85
7.30
7.16
7.33
10.0
12.6
13.3
13.5
14.9
17.2
18.6
19.1
19.4
19.5
19.8
19.9
20.0 .
20.2
20.0
20.0
20.1
20.4
20.9
21.1
21.2
21.4
21.4
21.4
21.9
22.4
22.7
23.0
23.0
23.0
22.9
22.8
22.6
22.5
22.4
22.2
22.1
22.0
21.8
21.7
21.6
8J. values are in units
\
Equinox8
0.0000542
0.0718
0.992
2.48
4.39
4.79
5.41
5.66
7.06
6.92
7.08
9.70
12.3
12.8
13.0
14.4
16.6
17.9 .
18.5
18.7
19.0
19.1
19.2
19.3
19.4
19.3
19.2
19.4
19.7
20.1
20.3
20.5
20.6
20.6
20.6
21.1
21.5
21.8
22.1
22.1
22.1
22.0
21.9
21.8
21.6
21.5
21.4
21.3
21.1
21.0
20.9
20.7
Winter
Solstice8
0.00000235
0.0381
0.698
1.934
3.55
3.96
4.51
4.76
5.98
5.b9
6.07
8.34
10.6
11.1
11.3
12.6
14.5
15.7
16.2
16.5
16.5
16.6
16.9
17.0
17.1
17.0
17.0
17.1
17.4
17.7
17.9
18.1
18.2
18.1
18.0
18.6
19.1
19.4
19.6
19.7
19.7
19.7
19.6
19.5
19.3
19.2
19.1
19.0
18.9
16.8
18.7
18.6
Wavelength
Center*
290
300
310
320
330
340
350
360
370
380
390
400
410
420
430
440
450
460
470
480
490
500
510
520
530
540
550
560
570
580
590
600
610
620
630
640
650
660
670
680
690
700
710
720
730
740
750
760
770
780
790
800
Fall or
Winter Avg.8
0.00000879
0.0517
0.823
2.17
3.91
4.32
4.89
5.15
6.44
6.33
6.50
8.92
11.4
11.9
12.1
13.3
15.4
.16.6
17.2
17.4
17.5
17.8
17.9
17.9
18.1
18.0
17.9
18.1
18.3
18.7
18.9
19.1
19.2
19.1
19.1
19.6
20.1
20.4
20.7
20.7
20.7
20.7
20.5
20.4
20.3
20.2
20.1
20.0
19.8
19.7
19.6
19.5
Spring or
Summer Avg ,a
0.0000589
0.0742
1.02
2.55
4.51
4.93
5.56
5.82
7.26
7.11
7.28
9.97
12.7
13.2
13.4
14.8
17.0
18.4
19.0
19.2
19.3
19.6
19.8
19.8
20.0
19.8
19.8
19.9
20.2
20.7
20.9
21.0
21.2
21.2
21.2
21.7
22.1
22.5
22.7
22.7
22.7
22.7
22.5
22.4
22.3
22.1
22.0
21.9
21.7
21.6
21.4
21.3
Wavelength
Center"5
290
300
310
320
330
340
350
360
370
360
390
400
410
420
430
440
450
460
470
480
490
500
510
520
530
540
550
560
570
580
590
600
610
620
o30
640
650
660
670
680
690
700
710
720
730
740
750
760
770
780
790
800
of 1019 photons cm day.
Wavelength intervals are uniformly 10 nm wide, extending from 5 nm lower
than the center wavelength to 5 nn higher. Thus, the first Interval centered
on 290 extends froo 285-295 nm.
-38-
-------
Table 5
J. VALUES AT 20°N. LATITUDE
Wavelength
Center15
290
300
310
320
330
340
350
360
370
380
390
400
410
420
430
440
450
460
470
480
490
500
510
520
530
540
550
560
570
580
590
600
610
620
630
640
650
660
670
680
690
700
710
720
730
740
750
760
770
780
790
800
Sooner
Solstice8
0.0000811
0.0810
1.10
2.74
4.82
5.27
5.94
. 6.22
7.76
7.60
7.77
10.6
13.5
14.1
14.3
15.8
18.2
19.7
20.2
20.5
20.6
20.9
21.1
21.1
21.3
21.2
21.1
21.3
21.6
22.1
22.3
22.5
22.6
22.6
22.6
23.1
23.6
24.0
24.3
24.3
24.3
24.2
24.1
23.9
23.8
23.6
23.5
23.3
23.2
23.1
22.9
22.6
Equinox8
0. 0000013 L
0.0611
0.9148
2.35
4.20
4.61
5.22
5.47
6.84
6.71
6.88
9.44
12.0
12.5
12.7
14.1
16.2
17.5
18.1
18.3
18.4
18.7
18.8
18.9
19.0
19.0
18.6
19.0
19.3
19.7
19.9
20.0
20.2
20.1
20.1
20.6
21.1
21.4
21.7
21.7
21.7
21.7
21.5
21.4
21.3
21.1
21.0
20.9
20.8
20.6
20.5
20.4
Winter
Solstice3
0.000000108
Wavelength
Center"
290
Fall or
Winter Avg."
0.000000896
0.0212
0.499
1.52
2.90
3.28
J.77
4.01
5.06
5.02
5.19
7.17
9.17
9.65
9.85
11.0
12.7
13.7
14.2
14.4
14.5
14.8
14.9
14.y
15.1
15.0
14.9
15.1
15.3
15.7
15.8
15.9
16.0
16.1
16.2
16.6
16.9
17.2
17.4
17.5
17.5
17.5
17.4
17.3
17.2
17.2
17.1
17.0
lo.9
16.8
16.7
16.7
300
310
320
330
340
350
360
370
380
390
400
410
420
430
440
450
460
470
480 '
490
500
510
520
530
540
550
560
570
580
590
600
610
620
630
640
650
660
670
680
690
700
710
720
730
740
750
760
770
780
790
6.0359
0.663
1.855
3.42
3.82
4.36
4.61
5.79
5.71
5.88
8.10
10.3
10. d '
11.1
12.2
14.1
15.3
15.8
16.0
16.1
16.4
16.4
16.5
16.7
16.6
16.5
16.7
16.9
17.3
17.5
17.6
17.7
17.7
17.7
18.2
18.6
18.9
19.2
19.2
19.2
19.2
19.1
19.0
18.9
18.8
18.7
18.6
18.5
18.4
18.3
800
18.2
aj values are In units of 10 photons cn"^ day .
Ft
Klavelength Intervals are uniformly 10 nm wide, extending from 5 nm lower
than the center wavelength to 5 nm higher. Thus, the first Interval
centered on 290 extends from 285-295 nm.
-39-
Spring or
Summer Avg.a
0.0000625
0.0769
1.05
2.62
4.63
5.06
5.71
5.98
7.46
7.31
7.48
10.2
13.0
13.6
13.7
15.2
17.5
18.9
19.5
19.8
19.8
20.
20.
20.
20.
20,
20.3
20.5
20.8
21.2
21.5
21.6
21.8
21.8
21.7
22.3
22.8
23.1
23.4
23.4
23.4
23.0
23.2
23.0
22.9
22.8
22.6
22.5
22.3
22.2
22.1
21.9
Wavelength
Centerb
290
300
310
320
330
340
350
360
370
380
390
400
410
420
430
440
450
460
470
480
490
500
510
520
530
540
550
560
570
580
590
600
610
620
630
640
650
660
670
680
690
700
710
720
730
740
750
760
770
780
790
800
-------
Wavelength
Center1
290
300
310
320
330
340
350
360
370
380
390
400
A 10
420
i30
440
450
460
470
480
490
500
510
520
530
540
550
560
570
580
590
600
610
620
630
640
650
660
670
680
690
700
710
720
730
740
750
760
770
780
790
800
Summer
Solstice8
0.0000768
O.OB31
1.14
2.84
5.02
• 5.49
6.28
6.49
8.09
7.93
8.12
11.1
14.1
14.7
14.9
16.5
19.0
20.6
21.2
21.5
21.5
21.9
22.1
22.1
22.3
22.1
22.1
22.6
22.6
23.1
23.3
23.5
23.7
23.6
23.6
24.2
24.7
25.1
25.4
25.4
25.4
25.3
25.2
25.0
24.9
24.7
24.6
24.4
24.3
24.1
24.0
23.8
Equinox3
0.00000203
0.0457
0.787
2.13
3.88
4.30
4.88
5.15
6.45
6.25
6.53
8.97
11.4
12.-
12.2
13.5
15.5
16.8
17.3
17.6
17.7
18.0
18.1
18.1
18.3
18.2
18.1
18.3
18.6
19.0
19.2
19.3
19.5
19.3
19.2
19.8
20.4
20.7
21.0
21.0
21.0
21.0
•20.6
20.7
20.6
20.5
20.4
20.3
20.1
20.0
19.9
19.8
Table 6
Jx VALUES AT 30°N. LATITUDE
Winter Wavelength Fall or
Solstice3 Center"* Winter Avg.a
Spring or
Summer Avg.a
Wavelength
Center"
0.000000213
0.00835
0.300
1.06
2.13
2.48
2.89
3.10
3.95
3.95
4.12
5.73
7.37
7.81
8.00
8.94
10.4
11.3
11.7
11.9
12.0
12.2
12.3
12.4
12.5
12.4
290
0.000000457 0.0000352
12.4
12.5
12.7
13.0
13.2
13,
13
13.6
13.7
14.0
14.2
14.4
14.7
14.7
14.8
14.8
14.7
14.6
14.6
14.5
14
14,
14
14,
14
14.2
300
310
320
330
340 '
0.0208
0.480
1.47
2.81
3.19
0.0704
1.02
2.60
4.62
5.08
350
360
370
380
390
400
410
420
430
440
450
460
470
480
490
500
510
520
530
540
550
560
570
580
590
600
610
620
630
640
650
660
670
680
690
700
710
720
730
740
750
760
770
780
790
3.68
3.91
4.94
4.91
5.08
7.02
8.99
9.46
9.66
10.8
12.4
13.5
13.9
14.2
14.3
14.5
14.6
14.7
14.8
14.7
14.7
14.8
15.1
15.4
15.6
15.7
15.8
15.9
16.0
16.3
16.7
16.9
17.2
17.2
17.3
17.3
17.2
17.1
17.0
16.9
16.8
16.8
16.7
16.6
16. 5
800
16.4
*J values are in units of 1019 photons cm"2 day"1.
^Wavelength Intervals are uniformly 10 nm wide, extending from 5 nm lower
than the center wavelength to 5 nm higher. Thus, the first interval
centered on 290 extends from 285-295 nm.
-40-
5.74
6.02
7.51
7.37
7.55
10.4
13.2
13.7
13.9
15.4
17.8
19.2
19.8
20.1
20.1
20.5
20.6
20.7
20.9
20.6
20.6
20.8
21.1
21.6
21.8
22
22
22
22
22.6
23.1
23.5
23.8
23.8
23.8
23.7
23.6
23.4
23.3
23.2
23.0
22.9
22.7
22.6
22.5
22.3
290
300
310
320
330
350
360
370
380
390
400
410
420
430
440
450
460
470
480
490
500
510
520
530
540
550
560
570
580
590
600
610
620
630
640
650
660
670
680
690
700
710
720
730
74u
750
760
770
780
790
800
-------
Table 7
VALUES AT 40N. LATITUDE
Uavelenj
Center
290
300
310
320
330
340
350
360
370
380
390
400
410
420
430
460
450
460
470
480
490
500
510
520
530
540
550
560
570
580
590
600
610
620
630
640
650
660
670
680
690
700
710
720
730
740
750
760
770
780
790
800
'th Summer
b Solstice8
0.0000136
0.0769
1.12
2.87
5.11
5.62
6.35
6.61
8.32
8.17
8.37
11.5
14.6
15.2
15.5
17.1
19.7
21.3
22.0
22.3
22.3
22.7
22.9
22.9
23.2
23.0
22.9
23.1
23.5
24.0
24.2
24.4
24.6
24.5
24.5
25.1
25.7
26.1
26.4
26.3
26.4
26.4
26.2
26.1
25.9
25.8
25.6
25.5
25.3
25.2
25.0
24.8
Eoulnox8
0.000000121
0.0293
0.618
1.81
3.41
3.83
4.39
4.65
5.86
5. BO
5.99
8.26
10.5
11. 1
11.3
12.5
14.5
15.7
16.2
16.5
16.6
16.9
17.0
17.0
17.2
17.1
17.0
17.2
17.4
17.8
18.0
18.2
18.3
18.3
18.3
18.8
19.2
19.5
19.8
19.9
19.9
19.9
19.8
19.7
19.6
19.5
19.4
19.3
19.2
19.1
19.0
1.89
Winter
Solstice8
0.000000000615
0.00145
0.132
0.591
1.31
1.58
1.88
2.05
2.64
2.67
2.82
3.97
5.15
5.51
6.69
6.41
7.47
8.15
8.51
8.74
8.83
8.99
9.07
9.14
9.24
9.18
9.15
9.23
9.38
9.62
9.79
9.85
9.93
10.2
10.2
10.5
10.7
10.9
11.1
11.1
11.2
11.3
11.2
11.2
11.2
11.2
11.2
11.2
11.3
11.3
11.2
11.2
Wavelength
Center''
290
300
310
320
330
340
350
360
370
380
390
400
410
420
430
440
450
460
470
480
490
500
510
520
530 .
540
550
560
570
580
590
600
610
620
630
640
650
660
. 670
660
690
700
710
720
730
740
750
760
770
780
790
800
Fall or
Winter Avg.a
0.0000000814
0.00939
0.298
1.04
2.90
2.43
2.84
3.05
3.88
3.88
4.05
5.64
7.26
7.69
7.89
8.82
10.2
11. 1
11.5
11.8
11.9
12.1
12.2
12.3
12.4
12.3
12.3
12.4
12.6
12.9
13.1
13.2
13.2
13.4
13.5
13.8
14.1
14.3
14.5
14.6
14.6
14.7
14.6
14.6
14.5
14.5
14.4
14.4
14.3
14.3
14.2
14.1
Spring or
Summer Avg.8
0.00000349
0.0587
0.940
2.49
4.49
4.77
5.64
5.93
7.43
7.30
7.50
10.3
13.1
13.9
15.4
17.8
19.2
19.8
20.1
20.2
20.6
20.7
20.8
21.0
21.0
20.8
20.7
20.9
21.2
21.9
21.9
22.1
22.2
22.2
22.1
22.7
23.3
23.6
24.0
24.0
24.0
24.0
23.9
23.7
23.5
23.4
23.3
23.1
23.0
22.4
22.7
22.6
Wavelength
Center"1
290
300
310
320
330
340
350
360
370
380
390
400
410
420
430
440
450
460
470
480
490
500
510
520
530
540
550
560
570
580
590
600
610
620
630
640
650
660
670
680
690
700
710
720
730
740
750
760
770
780
790
800
aj. values are in units of 1019 photons cm"2 day"1.
^Wavelength intervals are uniformly 10 nm wide, extending from 5 nm lower than the center
wavelength to 5 nm higher. Thus, the first interval centered on 290 extends from 285-295
-41-
-------
Wavelength
Center^
290
300
310
320
330
340
350
360
370
380
390
400
410
420
430
440
450
460
470
480
490
500
510
520
530
540
550
560
570
580
590
600
610
620
630
640
65U
660
670
680
690
700.
710
720
730
740
750
760
770
780
790
800
Stumer
Solstice*
0.00000185
0.0635
1.05
2.81
5.10
5.64
6.41
6.75
8.46
8.32
8.56
11.8
15.0
15.7
15.9
17.6
20.3
22.0
22.7
23.1
23.1
23.5
23.7
23.8
24.0
23.8
23.7
24.0
24.3
24.8
25.1
25.3
25.5
25.4
25.3
26.0
26.7
27.1
27.5
27.5
27.5
27.5
27.3
27.2
27.0
26.9
26.7
26.6
26.4
26.3
2.61
26.0
Equinox8
0.000000200
0.0140
0.423
1.41
2.78
3.19
3.70
3.96
5.03
5.01
5.21
7.22
9.27
9.79
10. 0
11.2
12.9
14.0
li.5
14.8
15.0
15.2
15.3
15.4
15.6
15.5
15.4
15.5
15. B
16.1
16.4
16.5
16.6
16.8
17.0
17.3
17.6
17.8
18.1
18.2
18.2
18.2
18.1
18.1
18.0
17.9
17.8
17.8
17.7
17.6
17.5
17.4
Table 6
Jx VALUES AT
Winter
Solstice8
50°N. LATITUDE
Wavelength
Center"
Fall or
Winter Avg.a
Spring or
Summer Avg.a
Wave length
Center''
0.0000000112
0.0000681
0.321
0.214
0.555
0.711
0.864
0.953
1.25
1.28
1.37
1.95
2.57
2.79
2.92
3.33
.92
.31
4.54
4.70
4.78
4.88
4.94
4.98
5.05
5.02
5.01
5.04
5.11
5.27
5.38
5.42
5.47
5.61
5.77
5.93
6.10
6.24
6.39
6.47
6.56
6.64
6.67
6.72
6.75
6.78
6.82
6.82
6.82
6.82
6.80
6.80
290
800
0.0000000391 0.00000152
300
310
320
330
340
350
360
370
380
390
400
410
420
430
440
450
460
470
480
490
500
510
520
530
540
550
560
570
580
590
600
610
620
b30
640
650
660
670
680
690
700
710
720
730
740
750
760
770
780
790
0.00296
0.147
0.610
1.33
1.59
1.88
2.04
2.63
2.66
2.80
3.93
5.09
5.45
5.62
6.33
7.37
8.05
8.40
8.62
8.72
8.87
9.00
9.03
9.12
9.07
9.05
9.11
9.26
9.50
9.66
9.73
9.80
9.96
10.1
10.4
10.6
10.8
11.0
11. 0
11. 1
11.2
11.2
11.2
11.2
11.2
11. 1
11. 1
11.1
11.1
11.0
0.0433
0.810
2.28
4.23
4.73
5.40
5.71
7.18
7.09
7.31
10.1
12.8
13.5
13.7
15.2
17.6
19.0
19.7
20.0
20.1
20.4
20.6
20.6
20.8
20.7
20.6
20.8
21.1
21.6
21.8
22.0
22.1
22.1
22.1
22.7
23.3
23.6
24.0
24.0
24.0
24.0
29.9
23.8
23.6
23.5
23.4
23.3
23.1
23.0
22.9
11.0
22.8
8J, values are in units of 10 photons cm day .
A
Wavelength intervals are uniformly 10-nm wide, extending from 5 no lower than
the center wavelength to 5 no higher. Thus, the first Interval centered on 290 extends
from 285-295 no.
290
300
310
320
330
340
350
360
370
380
390
400
410
420
430
440
450
460
470
480
490
500
510
520
530
540
550
560
570
580
590
600
610
620
630
640
650
660
670
680
690
700
710
720
730
740
750
760
770
780
790
600
-42-
-------
Wavelength
Center
290
300
310
320
330
340
350
360
370
380
390
400
410
420
430
440
450
460
470
480
490
500
510
520
530
540
550
560
570
580
590
600
610
620
630
640
650
660
670
680
690
700
710
720
730
740
750
760
770
780
790
800
Summer
Solstice*
0.00000155
0.0466
0.024
2.67
4.99
5.60
6.41
6.79
8.55
8.45
8.72
17.0
15.4
16.1
16.4
18.3
21.1
22.8
23.6
24.0
24.1
24.5
24.7
24.8
25.0
24.9
24.8
25.0
25.4
25.9
26.2
26.4
2b.6
26.6
26.5
27.3
28.0
28.5
28.9
28.9
29.0
29.0
28.9
28.7
28.6
28.5
28.3
28.2
28.0
27.9
27.7
27.6
Equinox8
0.00000000845
0.00411
0.231
0.937
2.00
2.38
2.80
3.03
3.90
3.62
4.12
5.77
7.46
7.95
8.19
9.19
10.7
11.6
12.1
12.4
12.5
12.8
12.9
13.0
13.1
13.0
13.0
13.1
13.3
13.6
13.8
13.9
14.0
14.2
14.4
14.7
15.0
15.3
15.5
15.6
15.7
14.7
15.7
15.6
15.6
15.6
15.5
15.5
15.4
15.4
15.3
15.3
Table
Jx VALUES AT 60
Winter
Solstice*
0.00000000136
0.0000297
0.0000297
0.0277
0.0878
0.140
0.175
0.190
0.246
0.249
0.264
0.375
0.491
0.530
0.553
0.630
0.740
0.813
0.857
0.885
0.899
0.909
0.915
0.918
0.917
0.904
0.896
0.890
0.889
0.918
0.943
0.953
0.961
1.01
1.05
1.11
1.17
1.22
1.27
1.30
1.34
1.42
1.47
1.53
1.58
1.64
1.69
1.70
1.71
1.72
1.73
9
°N. LATITUDE
Wavelength
Center*
290
300
310
320
330
340
350
360
370
380
390
400
410
420
430
440
450
460
470
480
490
500
510
520
530
540
550
560
570
580
590
600
610
620
630
640
650
660
670
680
690
700
710
720
730
740
750
760
770
780
790
Fall or
Winter Avg.a
0.00000000486
0.000556
0.0544
0.275
0.656
0.818
0.921
1.07
1.39
1.42
1.50
2.12
2.77
2.99
3.10
3.52
4.11
4.51
4.72
4.87
4.94
5.03
5.08
5.12
5.18
5.14
5.13
5.16
5.23
5.38
5.49
5.53
5.57
5.69
5.83
6.00
6.14
6.20
6.42
6.48
6.56
6.64
6.67
6.71
6.75
6.78
6.82
6.81
6.81
6.81
6.79
Spring or
Sumuer Ave.a
0.000000441
0.0273
0.643
1.99
3.83
4.36
5.02
5.35
6.77
6.72
6.97
9.64
12.3
13.0
13.3
14.8
17.1
18.6
19.2
19.6
19.7
20.0
20.2
20.3
20.5
20.3
20.3
20.5
20.8
21.2
21.5
21.7
21.8
21.9
22.0
22.6
23.1
23.1
23.8
23.8
23.9
23".9
23.8
23.7
23.6
23.5
23.4
23.3
23.2
23.1
23.0
1.75
800
6.79
22.9
800
aj values are in units of 19 photons
19
day
"1
''Wavelength intervals are uniformly 10-nm vide, extending from 5 nn lower than the center
wavelength to 5 nm higher. Thus, the first interval centered on 290 extends froo 285-295 nm.
-43-
-------
Table 10
VALUES AT 70°N. LATITUDE
Wavelength
Center"
290
300
310
320
330
340
350
360
370
380
380
400
410
420
430
440
450
460
470
480
490
500
510
520
530
540
550
560
570
580
590
600
610
620
630
640
650
660
670
680
690
700
710
720
730
740
750
760
770
780
790
800
Summer
Solstice*
0.000000223
0.0280
0.764
2.49 .
4.92
5.66
6.57
7.02
8.91
.8.87
9.22
12.8
16.4
17.4
17.8
19.8
23.0
24.9
25.8
26.4
26.6
27.0
27.2
27.4
27.6
27.4
27.3
27.6
28.0
28.6
29.0
29.2
29.4
29.8
30.1
30.8
31.3
31.9
32.4
32.5
32.7
32.8
32.7
32.6
32.5
32.4
32.3
32.2
32.1
32.0
31.8
31.7
Equinox8
0.000000145
0.0000459
0.0822
0.466
1.13
1.42
1.71
1.88
2.45
2.50
2.66
3.77
4.94
5.33
5.54
6.30
7.37
8.09
8.48
8.75
8.89
9.05
9.15
9.23
9.34
9.29
9.27
9.33
9.1.7
9.74
9.93
10.0
10.1
10.3
10.5
10.8
11.1
11.1
11.5
11.6
11.8
11.9
11.9
12.0
12.0
12.0
12.1
12.0
12.0
12.0
12.0
12.0
a
;J, values are in units of
Winter
Solstice'
0.00
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
photons cm"2 day"1.
Wavelength
Center"
290
Fall or
Winter Avg.a
Spring or
Summer Avg.
800
0.00000000290 0.000000176
300
310
320
330
340
350
360'
370
380
390
400
410
420
430
440
450
460
470
480
490
500
510
520
530
540
550
560
570
580
590
600
610
620
630
640
650
660
670
680
690
700
710
720
730
740
750
760
770
780
790
0.0000247
0.0134
0.0869
0.230
0.299
0.364
0.400
0.521
0.532
0.568
0.807
1.059
1.147
1.20
1.36
1.60
1.76
1.85
1.91
1.95
1.98
2.00
2.02
2.04
2.03
2.02
2.03
2.05
2.11
2.16
2.16
2.20
.2.26
2.33
2.40
2.48
2.54
2.61
2.64
2.69
2.74
2.77
2.81
2.84
7.87
2.91
2.91
2.92
2.92
2.92
0.0136
0.460
1.64
3.34
3.91
4.57
4.91
6.27
6.27
6.56
9.13
11.8
12.5
12.8
14.4
15.7
18.1
18.8
19.2
19.4
19.7
19.9
20.0
20.2
20.1
20.0
20.2
20.5
21.0
21.3
21.5
21.6
21.9
22.2
22.7
23.1
23.5
23.9
24.0
24.1
24.2
24.1
24.1
24.0
24.0
23.9
23.8
23.8
23.7
23.6
2.92
23. 5
Wavelength
Center"
290
300
310
320
330
340
350
360
370
380
390
400
410
420
430
440
450
460
470
480
490
500
510
520
530
540
550
560
. 570
58C
590
600
610
620
630
640
650
660
670
680
690
700
710
720
730
740
750
760
770
780
790
800
Wavelength intervals are uniformly 10-nm wide, extending from 5 no lower than
the center wavelength to 5 no higher. Thus, the first interval centered on 290
extends from 285-295 nm.
-44-
-------
Appendix B. Operation of the Gas Handling System
The following procedure briefly describes the recommended
typical and detailed operation of a gas handling system.
[Adapted from the report by Pitts et al. (1981)].
(1) Close all stopcocks and turn on the rotary pump (A).
Open stopcock 4 and place a Dewar containing liquid nitrogen
around trap (D). Measure the pressure with the thermocouple
gauge H^. When the pressure is less than 0.1 torr «0.013 kPa)
open stopcocks 5 and 10, pump out this portion of the manifold/
and measure the pressure with the thermocouple gauge F^. When
— 2 —3
the pressure falls below 10 torr «1.3 x 10 - kPa), open
stopcock 7 and evacuate F containing activated Linde Molecular
Sieve 4A or an equivalent grade. Heat F to approximately 150 °C
for 1-2 h under vacuum until the pressure falls to less than
~? -3
10 torr (<1.3 x 10 kPa) as measured on thermocouple gauge
H2« Open stopcocks 6, 9, and 11 and pump until ^2 falls below
10~2 torr «1.3 x 10"3 kPa).
(2) Turn on the diffusion pump (C) and when this pump has
reached operating temperature, open stopcocks 2 and 3 and close
stopcock 4. Pump on the manifold until the pressue is
10" torr ( 1.3 x 10 kPa) as measured by the ionization
gauge (I) and zero on the capacitance manometer (G). It should
be noted that the ionization gauge (I) should only be used when
— 2 —3
H2 indicates a pressure less than 10 torr (<1.3 x 10 kPa).
(3) It is good practice, after the gas-phase spectrum has
been obtained, to evacuate the gas absorption cell (K) and the
trap (F) prior to shutting down the gas handling system. The gas
«
-45-
-------
handling system can be shut down by the following procedure: (a)
close stopcocks 5 to 11, (b) switch off the diffusion pump; (c)
close stopcocks 2 and 3 and open 4, after the diffusion pump is
cool; (d) remove the Dewar from trap (D) and allow it to warm up;
(e) then close stopcock 4 and switch off the rotary pump; and (f)
open stopcock 1 to admit air to the rotary pump, thus preventing
"suck-back" of the rotary pump oil. with this procedure, the
vacuum manifold, the trap D, and the diffusion pump are left
under vacuum. The method of cleaning the liquid reservoir (J) is
left to the discretion of the tester. However, as a final step
it should be cleaned with reagent grade methanol or
dichloromethane as solvent and dried. . it is then ready for
use. In operating a vacuum system with the diffusion pump
working, do not expose the diffusion pump to pressures
> 0.1 torr of air « 1.3 x 10"2 kPa)to avoid the degradation of
the pump oil.
REFERENCES
Benson, S.W. 1976. Thermochemical Kinetics. Second Edition.
Wiley-Interscience, NY.
Braslau, N. and Dave, J.V. 1973a. Effect of Aerosols on the
Transfer of Solar Energy Through Realistic Model Atmospheres.
PART I: Nonabsorbing Aerosols. J. Appl. Meteor. 12, 601.
Braslau, N. and Dave, J.V. 1973b. Effects of Aerosols on the
Transfer of Solar Energy Through Realistic Model Atmospheres
PART II: Partly Absorbing Aerosols. J. Appl. Meteor. 12, 616,
Calvert, J.G. and Pitts, J.N., Jr. 1966. Photochemistry.
Wiley, N.Y. Y
-46-
-------
Dave, J.V. 1972. Development of Programs for Computing
Characteristics of Ultraviolet Radiation. Final Report under
Contract NAS 5-21680. NASA Report CR-139134. Nat. Aeron. and
Space Admin., Goddard Space Flight Center, Greenbelt, MD (NTIS
No. N75-10746/6SL). 27 pp.
Davenport, J.E. 1985. SRI International, Menlo Park, CA,
personal communication. Tables of J...
Demerjian, K.L. 1974. The Mechanism of Photochemical Smog
Formation. Adv. Env. Sci. and Tech. _4_, 1.
Demerjian, K.L., Schere, K.L., and Peterson, J.T. 1980.
Theoretical Estimates of Actinic (Spherically Integrated) Flux
and Photolytic Rate Constants of Atmospheric Species in the Lower
Troposphere. Adv. Sci. and Tech. 10, 369.
-p-inlayson-Pitts, B.J. and Pitts, J.N., Jr. 1986. Atmospheric
emistry: Fundamentals and Experimental Techniques. J. Wiley-
.iterscience, N.Y.
Hendry, D.G. and Kenley, R.A. 1979. Atmosphere Reaction
Products of Organic Compounds. EPA-500/12-79-001.
Herron, J.T., Huie, R.E., and Hodgeson, J.A. 1979. Chemical
Kinetic Data Needs for Modeling the Lower Troposphere. National
Bureau of Standards Publication 557.
Leighton, P.A. and Perkins, W.A. 1956. Solar Radiation,
Absorption Rates, and Photochemical Primary Processes in Urban
Air. Rept. No. 14, Air Poll. Found., Los Angeles, CA.
Leighton, P.A. 1961. Photochemistry of Air Pollution. Academic
Press, N.Y.
Leifer, Asa. (USEPA). 1983. Chemical Fate Test Guidelines and
Support Documents. Gas Phase Absorption Cross Section and
Sunlight Photolysis. CG, CS-7000. U.S. Environmental Protection
Agency, Office of Toxic Substances, Washington, DC 20460.
EPA/6-83-003. Published by National Technical Information
Service. PB 83-257717. 1983. Springfield, VA 22151.
Leifer, Asa. (USEPA). 1985. Fed. Reg. 50_ 39252-39516. 40 CFR
796, 797, and 798. Toxic Substances Control Act Test
Guidelines: Final Rules. § 796.3800. Gas-Phase Absorption
Spectra and Photolysis, p. 39311. § 796.1050. Absorption
Spectra in Aqueous Solution: Ultraviolet/visible spectra, p.
39472.
Leifer, Asa. 1989. Determination of Rates of Reaction in the
Gas-Phase in the Troposphere. Theory and Practice. 1.
Hierarchal Test Scheme. U.S. Environmental Protection Agency,
Office of Toxic Substances, Washington, DC 20460. EPA-_ "
-47-
-------
Mill, T., Mabey, W.R. , Bomberger, D.C., Chou, T-W. , Hendry, D.G.,
and Smith, J.H. 1982. Laboratory Protocols for Evaluating the
Fate of Organic Chemicals in Air and Water. Chapter 5.
Atomspheric Chemistry by Hendry, D.G. EPA-600/3-82-002.
Mill, T., Davenport, J.E., Winterle, J.S. , Mabey, W.R., Drossnan,
H., Tse, D., and Liu, A. 1983. Toxic Substances Process
Generation and Protocol Development. Work Assignment 12. Draft
final report. Appendix.A. Lower and Upper Tier Protocols for
Air Photolysis Rate Constants. J.E. Davenport. USEPA, Office of
Research and Development and Office of Toxic Substances, Athens,
GA and Washington, DC, respectively.
Mill, T., Winterle, J.S., Fischer, J.S., Tse, D., Mabey, W.R.,
Drossman, H., Liu, A., Davenport, J.E. 1985. Toxic Substances
Process Generation and Protocol Development. Work Assignment
12. Draft Final Report. Section 5. Photolysis in Air by J.E.
Davenport. USEPA, Office of Research and 'Development and Office
of Toxic Substances, Athens, GA and Washington, DC, respectively.
Peterson, J.T. 1976. Calculated Actinic Fluxes (290-700 nn) for
Air Pollution Photochemistry Applications. EPA-600/4-76-025.
Pitts, J.N., Jr., Winer, A.M., Fitz, D.R., Knudsen, A.K., and
Atkinson, R. 1981. Experimental Protocol for Determining
Absorption Cross Sections of Organic Compounds. EPA-600/3-81-
051. • .
Prutton, C.F. and Maron, S.H. 1951. Fundamental Principles of
Physical Chemistry. Chapter XXII. Macmillan, NY.
Reynolds, S.D. 1973. Mathematical Modeling of Photochemical Air
Pollution—I. Formulation of the Model. Atm. Environ. ]_, 1033.
Schere, K.L. and Denerjian, K.L. 1977. Calculation of Selected
Photolytic Rate Constants Over a Diurnal Range. EPA-600/4-77-
015.
Zepp, R.G. and Cline, D.M. 1977. Rates of Direct Photolysis in
Aquatic Environment. Env. Sci. and Tech. _1_, 359.
-48-
-------
NO.
EPA 560/5-89-007
50377 -I
REPORT DOCUMENTATION |.»-_REroRT
PAGE
4. TKie and subtitle Determination of Rates of Reaction in the Gas-Phase
in the.Troposphere. Theory and Practice. 2. Rate of Direct Photo-
reaction: Screening-Level Test Guideline-Spectroscopic Determina-
tion of the Cross Section and the Maximum Rate of Direct Photo-
7. Aott>or reaction in buniignt
Asa Leifer
f. Performing Organization Name and Address
J.S. Environmental Protection Agency
Office of Toxic Substances
Exposure Assessment Branch (TS-798)
401 M Street, SW
Washington, DC 20460
X Recipient* • Accession No.
5. Report Date
November 1989
«- *irtonnl«i Ofga«Uation Mept. No.
10. ProJect/Task/Work Unit No.
11. Cootn»ct(O or Grant(G) No.
(C)
(G)
12. Sponsoring Organization Name and Address
U.S. Environmental Protection Agency
Office of Toxic Substances
401 M Street SW
Washington, DC 20460
13. Type of Report A Parted Covered
14.
15. Supplementary Notes
1ft. Abstract (Limit 200 words)
This report describes in detail a simple and cost-effective
screening test for estimating an environmentally relevant maximum
rate constant and minimum half-life for direct photoreaction of a
chemical in the gas-phase in the troposphere. This report has two
main sections: PART I. THEORY AMD DEVELOPMENT OF THE SCREENING
TEST AND PART II. TEST PROCEDURES AND DATA REPORTING. PART II
describes detailed procedures for measuring the cross section of
a chemical in the gas-phase in the laboratory by spectroscopic
techniques and data reporting for sections 4 and 5 of TSCA. Tables
of solar irradiance (JA ) are given from 0° to 70° North latitude in
10° increments as a function of season of the year to cover the
continental United States and other parts of the U.S. such as
Alaska, Hawaii, etc. An example is given to illustrate how to use
all the experimental cross section data and solar irradiance data
(J^ ) to estimate the maximum rate of direct photoreaction
and the minimum half-life
17. Document Analysis a. Descriptor*
b, IdontlflerB/Open-Ended Terms
Rate of direct photoreaction in the troposphere, Screening-level test method, maximum
direct photoreaction rate constant, minimum half-life for direct-photoreaction, absorption
spectroscopy in the gas-phase, cross section, test guideline for the Toxic Substance ;
Control Act, Sunlight photoreaction, Tables of solar irradiance
e. COSATI Field/Group
It. Availability Statement
Release Unlimited
». Security Class (This Report)
Unclassified
20. Security Class (This Page)
21. No. of Paces
48
22. Price
(See ANSI-Z39.18)
See Instructions on Reverse
OTTIONAL FORM 272 (4-7
(Formerly NTIS-35)
Department of Commerce
------- |