United States Prevention, Pesticides EPA712-C-98-066
Environmental Protection and Toxic Substances January 1998
Agency (7101)
vvEPA Fate, Transport and
Transformation Test
Guidelines
OPPTS 835.2310
Maximum Direct
Photolysis Rate in Air
from UVA/isible
Spectroscopy
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INTRODUCTION
This guideline is one of a series of test guidelines that have been
developed by the Office of Prevention, Pesticides and Toxic Substances,
United States Environmental Protection Agency for use in the testing of
pesticides and toxic substances, and the development of test data that must
be submitted to the Agency for review under Federal regulations.
The Office of Prevention, Pesticides and Toxic Substances (OPPTS)
has developed this guideline through a process of harmonization that
blended the testing guidance and requirements that existed in the Office
of Pollution Prevention and Toxics (OPPT) and appeared in Title 40,
Chapter I, Subchapter R of the Code of Federal Regulations (CFR), the
Office of Pesticide Programs (OPP) which appeared in publications of the
National Technical Information Service (NTIS) and the guidelines pub-
lished by the Organization for Economic Cooperation and Development
(OECD).
The purpose of harmonizing these guidelines into a single set of
OPPTS guidelines is to minimize variations among the testing procedures
that must be performed to meet the data requirements of the U. S. Environ-
mental Protection Agency under the Toxic Substances Control Act (15
U.S.C. 2601) and the Federal Insecticide, Fungicide and Rodenticide Act
(7U.S.C. I36,etseq.).
Final Guideline Release: This guideline is available from the U.S.
Government Printing Office, Washington, DC 20402 on The Federal Bul-
letin Board. By modem dial 202-512-1387, telnet and ftp:
fedbbs.access.gpo.gov (IP 162.140.64.19), or call 202-512-0132 for disks
or paper copies. This guideline is also available electronically in ASCII
and PDF (portable document format) from EPA's World Wide Web site
(http://www.epa.gov/epahome/research.htm) under the heading "Research-
ers and Scientists/Test Methods and Guidelines/OPPTS Harmonized Test
Guidelines."
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OPPTS 835.2310 Maximum direct photolysis rate in air from UV/visi-
ble spectroscopy.
(a) Scope — (1) Applicability. This guideline is intended to meet test-
ing requirements of both the Federal Insecticide, Fungicide, and
Rodenticide Act (FIFRA) (7 U.S.C. 136, et seq.) and the Toxic Substances
Control Act (TSCA) (15 U.S.C. 2601).
(2) Background. The source material used in developing this har-
monized OPPTS test guideline is 40 CFR 796.3800 Gas Phase Absorption
Spectra and Photolysis.
(b) Introduction — (1) Background and purpose. Numerous chemi-
cals enter the atmosphere from a variety of sources. For example, chemi-
cals enter the atmosphere as a result of the burning of coal, from the com-
bustion of gasoline in cars and diesel fuel in trucks, and from the release
of volatile organic chemicals during manufacture, processing, use, and dis-
posal. Pesticides, applied from airplanes, enter the atmosphere directly and
volatilize from soils and water bodies. Chemical pollutants present in the
atmosphere can undergo photochemical transformation in the environment
by direct photolysis in sunlight. Quantitative data in the form of rate con-
stants and half-lives are needed to determine the importance of direct pho-
tolysis of pollutants in the atmosphere. This test method describes a first-
tier screening level test method to estimate the maximum direct photolysis
rate constant and minimum half-life of chemicals in the atmosphere in
sunlight as a function of latitude and season of the year in the United
States.
(2) Definitions and units. The definitions in section 3 of TSCA and
in 40 CFR Part 792— Good Laboratory Practice Standards (GLP) apply
to this test guideline. The following definitions also apply to this test
guideline.
Absorbance (A^) is defined as the logarithm of the ratio of the initial
intensity (Io) of a beam of radiant energy to the intensity (I) of the same
beam after passage through a sample at a fixed wavelength X. Thus,
= log (Io/I).
The actinic solar irradiance in the atmosphere (J^) is related to the
sunlight intensity in the atmosphere and is proportional to the average light
flux (in units of photons per square centimer per day) that is available
to cause photoreaction in the wavelength interval AX, centered at X, over
a 24-hour day at a specific latitude and season date. It is the irra-
diance which would be measured by a weakly absorbing spherical acti-
nometer exposed to direct solar radiation and sky radiation from all direc-
tions.
The Beer-Lambert law states that the absorbance of a chemical in
the gas phase, at a fixed wavelength, is proportional to the thickness of
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the absorbing material (1), or the light pathlength, and the concentration
of the absorbing species (C).
Cross section fo/) is defined as the proportionality constant in the
Beer-Lambert law. Thus, AX = CTX' Cl, where AX is the absorbance, C
is the concentration in molecules per cubic centimeter and 1 is the
pathlength in centimeters. The units of the cross section ax' are square
centimeters per molecule. Numerical values of the cross section depend
upon the nature of the absorbing species.
Direct photolysis is defined as the direct absorption of light by a
chemical followed by a reaction which transforms the parent chemical into
one or more products.
A first-order reaction is defined as a reaction in which the rate of
disappearance of a chemical is directly proportional to the concentration
of the chemical and is not a function of the concentration of any other
chemical present in the reaction mixture.
The Grotthus-Draper law, the first law of photochemistry, states that
only light which is absorbed can be effective in producing a chemical
transformation.
The half-life (t\/2) of a chemical is defined as the time required for
the concentration of the chemical being photolyzed to be reduced to one-
half its initial value.
Radiant energy, or radiation, is defined as the energy traveling as
a wave unaccompanied by transfer of matter. Examples include X-rays,
visible light, UV light, radio waves, etc.
The reaction quantum yield ((f)?i) for an excited state process is de-
fined as the fraction of absorbed light that results in photoreaction at a
fixed wavelength A,. It is the ratio of a number of molecules that photoreact
to the number of quanta of light absorbed or the ratio of the number of
moles that photoreact to the number of einsteins of light absorbed at a
fixed wavelength X.
The Stark-Einstein law, the second law of photochemistry, states that
only one molecule is activated to an excited state per photon or quantum
of light absorbed.
The sunlight direct potolysis rate constant (kpE) is the first-order rate
constant (in units of day *) and is a measure of the rate of disappearance
of a chemical in the gas phase in sunlight.
(3) Principle of the test method, (i) For weak absorbance of a chemi-
cal in the atmosphere, the first-order direct photolysis rate constant, kpe,
is given by the equation
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Equation 1
kpE = 2.30
where (f>x is the reaction quantum yield; §\ is the cross section (in units
of cm2 molecule *) averaged over a wavelength interval AX, centered at
X; Jx is the actinic solar irradiance (in units of photons cm 2 day *) aver-
aged over the wavelength interval AX, centered at X; and the summation
is taken over the range AX = 290 to 800 nm. Jx is the solar actinic irradi-
ance in the atmosphere under clear sky conditions and is a function of
latitude and season of the year.
(ii) Since this photolysis process is first-order, the half-life (ti/i) of
a chemical is given by
Equation 2
ti/2 = 0.693/kpe
(iii) A simple first-tier screening test has been developed using Equa-
tion 1. As an approximation, it is assumed that the reaction quantum yield
4>x is equal to 1, the maximum value. As a result, the upper limit for
the direct photolysis sunlight rate constant in the gas phase is obtained
and Equation 1 becomes
Equation 3
(kpE)max = 2.30 Ła\Jx
Using Equation 3 in Equation 2, the lower limit for the half-life is given
by
Equation 4
(tl/2)min = 0.693/(kpE)max
The cross section can be determined experimentally by the procedures out-
lined in paragraph (c) of this guideline and the values of Jx are given
in Tables 1 to 4 under paragraph (c)(3) of this guideline as a function
of latitude and season of the year in the United States. These data can
be used in Equation 3 to calculate (kpE)max. Finally, (kpE)max can be sub-
stituted in Equation 4 to calculate (ti/2)min.
(4) Applicability and specificity, (i) This test method is applicable
to all chemicals which have UV/visible absorptions in the range 290 to
800 nm. Some chemicals only have absorptions below 290 nm and con-
sequently cannot undergo direct photolysis in sunlight (e.g. chemicals such
as alkanes, alkenes, alkynes, dienes, and fluoroalkanes).
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(ii) This test method is only applicable to pure chemicals and not
to the technical grade.
(iii) The first-tier screening test can be employed to estimate (kpE)max
and (ti/2)min. If these data indicate that gas phase photolysis is an important
process relative to other gas phase transformation processes (e.g. oxidation
with hydroxyl radicals or ozone), it is recommended that an upper-tier
photolysis test be carried out to determine the reaction quantum yield and
thus obtain more precise environmentally relevant rate constants and half-
lives in sunlight. The data obtained from this first-tier test method can
be used to determine (kpE)max for a test chemical as a function of latitude
and season of the year in the United States under clear sky conditions.
These rate constants are in a form suitable for preliminary mathematical
modeling for environmental fate of a test chemical.
(c) Test procedures. The procedures outlined in this test method are
based on the method proposed by Mill et al. under paragraph (e)(l) of
this guideline and developed by Pitts et al. under paragraph (e)(2) of this
guideline. It is also recommended that OPPTS 830.7050 be consulted for
additional guidance.
(1) Test conditions—(i) UV/visible spectrophotometer. Although
single-beam spectrophotometers may be used, recording double beam
spectrophotometers are recommended. It is extremely important that the
spectrophotometer be able to scan over the wavelength region 270 to 800
nm and have an absorbance sensitivity, at a signal/noise ratio of one, of
approximately 0.001. It is important that the spectrophotometer be able
to attain a 90 percent separation of two monochromatic spectral features
approximately 4 nm apart, peak to peak (i.e. the resolution should be at
least 4 nm). It is also desirable to have a spectrophotometer that can ac-
commodate absorption cells of length >10 cm. A Gary 219 UV/Visible
Spectrophotometer, or an equivalent model, is recommended.
(ii) Vapor and liquid absorption cells. (A) Long pathlength cells
are preferable; however, many commercial spectrophotometers will only
accept absorption cells of 10 cm or less. A suitable vapor cell is depicted
in the following Figure 1.
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FIGURE 1—GAS ABSORPTION CELL
IT on i e-tiiw
on
>3U A FiH ;
(B) A suitable vapor cell can be constructed as follows. The vapor
cell should be constructed of Pyrex, 1 cm O.D. and 10 cm in length, and
be fitted with plane parallel quartz windows at each end. The quartz win-
dows can be conveniently attached to the Pyrex cell with vaccum 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 con-
nected to the cell and contain an O-ring joint. The O-ring joint (e.g. no.
7 or no. 9, Kontes or Ace Glass) must match the one on the vacuum
rack. Viton O-rings are 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 be-
tween the cells can be compensated for by running a blank with the sample
and reference cells in the spectrophotometer. The use of stopcock grease
is not required with these cells and should be avoided.
(C) A matched pair of liquid absorption cells is very desirable but
is not essential. A pair of quartz UV absorption cells, 10 cm in length,
having ground glass or Teflon stoppers are recommended. These liquid
absorption cells are readily available commercially.
(iii) Vacuum gas handling system. A suitable gas handling system
is shown diagramatically in the following Figure 2 and should be con-
structed completely with Pyrex glass.
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FIGURE 2—SCHEMATIC OF GAS HANDLING VACUUM RACK
PINCH CLAMP
ULTRA-HIGH
PURITY AIR
CYLINDER
A ROTARY PUMP
B RUBBER TUBING (THICK WALLED)
C DIFFUSION PUMP
D TRAP AT LIQUID NITROGEN
TEMPERATURE
E #7 OR 9 O-RING JOINTS
F MOLECULAR SIEVE 4A TRAP
G CAPACITANCE MANOMETER
H THERMOCOUPLE GAUGE
I IONIZATION GAUGE
J LIQUID RESERVOIR
K GAS ABSORPTION CELL
VENTED EXHAUST
t
0-4 OR 0-5 mm
STOPCOCKS
) 0-8 OR 0-1 Omm
STOPCOCKS
The components of the gas handling system are discussed below. The use
of stopcock grease is not required and should be avoided.
(A) Vacuum pumping system. (7) In order to achieve a good vacu-
um, 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.
(2) The second pump, a high vacuum model, should be a multistage
oil diffusion pump (C) (e.g. a Consolidated Vacuum Corp. 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 6 torr (1.3 x 10 7 kPa)
(e.g. Dow-Corning D.C. 702 or 703, or an equivalent grade).
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(3) 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 requires only 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.
(B) Vacuum rack. The recommended vacuum rack assembly is de-
picted in Figure 2 under paragraph (d)(l)(iii) of this guideline. 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) (no. 7 or no. 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).
(C) Pressure Gauges. Three pressure gauges are required:
(7) An ionization gauge to measure high vacuum (<10 3 torr
(1.3x10 4 kPa)).
(2) A thermocouple gauge to monitor the pressure in the range 10 3
to 1 torr (1.3 x 10 4 to 0.13 kPa). A convenient pressure monitoring system
which contains ionization and thermocouple gauges is a Consolidated Vac-
uum Corp. Model GIC-300A or an equivalent model.
(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 exam-
ple, an MKS Baratron 310 BHS-1000 with the associated 170-6C elec-
tronics unit and a digital readout or an equivalent model. While this vacu-
um gauge exhibits a slow zero drift, it can be readily rezeroed using the
ionization gauge, i.e. when the ionization gauge reads approximately
10 3 torr (0.00013 kPa) or less.
(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 proce-
dure described in paragraph (d)(5) of this guideline is recommended.
(3) Preparation of samples—(i) Preparation of the gas phase test
chemical sample: Preliminary Steps. (A) If the test chemical is a gas
at room temperature, attach the gas container to the O-ring at the point
where the liquid reservoir (J) is placed. Close stopcocks 2 and 3 and open
4. Pump until the pressure is <10 2 torr (1.3 x 10 3 kPa) as read on ther-
mocouple gauge (H2). Then open stopcocks 2 and 3 and close 4 and pump
until the pressure is less than 10 5 torr (1.3 x 10 6 kPa) as read on the
ionization gauge (I).
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(B) If the test chemical is a liquid at room temperature, add a few
cubic centimeters of liquid to a reservoir tube (J), sealed at one end and
containing an O-ring at the other end, and connect the tube via the CD-
ring to stopcock 6. Freeze the sample with a Dewar containing liquid nitro-
gen, 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) Introduction of the test chemical into the gas absorption cell.
(A) 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,
stopcock 6 should be opened and the gas container valve is 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 ma-
nometer (G). Close the gas container valve and stopcock 6 and allow ap-
proximately 5 min before the final pressure at (G) is read. If the pressure
has not stabilized in approximately 5 min allow the cell to condition for
several hours before the final pressure at (G) is read.
(B) 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 min before the final
pressure at (G) is read. If the pressure has not stabilized in approximately
5 min, allow the cell to condition for several hours before the final pressure
at (G) is read.
(C) 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 pres-
sure less than 10 5 torr (1.3 x 10 6 kPa). Stopcocks 5 and 10 are then
closed and ultra-high purity air from a cylinder is admitted into the gas
handling manifold via stopcock 8 and through the trap (F) containing Mo-
lecular Sieve 4A. When the manifold is at one atmosphere pressure, as
measured by pressure gauge (G), stopcock 11 is briefly opened to pressure
the gas absorption cell to one 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 photolysis.
(D) Based on the pressure P of the test chemical, as measured by
gauge (G), the concentration of the gas sample is
Equation 5
8
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C (molecules cm 3) = 9.657 x 1018 P(torr)/T( K)
Equation 5 a
C (molecules cm 3) = 1.287 x 1018 P(kPa)/T(K)
where T is the room temperature in degrees Kelvin, which should be rou-
tinely monitored with a thermometer.
(F) 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.
(iii) Preparation of solution phase test chemical sample. (A) If the
properties of the test chemical (i.e. small cross sections, low vapor pres-
sure) 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.
(B) The following spectroscopic grade chemicals are recommended
to prepare solutions: chloroform, w-hexane, acetonitrile, and cyclohexane.
Solutions of up to 10 percent by volume of test chemical can be prepared
in one of these solvents in the standard manner.
(C) The concentration of the test chemical is given by the following
equations
Equation 6
C (molecules cm 3) = 6.022 x 1023 mass (gms)/FW (Vd)
Equation 6 a
C (molecules cm 3) = 6.022 x 1023 Vsp/FW (Vd)
where Vs is the volume of test chemical delivered into a volume Vd of
solvent cubic centimeters, FW is the formula weight of the test chemical
in grams, and p is the density of the test chemical in grams per cubic
centimeter at the room temperature the solution was prepared.
(4) Procedure for obtaining the spectrum. As a general guide to
obtaining UV/visible absorption spectra, the procedures outlined in OPPTS
830.7050 are recommended. Since the method presented in this procedure
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was developed by Pitts et al. (1981), it is recommended that this report
be consulted for further details.
(i) Determination of the cell pathlength. The method for determin-
ing the cell pathlength of gas or liquid cells is left to the discretion of
the tester. However, the method listed in OPPTS 830.7050, using one of
the reference compounds, is recommended.
(ii) Gas phase spectrum. Measure the absorbance of the test chemi-
cal in duplicate relative to a matched cell filled with ultra-high 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 same reference cells are 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,
a'x, at the appropriate wavelength intervals, centered at wavelength A,, list-
ed in Tables 1 through 4, under paragraph (d)(3) of this guideline.
(iii) Solution phase spectrum. (A) Measure the absorbance of the
test chemical in duplicate relative to a matched cell containing the solvent.
The absorbance should be measured for wavelengths A > 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'x, for the appropriate wavelength
intervals, centered at A, listed in Tables 1 through 4 under paragraph (d)(3)
of this guideline.
(B) The concentration of the test chemical should be in the range
where the Beer-Lambert law is obeyed. A check on whether the test chemi-
cal obeys this law can be accomplished by demonstrating the constancy
of the cross section at three concentrations differing by a factor of 10.
(d) Data and reporting—(1) Treatment of results—(i) Determina-
tion of the cross section from the gas phase spectrum. (A) The cross
section, ax, can be determined from the gas phase absorption spectrum
and the Beer-Lambert law in the form
Equation 7
ax' = Ax/Cl
where AX is the absorbance at wavelength A, centered in the wavelength
interval >A, C is the concentration of test chemical in molecules per cubic
centimeter, and 1 is the cell pathlength in centimeters. The cross section
of the test chemical should be determined for the wavelength intervals
listed in Tables 1 through 4 under paragraph (d)(3) of this guideline.
10
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(B) There are at least three nondestructive methods of determining
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 AX x nm) followed by division by the width of the region in nm to
obtain absorbance. The method using a compensating polar planimeter is
the most accurate and is recommended. The absorbance should be obtained
from the average of three tracings.
(ii) Determination of the cross section from the solution phase
spectrum. The cross section, o'x, can be determined from the solution
phase spectrum using Equation 7 for the wavelength intervals listed in
Tables 1 through 4 under paragraph (d)(3) of this guideline. For solution
spectra, estimating an average absorbance over the wavelength intervals
is sufficient to yield accurate results.
(iii) Estimation of the maximum direct photolysis rate constant
and minimum half-life in the gas phase. (A) Using the cross sections
obtained from the spectra and the values of Jx from Tables 1-4 under
paragraph (d)(3) of this guideline, the maximum direct photolysis rate con-
stant (kpE)max can be calculated at a specific latitude and season for the
year using Equation 3. The minimum half-life, (ti/2E)min, can be calculated
using this (kpE)max in Equation 4.
(B) An example is presented in under paragraph (d)(4) of this guide-
line, to illustrate how the test data obtained in this section can be used.
(2) Test data report, (i) 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.
(ii) Gas phase spectra. (A) Report the pressure of the test chemical
in torr (or kPa), the concentration in molecules per cubic centimeter, and
the pathlength of the sample cell in centimeters. Describe the method used
to determine the pathlength and report the experimental data.
(B) Report the wavelength A,, the wavelength interval for each
10 nm over the region of absorption, the value of the absorbance (Ax)
for each replicate, the mean absorbance, and the mean cross section in
square centimeters per molecule.
(C) Report the estimated maximum direct photolysis rate constant in
units of reciprocal days and the corresponding minimum half-life in days
at 20°, 30°, 40°, and 50° north latitude for the summer and winter solstices.
11
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(iii) Solution phase spectra. (A) Report the concentration of the test
chemical in molecules per cubic centimeter, the type of cell used (quartz
or borosilicate), and the pathlength in centimeters, the method used to de-
termine the pathlength and report the experimental results.
(B) Report the identity of the solvent.
(C) Report the wavelength A,, the wavelength interval over the region
of absorption, the value of the absorbance (Ax) of each replicate, the mean
absorbance, and the mean cross section square centimeter per molecule.
(D) Report the estimated maximum direct photolysis rate constant in
days * and the corresponding minimum half-life in days at 20°, 30°, 40°,
and 50° north latitude for the summer and winter solstices.
(iv) Report the name, structure, and purity of the test chemical.
(v) Submit a recent spectrum on appropriate reference chemicals for
photometric and wavelength accuracy.
(vi) Report the name and model of the spectrophotometer used.
(vii) Report the various control settings employed with the
spectrophotometer. These might include scan speed, slit width, given, etc.
(viii) Report anything unusual about the test; e.g. if the Beer-Lambert
law is not obeyed at a pressure of 1 to 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 concentra-
tions, report the concentration at which the deviation was overcome and
the experimental data.
(ix) Report any other relevant information.
(3) Tables of solar irradiance
Table 1—Jx Values at20°N. Latitude
Wavelength
centerb
290
300
310
320
330
340
350
360
370
380
390
400
410
420
430
440
450
460
470
Summer sol-
stice a
0.000081 1
0.0810
1 10
2.74
4.82
527
5.94
6.22
776
7.60
7.77
106
13.5
14.1
143
15.8
18.2
197
20.2
Equinox3
0.00000131
0.0611
09148
2.35
4.20
461
5.22
5.47
684
6.71
6.88
944
12.0
12.5
127
14.1
16.2
175
18.1
Winter sol-
stice a
0.000000108
0.0212
0499
1.52
2.90
328
3.77
4.01
506
5.02
5.19
7 17
9.17
9.65
985
11.0
12.7
137
14.2
Wave-
length cen-
terb
290
300
310
320
330
340
350
360
370
380
390
400
410
420
430
440
450
460
470
Fall or winter
average a
0.000000896
0.0359
0663
1.855
3.42
382
4.36
4.61
579
5.71
5.88
8 10
10.3
10.8
11 1
12.2
14.1
153
15.8
Spring or
summer aver-
age3
0.0000625
0.0769
1 05
2.62
4.63
506
5.71
5.98
746
7.31
7.48
102
13.0
13.6
137
15.2
17.5
189
19.5
Wavelength cen-
ter*
290
300
310
320
330
340
350
360
370
380
390
400
410
420
430
440
450
460
470
12
-------
Table 1—Jx Values at 20 °N. Latitude— Continued
Wavelength
centerb
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 sol-
stice a
20.5
206
20.9
21.1
21 1
21.3
21.2
21 1
21.3
21.6
22 1
22.3
22.5
226
22.6
22.6
23 1
23.6
24.0
243
24.3
24.3
242
24.1
23.9
238
23.6
23.5
233
23.2
23.1
229
22.8
Equinox a
18.3
184
18.7
18.8
189
19.0
19.0
188
19.0
19.3
197
19.9
20.0
202
20.1
20.1
206
21.1
21.4
21 7
21.7
21.7
21 7
21.5
21.4
21 3
21.1
21.0
209
20.8
20.6
205
20.4
Winter sol-
stice a
14.4
145
14.8
14.9
149
15.1
15.0
149
15.1
15.3
157
15.8
15.9
160
16.1
16.2
166
16.9
17.2
174
17.5
17.5
175
17.4
17.3
172
17.2
17.1
170
16.9
16.8
167
16.7
Wave-
length cen-
terb
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
average a
16.0
16 1
16.4
16.4
165
16.7
16.6
165
16.7
16.9
173
17.5
17.6
177
17.7
17.7
182
18.6
18.9
192
19.2
19.2
192
19.1
19.0
189
18.8
18.7
186
18.5
18.4
183
18.2
Spring or
summer aver-
age3
19.8
198
20.2
20.3
203
20.5
20.4
203
20.5
20.8
21 2
21.5
21.6
21 8
21.8
21.7
223
22.8
23.1
234
23.4
23.4
230
23.2
23.0
229
22.8
22.6
225
22.3
22.2
22 1
21.9
Wavelength cen-
ter*
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
aJx values are in units of 1019 photons cm-2 day-1.
b 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
Table 2—Jx Values at 30° 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
Summer sol-
stice a
0 0000768
0.0831
1 14
284
5.02
549
628
6.49
809
793
8.12
11 1
14 1
14.7
149
165
19.0
206
21 2
21.5
21 5
21 9
22.1
22 1
223
22.1
22 1
226
22.6
23 1
23.3
Equinox a
0 00000203
0.0457
0787
2 13
3.88
430
488
5.15
645
625
6.53
897
11 4
12.-
122
135
15.5
168
173
17.6
177
180
18.1
18 1
183
18.2
18 1
183
18.6
190
19.2
Winter solstice3
0 00000021 3
0.00835
0300
1 06
2.13
248
289
3.10
395
395
4.12
573
737
7.81
800
894
10.4
11 3
11 7
11.9
120
122
12.3
124
125
12.4
124
125
12.7
130
13.2
Wave-
length cen-
ter b
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
Fall or winter
avg.a
0 000000457
0.0208
0480
1 47
2.81
3 19
368
3.91
494
491
5.08
702
899
9.46
966
108
12.4
135
139
14.2
143
145
14.6
147
148
14.7
147
148
15.1
154
15.6
Spring or
summer
avg.a
0 0000352
0.0704
1 02
260
4.62
508
574
6.02
751
737
7.55
104
132
13.7
139
154
17.8
192
198
20.1
20 1
205
20.6
207
209
20.6
206
208
21.1
21 6
21.8
Wavelength cen-
ter*
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
13
-------
Table 2—Jx Values at 30° N. Latitude—Continued
Wavelength
center*
600
610
620
630
640
650
660
670
680
690
700
710
720
730
740
750
760
770
780
790
800
Summer sol-
stice a
23.5
237
23.6
23.6
242
24.7
25.1
254
25.4
25.4
253
25.2
25.0
249
24.7
24.6
244
24.3
24.1
240
23.8
Equinox3
19.3
195
19.3
19.2
198
20.4
20.7
21 0
21.0
21.0
21 0
20.8
20.7
206
20.5
20.4
203
20.1
20.0
199
19.8
Winter solstice3
13.3
134
13.6
13.7
140
14.2
14.4
147
14.7
14.8
148
14.7
14.6
146
14.5
14.5
144
14.3
14.3
142
14.2
Wave-
length cen-
ter b
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.a
15.7
158
15.9
16.0
163
16.7
16.9
172
17.2
17.3
173
17.2
17.1
170
16.9
16.8
168
16.7
16.6
165
16.4
Spring or
summer
avg.a
22.0
22 1
22.1
22.1
226
23.1
23.5
238
23.8
23.8
237
23.6
23.4
233
23.2
23.0
229
22.7
22.6
225
22.3
Wavelength cen-
ter1-
600
610
620
630
640
650
660
670
680
690
700
710
720
730
740
750
760
770
780
790
800
aJxvalues are in units of 1019 photons cm-2 day-1.
b 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
Table 3—J, Values at 40° 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
Summer sol-
stice a
1 36 x 1 0-5
0.0769
1 12
287
5.11
562
635
6.61
832
8 17
8.37
11 5
146
15.2
155
17 1
19.7
21 3
220
22.3
223
227
22.9
229
232
23.0
229
23 1
23.5
240
242
24.4
246
245
24.5
25 1
257
26.1
264
263
26.4
264
26.2
Equinox a
1 21 x 10-7
0.0293
0618
1 81
3.41
383
439
4.65
586
580
5.99
826
105
11.1
11 3
125
14.5
157
162
16.5
166
169
17.0
170
172
17.1
170
172
17.4
178
180
18.2
183
183
18.3
188
192
19.5
198
199
19.9
199
19.8
Winter solstice a
615x1 0-10
0.00145
0 132
0591
1.31
1 58
1 88
2.05
264
267
2.82
397
5 15
5.51
669
641
7.47
8 15
851
8.74
883
899
9.07
9 14
924
9.18
9 15
923
9.38
962
979
9.85
993
102
10.2
105
107
10.9
11 1
11 1
11.2
11 3
11.2
Wave-
length cen-
terb
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
Fall or winter
avg.a
814x10-8
0.00939
0298
1 04
2.90
243
284
3.05
388
388
4.05
564
726
7.69
789
882
10.2
11 1
11 5
11.8
11 9
12 1
12.2
123
124
12.3
123
124
12.6
129
13 1
13.2
132
134
13.5
138
14 1
14.3
145
146
14.6
147
14.6
Spring or
summer
avg.a
3 49 x 1 0-6
0.0587
0940
249
4.49
477
564
5.93
743
730
7.50
103
13 1
13.9
154
178
19.2
198
20 1
20.2
206
207
20.8
21 0
21 0
20.8
207
209
21.2
21 9
21 9
22.1
222
222
22.1
227
233
23.6
240
240
24.0
240
23.9
Wavelength cen-
ter*
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
14
-------
Table 3—Jx Values at 40° N. Latitude—Continued
Wavelength
center*
720
730
740
750
760
770
780
790
800
Summer sol-
stice a
26 1
25.9
258
25.6
255
25.3
25.2
250
24.8
Equinox a
197
19.6
195
19.4
193
19.2
19.1
190
1.89
Winter solstice a
11 2
11.2
11 2
11.2
11 2
11.3
11.3
11 2
11.2
Wave-
length cen-
terb
720
730
740
750
760
770
780
790
800
Fall or winter
avg.a
146
14.5
145
14.4
144
14.3
14.3
142
14.1
Spring or
summer
avg.a
237
23.5
234
23.3
23 1
23.0
22.4
227
22.6
Wavelength cen-
terb
720
730
740
750
760
770
780
790
800
aJx values are in units of 1019 photons cm-2 day-1.
b Wavelength intervals are uniformly 10nm 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
Table 4—Jx Values at 50° 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
800
Summer sol-
stice a
0 000001 85
00635
1.05
281
5.10
564
6.41
670
8.46
832
8.56
11 8
15.0
15.7
159
17.6
203
22.0
227
23.1
23 1
23.5
237
23.8
240
238
23.7
240
24.3
248
25.1
253
25.5
254
25.3
260
26.7
27.1
275
27.5
275
27.5
273
27.2
270
26.9
267
26.6
264
263
2.61
26.0
Equinox3
0 000000200
00140
0.423
1 41
2.78
3 19
3.70
396
5.03
501
5.21
722
9.27
9.79
100
11.2
129
14.0
145
14.8
150
15.2
153
15.4
156
155
15.4
155
15.8
16 1
16.4
165
16.6
168
17.0
173
17.6
17.8
18 1
18.2
182
18.2
18 1
18.1
180
17.9
178
17.8
177
176
17.5
17.4
Winter solstice a
00000000112
0 0000681
0.321
0214
0.555
0711
0.864
0953
1.25
1 28
1.37
1 95
2.57
2.79
292
3.33
392
4.31
454
4.70
478
4.88
494
4.98
505
502
5.01
504
5.11
527
5.38
542
5.47
561
5.77
593
6.10
6.24
639
6.47
656
6.64
667
6.72
675
6.78
682
6.82
682
682
6.80
6.80
Wave-
length cen-
terb
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.a
0 0000000391
0 00296
0.147
0610
1.33
1 59
1.88
204
2.63
266
2.80
393
5.09
5.45
562
6.33
737
8.05
840
8.62
872
8.87
900
9.03
9 12
907
9.05
9 11
9.26
950
9.66
973
9.80
996
10.1
104
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
11.0
Spring or
summer
avg.a
000000152
00433
0.810
228
4.23
473
5.40
571
7.18
709
7.31
10 1
12.8
13.5
137
15.2
176
19.0
197
20.0
20 1
20.4
206
20.6
208
207
20.6
208
21.1
21 6
21.8
220
22.1
22 1
22.1
227
23.3
23.6
240
24.0
240
24.0
299
23.8
236
23.5
234
23.3
23 1
230
22.9
22.8
Wavelength cen-
ter*
290
300
310
320
330
340
360
350
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
aJx values are in units of 1019 photons cm-2 day -1.
b 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
15
-------
(4) Example of application of methodology, (i) Consider a chemical
plant located in Freeport, Texas, 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° north latitude. Estimate the maximum sunlight direct photolysis rate
constant and the corresponding minimum half-life in the atmosphere in
the vicinity of the plant for the winter and summer season solstices under
clear sky conditions.
(ii) The vapor phase spectrum of acrolein was obtained by the proce-
dure outlined in this test method and is depicted in the following Figure
3:
FIGURE 3—GAS PHASE ABSORPTION SPECTRUM OF ACROLEIN
0.04 r
430
The spectral data were taken from the work of Pitts et al. (1981) under
paragraph (d)(2) of this guideline. The pathlength of the sample gas ab-
sorption 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 absorp-
tion 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
(Ax) was obtained from these spectra and the mean cross section (tf'x)
was obtained using Equation 7 under paragraph (d)(l)(i)(A) of this guide-
line for each wavelength interval, centered at A,. All the results are summa-
rized in the following Table 5:
16
-------
Table 5—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 (AX)
0.0037
0.0066
00104
0.0137
0.0156
00156
0.0151
0.0096
00073
0.0031
0.0016
00004
0.0003
0.0000
Mean cross section o\)
(cm2 molecule-1)
5.69 x 10-21
1.01 x ID-20
1 60 x 1 0-20
2.11 x ID-20
2.40 x 10-20
2 40 x 1 0-20
2.32 x 10-20
1.48 x 10-20
112x1 0-20
4.76 x 10-2i
2.46 x 10-2i
615x1 0-22
4.61 x 10-22
0.00
1 6.52 x 1Qi6 molecules cm-3 in a 9.98 cm gas absorption cell
(iii) A sample calculation is given for the wavelength X = 305 nm,
centered over the wavelength interval 345 to 355 nm. For convenience,
the area A, corresponding to 100 squares was blocked off in this absorp-
tion area 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./(0. 148 v.u./square) = 49 squares
and the total area in the spectrum in the wavelength interval 345 to 355,
centered at X = 350 nm, is 149 squares. This number of squares cor-
responds to 0.0149 absorbance units:
(149 squares)(0.001 A/square)/10 = 0.0149 A
From the blank spectrum, the baseline absorbance (Ax 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 sample absorbance is
then equal to 0.0150 (0.0149 + 0.0001). The absolute corrected absorbance
for the sample is given by
** Xsample •*»• Xsample
AcorrXsample = 0.0150 - (-0.001) = 0.0151 A
(iv) Using Equation 7 under paragraph (d)(l)(i)(A) of this guideline
and the values for the corrected sample absorbance, 1, and C, the mean
cross section for the wavelength X = 350 nm, centered over the wavelength
interval 345-355 nm, is
a'?i = 0.01517(6.52 x 1016 molecules cm 3) (9.98cm)
= 2.3 x 10 20 cm2molecule !
(v) Since the plant is located at 29° north latitude, the closest Jx val-
ues are at 30° north latitude. These values are obtained from Table 2 under
17
-------
paragraph (d)(3) of this guideline and are summarized in Table 6 for the
summer and winter season solstices. Using the data in Tables 5 and 6
under paragraph (d)(4)(ii) of this guideline, the products a?Jx are cal-
culated for each wavelength interval, centered at A,, and the results are
summarized in the following Table 6 for each of the solstices:
Summer
(kpE)max = 16.9days-i
(ti/2)mm = 0.041 days
Winter
(kpE)max = 7.60 days-i
(ti/2)max = 0.091 days
The terms Ła?Jx are also summarized for each solstice at the bottom of
Table 6. Using these data in Equations 3 and 4 yields:
(ti/2)
Summer
ax= 16.9days-i
m = 0.041 days
Winter
(kpE)max = 7.60 days-i
(ti/2)mm = 0.091 days
Thus, acrolein transforms rapidly under clear sky conditions in the vicinity
of the plant at Freeport, Texas on the summer and winter season solstices
Table 6—Calculation of ^fpE)max For Acrolein Vapor; 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 solstice
Jx photons (cm-2
day-')
1.0 x 1015
8.31 x1017
1.14x 1019
2.84 x1019
5.02 x 1019
5.49 x1019
6.28 x 1019
6.49 x 1019
8.09 x1019
7.93 x 1019
8.12 x1019
1.11 x 1020
1.41 x1020
1.47 x 1020
o'xJx (day -')
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
So'xJx = 7.347
Winter solstice
Jx photons (cm-2
day-1)
2.1 x 1012
8.35 x1016
3.00 x 1018
1.06x1019
2.13 x 1019
2.48 x1019
2.89 x 1019
3.10 x 1019
3.95 x1019
3.95 x 1019
4.12 x1019
5.73 x 1019
7.37 x1019
7.81 x 1019
o'xJx (day -')
0.000
0.001
0.048
0.224
0.511
0.595
0.671
0.459
0.442
0.188
0.101
0.035
0.034
0.000
So'xJx = 3.304
(5) Operation of the gas handling system. The following procedure
briefly describes the recommended typical and detailed operation of a gas
handling system
(i) Close all stopcocks and turn on the rotary pump (A). Open stop-
cock 4 and place a Dewar containing liquid nitrogen around trap (D).
Measure the pressure with the thermocouple gauge HI. 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 H2. When the pressure falls below 10 2 torr (1.3 x 10 3 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 to 2
18
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hours under vacuum until the pressure falls to less than 10 2 torr
(1.3 x 10 3 kPa) as measured on thermocouple gauge H2. Open stopcocks
6, 9, and 11 and pump until H2 falls below 10 2 torr (1.3 x 10 3 kPa).
(ii) 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 pressure is <10 5 torr (1.3 x 10 6 kPa) as meas-
ured 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 H2 indicates a pressure less than 10 2 torr (1.3 x 10 3 kPa).
(iii) It is good practice, after the gas phase spectrum has been ob-
tained, to evacuate the gas absorption cell (K) and the trap (F) prior to
shutting down the gas handling system. The gas handling system can be
shut down by the following procedure: (A) closing stopcocks 5 to 11;
(B) switching off the diffusion pump; (C) closing stopcocks 2 and 3 and
opening 4, after the diffusion pump is cool; (D) removing the Dewar from
trap (D) and allowing it to warm up; (E) then closing stopcock 4 and
switching off the rotary pump; and (F) opening 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
(e) References. The following references should be consulted for ad-
ditional background information on this test guideline:
(1) Environmental Protection Agency. Mill, T. et al., Section 5. Pho-
tolysis in Air, by J.E., Davenport, Toxic Substances Process Generation
and Protocol Development. Work Assignment 12, Draft final report. (Ath-
ens, Georgia, and Washington, DC, 1984).
(2) Mill, T. et al., Laboratory Protocols for Evaluating the Fate of
Organic Chemicals in Air and Water. Chapter 5. EPA 600/3-82-022
(1982).
(3) Pitts, J.N., Jr. et al., Experimental Protocol for Determining Ab-
sorption Cross Sections of Organic Chemicals, EPA Report No. 600/3-
81-051 (1981).
19
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