r/EPA
United States
Environmental Protection
Agency
Environmental Sciences Research EPA-600/3-78-057
Laboratory June 1978
Research Triangle Park NC 27711
Research and Development
Application of
Fourier Transform
Spectroscopy to
Pollution Problems
Interim Report-1977
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ECOLOGICAL RESEARCH series. This series
describes research on the effects of pollution on humans, plant and animal spe-
cies, and materials. Problems are assessed for their long- and short-term influ-
ences. Investigations include formation, transport, and pathway studies to deter-
mine the fate of pollutants and their effects. This work provides the technical basis
for setting standards to minimize undesirable changes in living organisms in the
aquatic, terrestrial, and atmospheric environments.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/3-78-057
June 1978
APPLICATION OF FOURIER TRANSFORM SPECTROSCOPY TO AIR POLLUTION PROBLEMS
Interim Report - 1977
by
Yoon S. Chang
J. H. Shaw
Edward Niple
J. G. Calvert
W. H. Chan
S, Z. Levine
W. M. Uselman
The Ohio State University
Research Foundation
Columbus, Ohio 43212
Grant Number R803868-2
Project Officer
John Spence
Atmospheric Chemistry and Physics Division
Environmental Sciences Research Laboratory
Research Triangle Park, North Carolina 27711
ENVIRONMENTAL SCIENCES RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, NORTH CAROLINA 27711
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DISCLAIMER
This report has been reviewed by the Environmental Sciences Research
Laboratory, U.S. Environmental Protection Agency, and approved for publi-
cation. Approval does not signify that the contents necessarily reflect
the views and policies of the U.S. Environmental Protection Agency, nor
does mention of trade names or commercial products constitute endorse-
ment or recommendation for use.
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ABSTRACT
Progress in the application of Fourier Transform Spectroscopy to air
pollution problems is described. An atlas of observed and calculated air
spectra from 700 to 2300 cm"1 has been prepared. Methods of analyzing
air spectra to identify spectral features and to determine simultaneously
the abundances of atmospheric gases such as CO, N20, CIU, 03, H20, and
C02 have been explored. These methods include ratioing observed and cal-
culated spectra and correlation analysis of absorption bands to obtain
abundances by linear regression and non linear least squares methods.
Absorbing features of atmospheric gases such as ©3, HgO, and N20 have been
removed from solar spectra to isolate underlying features of F-12 near
1160 cm"1.
During the past year kinetic studies of several systems of general
interest to atmospheric chemists have been completed using the FTIRS-
photochemical reactor system. New data were obtained related to the rate
constant for the reaction, HO + CO -»H + C02, as a function of pressure.
This rate constant is pressure sensitive: k = ^39 ± 24 ppnT-hmin""1 at
700 Torr air; k = 203 ± 29 ppnT^-min"1 in air at 100 Torr. Atmospheric
scientists should note that the adjustment of the HO-radical rate con-
stants with other reactants in the lower atmosphere must be made where
these estimates have been based on the low pressure value of this con-
stant .
The FTIRS system was employed in other studies to determine the rate
constants for the reactions: H02 + N02 -»H02N02 (Ref. 22) and
H02 + N02 ->HONO + 02 (Ref. 21); in 700 Torr of air at 25 ± 2°C, the data
suggest k22 = 7-2 x 101 and k2i s 5.3 x 101 ppm~1min~1. Simulations of
the reactions in a typical NOx-RH-RCHO-polluted atmosphere exposed to
sunlight show that the theoretical rate of H02N02 generation is similar
in magnitude to those expected (and observed in real atmospheres) for
peroxyacylnitrates.
This report was submitted in fulfillment of Grant Number R803868-2
by The Ohio State University under the sponsorship of the U.S. Environ-
mental Protection Agency. This report covers a period from 7/15/76 to
7/1V77.
iii
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CONTENTS
Abstract iii
Figures , vi
Tables xii
1. Introduction 1
2. Conclusion 2
3. Recommendations 3
4. Analysis of Long Path Air Spectra 6
Introduction 6
Methods of spectral analysis 15
Comparison of observed and calculated spectra
of individual gases 42
Acquisition of a high resolution interferometer 42
Stratospheric simulation chamber 49
5. Study of Some Key Reactions of Probable Importance In
Photochemical Smog Formation., 54
Introduction 54
The pressure dependence of the rate constant for
the reaction: HO + CO •*• H + C02 55
The kinetics and mechanism of the H02-N02 reaction
the significance of peroxynitric acid formation
in photochemical smog , 62
Experimental details of FTIRS and photolysis cell ,.t 80
Experimental detail of photochemical and spectral
measurements ,,,,, 82
Infrared spectra of compounds 87
Future plans 97
References 98
Appendices 104
A. Summary of objectives form 1975 proposal, , , 104
B, Papers presented at meetings 106
C, Papers published or accepted for publication 107
v
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FIGURES
Number Page
1 The transmittance (T) of an absorbing path is defined
as P/PQ where Po is the incident and P is the emerging
radiant power 7
2 (a) Frequency dependence of the absorption coefficient
of an absorption line with a Lorentz shape; (b) De-
pendence of the transmittance due to a Lorentz line on
the k(v)p^ product . 9
3 The dependence of the transmittance of an air path
containing various number densities of an absorbing
gas with an absorption coefficient k on path length n
k (a) Laboratory spectrum of HC1 between 2700 and
2900 cm"1 of 0.02 Torr HC1 and 50 Torr Wg in
171 m path; (b) Corresponding region of the solar
spectrum (large zenith angle); (c) Spectrum of HC1 be-
tween 27^0 and 2780 cm"1; (d) Corresponding region of
the solar spectrum 12
5 (a) Spectrum of 8.5 m path of air with some COg and H20
removed; (b) Spectrum of 993 m path of ground level
air, T = 296 K, P = 750 Torr; (c) Solar spectrum re-
corded at Columbus, Ohio, solar zenith angle 86° 13
6 (a) Spectrum of 7-0 m ground level air, T = 29k K,
P = 750 Torr; (b) Spectrum of 993 m ground level air,
T = 29^ K, P = 750 Torr; (c) Solar spectrum, solar
zenith angle =82° lU
7 (a) Background spectrum of evacuated absorption cell
between 650 and 1350 cm"1; (b) Spectrum of absorption
cell containing a sample of N02 and N204; (c) Ratio of
spectrum b/spectrum a . 16
8 (a) Laboratory spectrum of CHCCF2 between 760 and 900
cm"1; (b) Laboratory spectrum of CHC12F between 760
and 900 cm"1; (c) Laboratory spectrum of CC14 between
760 and 900 cm"1; (d) Laboratory spectrum of CC13F be-
tween 760 and 900 cm"1; (e) Ground level solar spec-
trum between 760 and 900 cm"1 19
9 (a) Spectrum of 51 Torr C02 in 171 m path at 295 K be-
tween 800 and 820 cm"1; (b) Calculated spectrum of C02
for the same conditions 20
VI
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FIGURES (Continued)
Number
10 (a) Calculated spectrum of CO between 2170 and 2250
cm"1; (b) Calculated spectrum of C02 between 2170 and
2250 cm"1; (c) Calculated spectrum of N20 between
2170 and 2250 cm"1; (d) Observed spectrum of 171 m of
air at 29^ K and 700 Torr 23
11 (a) The ratio of the spectra d and a in Fig. 10; (b)
The ratio of the spectra in Fig. lla and Fig. lOb; (c)
The ratio of the spectra in Fig. lib and Fig. lOc; (d)
Observed spectrum of 171 m of air at 29*4- K and 700 Torr ^4
12 (a) Ratio of the spectra in c and b; (b) Calculated
spectrum of COs between 2230 and 2250 cm"1; (c) Ob-
served spectrum of C02 broadened to atmospheric pres-
sure with air 25
13 (a) Calculated spectrum between 1155 and 1165 cm"1 of 03
in an atmospheric slant path; (b) Calculated spectrum
between 1155 and 1165 cm"1 of H20 in an atmospheric
slant path; (c) Calculated spectrum between 1155 and
1165 cm"1 of N20 in an atmospheric slant path; (d)
Observed solar spectrum (solar zenith angle U5°) 27
lU (a) Laboratory spectrum of F-12 between 1155 and 1165
cm"1; (b) Solar spectrum with 03) N20, and 1^0 lines
ratioed out; (c) Calculated solar spectrum; (d) Observed
solar spectrum 28
15 Portion of a spectrum of 171 m path of air at 29^ K and
700 Torr. The intervals chosen for the linear regres-
sion method of obtaining abundances are indicated to-
gether with the position of the H20 line and the PQ(V)
position. 33
16 (a) Ratio of observed P(V) and values obtained from non
linear least squares method; (b) Air spectrum between
2190 and 2210 cm'1 38
17 (a) Ratio of spectra in Fig. 17b and 17c; (b) Observed
spectrum of 1.52 x 10~3 Torr of N20 and 100 Torr N2 in
171 m path, at 2$k K; (c) Calculated spectrum of N20
for the same conditions as used to obtain Fig. 17b 39
18 (a) Ratio of the spectra shown in b and c; (b) Calcu-
lated solar spectrum corresponding to the conditions
under which Fig. l8c was obtained; (c) Observed low
sun spectra between 1158.0 and 1163-0 cm"1, spectral
resolution ~ 0.25 cm"1, solar zenith angle 81° hi
vii
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FIGURES (Continued)
Number
19 (a) 300 Torr C02 in 171 m path at room temperature;
(b) Calculated spectrum for same conditions; (c) 51
Torr C02 in 1?1 m path at room temperature; (d) Cal-
culated spectrum for same conditions ^3
20 (a) 300 Torr C02 in 171 m path at room temperature;
(b) Calculated spectrum for same conditions; (c) 51
Torr C02 in 171 m path at room temperature; (d) Cal-
culated spectrum for same conditions ^
21 (a) 0.15 Torr N20 and 700 Torr N2 in 171 m path; (b)
Calculated spectrum for same; (c) 0.015 Torr N20 and
700 Torr N2 in 171 m path; (d) Calculated spectrum
for same ^5
22 (a) 0.15 Torr N20 and 700 Torr N2 in 171 m path; (b)
Calculated spectrum for same; (c) 0.015 Torr N20 and
700 Torr N2 in 171 m path; (d) Calculated spectrum
for same ^6
23 (a) 0.38 Torr CH4 and 700 Torr N2 in 171 m path; (b)
Calculated spectrum for same; (c) 0.076 Torr CH4 and
700 Torr N2 in 171 m path; (d) Calculated spectrum
for same ^7
2k (a) k.l& x 10~3 Torr CO and 700 Torr N2 in 171 m path;
(b) Calculated spectrum for same; (c) 1.1*4- x 10~3 Torr
CO and 100 Torr N2 in 171 m path; (d) Calculated spec-
trum for same U8
25 -Details of mirror adjusting system 50
26 Details of mirror adjusting system 51
27 The experimental photolysis system employed in this
work 57
28 Plot of the ratio [C02]t/[AC4Hlo]t versus [C0]o/[iso-
C4H10]0 from the photolysis of HOWO, CO, iso-C4Hlo,
NOX mixtures in synthetic air; open circles refer to
experiments at 700 Torr total pressure; squares are
from experiments at 100 Torr total pressure 6l
Vlll
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FIGURES (Continued)
Number page
29 Spectra of uv-irradiated HONO, NOX, CO, air and C12,
N02, H2, air mixtures; (a) spectrum of cell contents
after 5-9 mi*1 irradiation of the initial mixture;
total [HONO]0 = 2.70, [N0]o = 2.77, [M32]0 = 1-5,
[C0]0 = 0.0 ppm in synthetic air, 700 Torr; (b) re-
sidual spectrum resulting from that of (a) following
computer subtraction of remaining cis, trans-HONO,
HON02, and H20; note absence of H02N02 67
(c) spectrum of cell contents following 5-9 mi-n irrad-
iation of the initial mixture: total [HONO]O = ^.29,
[MD]0 = 2.8, [N02]0 = 1.1, [C0]0 = 3.8 x 104 ppm in
synthetic air, 700 Torr; (d) residual spectrum result-
ing from that of (c) following computer subtraction of
remaining cis, trans-HONO, CH4, and H20 68
(e) spectrum of cell contents following 6.0 min irrad-
iation of the initial mixture: [C12]O = 30, [N02]0 =
22 j [H2]o = 8026 ppm in synthetic air at 700 Torr;
(f) residual spectrum resulting from that of (e) fol-
lowing computer subtraction of the remaining HON02 and
C1N02 products; compare the characteristic absorption
peaks of H02W02 at 802.7 and 1303-9 cm"1 in (d) and (f) 69
30 Comparison of observed total [HONO]- and [C02]-time
data with those predicted by the simulation model for
irradiated HONO, NOX, CO mixtures in air; (a) initial
concentrations: total [HONO]0 = 2-70, [N0]o = 2.77,
[N02]0 = 1.5 ppm in synthetic air, 700 Torr; (b) ini-
tial concentrations: total [HONO]0 = U.35, [N0]o =
20.U, [N02]0 = 17-^, [C0]0 = 2.23 x 103 ppm in syn-
thetic air, 700 Torr. 71
31 Comparison of observed total [HONO]-, [C02]-, and
[H02NOP]-time data with those predicted by the simula-
tion model involving reactions (21) through (^9),
Table VII, initial concentrations, total [HONO]O =
U.29, [K)]0 = 2.8, [N02]0 = 1.1, [C0]0 = 3.8 x 104
ppm, in synthetic air, 700 Torr; values of k21/k22
chosen in simulations: M (~"O—)j 5-0 ( ); 0.7^-
( ); 0.00 ( ); k23/(k21 + k22) . 10 in all
runs shown 73
fcc
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FIGURES (Continued)
Number Page
32 The first order loss of H02N02 in three different
dark runs; the squares are from data taken from a run
with HONO-NO-N02-CO mixture; the remaining data
points are from two different C12-H2-NO-N02 mixtures.
The slope of this plot gives a first order loss con-
stant of 9.1 x 10-2 min'1 7^
33 (a) 3.2 ppm HOND; (b) initial conditions of C12 = 7-5,
H2 = 8026, NO = 3.25 and N02 = 2.7^ ppm. In (b) the
spectrum 1 represents the filled cell at start before
the lights are turned on, 2 is the spectrum after al-
most 1 min of irradiation time, 3 is the same mixture
as spectrum 2 but with CH4 subtracted out, h is the
same mixture as spectrum 2 but with CH4 and 6% of
spectrum (a) subtracted out 76
3^ Photolysis of Clg, H2, NOX, mixture in synthetic air;
initial concentrations (ppm): (Cl^) = 7-5; (H3) =
8026; (NO) = 3.25; (N02) = 2.71*; air added to a total
pressure of 700 Torr; (a) experimental data; (b) com-
puter simulation 78
35 Photolysis of C12, H2, NOX, mixture in synthetic air;
initial concentrations (ppm): (C12) = 15; (H2) =
8026; (NO) = 1.28; (N05) = 11.1; total pressure of
700 Torr; (a) experimental data; (b) computer simu-
lation 79
36 Infrared spectrum of CUO (nitrosyl chloride), top
spectrum = 0.10 ppm, bottom spectrum = 1.36 ppm 88
37 Infrared spectrum of ClJNOg (nitryl chloride), top
spectrum = 0.88 ppm, bottom spectrum = 3-38 ppm 89
38 a) 7-5 ppm HONOa
b) « 1.5 ppm C10N02 and 7.5 ppm HOW02 formed during
photolysis (0.7~min) of C12 (90 ppm), N02 (13
ppm), 03 (18 ppm) in a synthetic air mixture
(PT = 700 Torr) 90
39 HOCl formed during photolysis of C12 (90 ppm), 03
(20 ppm), hydrocarbon (5 ppm) mixtures in synthetic
air (PT = 700 Torr)
a) from i so -butane (2 min photolysis) with U.3 ppm
(CH3)pCO removed
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FIGURES (Continued)
Number
39(cont.)
b) from propane (l min photolysis) with 3.2 ppm
(CH3)3CO removed
c) from ethane (2 min photolysis) 91
UO Infrared spectrum of HC1, top spectrum = 1.83 ppm>
bottom spectrum = 68.3 ppm 92
hi Infrared spectrum of HONOp, top spectrum = 0.39 ppm,
bottom spectrum = 3*^3 ppm 93
h2 Infrared spectrum of 03, top spectrum = 0.26 ppm, bot-
tom spectrum = 12.0 ppm 9^
k-3 Infrared spectrum of N305, top spectrum = O.h ppm,
bottom spectrum = 2.2 ppm 95
W* H02NOa (1.1 ppm)
c) spectrum of cell contents following 5.9 min irrad-
iation of the initial mixture: total [HONO]O = ^-3
ppm, [K0]0 = 2.8, [K02]0 = 1.1, [C0]o = 3.8 x 104
ppm in synthetic air
d) residual spectrum resulting from c) following com-
puter subtraction of cis, trans-HO KID, CH4, and H20 96
XI
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TABLES
Number
II
III
IV
V
VI
VIII
Abundances of CO, N20, and C02 Obtained by Ratioing
Observed and Calculated Spectra of a 171 m Air Path
Absorption Coefficients of CO, N20, and H20 Calculated
from the AFCRL Listing and for a Spectral Resolution
of 0.075 cm'1 Between 2000 and 2005 cm"1
Dependence of Abundance Values of N20, CO, and H20
Determined by Unweighted Linear Regression Analysis of
Air Spectra on Spectral Regions Analyzed. PO(V) is
1.00 in All Cases
Dependence of Abundance Values of N20, CO, and H20
Determined by Unweighted Linear Regression Analysis of
Air Spectra on Assumed Value of PO(V). Spectral Region
Analyzed 2190 to 2210 cnf1
Dependence of the Abundance of N20, CO, and H20 Deter-
mined by Non Linear Least Squares Analysis of Air
Spectra on the Spectral Region Analyzed
Summary of Rate Data from the Photolysis of HONO in
Mixtures with CO, iso-C4Hl0, NOX, in Synthetic Air
Page
22
32
VII Summary of the Reaction Mechanism and Rate Constants
Employed in the Simulation of HQNO, NO,., CO, Air Mix-
ture Photolyses
Additional Reactions and Rate Constants Required in the
Simulation of the Dilute C12, N02, NO, H2 Mixtures in
Air
Extinction Coefficients (base e, 1 cm"1 resolution, 700
Torr pressure, 25°C, 170 meter path, box-car apodiza-
tion)
37
60
65
77
83
Xll
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1. INTRODUCTION
This report summarizes progress made during the second year of EPA
Grant No. R803868. This grant began in July 1975 and was a successor to
EPA Grant No. R803075 which extended from April 1974 to July 1975. The
work completed under the initial grant is described in the EPA Ecological
Research Series Report EPA-600/3-76-084 and the work accomplished during
the first year of the grant R803868 is described in a report to EPA
issued in 1976. A summary of the research objectives in the proposal for
this latter grant is given in Appendix I.
During the first year of the present grant methods of analyzing air
spectra were developed. These included generating programs for calculat-
ing synthetic spectra from the line parameters of gases. By comparing
calculated and observed spectra, features of F-12 were identified in solar
spectra. In the current year an atlas of observed and calculated air
spectra covering the region from 700 to 2300 cm""1 has been issued and quan-
titative estimates of the abundance of F-12 in the troposphere have been
made. A variety of methods of analyzing both ground level air spectra
and solar spectra has been developed. It has been shown that the abun-
dances of gases such as N20, CO, and C02 can be simultaneously determined
from a spectrum with precisions of the order of 1%. It is also possible
to remove features of N20, Oa, and H20 from solar spectra to isolate
spectral features of gases such as F-12.
A multiple traversal cell to simulate the stratospheric environment
has been constructed and it is currently being used to obtain spectra of
ozone.
The FTIRS system and the photochemical reactors built in the first
years of this study are well suited for the measurement of the rates of
chemical change in systems designed to simulate the conditions present in
NOx-RH-polluted urban atmospheres and in the NOX and Freon contaminated
stratosphere. During the past year kinetic studies of several systems of
general interest have been made. These relate largely to the reactions
of the HO and H02 radicals, the two dominant chain carrying species which
promote many of the important changes which occur in the atmosphere. The
results obtained in these chemical studies provide very significant new
information of special significance to both the chemistry of the tropo-
sphere and the stratosphere.
As a result of this work a number of papers have been presented at
meetings, published, or accepted for publication. These are described
in Appendices II and III, respectively.
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2. CONCLUSIONS
Synthetic spectra calculated from line parameters can be used to
interpret spectra of long air paths. By using these line parameters the
abundances of gases such as H20, C02, N20, CH4, and CO can be simultane-
ously determined with precisions of 1% by correlation analyses employing
linear regression and non-linear least squares techniques to the analysis
of ground level air spectra. Similarly, the total amounts of these gases
and of other gases such as F-12 in a vertical column through the atmo-
sphere can be simultaneously obtained by applying these methods to the
analysis of solar spectra. These methods can be adapted to the analysis
of laboratory spectra provided suitable computing facilities are avail-
able. These procedures increase the accuracy with which the abundances
of gases can be obtained compared with many other methods. By using
these line parameters or by exchanging information on the measured
spectral absorption coefficients of entire bands of gases, it is possible
to standardize measurements made in different laboratories and to make
them independent of the particular instrumentation used.
New data have been obtained in this work which prove that the reac-
tion, HO + CO ->H + C02, is pressure sensitive; the results show that
the rate constant for this reaction is a factor of two larger (at one
atmosphere in air) than that derived by many workers from results at
relatively low pressures of added inert gases. The result is of great
value in the estimation of the correct lifetime of the CO molecule in
the atmosphere. In addition, the present results bear directly on the
estimate of the reaction rate constant for the HO-radical with many other
atmospheric contaminants. Thus the rate constant for the seemingly im-
portant atmospheric reaction of S02 oxidation, HO + S02(+M) ->HOS02(+M),
is twice the value suggested earlier from comparative rate measurements
based upon the low CO - HO rate constant.
The reactions of H02 radicals with N02 have been studied using two
different ultraviolet irradiated systems: dilute HONO, NOX, CO mixtures
in air; and, dilute C12, H2, NOX mixtures in air. One important product
of this mixture, peroxynitric acid, arises from the reaction,
H62 + N02 ->H02N02. The first direct estimates of the rate constant for
this reaction have been determined in this study. The application of
these estimates in computer simulation of the reactions in an NOX,
RH-RCHO-polluted atmosphere suggest that peroxynitric acid may be a sig-
nificant component of.photochemical smog. In view of its recognized
highly oxidizing character, H02N02 may contribute to the eye irritation
and other manifestations of photochemical smog.
New infrared spectral data have been determined for several compounds
of interest to the atmospheric scientists: N02C1, NOC1, C10N02, HOC1,
H02N02, N205, HC1, HONOa, and 03.
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3. RECOMMENDATIONS
The development of accurate methods of quantitatively analyzing
spectra should be continued with emphasis on refining the procedures to
increase the speed and ease of application to actual spectra. Particular
emphasis should be placed on the application of these methods to inter-
preting solar spectra, but their use in obtaining information from other
types of spectra should be explored.
The accuracy of the line parameters used to calculate spectra should
be verified by comparison with laboratory spectra of individual gases,
especially for those lines which appear in air spectra and interfere
with the identifications of features .of pollutant gases.
A program of applying these analytical methods to the analysis of
air spectra should be undertaken. This will require the continuation of
the collection of air spectra with the highest available spectral reso-
lution through the use of the Nicolet interferometer which is scheduled
for delivery in May 1977-
It is also recommended that a cooperative effort be initiated among
interested workers to establish a library of accurate spectral absorption
coefficient data or line parameter information so that standardized
methods of interpreting spectral data can be established based on the
analytical techniques described above. This program should also estab-
lish the ranges of physical conditions of the gas samples for which the
absorption coefficient data are reliable.
*
The FTIRS system and the photochemical reaction chamber have been
shown to be well designed to study reaction mechanisms and to determine
rate constants which are of special interest to the understanding of
photochemical smog formation and its control, and reactions in the pol-
luted stratosphere. There are several key systems which we plan to study
during this last year of the current project. These include: (l) the
reactions of the H02, CH302, and t-C4Hg02 radicals with NO
(R02 + NO ->RO + N02) and with N02 (R02 + N02 ->R02N02); (2) the role of
the aldehydes (CH20, and CH3CHO) in photochemical smog formation; (3)
some potentially important removal mechanisms for S02 in the atmosphere;
and (h) the effects of C13CF addition on 03 generation under stratospheric
conditions. These are outlined in the following sections.
THE REACTIONS OF THE ALKYLPEROXY RADICALS WITH NITRIC OXIDE AND NITROGEN
DIOXIDE.
Present computer models of photochemical smog invoke the reactions,
R02 + NO -*RO + N02, as the most important reactions necessary to ration-
alize the rapid conversion of NO to N02 which occurs in irradiated RH,
NOX, air systems. However, there are no accurate estimates of the rate
constants of these reactions with varied size of the alkyl group R. In
this work we will follow the NO to N02 conversion in irradiated (CH3)2N2,
-------
NO, air mixtures and (t-C4H9)2N2v WO, air mixtures. From our knowledge
of the absolute values of the rate constants of the reactions,
2CH302 -»Products, and 2t-Bu02 ->Products, and the product rates, esti-
mates of the rate constants for the seemingly important reactions,
CH302 + NO ->CH30 + N02, and t-Bu02 + NO -»t-BuO + N02 will be derived.
The effect of structure of the alkyl group on the rate of the NO oxida-
tion which we will learn from these experiments, will be very valuable
in assigning realistic rate constants to the many similar reactive R02
species encountered in smog simulation mechanisms.
The studies of the past year which dealt with the unusual H02N02
compound and the rate constant for its formation will be continued and
extended to include studies of the structurally similar compounds,
CH302N02 and t-C4Hg02N02. Our preliminary estimates of the rate constant
for the reaction, H02 + N02 ->H02N02 carried out at 700 Torr (air) will
be refined in further experiments, and the pressure dependence of this
rate constant will be established in similar experiments at 100 and 10
Torr of added air. The evaluation of the possible role of the peroxy-
nitric acid as a sink for N02 in stratospheric reactions requires such
kinetic information.
Preliminary experiments performed in our laboratory using
(CHa)2N2 (5ppm), N02 (5 ppm) in synthetic air mixtures gave an indication
of the formation of some transient compound with absorption in the
790-800 cm"1 range and with a half life in the dark of less than 3 niin.
This is the characteristic absorption region for one of the bands asso-
ciated with the peroxynitrate grouping, and the data suggest that
CHs02N02 may have been formed here.
A similar experiment was performed employing a t-Bu2N2, NO mixture
in synthetic air, and transient bands at 1300, 790j and 860 cm"1 were
observed. The band at 790 cm"1, characteristic of the peroxynitrate
group, had a dark halflife of about 14 min in this case. It appears
likely from these preliminary data that alfcylperoxynitrate compounds,
analogues to the recently identified H02N02, do participate in these
smog simulation systems. Rate constants for their formation and decay
paths will be derived in this study so that the possible significance
of these compounds in the real atmosphere can be determined.
THE ROLE OF ALDEHYDES IN PHOTOCHEMICAL SMOG FORMATION.
The aldehydes, demonstrated products of combustion reactions and
smog reactions involving hydrocarbon-03 and hydrocarbon-OH reaction, have
the potential of generating free radicals to stimulate smog formation.
However, present data do not allow an unambiguous assignment of the pri-
mary rates of radical generation from CH20 and CH3CHO irradiated in the
lower atmosphere. In this study dilute mixtures of CH20 in air; CH20,
NO in air, CH3CHO in air; and CH3CHO, NO, in air, will be photolyzed.
From the rates of aldehyde loss and products formed in these experiments,
coupled with the known wavelength distribution of the UV-light and its
absolute intensity, we can estimate the quantum efficiency of the primary
-------
steps in the aldehyde photolyses. The similarity of the wavelength dis-
tribution and the intensity of the UV-light in the photochemical chamber
employed in our work to that of the solar distribution will allow a
reasonable extrapolation of our results to the real atmosphere. This
information is of particular value in the evaluation of ozone generation
in the long range transport of urban air masses.
In addition, attempts will be made in CH20, NOX, HONO, air photo-
lyses to generate the elusive peroxyformylnitrate which has not been
observed to date.
A STUDY OF SOME POTENTIALLY IMPORTANT ATMOSPHERIC S02 REMOVAL MECHANISMS.
The relatively simple chemical systems which we plan to employ in
these studies should provide a new and more direct measure of the rates
of several seemingly important reactions leading to the homogeneous oxi-
dation of S02 in the RH-NOX-polluted atmospheres. By proper choice of
initial levels of HONO, S02, and CO'in air we should be able to derive
rather directly the rate constants for the reactions,
HO + S02 (+M) -»HOS02 (+M) and H02 + S02 ->HO + S03.
THE NATURAL REMOVAL MECHANISMS OF FREONS AND THEIR INFLUENCE ON 03
LEVELS IN THE STRATOSPHERE.
The new photochemical reactor which has been constructed will be
tested in a series of experiments designed to simulate the stratospheric
conditions of pressure and temperature. The generation of ozone by short
wavelength irradiation (1750-2200 A) in relatively pure air will be fol-
lowed using infrared analysis; the effect of added CFCla on this process
will be determined in subsequent experiments. Through these experiments
we will be able to evaluate the importance of unwanted wall reactions in
the chamber. The data will be used to improve the cell construction to
better simulate the stratospheric reactions and further study the reac-
tions of the primary CC12F and Cl fragments for the simulated strato-
spheric conditions.
-------
b. ANALYSIS OF LONG PATH AIR SPECTRA
INTRODUCTION
The objectives of this phase of the work include:
1. The identification of the absorption features of air pollutants
in long path air spectra;
2. The quantitative determination of the abundances of atmospheric
gases by analyses of air spectra.
During the past three years spectra of long path lengths of ground
level air and also of solar spectra have been obtained with the inter-
ferometer available to us. Since these spectra are recorded digitally
the principal methods explored to analyze these spectra have been based
on the computer manipulation of the data and the search for rapid methods
of achieving the above objectives. Some of these methods are described
in this section after the basic theory of atmospheric transmittance and
its dependence on the absorbing characteristics of air molecules has been
discussed.
If radiant energy of power PQ(V) at some frequency v is incident on
an absorbing path, as shown in Fig. 1, and the emerging power is P(V),
the transmittance T(V) of the path is defined as
T(v) = P(v)/P0(v) . (1)
For the conditions with which the data described in this report were
collected, the transmittance is related to the absorbing properties of
the path by
T(v) = P(v)/P0(v) = exp[-k(v)u] , (2)
when k(v) is the monochromatic absorption coefficient of the medium and
u is a measure of the amounts of the absorbing constituents in the path.
For a homogeneous path containing m absorbing gases each with a charac-
teristic absorbing coefficient ki(v) and a number density pt a more
general form of Eq. (2) is required
- £ k1(v)pi^ ,
L i=l J
T(v) - exp - £ k1(v)pi^ , (3)
where & is the optical path length.
If the path is not homogeneous, Eq. (3) becomes
-------
P
TRANSMITTANCE T=P/P0
Fig. 1 - The transmittance (T) of an absorbing path is defined as P/PO when Po is the incident and
P is the emerging radiant power
-------
T(v) = exp
where ki(v) and pt may vary along the path.
For purposes of calculation, Eq. (k) can be approximated by
[N m -I
- £ £ kik(v)Pik^k »
k=l 1=1 KJ
where the path is divided into N layers, each sufficiently thin that it
may be considered homogeneous. Eq. (5) is used for calculating the
transmittance of the atmospheric path traversed by solar radiation.
We have investigated the spectral region between approximately
400 and 1*000 cm"1. Most of the atmospheric absorption features in this
region are due to HgO., C02, 03, N20, CH4, and CO, and, in some spectral
regions, these are sufficiently strong to reduce the transmittance of
long path lengths of air to zero. Between these opaque regions there
are atmospheric "windows" in which the atmosphere has a relatively high
transmittance even for very long air paths. These windows also contain
absorption features of atmospheric gases.
The absorption by atmospheric gases in the infrared is primarily
associated with rotation-vibration bands. A typical band consists of
many individual absorption lines, each of which corresponds to a tran-
sition of the absorbing molecule from a lower energy state E" to an up-
per state Ef. At pressures greater than a few torr the absorption coef-
ficients of the lines can be described, to a good approximation, by the
Lorentz line shape
k(v) = SaM(v-vo)2 + a2] , (6)
where S is the line intensity, a is the half width, and v0 is the posi-
tion of the line center. The dependence of k(v) on frequency is illus-
trated in Fig. 2 (a) .
The transmittance of a homogeneous path containing a gas with a
single absorption line of the shape given by Eq. 6 can be calculated
from Eq. (3)'. The transmittance depends on the product k(v)p# and de-
creases with increasing path length as drawn in Fig. 2(b). If the num-
ber density or mixing ratio of a gas is to be determined from such
transmittance measurements it is readily shown that, for a given signal
to noise ratio in the observed spectrum, the most accurate measurements
can be made for transmittance values T(V) ~ 1/e « 0.37- Thus, to deter-
mine the abundance of a gas with a fixed absorption coefficient and a
variable mixing ratio it is desirable to adjust the absorbing path length
so that the observed transmittance lies in the range 0.1 to 0.9. The
8
-------
A
V
T = P/ Pa =
Fig. 2a - Frequency dependence of the absorption coefficient of an
absorption line with a Lorentz shape
2b - Dependence of the transraittance due to a Lorentz line on the
product
9
-------
dependence of the transmittance of homogeneous air paths containing dif-
ferent number densities of an absorbing gas with an absorption coefficient
typical of that of the stronger lines of many gases is shown in Fig. 3-
Some of the gases which occur in the atmosphere with relatively
high number densities (such as H20, approximately 1% by volume, or C02
about 330 ppn by volume) give rise to absorption lines with minimum
transmittances of less than 0.5 in ground level air paths of a few meters.
Gases such as CH-i, N20, and CO, with mixing ratios at ground level of
the order of 1 ppm, give recognizable absorption features in paths of
the order of 100 m; however, many gases with mixing ratios in the ppb
range or less will not produce recognizable absorption features unless
path lengths of many kilometers are used. Because of the range of the
mixing ratios of the gases of interest to this study we have obtained
spectra of atmospheric paths of different lengths.
As the path length is increased to produce measurable absorption'
features by a gas with a low mixing ratio, the total amounts of the more
abundant absorbing gases also increase, and this causes numerous weak
lines of these gases to become visible. These latter often interfere
with the absorption features which are being sought. An example is
shown in Fig. k. The top spectrum is a laboratory sample of HC1. It
shows the widely spaced lines of the 1-0 band between 2700 and 2900 cm"1.
Beneath this is the corresponding region of a solar spectrum observed at
ground level at Columbus. The bottom two spectra are small portions of
the upper two spectra between 27^0 and 2780 cm"1. Most of the structure
in the solar spectrum is due to HDO, H20, and CIU. Although HC1 features
have been observed (1-4) in solar spectra taken at high altitudes where
there is much less interference by water vapor, it is difficult to make
a positive identification of the HC1 features in the spectra of Fig. 4.
It is clear that this would require the identification of the sources of
the interfering structure in these spectra.
Other examples of long path atmospheric spectra are shown in Fig. 5
and 6. Figure 5 shows spectra of approximately 8 m, and 1000 m of ground
level air and a solar spectrum over the region from 700 to 1500 cm"1.
Figure 6 shows a similar set of spectra of the region from 1800 to
2300 cm"1. As the path length increases numerous weaker lines become
visible throughout the entire region. The extent of the "windows" is
curtailed in solar spectra by strong bands of C02 and H20. The inten-
sities of these bands is decreased by making observations at high alti-
tudes and studies of the solar spectrum by high flying aircraft, balloons,
etc., and other detection methods (5-19) have enabled a number of gases
such as F-ll, F-12, HN03, and HC1 to be identified as atmospheric con-
stituents. Little is known about the abundances of some of these gases
in the troposphere; hence, the analyses of solar spectra observed at
ground level can serve as a unique resource for such investigations.
Many of the lines of H20, C02, 03, N20, CH4, and CO in Figs. U, 5,
and 6 can be identified by comparing their positions and intensities
with the corresponding spectra of individual gases obtained in the
10
-------
QJ
O
cn
or
1.0
0.8
0.6
04 -
0.2-
oo-
0.01
100 (km)
PATH LENGTH
Fie 3 - Hie dependence of the transmittance of an air path containing various number densities of an
absorbing gas with an absorption coefficient k on path length
-------
n n
UJ
o
CO
z:
<
cr
'
v
,
0-U
2740
2900
I/I/ i
v • I/
2750 2760 2770
WAVENUMBER(cm")
2780
Fig. k& - Laboratory spectrum of HC1 between 2700 and 2900 cm"1 0.02
Torr HC1 in 171 m and 50 Torr N2 in 171 m path
Corresponding region of the solar spectrum (large zenith angle)
Spectrum of HC1 between 27^0 and 2780 cm"1
Corresponding region of the solar spectrum
kc
Ud
12
-------
o
CO
CO
CO
2
<
cr
B
c
I
1
700 800 900 1000 . 1100 1300 1300 1400 1500
WAVENUMBER(CM-')
Fig. 5a
5b
5c -
Spectrum of 8.5 m path of air with seme C02 and HgO removed
Spectrum of 993 m path of ground level air, T = 290 K,
P = 750 Torr
Solar spectrum recorded at Columbus, Ohio, solar zenith angle
86°
13
-------
o
CO
CO
00
2
<
cr
A
B
C
L0-,:
l?'lltl
H ii'Hiii-
iiii-'K
1800 1900 2000 2100 2200
WAVENUMBER (CM'1)
2300
Fig. 6a - Spectrum of 7.0 m ground level air, T = 2$k K, P = 750 Torr
6b - Spectrum of 993 in ground level air, T = 29^ K, P = 750 Torr
6c - Solar spectrum, solar zenith angle = 82°
-------
laboratory. However, because of the low vapor pressure of H20 at room
temperature, it is not possible, even with the long path lengths avail-
able in the multiple traversal cells in our laboratory, to obtain spectra
of a sufficient amount of this gas to match the amount occurring in the
atmospheric paths traversed by solar radiation. Thus not all the water
lines in solar spectra can be readily identified. This is of concern
because water vapor lines occur throughout the spectral region of
interest. However, as all who have attempted to do so have found, it
is time-consuming to identify individual features line by line even for
frequency comparisons only. Even when the lines have been identified,
obtaining quantitative estimates of the mixing ratios of the gases from
the spectra is difficult and subject to inaccuracies if only individual
lines are analyzed.
During the past year we have investigated other techniques of
analyzing spectra with the aim of reducing the time taken for the analy-
sis and to improve the accuracy of the measurements. The progress in
this area is described below.
METHODS OF SPECTRAL ANALYSIS
Spectral ratioing
Spectral rationing is a commonly used technique for investigating
spectra. An example is illustrated in Fig. 7- The top spectrum is that
of an evacuated cell and the few meters of air in the transfer optics
path between 650 and 1350 cm"1. Bands of C02 near 700 cm"1 and H20
beyond 1200 cm"1 are superposed on the background, which is determined
primarily by the variations in spectral sensitivity of the Cu:Ge detector.
The middle spectrum shows absorption bands of N02 after this gas had been
introduced into the cell. Both of these spectra were recorded digitally
at equally spaced frequency intervals, and they can be ratioed at each
frequency as shown in the bottom curve. In this ratioed spectrum the
detector spectral sensitivity variations have been,removed as well as
most of the features due to C02 and H20, thus allowing a direct measure-
ment of the N02 transmittance to be obtained. If the amount of N02 in
this sample were not known, it could be estimated by ratioing this trans-
mittance spectrum with other transmittance spectra of samples containing
known amounts of N02 at the same temperature and pressure as the unknown
sample.
The transmittance of long air paths in multiple traversal cells can
also be obtained by ratioing spectra with the cell evacuated and con-
taining the air sample. The absorption features of the individual gases
can then be removed by ratioing the air transmittance spectra with trans-
mittance spectra of each of the gases present. This allows both the
abundance of these gases.to be estimated and also underlying features of
other gases can be made more easily visible in the ratioed spectra.
We have applied this technique to the study of ground.level air
spectra obtained with a spectral resolution of 0.1 cm"1 at Columbus,
15
-------
U
0
3
1-
H
2
<
tr
i-
i
|-| Mr1! -_^ _|T|. 1— l--_r-J-.y__ ^-' - - .--•-_ _*_
'^n'Vit'hP \ /T^T ' ]' T-*'^"-— i— "^ ••*>. ,^»ti I"
•i':!Trr\ r\ M ^ -^ !;
i •• i •
i
't' !
\ \ .
,-^
650
S50 1050 ,
WAVENUMB£RS(CM )
1250
Fig. 7a - Background spectrimi of evacuated absorption cell between 650
and 1350 cm"1
7b - Spectrum of absorption cell containing a sample of N02 and
N204
7c - Ratio of spectrum b/spectrum a
16
-------
Ohio. The precision of the abundance values obtained by these techniques
is not high, the uncertainty typically being of the order of 10$. This
inaccuracy is caused in part by the noise level in the spectra and the
uncertainty in the amount of gas in the standard sample. It has been
found that most of the expected air pollutants occur at such low levels
in the Columbus atmosphere that their absorption features cannot readily
be detected with the path lengths (~ 1 km) and spectral resolution avail-
able, and that, as indicated in Fig. 3j the longer path lengths obtained
in solar spectra are required. Unfortunately solar spectra cannot read-
ily be ratioed with spectra of individual gases because:
1. It is not possible to obtain a background spectrum for solar
spectra.
2. The temperature and pressure vary along the atmospheric path
traversed by the solar energy and these effects cannot readily
be simulated in the laboratory.
3- The large amounts of H20 in the solar path cannot be obtained
in laboratory spectra.
Comparison of observed spectra and synthetic spectra
In view of the difficulties noted above, we have considered the
information obtained by comparing air spectra, and in particular, solar
spectra with calculated spectra. Synthetic spectra can be calculated
provided the parameters of all the absorbing lines of atmospheric gases
in the spectral region of interest are known and the pressure, tempera-
ture, path length, and the mixing ratios of the absorbing gases are spe-
cified: This information can then be used with Eq. (5) and (6) to cal-
culate the transmittance of the path.
Recently the Air Force Cambridge Research Laboratory (AFCRL) - now
the Air Force Geophysics Laboratory (AFG£) - has prepared a listing of
the parameters of atmospheric lines (20) which we have used to calculate
synthetic atmospheric spectra corresponding to observed spectra. This
work, described in an Interim Technical Report (21), shows observed and
calculated spectra over the region from 700 to 2300 cm"1 for approxi-
mately 10, 100, and 1000 m paths of ground level air and for high and
low sun spectra observed at Columbus, Ohio. A letter to the editor of
Applied Optics describing this atlas has been accepted for publication
and is included as Appendix III of this report. Comparisons of the
observed and calculated spectra in this atlas show that, in general,
the line positions and relative intensities in the calculated spectra
are in good agreement with those in the observed spectra, over the en-
tire region. These spectra are intended to serve as references for the
continuing detailed analysis of such spectra.
A detailed line-by-line comparison of these observed and calculated
spectra has been made over the past year. Instances of incorrect line
positions and relative intensities, and, in some cases, missing lines,
17
-------
are found in the calculated spectra. Most of these differences can be
seen by comparing the spectra in the interim report (21) and are not
described here. Caution must be exercised in the use of calculated
spectra until the accuracies of the line parameters have been verified.
One of the conclusions reached from these comparisons is that ab-
sorption features due to gases whose line parameters are not given in
the line listing do not give recognizable features in the ground level
air spectra and these features are also difficult to identify even in
solar spectra because of one or more of the following reasons:
1. They may not consist of discrete lines but rather form a con-
tinuous absorption band which is difficult to recognize due to
the presence of the absorption lines of the permanent gases.
2. They are too weak to be observed, even if they consist of dis-
crete lines.
3- They lie in spectral regions occupied by features of other
gases which interfere with the identification.
Some of these problems are indicated in Fig. k.
The calculated spectra have, however, allowed absorption features
of F-12 to be identified in solar spectra and estimates of its tropo-
spheric abundance to be obtained. A preliminary account of this work
was presented in an earlier report (22). A more detailed description
of these results will be published in Applied Spectroscopy later this
year and a preprint of this paper is given in Appendix III.
The weakness of the F-12 features in these spectra is typical of
that expected for many other trace atmospheric gases. Laboratory spec-
tra of relatively large amounts of CHClFa, CHClaF, CC14, and CClaF are
shown in Fig. 8 together with a corresponding portion of a ground level
solar spectrum between 760 and 900 cm"1. Most of the structure in the
solar spectrum is due to R20 and C02 and this obscures the weak features
of the halocarbons if they are present. This spectral region is of in-
terest because the observed low sun solar spectra (21) show a series of
regular spaced weak lines between approximately 800 and 820 cm"1 which
do not appear in the calculated spectra. By comparing laboratory spec-
tra of C02 with the corresponding calculated spectra, as shown in Fig.
9, the weak lines in the solar spectrum have been identified with C02,
although we have not been able to assign the vibration rotation band to
where they belong. Similar comparisons of laboratory spectra and cal-
culated spectra for other gases are described elsewhere in this report.
Progress in ratioing observed and synthetic air spectra
Analysis of ground level air spectra—
The identification of F-12 features in solar spectra has illustrat-
ed the usefulness of the synthetic spectra. In their present form these
18
-------
uj o1 ••
O 760
CCL
800
840
880
\
760
800 840
WAVENUMBER(cnr')
880
Fig. 8a - Laboratory spectrum of CHCCFa between 760 and 900 cm"1
8b - Laboratory spectrum of CHClaF between ?60 and 900 cm"1
8c - Laboratory spectrum of CC14 between ?60 and 900 cm"1
8d - Laboratory spectrum of CClsF between 760 and 900 cm"1
8e - Ground level solar spectrum between 760 and 900 cm"1
19
-------
rvj
o
UJ
O
CO
z:
<
a:
A
0.0
1.0
B
0.0
800
810
820
Fig. 9a -
WAVENUMBER ( cm-' )
Spectrum of 51 Torr C02 in 1?1 m path at 295 K between 800 and 820 cm"1
Calculated spectrum of Co2 for the same conditions
-------
calculated spectra are not suitable for the quantitative determination
of the abundances of pollutants or other permanent gases primarily be-
cause a relatively large change in the abundance (» 20$) of a gas causes
a much smaller change (» 5$) in the peak absorptance of a typical line.
These changes are difficult to detect by visual comparisons of the spec-
tra. A higher accuracy may be achieved by ratioing observed and calcu-
lated spectra. As discussed earlier, this technique, provided the line
parameters used are accurate, will allow estimates of the permanent gas
abundances to be made and, at the same time allow these features to be
"removed" from the spectra to reveal the underlying structure due to
other gases.
Several difficulties were encountered in attempting to ratio ob-
served and computed spectra. These included the limited capability of
the present spectrometer system which does not allow the required compu-
tations to be performed readily. The university IBM 370 computer has
therefore been used to perform the ratioing. This required devising
methods of allowing the IBM computer to read the magnetic tapes contain-
ing spectral information generated by the spectrometer. We wish to
acknowledge the assistance of Dr. Peter Griffiths of Ohio University in
developing this latter procedure. It was found that the IBM.computer
was unable to read the end of file markers put on the tape by the spec-
trometer. For several months this necessitated transferring only a sin-
gle spectrum to each tape read by the IBM computer and caused delays in
the data processing. During a visit by a spectrometer engineer it was
found that this defect was due to the spectrometer system and several
spectral files can now be read from each tape.
The program used for calculating the spectra in the air atlas was
then modified to allow transmittances to be calculated at the same fre-
quency intervals as on the observed spectra. These spectra are obtained
from interferograms. If the beginning and ending frequencies in its
observed spectra are vj. and v2 respectively, and these are N points in
the spectra, then spectral information is obtained at discrete spectral
intervals Av when
Av = (va - vL)/(N - a.) . (7)
A test of the feasibility of ratioing observed and calculated spec-
tra was made by analyzing a spectrum of CO. A description of this work
is given in Appendix III which is a preprint of an article to be pub-
lished in Applied Optics later this year. This study showed that esti-
mates of the abundance of a gas in the sample can be obtained from such
ratios. For the particular spectrum analyzed it was necessary to match
the positions of the observed and calculated line positions to better
than 0.002 cnT1 and to match the spectral resolutions of the spectra to
better than 5$ in order to obtain the best ratio (indicated by the best
approximation to a straight line). Under these conditions abundances
were obtained, for the case of the CO spectrum analyzed, to better than
10$. Although reasonably accurate abundances are obtained by this pro-
cedure the trial and error process of matching the spectra was time
consuming both to the computer and to the operator.
21
-------
This technique was then applied to the analysis of the spectrum of
a 171 m path of ground level air at 294 k and 700 Torr between 2170 and
2250 cm"1 shown in Fig. 10(d). The absorption lines are due to CO, N20,
C02, and H20. Curves a, b, and c of Fig. 10 show calculated spectra of
CO, C02, and N20 respectively corresponding to the amounts of these gases
in the air spectrum. The results of ratioing these spectra are shown in
Fig. 11. The top curve in Fig. 11 shows the result of ratioing out the
CO lines, the next curve shows the air spectrum with both CO and C02
removed and curve c shows the air spectrum with CO, C02, and N20 re-
moved. By trial and error matching of these spectra the abundances
shown in Table I were obtained. The estimated precisions of these abun-
dances were obtained by calculating spectra of varying amounts of these
gases until significant deviations from a straight line were noted in
the ratioed spectra. It should be noted that if the values of the line
parameters in the AFCRL listing are incorrect systematic errors in the
abundances will be made. No uncertainty is given for the C02 abundance
because of the difficulties in ratioing the spectra.
Table I. Abundances of CO, N20, and C02 Obtained by Ratioing
Observed and Calculated Spectra of a 171 m Air Path
Gas
CO
C02
N20
Abundance
0.78 ± o
320
0.29 ± o
(ppm)
.03
.02
Examination of Fig. ll(c) reveals two weak absorption features at
2186.9 cm"1 and 2205.2 cm"1. These are weak water vapor lines which
have not been ratioed out although these line parameters are included in
the AFCRL line listing.
The poor ratioing of the C02 lines indicates errors in the values
of the parameters of these lines. This effect is shown in more detail
in Fig. 12. A small portion of a C02 spectrum from 2230 to 2250 cm"1
from Fig. 10 is shown in curve c, curve b shows the corresponding cal-
culated spectrum of C02, and the ratio is seen in curve a. Both line
shifts and relative line intensity differences can be recognized in the
ratioed spectrum. These differences do not appear as large for either
the CO or N20 parameters.
It would also have been possible to obtain estimates of the abun-
dances of the individual gases by ratioing the spectra in Fig. 10 against
22
-------
Tco
TTTTTTT
Tco.
fV>
Tobi
WAVENUMBERl cm-' )
Fig. lOa - Calc\ilated spectrian of CO between 2170 and 2250 cm -1
lOb - Calculated spectrum of C02 between 2170 and 2250 cm"1
lOc - Calculated spectrum of N20 between 21?0 and 2250 cm"1
lOd - Observed spectrum of 171 m of air at 2$k K and 700 Torr
-------
ro
Tobs
Too
Tot>s
TcoTco,
fobs
TcoTco,TN,o
Tubs
o .
2170
-^I^WWTYWVY^^
22OO 2210 222O
WAVE NUMBER (cm-')
2250
Fig. lla - The ratio of the spectra d and a in Fig. 10
lib - The ratio of the spectra in Fig. lla and Fig. lOb
lie - The ratio of the spectra in Fig. lib and Fig. lOc
lid - Observed spectrum of 171 m of air at 29k K and 700 Torr
-------
Tobs
Teal
l.O
Tcol
Tobs
2230
2240
WAVENUMBER ( em-' )
2250
Fig. 12a - Ratio of the spectra in c and b
12b - Calculated spectrum of C02 between 2230 and 2250 cm
12c - Observed spectrum of C02 broadened to atmospheric pressure with air
25
-------
Deserved spectra or the individual gases. These abundance values would
depend on the accuracy with which the amounts of the gases in the stand-
ard spectra are known. The reproducibility of transmittance measurements
in most infrared measurements is rarely better than a few percent. If
the AFCRL line parameters are used to calculate the individual gas spec-
tra, a calibration standard independent of the particular set of experi-
ments is obtained. If data obtained at different institutions are to be
compared, this ability to transfer standards becomes particularly im-
portant .
Analysis of solar spectra —
Since it is possible to use the line listing to calculate spectra
of inhomogeneous paths, these ratioing techniques can be applied to
solar spectra.
Our progress in ratioing solar spectra is illustrated in Figs. 13
and 14. These show a small spectral region between 1155 and 1165 cm"1
which contains strong absorption features of F-12. The bottom curve in
Fig. 13 is a solar spectrum taken with a solar zenith angle of ^5° and
corresponds to the spectrum shown in the air atlas (21). The nominal
resolution was 0.1 cm"1. The air atlas spectrum (21) was shown with es-
sentially box car apodization but, to remove some of the worst features,
a triangular apodization was chosen to obtain the spectrum in Fig. 13(d).
In addition, after the interferogram was transformed, three additional
points were interpolated between each of the resulting observed spectral
transmittance values by using computer programs supplied by the spectro-
meter manufacturer. The top three curves in Fig. 13 show calculated
spectra of Oa, N20, and H20 as they are expected to appear in the solar
spectrum. N20 was assumed to have a constant mixing ratio with height,
but the distribution of H20 and 03 were assumed to be those described in
the air atlas report (21).
The results of removing 03, N20, and H20 features from the solar
spectrum are shown in Fig. ih. Figure l^(a) is a laboratory spectrum
of a trace amount of F-12. Figure lU(b) shows the ratioed solar spec-
trum after removal of 03, N20, and HgO features. The calculated and
observed solar spectra are shown in Fig. l^(c) and lU(d), respectively.
The weak feature in the ratioed spectrum near Il6l cm"1 agrees in posi-
tion and contour with the strongest feature in the laboratory spectrum
of F-12 although the other features are too weak to be seen in the ratioed
spectrum. From the amounts of gases required to obtain the calculated
spectra in Fig. 13 the total amounts of 039 N20, and H20 in a vertical
path through the atmosphere can be' determined. The amount of N20 was
determined to correspond to a mixing ratio of 0.23 ppm. This is a much
lower number than expected. It has not yet been determined if this is
due to inaccuracies in the program used or the line parameter listing.
The residual fluctuations in Fig. l^(b) are due partly to the in-
herent noise in the observed spectrum. Part is also caused by inaccura-
cies in the line parameters - the shift of the H20 line at 116U cm"1 is
26
-------
To,
TH.O
1.0.
L0.
TN.O
rv>
Toes
8
.A
D
1155
1160
WAVENUMBERUm-')
1165
Fig. 13a - Calculated spectrum between 1155 and 1165 cm"1
13b - Calculated spectrum between 1155 and 1165 cm"1
13c - Calculated spectrum between 1155 and 1165 cm"1
13d - Observed solar spectrum (solar zenith angle 1*5
of 03 in an atmospheric slant path
of H20 in an atmospheric slant path
of N20 in an atmospheric slant path
-------
1.0— :' * -
TFC-
12
\
Tc
Toes
1155
1160
WAVENUMBER (cm->)
1165
Fig. Ita
lUb
lUc
- Laboratory spectrum of F-12 between 1155 and 1165 cm 1
- Solar spectrum with 03 , NaO, and H20 lines ratioed out
- Calculated solar spectrum
- Observed solar spectrum
28
-------
particularly obvious - and also to approximations in the model used to
represent the atmospheric path, to uncertainties in the actual pressure
and temperature variations with height in the atmosphere on the day the
spectrum was obtained, to possible deviations in 'the actual 03 and HaO
distributions from those assumed in the model, and to incorrect line
shapes - a Voigt line profile would be more appropriate than the Lorentz
line shape in representing the shapes of the 03 lines. We are currently
investigating some of these effects to determine their influence on our
measurements.
The abundance of F-12 was estimated by measuring the equivalent
width of the absorption feature near Il6l in the ratioed spectra of Fig.
l^(b) and by using the laboratory calibration curve shown in Appendix V.
A value of 80 parts per trillion was obtained if a uniform mixing ratio
in the troposphere is assumed. This value is in reasonable agreement
with the value of 110 ppt obtained in Appendix III. The present results
must be regarded as tentative until more data have been analyzed.
Abundances by using linear regression techniques
The precision we have obtained for the abundances of gases found by
ratioing observed and calculated spectra of both homogeneous or inhomo-
geneous paths is of the order of 10$. This uncertainty is due partly
to the noise level in the original spectra and also to the method of
estimation which relies on an observer making judgments of the goodness
of the ratio point by point through the spectrum. If all the spectral
information concerning the absorptance by a gas could be summarized in
one measurement, an improved accuracy could be obtained. As pointed out
by Harries and Chamberlain (23) this approach has been used by a number
of workers in designing instruments to detect the presence of a gas by
correlation methods. Examples of such instruments include the Barringer
Research Corporation correlation spectrometer (2k), the selective chopper
and pressure modulated spectrometers described by Houghton et al. (25,
267, Smith et al. (2?), and Goody (28).
The concept of spectral correlation to determine abundances of at-
mospheric gases from the direct analysis of spectra has also been dis-
cussed by Derr et al. (29). Other approaches to this problem are
discussed below.
The monochromatic absorbance A(V) at frequency v of a single gas in
a homogeneous sample is obtained from Eq. (2)
A(v) = ^ - P(v)/P0(v) = k(v)u , (8)
when u is the amount of absorber in the sample and k(v) is the sum of the
absorption coefficients of all the lines at frequency v. Provided PO(V)
is known, an estimate of the abundance of the gas can be obtained at each
frequency at which the gas absorbs
ut = A(v1)/k(Vl) . (9)
29
-------
If the abundance is determined at N positions in the spectrum the
average value of the abundance u
N
u = (1/N) £ A(vt)/k(vi) • (10)
1=1
If all the measurements are of equal weight then the precision in
determining u will be increased over that of a single measurement by a
factor of .JN. Many bands of gases extend over intervals of 50 cm"1 or
more, and if spectra of 0.1 cm"1 resolution are obtained, as with our
interferometer, there will be ~ 800 observations over such bands causing
an increase in the precision by a significant factor. If the measure-
ments are not of equal weight the precision can be increased by suitably
weighting the individual observations.
The above method is not directly applicable to the analysis of most
air spectra because of the overlapping of lines and bands which occurs
throughout the spectrum. In this case Eq. (8) must be modified,
m
A(v) =Sn (-P(vi)/Po(vi) = £ MVI)UJ (U-)
3=1
when m is the number of gases which absorb in the spectral region inves-
tigated. Again, provided the absorbance can be measured at a sufficient
number, N, of frequencies and provided the absorption coefficients of
each gas are known, the abundances of the individual gases can be ob-
tained by solving the N equations of the form of Eq. (ll) by standard
mathematical procedures of linear regression (30).
The absorption coefficients of the individual gases can be obtained
from spectra obtained with the same instrument (it is implicitly assumed
that all the measurements will be made at the same spectral resolution)
or from calculated spectra. In order to obtain the calculated absorp-
tion coefficients it is necessary to find the spectral transmittance
T'(v) of a known amount of the gas Up for the same spectral resolution as
the spectrum to be analyzed:
T'(v) = j" fexp-k(v) uFl a(v,v') dv'/f 0. In our
work we have used both triangular and Gaussin shapes for this function.
It is then assumed that Beer's Law holds for the observed trans-
mittance and that an apparent absorption coefficient can be obtained
from
T'(v) = exp(-k'(v) UF) (13)
30
-------
when k'(v) is dependent on spectral resolution. The same assumption is
also made when the absorption coefficient is derived from direct measure-
ments of spectra.
We have tested this assumption on computer generated spectra. For
the few cases so far investigated this appears to be a reasonable approx-
imation provided the range of abundances for which a given value of
k'(v) is assumed is not large. We plan to make more extensive investi-
gations of this assumption for various gases and spectral resolutions as
time permits. This assumption is also made for cases when the absorp-
tion coefficients are obtained from experimental spectra and again it
_appears to be valid over small abundance ratios and is universally used
in quantitative spectroscopy to obtain concentrations of absorbers in
samples.
This method of analysis has been used to obtain the abundances of
CO, NgO, and H20 in the air path giving rise to the spectrum shown in
Fig. 10(d). Absorption coefficients for the individual gases were cal-
culated from Eqs. (12) and (13) and the AFCRL line parameters listing
and by choosing values for up and the spectral resolution equal to those
obtained from the direct ratioing method. A small section of these tab-
ulated values is shown in Table II.
In this table, which also contains information discussed in a later
section, the final column shows the wavenumber for which the information
shown in the other columns was calculated. The penultimate three columns
show values relating to the degraded absorption coefficients of NgO, CO,
and ES0. The values actually shown are the kj(v) Pt.6 products defined
by Eq. (3) where J5 = 171 m and the pt values were obtained from Table I.
An arbitrary value of 2.72 x 10~3 was assumed for the E^O mixing ratio
(this spectrum was taken during the winter months).
The abundances were then determined by analysing the sections of
the spectrum shown in Fig. 15 and assuming that the incident power Po(v)
corresponded to the straight line shown in Fig. 15. The results are
shown in Table III, which gives the ratio of the abundances determined
by the linear regression method to those given in Table I. There is a
considerable improvement in the precision compared with that obtained by
direct ratioing of the spectra and the results are consistent with the
previous values. No information concerning KgO was obtained from the
region from 2190 to 2200 cm'1 since there is no significant absorption
in this region. The differences between the values of the abundances
determined from the different spectral regions may be due to the incor-
rect placement of PO(V), or to small errors in the line parameters which
would not be detectable by spectral ratioing of our spectra.
The effect of varying the position of PO(V) on the abundances is
shown in Table IV. The abundances were determined by analysing the en-
tire spectral region from 2190 to 2210 cm'1 and by changing PQ(V) by ± 1%
from its previous position. Although the precision of measurement was
essentially unchanged, the fractional change in the position of PQ(V) is
31
-------
Table II. Absorption Coefficients of CO, N20y and H20 Calculated from^
the AFCRL Listing and for a Spectral Resolution of 0.075 cm"1
Between 2000 and 2505 cm"1
&
iiS2:MZz:
22Je.*Mr-S
1*04*4^1? L_
32
-------
LU
O
OO
CO
o:
h-
0.0
2180
2190 22OO 2210
WAVENUMBER(cm-')
2220
Fig. 15 - Portion of a spectrum of 171 m path of air at 2$& K and 700 Torr. The intervals chosen for
the linear regression method of obtaining abundances are indicated together with the posi-
tion of the H20 line and the Po(v) position.
-------
Table III. Dependence of Abundance Values of N20, CO, and H20 Determined
by Unweighted Linear Regression Analysis of Air Spectra on
Spectral Regions Analyzed. Po(v) is 1.00 in All Cases
\Spectral
\Region
GasNy
N20
CO
HgO'
Abundance Ratio*
2190-2200
cm"1
0.918 ± 0.009
0.941 ± 0.014
2195-2205
cm"1
0-933 ± 0.008
0.928 ± 0.023
0.680 ± 0.056
2200-2210
cm"1
0.958 ± 0.007
0.867 ± 0.038
0.655 ± 0.059
2190-2210
cm"1
0.947 ± 0.005
0.917 ± o.oi4
0.660 ± 0.051
*This value is the abundance determined by linear regression divided by
the corresponding abundance determined by visually ratioing the spectra
(see Table I).
Table IV. Dependence of Abundance Values of NaO, CO, and H20 Determined
by Unweighted Linear Regression Analysis of Air Spectra on
Assumed Value of PQ(V). Spectral Region Analyzed 2190 to
2210 cm"1
Gas
N20
CO
H20
Abundance Ratio*
Po(v) = 0.99
0.897 ± 0.006
0.883 ± 0.017
0.595 ± 0.061
P0(v) = 1.00
0.9^7 ± 0.005
0.917 ± o.oiU
0.660 ± 0.051
P0(v) = 1.01
0.997 ± 0.005
0.950 ± 0.013
0.724 ± 0.048
*This value is the abundance determined by linear regression divided by
the best value obtained by visual ratioing of the spectra (see Table l)
34
-------
reflected as a much larger fractional change in the abundances. It is
clear that it is necessary to determine the position of P0(v) accurately
to avoid systematic errors and that the calculated precision does not re-
flect the absolute accuracy.
Other errors may occur if there are additional unrecognized absorp-
tion features present. A suitable strategy to avoid these difficulties
in the case when the abundance of a known atmospheric constituent is to
be determined is to ratio observed and calculated spectra and look for
additional features before analyzing with the linear regression method.
Hon Linear least squares methods of obtaining abundances
The linear regression method of determining abundances gives results
which have a higher precision than can be obtained by direct ratioing of
spectra but requires the position of PQ(V) to be guessed and the absorp-
tion coefficient of all the gases contributing to the absorption in the
spectral region being investigated to be known. It is not always pos-
sible to estimate the position of PO(V) accurately, and since we also
wish to locate unidentified absorption features an analytical method of
searching for them is of value.
Recently Chang and Shaw (31) have described a non linear least
squares method of retrieving line intensities and half widths from spec-
tra degraded by a finite instrumental resolving power. A modification
of this method can be used to determine both the abundances of gases and
the best position of the PO(V) curve from analysis of observed spectra.
From Eqs. (ll) and (13)
m
fcP'(vi) =««P0(vi) - £ k.j(vt) ut , (1U)
3=1
where P'(vt) is a measure of the power in the observed spectrum at vi
and kj(vt) is the apparent absorption coefficient of the jth absorbing
gas. If the shape of PO(V) is assumed to be of the form
PO(VI) = a + b(vi-vo) + c(vi-vo)2 , (15)
when a, b, and c are constants and VQ is some known frequency then
= bi a + b(vi-vo) + c(vi-vo)2 - £ kj
L J j=i
en P'(vi) = bi a + b(vi-vo) + c(vi-vo)2 - £ kj(Vl) ut . (l6)
j
If observations of P'(VI) are made at N frequencies in a given spectral
region a series of N equations of the form of Eq. (16) is obtained which
can be solved by the application of the non linear least squares method
to retrieve the best values for a, b, c, and the abundances ut. This
program also gives the best fit calculated values PC(VI) and the
35
-------
differences Pf(vi) - P^(vi). If anomalous values of these differences
occur, these can be interpreted as indicating the presence of unassigned
absorption features.
We have used this method to analyze the three spectral regions shown
in Fig. 15 of the. 171 m air path spectrum. The results of the analysis
are shown in Table V.
Other output from the analysis is shown in Table II. The first few
columns in this table give the observed value of ^zP'(vj) as defined by
Eq. (16), the calculated value Sm PC(VI) and its standard deviation and
the difference between the observed and calculated values.
Inspection of the data in Table V and comparison with the values
in Tables I, III, and IV shows that the precision of abundance determina-
tions is similar to that obtained by the method of linear regression, but
that the spread of the abundance values in Table V is considerably less
than in Table III. This is attributed to the better determination of
PO(V) by the non linear least squares method. The value obtained for
PO(V) by considering the entire region from 2190 to 2210 cm"1 is close
to one of the values assumed in Table IV (Po(v) = l.Ol) and the abun-
dances determined for this value in Table IV agree well with the cor-
responding values and precisions in Table V indicating the uniqueness of
the solutions.
Figure 16 shows the difference between the observed and calculated
values (obtained from the set of constants shown in the last column of
Table V) of P(v) over the region from 2190 to 2210 cm'1, the correspond-
ing observed spectrum is shown in Fig. l6(b).
The abundances of CO and H20 shown in Table V retrieved by analyzing
different spectral regions agree within the accuracy of the measurements.
The agreement between the different values obtained for N20 are not so
consistent, and this suggests the possibility of line parameter errors
for this gas. The increasing N20 abundances obtained as the frequency
is increased indicates the relative intensities of tabulated line para-
meters decrease to higher frequencies. This has been verified by ratio-
ing observed and calculated spectra of NgO as shown in Fig. 1?. It is
seen that there are apparent line intensity anomalies near 2210 cm"1 and
that, as indicated by the values in Table V, the calculated spectrum is
weaker than the observed spectrum.
Comparison of spectra by using the interactive mode of computer
operation
Several methods of obtaining abundances of gases by analyses of
spectra have been discussed. We have stressed the comparison of observed
and calculated spectra since this appears to be the only feasible method
of analysing spectra of inhomogeneous paths such as solar spectra. How-
ever, the accuracy with which these abundances can be retrieved and the
ability to locate unidentified spectral features in all of these methods
36
-------
Table V. Dependence of the Abundance of NgO, CO, and H20 Determined by Non Linear Least Squares Analysis of Air Spectra
on the Spectral Region Analyzed
U)
^^v^ Spectral Region
Abundance Ratios"*^
H20
CO
H20
PO(V) Constants
a
b
c
2190-2200
cm"1
0.956 ± 0.012
0.9U3 ± 0.013
—
1.0005 ± 0.0020
- 0.0036 ± 0.0009
- O.OOOl»2 ± 0.00009
2195-2205
cm'1
0.982 ± 0.011
0.957 ± 0.022
0.790 ± 0.057
1.0062 ± 0.0017
- O.OOO21 ± 0.00035
•f O.OOOU2 ± 0.00013
2200-2210
cm'1
1.012 ± 0.008
0.950 ± 0.035
0.777 ± 0.05U
1.00l|l» ± 0.0037
+ 0.00149 ± 0.0016
- 0.00048 ± O.OOOlU
2190-2210
cm'1
0.997 ± 0.007
o.9»»o ± o.oik
0.736 ± O.0l»9
1.0110 ± 0.0011
0.00031* ± O.O0011
- 0.000055 ± O.CO0020
-------
CO
OBS
T.
CAL
.0- W'^VvAAtyv^VVv/^^
LO.O
.0
T
OBS
0.0
2190
2200
WAVENUMBER (cm-)
2210
Fig. l6a - Ratio of observed P(V) and values obtained from non linear
least squares method
l6b - Air spectrum between 2190 and 2210 cm"1
-------
I DBS
ICAL
10
00-—
U)
VD
lOBS
B
o.o, ^
I 0
0 0.—.-
2150
2170
2190
2210
2230
2250
2270
Fig. l?a
17b
17c
Ratio of spectra in Fig. 17b and l?c
Observed spectrum of 1.52 x 10~3 Torr of N20 and 100 Torr N2 in 1?1 m path, at
Calculated spectrum of N20 for the same conditions as used to obtain Fig. 17b
K
-------
depends on the accuracy with which the spectra can be calculated. It
has been shown that the AFCRL line parameter listing is not completely
accurate in its present form. Although improved versions of this list-
ing are being prepared (32) it is desirable to incorporate changes based
on our observations when necessary. Although in some instances only a
few spectral lines in a spectral region have incorrect parameters (for
example, the HgO line near 116^ cm"1 in Fig. lU) in other spectral re-
gions many line parameters need improvement (for example, the COa lines
near 800 cm"1 in Fig. 9 and 22i+0 cm"1 in Fig. 12). Other examples of
incorrect parameters have been noted by Nordstrom and Skinner (33).
Since each line has three adjustable parameters (intensity, position,
and width), the present trial and error method of adjusting these para-
meters to obtain the best fit between observed and calculated spectra is
excruciatingly slow. Thus, after the line parameters have been changed,
a program is submitted to the computer which provides an output deck of
cards to be submitted to the plotter to obtain the revised spectrum.
Additional line parameter changes are made, and the procedure iterated
until the best set is chosen. An alternative approach to obtaining the
parameter is to apply the non linear least squares method to several lines
in a spectral region as described by Chang and Shaw (31). This method
has been investigated but is not suitable for application to the data
obtained from the present interferometer. The limited spectral resolu-
tion (0.1 cm"1) and limited storage capacity of the memory associated
with this instrument typically allow spectral information to be obtained
only at intervals of 0.05 cm"1 or greater. Thus, over the interval oc-
cupied by a typical absorption line with a half width (at atmospheric
pressure) of approximately 0.1 cm"1, spectral information is collected
at a very small number of points. These data are insufficient to retrieve
the desired line .parameter information. This technique may be useful if
a higher resolution instrument were available.
In view of these instrument limitations, we are exploring the use
of the interactive mode of operation of the University IBM 370 computer
to perform on-line ratioing of spectra.
In the first phase of this work a magnetic tape containing spectral
information from the interferometer is submitted to the computer which
is programmed to display the required spectral region on an oscilloscope
(CRO) with appropriate frequency and ordinate scales. The AFCRL line
parameter magnetic tape is also available to the computer and the comput-
er can be asked to display a calculated spectrum on the same CRO and also
the ratio of the two spectra. The commands to the computer are made from
a teletype associated with the CRO. A hard copy of the CRO display can
be obtained, if required. An example of such a copy is shown in Fig. 18.
The top curve in this figure is the ratio of the two lower spectra. The
middle curve is a calculated solar spectrum between 1158.0 and 1163.0 cm"1
for a spectral resolution of 0.25 cm"1 and the bottom spectrum is the ob-
served solar spectrum. The ratio is not as flat as in some.other spectra.
The causes of this departure from flatness have not yet been established.
ko
-------
. v..«r
•.-L/rs- j.ROUNDS- usa.oeceo . uss.
•»37tl87JE+l«. .1S17SS4S4E-77. .1517686326-77,
rSJTS-MSGEr-T?. 151686«96Se-77. .15169*3896-77.DCLX-
. rn.v- .soeeeeeee , DISTX- i.eeeeeeee .xa- 0
A
B
1158
1160
WAVENUMBERlcnr1)
Fig. l8a - Ratio of the spectra shown in b and c
l8b - Calculated solar spectrum corresponding to the conditions
under which Fig. l8c was obtained
l8c - Observed low sun spectra between 1158.0 and 1163.0 cm"1, spec-
tral resolution ~ 0.25 cm"1, solar zenith angle 8l°
-------
Several applications of this system are under consideration.
(l) In spectral regions when the AFCRL line parameters are accurate,
a rapid examination of observed air spectra for unidentified features can
be made by ratioing observed and calculated spectra.
(2) Spectral regions when the AFCRL parameters are inaccurate can
be identified and the particular gas whose lines are in error can be
isolated. Laboratory spectra of this gas obtained under known conditions
are compared with calculated spectra by the same method. The AFCRL tape
can then be updated by displaying the stored line parameters for this gas
on the CRO, changing the displayed parameters of a line or lines, and re-
calculating the spectrum until the desired agreement is obtained. This
updated version of the tape can then be used to investigate air spectra.
(3) An observed spectrum of a gas whose parameters are not in the
AFCRL listing can also be displayed. This spectrum can be manipulated
to obtain a display of the spectral absorbance of a band or bands of the
gas and, provided the amount of gas present in the sample is known, the
spectral absorption coefficients can be obtained by using Eqs. (8) or
(13). These absorption coefficients can be stored in various forms for
later retrieval. A library of absorption coefficients of many gases can
be collected in this manner. These absorption coefficients can be used
with the linear regression or non linear least squares fit methods de-
scribed above to obtain abundances of gases in other gas samples. These
methods offer the promise of higher accuracy in determining abundances
than the present techniques of ratioing spectra or of making hand measure-
ments at a restricted number of frequencies in a band.
COMPARISON OF OBSERVED AND CALCULATED SPECTRA OF INDIVIDUAL GASES
After the air atlas had been prepared and analyzed, it was recog-
nized that differences between the observed and calculated spectra exist
which must be attributed to incorrect line parameters in the listing.
A program for collecting individual spectra of the gases under controlled
laboratory conditions was initiated and spectra of C02, 03, CH4, NgO, CO,
and H20 were collected. Spectra of these gases for the same conditions
were calculated and compared with the observed spectra. Some of these
spectra are shown in Fig. 1? and Figs. 19 to 2k.
Some differences between these spectra are readily apparent, but
other differences which detract from the ability to ratio out features
in air spectra are not easy to detect on these figures. One of the pro-
grams to be pursued in the coming year will be the resolution of these
differences by using the appropriate analytical tools described above.
ACQUISITION OF A HIGH RESOLUTION INTERFEROMETER
The analyses of air spectra have indicated that the present inter-
ferometer with its limited spectral resolution (0.1 cm'1) and computer
capabilities is inadequate to explore fully all the information contained
-------
-p-
UJ
800 82O ' 840
WAVENUMBER ( CM-)
Fig. 19a - 300 Torr C02 in 1?1 m path at room temperature
19b - Calculated spectrum for same conditions
19c - 51 Torr C02 in 171 m path at room temperature
19d - Calculated spectrum for same conditions
-------
9OO
920
940
960
IOOO
111
D
92O 940 960
WAVENUMBER (CM--)
IOOO
Fig. 20a - 300 Torr C02 in 1?1 m path at room temperature
20b - Calculated spectrum for same conditions
20c - 51 Torr COs in 1?1 m path at room temperature
20d - Calculated spectrum for same conditions
-------
-p-
VJ1
UJ
o
2:
-------
-^___JPU^_
I28O
1340
O\
I22O
I24O
1340
WAVE NUMBER (CM-' )
Fig. 22a
22b
22c
22d
0.15 Torr N20 and 700 Torr N2 in 1?1 m path
Calculated spectrum for same
0.015 Torr N20 and 700 Torr N2 in 171 m path
Calculated spectrum for same
-------
UJ
o
H-
I-
B
to
i^
-------
OO
o
-a
I-
ITT
1 [
WAVENUMBERt
Fig.
2Ub
2Uc
- U.18 x 10~3 Torr CO and 700 Torr N2 in 1?1 m path
- Calculated spectrum for same
- l.lU x 10~3 Torr CO and 100 Torr N2 in 1?1 m path
- Calculated spectrum for same
-------
in solar spectra observed at ground level or in long paths of ground
level air. A higher resolution instrument is desirable for these stud-
ies, for other photochemical studies and for other investigations of
atmospheric transmittance.
As a result of a cooperative effort by Professor J. G. Calvert
(Chemistry), Professor R. K. Long (Electrical Engineering), and Professor
J. H. Shaw (Physics) it has been possible for the University to acquire
a Nicolet Instrument Corporation 7199 FT-IH System. This system includes
a Michelson interferometer with a germanium on KBr beamsplitter, variable
mirror rates of from 0.05 cm/sec to 4 cm/sec, a total optical retardation
length of 16 cm and a nominal aperture of 5 cm diameter. This system
will also include a NIC-1180 data system with a 40 k x 20-bit solidstate
memory, a 15-bit analog to digital converter, and a 6-inch CRT inter-
active display with alphanumerals. A NIC-294B dual drive disk memory
system with one fixed and one removable disk cartridge will provide a
storage capacity of U.8-million 20-bit words. This system will also in-
clude an interactive operating software package allowing data accumula-
tion of up to 512 k data points and disk FFT routines for up to one
million words. A mercury cadmium telluride detector will also be part
of this system.
This instrument is expected to be delivered in the spring of 1977
and to be operational soon after delivery. This instrument will be used
as required by several groups for their research work.
STRATOSPHERIC SIMULATION CHAMBER
The environments anticipated for the Stratochamber will be very
harsh. For this reason we decided to develop a bellows-type feedthrough
for optical adjustments during an experimental run. Such feedthroughs
have a static face seal as opposed to the more unstable rotary seal of
most feedthroughs. Unfortunately, most bellows designs only transmit a
short linear motion. By carefully selecting the proper size bellows we
were able to obtain about 1.25 cm of travel, which would be sufficient for
nearly all anticipated adjustments. Only the mechanism that controls the
number of traversals of the cell by the infrared radiation would require
more. For this control we designed a magnification scheme allowing us
to use the same bellows for all controls. The design of Blickensderfer
et al. (3^), in which rigid rods transmit the bellows motion to the mir-
rors was not well suited to our arrangement. We have all our optics
mounted on a sturdy stainless steel table which is kinematically supported
inside the cell. Consequently we wanted to avoid rigid connections be-
tween the cell wall and the optics. A common bicycle brake cable connect-
ing the bellows to the mirror mounts accomplished this. The further
problem of attaining sufficient stability in the system required a rather
complex mechanism to do the actual moving of the mirrors. Once all the
basic designs were developed, we had to construct everything out of cor-
rosion resistant materials. Figures 25 and 26 show the details of our
feedthrough-mirror control mechanisms. In both figures the handle (6) is
connected to a threaded shaft which turns in a threaded hole in the
-------
///////////////A/////////////Z7.
Fig. 25 - Details of mirror adjusting system
1. Cell wall
2. Stainless steel bellows
3. Seal
k. Center cable
5. Outer cable
6. Handle
7- Retaining plug
8. Nut
9- 3/16" diameter sapphire balls
10. Bearing adjustment bolt
11. Screw adjustment nut
12. Rod
13- Locking nut
-------
Fig. 26 - Details of mirror adjusting system
1. Cell wall
2. Stainless steel bellows
3. Seal
k. Center cable
5. Outer cable
6. Handle
7. Retaining plug
8. Screw adjustment nut
9. Plunger
10. Mirror mount base
11. Mirror holder
12. Spring
-------
feedthrough base. Turning the shaft one way pushes its end against the
end of the bellows and extends the bellows. Turning the shaft the other
way retracts it, pushing against the retaining pin (7) and compressing
the bellows. The motion of the end of the bellows with respect to the
base of the feedthrough is transmitted to the mirror control by the mo-
tion of the center cable (U) attached to the bellows end with respect to
the hollow cable (5) attached to the base of the feedthrough. The feed-
through base has a U-shaped groove cut in it designed to seal with any
.238 m (3/8") diameter wire (in, Teflon, etc.). The traversal control
is an adaptation of McCaa's original design. The traversal mirror of the
White mirror system can be swung about a vertical axis by a 1-meter long
arm attached to the mirror frame. This arm has a slot cut in its end
that fits over the rod (12). When the cable (k) moves, it turns the rod
(12) in a circle with the two sapphire balls (9) as bearings. This
swings the arm back and forth. By putting the maximum swing of the rod
at the position of maximum traversals, the sensitivity of the control
adjusts itself to the changing sensitivity in the mirror orientation.
Since the cable is wrapped around the axle, we gain the needed motion
magnification mentioned above.
The other mirror controls are like that shown in Fig. 26. The plung-
er (9) slides freely in a precision reamed hole. A ball on the end of
the plunger sits in a groove on the mirror frame, moving the mirror when
the control cable moves. All mirror controls have a screw adjustment
(8 in Fig. 26; 11 in Fig. 25) for initial alignment. Any realignment is
then done with the feedthroughs. Since the bellows can only pull one
direction, springs are used to pull the other direction.
The Stratochamber is designed to be portable. For ease in moving,
the bulky 6-in. thick styrofoam insulation is made in six pieces that
pound together with tongue-in groove joints.
The steel bath has been hot dip galvanized by the Brown Steel Gal-
vanize Co. to rust-proof it. We originally had planned to.use paint,
but a test piece, cooled to ?8 K, had its layer of paint crack off.
The'major problem with the operation was what to do about the stainless
steel bellows welded onto the end of the bath. By applying water glass
(Na2Si40g) to the bellows between the acid bath that removed the scale
(pickling stage) and the Immersion in the liquid zinc (galvanize stage),
we prevented the zinc from bonding to the bellows convolutions. The
steel flanges (now coated with zinc) were filed smooth, and the stainless
steel flange welded to the bellows had the zinc etched off by a dilute
sulphuric acid (HaS04) solution.
Currently the Stratochamber is being readied for its first cooling
trials. For these we will use chunks of dry ice surrounded by styrofoam
peanuts. The chamber has already been used to collect some room temper-
ature ozone spectra. With a Welch 1397 two-stage vacuum pump it takes
about an hour to pump down to 20 n through the 3«8l m (1.5") diameter
connection. The leak rate is about 50 |i/hour. The mirror control system
worked well at room temperature, and since it requires no lubrication,
52
-------
should function well at low temperatures too. A Stolab 921PL digital
platinum resistance thermometer will be used to monitor the temperature.
53
-------
5. STUDY OF SOME KEY REACTIONS OF PROBABLE
IMPORTANCE IN PHOTOCHEMICAL SMOG FORMATION
INTRODUCTION
One important aspect of the current work involves the kinetic study
of certain key reactions which appear to be of importance in photochem-
ical smog systems. During the first year of this study we have investi-
gated the kinetic behavior of nitrous acid through its formation reactions,
H20 + NO + NO;, -»2HONO, and its decomposition reaction, 2HONO -> H20 +
NO + N02.35>3S This study provided the necessary ground work to help
establish for us the kinetic behavior of HONO and the potential problems
associated with its use as a photochemical source of the important HO-
radical. The photochemical reactor which was constructed during the
first phase of this work, coupled with the FTIRS system provided to us
by the Environmental Protection Agency, have been utilized in this re-
search effort during the past year to obtain significant new information
related to several chemical systems of seeming importance in the lower
and upper atmosphere. The photolysis of dilute mixtures of HONO, N02,
and NO, in synthetic air provided the HO-radical through the reaction,
HONO + hv(?\ < k3QOK) ->HO + NO. Through the addition of CO gas to the
HONO, N02, N02 mixture in air, the controlled generation of H02 radicals
could be effected through the reactions, HO + CO -> H + C02, H + 02 + M -»
H0a + M. The system which we have picked is ideal in some respects to
follow the HO- and H02-radical reactions. The FTIRS system can establish
the [HONO] at any time, and this is directly related to the rate of HO-
radical generation by the photolysis of HONO. In addition, the [C02]
can be monitored directly with the FTIRS system and the rate of C02 for-
mation derived from these data is equal to the rate of H02-radical for-
mation. . By a careful control of the proportions of the mixture of HONO,
NO, N02/ and CO in air, either a dominance of HO or H09- radicals can be
easily obtained.
Two reaction systems have been studied in some detail during the
past year. The first of these involves the important reaction of HO-
radicals with CO: HO + CO ->H + C02. This reaction is not only of
intrinsic interest in its own right as an important sink for atmospheric
CO, but also has rather significant added importance since it is often
used as a reference reaction in the study of HO-reactions with many
species. In the following Section B of this report we describe the de-
termination of the rate constant for this reaction and identify conclu-
sively the pressure dependence of this constant. This work is of special
value in the determination of the rate constants for such important
reactions as, HO + S02 (+ M) -> HOS02 (+ M), HO + N02 (+ M) -> HON02 (+ M),
etc.
In the following Section C we present the results of our studies of
the H05 + ND2 reactions. This work provides the first direct kinetic
estimates of the rate constants for the formation of the highly reactive
compound, HOpNOg- The results of these studies indicate that this
species, peroxynitric acid, is a probable component of photochemical
-------
smog. Some of its kinetic properties have been determined, and further
studies of this and other related species are being made in continuing
work on this project.
In Sections D and E, experiments of photolysis work are discussed.
In Section F, infrared spectra of several compounds of special in-
terest in the study of both stratospheric and tropospheric reactions are
presented.
"THE PRESSURE DEPENDENCE OF THE RATE CONSTANT FOR THE REACTION: HO +
"co -> H + co2~.
The gas phase reaction of the hydroxyl radical with carbon monoxide,
HO + CO -» H + C02 (17)
is one of the most thoroughly studied of its many important reactions.
The high degree of interest in reaction (17) relates to its significance
in combustion processes and in atmospheric reactions. The early work on
this reaction has been reviewed by Baulch, Drysdale, and Lloyd (37) and
more recently by Wilson (38). A variety of both direct and indirect
methods of k.7 determination has been employed, and several new measure-
ments have appeared: the time dependence of the HO-radical concentration
was monitored by ESR in a flow reactor (39)> "by resonance fluorescence
(U0,^l) and by resonance absorption techniques following HO-radical
generation by pulse photolysis (1*2,1*3) or radiolysis (kk) of the approp-
riate gaseous mixtures. Our current interest in this reaction was stim-
ulated by the results of other recent studies which employed steady state
photolysis at total pressures up to one atmosphere; these involved the
competitive rate measurement of the HO-radical with CO and H2 in reactions
(17) and (18). (l*5,l*6).
HO + Ha -»H20 + H (18)
Both groups of workers concluded that the rate constant for reaction (17)
is pressure dependent and very much faster at 1 atm pressure than had
been assumed from the earlier low pressure studies. A unique test of the
pressure dependence of k1T was not possible from the work of Cox, et al.
(U5), since their experiments were carried out at a fixed pressure of 1
atm (largely air). However they found the ratio of \-T/\Q to be equal
to about twice that observed by other experimentalists who used much
lower pressures of reactants and added gas, and they suggested that the
hypothesis of a pressure dependent k17 seemed most compatible with these
results. In the work of Sie, et al. (U6), the pressure of added gases
(H2, He, SFg) was varied from 20 to 77*+ Torr with an observed increase
in k17 with pressure by over a factor of two in this pressure range of
added H2 or SF6.
The results of these findings seemed to us to be incompatible with
those of other recent studies in which a much more direct measure of the
[HOI was possible and no indication of a pressure dependence of k,7 was
seen; thus Davis, et al. (Ul), Greiner (U?), and Stuhl and Niki (t-0)
55
-------
found no change in k17 in varying added helium pressure from low pres-
sures up to 100 Torr. Smith and Zellner also reported an insensitivity
of this rate constant to variation of CO over a 3-fold pressure range
(U2). Also the value of kj_7 derived by Gordon and Mulac (M*) from pulse
radiolysis experiments with 10 Torr CO, 10 Torr H^O, and 710 Torr of
added Ar was identical, within the experimental error, to that found at
low pressures by previous workers (37,38). The earlier work of Ung and
Back (U8) and of Overend, Paraskevopoulos, and Cvetanovic (U3) gave some
indication of a pressure dependence to k^, and both groups of workers
have invoked the influence of third body M on the reaction of HO with
CO as one alternative in the explanation of their results. However, both
studies involved complications attendent with the photolysis of H^O vapor
containing systems, and both groups remained unconvinced of the unique-
ness of this explanation.
It is most important to atmospheric scientists that further confir-
mation be obtained of the apparent pressure effect on reaction (17) for
several reasons. First, a potential factor of two increase in k17 over
the range of pressure 100-760 Torr results in a serious perturbation of
the simulated rates of reaction (17) in the troposphere and the strat-
osphere. Second, many of the rate constants .of other reactions of HO-
radicals which are employed in the simulations of the atmospheric
reactions are based upon relative rate measurements using the low pres-
sure value of k17 as the reference value; obviously if k1T is a factor
of two larger than formerly believed, then several recent estimates of
the rate constants for the reactions of HO with NO, N02, and SO are
also a factor of two faster than originally suggested. Last, if we are
to apply these kinetic considerations to the actual atmosphere, then it
is necessary that we determine the effect on the value of kiy of varied
pressures of the actual molecules present in air (l^ ,02), since the
effects noted to date appear to be strongly dependent on the nature of
the added gas; helium shows little effect, while added SF6 and 1^ cause
a rather marked influence. (U6)
With these considerations in mind, we have carried out a series of
kinetic experiments designed to determine k17 for conditions comparable
to those present in the troposphere and stratosphere. We have photo-
lyzed dilute mixtures of HOMO, CO, isobutane, and NOX in synthetic air
at 700 and 100 Torr pressure in a large photochemical reactor. The
product rate data were determined unambiguously using a long path
Fourier transform infrared system. These results provide a direct test
of the sensitivity of k^ to the air pressure and provide a firm basis
for the choice of a rate constant for reaction (17) which is appropriate
for the simulation of chemical changes in the troposphere.
The photolysis cell, 6.3 m in length and UU5 liters in volume, was
constructed of 30.5 cm diameter Pyrex tubing. Its construction is il-
lustrated in Figure 27. The cell was evacuable and enclosed the modified
White optics of a multiple reflection system used for the in situ, infra-
red analysis of the reactants and products (1+9); a 170 m path was employed
in this work normally. The cell was surrounded by black-light fluorescent
56
-------
VJ1
-d
IR SOURCE
*
i
INTERFEROMETER
DETECTOR
COMPUTER
RECORDER
REFLECTOR
LAMP
I I I i I I C
1 1
n
CELL
i i
H
i i
ff
1 1
GAS
HANDLING
VACUUM
PUMP
F
A
N
VACUUM
PUMP
Figure 2?. The experimental photolysis system employed in this work.
-------
lamps and an outer reflective shield of aluminum. The lighting of the
cell was designed to mimic the solar intensity and wavelength distribu-
tion in the photochemically important region from 300 to ^30 nm. The
rate of photo-dissociation of W03 in the cell was estimated directly
from the rate of the photolysis of pure N02 at low pressures [-%-> = 2
(Rate of 0-atom formation)] and by computer simulation of reactairc2and
product rates measured in mixtures with synthetic air at 700 Torr pres-
sure. These measurements gave k^Q = 0.60 min'1 where d[0]/dt = [W02]kNQ
gives the rate of the elementary s?ep, W02 + hv ->0 + WO. Integrated *
measurements with a radiant flux detector gave similar results and in-
dicated a reasonable homogenity of the light flux throughout the cell
volume. The temperature of the cell was maintained in the range 25 ±
2°C by means of room air circulated between the lamps and the cell.
•Gas mixtures of CO (1039-2078 ppm), isobutane (30-220 ppm), HOWO
(< h ppm), N02 (< 10 ppm), and NO (< 10 ppm) were prepared by measure-
ments of the individual components in an all glass introduction system
equipped with standard volume bulbs, Teflon valves, and a glass spiral
gauge used as a null instrument. The mixtures of reactant gases and 02
and N2 (added to either 700 or 100 Torr) were standard commercial pro-
ducts, and the HONO vapors were generated as we have described previous-
ly (36). Interferograms of the infrared spectra of the reacting mixture
were recorded at regular intervals during the runs, and the data were
resolved into wavelength-transmission spectra by computer. The concen-
tration-time dependence of the reactants and products were derived by
computer comparison of the absorbance data with those of the pure com-
pounds. The major products of the reaction were: C02, WO, W02,
t-C4HgON02, CHjCOCHg, HON02, 03, CH20 together with smaller amounts of
other nitrates and other products. For our considerations here only the
C02,.organic nitrates, and acetone analyses are important. In the de-
termination of the product C02, special precautions had to be taken to
avoid unpredictable variation in the background absorption of carbon
dioxide in the infrared analysis beam outside of the reaction chamber.
This was accomplished by enclosing the complete optical train associated
with the Wernst glower, the interferometer, and the detector in a special
housing in which background C02 and H20 vapors were controlled, through
the use of nitrogen flushing gas and exposed dishes of KOH and NaOH
pellets. The C02 product in the runs was estimated from its character-
istic absorption at 720 cm'1 using e = 1.70 x lO^.ppm'^'1; ln(lo/l) =
ec i. All data were collected at 1 cm"1 resolution. The acetone absorp-
tion was estimated at 1218 cnr1 using e = 6.U x lO^ppm'^'1 after com-
puter removal of the small, overlapping absorption from the tail of the
isobutane reactant. Previous workers (50,51) have observed that the po-
sition and the extinction of the structureless, broad band of the organic
nitrates (RON03) near 1300 cm"1 is insensitive to the structure of R.
We have taken e = U.5 x 10~3ppm~1m"1 at 1310 cm"1 in our estimation of
the organic nitrates. The extent of the reaction of the CO and iso-C^ o
reactants during these experiments amounted to only a few percent of the
starting materials.
-------
We have measured the rate constant of reaction (1?) through the use
of the competitive reactions of the HO-radical with CO and isobutane:
HO + CO ->H + C02 (17)
HO + iso-C4H10 -»H20 + t-C4H9 (l$a)
->H20 + iso-C^c, (I9b)
The rate constant \g = kj_g-a + ^igb as measured by Greiner (52) was ac-
cepted as the reference in the estimation of k^. The primary source of
HO-radicals in this work was the photolysis of HOMO. Photochemical ex-
periments with mixtures of HOMD, is£-C4Hlo, N02, NO in air in the absence
of added CO gave negligible amounts of C02 product, and it is reasonable
to assume that C02 is formed almost exclusively through reaction (17)
in the CO-containing mixtures of HO NO and iso-C4.E| n in air, at least
during the early minutes of the experiments. Also it can be shown by a
detailed kinetic analysis of the system that the only significant agent
which results in isobutane decomposition for our conditions is the HO-
radical and the primary reactions (l°/a) and (I9b). Also about 99/o of
the rate of the HO attack on isobutane molecules can be accounted for in
the summation of the rates of formation of the organic nitrates (largely
t-C4H9ONQ2) and acetone for our conditions; [AC4H10]t ^ [C4H9ON02]-t +
[CHgCOCHglt- Thus the rate of C03 formation can be used to monitor the
rate of (17) > and the sum of the rates of organic nitrates plus acetone
formation is a good measure of the sum of the rates of reactions (19&)
and (I9b). The ratio of the product concentrations, [COs]-t/[AC4Hlo]^ at
a given time t should be related to the ratio of the rate constants,
k^/l^g, by the simple relation (20):
[C03]t/[AC4H10]t = (\7/\9) ([CO]t/[C4H10]t (20)
The reactant concentrations and product ratios obtained in separate
sets of experiments carried out in this work at total pressures of 700
and 100 Torr of air are summarized in Table VI. The appropriate product
data have been plotted versus the [CO]/[C4H10] ratio in Figure 28. It
is seen that the theoretically expected linear form of relation (20)
describes the two sets of data well, and the intercepts of the least
squares lines through the points are equal to zero within the statistical
standard deviation. The 700 Torr data define the line: y = -(0.0^0 ±
0.23) + (0.127 ± 0.007)x; the 100 Torr data are represented by: y =
(0.10 ± 0.38) + (0.0586 ± 0.008k)x. From the slopes of these lines and
the value of kig reported by Greiner for 25°C (52), k^ = 3.k6 x 103
ppm'^-min-1, we estimate kj_ = 1*39 ± 2U ppm^min"1 in air at 700 Torr;
kLT = 203 ± 29 ppm'^-min"1 in air at 100 Torr (25°C). These estimates
for kX7 are in reasonable accord with those derived by Cox, et al.
and Sie, et al. (U6) ; Cox and co-workers estimated k, _ = 398 ± 29 ppm-1
min-1 in air at 760 Torr. Sie, et al., give k17 = l+68± U2, 507 ± 32,
and 216 ± lb ppm'^-min'1 for added H2 pressures of 77U, 702, and 82 Torr,
respectively. Preliminary recent data of Paraskevopoulos and colleagues
(53) give k1T = ^80 ± U8 for added pressures of SF6 of 350 and 200 Torr,
and k17. = 301 ± 30 ppm^min'1 at 50 Torr of added He.
59
-------
TABLE VI
Summary of Rate Data from the Photolysis of HOND in
Mixtures with CO, ij3o-C4H10, WOX, in Synthetic Aira'
Initial concentrations, ppmb) [CO]0/[iso-C4H10]o
[CO] [is
(a) Total
2078
2078
2078
2078
2078
1039
1039
(b) Total
2078
2078
2078
2078
pressure, 700 Torr
195
103
73.1
l»2.9
30.0
220
158
pressure, 100 Torr
219
73.1
kO.7
30.2
10.7
20.2
28. h
U8.U
69.3
k.72
6.58
9.^9
28. h
51.1
68.8
1.33 ± 0.12
2.7^ ± 0.12
2.88 ± 0.02
5.93 ± o.oU
9.10 ± 0.15
0.80 ± 0.05
0.90 ± 0.08
0.61 ± 0.03
1.6U ± 0.05
3.53 ± 0.09
3.87 ± 0.07
a) Temperature, 25 ± 2 C.
' The unit ppm used here is defined as [pressure(Torr)/760] x 106
at 25°C.
C^ [AC4H10]t = [C4H9OIil02]t + [CH3COCH3]t; the average of the ratios,
[C03]-t/[AC4HLO]t was calculated from data taken at four 5-min
intervals during the first 20 min of the experiment.
60
-------
10
8
PT = 700 Torr
PT= 100 Torr
0
20 40
[COJ0/[C4H,0]0
60
Fig. 28 Plot of the ratio [C0a]./[AC^oL versus [CO]0/[iso-C4HlO]0
from the photolysis of HONO, CO, iso-C4Hlo, KOX mixtures in
synthetic air; open circles refer to experiments at 700 Torr
total pressure; squares are from experiments at 100 Torr total
pressure.
61
-------
In conclusion, we confirm that the rate constant for reaction (17)
is pressure dependent in the range 100-700 Torr of air in accord with
the original ideas of Ung and Back (1*8) and Overend, et al. (^3) and in
agreement with the recent more extensive studies of Cox, et al. (U5),
and Sie, et al. (^6) We recommend that an average "best estimate" value
in the range k^ = ^53 ± 33 ppm~1min~1, be used by modellers of chemical
reactions in the lower troposphere, and an average of the present and
previous estimates, (37-^2), 2l6 ± 11 ppm~1min-1, be chosen for strat-
ospheric conditions at pressures of 100 Torr and below. Furthermore,
the atmospheric scientist should note that the adjustment of the HO-
radical rate constants with other reactants in the lower atmosphere must
be made where these estimates have been based on the low pressure value
of k.
THE KINETICS AND MECHANISM OF THE H02-N02 REACTIONS; THE SIGNIFICANCE OF
FEROXYNITRIC ACID FORMATION, IN PHOTOCHEMICAL SMOG
Recent studies have suggested that there are two possible reaction
modes which may occur as a result of an encounter between an H02 radical
and an N02 molecule in the gas phase:
H02 + N02 -» HONO + 02 (21)
H02 + N02 (+M) ->H02N02 (+M) (22)
In view of the highly reactive, oxidizing character of the potential
product, peroxynitric acid (5*0» and the high potential for its formation
in the atmosphere, it is important to obtain meaningful estimates of
the rate constant k^ under atmospheric conditions. Current estimates
of the relative importance of reactions (21) and (22) extend over a wide
range from k21/k22 =* » to k21/k22 ^ 0. Simonaitis and Heicklen (55)
suggested in their first study of this system that reaction (21) alone
was significant; they observed through visible absorption spectroscopy,
the rates of N03 formation and decay in the 213.9 n^1 photolysis of N20
in 02, H2, NO, and N02 mixtures. For their conditions (temperature,
25°C, % = 700 Torr), they estimated k^/k^ = 7 ± 1.
H02 + NO -» HO + N03 (23)
Cox and Derwent (56) arrived at a very similar conclusion; they photo-
lyzed dilute mixtures of HONO with CO, NO, and N02 in air at 1 atm and
23 ± 2°C. Using chemi luminescence measurements the rates of formation
and decay of NO and NOX (NO + N02) were determined, and the rate constant
ratio, kgs/k^ = 10 ± 2 was derived. Taking kg4 = 3-3 x 10~1£> cc molec"1
sec"1, they estimated: k23 = (1.2 ± 0.3) x 1Q-12; k^ = (1.2 ± 0.3) x
10~13 cc molec~1sec~1.
2H02 -» H202 + 02 (2U)
Reaction (22) was not considered to be significant.
62
-------
Recently Simonaitis and Heicklen (57) have restudied the 213-9 nm
photolysis of N20 in mixtures of H2, 02, and NO. In this study they
followed the concentration of NO as a function of time by chemilumin-
escence analysis methods. These rate data showed an interesting and
unexpected result: the oxidation of NO continued to occur after termin-
ation of the initiating radiation. This observation and the kinetics of
the [NO]-time data suggested to the authors that an intermediate species
of finite lifetime, presumably H02N02, was formed and that reaction (22)
as well as (21) occurred in this H02-N02 system. From their results they
estimated that k5,P/(k21 + kaa) was in the range, 0.3 to 1; assuming k24 =
3.3 x 10~12> cc molec-^sec-1, they obtained k^ + k22 = (2.0 ± 0.7) x lO'13
and k22 = 9.3 x 10~13 cc molec~1sec~1. However, in none of the previous
work was any direct evidence for the presence of HONO or HQ3N03 products
obtained; their involvement was inferred from the measurements of NO
and/or N03.
Recently Niki, et al (58), have identified for the first time
through FTIR spectroscopy, the formation of peroxynitric acid in irrad-
iated dilute mixtures of Cl^, H2, and NO;, in air. It was suggested
that reaction (22) was the origin of this product. The spectrum now
attributed to H02N03 is the same as that observed previously in irrad-
iated dilute C12, CH20, N03, air mixtures by Gay, et al. (59)> and Niki,
et al. (60); this was first attributed to peroxyformyl nitrate by both
research groups. However, in view of the facts that there was no car-
bonyl absorption band in the unknown compound spectrum and that the
formyl group need not be present in the reactants to form the observed
product in Niki's work, it was reasoned that HD2N02 and not HC002N05 was
the likely compound. Hanst and Gay (6l) now accept the recent H03NOS
assignment of Niki, et al. (58). Both groups concluded that reaction
(22) may be the exclusive route of the H03-N03 interaction, since HONO
could not be detected among the products in their systems.
We wish to report here significant new information related to
reactions (21) and (22) and further confirmation of the nature of the
proposed product, H03N02. We have conducted a series of experiments
employing an FTSIR, long-path system in the study of HONO photolysis in
mixtures of interest to atmospheric chemists. As part of these studies
a series of experiments were carried out using HONO, CO, NOX mixtures
in air. Time dependent reactants and products (C02, Oa, HON03, N30s,
H02N02, HONO, NO, N02) of the reactions were followed as a function of
time directly through their characteristic infrared absorption band.
Computer simulation of these kinetic data provide new evidence of the
H03N02 identification and kinetic parameters related to reactions (21)
and (22).
The experimental data for the present study were obtained using a
Digilab k$6 interferometer in a manner described previously (36), but
some minor differences should be noted. The multiple-pass, modified
White optical system was housed in a.borosilicate glass cell, 6 m in
length with an internal diameter of 30 cm. The optical path between
mirrors was 5-3 m; 32 traversals were used in this study, giving a
63
-------
total path length of 170 m. The HONO, NO, and N02 gases, all in the ppm
range, were introduced into the cell with varied quantities of CO and
pressurized to 700 Torr (2k ± 2°c) with synthetic air. The method of
HONO addition inadvertently introduced small quantities of water vapor
(< 100 ppm) . HONO photolysis was induced using "banks of black-light
fluorescent tubes surrounding the cell such that the total intensity of
light within the HONO and N02 chemically active absorption regions (A
< U300 X.) was very near that in sunlight at sea level and solar zenith
angle, 0°. All of the IR spectra were recorded at 1 cm"1 spectral res-
olution.
The kinetic model used for the present computer simulation of the
HONO -WO -NO 2 -CO -air system consisted of 30 reactions summarized in Table
VII; the rate constants for the well studied reactions used in this
model were obtained from the NBS tables (62) with the updating of those
values which have been redetermined since the original compilation.
Detailed kinetic analysis of product and reactant rates in simple N02
and HONO systems irradiated in our system gave the values of k25 = 0.60
and k3l = 0.11 min"1 . Our recent estimate of k,7 = k.k x 102>ppm~1min~1,
in accord with other recent high values (U5,U6,o3) , was chosen. The
latest evaluation (^5) of kgg and k30 which utilized the "high" value of
k24, places these constants for 1 atm air at ~2.0 x 104 ppm min'1. For
our system (700 Torr air), we have taken k29 = 1.6 x 104 and k3o = 1.9
x 104 ppm~1min~1, reflecting the somewhat lowered efficiency of reaction
(29) compared to (30) which is expected to accompany the smaller number
of degrees of freedom in the HO-NO system. We have chosen kgs = 1.25 x
103 ppm"1min~1 in this work, an average of the earlier values reported
by Hack, et al. (6U), Davis, et al. (65), and the more recent estimates
of Cox and Derwent (56), and Simonaitis and Heicklen (57)- The rate
constant for reaction (32) has been taken as 8.5 x 103 ppm~1min~1, in
accord with the recent estimate of Cox, et al.
The infrared spectral features tentatively assigned by Niki, et al.
(58) to the molecule HOON02, consist of bands attributed to the nitrate
group (1728.3, 1303.9, and 802.7 cm"1), an OH-bending mode (1396.5 cnTi),
an OH-stretching mode (35^0.1 cm~i), and a broad combination band eommon
to nitrate compounds (»3000 cm"1') . These characteristic absorption peaks
have been identified as resulting from a product formed in both the ir-
radiated C12, H3, N02, air system and the C12, CH20, K)2, air systems.
Attributing these features to the H02N02 molecule seems to be a most
reasonable hypothesis to us, and reaction (22) is the probable source
of the product. In the C12, CH20, N02, air system the H02 reactant in
reaction (22) is likely formed through the sequence:
CL, + hv -* 2C1
ft ~*
Cl + CH20 -»HC1 + HCO
HCO + 02 H. H02 + CO
-------
TABLE VII
Summary of the Reaction Mechanism and Rate Constants Employed in
the Simulation of HOHO, HO , CO, Air Mixture Photolysesa)
X.
Reaction Rate Constant13)
(21) H02 + H02 -» HOHO + 02
(22) H02 + HOp (+M) -»H02N02 (+M)
(23) HOp + HO~-» HO + H02
(24) 2H02 -* H20p + OP
(25) HOp + hv -» HO + 0
(26) 0 + OP (+M) -* 03 (+M)
(27) HO + 03 -» HO, + 02
(17) HO + CO -» H + C02
(28) H + OP (+M) -» H02 (+M)
(29) HO + HO (+M) -» HOHO (+M)
(30) HO + HOp (+M) -»HOH02 (+M)
( 31) HOHO + hv -» HO + HO
(32) HO + HOHO -»H20 + H02
(33) HOp + 03 -» HD3 + OP
(34) HO + H03 -»2H02
(35) HOp + H03 -*Hp05
(36) HOp + H03 -» H02 + HO + OP
(37) 2H03 -» 2H02 + OP
(38) Hp05 + HpO -*2HOHOp
(39) HOp + 0 -^HO + OP
(40) HOp + 0 (+M) -»H03 (+M)
(41) H265 -»HOp + HD3
(42) 2HD + OP -» 2HOp
(43) 2HOHO -» HO + HOp + H90
(44) NO + N02 + HpO -^ 2HOHO
(45) HpOp + hv -»2HO
(46) 0 +"HD (+M) -* HOp (+M)
(47) HOpHOp -»HOpHDp (Wan)
(48) HOpHOp (Wall) -»HOHO (Wall) + OP
(49) 2HOHO (Wan) -* HO + HOp + HpO
5.3 x 101
7.2 x 101
1.25 x 10s
5.3 x 103
0.60
2.0 x 101
2.2 x 101
4.4 x 10?
1.7 x 103
1.6 x 104
1.9 x 104
o.n
8.5 x 103
4.6 x 10-?
1.5 x 104
5.6 x 103
1.2 x 101
3.2 x 10-1
2.5 x 10-3
1.3 x 104
3.4 x 103
1.5 x 101
7.5 x 10-10
1.4 x 10~3
2.2 x 10-9
1.5 x 10-3
3.6 x 103
9.1 x 10-?
large
large
Temperature, 24 ± 2°C: pressure of air, 700 Torr.
The units on rate constants are ppm-1min-1 for all but reactions
(25), (31), (41), (45), and (47) which are min-1, and (42) and
(l^li) which are ppm-^min"1; the unit ppm used here is defined as
[pressure(Torr)/760] x 10s at 24°C. Data are from reference
[62] except as noted in the text.
65
-------
In the Clg, H2, N02, air experiments the major source of the H02 is the
reaction sequence:
CL, 4- hv -» 2C1
Cl + H2 -» HC1 + H
H + 02 (+M) -»H02 (+M)
In this work a product with the identical infrared spectral properties
was formed in irradiated dilute mixtures of HONO, NO, N02, CO, in air.
Note in Figure 29a and 2$fb that in the absence of added CO, irradiation
of the HDNO, NO, N02 mixture in air gives no evidence after 5-9 min of
the formation of the characteristic bands at 802.? and 1303.9 cm"1 at-
tributed to K)2N02. This is quantitatively predictable from the known
kinetic character of this system; little H02 radical development is ex-
pected in.this system. However when an excess of CO was added to the
HO NO-NO -air mixture, the irradiation for 5-9 min created peaks attrib-
utable to H02N02; in Figure 29d the absorptions at 802.7 and 1303.9 cm'1
are seen readily after computer subtraction of the bands due to HONO,
CH4, and H20 from the complete product spectrum shown in Figure 29c.
Absorptions due to ozone and N205 have not been ratioed from the spectrum
in that there is no significant contribution from these compounds to the
H02N02 absorption regions, and further product ratioing increases the
noise level of the remaining spectral features. There is an exact
correspondence of the characteristic absorption bands with those of the
product designated as H02N02 obtained in the C12, H2, N02, air system
by Niki, et al. (58) and the irradiated C13, CH20,'N02, air system by
Hanst and Gay (60). This can be seen in Figures 2ge and 29f. The IR
absorptions due to products of the C12, H2, NOp, air mixture irradiated
in our system for 6.0 min are shown in Figure 2§e. In Figure 29f the
absorptions due to C1N02 and HON02 have been computer subtracted using
pure compound spectra, and the characteristic bands attributable to
H03N02 at 802.7 and 1303.9 cnT1 are seen. These observations lend sup-
port to the assignment of these bands to H02N02 by Niki et al. (58), and
Hanst and Gay (60). There is no other obvious product which would be
common to these rather diverse systems and to which one might attribute
these absorptions. It appears to us that the HONO, CO, N02, air system
employed in our studies offers the simplest route to H02N02 yet observed.
Here the source of the H02 radical is largely the reaction sequence:
HONO + hv -» HO + NO
HO + CO -4 H + CO,
H + 02 (+M) -* H03 (+M)
There are some significant advantages of the HONO, CO, N02 system over
the CIP-containing ones for the study of the H02N02 formation and decay
kinetics. The complexity of products of the C12-containing systems,
including C1N02, C1NO, and HC1, is eliminated. The infrared observable
66
-------
lOOi
2
o
CO
en
oc
0
(05-HONO
+ HN03
as1 MONO
//ms-HONO
-0-
co
§50
01
-b-
700 800 900 1000 MOO 1200
I /A., cm
Fig. 29 Spectra of uv-irradiated MONO, NO , CO, air and C13, N02, H2,
air mixtures; (a) spectrum of cell contents after 5.9 min ir-
radiation of the initial mixture; total [HONO]O = 2.70, [N0]o =
2.77, [K02]0 = l-5> [COlo = °-° PP111 in synthetic air, 700 Torr;
(b) residual spectrum resulting from that of (a) following com-
puter subtraction of remaining cis, trans-HOMO, HON02, and HP0;
note absence of HD2N03.
67
-------
lOOr
800 900 1000 MOO 1200 1300
I/A, cm
Fig. 29 (c) spectrum of cell contents following 5-9 fflin irradiation of
the initial mixture: total [HQND]0 = ^.29, [N0]o = 2.8, [NDS]0 =
1.1, [C0]0 = 3.8 x 104 ppm in synthetic air, 700 Torr; (d) resid-
ual spectrum resulting from that of (c) following computer sub-
traction of remaining cis, trans-HONO, CH4, and H20.
68
-------
"I
H02N02
800 900
1000 1100
I /A. cm
1200 1300
Fis 29 (e) spectrum of cell contents following 6.0 min irradiation of
the initial mixture: [C1P]0 = 30, [K)a]0 = 22> ^lo = 8026 ppm
in synthetic air at 700 Torr; (f) residual spectrum resulting
from that of (e) following computer subtraction of the remaining
HON03 and C1W02 products; compare the characteristic absorption
peaks of HOPNOp at 802.7 and 1303-9 cm'1 in (d) and (f).
69
-------
product C02 and reactant HONO provide a rather direct monitor of the
H02 and HO radical formation steps, while the direct observation of the
infrared transparent reactant C12 in the C12-containing systems cannot
be made, but its presence must be inferred from the initial charge of
Clg and the mass balance of HC1, C1N02, NOC1, etc., calculated to be
present from the absorption spectrum. In addition, HONO vapors are
attacked readily by Cl-atoms so that a sensitive measure of the extent
of the possible alternative reaction (21) between H02 and N02 is not
possible from the C12-containing systems.
A first series of experiments was carried out using a very simple
dilute mixture of HONO, NO, and N02 in air in order to test the accuracy
of the rate parameters related to our primary photochemical radical
source, HONO. With this mixture we minimize the generation of H02 and
eliminate its series of reactions which complicate the resolution of the
rate parameters related to HONO. The observed [HONO]-time profiles and
those calculated employing the reactions summarized in Table VII are
shown in Figure 30a for one of these runs. The agreement is reasonably
good,1 and deviations from run to run are relatively random with the
choice of rate data finally selected. In this case HONO formation occurs
largely through the recombination reaction (29), while the loss reactions
involve the photolysis reaction (3l)» and to some extent the HO-radical
attack on HONO, reaction (32).
In a second series of runs, a moderate amount of CO gas was added
so that a rather direct monitor of the [HO] profile during the run was
possible from the measured rates of C02 formation; the dominant source
of C0? is reaction (l?) for our conditions. The measured and calculated
[HOND]- and [C03]-time profiles are shown in Figure 30b for one run in
this series for which [C0]o = 2.23 x 103, [N0]o = 20.U, [N02]o = Yf.k,
[HONOJo = ^.35 ppm. For these initial reactant concentrations the rate
of HO attack on CO is about twice the total rate of its reaction with
NO, NOp, and HONO. Again, a reasonably good match of the experimental
and simulated concentration profiles is seen. The reactions which influ-
ence the [HONO] in this case are largely (29) and (31); reaction (32) is
no longer important since almost all of the HO produced now reacts with
CO, NO, and N02. Although the H02 radical is formed at a significant
rate in this system, reactions (21) and (22) should be relatively unim-
portant here since the H02-N0 reaction (23) is the dominant loss reaction
for H02 under these conditions. The combined effect of the NO and N02
formation and decay reactions leads to an [NO] increase during the course
of the run; after 1 hr irradiation, the simulation predicted an [NOl of
29 ppm compared to the observed concentration of 26 ppm. Thus, reactions
(21) and (22) cannot be important here, and H02N02 w&s below the detec-
tion limits for these conditions, as expected from simulations of this
system.
With the general accuracy of the model now proven for the simplest
reaction mixtures, the influence of reactions (21) and (22) could be
tested by selecting conditions which favor these reactions. This was
accomplished in another series of experiments by increasing the [CO]Q
70
-------
Q.
Q.
(J
C
o
u
Fig. 30 Comparison of observed total [HONO]- and [C03]-time data with
those predicted by the simulation model for irradiated HONO,
ND , CO mixtures in air; (a) initial concentrations: total
[HONDlo = 2-70, [ND]0 = 2.77, [N03]0 = 1-5 ppm in synthetic air,
700 Torr; (b) initial concentrations: total [HONO]0 = ^-35,
[K)]0 = 20.k, [N03]0 = 17.U, [C0]0 = 2.23 x 103 ppm in synthet-
ic air, 700 Torr.
71
-------
about an order of magnitude, while decreasing the [NOJo and [N02]o« In
one run in this, series [C0]o = 3.8 x 104, [N0]0 = 2.8, [ND2]O = 1.1;
[HONO]0 = U.29 ppm; the HONO and C03 concentration-time profile.s for
this run are shown in Figure 31. Under these conditions we expect nearly
all of the HO-radicals produced in the system to react with CO in reac-
tion (l?), so that reactions (29) and (32) are no longer important.
The increase in rate of reaction (17) results in a corresponding increase
in the rate of reaction (23), [N02] increases at the expense of the [NO],
and reactions (21) and (22) can become competitive with (23). The com-
puter simulation of the [HONO]- and [C02]-time data for this high [CO]
system (Figure 31) has been made for several choices of the rate constant
ratio k21/k22; the rate constant ratio k22/(k51 + k22) was held at 10 in
these simulations. It can be seen that the choice of either extreme,
^51/^-25 = 0 or k21/k22 = oo leads to widely divergent rate curves. With
the former choice, no HONO formation in (21), [C02] is underestimated
badly at long times, and the [HONO] is depleted much too rapidly. With
the choice of kg2 = 0 and k23/k21 =10, the [C02] is overestimated badly
and the [HONO] is depleted much too slowly. Clearly the data suggest
that 'both reactions (21) and (22) occur. Simulations employing several
rate constant ratio choices show that the data are described reasonably
well for k21/k22 ^ 0.7 ± O.k.
The peroxynitric acid concentration-time data from the same high
[CO] run provides further information. In runs in which the uv-lights
were extinguished, the HO;jN02 spectrum decayed with an apparent half-
life of about 8 min, in accord with the observations of Niki, et al.
(58), and Hanst and Gay (6l) . See Figure 32. In reactant -depleted mix-
tures no significant change in this rate was observed with the lights on
or off. In view of the very low ultraviolet absorption of peroxyacetyl
nitrate for 7\ > 3000 X. (66), the direct photochemical decomposition of
H05N02 within our system or in the lower atmosphere is probably slow.
It appears likely that the decay process for H02N02 which we observe,
reflects largely the rate of transport of H02N02 to the wall of the cell
where subsequent decomposition results. Simonaitis and Heicklen (55)
observed indirectly much shorter lifetimes of the intermediate which
they suggested to be HO^NO^ (~50 sec), but this is understandable since
their reaction cell was a 1 liter bulb (12.^ cm diameter) with a lower
gas to wall transport time than in the larger diameter glass tanks em-
ployed by Niki et al. (58), Hanst and Gay (59)j and in our work (30 cm
diameter cylinder of considerable length) . We observed that N02 rises
as H02N02 decays in the dark. A simple mechanistic route which may
rationalize this course of events is the following:
H02N03 ->H02N02(Wall)
H02N02(Wall) -» HONO (Wall) + 02 (U8)
2HONO(Wall) -» N02 + NO + H20
Thus we picture the wall as a catalytic surface which promotes the simple
rearrangement of H02N02 to HONO and 02 with the further decomposition of
72
-------
£
^
o
1
t:
CD
O
u
2QOOOOQOOOOC
'0 10 20 30 40 50 60
t;min
Fig. 31 Comparison of observed total [HONO]-, [C02]-, and [H02N03]-time
data with those predicted by the simulation model involving
reactions (21) through (^9)> Table VII, initial concentrations,
total [HOKOJo = ^-29, [N0]0 = 2.8, [N02]o = !•!> [C0]0 = 3-8 x
104 ppm, in synthetic air, 700 Torr; values of k21/k22 chosen
in simulations: « (—O—); 5.0 ( ); 0.7^ ( ); 0.00
( ); k23/(k21 + k22) = 10 in all runs shown.
73
-------
0
0
10 20
DARK TIME/ MIN.
30
Fig. 32 The first order loss of H02N02 in three different dark runs; the
squares are from data taken from a run with HONO-WO-N02-CO mix-
ture; the remaining data points are from two different C12-H2-
NO-KOp mixtures. The slope of this plot gives a first order
loss constant of ~9.1 x 10~? min"1.
-------
HONO to its gaseous products. For our conditions of [NO], [N03], and
[H20] present in the cell, the equilibrium level of HOND is very low
(«10~2ppm), and the catalysis at the wall will result largely in HOND
decomposition. Presumably the NO released in (U9) will be oxidized
quickly to N02 through its dark reactions with the products 03 and N03
(Na05), reactions (27) and (3*0, so that the only significant product
which we see increase experimentally would be N09.
The simulations of [H02N02]-time profiles are given in Figure 31
for several choices of the rate constant ratio k-^/k^. It is evident
that the general form of the concentration-time profiles can be described
adequately using k21/k22 ratios which are most consistent with the [HONO]
and [C02]-time curves as well. It appears to us that a ratio in the
range k^/kga = 0.7 ± OA leads to the most consistent match of the
kinetic data at hand. It is in qualitative agreement with the indirect
estimate, k^/k^g = 1.1 ± 1.1, of Simonaitis and Heicklen from experi-
ments without observation of either HONO or H02N02 (57). It is our
feeling that the failure of previous workers to observe HONO in irradi-
ated Cl^, H2, N02, air and C15, CH20, ND2, air systems, and thus consid-
eration of reaction (21) as unimportant relative to (22), may be a
consequence of the expected high reactivity of HONO toward Cl-atoms:
Cl + HONO -» HC1 + N02. In fact, we do observe very small amounts of
HONO among the products («0.2 ppm) after only a short irradiation (l min)
of Clp, N02, H2, air mixtures similar to those employed by Niki, et al.
(58). This is the order of magnitude of HONO expected if reaction (21)
occurs, as we suggest, but the HONO-C1 reaction rate constant is large.
See Figure 33- The characteristic spikes of the HONO spectrum (Figure
33a) are seen clearly in the products of the Cl^, H2, NO, N02 photolysis
after 1 min irradiation time (Figure 33^-2). This is more clearly dem-
onstrated in the spectrum shown in 33b-3 where the CH4 contribution
(impurity in the 02 used to prepare the synthetic air) has been removed.
That the peaks in this spectrum are truly at exactly those positions due
to HONO is evident in the removal of the three peaks by absorbance sub-
traction of the spectrum 33-a from that of 33b-3; this is shown in
spectrum
The preliminary kinetic analysis of some of the dilute Cl^, N02, NO,
H2 mixtures in synthetic air has been made. The mechanism is much more
complex in the Cl2-H2-N02-air system. The additional reactions (50)
.through (65) (see Table VTIl) are added to (21-1*9) in this case to sim-
ulate the chemical changes. The experimental product time data (curves
a) and the computer simulations using reactions (21-65), curves b, may
be compared in Figures 3^ and 35. The initial reactant concentrations
are shown in the captions of each figure.
In the simulations shown in Figures 3U and 35, the best fit of the
data was had with the rate constants for reactions (21) and (22) chosen
to be 3.5 x 101 and 9«0 x 101 ppm~1min"1, respectively. This checks
well within the experimental error determined earlier in the HOND, NDX,
CO system.
75
-------
750 800 850 1250
cm"'
Fig. 33 (a) 3.2 ppm HONO; (b) initial conditions of C12 = 7-5, H2 =
8026, NO = 3.25 and N02 = 2.7^ ppm. In (b) the spectrum 1
represents the filled cell at start before the lights are
turned on, 2 is the spectrum after almost 1 min of irradiation
time, 3 is the same mixture as spectrum 2 but with CH4 sub-
tracted out, k is the same mixture as spectrum 2 but with CH4
and 6% of spectrum (a) subtracted out.
76
-------
TABLE VIII
Additional Reactions and Rate Constants Required in the Simulation
of the Dilute C12, N02, NO, H2 Mixtures in Air.a
Reaction Rate Constant
(50) C12 + hv -»2C1 0.10
(51) C1+ 02 (+M) -»C102 (+M) 2.0 x 101
(52) C102 (+M) -» C1+ 02 (+M) 1.8 x 10s
(53) Cl + H2 -+H + HC1 1.5 x 101
(5*0 HO + H3 -» H30 + H 1.03 x 101
(55) HO + HC1 -» H20 + Cl 1.0 x 103
(56) Cl + HONO -»HC1 + ND2 1.0 x IQ5
(57) C1+ 03 -» CIO + 02 2.7 x 104
(58) Cl + H202 -»HC1 + H02 8.0 x 10?
(59) Cl + NO (+M) -» CUTO (+M) 3.7 x 103
(60) CUNO + hv -» C1+ KO 0.3^
(61) Cl + N02 (+M) -» C1N02 (+M) 1.0 x 104
(62) C1N02 + hv -» Cl + MD2 0.03
(63) Cl + CUK>2 -^ C12 + M02 5.0 x 101
(6k} C1D + NO -» N02 + Cl . 2.5 x 104
(65) 2C10 -* C12 + 02 3.U x 103
aThese reactions and those in Table VII were used to simulate the
system.
77
-------
2 4
Time/ min.
Fig. 3^ Photolysis of C12, Ha, NOX, mixture in synthetic air; initial
concentrations (ppm): (cis) = 7.5; (Ha) = 8026; (NO) = 3.25;
(N02) = 2.?l|; air added to a total pressure of 700 Torr; (a)
experimental data; (b) computer simulation.
78
-------
2468
Time/ min.
Fig. 35 Photolysis of CL,, H2, NO , mixture in synthetic air; initial
concentrations (ppm): (C13) = 15; (H2) = 8C)26; (NO) = 1.28;
(NDP) = 11.1; total pressure of 700 Torr; (a) experimental
data; (b) computer simulation.
79
-------
The preliminary analysis given here for the H02N02 reactions is
under further study. Alternative H02N02 loss mechanisms are under test,
and further work to firm up the mechanism is to be continued during the
coming year.
Years ago Schwarz (5^) prepared H02H02 through the reaction between
pulverized solid samples of H202 (100$) and N205 mixed at -80°C in a
vacuum line. The evidence which he presented suggests strongly that the
reaction: H202 + N305 -* H02M)2 + HON02, did occur on warming the mixture.
Isolation and quantitative characterization of the H09N02 was not pos-
sible in Schwarz's work, since the product decomposed rapidly, liberating
a great deal of heat, 02 gas, and some N02, when warmed to -30°C. How-
ever, in dilute solutions of HONOp and H202 in glacial acetic acid, the
product formed, presumably H02N02, was reasonably stable; under these
conditions the highly oxidizing product readily released Br2 from KBr
solution. It is apparent from these early studies that HD2N02 is an
unstable, highly reactive, powerful oxidizing agent.
Since the wall destruction of H02W02, dominant in our systems, will
be essentially absent in the atmosphere, it is likely that its lifetime
in the lower atmosphere will be much greater than that which we observed
here. Furthermore, simulations of the reactions in a typical NO -RH-RCHO-
polluted atmosphere exposed to sunlight show that the theoretical rate
of H02N02 generation is similar in magnitude to those expected (and ob-
served in real atmospheres) for the peroxyacylnitrates. In view of these
findings, we conclude that H09N02 may be an important product of photo-
chemical smog. Because of its reported highly oxidizing character
which was discovered years ago (5*0» we feel that it may contribute to
eye irritation, plant damage, and other undesirable aspects of smog, as
Hanst and Gay suggest. (6l) It is important that specific analyses for
HD2M)2 be made in urban atmospheres to evaluate directly the concentra-
tions and the effects of this seemingly important compound. Niki, et
al. (58), have proposed that H02ND2 may be a potential sink for NOX in
the stratosphere; it is difficult to test this hypothesis on the basis
of our present rate data, since the effect, if any, of the lower pressure
of the stratosphere on the rate constant of the H02-N02 combination
reaction (22) is unknown. Our studies are continuing to define better
the kinetic behavior of this interesting compound both at tropospheric
and stratospheric pressures.
EXPERIMENTAL DETAILS OF FTIRS AND PHOTOLYSIS CELL
The various chemical and photochemical experiments were carried out
using a Digilab FTS-20 Fourier Transform Spectrometer (model U96 inter-
ferometer) coupled to a photolysis cell constructed of 30.5 cm diameter
pyrex tubing 6.3 m long (lUt-5 |) (see Figure 27). The cell housed modi-
fied White optics (k$) giving traversal in increments of eight (instead
of the usual four) with a base path of 5-3 m. All experiments were
carried out at 170 m (32 traversals) which gave adequate absorption for
compounds in the ppm concentration range having extinction coefficients
of 10~4 - 10~? ppm"1!!!-1 (at 1 cm"1 resolution and 700 Torr).
80
-------
In order to study kinetics occuring on the minute time scale and
have spectra of adequate signal-to-noise ratio, an appropriate choice
"of resolution "and number of coadded inter ferograms must be chosen (both
of these require time) . For our experimental system, in conjunction
with our apparatus, we chose 1 cm"1 resolution (l cm optical retardation)
and usually four scans (0.08 minutes per scan and 0.12 minutes delay for
the first scan with out apparatus). Another convenient time-saving de-
cision was to collect only 8K data points per interferogram by collecting
data every other laser fringe (time saved in computation is more than a
factor of two for 8K versus l6K) . The resolution is not affected by
such undersampling (the optical retardation is still 1 cm) and the use-
ful spectral range is 0 to 1*000 cm'1 (versus 0 to 8000 cm"1 for l6K data
points) which is still greater than our useful system spectral window
of 1*50 to 2**00 cm"1. This window is determined by our Nernst glower,
Mullard liquid helium cooled Cu:Ge detector and KBr windows. The region
from 1800 to > 1*000 cm"1 can be covered by our Santa Barbara Research
liquid nitrogen cooled In:Sb detector. The spectra were computed from
interferograms in conjunction with box-car apodization in order not to
sacrifice our 1 cm"1 nominal resolution.
The cell lighting was designed to mimic ground level solar radiation
both in distribution and intensity which it does quite well. In Figure
18 from the previous final report (for Grant Number R803868-1) the dis-
tribution from 300 to 1*00 nm is similar. Our N02 photolysis rate of
0.6 min'1 is typical of atmospheric values for low zenith angles attest-
ing to our intensity being in the range of ground level solar intensities.
In order to obtain a more uniform light distribution within the cell
it is surrounded by an outer reflective shield of aluminum foil. Meas-
urements with a Hewlett-Packard Radiant Flux Detector (model SSS^A) at
four different locations within the cell indicate uniformity to within
Temperature control during photolysis work is obtained by circulat-
ing room air between the cell and lights with a fan. A 2°C temperature
rise within the cell is observed in 10 min with a 2°C differential be-
tween the two ends of the cell on the outside.
In order to overcome problems of varying water vapor and C02 absorp
tion in the transfer optics between the Nernst glower source, interfer-
ometer, cell and detector the entire optical system was enclosed in a
plastic (acrylic) box and purged with nitrogen with exposed dishes of
NaOH and KDH. Absorptions due to degassing from the plastic were not a
problem.
The gases were measured out in an all glass grease and mercury free
system employing teflon stopcocks. The mechanical pump was isolated
from the gas handling system by a liquid nitrogen trap. Pressures were
measured using a glass spiral gauge which was set using Wallace-Tiernan
absolute pressure gauges which insured that the gases only came in con-
tact with glass or teflon. The gas handling rack was constructed with
81
-------
eight calibrated volumes (l to 100 ml) with double valves for positive
injection of samples. Larger calibrated bulbs were readily hooked up
to the system with Cajon stainless steel quick-release vacuum pittings
for injection of larger samples, or for use with gases having low work-
ing pressures.
The main surfaces inside the cell with which the gas mixtures come
into contact (mainly through turbulent mixing of the gases due to temper-
ature gradients) are pyrex and stainless steel (mirror supports, cell
tubing spacers and end plates). Some corrosion of the stainless steel
has been observed probably due to the action of HC1 on the slightly
moist surface. The teflon surface area due to the teflon sealing gaskets
(8) between the pyrex cell tubing sections and end plates is small. The
glass mirrors with aluminum reflective surfaces have a thin (1/8 wave)
overcoat of silicon monoxide and show no signs of damage after fourteen
months of use. The KBr windows (2 i/h in. diameter) are transparent at a
slightly longer wavelength than Nad.
The treatment of time dependent transmission spectra from individual
runs consisted of determining absorbances for individual species when no
overlapping of spectral features occur. Concentrations were then obtained
by using extinction coefficients for various gases determined at the same
total pressure, resolution and transform method (8K data points, no zero
filling of the interferogram and box-car apodization). See Table IX.
In cases where spectral features of two species overlap, one species is
removed by absorbance subtraction using calibrated reference files and
the remaining species is then measured.
Various types of experiments have been carried out in the photo-
chemical reactor. Numerous calibrations of gas used in the experiments
were done either by direct pressure measurement of the gas, by chemical
synthesis of the species in conjunction with mass balancing, or by si-
multaneously taking the spectrum and titrating another sample in the
case of nitric acid. The cell was designed mainly to photolyse samples
and study the kinetics of various system of interest from a stratospheric
air pollution standpoint. A starting point for studying the kinetics
of any photochemical system is to determine the primary photolysis rate
for all species undergoing photodecomposition in our cell.
EXPERIMENTAL DETAIL OF PHOTOCHEMICAL AND SPECTRAL MEASUREMENTS
Peroxynitric acid (H02NOS) formation by Cla photolysis with N0g and E2
present in air
Mixtures of Clg (7.5 to 30 ppm), N02 (3 to 25 ppm) , NO (0.7 ppm,
due to inadvertant N09 photolysis during injection or from the slightly
decomposed ND3 sample], a, (UOOO to 3^000 ppm), N2 (560 Torr) and 6?
(1^0 Torr) were photolysed to form peroxynitric acid (HOgNOg). The
gases were standard commercial products used without further purifica-
tion except for N03 which was degassed at 0°C. Methane (2 ppm) and CO
(O.lU ppm) impurities were present.
82
-------
TABLE IX
Extinction Coefficients
(base e, 1 cm"1 resolution, 700 Torr pressure,
25°C, 170 meter path, box-car apodization)
Molecule Wavenumber (cm"1) g (ppm"1 m"1)
CO?
NO"
NOg
03
cis-HONO
trans -H01O
HONO?
N205
C1ED
CW03
H02N03
CH4
HCOpH
H2CO
720
1876
826
1575f
1585+
l600f (10 cm"1 res)
1627+ (10 cm"1 res)
lOOOf
1055*
1055* (Prn = 100 Torr)
853 T
126U
762
878
89^
7^0+
I8o8f
780f
793
1267
802.7
8lOf
1305
1105
17^^
1.70 x 10'4
2.7^ x 10"4
3.^0 x 10"5
»*.Ul x 10"4
1.23 x 10"3
1.99 x 10"3
2.69 x 10"3
1.29 x 10"4
9.7^ x 10 "4
8.62 x 10"4
6.06 x lO"3
3.8^ x 10-3
5.»+6 x 10"4
1.75 x 10~3
1.23 x 10"3
U.O x 10-3
5.51 x 10"3
U.65 x 10"4
2.1+6 x 10-3
1.19 x 10~3
2.35 x ID'3
1.114- x 10-3
1.67 x 10-3
3.28 x ID'3
1.11 x 10-3
+ broader structure - less resolution dependent
83
-------
The lights were on for 6 to 15 minutes and the cell contents were
monitored for another UO minutes in the dark. Each spectra is computed
from four coadded interferograms which requires 0.32 minutes to collect.
The measurement of most species in the spectra were from absorption
measurements of selected spectral features. Nitryl chloride (ciEDp) was
removed and measured through absorbance subtraction using a calibrated
reference file in order to measure the underlying H03N02 at around
800 cm .
Mass balance of nitrogen and chlorine is not good in these runs,
particularly at late times, due to chlorine and nitrogen active species
on the walls forming stable compounds and coming off the walls. Spur-
ious C1N02 and HN03 have been observed. Before chlorine gas and other
chlorine containing species were introduced into the system, these prob-
lems were not observed. We concentrate our analysis on data from the
first few minutes when wall effects should be less important.
C12 photolysis in H2 and air
30 ppm of C12 was photolysed in 8066 and 3^211 ppm of H2 in a syn-
thetic air mixture (700 Torr total pressure) in order to determine the
primary photolysis rate of Cl^ in our cell. Standard unpurified commer-
cial gases were used. Methane (2 ppm) and CO (0.1^ ppm) were present.
The photolyses were 15 min long with each spectrum corresponding to
one interferogram (0.08 minutes collection time). A liquid nitrogen
cooled In:Sb detector was used to follow the growth of HC1 with time.
Since HC1 lines did not follow Beers Law, absorbance versus concentra-
tion curves (up to .60 ppm) were plotted for many of the HC1 lines and
used to measure HC1 in the C12 photolysis spectra.
Nitrosyl Chloride (CINQ) photolysis in E3 and N2
1 to 20 ppm of C1NO was photolysed in 3^211 ppm of H3 and 6?U Torr
of N9 - 700 Torr total pressure. Standard commercial gases were used.
The C1NO was degassed at liquid nitrogen temperature.
The mixtures were photolysed from 10 to 30 minutes with four scans
(0.32 minutes) collected per spectrum. The Cu:Ge detector was used in
all but one experiment (ln:Sb detector used). Both C1NO decay and NO
growth were followed by the absorption.
Nitryl Chloride (C3JT02) synthesis and photolysis
Two methods were used to synthesize C1N02 in order to calibrate its
absorption strength and to photolyse it.
The first method involved photolysis of C12 (7 to 30 ppm) and N0?
(7 tp 35 ppm) in either nitrogen or synthetic air at 700 Torr total
pressure for ten to thirty minutes. Each spectra resulted from four
/
81*
-------
coadded interferograms (0.32 minutes). C1N02 quantities were determined
from nitrogen mass balances (W02, HO, N205, KN03, C1N02). Unfortunately,
extinction coefficient consistency between runs and precision within a
run was poor due to spurious wall effects.
The more successful quantitative method for measuring C1TO2 involved
the dark reaction between 03 and CINO.
Ozone was generated by applying a Tesla coil discharge externally
on glass tubing through which oxygen was flowing into the cell. 2 to 7-5
ppm of 03 was mixed with 1.5 ppm C1NO (degassed at liquid N2 tempera-
ture). These mixtures contained from 6 to 50 Torr of 02 and were pres-
surized to 700 Torr with N2. The growth of C1N02 was monitored for a
time period of 1 1/2 to h hours. Four interferograms were recorded for
each spectra. The drop in CINQ was used as the measure for C3JD2 with
precision of the extinction coefficients better than 10$ within a run.
One mixture which sat for four hours was photolysed in an attempt
to measure the rate of C1N02 photolysis. It contained 1 ppm C1N03,
0.16 ppm 03, O.U ppm CBD, 0.38 ppm N02, 18 Torr Oa and 682 Torr of W2
when the lights were turned on. The ciN02 absorbance exhibited first
order kinetics over the ten minute period that the lights were on.
Chlorine nitrate (C10N02) synthesis
C10IO2 was synthesized by photolysing mixtures of C12 (90 ppm),
N02 (7 to 13 ppm) and 03 (l8 to 28 ppm) in synthetic air at 700 Torr
for one to two minutes. It is very unstable at photolysis times longer
than one minute due to reactions with other species and the walls. It
was stable in the dark for 23 minutes.
Standard commercial gases were used. The N02 was degassed at ice
temperature. 03 was generated by discharging a Tesla coil externally on
glass tubing through which oxygen was flowing into the cell. Methane
(3.5 ppm) and CO (O.lU ppm) were present as impurities.
Spectra were derived from single scan interferograms (0.08 minutes)
Mass balancing of nitrogen was not good as observed in other C12 photo-
,lysis work due to wall problems (C1W03 always appears when 03 and NO-,
are present). CIONO^ was monitored using infrared extinction data from
the literature (67) which was recorded at 125 Torr total pressure (the
pressure correction for 700 Torr is not known) .
HOC1 synthesis
Mixtures of 015 (60 ppm), 03 (« 20 ppm), and hydrocarbons (ethane,
propane or isobutane at 5 ppm) in synthetic air at 700 Torr were photo-
lysed for four minutes. The maximum amount of HOC1 was observed at two
minutes and was gone at four minutes probably due to photodecomposition.
85
-------
Standard commercial gases were used without further purification.
The small methane impurity («2 ppm) resulted in no detectable HOC1 for-
mation in a blank run, although spurious HW3 formation was seen. Ozone
was formed by discharging a Tesla coil externally on glass tubing through
which oxygen was flowing into the cell.
The spectra were derived from four coadded interferograms (0.32
minutes). In the rune with propane and isobutane, the acetone which is
formed interferes with the HOC1 absorption and was removed by computer
subtraction of a calibrated reference acetone spectrum. Mass balancing
of chlorine containing species would allow the quantitative determination
of. HOC1. Unfortunately, the frequency range of our system does not allow
the simultaneous monitoring of HOC1 and HC1 which is necessary to carry
out the chlorine mass balance.
N20^ synthesis
Mixtures 'of N02 (2 to 15 ppm) and 03 (2 to 8 ppm) in 02 (« 20 Torr)
and N2 (« 680 Torr) react quickly in the dark. to form N205 which slowly
decays away.
Standard commercial gases were used. The NO, was degassed at ice
temperature. Ozone was formed by discharging a Tesla coil externally
on glass tubing through which oxygen was flowing into the cell.
Four or twenty interferograms were coadded for each spectrum.
CUOp is always observed when N205 is present, presumably due to some
reactive chlorine species on the walls. The validity of nitrogen mass
balancing in this work is valid only if no extra nitrogen comes off the
wall or is lost to the wall.
Nitric Acid calibration
The vapor above a degassed sample of 70% nitric acid solution was
allowed to enter two standard volumes and one calibrated trap simultan-
eously (the combined HON02 and H20 vapor pressure was between 5 and 6
Torr at room temperature). The contents of the calibrated trap was
frozen at liquid nitrogen temperature and titrated with a standard NaOH
solution using the phenolphthalein end point. The contents of one of
the calibrated volumes was then frozen into the trap at liquid nitrogen
temperature and another titration performed. The two titrations were
checked for consistency taking into account the different volume sizes.
The contents of the third calibrated bulb was injected into the cell
and pressurized to 700 Torr with nitrogen. Twenty interferograms were
CQ -added per spectrum and usually two spectrum were taken for averaging
of absorbance data.
From the titration data, the volume sizes, and the ideal gas law,
the concentration of nitric acid in a given spectrum was readily calcu-
lated. A standard deviation of 20% was obtained for extinction coef-
ficients determined from eight different nitric acid samples.
86
-------
INFRARED SPECTRA OF COMPOUNDS
The following are infrared spectra of compounds used in the photol-
ysis work and not included in the previous report of this project. All
were recorded at 25 ± 2°C, 170 m path length, 1 cm"1 resolution (l cm
retardation), 8192 data points per interferogram with box-car apodiza-
tion, usually 20 interferograms coadded per spectra, and 700 Torr total
pressure.
87
-------
en
CO
o:
h-
5*
^lW^lllM^^I^ . I
I Vly
CINO
o
CO
CO
o:
ol
1500
toflfTpn
N02
NO
1600 1700 1800
WAVENUMBER (cm")
1900
2000
Fig. 36 Infrared spectrum of C1M3 (nitrosyl chloride), top spectrum
0.10 ppm, bottom spectrum = 1.36 ppm
-------
i t/j*r*HYi*»**Vi«*^^
700 800
900 1000 1100
WAVENUMBER (cm-1)
1200
1300
1400
Fig. 37 Infrared spectrum of C1N02 (nitryl chloride), top spectrum
0.88 ppm, bottom spectrum = 3-38 ppm
89
-------
lOO-i
800
900
••I
WAVENUMBER (cm"1)
Fig. 38 a) 7.5 ppm HON02
b) « 1.5 ppm ClONDg and 7-5 ppm HONO;, formed during photolysis
(0.7 min) of Clg (90 ppm), W2 (13 ppm), 03 (18 ppm) in a
synthetic air mixture (PT = 700 Torr)
90
-------
HOCI
100-
-0-
100-
C/)
CD
o:
>»9
^ 0
lOO-i
^^^^^
-b-
-c-
1200 1300
WAVENUMBER (cm'1)
1400
Fig. 39 HOCI formed during photolysis of C13 (90 ppm), 03 ( 20 ppm),
hydrocarbon (5 ppm) mixtures in synthetic air (PT = 700 Torr)
a) from JLSO-butane (2 min photolysis) with U.3 ppm (CH3)2CO
removed
b) from propane (1 min photolysis) with 3.2-ppm_(CH3)pCO re-
moved ^
c) from ethane (2 min photolysis)
-------
ro
n:
o __
2500
rfMM
I r •
HCI
28OO
WAVENUMBER (cm")
\ M f-
Wl
29OO
- I I
3OOO
Fig. ij-0 Infrared spectrum of HCI, top spectrum = 1.83 ppm, bottom spectrum = 68.3 ppm
-------
tr
MONO,
2000
WWENUMBER (cm")
Fig. Ul Infrared spectrum of HON03, top spectrum =0.39 PPm, bottom spectrum = 3.^3
-------
cn
en
or
0,
-'YrnrTH'WJ'f-
o
en
z
o:
^p
ol
700
800
900
1000
1100
WAVENUMBER (cm-')
1200
1300
Fig.
Infrared spectrum of 03, top spectrum = 0.26 ppm, bottom spec-
trum = 12.0 ppm
-------
IOO
VO
v_n
70O
800
90O IOOO 1100
WAVENUMBER (cm-)
1200
1300
1400
Fig. U3 Infrared spectrum of N205j top spectrum = O.U ppm, bottom spectrum = 2.2 ppm
-------
lOOr
800 900 1000 1100 1200 1300
I /A., cm
Fig. l*U K)2N03 (1.1 ppm)
c) spectrum of cell contents following 5.9 min irradiation of
the initial mixture: total [HOND]0 = U.3 ppm, [N0]0 - 2.8,
[N02]0 = 1.1, [C0]0 = 3.8 x 104 ppm in synthetic air
d) residual spectrum resulting from c) following computer sub-
traction of cis, trans-HOND, CH4, and H-,0
96
-------
A. Identification of Trace Atmospheric Constituents
1. Solar spectra collection and analysis
2. Spectra of long paths of ground air
3- Exploration of techniques for spectral data
reduction and analysis
B. The Study of Some Key Reactions of Possible
Importance in Photochemical Smog Formation and the
Natural Removal Mechanisms of Freons and Their
Influence on 03 Levels in the Stratosphere
1. Reactions of alkylperoxy radicals with NO and N02
2. Role of aldehydes in photochemical smog formation
3' A study of some potentially important atmospheric
S03 removal mechanisms
k. Natural removal mechanisms of freons
C. Library of Spectra
D. Research on Problems Identified from Previous Work
1. Computer generated spectra
2. Band intensity measurements and parameter ratios
3. Installation of Nicolet interferometer
Year III
major effort
minor effort
minor effort
major effort
minor effort
minor effort
minor effort
minor effort
minor effort
minor effort
major effort
-------
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by Pulse Radiolysis of Water Vapor, Int. of Chem. Kinet.; Symp.
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45- R. A. Cox, R. G. Derwent, and P. M. Holt, Relative Rate Constants
for the Reactions of OH Radicals with H2, CH4, CO, NO, and HONO at
Atmospheric Pressure and 296° K, J. Chem. Soc., Faraday Trans. 1:72,
2031-2043 (1976).
46. B. K. T. Sie, R. Simonaitis, and J. Heicklen, The Reaction of HO
with CO, Int. J. Chem. Kinet.:8, 85-98 (1976).
47. R. Greiner, Hydroxyl-Radical Kinetics by Kinetic Spectroscopy, I,
Reactions with H2, CO, and CH4 at 300° K, J. Chem. Phys.;46,
2795-2799 (1967).
48. A. Y. M. Ung and R. A. Back, The Photolysis of Water Vapor and
Reactions of the HO-Radicals, Can. J. Chem.:4_2, 753-763 (1964).
49. P. L. Hanst, Spectroscopic Methods for Air Pollution Measurements,
Adv. Environ. Sci. Technol.:2, 91-213 (1971).
50. R. A. G. Carrington, The Infra-Red Spectra of Some Organic Nitrates,
Spectrochem. Acta:l6, 1279-1293 (1960).
101
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51. T. Urbanski and M. Witanowski, Infra-Red Spectra of Nitric Esters,
Trans. Faraday Soc.:59_, 1039-10^5 (1963). •
52. R. Greiner, Hydrcocyl Radical Kinetic Spectroscopy, VI, Reactions
with Alkanes in the Range 300-500° K, J. Chem. Phys.:53, 1070-1076
(1970).
53« G. Paraskevopoulos, Private Communication to One of the Investiga-
tors (J.S.C.)
5^-. R. Schwarz, Uber die Peroxysalpetersaure, Feit. Anorg. Chem.:25_6,
3-9 (19^8).
55. R. Simonaites and J. Heicklen, Reaction of H02 with NO and N02,
J. Phys. Chem.:78, 653-657 (197*0-
56. R. A. Cox and R. G. Derwent, Kinetics of the Reaction of H02 with
NO and N02, J. Photochem.:k, 139-153 (1975).
57. R. Simonaitis and J. Heicklen, Reactions of H02 with NO and N02
and of OH with NO, J. Phys. Chem.:80, 1-7 (1976).
58. H. Niki, P. D. Maker, C. M. Savage, and L. P. Breiteribach, Fourier
Transform IR Spectroscopic Observations of Pernitric Acid Formed
Via H02 + N02 -»H02N02, Submitted for publication, Chem. Phys.
Letters, September 1976.
59- B. W. Gay, Jr., R. C. Noonan, J. J. Bufalini, and P. L. Hanst,
Photochemical Synthesis of Peroxyacyl Nitrates in Gas Phase Via
Chlorine-Aldehyde Reaction, Environ. Sci. Technol.rlO, 82-85 (1976).
60. H. Niki, P. Maker, C. Savage, and L. Breitenbach, Paper N2, IR
Fourier-Transform Spectroscopic Studies of Atmospheric Reaction,
Extended Abstracts of 12th Informal Conference on Photochemistry:
June 28, 1976, N.B.S., Gaithersburg, Maryland, p. N2-1 to N2-4.
61. P. L. Hanst and B. W. Gay, Jr., Photochemical Reactions among
Formaldehyde, Chlorine, and Nitrogen Dioxide in Air, Environ. Sci.
Technol.:submitted for publication, September 1976.
62. R. F. Hampson, Jr. and D. Garvin, Chemical Kinetic and Photochemical
Data for Modelling Atmospheric Chemistry, N.B.S. Technical Note
866 (1975).
63. W. H. Chan, W. M. Uselman, J. S. Calvert, and J. H. Shaw, The
Pressure Dependence of the Rate Constant for the Reaction:
HO + CO -»H + C02, Chem. Phys. Letters:^, 2kO-2kk (1977).
6k. W. Hack, K. Hoyerman, and H. G. Wagner, The Reaction NO + H02 -»
N02 + OH with OH + H202 -»H02 + H20 as the H02-Source, Inst. of
Chem. Kinet.:Symp. No. 1, 329-339 (1975).
102
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65. W. A. Payne, L. J. Stief, and D. D. Davis, A Kinetic Study of the
Reaction of H02 with S02 and NO, J. Amer. Chem. Soc.:95, ?6lU-76l9
(1973).
66. E. R. Stephens, The Formation, Reactions, and Properties of
Peroxyacyl Nitrates (PANs) in Photochemical Air Pollution, Adv.
Environ. Sci.:l, 119-1^6 (1969).
6?. R. A. Graham, E. C. Tuazon, A. M. Winer, J. N. Pitts, Jr.,
L. T. Molina, L. Beaman, and M. J. Molina, High Resolution Infrared
Absorptivities for Gaseous Chlorine Nitrate, Geophys. Res. Letters:
it, 3-5 (1977).
103
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APPENDIX A
V
SUMMARY OF OBJECTIVES FROM 1975 PROPOSAL
I. SUMMARY OF OBJECTIVES
The primary objective of the research outlined in this proposal is
to develop infrared fourier transform spectroscopic (FTS) techniques to
characterize certain key air pollutants, their precursors and reaction
products, and to establish quantitative kinetic and mechanistic details
of the interrelationships between these pollutants both in simulated
and real atmospheres. We have chosen for study during the three year
period of this research effort the following important, yet unresolved,
problems related to the transformations of contaminants in both the
troposphere and stratosphere. These systems are particularly well suited
for study with the FTS system and associated equipment now in use at
the Ohio State University laboratories.
A. Study of the natural removal mechanisms of the Freons and their
influence on the ozone concentration in the stratosphere:
1. The chlorine atom sensitized decomposition of ozone. The
chemical kinetics and mechanism of interactions in the
irradiated Os, NO, N02, C12 system.
2. /The fate of the organic free radicals formed by photo-
dissociation of the Freons in the stratosphere.- The
chemical kinetics and mechanisms of the reactions of the
CF2Cl and CC12F free radicals in air at stratospheric pres-
sures .
3. The alteration of the stratospheric ozone concentration
through Freon addition. The laboratory simulation of the
photochemistry of the stratosphere perturbed by Freon addi-
tion.
B. Study of certain key reactions, seemingly important in photo-
chemical smog systems:
1. The role of nitrous acid in the development of the impor-
tant free radical chain carrier, HO, and its relation to
smog formation in the urban atmosphere. A kinetic study of
the NO, N02, MONO, CO system. The quantum efficiency of
HO radical formation in the sunlight photolysis of HONO in
air. The determination of important rate constants for
the HO reactions with NO and N02, and H02 with NO will be
made.
2 . The role of the aldehydes in smog development in the urban
atmosphere. The nature and mechanism of the formation of
104
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the products formed in the photooxidation of formaldehyde.
A kinetic study of the CH20, NO, N02, air, and the CH20,
NO, N02j C12, air systems. A search for the illusive per-
oxyformyl nitrate.
A study of some potentially important S02 removal mechanisms
in the lower atmosphere. The rates of the primary reac-
tions of HO and H02 with S02 from the FTS study of the CH20,
S02, CO, air and HONO, S02, CO, air systems. The nature
of the S02-oxidizing species formed in the 03-olefin dark
reaction.
The determination of high resolution infrared spectra of
the common atmospheric contaminants and their products.
Cataloging of the absorption coefficient-wavelength data
for use in this work and by other investigators in the
field.
Direct observation of the infrared absorption spectra of
air samples in Columbus, Ohio. We will employ both in situ
samples, observed using solar infrared transmission spectra
in long atmospheric paths near sunset and sunrise, and con-
fined samples in the laboratory long-path system (up to
1.5 km); spectra will be taken at regular intervals through-
out the period.
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APPENDIX B
PAPERS PRESENTED AT MEETINGS
1. "An IRFTS Spectroscopic Study of the Kinetics and the Mechanism of
the Reactions in the Gaseous System, HONO, NO, N02, H20." Walter
H. Chan, Robert J. Nordstrom, Jack G. Calvert and John H. Shaw, pre-
sented at the Centennial ACS meeting, New York City, April, 1976.
2. "A Partial Analysis of HONO Bands Between 750 and 1300 cm"1."'
Walter H. Chan, C. Weldon Mathews and Robert J. Nordstrom, presented
at the 31st Symposium of Molecular Structure and Spectroscopy,
Columbus, Ohio,, June, 1976.
3. "Infrared Spectroscopic Detection of Fluorocarbon-12 in the Atmo-
sphere." Robert J. Nordstrom, W. R. Skinner, J. H. Shaw, W. H. Chan,
W. M. Uselman, and J. G. Calvert, presented at the 31st Symposium of
Molecular Structure and Spectroscopy, Columbus, Ohio, June, 1976.
k. "Comparison of Measured and Computer Spectra of Air Samples."
R. J. Nordstrom, W. R. Skinner, J. H. Shaw, W. H. Chan, W. M.
Uselman, and J. G. Calvert, presented at the 31st Symposium of Mo-
lecular Structure and Spectroscopy, Columbus, Ohio, June, 1976.
5. "Detection and Photochemistry of Selected Air Pollutants Using
FT-IR Techniques." J. Shaw, Invited Paper, Coblentz Award Symposium,
Pittsburgh Conference, March, 1977.
6. "Computer Assisted Technique of Analyzing Spectra." Y. S. Chang,
J. H. Shaw, J. G. Calvert, and W. M. Uselman, presented at the 32nd
Symposium of Molecular Spectroscopy Symposium, Columbus, Ohio, June,
1977.
7. "Investigations of Atmospheric Spectra." J. H. Shaw, Y. S. Chang,
J. G. Calvert, and W. M. Uselman, presented at the International
Conference on Fourier Transform Infrared Spectroscopy, Columbia,
South Carolina, June, 1977.
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APPENDIX C
PAPERS PUBLISHED OR ACCEPTED FOR PUBLICATION
1. "An IRFTS Spectroscopic Study of the Kinetics and the Mechanism of
the Reactions in the Gaseous System, HONO, NO, N02, H20." Walter H.
Chan, Robert J. Nordstrom, Jack G. Calvert, and John H. Shaw, Chemical
Phys. Letters, 37, Mn-I*U6 (1976).
2. "A Kinetics Study of HONO Formation and Decay Reactions in Gaseous
Mixtures of HONO, N02, H20 and N2." Walter H. Chan, Robert J.
Nordstrom, Jack G. Calvert and John H. Shaw, Environmental Science
,and Technology, 10, 67^-682 (1976).
3. "A Spectroscopic Study of the N02-N204 System by the Infrared
Absorption Technique," Robert J. Nordstrom and Walter H. Chan,
J. Phys. Chem., §0, 81*7-850 (1976).
U. "Accuracy of the AFCRL Atmospheric Absorption Line Parameters Com-
pilation in the 10-nm Atmospheric Window." W. R. Skinner and R. J.
Nordstrom, Appl. Opt. 15, 26l6 (1976).
5. "Use of the AFCRL Line Parameters Compilation to Test the Performance
of an Infrared Spectrometer System." Y. S. Chang, J. H. Shaw, W. M.
Uselman, and J. A. Calvert, to appear in Applied Optics, 1977.
6. "Long Path Air Spectra." R. J. Nordstrom, W. R. Skinner? J. H. Shaw,
W. H. Chan, J. G. Calvert, and W. M. Uselman, to appear in Applied
Optics, June 1977-
7. "Application of Computer Simulated Infrared Solar Spectra to the
Detection of Atmospheric Fluorocarbon-12." R. J. Nordstrom, J. H.
Shaw, W. R. Skinner, W. H. Chan, J. G. Calvert, and W. M. Uselman,
to appear in Applied Spectroscopy, 1977.
8. "The Pressure Dependence of the Rate Constant for the Reaction
HO + CO -*H + C02." W. H. Chan, W. M. Uselman, J. G. Calvert and
J. H. Shaw, Chem. Phys. Letters 1*5, 2kO-kk, (1977)
9. "The Kinetics and Mechanism of the H02-N02 Reactions. The Signifi-
cance of Peroxynitric Acid Formation in Photochemical Smog." S. Z.
Levine, W. M. Uselman, W. H. Chan, J. G. Calvert and J. H. Shaw, to
appear in Chem. Phys. Letter, 1977.
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/3-78-057
2.
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
APPLICATION OF FOURIER TRANSFORM SPECTROSCOPY TO AIR
POLLUTION PROBLEMS
Interim Report-1977
5. REPORT DATE
June 1978
6. PERFORMING ORGANIZATION CODl£
7'
. Chang, J.H. Shaw, E. Niple, J.G. Calvert,
W.H. Chan, S.Z. Levine, and W.M. Uselman
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
The Ohio State University Research Foundation
1314 Kinnear Road
Columbus, Ohio 43212
10. PROGRAM ELEMENT NO.
1AA603 AI-03 (FY-77)
11. CONTRACT/GRANT NO.
R803868-2
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Sciences Research Laboratory-RTP.NC
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
13. TYPE OF REPORT AND PERIOD COVERED
Interim
14. SPONSORING AGENCY CODE
EPA/600/09
15. SUPPLEMENTARY NOTES
See companion reports EPA-600/3-77-026, EPA-600/3-77-025
-1
16. ABSTRACT
An atlas of observed and calculated air spectra from 700 to 2300 cm ^ has been
prepared. Methods of analyzing air spectra to identify spectral features and to
determine simultaneously the abundances of atmospheric gases such as CO, N20, CH,,
0., H.O, and CO. have been explored. These methods include ratioing observed and
calculated spectra and correlation analysis of absorption bands to obtain abundances
by linear regression and non linear least squares methods. Absorbing features of
atmospheric gases such as 0_, H.O, and N~0 have been removed from solar spectra to
isolate underlying features of F->12 near 1160 cm
New data were obtained related to the rate constant for the reaction, HO + CO
H + C02, as a function..of pressure. This rate constant is pressure sensitive:
k = 439 + 24 ppm~ min at 700 Torr air; k = 203 + 29 ppm~ min in air at 100
Torr. The FTIRS system was employed in other studies to determine the rate constants
for the reactions: HO + NO- HO NO (Ref.22) and HO + NO HONO + 0 (Ref. 21);
in 7{0 Tojr of air at 25 + 2°C, the data suggest k22 7.2 x 10 and k« 5.3 x 10
ppm min . Simulations of the reactions in a typical NO -RH-RCHO-polIuted
atmosphere exposed to sunlight show that the theoretical rate of H02N02 generation
is similar in magnitude to those expected (and observed in real atmospheres) for
peroxyacylnitrates.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COS AT I Field/Group
* Air pollution
* Infrared spectroscopy
* Optical equipment
Solar spectrum
* Reaction kinetics
* Photochemical reactions
Fourier transform
spectroscopy
13B
14B
20F
03B
07D
07E
8. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)
UNCLASSIFIED
21. NO. OF PAGES
120
20. SECURITY CLASS (Thispage)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
108
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