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ENVIRONMENTAL HEALTH SERIES
Air Pollution
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PILOT vSTUDY
OF ULTRAVIOLET RADIATION
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IN LOS ANGELES \
OCTOBER ^igesX \
U. S. DEPARTMENT OF HEALTH,
EDUCATION, AND WELFARE \
*
Public Health Service
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PILOT STUDY OF ULTRAVIOLET
RADIATION IN LOS ANGELES
OCTOBER 1965
A Report on Concurrent Measurements Made by
Cooperating Organizations by Various Methods
Edited by John S. Nader
Control Technology Research and Development Programs
U. S. DEPARTMENT OF HEALTH, EDUCATION,
AND WELFARE
Public Health Service
National Center for Air Pollution Control
Cincinnati, Ohio
1967
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The ENVIRONMENTAL HEALTH SERIES of reports was established
to report the results of scientific and engineering studies of man's
environment: The community, whether urban, suburban, or rural,
where he lives, works, and plays; the air, water and earth he uses
and reuses; and the wastes he produces and must dispose of in a way
that preserves these natural resources. This SERIES of reports
provides for professional users a central source of information on
the intramural research activities of the Centers in the Bureau of
Disease Prevention and Environmental Control, and on their co-
operative activities with State and local agencies, research institu-
tions, and industrial organizations. The general subject area of
each report is indicated by the letters that appear in the publication
number; the indicators are
AP - Air Pollution
RH - Radiological Health
UIH Urban and Industrial Health
Triplicate tear-out abstract cards are provided with reports in the
SERIES to facilitate information retrieval. Space is provided on the
cards for the user's accession number and additional key words.
Reports in the SERIES will be distributed to requesters, as supplies
permit. Requests should be directed to the Center identified on the
title page.
Public Health Service Publication No. 999-AP-38
ii
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ACKNOWLEDGMENT
The Public Health Service acknowledges the contributions of the
cooperating participants to this study of ultraviolet radiation in Los
Angeles. Appreciation for assistance in executing the study is ex-
pressed to the Los Angeles County Air Pollution Control District for
the use of their facilities both on the laboratory rooftop and within the
laboratory; to the Mt. Wilson Resort for use of grounds as nonurban
sampling site; to station KCET for access to their facilities on Mt.
Wilson and to Mr. James Mead, the station engineer; to Mr. Ralph
Keith, Senior Meteorologist with LACAPCD, for his work in forecasting
and calling the flight days; to Mr. George Kalstrom, Meteorologist,
Los Angeles Weather Bureau, for assistance in locating a nonurban
sampling site; and in particular, to Mr. C. Frederick Smith, Public
Health Service, who coordinated the efforts of the participants and
made many of the decisions required for the successful execution of
the study involving concurrent measurements coordinated with special
flight days.
Mr. J. S. Nader acknowledges the advice and comments of Drs.
J. H. Ludwig, B. J. Steigerwald, and A. P. Altshuller, and Mr. R. A.
McCormick, Public Health Service, in the planning, coordination, and
execution of this study.
111
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COOPERATING PARTICIPANTS
Organization Responsible Individual
Vehicle Pollution Laboratory Dr. Robert J. Gordon
Bureau of Air Sanitation Supervisory Physicist
Division of Environmental Sanitation
California Department of Public Health
434 South San Pedro Street
Los Angeles, Calif. 90013
Los Angeles Country Air Pollution Mr. Robert J. Bryan
Control District Director of Technical
434 South San Pedro Street Services
Los Angeles, Calif. 90013
National Bureau of Standards Mr. Ralph Stair
Meteorology Division Physicist
Gaithersburg Maryland 20760
Pennsylvania State University Dr. Hans Neuberger
College of Earth and Mineral Sciences Chairman
University Park, Pa. 16802 Dept. of Meteorology
Public Health Service Mr. John S. Nader, Chief
National Center for Air Pollution Physical Measurements
Control
Chemical and Physical Research and
Development Program
4676 Columbia Parkway
Cincinnati, Ohio 45226
University of California, Riverside Dr. J. N. Pitts
Riverside, Calif. Professor of Chemistry
IV
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PREFACE
To our knowledge, this pilot study represents the first field effort
of several research groups to obtain simultaneous data on available
ultraviolet (UV) radiation in the atmosphere of a large urban community
under representative environmental conditions. This study was
initiated to evaluate possible methods of measuring the UV important
in photochemical reactions, in the range from 300 to 400 nanometers,
under realistic field conditions. At the same time some preliminary
data were obtained on the UV energy available with respect to location,
elevation, and time of day for various levels of air pollution.
Los Angeles was selected for the study because its smog environ-
ment is primarly associated with photochemical reactions. October
was selected because a wide range of air pollution conditions, particu-
larly those associated with photochemical smog, are usually experienced
at that time.
Organizations who had developed methods of UV measurements
were invited to participate in this study as a means of evaluating their
techniques against those of others. The Public Health Service investi-
gators used physical detection methods (filter photocell and photo-
chromic glass); the National Bureau of Standards and Pennsylvania
State University also used physical methods (filter phototube and
photosensitive plastic, respectively); the University of California
at Riverside and California State Department of Health used chemical
methods (actinometers involving gas, liquid, and solid reactions). The
Los Angeles County Air Pollution Control District conducted chemical
analyses and provided meteorological and air quality data as support-
ing information.
The rooftop of the laboratory of the Los Angeles County Air
Pollution Control District in downtown Los Angeles was the site for
measurements of incoming UV radiation at ground level below the
urban smog envelope. A clearing near the KCET transmission tower
on Mt. Wilson at an elevation of 5,700 feet was the site for measure-
ments of incoming radiation representative of that incident on top of
the Los Angeles smog envelope.
Aircraft flights were made over downtown Los Angeles to measure
the outgoing radiation reflected from the ground and from smog layers.
Within the 4 weeks of the study, flights were made on 5 days to encom-
pass environmental conditions ranging from clear atmospheres to
relatively heavy smog. On all 5 days the skies were essentially free
of cloud cover. During these flights simultaneous measurements were
made of meteorological parameters, air quality relative to pollutants,
and ultraviolet radiation incident on a horizontal plane surface and on a
volumetric actinometer. Four flights were made on each of the 5 flight
days. Measurements in the aircraft were made in each flight at eleva-
-------
tions ranging from 5,700 feet, corresponding to the elevation of the
Mt. Wilson site, to a minimum of about 1,300 feet.
This report is a compilation of the data obtained on the 5 flight
days by the various participants. The contribution of each participant
is presented as a separate section, intact, with a brief explanation of
the instrumentation and procedure used to obtain the data together with
a tabulation of the data reduced to a format permitting convenient use
of information by interested researchers. Both the PHS and NBS con-
tinuous recorder data have been put on punch cards and are available
as relatively instantaneous values throughout the day as well as in the
summary form presented in this report.
In the final section related data from the various contributor sec-
tions are discussed. Some limited effort is made to relate concurrent
data of measurements by different methods and at various locations
and to summarize some of the conclusions.
As a result of this study, the National Center for Air Pollution
Control plans to pursue the measurement of the UV incident on a volume
in space in addition to the horizontal-plane technique currently available,
which represents only the UV component normal to the plane of
incidence. This study also provides the basis on which plans will be
formulated for a large-scale systematic study of available UV radiation
and its reduction in atmospheres of several large cities and the rela-
tionship of UV intensity levels to potential photochemical smog.
John S. Nader
Cincinnati, Ohio
1967
VI
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CONTENTS
ACKNOWLEDGMENT iii
COOPERATING PARTICIPANTS iv
PREFACE v
INTRODUCTION 1
1 FILTER-PHOTOCELL MEASUREMENTS 5
Public Health Service
2 x FILTER-PHOTOTUBE MEASUREMENTS 21
National Bureau of Standards
3 PHOTOCHEMICAL MEASUREMENTS 37
California Department of Health
4 PHOTOCHEMICAL MEASUREMENTS 49
University of California at Riverside
5 PHOTOSENSITIVE PLASTIC MEASUREMENTS 59
The Pennsylvania State University
6 PHOTOCHROMIC GLASS MEASUREMENTS 65
Public Health Service
7 METEOROLOGICAL AND AIR QUALITY MEASUREMENTS . 69
Los Angeles County Air Pollution Control District
8 DISCUSSION AND SUMMARY 79
Public Health Service
vn
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ABSTRACT
Several research groups combined efforts to measure simultaneously the
available ultraviolet radiation of the urban atmosphere of Los Angeles
under representative environmental conditions. The study was planned to
permit evaluation of possible methods of measuring the UV radiation im-
portant in photochemical reactions (in the range from 300 to 400 nanom-
eters) and to obtain preliminary data on the UV radiation energy with res-
pect to location, elevation, and time of day. Measurements were made on
five days at various levels of air pollution ranging from no smog to mod-
erate-to-heavy smog.
This report is a compilation of data obtained by the several participants,
with brief accounts of instrumentation and procedures. The instrumental
sensors used to detect the UV radiation were filter photocell, filter photo-
tube, photochemical sensors, photosensitive plastic, and photochromic
glass. Air quality and meteorological data for the sampling periods are
also presented. A discussion and summary relates the data obtained in
measurements by the different methods and at the various locations.
vm
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INTRODUCTION
The Los Angeles measurement site on the rooftop of the laboratory
building was about 350 feet above sea level. Measurements of incoming
UV radiation were made with the filter-photocell and filter-phototube
sensors, photochromic glass and photosensitive plastic, photochemically
treated filter paper, and photochemical gas and liquid reaction cells
(Figures 1 and 2). Supporting data on air quality and meteorology were
also obtained at this site.
At the Mt. Wilson site the instrumentation was on ground level at
an elevation of 5,700 feet. This site was located in a clearing about
200 feet to the right of the KCET television station building (Figure 3).
The only measurements at this site were of incoming UV radiation
made with the filter-phototube sensor, which was a duplicate of that at
the Los Angeles site.
The measurements of outgoing radiation were made in a Cessna
180 aircraft. Figure 4 shows the wing mounting of the sensor for the
outgoing radiation. This radiation was measured with a filter-photocell
sensor, which was a duplicate of that at the Los Angeles site. Both in-
coming and outgoing radiation were also measured by photochemically
treated filter paper. Air quality measurements were made on air
samples collected only on the first flight of each scheduled flight day
at three elevations. Temperature readings were also taken at all times.
The 5 flight days were October 6 (Wednesday), 12 (Tuesday), 16
(Saturday), 18 (Monday), and 20 (Wednesday), 1965. These 5 days
were classified by the Air Pollution Control District according to a
rating based on observed smog effects: moderate to heavy (M-H),
light to moderate (L-M), none (N), light (L), and light (L). The ob-
served smog effects were one or more of the following three: ozone
concentration, visibility, and eye irritation.
The wavelengths are given in nanometers (nm = 10 ~9m). Irradiance
(incident flux density) is in watts per square meter (w/m2), consistent
with the MKS system of basic units and the internationally recognized
system of prefix notation for multiples and submultiples of basic units.
Calculations of time of day were based on an average approximation
that true solar time (TST) is equal to Pacific daylight time (PDT)
minus 40 minutes. Thus, 12:00 noon (TST) is 12:40 p.m. (PDT).
-------
Figure 1. Instruments on rooftop at Los Angeles measurement site.
Figure 2. NBS filter-phototube equipment at Los Angeles site.
ULTRAVIOLET RADIATION MEASUREMENTS
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Figure 3. Aerial view of Mt. Wilson measurement site.
Figure 4. Wing-mounted sensor for measurements from aircraft.
Introduction
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Public Health Service
1: FILTER-PHOTOCELL MEASUREMENTS
John S. Nader and C. Frederick Smith
National Center for Air Pollution Control
INSTRUMENTATION AND METHOD*
The Eppley sensors used in surface measurements were designed
by and constructed at the Eppley Laboratory for the Public Health
Service. The sensor used in the aircraft was constructed by the Na-
tional Bureau of Standards in accordance with the Eppley filter-photo-
cell design. The filter-photocell sensor (Figure 1-1) consisted of a
Weston selenium barrier-layer photovoltaic detector cell with a sealed-
in quartz window, a bandpass interference filter to restrict the ultra-
violet radiation incident on the photocell to the range of interest, a
diffusing disc of opaque quartz protected from weathering effects by a
quartz hemispherical envelope (2-mm wall thickness), and a circular
spirit level mounted on the sensor stand with levelling screws.
The diffusing disc was designed and constructed to reduce the
light intensity at the photocell for improved stability with exposure
time and also to optimize the response of the sensor in accordance with
the Lambert cosine Law (Table 1-1). The disc is nearly uniformly dif-
fusing over the wavelength of interest as well as geometrically within
the system. The terminals of the photocell are connected through a
precision resistor (1,500 ohms), across which a voltage signal is devel-
oped. This arrangement restricts light flux to the order of 1 to 2 foot-
candles and the resulting current in the circuit to a few mircroamperes
at most, thus maintaining photocell stability.
Three Eppley instrument systems were used to isolate the wide
band, 300 to 380 nm, and two narrow bands within this range, namely,
315 to 330 nm (low) and 357 to 372 nm (high). Each narrow-band system,
in addition to its sensor included a d-c amplifier with full-scale input
ranges of 50, 100, 200, 500, 1000, and 2000 microvolts and constant
full-scale output range of 10 millivolts. All systems used in downtown
Los Angeles to measure the incoming radiation continuously incorpor-
ated recording millivolt potentiometers with adjustable full-scale
r Mention of commercial products throughout this report does not constitute endorsement by
the Public Health Service.
Filter Photocell
-------
settings within the ranges of 3 and 30 millivolts. The wide-band system
used on the aircraft to measure outgoing radiation incorporated an
indicating microvoltmeter, from which the attending technician observed
and recorded the electrical readings at prescribed elevations.
These systems were calibrated by the Eppley Laboratory to con-
vert the detected electrical signal into absolute energy values for the
UV flux incident on the horizontal plane sensor. Calibration of the
wide-hand system (1) involved the use of a calibrated differential
thermopile detector as a standard reference sensor and exposure of
both test and reference instruments simultaneously to solar radiation.
The outdoor exposure method referred to above could not be used for
calibration of the narrow-band filters because the thermopile detector
lacked the sensitivity required for the low energy levels involved. In
this case, exposure to an NBS lamp standard of spectral irradiance (2)
was made in the laboratory. From knowledge of the energy at the photo-
cell and the factor for the diffuser (determined through exposure to the
sun and sky), the first approximation of the required calibration was
obtained. From consideration of: (1) the specific UV band being
isolated; (2) the shape of the transmission curve of the filter defining
this region (Figure 1-2); (3) the shape of the spectral response curve of
the photocell (Figure 1-3); and (4) the deviation between the relative
spectral emission curves of the calibrating lamp and natural daylight
in the wavelength region of interest (Figure 1-4), appropriate correc-
tions were applied as deemed necessary (1). The adopted calibration
values given in Table 1-2 include the value for the wide-band sensor
used on the aircraft.
A test unit was provided to verify the calibration stability of each
system during field use. It consisted of a 45-watt quartz tungsten-
iodine lamp as a light source and a regulated power supply from a
12-volt automobile battery.
The Eppley sensor for the aircraft measurements was mounted
underneath the wing of the aircraft, and a signal cable transmitted the
sensor output voltage to an indicating microvoltmeter in the cabin of
the aircraft.
RESULTS
Instantaneous values of the incoming radiation in downtown Los
Angeles at 5-minute intervals were taken from the continuous chart
records and put on punch cards. These recorder values were reduced
to absolute energy values and averaged for 30-minute intervals. Tab-
ulated results are given for the incoming radiation in the two narrow-
band ranges and in the wide-band range in Tables 1-3, 1-4, and 1-5,
respectively. Figures 1-5, 1-6, and 1-7 give graphic representations
of these data as a function of time of day for the 5 flight days.
Measurements of the outgoing UV radiation taken from the aircraft
over downtown Los Angeles were instantaneous values taken at different
6 ULTRAVIOLET RADIATION MEASUREMENTS
-------
elevations over a span of time. Since these measurements did not
correspond exactly either for the same elevation in different flights or
for the same time of day on different days, the results, reduced to
absolute energy values, were tabulated to correspond both to identical
elevation intervals and to identical intervals of time. Thus, the data
are given in Table 1-6 in a cell array of radiation energy values as a
function of time and of elevation intervals. In the graphical representa-
tions of the data the midpoints of these intervals were plotted to give
two sets of curves. Figures 1-8 and 1-9 give the outgoing radiation as
a function of elevation for various flight-time intervals. Figures 1-10
and 1-11 give the outgoing radiation as a function of time of day for
various elevation intervals.
The outgoing radiation as a function of elevation was plotted on
semilog paper with the elevation on log scale. Initially, a rectilinear
plot showed a trend toward an exponential relationship similar to that
in lightscatter measurements from a turbid medium wherein lightscatter
increases with increased turbidity and increased medium thickness. If
this is the case, a semilog plot should give a linear relationship with
elevation except when a sharp change in the turbidity of the medium
may occur, as may be the situation in going through the bottom or top
of an inversion layer.
The experimental points for the plot of outgoing radiation as a
function of time of day were limited to four values corresponding to
the four flight trips per day. Nonetheless, a relatively smooth curve
was anticipated relating to the sine function of the sun's elevation.
Accordingly, points between the experimental values were calculated
on the basis of a least-squares best-fit equation (3rd order) to give
the curves shown.
Data on outgoing radiation were plotted only for the two extreme
smog conditions, the no-smog day (October 16) and the moderate-to-
heavy-smog day (October 6). These graphs adequately encompass
what would be portrayed by the data for the remaining 3 days, on which
smog conditions were within the range of the two extremes.
The temperature data taken at various elevations during all of the
flights were used to determine the temperature profiles (Figure 1-12)
from which the location of the ground inversion layer was determined.
Since the lowest elevation at which the temperature measurements
were made was about 1,300 feet, information about location of inversion
layer boundaries was limited to those between 1,300 and 6,000 feet.
Table 1-7 gives the elevation of the top of the inversion layer nearest
ground level, based on the elevation at which the temperature ceases
to increase with further increase in elevation.
Filter Photocell
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REFERENCES
1. Drummond, A. J. Instrumentation for Measurement of Ultravio-
let Radiation. In: Proceedings of the Fourth International Con-
gress of Biometeorology, August 1966, Rutgers University (in
press).
2. Stair, R., W. E. Schneider, and J. K. Jackson. A New Standard
of Spectral Irradiance. Appl. Optics. 2:1151 (1963).
ULTRAVIOLET RADIATION MEASUREMENTS
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Table 1-1. COSINE RESPONSE OF THE EPPLEY
FILTER-PHOTOCELL SENSOR
Zenith angle,
degrees
Total (300-380 run)
20
30
40
50
60
70
Low (315-330 nm)
20
30
40
50
60
70
Equivalent
elevation angle,
degrees
High (357-372 nm)
70
60
50
40
30
20
70
60
50
40
30
20
Relative
response0
1.02
1.00
1.00
1.06
1.02
1.09
1.32
1.11
1.00
0.96
0.96
1.00
aValues are normalized to 45-degree angle; range of solar
elevation at Los Angeles from 0800 to 1600 1ST during
experiment was 20 to 55 degrees.
Table 1-2. ABSOLUTE CALIBRATION VALUES FOR EPPLEY-DESIGNED SENSORS
Conversion factor,
Photocell sensor Range, nm Serial No. w-m-2/mv
Eppley wide-band UV 300-380 E-7368 10.7
Eppley High UV 357-372 E-7369 25.0
Eppley Low UV 315-330 E-7370 149.0
NBS wide-band UV 300-380 17.8
Filter Photocell
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Table 1-3. AVERAGE INCOMING 315- TO 330-nm RADIATION FOR
30-MINUTE INTERVALS, DOWNTOWN LOS ANGELES
(w/m2)
Midpoint of
time interval
(1ST)
0545
0615
0645
0715
0745
0815
0845
0915
0945
1015
1045
1115
1145
1215
1245
1315
1345
1415
1445
1515
1545
1615
1645
1715
1745
Oct
6
0.0268
0.0424
0.206
0.558
0.922
1.30
1.65
2.07
2.31
2.37
2.38
3.09
3.52
3.65
3.57
3.41
3.16
2.80
2.10
1.58
1.26
0.729
0.331
0.0781
0.0275
Oct
12
0.0223
0.0252
0.119
0.380
0.686
0.917
1.18
1.47
1.83
2.21
2.63
2.90
2.93
3.13
3.27
3.08
2.90
2.51
2.04
1.59
1.11
0.620
0.258
Oct
16
0.0044
0.0163
0.142
0.451
0.882
1.44
2.03
2.61
3.19
3.58
3.95
4.26
4.22
4.07
3.94
3.67
3.30
2.82
2.30
1.77
1.19
0.697
0.326
0.122
0.0521
Oct
18
0.0268
0.0275
0.147
0.430
0.795
1.29
1.66
2.20
2.71
3.18
3.43
3.37
3.12
2.73
2.37
2.41
2.11
1.85
1.71
1.40
0.945
0.521
0.191
10
ULTRAVIOLET RADIATION MEASUREMENTS
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Table 1-4. AVERAGE INCOMING 357- TO 372-nm RADIATION FOR
30-MINUTE INTERVALS, DOWNTOWN LOS ANGELES
(w/m2)
Midpoint of
tirtie interval
(1ST)
0545
0615
0645
0715
0745
0815
0845
0915
0945
1015
1045
1115
1145
1215
1245
1315
1345
1415
1445
1515
1545
1615
1645
1715
1745
Oct
6
0.0225
0.0962
0.590
1.31
2.08
2.84
3.56
4.28
4.69
4.67
4.72
6.30
6.99
7.16
7.22
6.97
6.59
6.04
4.64
3.52
3.01
1.99
1.14
0.520
0.120
Oct
12
0.0075
0.0275
0.350
0.888
1.52
1.98
2.41
2.87
3.50
4.34
5.13
5.65
5.72
6.27
6.68
6.42
6.22
5.54
4.60
3.78
2.89
1.33
1.03
0.396
0.0825
Oct
16
0.0075
0.0462
0.534
1.48
2.65
3.92
5.16
6.31
7.31
8.41
8.90
8.80
8.48
8.32
8.00
7.39
6.58
5.63
4.55
3.32
2.21
1.24
0.538
0.070
Oct
18
0.0150
0.0287
0.441
1.26
2.17
3.24
3.98
5.12
6.16
6.95
7.16
6.97
6.43
5.55
5.19
5.41
4.78
4.21
4.11
3.51
2.65
1.70
0.950
0.400
0.075
Filter Photocell
11
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Table 1-5. AVERAGE INCOMING 300- TO 380-nm RADIATION FOR 30-MINUTE
INTERVALS, DOWNTOWN LOS ANGELES
(w/m2)
Midpoint of
time interval
(TST)
0545
0615
0645
0715
0745
0815
0845
0915
0945
1015
1045
1115
1145
1215
1245
1315
1345
1415
1445
1515
1545
1615
1645
1715
1745
Oct
6
0.374
0.641
2.27
4.84
7.99
11.5
14.4
17.4
19.0
19.0
19.1
25.3
28.8
29.9
30.1
28.8
27.1
24.8
19.2
14.9
12.4
8.30
4.82
2.38
0.677
Oct
12
0.321
0.606
2.02
4.09
6.43
8.35
10.0
12.1
14.6
18.2
21.3
23.4
23.9
26.2
27.9
26.9
26.1
22.9
19.0
15.6
11.7
7.55
4.37
1.97
0.552
Oct
16
0.365
0.623
2.63
6.18
10.6
15.5
20.2
24.7
28.8
31.5
33.9
36.0
36.0
34.7
34.2
32.8
30.2
26.5
22.6
18.2
13.3
8.66
4.86
1.94
0.507
Oct
18
0.428
0.588
2.26
5.24
8.68
12.8
15.8
20.7
24.8
28.3
29.6
29.3
27.0
23.3
21.9
22.5
19.9
17.5
17.0
14.2
10.7
7.04
3.83
1.46
0.419
Oct
20
0.277
0.434
1.97
5.02
9.06
13.6
17.8
21.5
24.7
25.9
26.7
30.5
33.4
32.9
29.8
27.3
23.7
21.4
18.6
14.4
10.7
7.30
3.66
1.27
0.291
12
ULTRAVIOLET RADIATION MEASUREMENTS
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Table 1-6. INSTANTANEOUS OUTGOING 300- TO 380-nm RADIATION
MEASURED FROM AIRCRAFT
(w/m2)
Elevation, thousands of feet
Time
interval
(1ST)
Oct6
0830-0930
1030-1130
1230-1330
1430-1530
Oct 12
0800-0900
1000-1100
1200-1300
1400-1500
Oct 16
0800-0900
1000-1100
1200-1300
1400-1500
Oct 18
0800-0900
1000-1100
1200-1300
1400-1500
Oct 20
0800-0900
1000-1100
1200-1300
1400-1500
1.0-1.5
4.09
4.45
2.14
3.56
4.63
5.52
4.18
1.78
2.49
2.31
1.42
2.67
2.85
3.12
1.50
1.78
2.94
2.49
1.96
1.6-2.0
4.45
5.34
5.60
2.49
4.27
5.70
6.23
5.34
1.96
2.67
2.85
1.96
3.20
3.92
4.45
2.14
2.31
3.03
2.6-3.0
5.07
6.94
6.74
4.19
5.52
7.12
7.20
5.60
2.49
3.12
3.38
2.31
3.20
4.45
6.23
4.27
2.58
3.92
3.92
3.03
3.6-4.0
5.34
7.30
5.34
5.34
7.48
7.83
6.05
2.67
3.92
3.92
3.03
3.56
5.16
6.76
5.70
3.03
4.45
4.81
4.09
4.6-5.0
5.87
8.19
7.48
5.70
5.70
8.28
7.95
6.76
2.84
4.27
4.45
3.56
3.92
5.43
7.83
6.23
3.03
4.09
5.6-6.0
5.87
8.54
8.01
5.70
5.34
8.19
8.54
6.94
2.94
4.63
4.81
3.92
3.83
5.70
8.10
6.76
3.21
5.16
5.43
5.16
6.1-6.5
5.70
8.54
6.06
Table 1-7. ELEVATION OF THE TOP OF THE INVERSION LAYER NEAREST GROUND
LEVEL (feet)
Time
Interval
(TST)
0830-0930
1030-1130
1230-1330
1430-1530
0800-0900
1000-1100
1200-1300
1400-1500
Oct 6
3,150
3,000
2,900
2,500
Oct 12 Oct 16
3,000
2,000
2,500 2,000
2,000
Oct 18 Oct 20
1,300°
2,900b
c
d
Inversion bottom of second layer at 4,000 feet.
Inversion bottom of second layer at 4,500 feet.
Second inversion layer bottom at 4,000 feet and top at 5,000 feet.
Second inversion layer bottom at 3,000 feet and top at 4,000 feet.
Filter Photocell
13
-------
QUARTZ HEMISPHERE
QUARTZ DIFFUSER
.SEALED (CEMENTED)
O-RING SEAL
OR SUBDIVIDED
SPECTRALLY
DESICCATOR CONTAINER
VOLTAGE-DROPPING
CIRCUIT
(SELENIUM WITH
QUARTZ ENVELOPE)
u
O-RING SEAL
(3) LEVELING SCREWS
EWS kJ
Figure 1-1. Eppley filter-photocel I UV sensor.
14
ULTRAVIOLET RADIATION MEASUREMENTS
-------
t-
t 0.20
3
TOTAL UV/
LOWUV
HIGH UV
290 300 310 320 330 340 350 360 370 380
WAVELENGTH, m/u
Figure 1-2. Spectral transmission of the interference filters in Eppley sensors.
250 300 350 400 450 500 550 600 650 700
WAVELENGTH, ny*.
Figure 1-3. Relative spectral response of the selenium photocell in the
Eppley UV sensors.
~iI i I I I I 1 1 1 T
SUN (NEW MEXICO : AIRMASS=1)
uj 1.5
—I'
TUNGSTEN STANDARD LAMP
I I I I I I I
Figure
290 300 310 320 330 340 350 360 370 380 390 400
WAVELENGTH, m/u
1-4. Relative spectral emissions of the standard tungsten lamp and
of the sun for air mass 1.
Filter Photocell
15
-------
4.5
4.0 —
3.5 —
3.0
2.5
1.5 —
1.0 —
0.5 —
o OCT 6 M-H
OCT 12 L-M
x OCT 16 N
0500 0600 0700 0800 0900 1000 1100 1200 1300 1400 1500 1600 1700
Figure 1-5. Average incoming 315- to 330-nm radiation for 30-minute intervals, as function of
time of day on various days of smog in downtown Los.Angeles.
XN I I I I
0500 0600 0700 0800 0900 1000 1100 1200 1300 1400 1500 1600 1700
1800
16
Figure 1-6. Average incoming 357- to 372-nm radiation for 30-minute intervals, as function of
time of day on various days of smog in downtown Los Angeles
ULTRAVIOLET RADIATION MEASUREMENTS
-------
0500 0600 0700 0800 0900 1000 1100 1200 1300 1400 1500 1600 1700 1800
TRUE SOLAR TIME, hour
Figure 1-7. Average incoming 300- to 380-nm radiation for 30-minute intervals, as function of
time of day on various days of smog in downtown Los Angeles.
TST, hour
x—X 1030-1130
.01230-1330-
A1430-1530
i
O 0830-0930
2 345
ELEVATION, thousands of feet
Figure 1-8. Outgoing 300- to 380-nm radiation as function of elevation over Los Angeles at
different times of day, October 6 (M-H Smog).
Filter Photocell
17
-------
2 3
ELEVATION, thousands of feet
Figure 1-9. 300- to 380-nm radiation as function of elevation over Los Angeles
for different times of day, October 16 (no smog).
"1 1 T
ELEVATION, feet
a
<
8
CO
O
-z.
O
0
0800
1100 1200 1300
TRUE SOLAR TIME, hour
Figure 1-10. Outgoing 300- to 380-nm radiation as function of time of day for
various elevations over Los Angeles, October 6 (M-H Smog).
18
ULTRAVIOLET RADIATION MEASUREMENTS
-------
10.0
o
Q
<
O
f-
8.0 —
.6.0 —
4.0
I 2'°
I I I
ELEVATION, feel
5,600-6,000 —
4,600-5,000
3,600-4,000
2,600-3,000
1,600-2,000"
1,100-1,500
_L
_L
_L
0800
0900
1100 1200 1300
TRUE SOLAR TIME, hour
1400
1500
Figure 1-11. Outgoing 300- to 380-nm radiation as function of time of day for
various elevations over Los Angeles, October 16 (no smog).
Filter Photocell
19
-------
10
OCT. 16, 1965
1430-1530
1230-1330
1030-1130
0830-0930
OCT. 6, 1965
1400-1500
1200-1300
1000-1100
0800-0900
20
30 5
TEMPERATURE, °C
15
Figure 1-12. Temperature profiles at Los Angeles.
20
ULTRAVIOLET RADIATION MEASUREMENTS
-------
National Bureau of Standards
2: FILTER-PHOTOTUBE MEASUREMENTS*
Ralph Stair
Meteorology Division
National Bureau of Standards
John S. Nader
National Center for Air Pollution Control
INTRODUCTION
The literature of the past 50 years contains many data on the total
solar irradiances at various locations and different seasons of the year.
These data have usually been obtained with some type of pyrheliometer
in the form of a blackened horizontal receiver housed in a glass envelope.
As a result, the short-wave ultraviolet and long-wave infrared are not
included in the measurements (1). Furthermore, the uncertainty in the
measurements has been of the order of a few percent a magnitude
approximating that of the total ultraviolet irradiance. Hence, the great
amount of available data gives little information concerning the solar
ultraviolet irradiance present in any locality. Only in those researches
wherein special equipment has been employed are any quantitative
ultraviolet data available. Measurements of this type have usually
been made at high altitudes or in locations having relatively unpolluted
atmospheres. Since the primary purpose of this investigation was to
evaluate the available solar ultraviolet irradiation in both a polluted
area and a nearby area relatively free of pollution, special instrumenta-
tion and techniques were required.
INSTRUMENTATION AND METHOD
There is considerable interest in photochemical processes to which
gaseous and particulate material in the atmosphere are subjected. Al-
though these processes are directly related to absorption of radiation
incident from any direction (a volume effect), it is to be noted that our
instrumentation set up in downtown Los Angeles and on Mt. Wilson
measures the solar ultraviolet irradiance (at selected wavelengths) on
a horizontal surface. For best results, this measurement requires the
use of a detector having sensitivity over its surface in accordance with
the cosine law for all angles from 0 degree (the horizon) to 90 degrees
* This section is based on original data collected by the National Bureau of Standards for work
sponsored by the U. S. Public Health Service.
Filter Phototube 21
-------
(the zenith). Hence, equipment of special design was required and was
built.to separate narrow spectral bands and at the same time not upset
the cosine-law response for angular elevation of source (the sun and
sky).
Figure 2-1 is a layout diagram of the photoelectric equipment
assembled for this work. The solar irradiance (sun and sky) was
collected in an integrating sphere, which was coated with a thick layer
of BaSC>4. The entrance and exit ports were each 1/2 inch in diameter;
the sphere, 4 inches. The entrance port was fashioned with a "knife-
edge" opening, which was in the plane of the topmost section of the box
and was adjusted precisely to a horizontal position. The exit opening
was placed to the east or west, (so that at no time did direct sunlight or
the sun's primary reflection fall directly into its view) and was covered
by a shield and Corning filter 9863 having high opacity within the visi-
ble spectral region.
A filter wheel carrying nine narrow-band and one wide-band inter-
ference filter and two blanks (zero transmittance) was set about 6 inches
from the sphere exit port so that a narrow beam of ultraviolet flux
passed (nearly perpendicular) through each of the filters onto a type
RCA-935 phototube as the filter wheel was step-rotated by a synchronous
motor and geneva-drive mechanism. In this manner each filter and each
blank (zero transmittance) was set in position for a period of about 10
seconds (enough time for the pico-ammeter and recorder to register a
definite value on a strip chart). Thus the magnitude of each spectral
irradiance was registered once in each interval of approximately 2
minutes (about 30 times per hour). For purposes of calibration at
intervals during each day a 1,000-watt quartz iodine lamp, standard
of spectral irradiance mounted in a special carriage to eliminate all
sun and sky irradiance was placed above the integrating sphere (at a
measured distance) and the output through the 10 filters was recorded
over a period of several minutes (two to three rotations of the filter
disk).
The spectral transmittances of each of the nine narrow-band inter-
ference filters used at Mt. Wilson are depicted in Figure 2-2 and of the
wide-band in Figure 2-3. Each narrow-band filter has a half-band width
of approximately 10 nm, and its centroid is situated near even 10-nm
intervals from 310 to 390 nm.
Table 2-1 lists (in column 2) the relative responses of the RCA
type 935 phototube (No. 5) when irradiated by a 1,000-watt quartz-iodine
lamp standard of spectral irradiance No. 131 through Corning filter
9863 and each interference filter in turn, (in column 3) the wavelength
centroid under these same conditions and (in column 4), as an example,
the correction that should be applied when the spectral energy distri-
bution of the irradiating source is that of the sun as determined at
Sacramento Peak, New Mexico (2), for air mass 1.0 rather than that of
lamp standard No. 131. The spectral data on these sources, this detec-
tor, and Corning filter 9863 'are also included in Figure 2-2. Because
22 ULTRAVIOLET RADIATION MEASUREMENTS
-------
corrections as listed in column 4 of Table 2-1 are smaller than the
uncertainties in this type of measurement, they were not applied in com-
puting the values reported in the results of -this report. Other small
corrections that are worthy of note but are neglected in this report
arise from the following considerations: (1) the data herein reported
in detail apply to the Mt. Wilson instrumentation, a "duplicate" of
which, with filters cut from the same stock, was set up and operated
in downtown Los Angeles; the differences between the instruments are
considered to be minor; (2) an additional correction of approximately
1 percent could be applied to cover loss of sky irradiance passing dir-
ectly through the two sphere openings and missing the detector entirely
(see Figure 2-1); however, a nearly equal but opposite error occurs
for sky irradiance reflected on first reflection from the sphere wall
directly onto the detector. (Note that all of the flux from the quartz-
iodine standard and nearly all of the sky flux is multiply reflected in
the sphere before it is incident on the detector.)
The instrumentation required little attention since all operations,
except setting up and operating the standard lamp for calibration, were
automated. The usual service consisted of keeping the quartz hemi-
sphere cover clean, keeping the recorder pen cleaned and filled, and
recording time indications and other pertinent weather and air pollution
information on the recorder strip chart or an associated notebook.
Column 2 of Table 2-1 shows differences of a factor of more than
10 between the highest and lowest integrated instrumental reading at
one total irradiance. A similar variation, nearly tenfold, occurred be-
tween the early morning (or late afternoon) readings and those obtained
near the noon hour. Since it is impractical to change instrumental
sensitivity either between the interposition of filters or during the day,
another method was employed to keep all data on a reasonable chart
scale. This method consisted of placing (permanently) perforated
metal screens (of various transmittances) over most of the filters so
that in all cases the short-wave spectral regions produced readable
deflections while the other spectral regions produced deflections not
exceeding the chart limits or the fatigue level for the phototube. The
transmittance values for these screens were not required and have not
been obtained in reduction of the data.
RESULTS
Ultraviolet spectral solar and sky irradiance on a horizontal sur-
face were made daily over a period of about 1 month between about
September 20 and October 20, 1965, at Mt. Wilson and downtown Los
Angeles. This report summarizes the data obtained during the 5
flight days with the instrumentation described above. The data obtained
with the narrow-band interference filters are summarized in Tables
2-2, a-i, for Mt. Wilson and for downtown Los Angeles. These data are
plotted in Figures 2-4 to 2-7 for only the 2 days involving the extreme
smog conditions, i.e., no smog (October 16) and moderate-to-heavy
smog (October 6).
Filter Phototube 23
-------
The summation of energy values for the narrow-band filters in the
range from 300 to 380 nm, to give another measure of the wide-band
energy in this range, was calculated from the narrow-band filter
measurements as follows:
The energy for the narrow-band filters 310 through 370 nm was
summed directly, and one-half of the energy value for the 380-nm filter
was added together with an extrapolated value for the energy in the range
from 300 to 305 nm. This latter value is calculated as 1/8 of the energy
for the 310-nm filter. The two sets of data for the spectral region from
300 to 380 nm are given in Table 2-3 and 2-4; results for the wide-band
filter are shown graphically in Figures 2-8 and 2-9 for Mt. Wilson and
downtown Los Angeles, respectively.
Note that precise values of spectral response of the particular
phototube (set up at Mt. Wilson) as well as of the spectral irradiance
of the NBS standard lamp and of the spectral transmittance of the wide-
band filters used at that station were used in reducing the measure-
ments made on Mt. Wilson with the wide-band filters. Under these con-
ditions the two sets of data for the spectral region of 300 to 380 nm
agree within about 1 percent, which may be considered unexpectedly good
considering that a solar curve for M = 1 for Sacramento Peak, New
Mexico, was used as a basis (rather than the true curve) for reducing
the measurements with the wide-band filter.
Wider disagreement (2.5 to 3.0%) occurs in data from the downtown
Los Angeles measurements for the wide-band spectral region of 300 to
380 nm. Possibly wider divergencies exist between the true and the
solar curve (M = 1.0 for Sacramento Peak) employed. Or the greater
discrepancy results because of our assumption that relative spectral re-
sponses of the two phototubes were the same. A difference of 2.5 to
3.0 percent is small, but since all measurements fall within the range
of 2.5 to 3.0 percent, the indication is that the error is related to some
of the basic factors common to all the measurements. Possibly the
wide-band filter transmittance was significantly different at Los Angeles
from what it was when measured after the work in the field. We know
that all the interference filters used in this work solarized significantly
during the investigation; however, since lamps were calibrated at least
twice daily, any error resulting because of filter solarization is con-
sidered insignificant except possibly for the wide-band unit.
ACKNOWLEDGMENT
Development of the instrumentation used in this investigation was
sponsored jointly by the United States Public Health Service and the
National Aeronautics and Space Administration. Operation of the
field equipment and collection of data were conducted with the help
of Messrs. William R. Waters and John K. Jackson of NBS. Reduction
of data and calculation of results were done with the help of Thomas
A. Ante of the Public Health Service.
24 ULTRAVIOLET RADIATION MEASUREMENTS
-------
MISCELLANEOUS NOTES ON WEATHER AND SMOG
October 6 Sky clear on Mt. Wilson during most of the day but with
very slight haze. Little or no wind at both stations. Smog layer
appearing early over basin. Overcast and smoggy in downtown Los
Angeles all day. Some clouds on Mt. Wilson after 2:00 p.m. A very
smoggy day.
October 12 Sky very clear on Mt. Wilson in early morning. Thin layer
of reddish-brown smog present at about 1,000 feet below Mt. Wilson
station. No wind. By 2:30 p.m. smog layer reached Mt. Wilson station.
Ozone meter responds to incoming oxidants. Downtown overcast all
day. Intermediate smog.
October 16 Sky clear on Mt. Wilson all day. Good visibility downtown.
Northwest wind at both stations, about 30 mph on Mt. Wilson. A clear
and windy day. Little smog.
October 18 - Sky clear on Mt. Wilson all day. Light haze and smog
over basin. Little or no wind at both stations. A relatively clear and
calm day.
October 20 Sky clear on Mt. Wilson all day except for a few thin
scattered clouds in afternoon. Some cloudiness and haze over basin
all day. Little or no wind at either station. Light to moderate smog in
downtown Los Angeles.
REFERENCES
1. IGY Instruction Manual, Part VI, Radiation Instruments and
Measurement. Pergamon Press, New York, N. Y. (1958).
(The glass envelope of pyrheliometers is opaque to the infrared
of wavelengths longer than about 4 microns and to some of the
ultraviolet; new instruments have higher transmittances at 300
nm.)
2. Stair, R., and R. G. Johnston. Preliminary Spectroradiometric
Measurements of the Solar Constant. J. Research Nat. Bur.
Standards. 57: 205 (1956).
Filter Phototube 25
-------
Table 2-1. FILTER PHOTOTUBE DATA
Interference
filter
310 nm
320
330
340
350
360
370
380
390
Relative response
of the comb ined
lamp and
detection system
1,172
3,345
4,663
5,145
9,759
12,500
10,539
8,805
7,609
Wavelength
centroid,
nm
309.42
322.29
331 .58
340.65
352.70
360.22
371.80
381.33
392.10
Correction for
measuring solar
irradiance, percent
(air mass 1 .0)
+ 2.9
-3.0
+ 1.4
+ 0.8
+ 3.2
+ 0.2
+ 2.5
+ 1.9
-2.7
Table 2-2A. AVERAGE INCOMING 305- TO 315-nm RADIATION FOR 30-MINUTE INTERVALS
(w/m2)
Midpoint
of time
interval
(1ST)
0715
0745
0815
0845
0915
0945
1015
1045
ins
1145
1215
1245
1315
1345
1415
1445
1515
1545
Oct
6
0.055
0.168
0.281
0.490
0.683
0.924
1.22
1.36
1.40
1.44
1 48
1.44
1.31
1.04
0.950
0.580
0.439
0.246
Mt
Oct
12
0.103
0.236
0.422
0.630
0.873
1.060
1.22
1.30
1.39
1.40
1.38
1.20
1.07
0.897
0.672
0.455
0.247
Wilson
Oct
16
0.117
0.234
0.427
0.616
0.860
0.985
1.11
1.23
1.17
1.29
1.19
1.12
1.02
0.833
0.599
0.404
0.245
Oct
18
0.248
0.361
0.402
0.589
0.824
0.941
1.08
1.18
1.22
1.18
1.13
1.01
0.865
0.710
0.512
0.507
0.231
Oct
20
0.132
0.748
0.406
0.599
0.784
0.971
1.08
1.24
1.20
1.21
1.10
0.966
0.822
0.800
0.467
0.510
.0.231
Oct
6
0.045
0.090
0.165
0.235
0.343
0.410
0.464
0.497
0.672
0.784
0.855
0.861
0.816
0.644
0.596
0.436
0.294
0.191
Downtown Los
Oct Oct
12 16
0.102
0.153
0.170
0.228
0.325
0.438
0.547
0.629
0.633
0.698
0.750
0.705
0.657
0.535
0.417
0.315
0.185
0.038
0.121
0.214
0.317
0.455
0.614
0.772
0.802
0.914
0.933
0.903
0.887
0.829
0.721
0.602
0.436
0.295
0.158
Angeles
Oct
18
0.151
0.133
0.154
0.223
0.385
0.533
0.661
0.749
0.765
0.691
0.596
0.518
0.516
0.453
0.354
0.298
0.214
0.174
Oct
20
0.170
0.182
0.277
0.420
0.537
0.622
0.696
0.812
0.916
0.899
0.781
0.668
0.554
0.451
0.338
0.225
0.135
26
ULTRAVIOLET RADIATION MEASUREMENTS
-------
Table 2-2B. AVERAGE INCOMING 315- TO 325-nm RADIATION FOR 30-MINUTE INTERVALS
(w/m2)
Midpoint
of time
interval
(TST)
0715
0745
0815
0845
0915
0945
1015
1045
1115
1145
1215
1245
1315
1345
1415
1445
1515
1545
Oct
6
0.408
0.789
1.24
1.70
2.17
2.45
2.87
3.26
3.47
3.50
3.53
3.50
3.31
2.58
2.66
1.77
1.68
1.23
Mt. Wilson Downtown Los Angeles
Oct Oct Oct Oct Oct Oct Oct Oct Oct
12 16 18 20 6 12 16 18 20
0.274 0.256 0.517
0.685 0.627 0.684 0.616 0.479 0.353 0.465 0.471 0.485
1.12 1.03 1.06 1.11 0.702 0.491 0.830 0.738 0.805
1.57 1.48 1.44 1.43 0.930 0.638 1.21 0.978 1.12
2.02 1.93 1.88 1.87 1.19 0.745 1.56 1.33 1.45
2.23 2.08 2.29 2.27 1.18 1.00 1.92 1.66 1.73
2.71 2.57 2.63 2.62 1.29 1.25 2.22 1.98 1.90
3.11 2.96 2.89 2.88 1.37 1.52 '2.44 2.15 2.03
3.29 3.16 3.05 3.07 1.82 1.70 2.63 2.17 2.33
3.37 3.21 3.14 3.07 2.10 1.74 2.65 1.98 2.54
3.42 3.21 3.09 3.06 2.25 1.89 2.55 1.71 2.49
3.37 3.16 3.04 2.93 2.28 2.06 2.54 1.54 2.26
3.15 2.99 2.83 2.71 2.17 1.98 2.43 1.57 2.02
2.63 2.43 2.58 2.37 1.77 1.91 2.20 1.41 1.75
2.40 2.26 2.21 2.01 1.70 1.67 1.89 1.23 1.50
2.13 1.94 1.82 1.60 1.38 1.37 1.55 1.13 1.25
1.65 1.49 1.46 1.19 1.04 0.991 1.20 0.913 0.952
1.19 1.04 0.944 0.841 0.827 0.732 0.663 0.590 1.10
Table 2-2C. AVERAGE INCOMING 325- TO 335-nm RADIATION FOR 30-MINUTE INTERVALS
(w/m2)
Midpoint
of time
interval
(TST)
0715
0745
0815
0845
0915
0945
1015
1045
1115
1145
1215
1245
1315
1345
1415
1445
1515
1545
Oct
6
0.864
1.49
2.19
2.92
3.59
3.97
4.58
5.21
5.50
5.53
5.61
5.55
5.29
4.13
4.29
2.92
2.88
2.18
Oct
12
1.35
2.02
2.72
3.41
3.64
4.40
5.03
5.30
5.39
5.47
5.41
5.10
4.23
3.94
3.59
2.85
2.13
Mt. Wilson
Oct
16
1.27
1.92
2.61
3.29
3.39
4.23
4.84
5.13
5.20
5.19
5.11
4.89
3.92
3.75
3.33
2.64
1.94
Oct
18
1.21
1.91
2.55
3.22
3.85
4.36
4.72
4.97
5.09
5.05
4.94
4.66
4.29
3.75
3.14
2.48
1.73
Oct
20
1.22
1.84
2.52
3.20
3.80
4.33
4.73
'j 01
5.01
4.97
4.79
4.09
3.96
3.38
2.78
2.18
1.53
Oct
6
0.552
0.877
1.24
1.57
1.97
1.91
2.08
2.20
2.92
3.35
3.58
3.64
3.48
2.84
2.78
2.28
1.73
1.44
Downtown Los
Oct Oct
12 16
0.619
0.907
1.08
1.28
1.62
2.03
2.41
2.70
2.74
3.00
3.27
3.42
3.07
2.72
2.24
1.63
1.26
0.545
0.817
1.47
2.07
2.63
3.16
3.60
3.90
4.18
4.18
4.03
4.03
3.87
3.53
3.09
2.58
2.05
1.15
Angeles
Oct
18
1.04
0.855
1.31
1.67
2.04
2.70
3.19
3.42
3.43
2.99
2.73
2.48
2.55
2.29
2.01
1.89
1.57
1.10
Oct
20
0.816
1.41
1.91
2.38
2.80
3.05
3.20
3.65
3.97
3.87
3.54
3.20
2.59
2.44
2.06
1.61
1.52
Filter Phototube
27
-------
Table 2-2D. AVERAGE INCOMING 335- TO 345-nm RADIATION FOR 30-MINUTE INTERVALS
(w/m2)
Midpoint
of time
interval
(TST)
0715
0745
0815
0845
0915
0945
1015
1045
1115
1145
1215
1245
1315
1345
1415
1445
1515
1545
Oct
6
1.02
1.70
2.44
3.17
3.89
4.29
4.93
5.55
5.82
5.84
5.91
5.88
5.61
4.44
4.64
3.11
3.14
2.39
Mt. Wilson Downtown Los Angeles
Oct Oct Oct Oct Oct Oct Oct Oct Oct
12 16 18 20 6 12 16 18 20
0.690 0.672 1.28
1.52 1.53 1.53 1.42 0.992 0.749 1.03 1.02 0.989
2.22 2.23 2.22 2.25 1.36 1.04 1.70 1.50 1.61
2.94 2.97 2.85 2.79 1.71 1.19 2.37 1.87 2.14
3.64 3.68 3.55 3.50 2.11 1.43 2.94 2.45 2.64
3.94 3.85 4.18 4.10 2.05 1.77 3.51 3.00 3.07
4.67 4.68 4.68 4.64 2.21 2.18 3.93 3.51 3.31
5.30 5.29 5.03 5.05 2.34 2.61 4.29 3.73 3.45
5.54 5.60 5.28 5.32 3.12 2.91 4.58 3.73 3.94
5.63 5.65 5.39 5.31 3.57 2.96 4.57 3.41 4.26
5.72 5.64 5.36 5.27 3.54 3.25 4.41 2.95 4.16
5.68 5.56 5.26 5.08 3.86 3.55 4.40 2.72 3.82
5.36 5.30 4.98 4.74 3.72 3.43 4.23 2.80 3.52
4.54 4.37 4.60 4.22 3.06 3.32 3.88 2.52 2.79
4.22 4.15 4.05 3.62 3.01 2.95 3.47 2.22 2.64
3.82 3.68 3.41 3.02 2.44 2.45 2.86 2.11 2.24
3.06 2.95 2.81 2.50 1.88 1.81 2.15 1.76 1.76
2.31 2.21 1.97 1.73 1.57 1.41 1.32 1.27 1.78
Table 2-2E. AVERAGE INCOMING 345- TO 335-nm RADIATION FOR 30- MINUTE INTERVALS
(w/m2)
Midpoint
of time
i nterva 1
(TST)
0715
0745
0815
0845
0915
0945
1015
1045
1115
1145
1215
1245
1315
1345
1415
1445
1515
1545
Oct
6
1.04
1.72
2.47
3.21
3.94
4.39
5.03
5.59
5.86
5.86
5.97
5.92
5.68
4.65
4.75
3.24
3.18
2.44
Mt. Wilson Downtown Los Angeles
Oct Oct Oct Oct Oct Oct Oct Oct Oct
12 16 18 20 6 12 16 18 20
0.674 0.729 1.41
1.56 1.51 1.62 1.43 1.05 0.827 1.12 1.11 1.13
2.27 2.20 2.27 2.32 1.44 1.05 1.83 1.60 1.74
3.00 2.93 2.87 2.84 1.81 1.26 2.54 2.00 2.31
3.70 3.84 3.58 3.56 2.23 1.52 3.16 2.62 2.84
4.18 3.97 4.20 4.17 2.19 1.85 3.75 3.22 3.30
4.79 4.69 4.71 4.71 2.36 2.32 4.20 3.77 3.55
5.36 5.25 5.06 5.12 2.51 2.77 4.58 3.98 3.78
5.61 5.55 5.30 5.39 3.36 3.11 4.89 3.98 4.28
5.68 5.58 5.40 5.38 3.82 3.16 4.87 3.65 4.60
5.78 5.59 5.36 5.34 4.10 3.48 4.69 3.19 4.49
5.74 5.52 5.28 5.15 4.12 3.79 4.68 2.97 4.14
5.43 5.26 5.02 4.82 3.96 3.68 4.49 3.07 3.79
4.69 4.49 4.66 4.32 3.11 3.55 4.13 2.72 3.05
4.34 4.17 4.11 3.69 3.21 3.15 3.63 2.39 2.90
3.87 3.64 3.47 3.10 2.59 2.61 3.05 2.28 2.43
3.12 2.94 2.97 2.73 1.99 1.96 2.31 1.90 1.90
2.36 2.22 2.06 1.83 1.68 1.51 1.45 1.39 1.36
28
ULTRAVIOLET RADIATION MEASUREMENTS
-------
Table 2-2F. AVERAGE INCOMING 355- TO 365-nm RADIATION FOR 30-MINUTE INTERVALS
(w/m2)
Midpoint
of time
interval
(1ST)
0715
0745
0815
0845
0915
0945
1015
1045
1115
1145
1215
1245
1315
1345
1415
1445
1515
1545
Oct
6
1.04
1.73
2.51
3.30
4.03
4.56
5.20
5.72
6.00
6.00
6.11
6.08
5.80
4.90
4.95
3.17
3.25
2.47
Oct
12
1.58
2.31
3.07
3.80
4.27
4.97
5.49
5.78
5.85
5.95
5.91
5.57
4.90
4.48
3.95
3.17
2.38
Mt. Wilson
Oct
16
1.57
2.30
3.07
3.83
4.28
4.97
5.52
5.83
5.85
5.87
5.79
5.53
4.87
4.44
3.82
3.04
2.27
Oct
18
1.79
2.42
2.98
3.71
4.36
4.88
5.26
5.51
5.63
5.56
5.48
5.18
4.82
4.22
3.57
3.15
2.14
Oct
20
1.49
2.63
2.94
3.64
4.33
4.88
5.31
5.60
5.56
5.54
5.34
4.98
4.45
3.85
3.20
2.99
1.92
Oct
6
0.700
1.07
1.47
1.85
2.27
2.24
2.44
2.60
3.50
3.97
4.24
4.25
4.09
3.24
3.49
2.63
2.05
1.72
Downtown Los
Oct Oct
12 16
0.894
1.12
1.31
1.57
1.92
2.42
2.88
3.22
3.27
3.62
3.94
3.82
3.67
3.24
2.69
2.06
1.56
0.747
1.21
1.94
2.64
3.27
3.92
4.45
4.79
5.11
5.08
4.89
4.88
4.69
4.29
3.78
3.16
2.41
1.54
Angeles
Oct
18
1.72
1.20
1.68
2.09
2.75
3.38
3.95
4.26
4.18
3.81
3.34
3.16
3.26
2.85
2.51
2.38
1.93
1.47
Oct
20
1.29
1.84
2.36
2.99
3.49
3.72
3.91
4.54
4.71
4.77
4.39
4.03
3.23
3.07
2.56
2.00
1.46
Table 2-2G. AVERAGE INCOMING365- TO 375-nm RADIATION FOR 30-MINUTE INTERVALS
(w/m2)
Midpoint
of time
interval
(TST)
0715
0745
0815
0845
0915
0945
1015
1045
1115
1145
1215
1245
1315
1345
1415
1445
1515
1545
Oct
6
1.21
2.01
2.90
3.76
4.60
5.22
5.95
6.49
6.80
6.80
6.89
6.86
6.56
5.54
5.62
3.56
3.71
2.78
Oct
12
1.84
2.67
3.55
4.37
4.97
5.73
6.29
6.60
6.65
6.78
6.74
6.36
5.69
5.16
4.54
3.64
2.75
Mt. Wilson
Oct
16
1.77
2.61
3.50
4.34
4.90
5.60
6.15
6.49
6.49
6.52
6.45
6.16
5.53
5.02
4.31
3.46
2.59
Oct
18
2.09
2.79
3.39
4.22
4.94
5.51
5.93
6.20
6.30
6.24
6.18
5.84
5.43
4.79
4.04
3.68
2.74
Oct
20
1.69
3.22
3.34
4.17
4.89
5.50
5.97
6.27
6.22
6.21
5.99
5.58
5.03
4.36
3.63
3.52
2.21
Oct
6
0.828
1.26
1.72
2.18
2 68
2.65
2.88
3.09
4.16
4.70
4.99
5.00
4.82
3.85
4.18
3.14
2.39
2.02
Downt
Oct
12
1.05
1.32
1.53
1.83
2.24
2.81
3.36
3.68
3.83
4.24
4.62
4.45
4.26
3.77
3.14
2.41
1.82
own Los
Oct
16
0.866
1.43
2.26
3.08
3.81
4.57
5.08
5.51
5.89
5.84
5.62
5.61
5.41
5.03
4.36
3.65
111
1.80
Angeles
Oct
18
1.98
1.38
1.94
2.41
3.18
3.89
4.54
4.79
4.79
4.39
3.84
3.65
3.79
3.40
2.90
2.75
2.29
1.72
Oct
20
1.47
2.12
2.75
3.37
3.97
4.18
4.44
5.09
5.48
5.43
4.93
4.54
3.68
3.47
2.92
2.24
1.64
Filter Phototube
29
-------
Table 2-2H. AVERAGE INCOMING 375- TO 385-nm RADIATION FOR 30-MINUTE INTERVALS
(w/m2)
Midpoint
of time
inferva 1
(1ST)
0715
0745
0815
0845
0915
0945
1015
1045
1115
1145
1215
1245
1315
1345
1415
1445
1515
1545
Oct
6
1.22
2.05
2.95
3.81
4.65
5.36
6.11
6.59
6.84
6.84
6.96
6.93
6.65
5.75
5.86
3.52
3 77
2.84
Oct
12
1.82
2.66
3.52
4.33
5.17
5.78
6.23
6.54
6.55
6.69
6.68
6.31
5 86
5.21
4 52
362
2.72
Mt. Wilson
Oct
16
1.77
2.59
3.44
4.26
5.14
5.65
6.08
6.41
6.39
6.43
6.37
6.07
5.76
5.04
4.25
3.44
2.57
Oct
18
2.27
2 88
3.38
4.18
4.90
5.48
5.88
6.15
6.24
6.17
6.12
5.80
5.40
4.76
4.02
3.85
2.56
Oct
20
1.68
3.33
3.32
4.15
4.87
5.48
5.94
6.24
6.18
6.17
5.96
5.55
5.01
4.31
3.61
3.81
2.30
Oct
6
0.809
1.23
1.69
2.13
2.64
2.67
2.87
3.09
4.23
428
4.91
4.93
4.75
3.88
4.18
3.04
2.34
1.98
Downtown Los
Oct Oct
12 16
1.09
1.34
1.50
1.79
2.19
2.77
3.30
3.70
3.78
4.18
4.54
4.37
4.19
3.69
3.06
2.39
1.80
0.848
1.46
2.23
3.02
3.74
4.44
4.94
5.37
5.73
5.67
5.49
5.47
5.27
4.82
4.19
3.56
2.72
1.83
Angeles
Oct
18
1 95
1.36
1.89
2.36
3.11
3.82
4.42
4.67
4.68
4.36
3.78
3.61
3.74
3.26
2.84
2.69
2.23
1.72
Oct
20
1.60
2.06
2.72
3.35
3.89
4.15
4.32
5.03
5.38
5.25
4.86
4.48
3.60
3.43
2.83
2.19
1.65
Table 2-21. AVERAGE INCOMING 385- TO 395-nm RADIATION FOR 30-MINUTE INTERVALS
(w/m2)
Midpoint
of time
interval
(TST)
0715
0745
0815
0845
0915
0945
1015
1045
1115
1145
1215
1245
1315
1345
1415
1445
1515
1545
Oct
6
1.25
2.11
3.05
3.95
4.79
5.64
6 38
6 74
6 99
7.01
7.14
7.10
6.80
6.05
6.11
3.46
3.86
Mt. Wilson Downtown Los Angeles
Oct Oct Oct Oct Oct Oct Oct Oct Oct
12 16 18 20 6 12 16 18 20
0.819 0.856 2.11
1,89 1.84 2.53 1 72 1.26 1 16 1.55 1.42 1.76
2.77 2.71 3.10 3.83 1.71 1.41 2.28 1.94 2.11
3.64 3.62 3.50 3.43 2.16 1.51 3.06 2.40 2.78
449 4.49 4.34 4.28 2.67 1.80 3.78 3.16 3.39
5.51 5.66 5.09 5.44 2.77 2 22 4.47 3.89 3.93
6 07 5.99 5.63 5.61 2.84 2.81 4.94 4.47 4.16
640 6.35 6.02 6.09 3.16 3.35 538 4.71 4.34
6.69 6 69 6 31 6.39 4.24 3 74 5.77 4.72 5.40
6 73 6 66 6.39 6.30 4.39 3.80 5.69 4.34 5.40
6.87 6.71 636 6.27 4.99 421 5.50 3.85 5.28
6.88 6.64 626 6.08 499 d.55 5.47 3.72 488
6.48 633 5.96 5.66 4.82 4.38 5.27 3.83 4.51
623 6.25 5.56 5.11 3.98 4.20 4.81 3.32 3.63
5.46 5 36 4 88 4.46 4.28 3.71 4.26 2.91 3.47
467 4.42 412 3.68 308 2.48 3.59 2.75 2.85
3.71 3.56 4.15 4.19 2.39 2.48 2.76 228 222
2.81 2.67 2.69 2.02 1.84 1.90 1 81 1 71
30
ULTRAVIOLET RADIATION MEASUREMENTS
-------
Table 2-3. AVERAGE INCOMING 300- TO 380-nm RADIATION FOR 30-MINUTE INTERVALS,
WIDE-BAND FILTER
(w/m2)
Midpoint
of time
interval
(1ST)
0715
0745
0815
0845
0915
0945
1015
1045
1115
1145
1215
1245
1315
1345
1415
1445
1515
1545
Oct
6
6.47
10.9
15.8
20.7
24.4
28.1
32.5
36.7
37.9
38.1
38.7
38.3
36.6
29.0
30.4
19.6
19.9
15.1
Oct
12
9.80
14.4
19.1
23.7
26.1
30.9
34.6
36.3
36.7
37.5
37.0
34.8
29.9
27.4
24.5
19.5
14.7
Mt. Wils
Oct
16
9.46
14.0
18.7
23.3
25.1
30.2
33.9
35.8
36.0
36.1
35.5
33.8
29.2
26.5
23.0
18.5
13.6
on
Oct
18
10.2
14.5
18.3
22.8
27.0
30.3
32.6
34.4
35.0
34.7
34.0
32.0
30.0
26.0
21.8
18.5
12 5
Oct
20
9.08
14.5
18.1
22.8
26.8
30.3
33.0
34.8
34.6
34.4
33.1
30.7
27.4
23.4
19.3
17.1
11.3
Oct
6
4.44
6.87
9.38
11.8
14.6
14.3
15.4
16.5
22.1
25.2
26.7
27.0
25.9
20.1
22.6
16.8
13.1
10.7
Downtown Los
Oct Oct
12 16
5.31
6.83
8.28
9.94
12.2
15.5
18.2
20.2
20.6
22.7
25.4
23.8
22.9
20.1
16.8
12.6
9.62
4.67
7.21
11.9
16.4
20.3
24.5
27.5
29.9
31.9
31.7
30.7
30.8
29.3
26.7
23.3
19.6
14.2
9.23
Angeles
Oct
18
10.3
7.29
10.5
13.0
17.1
21.0
24.5
26.2
26.0
23.5
20.4
19.3
19.9
17.6
15.4
14.6
12.1
8.76
Oct
20
7.33
11.3
15.0
18.6
21.5
23.0
24.0
28.1
27.9
29.4
26.6
24.4
19.7
18.7
15.6
12.1
8.51
Table 2-4. AVERAGE INCOMING 300- TO 380-nm RADIATION FOR 30-MIHUTE INTERVALS,
SUM OF VALUES FROM NARROW-BAND FILTERS
(w/m2)
Midpoint
of time
interval
(1ST)
0715
0745
0815
0845
0915
0945
1015
1045
1115
1145
1215
1245
1315
1345
1415
1445
1515
1545
Oct
6
6.26
10.7
15.6
20.5
25.3
28.6
33.0
36.7
38.5
38.6
39.2
38.9
37.1
30.3
30.9
20.2
20.2
15.2
Oct
12
9.56
14.2
19.1
23.8
26.8
31.4
35.1
36.9
37.4
38.1
37.7
35.5
30.8
28.2
24.9
19.8
14.8
Mt. Wilson
Oct Oct
16 18
9.30
13.9
18.8
23.7
26.0
30.7
34.3
36.4
36.5
36.7
36.1
33.4
29.6
27.2
23.5
18.7
13.8
10.3
14.5
18.2
22.9
27.2
30.6
33.0
34.7
35.4
35.1
34.5
32.5
30.1
26.3
22.0
19.0
13.1
Oct
20
8.86
15.9
18.0
22.7
26.9
30.5
33.2
35.1
35.0
34.8
33.5
30.8
27.8
24.0
19.7
17.6
11.5
Oct
6
4.17
6.44
8.96
11.4
14.2
14.0
15.2
16.2
21.8
24.5
26.1
26.6
25.5
20.5
21.1
165
12.6
10.5
Downtown Los
Oct Oct
12 16
5.15
6.77
7.95
9.53
11.9
14.9
17.8
19.9
20.3
22.4
24.3
23.8
22.6
19.9
16.5
12.4
9.40
4.28
6.94
11.4
15.8
19.8
23.7
26.8
29.1
31.2
31.1
30.0
29.9
28.7
26.3
23.0
19.1
14.6
9.02
Angeles
Oct
18
9.09
6.87
9.89
12.4
16.4
20.4
23.9
25.5
25.5
23.2
20.3
18.9
19.5
17.3
15.1
13.0
11.7
8.60
Oct
20
7.17
10.8
14.3
17.8
20.9
22.5
23.8
27.3
29.3
28.8
26.4
24.1
19.5
18.2
15.3
11.8
9.84
Filter Phototube
31
-------
QUARTZ
HEMISPHERE
9863
INTEGRATING
SPHERE
PHOTO
TUBE
GENEVA
MOTOR
AND
GEAR
DRIVE
VOLTAGE
DIVIDER
110 AC
Figure 2-1. NBS filter-phototube UV system.
6 ° °
TYPE 935 PHOTOTUBE, NO. 5
340 350 360
WAVELENGTH, nm
370
380
390
Figure 2-2. Spectral characteristics of the filters, phototube, 1000-watt
quartz-iodine lamp standards of spectral irradiance, and the
sun. The ordinates are exact for the nine interference filters,
divided by 5 for Corning glass No. 9863, and relative only for
the phototube, standard lamp, and the sun.
32
ULTRAVIOLET RADIATION MEASUREMENTS
-------
300
310
320
330 340 350
WAVELENGTH, nm
360
380
Figure 2-3. Relative spectral response of wide-band filter in filter photometers
at Mt. Wilson and in Los Angeles.
Filter Phototube
33
-------
1 1
• 305 TO 315 nm , ,
x 315 TO 325 nm + B B
1 — 1 1
+ -1-
B B ±
o 325 TO 335 nm _^ g B
A 335
TO 345 nm
— A 345 TO 355 nm * 7V
V 355 TO 365 nm , V S ft
a 365 TO 375 nm . R o °
• 375
— + 385
TO 385 nm D V o
TO 395 nm A
B V 0
£
j. ¥ o
v v +• + —
* * y m '
0 o S D D
o
v v —
A A
A 0
+ ^ -
B n " * S
0 x x x x "
-
- *
I
fc
•* X
X
. •
X x
± *
Bo x
I
0 X
x
. • •
X •
•
•
1- "l 1
x AX
S a
0 0 g
x x
I
0
x x
• •
• X
• • —
• .
1 1 1 1 •
0700 0800 0900 1000 1100 1200 1300 1400 1500 1600
TRUE SOLAR TIME, hour
:igure 2-4. Average incoming radiation on Mt. Wilson, for 30-minute intervals
as function of time, October 6.
• 305 TO 315 nm
x 315 TO 325 nm
- o 325 TO 335 nm
A 335 TO 345 nm
A 345 TO 355 nm
V 355 TO 365 nm
• D 365 TO 375 nm
• 375 TO 385 nm
+ 385 TO 395 nm -
i i i
i +
n
•
V
£ V
£
V
A
V "I-
& i
n V
0700 0800 0900 1000 1100 1200 1300 1400 1500 1600
TRUE SOLAR TIME, hour
Figure 2-5. Average incoming radiation on Mt. Wilson, for 30-minute intervals
as function of time, October 16.
34
ULTRAVIOLET RADIATION MEASUREMENTS
-------
1
Q
O
1 1 1 1 1
- + 305 TO 315 nm *
X 315 TO 325 nm u
o 325 TO 335 nm
A 335 TO 345 nm Jr * y
— A 345 TO 355 nm V A
V 355 TO 365 nm A
D 365 TO 375 nm ™ A &
• 375 TO 385 nm , * °
- • 385 TO 395 nm _ I A
* + *
* B 2
a f f ° °
• o X
i ^ x x * *
S * x X . • •
o x ...
x . • '
. . 1 • 1 1 1 1
1 1 1
I
i
, , —
^ A
° ° V
£ ^ B
° 0
i ^
x §4
X I *"
X O
x —
• . X
•
1 1 1 •
1000 1100 1200 1300
TRUE SOLAR TIME, hour
1600
Figure 2-6. Average incoming radiation at Los Angeles for 30-minute intervals
as function of time, October 6.
7 0
6.0
5.0
CM
g 4-0
H
5
<
K 3.0
O
8
Z 2.0
1.0
0.0
1 1 1
—
* S g
• 305 TO 315 nm * *
X 315 TO 325 nm p V y
~o 325 TO 335 nm * A A V
A335 TO 345 nm a A A A A
A345T0355nm * V A A
V355T0365nm A ° ° o
D 365 TO 375 nm i Y A °
• 375 TO 385 nm w ^ o
+ 385 T0395 nm_
* I °
HL ° x x x
* 0
~ I x
to x
5? x
~i x ••.
S • *
ex ,
.X • 1 ' ' 1 1 1
_
a
* D
D
A V *
A A X *
o m> —
0 t X i
A
o X
A ^
X °
X x I
0 «-
x V
x ^
0 —
* • v
i r .
0700 0800 0900 1000 1100 1200 1300 1400 1500
TRUE SOLAR TIME, hour
Figure 2-7. Average incoming radiation in downtown Los Angeles for 30-minute
intervals as function of time, October 16.
Filter Phototube
35
-------
o
A
X
a
OOCT 6 M-H
liOCT 12 L-M
XOCT. 16 N
AOCT 18 L|
n OCT.20 L2
L
J_
_L
Fi
gur
0700 OSOO 0900 1000 1100 1200 1300 1400 1500 1600
TRUE SOLAR TIME, hour
!-8. NBS wide-band filter measurements of average incoming radiation
at Mt. Wilson for 30-minute intervals as function of time of day.
1000 1100 1200
TRUE SOLAR TIME, hour
Figure 2-9. NBS wide-band filter measurements of average incoming radiation
in downtown Los Angeles for 30-minute intervals as function of
time of day; October 1965.
36
ULTRAVIOLET RADIATION MEASUREMENTS
-------
California Department of Public Health
3: PHOTOCHEMICAL MEASUREMENTS
Robert J. Gordon
California Department of Public Health
INTRODUCTION
It is well recognized that the intensity of ultraviolet sunlight in the
lower atmosphere figures importantly in determining the progress of
photochemical smog reactions. Our Laboratory collaborated with PHS
by making a number of measurements with chemical actinometers.
These instruments were situated on the laboratory rooftop of the
Los Angeles County Air Pollution Control District adjacent to the
instruments used for physical measurements. The measurements were
made at the indicated times on the scheduled flight days except for
October 12 (an official holiday, for state and local government em-
ployees).
Two types of chemical actinometers were used. One was that of
Tuesday (1), in which the photolysis of nitrogen dioxide in nitrogen is
determined by analysis before and after exposure to light. The reaction
is
NO2 + hy NO + 0
The other system was the photoisomerization of o-nitrobenzaldehyde
to o-nitrosobenzoic acid proposed for ultraviolet actinometry by Pitts
and co-workers (2).
-CHO _/COOH
S_NO
N02 v
In this latter system liquid solutions were used. Isomerization was
followed by pH measurement. This system was later elaborated into
a trial model of a continuous recording actinometer.
EXPERIMENTAL PROCEDURE
NO2 Photolysis- For N©2 exposures a pillow-shaped bag of 0.001-inch
Mylar film having an inflated capacity of about 90 liters was used. The
dimensions flat were 60 by 104 centimeters; inflated, approximately 20
by 50 by 90 centimeters. The bag was heat-sealed and was equipped
with a half-inch bulkhead fitting of stainless steel. A short Tygon con-
nection closed with a Hoffman clamp was attached. The bag was en-
Photochemical Measurements 37
-------
closed for darkness in a fiber drum with an opaque cloth under the
metal lid. For about a minute before exposure the cloth served as
light protection when the lid was removed during that interval.
The bag was evacuated and purged with 10 to 20 liters of prepurified
nitrogen, then evacuated again. The bag was half-filled with nitrogen at
20 liters per minute through a Kel-F lubricated glass system. NO2
from a cylinder was passed through a heated section of the system,
closed off by stopcocks, and expanded into an evacuated bulb. The
original volume, now at reduced pressure, was then swept into the bag
with the remaining half of the nitrogen. Concentrations varied from
0.5 to 4.1 ppm NO 2.
After standing 30 to 45 minutes, the bag was attached to a continuous
nitrogen oxides analyzer (Saltzman reagent) (3). This analyzer requires
about a half liter of sample per minute and reaches a level reading in
about 20 minutes. The bag was left on the instrument for 30 minutes.
Within a few minutes after exposure the bag was attached again to the
analyzer for another 30 minutes. The same bag was used for all
measurements.
Exposure was made by attaching the exposed fitting of the covered
bag to a halyard, then uncovering and running the bag quickly up a
20-foot mast. At completion of the exposure the bag was quickly brought
down into the drum and recovered with the cloth. It is estimated that
time required for covering and uncovering the bag was about 5 seconds.
All exposures were for 2 minutes.
o-Nitrobenzaldehyde (ONBA) Photolysis Solutions of o-nitrobenzaldehyde
(Matheson-Coleman and Bell) were made in foil-covered vessels under
subdued light. The procedure was to dissolve 0.01 mole of the material
in 50 milliliters of chemically pure methanol, add slowly with stirring
to 800 to 900 milliliters of water in a liter volumetric flask, rinse
the weighing container with another 50 milliliters of methanol, and make
up to volume with water. This procedure gave a 0.01 M solution in
10 percent aqueous methanol.
Exposures were made in 100-milliliter spherical Pyrex flasks
filled just to the neck and closed with rubber stoppers. The outer
diameter of the flasks was 6.3 centimeters with wall thickness of
0.15 centimeter. A flask was attached by a wire loop under the lip to
the halyard. For exposure the foil covering was removed and the flask
was hoisted up the mast. Exposures were for 10 minutes. Since the
same halyard was used for NO2 bag exposures, the flask was brought
down (but not covered) briefly when the NO2 bag was sent up and again
when it was brought down. This changed the elevation of the flask, but not
the length of exposure, for an estimated 1 minute of the total 10 minutes.
Conversion of the ONBA to acid was estimated by pH measurement
on a Beckman Zeromatic pH meter. The pH of the unexposed solution
was essentially that of deionized water, approximately 5.5. (The
38 ULTRAVIOLET RADIATION MEASUREMENTS
-------
limiting pH for prolonged exposure to UV light in one example was 2.77.)
All flasks from a day of exposure were kept well-covered through the
day. The pH levels of the solutions were measured in succession in a
covered beaker at the end of the day. The meter was zeroed on pH 7
buffer reference. Corrections to the measured pH of exposed ONBA
solutions were made as required, based on the reading for a pH 3 buffer
reference.
Determinations by potentiometric titration were made of the dis-
sociation constant for o-nitrosobenzoic acid (obtained by photolysis of
ONBA solution). A set of triplicate runs using freshly boiled water and
a nitrogen blanket gave ka = 2.8 ± 0.3 x 10~4.
TREATMENT OF DATA
NO2 Photolysis - Tuesday's (1) method permits determination of the
apparent decomposition rate constant for NO2, kd, from the following
expression: . „ ann , ..._ .
F kd = 2.303 log (NO2)o
t (N02)t
where t is the exposure time (120 seconds in this case), (NO2)g the
initial NO2 concentration, and (NO2)t the final NO2 concentration. The
rate constant kd is composite, involving three reactions (4). To convert
it to the primary ka for the photolytic step itself, kd must be multiplied
by 1.45.
In order to infer from ka the intensity of incident radiation, IQ, in
the wavelength region absorbed by NO2, the absorption coefficients for
N02 (5) over 10-nm intervals were weighted and averaged as follows.
The transmission of the Mylar bag in each interval was estimated from
reference (6) (recalculated from 0.003 to 0.001 inch thickness). The
quantum yield estimated for each interval (7) transmissivities of the
Mylar, and the weighted distribution of solar ultraviolet for typical
conditions (8) were used to weight the NO2 absorption coefficients for
averaging. (The solar distribution used was not necessarily that
prevailing on the days of exposure, but it is closer to the actual than
the assumption of uniform distribution would be. The correction re-
sulting from its use is less than 5%.) The resultant average coefficient
over the 300-to-410-nm range was
oc= 1.47 x 10~19 cm2 /molecule
For weak absorption, as in this case, & , ka and IQ are related by
the expression (9)
Ka = 2.303°%
Io = 4.28 x 1018 photons/sec-cm2
since the use of consistent units and the quantum yield factors relate
molecules reacted to incident photons. Values calculated from this
Photochemical Measurements 39
-------
expression are given in Table 3-1. Assuming an average wavelength of
absorption of 350 nm, we converted the results to watts per square meter
and plotted the data for various days of smog (Figures 3-1, 3-2.)
ONBA Data Treatment From the dissociation constant for o-nitroso-
benzoic acid, the known concentration of the ONBA solution, and the pH
before and after exposure to light, the total acid produced could be
calculated. This is taken as equivalent to the amount of ONBA photo-
isomerized. To derive from this the light intensity entering the solution,
an expression similar to that of Pitts, Vernon and Wan (10) is used.
This expression is based on the assumption of complete absorption. For
the system used in the present work the transmission at 390 nm would
be about 1 percent, at 400 nm about 15 percent, and at 410 nm about
60 percent (10). No correction has been attempted for this. The flasks
were assumed to be perfect spheres, although the peak partially obscured
about 3 percent of the surface area.
13 = «St [
-------
where IQ = incident light intensity, photons/sec-crn^
Ta = average transmission relative to absorption
Tr = average transmission relative to reflection
As shown in the Appendix, Ta = 0.775 and Tr = 0.883. Thus
2
I0 = 1.173 x 1019 x(Acid)t, photons/sec-cm
Values derived from this expression are given in Table 3-1. Assuming
an average wavelength of absorption of 350 nm, we converted the re-
sults to watts per square meter and plotted the data for various days
of smog (Figure 3-2).
DISCUSSION
Table 3-1 shows the results of the two methods of measurement in
comparable terms. Pitts, Wan, and Schuck (2) proposed the use of ONBA
for actinometry of this sort because it absorbs with uniform quantum
yield throughout the wavelength range that is effective in NC>2 photoly-
sis. As pointed out by Pitts, Vernon, and Wan (10) the fall-off in
photodissociation of N(>> around 400 nm is at least roughly paralleled
by the fall-off in ONBA absorptivity in the same region.
The short wavelength cut-offs for Mylar and Pyrex are also roughly
parallel. Since the incident sunlight falls off rapidly in the same region,
any difference in transmissivity of the two materials is not thought to
be significant. The difference is in the direction of greater transmis-
sivity of Pyrex.
Examination of Table 3-1 shows that although results obtained by
the two methods are generally similar, the NO2 values seem to be
erratic. Since this method is quite reliable with rigid vessels (such
as a spectrometer cell), the scatter may be related to the use of bags.
• One possibility is the variation in orientation of the bag during ex-
posure as determined by the direction of the wind.
Another potential cause of difference between the two sets of
readings is that NO2 in this region has some vibrational structure (11),
whereas the ONBA in solution does not. Consequently if there is any
NO2 in the atmosphere, it will selectively absorb at wavelength maxima
that are exactly those to which the NO2 actinometer responds. The
ONBA actinometer, however, responds alike to light at wavelengths of
adjacent NO2 maxima and minima, and therefore gives a better idea of
radiation entering the upper levels of a polluted atmospheric layer.
Photochemical Measurements 41
-------
The N<>> actinometer corresponds to radiation, effective in NO£ photo-
lysis, which has survivied passage through the whole polluted layer.
The differences in the two sets of readings were shown to be signifi-
cantly correlated with the atmospheric NC>2 level by the t test (95%
confidence limits). This effect may not be small, since the correlation
suggests that 10 pphm NO2 would increase the difference by about 0.5 x
1016 photons per second per square centimeter.
Another limitation on accuracy is the factor 1.45 used to convert
kd (NO2) to ka values. This factor is derived (4) from elementary
rate constants in the literature that are not known with high precision.
It appears that either method is potentially suitable for solar UV
measurements in a relative sense, the ONBA method being considerably
simpler in execution. Several sources of uncertainty and approximation
are involved in reducing absolute values of light intensity by either
method, as discussed above. Since much of this relates to the con-
tainers, the uncertainty might be reduced somewhat by use of a container
of special properties, such as a thin-walled quartz bulb for the ONBA.
In any case the chemical methods are adequate for relative measure-
ments and have the useful property as applied of integrating radiation
from all directions.
APPENDIX3A: OPTICAL PROPERTIES OF SPHERICAL PYREX FLASK
The ultraviolet absorption characteristics of Pyrex were obtained
from catalog information of the Corning Glass Company. These are
given in Table 3-2. The refractive index was reported to be no = 1.474.
From known refractive index - wavelength variations for several other
types of glass, the index for Pyrex at 350 nm was estimated to be 1.494.
This value was used in computation.
Reflectances at the air-Pyrex interface were calculated. For nor-
mal incidence (i = 0°)
R = ,n-L2
Vr
where R = reflectance, n = refractive index of Pyrex, 1 = refractive
index of air. From this formula R = 0.0392. For other angles of
incidence Fresnel's formula was used:
R = 1/2
(i+r)
+
tan2
2 (i-r)1
2 (i+r)J
where i = angle of incidence and r = angle of refraction. The angle of
refraction r was obtained from the relation
sin i
sin r
Values of transmittance, (relative to reflection) Tr = 1-R, are given in
Table 3-3 for 10 percent annular increments in flux area (see below).
42 ULTRAVIOLET RADIATION MEASUREMENTS
-------
The reflection at the second surface between Pyrex and water was
considered in a similar way. For the worst case (i = 90 degrees from
Table 3-3) the reflectance at the glass-water interface is only 0.0072.
This effect was therefore neglected.
The distribution of light flux over various angles of incidence was
deduced as follows. For light from any particular direction, rays
striking the flask at angle i lie on a circle of diameter D sin i, where
D is the diameter of the flask. This circle projected on a plane normal
to the direction of the rays has an area A = -J (D sin i)2. Incremental
areas of annular rings on the plane of projection are given by
dA = iJf-D2 sin i cos i di.
To obtain values for the area between circles for given values of i,
the above expression is integrated:
A =/£• D2 sin i cos i di
= f D2 (sin 2i2 - sin 2iL)
Values of i have been tabulated for 10 percent increments in sin2i
(Table 3-4). These relative areas were used to weight Tr to arrive at
the average over-all Tr. Similarly the path length through the glass,
w = WO/CDS r (where WQ is the normal thickness of the flask wall) was
weighted for relative areas to derive the over-all w.
In Table 3-2 the absorbances AX for Pyrex at various wavelengths
are weighted by factors derived for solar intensities in the lower at-
mosphere (8). Multiplied by the average path-length w these allow the
value for the over-all average transmittance (relative to absorption),
Ta, to be derived.
A = 0.0647 (1 mm path)
wA = 0.1111 = -logTa
T = 0.775
a
Although the solar irradiance values used for weighting are esti-
mated for typical conditions, not necessarily the same as those pre-
vailing on the days of exposure, they represent a closer approach to
the accurate value of Ta than does no weighting at all. Without weight-
ing, Ta would be approximately 0.65 for the interval 300 to 400 nm, a
16 percent difference.
In Table 3-4 the solar intensity (8) weighting factors are used to
derive the average effective absorption coefficient for NC>2.
Photochemical Measurements 43
-------
REFERENCES
1. Tuesday, C. S. The Atmospheric Photooxidation of Trans-Butene
-2 and Nitric Oxide. In: Chemical Reactions in the Upper and
Lower Atmosphere, Interscience, New York, N. Y. (1961).
2. Pitts, J. N., Jr., J. K. S. Wan, and E. A. Schuck. Photochemical
Studies in an Alkali Halide Matrix. I. J. Am. Chem. Soc.
86:3606 (1964).
3. Thomas, M. D., L. H. Rogers, J. A. MacLeod, R. C. Robbins,
R. C. Goettelman, and R. W. Eldridge. Automatic Apparatus
. for Determination of NO and NO£ in the Atmosphere. Anal.
Chem. 28:1810-16 (1956).
4. Bufalini, J. J., and E. R. Stephens. The Thermal Oxidation of
Nitric Oxide in the Presence of Ultraviolet Light. Intern. J. Water
Pollution. 9:123-28 (1965).
5. Leighton, P. A. Photochemistry of Air Pollution, Academic Press,
New York, N. Y. (1961) p. 54.
6. Korth, M. W. Dynamic Irradiation Chamber Tests of Automotive
Exhaust. U. S. Public Health Service Publ. No. 999-AP-5
Cincinnati, Ohio (1963) p. 9.
7. Leighton op. cit, p. 55.
8. Leighton, op. cit., p. 29.
9. Leighton, op. cit., p. 27.
10. Pitts. J. N., Jr., J. M. Vernon and J. K. S. Wan. A Rapid
Actinometer for Photochemical Air Pollution Studies.
Intern. J. Air Water Pollution 9:595-600 (1965).
11. Hall, T. C., Jr., and F. E. Blacet. Separation of the Absorption
Spectra of NO2 and N204 in the Range of 2400 5000A. J.
Chem. Phys. 20:1745 (1952).
44 ULTRAVIOLET RADIATION MEASUREMENTS
-------
Table 3-1. ULTRAVIOLET RADIATION IN LOS ANGELES
Date"
Oct 6
Oct 16
Oct 18
Oct 20
Midpoint of
exposure
kd, N02,
interval (1ST) 10-3/sec
0850
1050
1250
1450
0835
1035
1235
1435
0835
1035
1235
1435
0835
1035
1235
1435
1.33
2.75
1.63
1.32
3.34
7.37
4.40
5.87
3.18
6.10
5.58
2.95
2.88
1.02
6.13
1.73
I0- N02
b
0.57
1.18
0.70
0.56
1.43
3.15
1.88
2.51
1.36
2.61
2.39
1.26
1.23
0.44
2.62
0.74
avg. 1 .539
C
32.5
67.3
39.9
31.9
81.5
180.0
107.0
143.0
77.5
149.0
136.0
71.8
70.1
25.1
149.0
42.2
(Acid) ,,
10-3 moles/1
0.84
1.26
1.58
1.21
1.17
1.64
1.70
1.41
0.84
1.51
1.04
1.01
1.13
1.70
1.51
1.17
I0, ONBA
b
0.99
1.48
1.85
1.42
1.37
1.92
1.99
1.65
0.99
1.77
1.22
1.19
1.33
1.99
1.77
1.37
avg. 1.519
C
56.4
84.4
105.0
80.9
78.1
109.0
113.0
94.0
56.4
101.0
69.5
67.8
75.8
113.0
101.0
78.1
. No data taken October 12.
lQl° photons/sec-cm .
Watts/m2 (assuming average energy at 350 nm).
Table 3-2. ULTRAVIOLET ABSORPTION CHARACTERISTICS OF PYREX
nm
300
310
320
330
340
350
360
370
380
390
400
T, 1 mm
0.34
0.55
0.71
0.80
0.86
0.88
0.89
0.90
0.90
0.91
0.91
A, 1 mm
0.468
0.260
0.149
0.097
0.065
0.055
0.050
0.046
0.046
0.041
0.041
Weight a
0.003
0.026
0.055
0.089
0.093
0.103
0.106
0.127
0.121
0.114
0.163
1.000
Weighted A
0.0014
0.0068
0.0082
0.0086
0.0060
0.0057
0.0053
0.0058
0.0056
0.0047
0.0066
A = 0.0647
a From Leighton (8) Table 8, 40 degree zenith angle (normalized from 300
to 400 nm).
Photochemical Measurements 45
-------
Table 3-3. TRANSMITTANCE OF PYREX FLASK
Relative annular
flux area
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0
18° 26'
26° 34'
33° 13'
39° 14'
45° 00'
50° 46'
56° 48'
63° 26'
71° 34'
90° 00'
0
12° 13'
17° 25'
21° 30'
25° 03'
28° 15'
31° 14'
34° 03'
36° 46'
39° 25'
42° 01'
Tr
r
0.9608
0.9605
0.9599
0.9583
0.9556
0.9506
0.9418
0.9252
0.8920
0.8085
0
Tr = 0.8833
avg. w = W0
av cos r
1.50
1.55
1.59
1.63
1.68
1.73
1.78
1.84
1.91
1.98
w = 1.719
Table 3-4. N02 ABSORPTION COEFFICIENT
X,A
3000
3100
3200
3300
3400
3500
3600
3700
3800
3900
4000
4100
TX
0.001 in. Mylar
0
0
0.65
0.80
0.83
0.85
0.86
0.87
0.88
0.89
0.90
0.91
a X' N02
1 / mole - cm
0
57
78 /
98
119
136
149
158
163
167
171
167
<£X(est.)
0.98
0.97
0.96
0.95
0.94
0.93
0.92
0.92
0.90
0.84
0.67
0.09
Weight
0.003
0.021
0.045
0.074
0.077
0.085
0.088
0.105
0.100
0.094
0.134
0.174
1.000
Weighted (oc\ T\ <£ \)
0
0
2.19
5.51
7.15
9.14
10.38
13.28
12.91
11.74
13.82
2.38
cx = 88.5
46 ULTRAVIOLET RADIATION MEASUREMENTS
-------
< 140
E
J 120
O
I—
8
o
u
T
oOCT. 6
xOCT. 16
AOCT. 18
DOCT. 20
M-H
N
L
L
BASED ON N02 PHOTOLYSIS AND ASSUMING AVERAGE
WAVELENGTH OF ABSORPTION OF 350 nm.
I | | | I
1000 1100 1200 1300
TRUE SOLAR TIME, hour
1400
1500
Figure 3-1. Incoming 300- to 410-nm radiation as function of time of day for
various days of smog.
I
O
z
0OCT. 6 M-H
x OCT. 16 N
AOCT. 18 L
a OCT. 20 L
1 1
BASED ON ONBA METHOD
AND ASSUMING AVERAGE
WAVELENGTH OF —
ABSORPTION OF 350-nm
0800 0900 1000 1100 1200 1300 1400 1500
TRUE SOLAR TIME, hour
Figure 3-2. Incoming 300- to 400-nm radiation as function of time of day for
various days of smog.
Photochemical Measurements
47
-------
University of California at Riverside
4: PHOTOCHEMICAL MEASUREMENTS
R. N. McCormick, J. M. Vernon, J. N. Pitts, Jr.
Department of Chemistry
University of California at Riverside
The relative intensity values and ratios of direct and reflected
intensities obtained during the cooperative ultraviolet study for the
Los Angeles basin were arrived at by using a special sensitized
actinometric paper impregnated with o-nitrobenzaldehyde (1). Upon
exposure to the wavelength range 300 - 400 nm in sunlight the
photoisomerization of o-nitrobenzaldehyde (1) o-nitrosobenzoic acid
(2) proceeds in gaseous, solution, and solid state with a quantum
yield of 0.5, which is independent of the exciting wavelength in the
prestated range of approximately 300 to 400 nm.
NO9 NO
(1) (2)
Since sunlight received by the earth's lower atmosphere contains
negligible radiation shorter than 300 nm, this o-nitrobenzaldehyde
actinometer offers an advantage over many others in that its effective
range corresponds almost precisely with the distribution of ultraviolet
radiation present in the lower atmosphere. Furthermore, because of
the simplicity of the procedure, the apparatus, and the calculations
the technique is well suited to the program. In this method the assump-
tion is made that the quantum yield for the rearrangement remains con-
stant at 0.5 in the impregnated paper. Since this method is applied only
to relative measurements, the exact quantum yield value is not
important.
The sensitized papers were prepared by uniformly wetting 5.5-
centimeter discs of filter paper with 0.5-milliliter portions of a
0.5 o-nitrobenzaldehyde solution in ethanol-water and allowing the
treated papers to dry in the dark (approximately 2 hours drying
time). Once dry, the sensitized papers were stored in a dark place
and all further handling was done in a dark room, away from direct
lighting. The sensitized papers are stable for extended periods if
kept dry and in the dark.
The apparatus for analyzing exposed papers consisted of a
Beckman Model G pH meter and an Ag/Ag-Cl combination electrode
Photochemical Measurements 49
-------
(single unit, one electrode built within the other). The exposed papers
were eluted with 20-milliliter portions of 1:1 ethanol-water, and the
pH was determined after it had stabilized (about 20 minutes). Readings
were reproducible within +0.01 unit. With the measured pH value,
relative ultraviolet intensity can be computed from equation (1), which
is simply the total number of acid molecules formed divided by the
exposure time.
-fe +
-------
RESULTS
The pH data and exposure times for the paper strips at B' eleva-
tions corresponding to the four flight intervals for the 5 flight days,
are summarized in Table 4-1, which includes data from measurements
on the laboratory rooftop at the Los Angeles measurement site. These
results are reduced to values of average energy absorped per unit
time by the sample strips during the exposure period given in Table
4-2. Ratios of outgoing to incoming radiation were calculated and are
given in Table 4-3.
In the summary of results the most significant values are the
ratio of intensities and the relative intensities, and not the stated
intensities. Thus, the stated intensities are expressed in Einsteins
per minute for the sample area (11.8 cm^) without reduction to a unit
area. Likewise, the value for energy per unit time was not converted
to watts. This conversion would normally require a summation over
the wavelength region of sensitivity, which varies with wavelength.
Furthermore, an absolute value of the radiation incident on the sensor
could not be calculated because data are not available to account for
the efficiency with which the incident radiation is absorbed and to what
extent it enters into the chemical reaction under various conditions of
exposure and other functioning parameters. If approximations are to
be made and assumptions tested, conversion of Einsteins per minute to
watts is suggested at the average wavelength of 367 nm.
The variations of incoming and outgoing radiation for the 2 days of
extreme conditions, i.e., moderate-to-heavy smog (October 6) and no
smog (October 16) are shown as a function of elevation (Figures 4-1
and 4-2) and as a function of time (Figures 4-3 and 4-4). Ratios of
outgoing to incoming radiation as function of elevation for various
days of smog are shown for the mid-morning flight (Figure 4-5) and
the late afternoon flight (Figure 4-6); they are also shown as a func-
tion of time for various days of smog for the lowest (Figure 4-7) and
highest (Figure 4-8) elevation interval.
REFERENCE
1. Pitts, J. N., Jr., J. M. Vernon, and J. K. S. Wan. A Rapid
Actinometer for Photochemical Air Pollution Studies. Intern
J. Air Water Pollution 9:595-600 (1965).
Photochemical Measurements 51
-------
Table 4-1. pH VALUES /EXPOSURE TIME (min) FOR INCOMING AND OUTGOING 300-TO
400-nm RADIATION
Exposure
interval
(1ST)
Oct6
0830-0930
1030-1130
1230-1330
1430-1530
Oct 12
0800-0900
1000-1100
1200-1300
1400-1500
Oct 16
0800-0900
1000-1100
1200-1300
1400-1500
Oct 18
0800-0900
1000-1100
1200-1300
1400-1500
Oct 20
0800-0900
1000-1100
1200-1300
1400-1500
Ground
3.87/15
3.83/15
3.79/15
3.95/14
5.54/2
5.06/2
4.22/4
4.48/4
4.24/4
4.19/4
4.53/4
4.91/4
4.25/4
4.42/4
4.63/4
5.56/2
4.75/2
4.68/2
5.01/2
Elevation
1-1.5 2.6-3.0
Incoming
4.04/5
5.14/2
4.69/2
4.33/2
4.75/1
5.05/1
4.46/2
4.67/1
5.07/1
5.04/1
4.55/1
4.70/1
5.41/1
5.18/2
4.33/2
4.67/2
5.06/2
4.06/5
3.98/4
3.98/4
4.14/4
5.08/2
4.52/2
4.23/2
4.58/1
5.32/1
4.42/2
4.66/1
4.80/2
5.21/1
4.50/1
4.54/1
4.84/1
5.55/2
4.78/2
4.53/2
4.90/2
thousands of feet
5.6-6
4.07/5
3.98/4
3.96/4
4.14/4
5.32/1
4.53/2
4.24/2
4.52/1
5.48/1
4.60/1
4.33/2
4.64/2
5.29/1
4.35/2
4.52/1
4.66/1
5.76/2
4.77/2
4.50/2
4.66/2
1-1.5
4.42/10
5.06/8
4.92/8
4.64/8
4.93/3
5.97/3
5.33/8
5.97/3
6.48/3
5.50/8
5.71/3
5.56/8
6.28/3
5.72/8
5.96/3
6.24/3
6.45/3
2.8-3.2
Outgoing
4.33/10
4.09/15
4.12/15
4.28/15
4.86/8
4.68/8
4.72/3
4.74/3
6.11/3
5.61/3
5.92/3
5.96/3
5.91/3
5.16/8
5.20/8
5.67/3
5.92/8
5.54/8
5.64/8
5.75/8
5.6-6
4.30/10
4.18/10
4.11/15
4.20/15
4.71/8
4.58/8
4.63/3
4.65/3
6.26/3
5.57/3
5.08/8
5.32/8
5.44/8
5.18/8
4.97/8
5.49/3
6.46/3
5.41/8
5.40/8
5.32/8
52
ULTRAVIOLET RADIATION MEASUREMENTS
-------
Table 4-2. INCOMING AND OUTGOING 300- TO 400-nm RADIATION
Exposure
Interval
(1ST)
Oct6
0830-0930
1030-1130
1230-1330
1430-1530
Oct 12
0800-0900
1000-1100
1200-1300
1400-1500
Oct 16
0800-0900
1000-1100
1200-1300
1400-1500
Oct 18
0800-0900
1000-1100
1200-1300
1400-1500
Oct 20
0800-0900
1000-1100
1200-1300
1400-1500
0.35
(Rooftop) 1
(10-7
9.39
13.7
13.0
6.72
0.294
1.09
8.69
3.37
8.03
9.62
0.117
0.840
7.74
4.15
2.01
0.280
2.75
3.42
1.26
.1-1.5
Incom
Elevation
2.6-3.0
ng
, thousands of feet
5.6-6.0
Einste iris/mi n-area)
13.9
0.869
3.32
11.5
5.50
2.24
7.20
7.10
0.678
2.31
10.6
6.46
0.834
0.778
2.14
3.55
1.09
12.9
22.4
24.4
11.8
1.03
5.84
16.7
9.48
1.06
8.30
7.33
2.36
1.43
12.6
10.9
4.14
0.288
2.50
5.64
1.74
12.4
22.4
22.4
11.8
1.06
5.64
16.1
11.7
0.692
8.92
11.5
3.91
1.15
10.7
11.7
7.39
0.163
2.58
6.26
3.67
1.1-1.5
(10-8
16.6
2.72
4.08
9.78
10.6
0.614
1.29
0.614
0.096
0.820
1.26
0.700
0.230
0.455
0.633
0.263
0.113
2.6-3.0
Outgoing
Einsteins/m
23.0
38.4
34.1
18.5
4.87
8.13
20.0
18.8
0.403
1.64
0.700
0.633
0.726
2.06
1.84
1.40
0.263
0.737
0.565
0.422
5.6-6.0
n-area)
25.7
40.5
35.4
25.0
7.80
11.8
26.9
25.2
0.246
1.82
2.57
1.33
9.62
1.94
3.53
2.25
0.107
1.04
1.07
1.32
Photochemical Measurements
53
-------
Table 4-3. RATIO OF OUTGOING TO INCOMING 300- TO 400-nm
RADIATION AT VARIOUS ELEVATIONS
Exposure interval
(1ST)
Oct6
0830-0930
1030-1130
1230-1330
1430-1530
Oct 12
0800-0900
1000-1100
1200-1300
1400-1500
Oct 16
0800-0900
1000-1100
1200-1300
1400-1500
Oct 18
0800-0900
1000-1100
1200-1300
1400-1500
Oct 20
0800-0900
1000-1100
1200-1300
1400-1500
Elevation
1.1-1.5 |
0.119
0.313
0.123
0.085
0.193
0.027
0.018
0.009
0.014
0.035
0.012
0.011
0.028
0.058
0.030
0.007
0.010
thousands
2.6-3.0
0.178
0.171
0.152
0.157
0.473
0.139
0.120
0.198
0.038
0.020
0.010
0.027
0.051
0.016
0.017
0.033
0.091
0.029
0.010
0.024
of feet
| 5.6-6,0
0.207
0.181
0.145
0.212
0.736
0.209
0.167
0.215
0.036
0.020
0.022
0.034
0.084
0.018
0.030
0.030
0.066
0.040
0.017
0.036
54
ULTRAVIOLET RADIATION MEASUREMENTS
-------
z
o
— P 32
<
Q
— , 16 —
(HOUR)
1030-1130
1230-1330
ELEVATION, thousands of feet
Figure 4-1. Incoming and outgoing radiation as function of elevation over
Los Angeles for different times of day, October 6 (M-H smog).
z
o
H
<
Q
o:
E
O
5 2
•
O
u
(HOUR)
1200-1300"
1000-1100
1400-1500
ELEVATION, thousands of feet
Figure 4-2. Incoming and outgoing radiation as function of elevation over
Los Angeles for different times of day, October 16 (no smog).
Photochemical Measurements
55
-------
, 1—I—I—I—I—T-
44 \~ ELEVATION, thousands of feot
I I I
0900 1000 1100 1200 1300 UOO 1500
0800 0900 1000 1100 1200 1300 1400 1500
TRUE SOLAR TIME, hour
Figure 4-3. Incoming and outgoing radiation as function of time for various
elevations over Los Angeles, October 6 (M-H smog).
ELEVATION, thousands of feet
•5-IST06.0
0800 0900 1000 1100 1200 1300 1400 1500 0800 0900 1000 1100 1200 1300 1400 1500
TRUE SOLAR TIME, hour
Figure 4-4. Incoming and outgoing radiation as function of time for various
elevations over Los Angeles, October 16 (no smog).
56
ULTRAVIOLET RADIATION MEASUREMENTS
-------
O OCT.6 M-H
AOCT 12 L-M
X OCT 16 N
AOCT 18 Li
O OCT 20 L2
ELEVATION, rhousonds of Feet
Figure 4-5. Ratio of outgoing to incoming radiation as function of elevation in time interval
1000 to 1100 for various days of smog.
O OCT. 6 M-H
AOCT. 12 L-M
X OCT 16 N
AOCT 18 L|
D OCT 20 L2
ELEVAT ION, thousands of feet
Figure 4-6. Ratio of outgoing to incoming radiation as function of elevation in time interval
1400 to 1500 for various days of smog.
Photochemical Measurements
57
-------
1100 1200 1300
TRUE SOLAR TIME, hour
Figure 4-7. Ratio oi outgoing to incoming radiation at 1,000 to 1,500 feet as function of
time of day for various days of smog.
0OCT 6 M-H
a, OCT 12 L-M
x OCT 16 N
AOCT 18 L|
° OCT 20 L2
Figure 4-8 Ratio of outgoing to incoming radiation at 5,600 to 6,000 feet as function of
ime of day for various days of smog.
58
ULTRAVIOLET RADIATION MEASUREMENTS
-------
The Pennsylvania State University
5: PHOTOSENSITIVE PLASTIC
MEASUREMENTS
Hans Neuberger
The Pennsylvania State University
Dep artment of Meteorology
Under Grant No. WBG-46 by the U. S. Weather Bureau to The Pen-
nsylvania State University (1, 2), a method was developed for integrating
UV irradiance from sun and sky by means of small plates of PLEXI-
GLAS*, type "G" of 0.03-inch thickness. These plates transmit wave-
lengths from about 340 nm upwards. Under exposure to UV transmit-
tance decreases in the spectral range from 340 to 410 nm with a max-
imum response at about 355 nm (Figure 5-1). This transmittance
change is due to photochemical action by wavelengths of =s345 nm.
The method of using these PLEXIGLAS plates [abbreviated P(.03G)j]
has been standardized as follows:
1. Plates 3-1/2 inch square and 3/4 inch thick are exposed horizontally
on the shiny side of a piece of household aluminum foil, which by its
reflection enhances the degradation of transmittance due to UV irradi-
ance. Exposure period is ordinarily from sunrise to sunset for deter-
mination of the UV dose for a whole day.
2. Degradation is evaluated by means of an optical densitometer, the
DENSICHRON by W. M. Welch Manufacturing Co. with blue probe
(S-4) covered by a Corning (CS 7-37) ultraviolet filter; the light source
is a clear-glass 150-watt, 120-volt tungsten light bulb (straight fila-
ment coil). The spectral response of this apparatus covers the range
from 320 to 395 nm with a broad maximum between 360 and 370 nm
(Figure 5-2).
3. The optical density of P(.03G) is measured before and after exposure,
the density difference being proportional to the UV dose that caused the
increase in optical density. For improved accuracy in measurements,
the plates are scored with a knife or stylus and broken into four pieces,
which are than stacked on top of each other for density measurement.
The reading accuracy of the Densichron meter is ±0.005 dimensionless
density units.
''Registered trade name of an acrylic plastic by Rohm and Haas Co.
Photosensitive Plastic 59
-------
4. The P(.03G) plates were calibrated by means of the NBS secondary
irradiance standard QM-52 (1,000 watt); the irradiance was restricted
to UV wavelength naturally occurring in sun and sky light by use of a
Corning (CS 0-54) filter, which transmits from 300 nm upwards. With
this filter the effective emission of the lamp in the range from 300 to
345 nm, to which Plexiglas is responsive, amounted to 0.134 watt/m
of UV.
5. The degradation of P(.03G) is independent of simultaneous irradiance
of visible and infrared radiation; it is unaffected by very high or very
low temperatures in dark storage and is stable in dark storage, after
exposure, for several weeks. Over a storage period of a year additional
spontaneous degradation (which does not take place in unexposed plates)
amounts to less than 10 percent.
6. The degradation is greater for exposures to a given UV dose at high
temperatures than at low temperatures (Figure 5-3). For this reason,
the measured density changes must be corrected to a standard temper-
ature, arbitrarily set at 113°F, which is above normally occurring air
temperatures and at which calibration was carried out. The measured
density changes are converted to UV doses by the formula:
I(UV) = 300 A D4 [l + 0.00794(113 T°F)] ,
Where I(UV) is the UV dose in w-hr/m2, 300 is the calibration factor,
A 04 is the density change of stacks of four plates due to UV irradiance,
and T°F is the average plate temperature during exposure. The average
air temperature during exposure has been found to provide a reasonable
estimate of the plate temperature.
7. The optical density change is a practically linear function of the UV
dose well beyond the values experienced on clearest midsummer days.
The accuracy of I(UV) is ±15 percent or better.
P(.03G) was exposed on the Los Angeles laboratory rooftop accord-
ing to the standard procedure described above. The plates were later
evaluated for degradation at the Pennsylvania State University laboratory
by measuring the optical density changes by the standard methods. The
results are given in Table 5-1.
Agreement between measurements by P(.03G) method and those by
the filter phototube method for integrating UV radiation in the range of
wavelengths from 300 to 345 nm, is within t!5 percent, which is con-
sidered to be the attainable accuracy of the plastic method.
60 ULTRAVIOLET RADIATION MEASUREMENTS
-------
REFERENCES
1. Neuberger, H., and D. R. Cochran. Integration of Ultraviolet by
Plastics, Final Report. Prepared for U.S. Department of Commerce,
Weather Bureau. The Mineral Industries Experiment Station, College
of Mineral Industries, Pennsylvania State University, University
Park, Pa. (October 31, 1965).
2. Neuberger, H. H. and D. R. Cochran, Ultraviolet Dosimetry by
Plastics. J. Appl. MeteoroL 5(3) :358-63. (June 1966.)
Photosensitive Plastic 61
-------
Table 5-1. INTEGRATED ULTRAVIOLET IRRADIANCE (300 to 345 nm)
MEASURED BY PHOTOSENSITIVE PLASTIC0
Exposure Expos. Average
interval time, temp,
(TST) hr °F
Oct 6
0720 9 75
71620
Oct 12
0705 9.25 70
71620
Density Irradiance Irradiance Difference
rhange (PlexiglasJ, (filter photo- relative to
(^.D4) w-hr/m tube), filter-
phototube
data,%
0.155 60 59.7 0.5
0.145 58 54.4 6.6
Oct 16
Sample lost in high winds
Oct 18
0650 9.5 70
71620
Oct 20
0720 9 86
71620
0.13 52 59.1 -12.0
0.16 58 66.5 -12.8
aPlexiglas, type G, 0.03-inch thick.
'-'Data by R. Stair and J. Nader {Section 2) reduced to same wavelength range and
exposure time of P(.03G) plates.
62 ULTRAVIOLET RADIATION MEASUREMENTS
-------
I 1 I l~l—I—I—I—I—I
360 380 400 420
WAVE LENGTH, nm
Figure 5-1. Transmittance of Plexiglas 0.07 in. thick.
340 360
WAVE LENGTH, nm
Figure 5-2. Sensitivity of filter and phototube.
Photosensitive Plastic
63
-------
0.25 I—
UJ
U
UJ
D_ 0.20 I—
ct:
LJ
Q-
z:
<
X
U
Figure 5-3. Degradation of Plexiglas (.03G) at different temperatures.
64
ULTRAVIOLET RADIATION MEASUREMENTS
-------
Public Health Service
6: PHOTOCHROMIC GLASS
MEASUREMENTS
Jerome P. Flesch and John S. Nader
National Center for Air Pollution Control
INSTRUMENTATION AND METHOD
Photochromic glass developed by Corning Glass Co. possesses
some unusual optical properties that were utilized in a prototype devel-
opment of a simple, inexpensive monitor of incident ultraviolet radiation.
Megla (1) has reported some of the important properties of this glass.
The glass contains suspended silver halide microcrystals, which de-
compose upon exposure to radiation between 320 and 420 nm and which
produce a visible darkening effect (optical density). The glass becomes
clear upon removal of the activation energy. Some of the properties of
the glass that bear on this application are: (1) the amount of darkening
is proportional to the amount of incident radiation within a prescribed
optical density range; (2) the cycle of darkening and clearing with in-
troduction and removal of activation energy is repeatable, and the re-
sponse time to both effects is quite rapid; (3) clearing (bleaching) also
depends upon the temperature (thermal bleaching) and upon the inci-
dence of long wavelength (550-650 nm) radiation (optical bleaching).
In principle a prototype UV monitor would consist of the photochro-
mic glass as the UV sensor and a simple transmissometer to accurately
monitor the optical density of the sensor. Absolute calibration would be
required to convert transmittance data to absolute values of incident
UV radiation. Data required for such a calibration include: (1) spectral
response of the glass in terms of optical density change per unit incident
energy as a function of wavelength over the range of activation; (2) the
effects of thermal and optical bleaching as functions of temperature and
wavelength; and (3) the response of the sensor as a function of angle of
incidence of activating radiation.
To evaluate the principle of operation of a photochromic-glass sen-
sor of UV radiation in the field, we constructed a prototype device
(Figure 6-1) and placed it at the Los Angeles measurement site, beside
the Eppley UV sensors.
The prototype instrument had a motor-driven turntable (1/2 rpm)
to permit measurement of; (1) the incident light from the transmissom-
eter light source through a clear opening in the turntable; (2) the zero
reference level through an opaque portion of the turntable; and (3) the
Photochromic Glass 65
-------
transmittance each of duplicate sample specimens of photochromic
glass exposed to incident UV radiation. A recorder provided continuous
data on the transmissometer measurements throughout the day.
RESULTS
The transmissometer data were reduced to half-hour average val-
ues of transmittance tabulations for the 5 flight days. Calibration data
were not available to permit reduction of the transmittance data to
absolute values of incident UV radiation. The transmittance data were
corrected for the attenuation (15%) by the unactivated glass and con-
verted to optical density values (Table 6-1). Data shown in Figure 6-2
(for sensor No. 1) indicate the variation of UV radiation in terms of
optical density as a function of time and its relative variation for the
two days of extreme smog conditions (none toQ heavy). These results
were not corrected for bleaching or for angular response characteris-
tics of the glass sensors.
REFERENCE
1. Megla, G. K. Optical Properties and Applications of Photochromic
Glass. Appl. Optics. 5: 945-60 (1966).
66 ULTRAVIOLET RADIATION MEASUREMENTS
-------
Table 6-1. AVERAGE FOR 30-MINUTE INTERVALS OF OPTICAL DENSITy DATA FROM
PHOTOCHROMIC GLASS UV SENSOR
Midpoint of
30-minute
interval (TST)
0745
0815
0845
0915
0945
1015
1045
1115
1145
1215
1245
1315
1345
1415
1445
1515
1545
1615
1645
1715
0
No. 1
0.30
0.32
0.32
0.33
0.33
0.32
0.32
0.32
0.33
0.34
0.33
0.36
0.39
0.39
0.37
0.36
0.37
0.36
ct6
No. 2
0.31
0.32
0.32
0.33
0.33
0.32
0.33
0.31
0.33
0.35
0.34
0.38
0.40
0.39
0.38
0.37
0.37
0.35
Oct
No. 1
0.32
0.33
0.33
0.34
0.35
0.37
0.36
0.36
0.36
0.36
0.37
0.38
0.39
0.40
0.39
0.38
12
No. 2
0.31
0.31
0.32
0.32
0.34
0.37
0.35
0.35
0.35
0.36
0.37
0.38
0.39
0.39
0.38
0.37
Oct
No.l
0.32
0.39
0.44
0.46
0.48
0.49
0.49
0.50
0.49
0.48
0.49
0.47
0.47
0.50
0.50
0.50
0.49
0.48
16
No. 2
0.33
0.40
0.43
0.46
0.48
0.48
0.49
0.49
0.49
0.48
0.49
0.47
0.47
0.49
0.48
0.48
0.48
0.45
Oct
No.l
0.33
0.37
0.38
0.39
0.38
0.38
0.38
0.36
0.35
0.35
0.33
0.33
0.35
0.37
0.39
0.40
0.40
0.38
18
No. 2
0.34
0.37
0.38
0.37
0.38
0.39
0.38
0.37
0.35
0.35
0.33
0.32
0.34
0.36
0.37
0.38
0.38
0.36
Oct
No.l
0.26
0.31
0.33
0.33
0.32
0.32
0.28
0.25
0.26
0.28
0.28
0.26
0.25
0.25
0.24
0.26
0.26
0.25
0.25
0.23
20
No. 2
0.27
0.31
0.32
0.32
0.32
0.32
0.28
0.27
0.27
0.30
0.30
0.29
0.28
0.26
0.25
0.27
0.26
0.25
0.24
0.21
Photochromic Glass
67
-------
TRIPOD SUPPORT
6-VOLT POWER SUPPLY
LAMP NO. 47
LENS
FILTER (YELLOW)
LEVEL 1/2-RPM
I MOTOR
-PHOTOCHROMIC GLASS
-LENS
• APERTURE
- WESTON PHOTOCELL 856
Figure 6-1. Schematic of photochromic-glass UV monitor.
- OCT. 6
- OCT. 16
0800 0900 1000 1100 1200 1300 1-100 1500 1600
TRUE SOLAR TIME, hour
Figure 6-2. Relative UV measurements by photochromic glass in terms of optical density
as function of time.
68
ULTRAVIOLET RADIATION MEASUREMENTS
-------
Los Angeles County Air Pollution Control District
7: METEOROLOGICAL AND AIR
QUALITY MEASUREMENTS
Robert J. Bryan and Robert E. Neligan*
Los Angeles County Air Pollution Control District
John S. Nader
National Center for Air Pollution Control
SAMPLING AND MEASUREMENT
Meteorological and air quality data were collected both at the
laboratory in downtown Los Angeles and in the aircraft at various
elevations over Los Angeles. All data from continuous stripcharts
were reduced to 1-hour averages.
Methods by which these measurements were made at the labora-
tory are described in Appendix 7A. Air quality data are presented in
Table 7-1 for carbon monoxide, total hydrocarbons, oxidant, nitrogen
dioxide, nitric oxide, sulfur dioxide, and particulate soiling. Meteoro-
logical data, presented in Table 7-2 include values for temperature,
relative humidity, wind direction and speed, 'weather,' sky cover, vis-
ibility, solar radiation, and turbidity coefficient (1).
Air quality data obtained from the aircraft over Los Angeles are
given in Tables 7-3 and 7-4. For these measurements samples were
collected in aluminized Scotch-Pak bags, approximately 60 liters in
volume. The samples were obtained by use of a 1/4-inch-diameter
stainless steel tube, the outlet being positioned on the leading edge of
the wing approximately 5 feet from the cabin. The sampling tube was
led back through the wing into the cabin, where a quick-disconnect
fitting was placed on the outlet. Flexible polyethylene tubing was con-
nected to this outlet and the bag. The bags were filled by the ram
action of the airplane flying through the air. Approximately 30 liters
of sample were obtained in 3 to 15 minutes, depending upon the speed
of the aircraft.
While samples were being taken aloft, a bag sample was also ob-
tained from the roof of Station No. 1 (DOLA). The same size alumin-
ized Scotch-Pak bags were used. The sample was collected by use of
a DeVilbis pump, the diaphragm having been covered with a seal of
aluminized Scotch-Pak film. Metering valves between the pump and
Meteorology and Air Quality 69
-------
the bag were preset to allow for the collection of 50 liters of air during
the period that the aircraft was over the Los Angeles Laboratory.
The bag samples from the aircraft were picked up at Cable Air-
port and brought to the laboratory. Immediately upon arrival at the
laboratory, samples were withdrawn for NC>2 and hydrocarbon analyses.
The samples had been in the bags approximately 3 hours.
Meteorological data from the aircraft were limited to temperature
measurements, which are summarized in Section I, Figure 1-12.
ANALYSES
Nitrogen dioxide analyses were performed by the Griess-Saltzman
method. Briefly the method consists of evacuating a 2-liter flask to a
pressure of about 20 millimeters. Ten milliliters of full-strength
reagent (5 g of sulfanilic acid, 140 ml of acetic acid, and 20 ml of 0.1%
N-(l-naphthyl)-ethylenediamine dihydrochloride solution, diluted to 1
liter with water) were injected into the flask. The sample from the bag
was allowed to expand into the evacuated bulb. It was then placed on a
mechanical shaker and shaken for 15 minutes for color development;
the absorbance of the solution was then read by a Beckman DU spec-
trophotometer.
The samples were analyzed for hydrocarbons by gas chromatog-
raphy. Two-liter glass bulbs were evacuated to less than 0.1 milli-
meter of pressure, the bulbs connected to the bags, and the contents
allowed to expand into the bulb. The bulbs were stored in a dark cab-
inet until the analysis was performed. Upon analysis, 1 liter of sample
from the glass bulb was transferred to a freeze-out trap, immersed
in liquid nitrogen, and packed with C-22 firebrick. The condensed
sample was then charged to the Loenco Model APCD, two-stage gas
chromatograph by heating the freeze-out trap. The sample first passed
through a 6-foot, 1/4-inch-OD column of 15 percent BB thiodipropioni-
trile on 42-60 mesh firebrick, and then into the second column, a 14-foot,
1/4-inch-OD column of 20 percent di-n-butyl maleate on 42-60 mesh
firebrick. As it exits from the second column the sample is split
equally. One stream flows through a 4-inch, 1/4-inch-OD column of
20 percent mercuric perchlorate, then to the flame ionization detector;
the other stream flows through a 4-inch, 1/4-inch-OD column of 20
percent polypropylene glycol on 42-60 mesh brick, then to a second
detector.
With proper valving and flow controls, this system separates most
hydrocarbons in the C± to C6 range. The data are summarized in Table
7-4 as groups of hydrocarbons more or less relative to their photo-
chemical reactivity. The contents remaining in the Scotch-Pak bags
were inserted into the sampling lines of the MSA infrared carbon mon-
oxide analyzer used for air monitoring. The sample was allowed to
purge the IR cell fully, and a reading was taken after the instrument's
response had come to equilibrium.
TO ULTRAVIOLET RADIATION MEASUREMENTS
-------
APPENDIX 7A
MEASUREMENT METHODS AND INSTRUMENTS USED AT LACAP
LABORATORY
Carbon Monoxide - CO Analyzer, Mine Safety Appliance Co. This
device measures the concentration of carbon monoxide on the basis of
infrared absorption principles. Data are shown on a continuous chart
with a linear scale.
Hydrocarbons - Flame lonization Detector, Beckman Instrument
Company. In this instrument the ionization flame is produced from a
fuel mixture composed of 40 percent hydrogen and 60 percent nitrogen
at a flow rate of 75 cubic centimeters per minute and a "breathing" air
flow rate of 200 cubic centimeters per minute. These instruments read
directly the hydrocarbon concentration in parts per million expressed
as methane.
Oxidant - Beckman Instrument Co. The instrument consists of a con-
tinuous air-liquid contacting device and a recording colorimeter. It
measures the total oxidant in the air by means of a chemical reaction
involving the release of iodide from potassium iodide solution. Data
are displayed on a continuous chart with a logarithmic scale.
Oxides of Nitrogen - NO/NO2 Analyzer, Borman Engineering Co. This
one instrument determines the separate atmospheric concentrations of
two contaminants. The chart-trace sequence involves the recording of
the NO2 concentration for 2 minutes, followed by a 1-minute trace of
NO, then repeating. The instrument consists of two air-reagent con-
tinuous contacting systems and a recording colorimeter. Saltzman's
reagent is the reactant, and potassium permanganante is used to oxi-
dize NO to NO2.
Sulfur Dioxide - Thomas Autometer. The instrument absorbs sulfur
dioxide in a wetted column, in which the sulfur dioxide is oxidized to
sulfuric acid and the change in the electorlytic conductivity of the sol-
ution is determined. Reagents are dilute sulfuric acid and hydrogen
peroxide. Data are displayed on a continuous chart with a linear scale.
Particulate Matter (Km) - Chaney Autosampler. Km values are mea-
surements of the light-reflecting properties of filter samples of par-
ticulate matter. A sample of air is passed through a filter paper each
hour of the day. One Kmunit represents that deposit of particulate
matter that produces an optical density value of 0.1 when 1 cubic meter
of air passes through 1 square centimeter of the filter.
Visibility - Defined as the greatest horizontal visual range averaged
over one-half of the horizon circle. Visibility is measured by the dis-
tance at which it is just possible to see and distinguish prominent
Meteorology and Air Quality 71
-------
objects or landmarks against the sky at the horizon. Although the
measurement of visibility is therefore a subjective procedure, it can
be done with great accuracy when the observer is provided with a
sufficient number of identifiable objects at known distances.
Solar Radiation - Measured by means of an Eppley Pyranometer of the
thermoelectric type. Radiation from the sun is allowed to fall on two
concentric silver rings, the outer ring covered with magnesium oxide
and the inner one covered with lamp black. The temperature difference
between the rings is measured by a thermocouple and recorded in units
of gram-calories per square centimeter per minute.
Turbidity Coeffecient - Calculated from measurements by Volz Sun-
photometer (1). The instrument is pointed at the sun to allow radiation
to enter the lens opening in whose focal plane a diaphragm is located to
limit the field of view to about 1 degree. The light is diffused by a
ground-glass plate and passes through a filter combination that trans-
mits a monochromatic beam with a peak transmission at 500 nm and
a bandwidth of about 60 nm at 50 percent of peak transmission. The
beam is incident upon a selenium photocell that gives a current output
read on a microammeter. By means of a pivoted scale mounted on the
instrument and appropriate alignment of the instrument for the sun's
elevation, a measure of the sun's optical path length is determined.
Calculations of particle concentration averaged through the atmos-
phere above the ground can be made from the relationships (2)
N = 17.3 x 106 B
and
M = 969 B
where N and M are the particle number and mass (/u.g) concentrations,
respectively, per cubic meter in the size range 0.2 to 2.0 microns in
diameter, and B is the turbidity coefficient.
REFERENCES
1. Volz, F. Photometer mit Selen-Photoelement zur Spektralen Messung
der Sonnenstrahlung und zur Bestimmung der Wellenlangenabhan-
gigkeit der Dunsttrubung. Arch. Meteorol. Geophys. Bioklimatol.,
Ser. B., 10(1): 100-31 (1959).
2. McCormick, R. A., and D. M. Baulch. The Variation with Height
of the Dust Loading over a City as Determined from the Atmos-
pheric Turbidity. JAPCA. 12:492-96 (1962).
72 ULTRAVIOLET RADIATION MEASUREMENTS
-------
Table 7-1. AVERAGE AIR QUALITY DATA FOR 1-HOUR INTERVALS
Midpoint of
time interval
(TST)
Oct 6
0550
0650
07-50
0850
0950
1050
1150
1250
1350
1450
1550
1650
1750
Oct 12
0550
0650
0750
0850
0950
1050
1150
1250
1350
1450
1550
1650
1750
Oct 16
0550
0650
0750
0850
0950
1050
1150
1250
1350
1450
1550
1650
1750
CO,
ppm
23
32
28
24
23
22
17
16
14
15
15
14
22
35
37
34
28
23
21
19
17
17
18
18
17
8
8
8
8
8
8
8
9
9
8
9
10
11
HC
(as methane),
ppm
10
12
9
8
7
8
4
4
3
3
3
3
3
8
12
14
16
12
9
8
6
5
4
4
4
4
2
2
2
2
2
2
2
2
2
2
2
2
2
03.
pphm
2
2
3
6
10
22
25
19
18
15
14
9
3
2
2
3
5
9
15
21
26
24
22
14
11
8
2
2
2
3
3
4
4
4
4
4
4
3
2
N02,
pphm
23
32
30
25
6
10
14
15
15
19
25
41
38
24
8
10
12
10
2
2
3
3
3
3
3
3
3
3
5
NO,
pphm
21
7
1
1
1
1
1
20
25
46
40
22
5
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
NOX,
pphm
44
39
31
26
7
11
15
35
40
65
65
63
43
26
9
11
13
11
3
3
4
4
4
4
4
4
4
4
7
S02,
pphm
4
4
4
4
4
4
2
3
2
1
2
2
2
1
1
2
1
3
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Particulate
reflectance,
Km units
11
13
11
9
9.5
9.8
5.8
4.8
4.0
3.2
3.8
4.0
3.2
5.1
9.0
6.9
3.9
2.0
1.5
1.3
2.5
0.9
1.3
1.1
0.9
0-9
0-4
0.9
0-8
0-7
0-9
0-9
0.9
1.3
1.3
1.1
Meteorology and Air Quality 73
-------
Table 7-1. AVERAGE AIR QUALITY DATA FOR 1-HOUR INTERVALS (Continued)
Midpoint of
time interval
(TST)
Oct 18
0550
0650
0750
0850
0950
1050
1150
1250
1350
1450
1550
1650
1750
Oct 20
0550
0650
0750
0850
0950
1050
1150
1250
1350
1450
1550
1650
1750
CO,
ppm
15
24
21
17
13
14
13
13
13
14
13
13
18
25
18
17
15
18
13
13
14
15
15
17
18
HC
(as methane),
ppm
6
8
9
5
3
3
3
3
3
3
3
3
3
5
7
5
5
4
5
3
3
3
3
3
3
4
°3'
pphm
1
1
1
2
3
8
8
18
16
8
5
5
4
1
1
2
3
7
18
14
15
20
17
9
5
3
N02,
pphm
10
10
12
14
18
12
9
8
9
14
12
16
10
12
16
22
24
20
8
10
14
16
NO,
pphm
20
40
40
20
10
2
1
1
1
2
1
17
34
30
18
6
1
1
1
1
1
6
N0x,
pphm
30
50
52
34
28
14
10
9
10
16
13
33
44
42
34
28
25
21
9
11
15
22
so2,
pphm
1
2
2
2
1
1
1
1
1
1
2
2
2
2
2
2
2
1
2
3
3
3
3
Particulate
reflectance,
Km units
4.4
11.
5.9
3.4
1.8
2.5
2.2
1.3
1.3
0.9
1.8
1.6
2.0
4.4
5.6
3.9
4.1
3.2
2.7
1.6
1.3
1.3
1.6
1.6
2.2
2.5
74
ULTRAVIOLET RADIATION MEASUREMENTS
-------
Table 7-2. METEOROLOGICAL DATA AT HOURLY INTERVALS
Time
(1ST)
Oct6
0520
0620
0720
0820
0920
1020
1120
1220
1320
1420
1520
1620
1720
Oct 12
0520
0620
0720
0820
0920
1020
1120
1220
1320
1420
1520
1620
1720
Oct 16
0520
0620
0720
0820
0920
1020
1120
1220
1320
1420
1520
1620
1720
Temper-
ature.
°F
61
63
69
73
77
79
81
77
76
75
75
73
61
62
65
66
70
72
75
78
74
72
69
66
59
60
62
66
69
71
72
71
69
70
67
69
Rel.
humid-
ity, %
86
75
62
58
53
51
48
73
74
76
78
85
97
94
94
90
83
80
75
69
80
85
95
99
48
47
45
39
36
33
36
36
37
37
50
43
Wind
direc-
a
tion
NE
N
E
E
S
S
sw
sw
sw
sw
sw
sw
S
E
E
S
S
S
SW
sw
sw
sw
w
w
w
w
N
N
NW
N
NW
NW
W
W
SW
SW
W
W
NW
Wind
da
,
mph
3
1
2
2
3
3
6
8
8
7
6
7
7
3
2
2
3
4
6
5
6
8
8
8
8
5
13
13
13
11
10
9
10
10
13
16
14
11
8
Weatherb
FHK
HK
HK
HK
HK
HK
HK
HK
HK
F
F
F
HK
HK
HK
HK
HK
Sky
cover
Clr
Clr
Clr
Clr
Clr
Clr
Clr
PC
PC
PC
Clr
Clr
Clr
Clr
Clr
Clr
Clr
Clr
Clr
Clr
Clr
Visi-
bility,
miles
1.0
0.8
0.8
0.5
1.0
2.0
2.5
3.0
3.0
0.5
0.5
0.5
0.8
1.0
1.2
1.0
1.5
25.
25.
25.
25-
Solar
radia-
a
tion,
w/m2
12
186
349
500
581
708
743
673
442
337
163
12
93
209
372
557
650
685
650
557
372
209
23
12
221
395
603
709
778
755
673
488
302
70
Turbidity
coeffi-
cient0
0.260
0.330
0.510
0.325
0.237
0.250
0.230
0.580
0.360
0.300
0.037
0.040
"Averages for the 1-hour interval starting at the indicated time.
bp-fog, H-haze, K-smoke, Clr-clear, PC-partly cloudy cover, PC-full cloud cover.
cReference 2.
Meteorology and Air Quality 175
-------
Table 7-2. METEOROLOGICAL DATA AT HOURLY INTERVALS (Continued)
Time
(TST)
Oct 18
0520
0620
0720
0820
0920
1020
1120
1220
1320
1420
1520
1620
1720
Oct 20
0520
0620
0720
0820
0920
1020
1120
1220
1320
1420
1520
1620
1720
Temper-
ature,
°F
57
58
59
65
71
74
77
77
73
71
70
68
68
66
71
78
88
90
94
95
95
93
90
88
Rel.
humid-
ity, %
74
69
68
60
52
39
35
35
47
51
57
55
47
51
41
36
33
29
25
25
25
25
27
28
Wind
direc-
tion0
NE
NE
NE
NE
E
SE
SE
S
SW
W
SW
w
w
N
NE
NE
NE
NE
SW
SW
S
SW
w
w
w
w
Wind
da
,
mph
4
3
3
3
3
3
2
4
9
10
8
7
6
4
4
7
4
2
4
5
5
6
7
9
6
3
Weather0
HK
HK
HK
HK
HK
HK
HK
HK
HK
HK
HK
HK
HK
HK
HK
Sky
cover
Clr
Clr
Clr
Clr
Clr
Clr
Clr
Clr
Clr
Clr
Clr
Clr
Clr
Clr
PC
PC
Clr
Clr
Visi-
bility,
mikes
6.
3.
4.
5.
5.
4.
4.
5.
6.
10.
4.
4.
4.
5.
8.
8.
6.
6.
Solar
radio-
tion a
w/m
58
163
360
511
650
673
616
557
476
349
139
139
349
546
650
720
720
639
487
291
128
Turbidity
coeffi-
cient0
0.100
0.110
0.340
0.181
^Averages for the 1-hour interval starting at the indicated time.
F - fog, H - haze, K - smoke, Clr - clear, PC - partly cloudy cover, FC - full cloud cover.
Reference 2.
76 ULTRAVIOLET RADIATION MEASUREMENTS
-------
Table 7-3. AIR QUALITY DATA OBTAINED BY AIRCRAFT
OVER LOS ANGELES
Time Interval (TST) /
Elevation, 103 ft
Oct 6 (M-H Smog)
0835-0905/0.35°
/0.35b
0940/1.35
0950/1.8
1000/2-5
Oct 12 (L-M Smog)
0835-0905/0.35°
/0.35b
0853-0906/1.35
0910-0918/1.8
0823-0834/2.5
Oct 16 (No Smog)
0820-0850/0.35°
/0.35b
0853-0900/1.4
0838-0852/3.0
0821-0830/5.7
Oct 18 (L-Smog)
0820-0920/0.35°
/0.35b
0854-0857/1.4
0907-0918/2.2
0820-0829/5.7
Oct 20 (L-Smog)
0820-0920/0.35°
/0.35b
0856-0908/1.3
0838-0852/3.0
0820-0830/5.7
CO,
ppm
24
21
11
9
9
34
29
14
10
8
8
8
7
7
7
16
17
11
9
9
17
17
10
10
HC HC
(as methane), (Carbon),
ppm ppm
3.7 8
2.96
1.61
1.66
1.67
5.63
2.51
1.75
1.60
1.1 2
1.54
1.49
1.54
1.47
2.5 5
2.33
1.63
1.66
1.48
2.1 5
2.07
1.46
1.47
1.45
NO-,
2'
pphm
23
61
8
3
3
25
58
13
6
6
3
8
2
3
1
16
17
4
< 1
<1
14
20
5
5
5
"Measurement made on air monitoring instruments at Laboratory.
bMeasurement made from samples collected in bag at same location.
Meteorology and Air Quality
-------
Table 7-4. GAS CHROMATOGRAPHIC DATA ON AIR SAMPLES
OBTAINED BY AIRCRAFT OVER LOS ANGELES
(ppm)
Time interval
(1ST) /
Elevation, 10^ ft
Oct 6
0835-0905/0.35
0940/1.35
0950/1.8
1000/2.5
Oct 12
0835-0905/0.35
0835-0906/1.35
0910-0918/1.8
0823-0834/2.5
Oct 16
0820-0850/0.35
0853-0900/1.4
0838-0852/3.0
0821-0830/5.7
Oct 18
0820-0920/0.35
0854-0857/1.4
0907-0918/2.2
0820-0829/5.7
Oct 20
0820-0920/0.35
0856-0908/1.3
0838-0852/3.0
0820-0830/5.7
Paraffins
1-3C
3.11
1.64
1.68
1.50
5.92
2.59
1.78
1.62
1.56
1.50
1.48
1.55
2.41
1.69
1.64
1.49
2.14
1.47
1.48
1.46
4-6 C
0.240
0.047
0.043
0.010
0.536
0.090
0.034
0.022
0.050
0.021
0.017
0.017
0.130
0.024
0.011
0.012
0.109
0.033
0.021
0.009
1-6C
3.35
1.68
1.72
1.51
6.45
2.68
1.82
1.64
1.61
1.52
1.50
1.57
2.54
1.71
1.65
1.50
2.25
1.51
1.50
1.47
Olefins
Ethy lene
(2C)
0.090
0.011
0.007
0.003
0.131
0.012
0.005
0.005
0.013
0.003
0.003
0.003
0.055
0.005
0.003
0.002
0.049
0.005
0.002
0.002
3-5C
0.046
0.004
0.002
0.003
0.114
0.007
0.003
0.004
0.012
0.002
0.003
0.003
0.029
0.003
0.003
0.003
0.032
0.008
0.003
0.003
2-5C
0.136
0.015
0.009
0.006
0.245
0.019
0.008
0.009
0.025
0.005
0.006
0.006
0.084
0.008
0.006
0.005
0.081
0.013
0.005
0.005
Acetylene
0.090
0.009
0.004
0.003
0.159
0.019
0.015
0.002
0.013
0.005
0.002
0.002
0.063
0.006
0.003
0.001
0.054
0.006
0.002
0.001
Aromatics
Ben-
zene
0.021
0.007
0.003
0.003
0.037
0.011
0.006
0.006
0.011
0.005
0.004
0.005
0.015
0.009
0.003
0.005
0.016
0.004
0.006
0.004
Tolu-
ene
0.027
0.011
0.004
0.006
0.077
0.018
0.000
0.000
0.000
0.000
0.000
0.000
0.036
0.008
0.004
0.009
0.024
0.016
0.012
0.007
ULTRAVIOLET RADIATION MEASUREMENTS
-------
Public Health Service
8: DISCUSSION AND SUMMARY
The foregoing sections discussed physical and chemical methods of
UV measurement and presented results of simultaneous measurements
by these methods at one or more locations. The measurements repre-
sent incoming radiation above the smog envelope and at ground level,
and outgoing radiation at various elevations within the smog layer. In
this section, the editor attempts to relate the measurements to each
other, wherever possible and to a limited extent. The methods of
measurement and the properties of UV radiation in a smog environment
are discussed. No effort has been made to be all-inclusive, and it is
hoped that this initial effort will stimulate more work; many questions
are provoked and left unanswered.
INCOMING RADIATION
UV Attenuation and Air Quality
Simultaneous measurement of incoming radiation by the filter-
phototube sensors of NBS both on Mt. Wilson and in downtown Los
Angeles permitted a calculation of the attenuation effects of the smog
envelope on the vertically incident UV radiation as a function of time
of day. The data of Table 2-3 were used to determine the ratio of Los
Angeles values to Mt. Wilson values for corresponding times of day to
give the data shown in Table 8-1 for the 5 flight days. A graphical
presentation of these data in Figure 8-1 shows that ratio measurements:
(1) eliminate the effect of the sun's elevation with time of day, which
normally gives the cosine type curves appearing in Figures 2-8 and
2-9 with peaks at solar noon; and (2) give a measure of the attenuation
of the vertical UV radiation by the intervening atmosphere between the
elevations of 350 feet in downtown Los Angeles and 5,700 feet on Mt.
Wilson. On the no-smog day the attenuation was fairly constant, aver-
aging about 14 percent. On the light-to-moderate and moderate-to-
heavy smog days the attenuation varied significantly through the day
depending upon the incidence of smog conditions. A maximum of 58
percent was observed, about 4 times that on the no-smog day.
A large attenuation appears in the time interval from about 0915
to 1145 on the moderate-to-heavy smog day (October 6). Air quality
and meteorological data during this period (Tables 7-1 and 7-2) show
high levels of O3,NO2, and particulate, and very low visibility; peak
values of pollutants and low values of visibility coincide with the peak
attenuation at about 1030 TST. At this time the 03 and NO2 concentra-
tions were 6 to 10 times those on the no-smog day and the visibility,
which was 25 miles on the no-smog day, was only 1/2 mile.
Discussion and Summary 79
-------
The data in Table 2-2 for the M-H smog day were also converted
to ratio values (Table 8-2) to determine whether the attenuation effects
of the smog environment were possibly wavelength-dependent within
the range from 310 to 390 nm. A plot of these data for the midmorning,
noon, and midafternoon periods (Figure 8-2) shows no significant de-
pendence of attenuation effects within this wavelength range. It is im-
portant to note that the instrumentation for these measurements, having
wide apertures, measures a good deal of stray light and does not give
the good resolution that true transmittance measurements provide.
Evaluation of Physical Methods
Ratios of measurements made with the Eppley wide-band sensor
(Table 1-5) in downtown Los Angeles to those made with the NBS wide-
band sensor (Table 2-3) at the same location were calculated to examine
the responses of the instruments relative to each other. The average
ratio among 90 values for the 5 days was 1.17, with a standard devia-
tion of 0.03. These values indicate that the Eppley sensor, on the aver-
age, gave a value 17 percent higher than that of the NBS sensor. Pos-
sible differences in adherence to the cosine response should be con-
sidered, particularly at low angles of elevation. Extreme ratio values
tended to occur early and late in the day, corresponding to low eleva-
tions of the sun.
Pyranometer data on solar radiation (Table 7-2) were plotted for
the 5 flight days in Figure 8-3 for comparative evaluation with the cor-
responding UV data shown in Figure 1-7. Although the pyranometer data
exhibit the same general trends relative to the smog environment as do
the UV data, the resolution of attenuation and transmission peaks is sig-
nificantly poorer. This would indicate that pyranometer data are not
adequate for inferring information on attenuation effects in the UV range
with any reasonable accuracy.
The photosensitive-plastic sensor was developed as a method of
integrating UV radiation incident on small plates of PLEXIGLAS and is
comparable to the filter-phototube sensor in being a horizontal-surface-
type receiver. Results of comparison (Table 5-1), in which the filter-
phototube data (Table 2-2) were integrated over the spectral response
range of the PLEXIGLAS and for the period of exposure, show that the
method is feasible for applications in the field, in which simple desimet-
ric type measurements are desired. The attainable accuracy is within
+ 15 percent in the UV wavelength range from 300 to 345 nm.
The photochromic-glass sensor is essentially a horizontal surface
sensor, very much like the Eppley sensor. Plots of UV radiation as a
function of time (compare Figure 6-2 for the photochromic glass sensor
with Figure 1-7 for the Eppley sensor) show that the photochromic glass
sensor fails to provide resolution of peak intensity near solar noon or
attenuation effects by smog. Possible factors that might contribute to
these results and that need investigation are (1) deviation of sensor from
cosine response; (2) spectral response; and (3) bleaching effects, which
80 ULTRAVIOLET RADIATION MEASUREMENTS
-------
may be directly related to time of day and tend to counteract the antici-
pated increase in UV radiation as a function of sun's elevation. Optical
bleaching is most likely the important factor, whereas thermal bleaching
would show less change since the temperature change through the day
was within 10°F. Qualitatively, the data show the decreased UV radia-
tion on the smog day as compared with the no-smog day, although they do
not show correctly the relative variation within the same day.
Evaluation of Chemical Methods
The photochemical method described in Section 4 gives a measure
of the UV radiation absorbed, but calibration data are not available to
convert this information to absolute values of the incident UV radiation.
Comparison of the data collected by this method (actinometer paper)
with data collected by the Eppley sensor on the same laboratory rooftop
leads to some very interesting observations.
Figure 8-4 is a plot of the relative incoming 300- to 400-nm radi-
ation as a function of time of day for various days of smog; the plot is
based on the actonometer paper measurements in Table 4-2. These
data compare qualitatively with those of the Eppley sensor in Figure
1-7 with respect to the relative variations within a given day. Note,
however, the inverse relationship between the two methods in the rela-
tive intensities for the no-smog day and the M-H smog day. In the Ep-
pley data, the intensity of incoming radiation is greater on the no-smog
day than on the M-H smog day. The actinometer paper absorbs sig-
nificantly more energy on the M-H smog day than on the no-smog day,
even though more energy is available on the no-smog day. Note, also,
that the peak energy absorbed by the actinometer paper on the M-H
day occurs within the time interval from 1030 to 1130. At about this
time the corresponding Eppley data show a large attenuation effect.
Data on outgoing radiation, discussed later in this section, show that
the attenuation of incoming radiation on smog days corresponds to an
increase in outgoing radiation; thus the data show that scattering is
more of a factor than absorption in the overall attenuation effects.
These observations seem to indicate that the actinometer paper
method may have a greater sensitivity to scattered radiation because
of its geometrical response and/or its spectral response characteris-
tics. Another possibility is that the smog environment may affect the
photochemical response of the sensor. Some significant observations
are that the actinometer paper method in its present method of appli-
cation (1) does not give an absolute measure of incident UV radiation
and (2) does not necessarily give a reliable measure of relative inci-
dent radiation levels.
The volumetric-type chemical actinometers described in Section 3
are used differently. The difference is essentially in the geometrical
exposure and response of the sensors. First, we will compare the two
o-nitrobenzaldehyde methods. The paper actinometer presumably acts
Discussion and Summary 81
-------
as a horizontal-surface-type sensor on which is incident radiation from
all directions within a hemisphere, and the vertical components of these
radiations are measured (assuming a cosine response sensor). The
volumetric actinometer exposes the same reagent, as a solution in a
spherical flask, to radiations from all directions about the sphere; in
principle at least, all radiation is measured equally, independent of di-
rection.
Since data obtained by the volumetric actinometer were calculated
in terms of absolute energy of incident radiation, comparison with the
corresponding absolute data obtained by the Eppley sensor is of interest.
The volumetric data (Figure 3-2) seem to compare much more favor-
ably with the Eppley data (Figure 1-7) than do the actinometer paper data
with respect to variation of relative intensity as a function of time of
day and various degrees of smoginess.
Note that the peak intensity measured by the volumetric actinometer
on the no-smog day is about 115 w/m2 as compared to about 36 w/m2
measured by the Eppley sensor, a factor of a little over 3. These val-
ues bring out a very important point with respect to UV radiation avail-
able to a volume in space. The vertical component radiation measured
by the Eppley sensor represents one of the six vector components (per-
pendicular to six plane surfaces of a cube) required to account for all the
radiation incident on a volume in space. If the radiation were uniformly
distributed with respect to all direction in space, then the volumetric
measurement of incident radiation would be expected to be 6 times the
vertical component measurement. For an anisotropic distribution, the
factor will most likely be less than 6 if it is assumed that the incident
vertical component approximates the horizontal components in magni-
tude. A calculation of the ratio of volumetric measurements to simul-
taneous horizontal plane measurements (Table 8-3) shows values for 4
of the 5 flight days ranging from 2.9 to 4.8. The ratios are lowest near
solar noon, as might be expected since the vertical component (in the
denominator) tends toward a maximum at noon.
OUTGOING RADIATION
Scattering Effects and Air Quality
Incoming radiation on Mt. Wilson was measured (filter-phototube
sensor) simultaneously with measurement of outgoing radiation on the
aircraft (filter-photocell sensor) at the same elevation of 5,700 feet.
From these two sets of values we could calculate the scattering effect
of the smog envelope on the vertically directed incident radiation (300
to 380 nm) as a function of time of day. The data of Table 2-3 and
Figure 1-11 were used to calculate the ratios of outgoing to incoming
radiation values. A plot of these ratio values in Figure 8-5 for the
various days of smog shows a significant shift toward higher ratios for
the smog days, higher by a factor of about 2. The outgoing radiation is
a combined measure of the incoming radiation scattered by the polluted
82 ULTRAVIOLET RADIATION MEASUREMENTS
-------
medium and the radiation reflected from the ground level and trans-
mitted through the polluted medium. The curve for the no-smog day is
indicative of the reflectivity of the ground, averaging about 15 percent
of the incident radiation and assuming negligible scatter from the rela-
tively unpolluted medium. On the M-H smog day, the polluted medium
causes a significant increase in the outgoing radiation, which averages
about 24 percent of the incident radiation. Note what appears to be a
buildup of pollution on October 18 (light smog); the ratio in the morning
corresponds to that for a no-smog day at about 18 percent and increases
gradually from mid-morning to noon, at which time it corresponds to the
ratios for the relatively smoggy days (L-M and M-H) at about 23 percent
while the value for the no-smog day has dropped to about 13 percent.
This is generally consistent with the turbidity and visibility data in Table
7-2. However, in relating air quality data obtained at ground level to
scattering at 5,700 feet, it is necessary to bear in mind that high scat-
tering values can reflect a buildup of pollution in the upper layers of the
atmosphere. This pollution in the upper layers may appear in the air
quality data obtained at ground level at some time earlier or later,
depending upon meteorological conditions near the ground and at the
higher elevations.
Figure 8-6 shows the results of measurement of outgoing radiation
with the sensor on the aircraft and the scattering effects of a polluted
medium as a function of elevation over Los Angeles for various days of
smog during the mid-morning flight interval (1000 to 1100 TST). These
plots suggest an exponential relationship between outgoing radiation and
elevation, as would be expected if the intervening medium between the
aircraft and ground is treated as a variable scattering medium whose
reflectivity is related to its concentration of particulate pollution
(turbidity) and its thickness (elevation). The increased pollution on
smoggy days displaces the curves toward higher outgoing radiation
values. Curves for both morning and afternoon flights showed that
values of outgoing radiation for the no-smog day are lower than those
for any of the smog days. Values of outgoing radiation for the rela-
tively heavy-smog days are higher than those for the no-smog day by a
factor of approximately 2.
Data on ratios of outgoing to incoming radiation measurements made
with the sensitized actinometer paper as a function of time for the
5600- to 6000-foot elevation interval (Figure 4-8) also show a signifi-
cant increase in ratio values for the relatively heavy-smog days rela-
tive to the no-smog day. Note the comparison of these data with the
corresponding data obtained with the physical sensors (filter photosen-
sors, Figure 8-5). The chemical sensor tends to show a greater in-
crease in the ratio values (a factor of about 6) for the M-H smog days
than do the physical sensors (a factor of about 2). This is consistent
with our earlier comments regarding what appears to be the abnor-
mally high sensitivity of the actinometer paper method to scattered
radiation.
Discussion and Summary 83
-------
SUMMARY
1. Incident and outgoing ultraviolet radiation (within the wavelength
range from 300 to 400 nm) in the Los Angeles urban area was mea-
sured during 5 days with conditions ranging from no smog to moderate-
to-heavy smog. Simultaneous UV measurements were made with
physical and chemical detection systems; concurrent with these mea-
surements, air quality and meteorological data were collected.
2. Absolute-energy data for radiation incident on a horizontal plane
surface were obtained by the filter photocell and filter-photo tube
methods of detection. The filter-photocell method on the average gave
a value 17 percent higher than that given by the filter-phototube method.
3. Incident 300 to 380 nm radiation on a no-smog day at an elevation
of 5,700 feet peaked to a value of about 36.1 w/m2 at solar noon. At an
elevation of 350 feet near ground level this UV radiation measured
simultaneously was 30.7 w/m2. The attenuation through the day was
relatively uniform, with a mean value of about 14 percent and a mini-
mum of about 3 percent for unpolluted air. On a moderate-to-heavy
smog day, the attenuation for the smog layer from 350 to 5,700 feet
varied significantly through the day; peak attenuation was as much as
58 percent with a mean value of about 38 percent or almost 3 times that
measured on the no-smog day.
4. Incident UV radiation was measured with nine narrow-band filters
having 10-nm bandwidths and centered at every 10 nm starting with
310-nm wavelengths through 390 nm. Results of attenuation measure-
ments through the moderate-to-heavy smog layer indicated that attenu-
ation effects were not significantly dependent on wavelength within this
range.
5. Pyranometer data indicated that such wide-band (300 to 2,500 nm)
radiation measurements were not adequate for inferring accurate in-
formation on attenuation effects in the UV (300 to 400 nm) range.
6. The photochromic-glass sensor was inadequate for providing infor-
mative UV data. Results showed significant lack of resolution, which
may be attributable to several factors requiring further study.
7. The photosensitive-plastic sensor used as a dosimeter gave a good
quantitative measure of incident UV (300 to 345 nm) radiation with a
calculated accuracy of about JT15 percent when compared to the filter-
phototube sensor.
8. The actinometer paper method in its present state of development
does not give an absolute measure of incident UV (300 to 400 nm) radi-
ation, and results of relative measurements were not reliable in the
prototype system. The initial system is capable of refinement and
further study that might overcome these obstacles. The high sensi-
tivity of this method to scattered radiation associated with smog condi-
84 ULTRAVIOLET RADIATION MEASUREMENTS
-------
tions may be of unique value in monitoring incidence of smog or other
smog-related measurements.
9. Measurements with the volumetric type of chemical actinometer
(ONBA) were higher than those with the horizontal-plate type sensor by
a factor ranging from 2.9 to 4.8, with a mean of 3.8
10. Outgoing radiation increased with elevation, tended to peak with
time of day approaching solar noon, and increased on smoggy days.
The ratio of outgoing radiation to incident radiation on relatively
heavy-smog days was approximately twice the ratio for a no-smog day
(0.23 to 0.13 at solar noon).
11. Data on the ratios of outgoing radiation to incident radiation mea-
sured by the actinometer paper method also reflected the increased
outgoing radiation on smoggy days. This method showed a greater
increase, indicating a higher sensitivity to scattered radiation than is
provided by the filter photocell method.
Discussion and Summary
85
-------
TableS-1 RATIO OF INCOMING 300- TO 380-nm RADIATION IN
LOS ANGELES (300 feet) TO INCOMING RADIATION
ON MT. WILSON (5,700 feet), 1965
Midpoint of
time interval
(1ST)
0715
0745
0815
0845
0915
0945
1015
1045
1115
1145
1215
1245
1315
1345
1415
1445
1515
1545
Oct 6
0.69
0.63
0.59
0.57
0.60
0.51
0.47
0.45
0.58
0.66
0.70
0.70
0.71
0.70
0.74
0.86
0.66
0.71
Oct 12
0.54
0.47
0.43
0.42
0.47
0.50
0.53
0.56
0.56
0.60
0.69
0.68
0.77
0.73
0.69
0.65
0.65
Oct 16
0.76
0.85
0.88
0.87
0.98
0.91
0.88
0.89
0.88
0.85
0.87
0.87
0.91
0.88
• 0.85' '
0.77
0.68
Oct 18
0.72
0.72
0.71
0.75
0.78
0.81
0.80
0.76
0.67
0.59
0.57
0.62
0.59
0.59
0.67
0.65
0.70
Oct 20
0.81
0.78
0.83
0.82
0.80
0.76
0.73
0.81
0.81
0.85
0.80
0.80
0.72
0.80
0.81
0.71
0.75
Table 8-2. RATIO OF INCOMING RADIATION IN LOS ANGELES (350 FEET) TO RADIATION
ON MT. WILSON (5700 FEET) ON OCTOBER 6 AT INDICATED WAVELENGTH (nm)
Midpoint
of time
interval
(TST)
0715
0745
0815
0845
0915
0945
1015
1045
1115
1145
1215
1245
1315
1345
1415
1445
1515
1545
310
0,82
0.54
0.59
0.48
0.50
0.44
0.38
0.36
0.48
0.54
0.58
0.60
0.62
0.62
0.63
0.75
0.67
0.78
320
0.66
0.61
0.57
0.55
0.55
0.48
0.45
0.42
0.52
0.60
0.64
0.65
0.66
0.69
0.64
0.78
0.62
0.67
330
0.64
0.59
0.57
0.54
0.55
0.48
0.45
0.42
0.53
0.61
0.64
0.66
0.66
0.69
0.65
0.78
0.60
0.66
340
0.68
0.58
0.56
0.54
0.54
0.49
0.45
0.42
0.54
0.61
0.60
0.66
0.66
0.69
0.65
0.79
0.60
0.66
350
0.65
0.61
0.58
0.56
0.57
0.50
0.47
0.45
0.57
0.65
0.69
0.70
0.70
0.67
0.68
0.80
0.63
0.69
360
0.67
0.62
0.59
0.56
0.56
0.4?
0.47
0.45
0.58
0.66
0.69
0.70
0.71
0.66
0.71
0.83
0.63
0.70
370
0.68
0.63
0.59
0.58
0.58
0.51
0.48
0.48
0.61
0.69
0.72
0.73
0.73
0.70
0.74
0.88
0.64
0.73
380
0.66
0.60
0.57
0.56
0.57
0.50
0.47
0.47
0.62
0.63
0.71
0.71
0.71
0.67
0.71
0.86
0.62
0.70
390
0.66
0.60
0.56
0.55
0.56
0.49
0.44
0.47
0.61
0.63
0.70
0.70
0.71
0.66
0.70
0.89
0.62
Average
0.68
0.60
0.58
0.55
0.55
0.49
0.45
0.44
0.56
0.62
0.66
0.68
0.68
0.67
0.68
0.82
0.63
0.70
86
ULTRAVIOLET RADIATION MEASUREMENTS
-------
Table 8-3. RATIO OF VOLUMETRIC MEASUREMENTS TO
CONCURRENT HORIZONTAL PLANE MEASUREMENTS
Midpoint of
exposure
interval (1ST)
Average UV radiation, w/m
ONBA
(Table 3-1)
Eppley
(Table 1-4)
Ratio
Oct 6
0850
1050
1250
1450
Oct 16
0835
1035
1235
1435
Oct 18
0835
1035
1235
1435
56.4
84.4
105.
80.9
78.1
109.
113.
94.0
56.4
101.
69.5
67.8
14.4
19.1
30.1
19.2
17.9
32.8
34.5
24.5
14.3
28.9
22.6
17.2
3.9
4.3
3.5
4.2
4.4
3.3
3.3
3.8
4.0
3.5
3-1
4.0
Oct 20
0835
1035
1235
1435
75.8
113.
101.
78.1
15.7
26-3
34.4
20.0
4.8
4.3
2.9
3.9
Discussion and Summary
87
-------
g
§
f£
o
<
fY.
OQCT.6 M-H
AOCT. 12 L-M
X OCT. 16 N
AOCT. 18 L|
a OCT. 20 l_2
0700 0800 0900 1000 1100 1200 1300 1400 1500
TRUE SOLAR TIME, hour
1600
Figure 8-1. Ratio of incoming 300- to 380-nm radiation at Los Angeles to that at
Mt. Wilson for various days of smog.
g
<
O
o
o
<
a:
l.o
0.8
0.6 J
0.4
0.2
0.0
310 320 330 340 350 360
WAVELENGTH;nm
370
380
*i20o TST|
1500 TST
0900 TSTl
390
400
Figure 8-2. Ratio of incoming radiation at Los Angeles to that at Mt. Wilson as
function of wavelength for different times of day on Oct. 6, 1965.
88
ULTRAVIOLET RADIATION MEASUREMENTS
-------
800
o OCT. 6
OCT. 12
X OCT. 16
A OCT. 18
a OCT. 20
0600 0700 0800 0900
1000 1100 1200 1300 1400 1500
TRUE SOLAR TIME, hour
1600
1700 1800
Figure 8-3. Average solar radiation measured with pyranometer for 1-hour intervals in
Los Angeles.
Discussion and Summary
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10
z
o
8
Q
LU
HI
O
CO
LU
>
S 2
O OCT. 6
A OCT. 12
XOCT. 16
A OCT. 18
Q OCT. 20
M-H
L-M
N
L|
L2
1000 1200 1400
TRUE SOLAR TIME, hour
1600
Figure 8-4. Relative absorbed incoming radiation measured with ONBA filter paper at
Los Angeles laboratory site.
90
ULTRAVIOLET RADIATION MEASUREMENTS
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o '
I—
<
O
<
O£
I 0.81-
u
S 0.4
8
0! 0.2
O
O
°OCT.6 M-H
AOCT. 12 L-M
XOCT. 16 N
AOCT. 18 L|
a OCT. 20 t_2
1000 1100 1200
TRUE SOLAR TIME, hour
1400 1500
Figure 8-5. Ratio of outgoing (from aircraft) to incoming 300- to 380-nm radiation at
elevation of 5,600 to 6,000 feet (Mt. Wilson).
ELEVATION, thousands of feet
Figure 8-6. Outgoing radiation as a function of elevation over Los Angeles for various
days of smog for the time interval 1000 to 1100.
Discussion and Summary
91
ft U. S. GOVERNMENT PRrNTDIG OFFICE : 1968 O - 291-029
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BIBLIOGRAPHIC: Nader, John S. Pilot study of
ultraviolet radiation in Los Angeles, October
1965. PHS Publ. No. 999-AP-38. 1967. 91pp.
ABSTRACT: Several research groups combined
efforts to measure simultaneously the available
ultraviolet radiation of the urban atmosphere of
Los Angeles under representative environmental
conditions. The study was planned to permit
evaluation of possible methods of measuring the
UV radiation important in photochemical reac-
tions (in the range from 300 to 400 nanometers)
and to obtain preliminary data on the UV radia-
tion energy with respect to location, elevation,
and time of day. Measurements were made on
five days at various levels of air pollution rang-
ing from no smog to mode rate-to-heavy smog.
BIBLIOGRAPHIC: Nader, John S. Pilot study of
ultraviolet radiation in Los Angeles, October
1965. PHS Publ. No. 999-AP-38. 1967. 91pp.
ABSTRACT: Several research groups combined
efforts to measure simultaneously the available
ultraviolet radiation of the urban atmosphere of
Los Angeles under representative environmental
conditions. The study was planned to permit
evaluation of possible methods of measuring the
UV radiation important in photochemical reac-
tions (in the range from 300 to 400 nanometers)
and to obtain preliminary data on the UV radia-
tion energy with respect to location, elevation,
and time of day. Measurements were made on
five days at various levels of air pollution rang-
ing from no smog to mode rate-to-heavy smog.
BIBLIOGRAPHIC: Nader, John S. Pilot study of
ultraviolet radiation in Los Angeles, October
1965. PHS Publ. No. 999-AP-38. 1967. 91pp.
ABSTRACT: Several research groups combined
efforts to measure simultaneously the available
ultraviolet radiation of the urban atmosphere of
Los Angeles under representative environmental
conditions. The study was planned to permit
evaluation of possible methods of measuring the
UV radiation important in photochemical reac-
tions (in the range from 300 to 400 nanometers)
and to obtain preliminary data on the UV radia-
tion energy with respect to location, elevation,
and time of day. Measurements were made on
five days at various levels of air pollution rang-
ing from no smog to mode rate-to-heavy smog.
ACCESSION NO.
KEY WORDS:
Instrumentation
Measurements
Methodology
Ultraviolet
Radiation
Photochemistry
Air Pollution
Smog
Ultraviolet
Detection
ACCESSION NO.
KEY WORDS:
Instrumentation
Measurements
Methodology
Ultraviolet
Radiation
Photochemistry
Air Pollution
Smog
Ultraviolet
Detection
ACCESSION NO.
KEY WORDS:
Instrumentation
Measurements
Methodology
Ultraviolet
Radiation
Photochemistry
Air Pollution
Smog
Ultraviolet
Detection
-------
This report is a compilation of data obtained by
the several participants, with brief accounts of
instrumentation and procedures. The instru-
mental sensors used to detect the UV radiation
were filter photocell, filter phototube, photo-
chemical sensors, photosensitive plastic, and
photochromic glass. Air quality and meteoro-
logical data for the sampling periods are also
presented. A discussion and summary relates
the data obtained in measurements by the differ-
ent methods and at the various locations.
This report is a compilation of data obtained by
the several participants, with brief accounts of
instrumentation and procedures. The instru-
mental sensors used to detect the UV radiation
were filter photocell, filter phototube, photo-
chemical sensors, photosensitive plastic, and
photochromic glass. Air quality and meteoro-
logical data for the sampling periods are also
presented. A discussion and summary relates
the data obtained in measurements by the differ-
ent methods and at the various locations.
This report is a compilation of data obtained by
the several participants, with brief accounts of
instrumentation and procedures. The instru-
mental sensors used to detect the UV radiation
were filter photocell, filter phototube, photo-
chemical sensors, photosensitive plastic, and
photochromic glass. Air quality and meteoro-
logical data for the sampling periods are also
presented. A discussion and summary relates
the data obtained in measurements by the differ-
ent methods and at the various locations.
------- |