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        ENVIRONMENTAL HEALTH SERIES
        Air Pollution
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!
          PILOT vSTUDY
          OF ULTRAVIOLET  RADIATION
           \    \   \    X
          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-

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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).

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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

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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

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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

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     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

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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

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                    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

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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

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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

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          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

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                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

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g
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f£
o
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                                                   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
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 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

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   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
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 LU
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 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 '
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           O£
            I 0.81-
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           S 0.4
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           O
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                                                        °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.

-------