LK\‘IKOY\IFN’IAI. RESLARCH14, 113 - 137 t 1977)
Intensity
Patterns
of Solar Ultraviolet
JOSEPH SCO,I.TO AND THOMAS
Received
August
Radiation
R. FEARS
24, 1976
Using field measurements of ultraviolet radiation. intensity patterns by time of day and time of year are examined. Depending on location. 39 to 80% of the half-hourly readings of sufficient intensity to produce minimum erythema occur between 10:00 ..I>$ and 1:OO F’XI during the late spring and early summer months of May through August. Most people, particularly those in Northern latitudes. can substantially reduce their exposure to erythema-producing ultraviolet radiation by avoiding sunlight during the noon-day hours. Individuals of light-skin pigmentation. i.e.. those who should limit their sunlight exposure. will find this work helpful.
INTRODUCTION
Each day the surface of the earth is exposed to the ultraviolet radiation (UV) of sunlight. Although living things have adapted and indeed are not completely dependent on sunlight, many of its effects are deleterious. Exposure to UV may produce various diseases of the skin and eye in man, such as inflammation, blistering, photokeratitis, cataracts, squamous cell carcinoma, basal cell carcinoma, and malignant melanoma. In an earlier paper (Scotto et al., 1976) we studied field measurements from ultraviolet meters by quantifying, in relative terms, ultraviolet insolation. However, total cumulative ultraviolet exposure may not be the most appropriate dose metameter for this agent. Rook and co-workers (1975) state, “The reaction of the skin to different dose-rates and different intervals between doses of ultraviolet light, e.g. frequent lower dose-rates as might be experienced by outdoor workers compared with less frequent higher dose-rates from week-end radiation, has not been established in man.” Indeed, it has been suggested (Hsu et al., 1975) that initiation of tumor cells may result from short, intense exposures. In this paper we examine the field measurements of ultraviolet radiation in order to quantify ultraviolet intensity patterns by time of day and time of year. As in the earlier work our purpose is to provide guidelines for those individuals who need to limit their sunlight exposure. MATERIALS
AND METHODS
In a cooperative effort of the Department of Transportation, Temple University, the National Oceanic Atmospheric Administration, and the National Cancer Institute, ultraviolet meters were placed at weather stations in nine continental locations.’ The locations were selected to represent a wide range of latitudes. The meters were designed by Donald F. Robertson (1969, 1972) so that after each half-hour each meter records a count which is proportional to the erythema (sunI Ft. Worth. Texas: Des Moines. Florida: El Paso. Texas: Albuquerque, Dakota.
Iowa: Minneapolis. Minnesota; New Mexico: Philadelphia.
113 Copyright 411
npht\
‘i
1977
OS reproduction
hy
Academic m any
Press.
Inc.
form
reserved.
Oakland, California; Tallahassee. Pennsylvania: and Bismarck. North
114
SCOTT0
AND
FEARS
burning) effectiveness of the ultraviolet B (in the broad wavelength band 280-320 nm) that has passed through its filters and photosensors. A count of four-hundred during a single half-hour is said to be sufficient to produce “minimal erythema,” i.e., slight redness, in untanned Caucasian skin. This level ofintensity will therefore be used as an intensity index. Since the action spectrum for skin erythema is usually taken to be the same or similar to that for skin cancer, measurements from these instruments have wide applicability and are therefore particularly well suited for the purpose of this study. Data for the entire calendar year 1974 were submitted to the National Cancer Institute for processing and analysis (Scotto ef nl., 1975). Monthly averages for each half-hourly time slot were used as estimates for missing recordings. All diurnal recordings relate to local standard time. RESULTS
In order to describe intensity patterns of UV radiation conveniently, six values were arbitrarily chosen: 100, 200, 300, 400, 500, 600. The number of days during which at least one half-hour UV count reaches the specified intensity at each location is provided in Table 1. Not unexpectedly, intensity values are more frequently exceeded at stations which are closer to the equator (low latitude), closer to the sun (high altitude), and which have clearer skies. Intensity values greater than 200 are frequently exceeded during the late spring and early summer (June through August), as shown in Table 2. When the northern hemisphere is tilted from the sun (November through January) high-intensity values occur infrequently. Table 3 shows the distribution of occasions during the year for which values of 200, 400, and 600 were exceeded, by time of day for each location. Intensity recordings of 400 or more occur most frequently during the noon time period; 93% of the recordings above 400 in Philadelphia were observed between 10:00 AM and 2:00 PM and 74% of the half-hourly readings above 400 occurred during the same time interval in El Paso.
N~t.~sw.
Station Tallahassee El Paso Ft. Worth Albuquerque Oakland Philadelphia Des Moines Minneapolis Bismarck
Latitude 30.4" 31.8"
32.8” 35.1" 37.7 39.9 4l.Y
44.9” 46.8"
TABLE I OF DAYS DURI~‘C, 1974 wrr~ AT LEASI. ONE HAI.F-HOUR IXAI‘ RF.ACHED SPECIFILD INTENSITY
Altitude
(ft) 5s
3918 537 5311 6
5 938 834 1647
Average daily sky cover in tenths: sunrise-sunset 5.67 3.96 5.23 4.57 4.54 6.28 6.05 6.37 6.25
COUNT
lntensity 600
value
500
400
300
200
100
0
79
153
203
279
338
359
365
173 82 131
215
255
134 180
171 219
312 233 257
352 293 320
361 343 360
365 365 365
61 14 4
133 60 94 64 71
170 117 180
210
262 222
339 299 299 264 259
365 365 365 365 365
18 22
III 118
167 171 147 154
221 196 192
INTENSITY
PATTERNS
OF SOLAR
UV
RADIATION
113
000000000
000000000
occlooooooo
ocooooooo
or-10000000
Total
16:30 17:oo
OS:00 OS:30 09:oo 09:30 IO:00 IO:30 I l:oo 11:30 12:oo 12:30 13:OQ 13:30 14:oo 14:30 15:oo 15:30
Intensity
I ialue
Time
200
‘2 II2 176 220 257 294 330 345 344 341 342 326 304 ‘69 236 100 134 61 0
4313
3507
El Paso
9; 145 199 741 266 281 308 307 304 308 290 255 205 166 106 31 0 0
Tallahassee
Fort
3170
65 122 163 201 ‘32 254 268 272 273 262 252 22s 202 151 131 93 4 0
0
Worth
3627
3 91 156 187 225 252 274 287 302 311 297 277 24.5 231 192 149 100 42 0
Albuquerque
2842
68 100 151 180 204 229 237 242 241 226 219 205 180 IS9 128 46 0
27
0
Oakland
Station
2139
38 85 119 147 169 182 184 190 193 185 I72 162 133 100 69 21 0 0
0
Philadelphia
2339
0 37 66 I02 134 I58 171 186 185 193 197 I88 174 164 134 112 91 45 2
Des Moines
0
1980
51 100 126 138 151 158 167 169 163 158 144 I38 119 96 57 23 0
'2
Minneapolis
2097
149 141 123 104 69 38 0
Bismarck
TCd
l5:30 16:OO
14:oo 14:30 15:oo
12:oo I?:30 13:oo l3:30
lo:00 IO:30 II:00 I I:30
09: 30
09:oo
itensity
,,
value
400
,,,,
I?‘9
0 0 1332
162 123 52 0
214 194
167 164 I58
132 99 47 6
I89 210 ‘31 1,35 235 227
83
112
IS1
1347
0 0
175 95 44
153 152 154 I39
135 145
0 10
13 95
161
92 IZI I61
0 21
,.
1834
IX 68 17 0
I89 174 149
197 198 100
I55 182
*
0 59 I?4
1369
3 0
146 I-15 64
IS3 I58 164 I63
38 89 I I9 146
I 0
6%
0 0
38 I4
98 86 82 61
1-7 52 79 88
0 2
936
104 91 75 46
108 109 109
40 65 83 104
0 0
(8
66’
0 0
,,,
‘0
33 36
92 89 79 71
47 66 83
0 0 21
36 0 0
95
100
83 91
61 78
.
< a .b 0
C
s
;j m z a
Total
Intensity 1o:oo IO:30 II:00 11:30 12:oo 12:30 13:oo 13:30 14:oo 14:30 15:oo 15:30 l6:OO
value
Time
600
213
0 2 21 43 49 52 32 13 I 0 0 0 0
Tallahassee
1085
10 87 128 144 157 154 147 131 88 39 0 0 0
El Paso
Fort
301
3 16 60 68 76 58 18 1 0 0 0 0
Worth
703
0 16 86 116 120 122 108 80 52 3 0 0 0
Station
31
214
0 0
0 0 I 5 12 9 4 0 0 0 0 0 0
Philadelphia
0 0 4 27 44 56 49 32 0 I
Oakland
3 (Cor~tinuc~I)
Albuquerque
TABLE
134
0 0 0 18 32 35 31 I6
Des Moines
35
0 0 0 0 8 16 8 3 0 0 0 0 0
Minneapolis
;i z 2 E
I4 20 15 2 0
54
s
3
R
0 0 0
Bismarck
INTENSITY
PATTERKS
OF
SOL,AR
LW
RhDIAl-ION
119
The interrelationship of intensity with location, season, and hour of day is given in Table 4, which provides the relative number of half-hour periods with counts exceeding 200, 400. and 600 for specified time intervals in each month at each location. During the spring and summer months (April through September), 28.5 to 56.4% of all the counts above 400 were received at each location during the noon time interval 1l:OO ASPto 1:OO PM. DISCUSSION
In all locations, intensities capable of producing erythema are found most frequently during the midday hours of the spring and early summer, but in northern latitudes this concentration of high-intensity recordings is quite remarkable. For example, in Bismarck 96.3% of all the recorded counts above 600 were observed between 1I:00 AM and 1:00 PM during June and July. In contrast in El Paso. at a much lower latitude 20.6% of all counts above 600 were observed during this period. This suggests that individuals (particularly those in northern latitudes) might easily reduce their exposure to higher intensities of short-wavelength ultraviolet radiation by avoiding the midday sun during just a few months. Using the tables presented here, one can consider quantitatively exposure to periods of high-intensity, short-wavelength ultraviolet radiation as well as evaluate plans for avoiding sunlight. Consider two hypothetical individuals. The first, a professional, is indoors on weekdays until 5:00 PM and outdoors during the other daylight hours. On weekends and during July, when he vacations, he is also outside from 1O:OO AM until 2:00 PM. The second individual is an auto mechanic. He is sheltered about 50% of the time during working hours, 7:00 AM--I 1:30 AM and 12:30 r+5:00 PM. and outside during lunch time, six days a week. Table 5 provides for each location the relative reduction in length of exposure to intensities exceeding 400 counts per half-hour that each individual can achieve by avoiding sunlight during one-hour and two-hour periods around noontime each day for 2, 4, and 12 months. By avoiding just one noon-time hour for 4 months. reduction in total exposure of from 16.7 to 35.7% is achieved by each individual. Reductions achieved by avoiding sunlight during two noon-time hours are surprisingly large, ranging from 23% for 2 months in El Paso to 58% in Des Moines for the whole year. In general, an avoidance scheme appears to be more effective at higher latitudes. For example, by avoiding sunlight for 1 hour in Bismarck the professional reduces exposure by 20% compared to 13% in Tallahassee. CONCLUSION
These data show that by using a simple plan of avoiding sunlight around noontime, an individual can drastically reduce his exposure to short periods of highintensity ultraviolet radiation.
120
SCOTT0
AND
FEARS
?‘c)r-? - r-i m *
--r-h - Pi ri ri
2 z +L?:8RI . ymmmv ~-i--i-;-i---3 m. 0 c, 0 -00 r,?‘---
INTENSITY
0000 6 d
c’
6
PATTERNS
d
o--o ri b’ ti
0.0 cddd
UV
0000 6666
~:3000* Cdid
6
SOLAR
0000 dddd
a--.ri -4 \d od
0000 d d
OF
0
3
&
121
RADIATION
ococ 6666
22
SCOTT0
9099 cd00
AND
FEARS
9993 0006
0000 ddo’i
--mm b’&iv;
90000’ 9 c. 0
0000 dddd
9900 0066
coo0 dddd
-0 4
w-i rnr-‘drn
c-1 0 od ri--
rti
Ici 9 --
CO*-M riti3dod
0000 d 6 c’ c:
*r-c+ ri i
r- od
qooo Odd6
go000 x ” 0 CTi 0 e,crmm* b-.-m.I I I I o--.-w ~momo &‘“OOM&MC
9900 0066
oo-6 6
c. 9 9-0 0006
0000 dddd
0’
c’
INTENSITY
PATl‘EKNS
OF
cz35 jssj
c. c1 c. c. ccc0
c--cn i od ri --
i
occc d c’
-1 I z---.rn=mo 52 ----i’s m---0
LIV
5355 cccs
cccc s’ r,
123
KAI)I.4’I’ION
CC3D ii&i
s’
c’
v:
c--d
SOLAR
c’
i
cc33 o666
i
c’
COGfo c’ i
I
I
occc c’dbs’
6
i
?CC? cocc
0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0
Paso, Texas 11:31-12:30 11:01-13:oo 10:31-13:30 IO:01 -14:oo
Fort Worth Texas 11:31-12:30 ll:Ol-13:oo 10:31-13:30 1O:Ol - 14:oo
Albuquerque, New 11:31-12:30 11:01~13:00 10:31-13:30 lO:Ol- 14:OO
Mexico
0.0 0.0 0.0 0.0
Florida
Tallahassee, 11:31-12:30 ll:Ol-13:oo 10:31-13:30 lO:Ol-14:oo
January
PERECENT
0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0
February
OF COUNTS
0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0
1.1 1.7 1.9 1.9
0.0 0.0 0.0 0.0
March
ABOVE
600
2.3 3.7 3.7 3.7
1.3 1.3 1.3 1.3
4.2 8.5 11.9 12.9
10.8 16.0 16.0 16.0
April
4c
7.0 14.1 19.8 21.2
11.6 21.9 27.2 28.2
5.3 10.5 15.2 18.9
10.8 21.1 29.1 29.1
May
7.7 15.5 22.5 26.6
18.9 37.5 39.2 39.5
5.5 11.1 16.6 21.8
11.3 20.2 25.4 26.3
June
SPECIFIED
TABLE WITHIN
8.4 16.2 23.0 26.2
9.6 16.6 20.3 20.3
4.8 9.5 13.7 17.3
7.0 12.2 14.6 15.0
6.4 12.4 16.2 17.2
6.3 9.6 10.3 10.3
3.9 7.8 11.5 14.2
5.2 9.4 9.9 9.9
FOR
2.7 4.7 4.7 4.7
0.0 0.0 0.0 0.0
3.4 5.9 7.9 7.9
2.3 3.8 3.8 3.8
September
BY MONTH
August
PERIOD Mnnth
July
TIML
1974
0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0
0.4 0.6 0.6 0.6
0.0 0.0 0.0 0.0
October
0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0
November
5
2
0.0
0.0
0.0 0.0 0.0 0.0
E
2
0.0
0.0 0.0 0.0 0.0
B c:
0.0
0.0
0.0 0.0
December
INTENSITY
PATTERNS
OF
SOLAR
UV
125
RADIATION
9999 0000
0000 dddc’
99=c1 0060
0000 6666
0000 6666
9909 0060
qooo Odd6
9900 oodd
0000 dc’dd
coot c’ d d c’
9900 OOdti
0000 6666
9999 0000
0000 ddc’c:
9900 oodd
9900 0066
0000 dddc:
9 c, OCdc’
0000 6666
ooco 6666
0000 dddd
9
0
0
coo0 cddd
0000 dddd
9909 0060
coo0 dddd
qqoo OOdd
0000 d 6
0
0
9
0
9
qqoo oojd
9009 cddo
9909 0060
0060
0000 6666
6
d
Z:848 . . . . ~Arnrn~ .ZA‘“T-7 I -Mm E: ”--00 0 ?-!0 m-e-x
0000 dddd
9930 0066
0000 dddd
9 9 0060
0000 dddd
9900 0056
0000 dddd
9900 0066
AhI-I:00
PSI
ASI-I:00
June-July May-August January-December
II:00
PM
Mechanic II:30 Axf-12:30 PM June-July May-August January-December
June-July May-August January-December
I I:00
Professional I I:30 AFT- I?:30 r?,I June- July May-August January-December
12.6
25.0 49.9
17.5
32.7 59.1
21.8 39.9
8.5 16.8 33.6
33.0 53.3
11.8
23.0
36.4 54.7
38.0 55.1
20.5
13.9 15.3 37.0
41.6 52.7
30. I
15.0 10.6 26.5
TABLE
30.2 52.9
15.7
10.5 20.2 35.7
26.2 36.8 53.3
18.6 27.1
13.2
Albuquerque
IS H-\LP-HOURLY SPKIFIED Trw
Worth
16.7 26.9
Fort
11.6
El Paso
75.7
27.9
13.1 1x.4
Tallahassee
A\,o~r)~uc;
REDU~TIOPI’ SL~NLIGH,I DVRINC:
PERCEST
39.6 55.5
20.0
13.x 26.4 37.0
30.2 43.1 53.8
'1.7 27.0
15.2
Oakland
53.0 66.3
28.6
18.7 35.7 45.3
38.7 s1.5 5X.3
26.0 29.8
19. I
Philadelphia
COUNTS EXCEEDISG 400 PFRI~DS AT EACH OF NINL
5
26.7 43.5 56.0
28.8 37.5
17.7
36.5 46.3 53.5
31.9
50.6 57.1
51.9 62.1
34.0 39.0
21.1
39.4 49.7 53.1
3.0 27.1
19.6
Bismarck
30.8
34.9 42.9
20.6
39.4 50.8 55.x
19.7 15.6 28.8
18.2
Minneapolis
23.0 26.9
Des Moines
LOCA.I.IONS
~1
2
7" 6
2
K 2
INTENSITY
PATTERNS
OF
SOLAR
UV
RADIATION
127
REFERENCES Hsu. J., Forbes, P. D., Harber, L. G., and La Kow, E. (1975). Introduction of skin tumors in hairless mice by a single exposure to UV radiation. Photockem. Photobiol. 21, 185-188. Robertson, D. F. (1969). “Long-Term Field Measurements of Erythemally Effective Natural Ultraviolet Radiation in The Biologic Effects of Ultraviolet Radiation.” Pergamon. New York. Robertson, D. F. (1972). “Solar Ultraviolet Radiation in Relation to Human Sunburn and Skin Cancer.” Thesis submitted to the University of Queensland, Brisbane, Australia. Rook, A., Wilkinson, D. S.. and Ebling, F. T. G. (1975).Zn “Textbookof Dermatology.” Znded, Vol. 2, pp. 1914-15. Blackwell Scientific Publication, Oxford London Edinburgh Melbourne. Scotto, J., Fears, T. R., and Gori, G. B. (1975). “Measurements of Ultraviolet Radiation in the United States and Comparisons with Skin Cancer Data.” DHEW No. (NIH) 761029. National Cancer Institute, Div. of Cancer Cause and Prevention. Scotto. J., Fears. T. R., and Gori. G. B. (1976). Ultraviolet exposure patterns. Environ. Res. 12, 22%237.
Intensity
Patterns
of Solar Ultraviolet
JOSEPH SCO,I.TO AND THOMAS
Received
August
Radiation
R. FEARS
24, 1976
Using field measurements of ultraviolet radiation. intensity patterns by time of day and time of year are examined. Depending on location. 39 to 80% of the half-hourly readings of sufficient intensity to produce minimum erythema occur between 10:00 ..I>$ and 1:OO F’XI during the late spring and early summer months of May through August. Most people, particularly those in Northern latitudes. can substantially reduce their exposure to erythema-producing ultraviolet radiation by avoiding sunlight during the noon-day hours. Individuals of light-skin pigmentation. i.e.. those who should limit their sunlight exposure. will find this work helpful.
INTRODUCTION
Each day the surface of the earth is exposed to the ultraviolet radiation (UV) of sunlight. Although living things have adapted and indeed are not completely dependent on sunlight, many of its effects are deleterious. Exposure to UV may produce various diseases of the skin and eye in man, such as inflammation, blistering, photokeratitis, cataracts, squamous cell carcinoma, basal cell carcinoma, and malignant melanoma. In an earlier paper (Scotto et al., 1976) we studied field measurements from ultraviolet meters by quantifying, in relative terms, ultraviolet insolation. However, total cumulative ultraviolet exposure may not be the most appropriate dose metameter for this agent. Rook and co-workers (1975) state, “The reaction of the skin to different dose-rates and different intervals between doses of ultraviolet light, e.g. frequent lower dose-rates as might be experienced by outdoor workers compared with less frequent higher dose-rates from week-end radiation, has not been established in man.” Indeed, it has been suggested (Hsu et al., 1975) that initiation of tumor cells may result from short, intense exposures. In this paper we examine the field measurements of ultraviolet radiation in order to quantify ultraviolet intensity patterns by time of day and time of year. As in the earlier work our purpose is to provide guidelines for those individuals who need to limit their sunlight exposure. MATERIALS
AND METHODS
In a cooperative effort of the Department of Transportation, Temple University, the National Oceanic Atmospheric Administration, and the National Cancer Institute, ultraviolet meters were placed at weather stations in nine continental locations.’ The locations were selected to represent a wide range of latitudes. The meters were designed by Donald F. Robertson (1969, 1972) so that after each half-hour each meter records a count which is proportional to the erythema (sunI Ft. Worth. Texas: Des Moines. Florida: El Paso. Texas: Albuquerque, Dakota.
Iowa: Minneapolis. Minnesota; New Mexico: Philadelphia.
113 Copyright 411
npht\
‘i
1977
OS reproduction
hy
Academic m any
Press.
Inc.
form
reserved.
Oakland, California; Tallahassee. Pennsylvania: and Bismarck. North
114
SCOTT0
AND
FEARS
burning) effectiveness of the ultraviolet B (in the broad wavelength band 280-320 nm) that has passed through its filters and photosensors. A count of four-hundred during a single half-hour is said to be sufficient to produce “minimal erythema,” i.e., slight redness, in untanned Caucasian skin. This level ofintensity will therefore be used as an intensity index. Since the action spectrum for skin erythema is usually taken to be the same or similar to that for skin cancer, measurements from these instruments have wide applicability and are therefore particularly well suited for the purpose of this study. Data for the entire calendar year 1974 were submitted to the National Cancer Institute for processing and analysis (Scotto ef nl., 1975). Monthly averages for each half-hourly time slot were used as estimates for missing recordings. All diurnal recordings relate to local standard time. RESULTS
In order to describe intensity patterns of UV radiation conveniently, six values were arbitrarily chosen: 100, 200, 300, 400, 500, 600. The number of days during which at least one half-hour UV count reaches the specified intensity at each location is provided in Table 1. Not unexpectedly, intensity values are more frequently exceeded at stations which are closer to the equator (low latitude), closer to the sun (high altitude), and which have clearer skies. Intensity values greater than 200 are frequently exceeded during the late spring and early summer (June through August), as shown in Table 2. When the northern hemisphere is tilted from the sun (November through January) high-intensity values occur infrequently. Table 3 shows the distribution of occasions during the year for which values of 200, 400, and 600 were exceeded, by time of day for each location. Intensity recordings of 400 or more occur most frequently during the noon time period; 93% of the recordings above 400 in Philadelphia were observed between 10:00 AM and 2:00 PM and 74% of the half-hourly readings above 400 occurred during the same time interval in El Paso.
N~t.~sw.
Station Tallahassee El Paso Ft. Worth Albuquerque Oakland Philadelphia Des Moines Minneapolis Bismarck
Latitude 30.4" 31.8"
32.8” 35.1" 37.7 39.9 4l.Y
44.9” 46.8"
TABLE I OF DAYS DURI~‘C, 1974 wrr~ AT LEASI. ONE HAI.F-HOUR IXAI‘ RF.ACHED SPECIFILD INTENSITY
Altitude
(ft) 5s
3918 537 5311 6
5 938 834 1647
Average daily sky cover in tenths: sunrise-sunset 5.67 3.96 5.23 4.57 4.54 6.28 6.05 6.37 6.25
COUNT
lntensity 600
value
500
400
300
200
100
0
79
153
203
279
338
359
365
173 82 131
215
255
134 180
171 219
312 233 257
352 293 320
361 343 360
365 365 365
61 14 4
133 60 94 64 71
170 117 180
210
262 222
339 299 299 264 259
365 365 365 365 365
18 22
III 118
167 171 147 154
221 196 192
INTENSITY
PATTERNS
OF SOLAR
UV
RADIATION
113
000000000
000000000
occlooooooo
ocooooooo
or-10000000
Total
16:30 17:oo
OS:00 OS:30 09:oo 09:30 IO:00 IO:30 I l:oo 11:30 12:oo 12:30 13:OQ 13:30 14:oo 14:30 15:oo 15:30
Intensity
I ialue
Time
200
‘2 II2 176 220 257 294 330 345 344 341 342 326 304 ‘69 236 100 134 61 0
4313
3507
El Paso
9; 145 199 741 266 281 308 307 304 308 290 255 205 166 106 31 0 0
Tallahassee
Fort
3170
65 122 163 201 ‘32 254 268 272 273 262 252 22s 202 151 131 93 4 0
0
Worth
3627
3 91 156 187 225 252 274 287 302 311 297 277 24.5 231 192 149 100 42 0
Albuquerque
2842
68 100 151 180 204 229 237 242 241 226 219 205 180 IS9 128 46 0
27
0
Oakland
Station
2139
38 85 119 147 169 182 184 190 193 185 I72 162 133 100 69 21 0 0
0
Philadelphia
2339
0 37 66 I02 134 I58 171 186 185 193 197 I88 174 164 134 112 91 45 2
Des Moines
0
1980
51 100 126 138 151 158 167 169 163 158 144 I38 119 96 57 23 0
'2
Minneapolis
2097
149 141 123 104 69 38 0
Bismarck
TCd
l5:30 16:OO
14:oo 14:30 15:oo
12:oo I?:30 13:oo l3:30
lo:00 IO:30 II:00 I I:30
09: 30
09:oo
itensity
,,
value
400
,,,,
I?‘9
0 0 1332
162 123 52 0
214 194
167 164 I58
132 99 47 6
I89 210 ‘31 1,35 235 227
83
112
IS1
1347
0 0
175 95 44
153 152 154 I39
135 145
0 10
13 95
161
92 IZI I61
0 21
,.
1834
IX 68 17 0
I89 174 149
197 198 100
I55 182
*
0 59 I?4
1369
3 0
146 I-15 64
IS3 I58 164 I63
38 89 I I9 146
I 0
6%
0 0
38 I4
98 86 82 61
1-7 52 79 88
0 2
936
104 91 75 46
108 109 109
40 65 83 104
0 0
(8
66’
0 0
,,,
‘0
33 36
92 89 79 71
47 66 83
0 0 21
36 0 0
95
100
83 91
61 78
.
< a .b 0
C
s
;j m z a
Total
Intensity 1o:oo IO:30 II:00 11:30 12:oo 12:30 13:oo 13:30 14:oo 14:30 15:oo 15:30 l6:OO
value
Time
600
213
0 2 21 43 49 52 32 13 I 0 0 0 0
Tallahassee
1085
10 87 128 144 157 154 147 131 88 39 0 0 0
El Paso
Fort
301
3 16 60 68 76 58 18 1 0 0 0 0
Worth
703
0 16 86 116 120 122 108 80 52 3 0 0 0
Station
31
214
0 0
0 0 I 5 12 9 4 0 0 0 0 0 0
Philadelphia
0 0 4 27 44 56 49 32 0 I
Oakland
3 (Cor~tinuc~I)
Albuquerque
TABLE
134
0 0 0 18 32 35 31 I6
Des Moines
35
0 0 0 0 8 16 8 3 0 0 0 0 0
Minneapolis
;i z 2 E
I4 20 15 2 0
54
s
3
R
0 0 0
Bismarck
INTENSITY
PATTERKS
OF
SOL,AR
LW
RhDIAl-ION
119
The interrelationship of intensity with location, season, and hour of day is given in Table 4, which provides the relative number of half-hour periods with counts exceeding 200, 400. and 600 for specified time intervals in each month at each location. During the spring and summer months (April through September), 28.5 to 56.4% of all the counts above 400 were received at each location during the noon time interval 1l:OO ASPto 1:OO PM. DISCUSSION
In all locations, intensities capable of producing erythema are found most frequently during the midday hours of the spring and early summer, but in northern latitudes this concentration of high-intensity recordings is quite remarkable. For example, in Bismarck 96.3% of all the recorded counts above 600 were observed between 1I:00 AM and 1:00 PM during June and July. In contrast in El Paso. at a much lower latitude 20.6% of all counts above 600 were observed during this period. This suggests that individuals (particularly those in northern latitudes) might easily reduce their exposure to higher intensities of short-wavelength ultraviolet radiation by avoiding the midday sun during just a few months. Using the tables presented here, one can consider quantitatively exposure to periods of high-intensity, short-wavelength ultraviolet radiation as well as evaluate plans for avoiding sunlight. Consider two hypothetical individuals. The first, a professional, is indoors on weekdays until 5:00 PM and outdoors during the other daylight hours. On weekends and during July, when he vacations, he is also outside from 1O:OO AM until 2:00 PM. The second individual is an auto mechanic. He is sheltered about 50% of the time during working hours, 7:00 AM--I 1:30 AM and 12:30 r+5:00 PM. and outside during lunch time, six days a week. Table 5 provides for each location the relative reduction in length of exposure to intensities exceeding 400 counts per half-hour that each individual can achieve by avoiding sunlight during one-hour and two-hour periods around noontime each day for 2, 4, and 12 months. By avoiding just one noon-time hour for 4 months. reduction in total exposure of from 16.7 to 35.7% is achieved by each individual. Reductions achieved by avoiding sunlight during two noon-time hours are surprisingly large, ranging from 23% for 2 months in El Paso to 58% in Des Moines for the whole year. In general, an avoidance scheme appears to be more effective at higher latitudes. For example, by avoiding sunlight for 1 hour in Bismarck the professional reduces exposure by 20% compared to 13% in Tallahassee. CONCLUSION
These data show that by using a simple plan of avoiding sunlight around noontime, an individual can drastically reduce his exposure to short periods of highintensity ultraviolet radiation.
120
SCOTT0
AND
FEARS
?‘c)r-? - r-i m *
--r-h - Pi ri ri
2 z +L?:8RI . ymmmv ~-i--i-;-i---3 m. 0 c, 0 -00 r,?‘---
INTENSITY
0000 6 d
c’
6
PATTERNS
d
o--o ri b’ ti
0.0 cddd
UV
0000 6666
~:3000* Cdid
6
SOLAR
0000 dddd
a--.ri -4 \d od
0000 d d
OF
0
3
&
121
RADIATION
ococ 6666
22
SCOTT0
9099 cd00
AND
FEARS
9993 0006
0000 ddo’i
--mm b’&iv;
90000’ 9 c. 0
0000 dddd
9900 0066
coo0 dddd
-0 4
w-i rnr-‘drn
c-1 0 od ri--
rti
Ici 9 --
CO*-M riti3dod
0000 d 6 c’ c:
*r-c+ ri i
r- od
qooo Odd6
go000 x ” 0 CTi 0 e,crmm* b-.-m.I I I I o--.-w ~momo &‘“OOM&MC
9900 0066
oo-6 6
c. 9 9-0 0006
0000 dddd
0’
c’
INTENSITY
PATl‘EKNS
OF
cz35 jssj
c. c1 c. c. ccc0
c--cn i od ri --
i
occc d c’
-1 I z---.rn=mo 52 ----i’s m---0
LIV
5355 cccs
cccc s’ r,
123
KAI)I.4’I’ION
CC3D ii&i
s’
c’
v:
c--d
SOLAR
c’
i
cc33 o666
i
c’
COGfo c’ i
I
I
occc c’dbs’
6
i
?CC? cocc
0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0
Paso, Texas 11:31-12:30 11:01-13:oo 10:31-13:30 IO:01 -14:oo
Fort Worth Texas 11:31-12:30 ll:Ol-13:oo 10:31-13:30 1O:Ol - 14:oo
Albuquerque, New 11:31-12:30 11:01~13:00 10:31-13:30 lO:Ol- 14:OO
Mexico
0.0 0.0 0.0 0.0
Florida
Tallahassee, 11:31-12:30 ll:Ol-13:oo 10:31-13:30 lO:Ol-14:oo
January
PERECENT
0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0
February
OF COUNTS
0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0
1.1 1.7 1.9 1.9
0.0 0.0 0.0 0.0
March
ABOVE
600
2.3 3.7 3.7 3.7
1.3 1.3 1.3 1.3
4.2 8.5 11.9 12.9
10.8 16.0 16.0 16.0
April
4c
7.0 14.1 19.8 21.2
11.6 21.9 27.2 28.2
5.3 10.5 15.2 18.9
10.8 21.1 29.1 29.1
May
7.7 15.5 22.5 26.6
18.9 37.5 39.2 39.5
5.5 11.1 16.6 21.8
11.3 20.2 25.4 26.3
June
SPECIFIED
TABLE WITHIN
8.4 16.2 23.0 26.2
9.6 16.6 20.3 20.3
4.8 9.5 13.7 17.3
7.0 12.2 14.6 15.0
6.4 12.4 16.2 17.2
6.3 9.6 10.3 10.3
3.9 7.8 11.5 14.2
5.2 9.4 9.9 9.9
FOR
2.7 4.7 4.7 4.7
0.0 0.0 0.0 0.0
3.4 5.9 7.9 7.9
2.3 3.8 3.8 3.8
September
BY MONTH
August
PERIOD Mnnth
July
TIML
1974
0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0
0.4 0.6 0.6 0.6
0.0 0.0 0.0 0.0
October
0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0
November
5
2
0.0
0.0
0.0 0.0 0.0 0.0
E
2
0.0
0.0 0.0 0.0 0.0
B c:
0.0
0.0
0.0 0.0
December
INTENSITY
PATTERNS
OF
SOLAR
UV
125
RADIATION
9999 0000
0000 dddc’
99=c1 0060
0000 6666
0000 6666
9909 0060
qooo Odd6
9900 oodd
0000 dc’dd
coot c’ d d c’
9900 OOdti
0000 6666
9999 0000
0000 ddc’c:
9900 oodd
9900 0066
0000 dddc:
9 c, OCdc’
0000 6666
ooco 6666
0000 dddd
9
0
0
coo0 cddd
0000 dddd
9909 0060
coo0 dddd
qqoo OOdd
0000 d 6
0
0
9
0
9
qqoo oojd
9009 cddo
9909 0060
0060
0000 6666
6
d
Z:848 . . . . ~Arnrn~ .ZA‘“T-7 I -Mm E: ”--00 0 ?-!0 m-e-x
0000 dddd
9930 0066
0000 dddd
9 9 0060
0000 dddd
9900 0056
0000 dddd
9900 0066
AhI-I:00
PSI
ASI-I:00
June-July May-August January-December
II:00
PM
Mechanic II:30 Axf-12:30 PM June-July May-August January-December
June-July May-August January-December
I I:00
Professional I I:30 AFT- I?:30 r?,I June- July May-August January-December
12.6
25.0 49.9
17.5
32.7 59.1
21.8 39.9
8.5 16.8 33.6
33.0 53.3
11.8
23.0
36.4 54.7
38.0 55.1
20.5
13.9 15.3 37.0
41.6 52.7
30. I
15.0 10.6 26.5
TABLE
30.2 52.9
15.7
10.5 20.2 35.7
26.2 36.8 53.3
18.6 27.1
13.2
Albuquerque
IS H-\LP-HOURLY SPKIFIED Trw
Worth
16.7 26.9
Fort
11.6
El Paso
75.7
27.9
13.1 1x.4
Tallahassee
A\,o~r)~uc;
REDU~TIOPI’ SL~NLIGH,I DVRINC:
PERCEST
39.6 55.5
20.0
13.x 26.4 37.0
30.2 43.1 53.8
'1.7 27.0
15.2
Oakland
53.0 66.3
28.6
18.7 35.7 45.3
38.7 s1.5 5X.3
26.0 29.8
19. I
Philadelphia
COUNTS EXCEEDISG 400 PFRI~DS AT EACH OF NINL
5
26.7 43.5 56.0
28.8 37.5
17.7
36.5 46.3 53.5
31.9
50.6 57.1
51.9 62.1
34.0 39.0
21.1
39.4 49.7 53.1
3.0 27.1
19.6
Bismarck
30.8
34.9 42.9
20.6
39.4 50.8 55.x
19.7 15.6 28.8
18.2
Minneapolis
23.0 26.9
Des Moines
LOCA.I.IONS
~1
2
7" 6
2
K 2
INTENSITY
PATTERNS
OF
SOLAR
UV
RADIATION
127
REFERENCES Hsu. J., Forbes, P. D., Harber, L. G., and La Kow, E. (1975). Introduction of skin tumors in hairless mice by a single exposure to UV radiation. Photockem. Photobiol. 21, 185-188. Robertson, D. F. (1969). “Long-Term Field Measurements of Erythemally Effective Natural Ultraviolet Radiation in The Biologic Effects of Ultraviolet Radiation.” Pergamon. New York. Robertson, D. F. (1972). “Solar Ultraviolet Radiation in Relation to Human Sunburn and Skin Cancer.” Thesis submitted to the University of Queensland, Brisbane, Australia. Rook, A., Wilkinson, D. S.. and Ebling, F. T. G. (1975).Zn “Textbookof Dermatology.” Znded, Vol. 2, pp. 1914-15. Blackwell Scientific Publication, Oxford London Edinburgh Melbourne. Scotto, J., Fears, T. R., and Gori, G. B. (1975). “Measurements of Ultraviolet Radiation in the United States and Comparisons with Skin Cancer Data.” DHEW No. (NIH) 761029. National Cancer Institute, Div. of Cancer Cause and Prevention. Scotto. J., Fears. T. R., and Gori. G. B. (1976). Ultraviolet exposure patterns. Environ. Res. 12, 22%237.
