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Long-Term Monitoring and Analysis of Hourly Solar
UV Radiation in the 290-380 nm Range in the
Middle Region of Saudi Arabia
a
a
b
A.M. Al-Dhafiri , M.S. Al-Ayed & M. Bin Mahfoodh
a
Physics Department , King Saud University , Riyadh , Saudi Arabia
King Abdulaziz City for Science & Technology , Riyadh , Saudi Arabia
b
Published online: 27 Dec 2011.
To cite this article: A.M. Al-Dhafiri , M.S. Al-Ayed & M. Bin Mahfoodh (2000) Long-Term Monitoring and Analysis of
Hourly Solar UV Radiation in the 290-380 nm Range in the Middle Region of Saudi Arabia, Journal of the Air & Waste
Management Association, 50:6, 1045-1049, DOI: 10.1080/10473289.2000.10464148
To link to this article: http://dx.doi.org/10.1080/10473289.2000.10464148
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TECHNICAL PAPER
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Copyright 2000 Air & Waste Management Association
Long-Term Monitoring and Analysis of Hourly Solar UV
Radiation in the 290–380 nm Range in the Middle Region of
Saudi Arabia
A.M. Al-Dhafiri and M.S. Al-Ayed
Physics Department, King Saud University, Riyadh, Saudi Arabia
M. Bin Mahfoodh
King Abdulaziz City for Science & Technology, Riyadh, Saudi Arabia
ABSTRACT
Wh ile each type of UV in duces sign ifican tly differ-
en t biological effects, UV with wavelen gth s below 290 nm
is biologically in sign ifican t, sin ce it is quickly absorbed
in th e atm osph ere before reach in g th e earth ’s surface.
Th e am oun t of UV radiation at an y location on th e
earth ’s surface gen erally depen ds on th e solar zen ith an gle
an d two oth er m ajor factors: atm osph eric ozon e con ten t
an d atm osph eric con dition s. Alth ough on ly a sm all frac-
tion of UV radiation is actually reach in g th e earth ’s sur-
face, such an am oun t would h ave a con siderable effect
Th e UV an d global solar radiation on a h orizon tal surface
at groun d level in Riyadh City (latitude 24° 34’ N, lon gi-
tude 46° 43’ E) h ave been m easured an d an alyzed. Mea-
surem en ts of UV radiation (295–385 nm ) were recorded
every 10 m in for five years (January 1983–Decem ber 1987).
Th e m axim um recorded h ourly m ean irradian ce UV ra-
2
diation was 28 W/m an d occurred in July, wh ile th e m in i-
2
m um was 14 W/m in Decem ber. A steady m on th ly value


UV 
H 
of
K
vh
=
was obtain ed an d equaled 2.9%. A sim ilar tren d

H 
 UV 
=
 H
3,4
was foun d for th e m on th ly variation of K =
an d
K
v

.
on all aspects of life. For exam ple, it is well-kn own th at
t



H
o

o

Maxim um values of 90% an d 2.6% were recorded in Jun e
UV radiation is a prim ary factor in m an y diseases such as
5
-10
for K an d K , respectively, wh ile m in im um values of 35%
skin can cer, cataracts, an d un usual pigm en tation . It h as
also been foun d respon sible for un desired ch em ical reac-
tion s in com m ercial ch em ical plan ts. However, UV also
h as som e ben eficial effects, such as in itialization of vita-
t
v
an d 1%, respectively, were obtain ed in Decem ber. A lin -
ear correlation was obtained between K and K . These find-
v
t
in gs were discussed an d con n ected to th e m eteorological
even ts. Th e results were com pared with th e region s of Ku-
wait, Bah rain , Dh ah ran , an d Makkah .
1
1-13
m in D syn th esis an d psoriasis treatm en t.
This work presents a comprehensive set of hourly mean
daily m easurem ents of UV solar irradiance in the wave-
length range of 295–385 nm (A and B spectra) and global
solar radiation over a period of five years (1983–1987) for
Riyadh City (latitude 24° 34’ N, longitude 46°43’ E). Present
data are also com pared with those reported for other re-
gion al location s (i.e., Kuwait, Bah rain , Dh ah ran , an d
Makkah).
INTRODUCTION
Th e UV radiation spectrum 100–400 nm can be divided
1
,2
in to th ree region s:
(
(
(
1) UV-A (315–400 nm): long-wave UV radiation, which
constitutes most of the UV radiation received at the
earth’s surface;
2) UV-B (280–315 nm ): m edium -wave UV radiation ,
wh ich is partially absorbed or scattered in th e
atm osph ere; an d
INSTRUMENTATION AND
EXP ERIMENTAL METH ODS
3) UV-C (100–280 nm): short-wave UV radiation, which
is com pletely absorbed by stratospheric ozone.
Measurem en ts of m eteorological param eters were carried
out in th e weath er station at Kin g Abdulaziz City for Sci-
en ce & Tech n ology (KACST), Solar Laboratories (Th e So-
lar Village), 40 km n orth west of Riyadh . Th e station is
capable of m on itorin g th e followin g m eteorological pa-
ram eters:
IMPLICATIONS
Our findings clearly indicate that the maximum UV radia-
tion (290–380 nm) in Riyadh occurs in July in the middle
of the day. At this time, UV radiation is twice as much as
in December. Irradiance levels in the neighboring coun-
tries exhibit very similar trends.
(
1) global irradian ce (Eppley, precision spectral
pyran om eter);
(
2) direct n orm al irradian ce (Eppley, n orm al in ci-
den ce pyrh eliom eter);
Volume 50 J une 2000
Journal of the Air & Waste Management Association 1 0 4 5

Al-Dhafiri, Al-Ayed, and Mahfoodh
(
(
3) ultraviolet irradian ce (Eppley, total ultraviolet ra-
diom eter);
particular h our. Th e daily average irradian ce power
2
(W/m /day) is th e average of th e h ourly values between
4) in frared irradian ce (Eppley, precision in frared ra-
diom eter);
sun rise an d sun set for a particular day. Th e daily m axi-
m um an d m in im um irradian ce power are th e h igh est an d
lowest values, respectively, for a particular day. Th e h ourly
(5) win d speed (Clim atron ics, caps);
(6) win d direction (Clim atron ics, van e);
(7) am bien t tem perature (Clim atron ics, th erm istor);
(8) relative humidity (Climatronics, hygrometrix); and
(9) sunshine hours (Cam pbell-Stock, spherical glass).
2
irradian ce en ergy (Wh /m ) is th e accum ulation of all 10-
2
m in readin gs with values greater th an 100 W/m of direct
n orm al irradian ce durin g th at particular h our. Th e daily
2
irradian ce en ergy (Wh /m /day) is th e sum m ation of th e
All solar and m eteorological instrum ents except the
sunshine recorder were interfaced with the Data Acquisi-
tion System (DAS) m odel IMP-803 from Clim atronics. The
DAS data logger was program m ed to record the average,
m axim um , and m inim um output signals from each instru-
m ent on m agnetic cassette every 10 m in. On a weekly ba-
sis, the cassette raw data were transferred to the hard disk
of a HP9845B com puter, where another com puter program
processed them and generated an error report. At the end
h ourly en ergy values for th at day. Th e sam e procedure
2
was repeated for th e m on th ly irradian ce en ergy (Wh /m /
m on th ). Th e research ers also used oth er com puter pro-
gram s to gen erate plots an d tables for th e above values.
RESULTS AND DISCUSSION
Global an d UV solar radiation were m easured in Riyadh ,
th e capital of Saudi Arabia an d th e cen ter of th e m iddle
region , from 1983–1987. Th e m on th ly h ourly m ean varia-
tion of UV solar radiation in ten sity is sh own in Figures 1–
4. An equation of a third order polynom ial in the following
form was used:
2
of each month, the 10-min irradiance (W/m ) readings were
aggregated between sunrise and sunset to hourly, daily, and
m onthly values by another com puter program .
2
2
Th e h ourly average irradian ce power is th e average
of six readings of the 10-m in values for the particular hour.
Th e m axim um an d m in im um h ourly irradian ce powers
are th e h igh est an d th e lowest values, respectively, for a
(1)
UV = A + Bt + Ct + Dt
wh ere UV is th e ultraviolet irradian ce an d t is th e local
tim e.
Figure 1 . Hourly UV profile for October through December from 1983
Figure 3. Hourly UV profile for July through September from 1983 to 1987.
to 1987.
Figure 2. Hourly UV profile for January through March from 1983 to 1987.
Figure 4 . Hourly UV profile for April through June from 1983 to 1987.
Volume 50 J une 2000
1
0 4 6 Journal of the Air & Waste Management Association

Al-Dhafiri, Al-Ayed, and Mahfoodh
It can be seen from th ese figures th at UV in ten sity
in creases with solar elevation , reach in g a m axim um be-
tween 12:30 an d 13:00 h ours an d decreasin g as th e eleva-
tion of th e sun decreases. A sim ilar tren d is observed for
all m on th s. Th e m axim um recorded h ourly m ean UV ir-
th e m axim um was attributed to very clear skies durin g
1
8,20
th at m on th .
Mean wh ile, a drop in UV radiation was observed in
Makkah durin g July, likely due to th e pilgrim age season ,
wh ich coin cided with th e tim e of th e data collected for
th at study. Durin g pilgrim age, usually a population of
m ore th an 2 m illion travels, m an y usin g buses an d cars
run by diesel an d gasolin e fuels. However, th e m axim um
m on th ly h ourly average values of UV radiation in Riyadh
-2
radian ce was 28 Wm in July, wh ile th e m in im um was 14
-2
Wm in Decem ber. It is in terestin g to n ote a drop of 50%
between th is m axim um an d m in im um . Th is large differ-
1
4,15
en ce is m ain ly due to th e lon g duration of cloud cover
-
2
an d th at th e zen ith an gle is at its m axim um in Decem ber,
wh ich reduces th e UV radiation . It is quite clear th at th e
values of th e m on th ly h ourly average for October, No-
vem ber, an d Decem ber (group 1) are alm ost sim ilar to
th ose of March , February, an d Jan uary (group 2), respec-
tively. On th e oth er h an d, th e values for th e m on th s of
July, August, an d Septem ber (group 3) are sim ilar to th ose
in Jun e, May, an d April (group 4), respectively. Th e m axi-
m um differen ce between each m on th in groups 1 an d 3
with its correspon din g m on th in groups 2 an d 4, respec-
tively, is about 10%. It sh ould be poin ted out th at a previ-
for July (28.5 Wm ) are about th e sam e as th ose cities
an d lie with in th e experim en tal error ran ge. In addition ,
th e m on th ly m in im um h ourly average value for Decem -
-2
ber (14 Wm ) is exactly th e sam e as th e value in Kuwait,
wh ile in th e oth er cities it is about 30% h igh er. Th is is
due to a sim ilarity of m eteorological ch aracteristics be-
1
5
tween Kuwait an d Riyadh durin g Decem ber.
Figures 5 an d 6 sh ow a typical win ter (Decem ber) an d
sum m er m on th (July), respectively, in th e variation of
h ourly m axim um , average, an d m in im um UV radiation
values for 1983. As can be deduced from th ese figures,
th e percen tage differen ce between th e m axim um an d
m in im um values of th e win ter m on th is m ore th an twice
th at of th e sum m er m on th . Th is is attributed to th e dif-
feren t atm osph eric con dition s, in addition to th e zen ith
an gle factor, between th e two season s, as th e sun m oves
faster in win ter th an in sum m er, affectin g th e am oun t of
UV radiation reach in g th e earth ’s surface.
1
6
ous work for Riyadh for alm ost th e sam e period of tim e
sh owed approxim ately 20% h igh er values of th e m axi-
m um an d m in im um of h ourly m ean UV irradian ce. Th is
discrepan cy m ust be attributed to th e differen t tech n iques
in data acquisition an alysis an d evaluation .
In a com parison study of UV radiation for Riyadh
1
7
with oth er region al cities (Dh ah ran [latitude 26° 32’ N,
UV
UV
H
1
8,19
o
Kv
=
, Kvh
=
lon gitude 50° 13’ E], Kuwait
[latitude 29 20’ N, lon gi-
The m onthly variation of the m ean ratio
H
o
H
2
0
tude 47° 57’ E], Bah rain [latitude 26° 14’ N, lon gitude
and K = H , where UV is the hourly ultraviolet radiation,
H is the hourly extraterrestrial radiation, and H is the hourly
t
o
2
1
5
3
0° 34’ E], an d Makkah [latitude 21° 5’ N, lon gitude
o
o
8 8’ E]) all of th ese cities appeared to h ave m axim um
global radiation, are presented in Figure 7 for the entire
period of m easurem ent. It can be seen that a steady rela-
an d m in im um values in th e sam e m on th s as Riyadh (July
an d Decem ber, respectively). However, wh ile Kuwait h ad
th e m axim um value in August rath er th an July, Bah rain
h ad its m axim um in Jun e. Th is is probably due to th e
san dstorm s in Kuwait, wh ich usually occur in July an d,
h en ce, reduce th e am oun t of UV radiation ; in Bah rain ,
tionship is obtained between the K and the m onth of the
v
year, with an average of about 2.9%. This is an expected
result, since a strong correlation exists between the hourly
m ean UV irradiance and hourly global radiation H. Such a
correlation can be deduced from Table 1. Statistical analysis
Figure 5 . Hourly maximum, average, and minimum UV irradiance
Figure 6 . Hourly maximum, average, and minimum UV irradiance
profile in December 1983.
profile in July 1983.
Volume 50 J une 2000
Journal of the Air & Waste Management Association 1 0 4 7

Al-Dhafiri, Al-Ayed, and Mahfoodh
Figure 7 . Comparisons of monthly average ratios of K (UV/H ), Kvh (UV/H), and K (H/H ).
v
o
t
o
1
6
2
of previous data shows a sim ilar correlation. A sim ilar
Kvh = 2.658 + 0.004 K (r = 0.4948)
(3)
t
trend is obtained for the m onthly variation for both K and
t
K , as can be seen from the figure. The m axim um percent-
with stan dard deviation s (sd) = 0.0898, 0.06738, an d
v
age of K is approxim ately 90% (in June and July), while
29.3851 for K , K , and K , respectively. As can be deduced
t
v
vh
t
the m inim um percentage, 35%, is observed in Decem ber.
Apart from the variation of the zenith angle and its ef-
from this equation, K increases as K increases linearly from
v t
January until it reaches a m axim um in June with K reach-
v
fect on the monthly value of K , which is partially respon-
ing 90%. Then it decreases in a sim ilar m anner (linearly)
t
sible for the difference between the maximum and minimum
until K reaches a m inim um value (about 35%) in Decem -
t
values of K , this large difference must be attributed to the
ber. It is clear that the sum m er m onths (June, July, and
t
frequent rainfall that usually occurs in December and re-
August) have high K values, because of high UV radiation
v
sults in a reduction of K to its minimum. The clear skies in
from clear skies (high K ). Figure 8 also shows that a steady
t
t
July result in an increase of K to maximum value. However,
relationship is obtained between K and K as a function of
t
vh
t
the reduction of K during summer can be attributed to the
the m onth of the year. This is due to the presence of clouds,
dust, sm oke, and pollutants in the sky that absorb or scat-
ter both UV and global radiation and, hence, affect the
value of both K and K in the sam e m anner.
t
presence of fine sand particles in the atmosphere due to sea-
1
5
sonal sandstorms in Riyadh. While the maximum percent-
age of K is observed in June (2.6%), the minimum is found
v
t
vh
in December (1%), because of the difference in the amount
of UV radiation received throughout the year due to the
same atmospheric factors stated above.
Th e presen t data are sum m arized in Table 1. Table 2
sh ows th e coefficien ts A, B, C, an d D of eq 1 for th e
m on th ly tren ds in Figures 1–4.
Figure 8 sh ows th e m on th ly average percen tage of Kv
an d K versus K as a fun ction of th e m on th of th e year. A
CONCLUSION
vh
t
lin ear relation sh ip between both K an d K with K is ob-
Measurem en ts of UV an d global radiation an d th eir ratio
in Riyadh were dem on strated for th e period from 1983 to
v
vh
t
tain ed usin g th e followin g equation s:
1
987. An alysis of th e an n ual average of th e h ourly values
2
K = –0.119 + 0.031 K (r = 0.9967)
(2)
of UV radiation an d global radiation in Riyadh revealed
v
t
Ta ble 1 . UV, global (H), extraterrestrial (Ho), Kv (UV/Ho), Kt (H/Ho), and KvH (UV/H) for the period 1983–1987.
1
UV
983 1984 1985 1986 1987 All (Avg) 1983
1984 1985
1986
H
1987 All (Avg)
All (Avg) All (Avg) All (Avg)
UV
UV
UV
UV
UV
H
H
H
H
H
Ho
Per. Kv
Per. Kt Per. Kvh
Jan 11.1
Feb 13.9
Mar 14.7
Apr 14.9
May 15.0
June 17.0
July 18.2
Aug 17.1
Sept 16.7
Oct 15.5
Nov 12.3
Dec 9.9
Avg 14.7
10.3
11.8
12.7
13.5
14.1
16.2
16.8
16.2
14.4
12.9
10.8
9.0
9.9
12.4
11.6
13.9
13.0
15.6
16.0
14.9
14.1
13.2
9.7
7.5
9.7
8.4
9.4
338.2
416.5
452.9
464.0
451.3
536.9
569.9
541.4
519.7
492.6
394.8
337.5
459.6
359.6 339.6
412.0 440.6
432.8 435.2
465.3 494.5
515.8 474.3
571.7 556.8
566.0 557.3
533.2 520.4
490.3 493.8
454.8 473.4
355.7 354.7
294.7 291.0
454.3 452.6
325.5
405.7
430.0
405.5
514.0
556.3
545.5
516.7
492.1
459.7
357.5
283.2
441.0
356.5
420.0
389.2
481.2
451.6
540.3
548.7
491.8
480.3
436.4
383.5
296.5
439.7
343.9
419.0
428.0
462.1
481.4
552.4
557.5
520.7
495.2
463.4
369.2
300.6
449.4
846.4
841.4
806.7
737.1
658.5
613.4
630.0
697.3
773.1
823.8
841.5
843.3
759.4
2.7
2.8
2.8
2.9
2.9
2.9
3.0
3.0
3.0
2.9
2.9
2.8
2.9
40.63
49.79
53.05
62.69
73.11
90.06
88.49
74.68
64.06
56.25
43.88
35.64
61.03
1.116
1.391
1.501
1.814
2.115
2.629
2.633
2.243
1.915
1.640
1.270
0.985
1.771
10.7
10.6
13.7
13.3
15.5
16.1
14.6
14.1
12.7
10.7
8.1
11.7
12.1
13.4
13.9
16.1
16.6
15.6
14.8
13.5
10.7
8.3
10.9
11.0
14.3
16.3
15.8
15.4
14.6
13.3
10.0
7.3
7.2
12.6
13.2
12.2
12.4
13.0
1
0 4 8 Journal of the Air & Waste Management Association
Volume 50 J une 2000

Al-Dhafiri, Al-Ayed, and Mahfoodh
3
4
.
.
Gwyn n -Jon es, D.; Joh an son , U. Growth an d Pigm en t Production in
Two Subarctic Grass Species un der Four Differen t UV-B Irradiation
Levels; Physiol. Plant 1996, 97, 701-707.
Al-Ayed, M.S. Growth an d Som e Metabolic Ch an ges in Cucurbita
Pepo un der Water Stress an d Ultraviolet-B Radiation ; Saudi J. Bio. Sci.
1
998, 5(1), 45-55.
5
6
.
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Holm -Han sen , O.; Helblin , E.W. Polyeth ylen e Bags an d Solar Ultra-
violet Radiation ; J. Science 1993, 259(509).
Lon gstreth , J.D.; de Gruji, F.R. Effects of In creased Solar Ultraviolet
Radiation on Hum an Health ; AMBIO: A Journal of the Human Environ-
ment 1995, 24(03).
7
8
9
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Caldwell, M.M.; Teram ur, A.H. Effects of In creased Solar Ultraviolet
Radiation on Terrestrial Plan ts; AMBIO: A Journal of the Human Envi-
ronment 1995, 24(03).
Tan g, X.; Madron ic, S. Effects of In creased Solar Ultraviolet Radiation
on Troposph eric Com position an d Air Quality; AMBIO: A Journal of
the Human Environment 1995, 24(03).
An drady, A.L.; Am i, M.B. Effects of In creased Solar Ultraviolet Radia-
tion on Materials; AMBIO: A Journal of the Human Environment 1995,
2
4(03).
1
1
1
0. Giese, A.C. Living with Our Sun’s Ultraviolet Rays; Plen um Press: New
York, 1982.
Figure 8 . Monthly average percent of Kv(UV/Ho) and Kvh(UV/H) versus
1. Sin gh , A. Growth , Ph ysiological an d Bioch em ical Respon ses of Th ree
Tropical Legum es to En h an ced UV-B; Can. J. Bot. 1996, 74, 135-13.
2. Han an , M.A.; El-Yazigi, F.A.H.; Al-Watban , A.; Feteih , N. Measure-
m en t of Solar Ultraviolet in Riyadh : Its Sign ifican ce in Studies on
Vitam in D Deficien cy in Saudi Arabia; The King Faisal Specialist Hos-
pital Medical Journal 1984, 4(4), 307-312.
Kt (H/HO).
Ta ble 2 . Equations’ coefficients of the monthly trends.
1
3. Galin do, I.; Fren k, S.; Bravo, H. Ultraviolet Irradian ce over Mexico
City; J. Air & Waste Manage. Assoc. 1995, 45, 886-892.
Month
A
B
C
D
14. Al-Ayed, M.S.; Al-Dh afiri, A.M.; Mah foodh Bin , M. Global Direct an d
Diffuse Solar Irradiance in Riyadh; Saudi Arabia, Renewable Energy 1998,
1
4(1-4), 249-254.
Jan
Feb
Mar
Apr
–71.638
–85.838
–128.44
–78.084
–88.508
–92.568
–87.108
–91.05
0.1315
0.1621
0.2821
0.1709
0.205
–0.00004
–0.00006
0.0002
–5E-09
–3E-09
3E-08
1E-08
1E-08
1E-08
5E-09
9E-09
1E-08
2E-08
–2E-08
9E-09
15. Al-Harbi, Y. G. Spectral Distribution of Global Solar Radiation un der
Varyin g Atm osph eric Dust Loadin g in Riyadh ; M. En g. Th esis, Kin g
Saud Un iversity, Riyadh , Saudi Arabia, 1995.
16. Mujah id, A.M. Correlation between Ultraviolet Radiation an d Glo-
bal Radiation in Riyadh , Saudi Arabia; J. Solar Energy Engineering 1994,
–0.0001
–0.0001
–0.0001
–0.00009
–0.0004
–0.0002
–0.0002
–0.0001
–0.00009
1
16, 63-66.
May
Jun
July
Aug
Sept
Oct
17. Elh adidy, M.A.; Abdel-Nabi, D.Y.; Kruss, P.D. Ultraviolet Solar Radia-
tion at Dh ah ran , Saudi Arabia; Solar Energy 1990, 44(6), 315-319.
0.2113
0.1936
0.2044
0.2157
0.28863
0.2517
0.1707
1
1
8. Al-Aruri, S.; Rasas, M.; Al-Jam al, K.; Sh aban , N. An Assessm en t of Glo-
bal Ultraviolet Solar Radiation in th e Ran ge (0.290–0-385 µm ) in
Kuwait; Solar Energy 1988, 41(2), 159-162.
9. Al-Aruri, S.D.; Am er, M.F. Em pirical Regression Models for Weath er
Data Measured in Kuwait durin g th e Years 1985, 1986 an d 1987; So-
lar Energy 1993, 50(3), 229-233.
–95.329
–128.2
2
2
0. Al-Naser, W.E. Solar Ultra-Violet Radiation Ch an ges in Bah rain ; Ap-
plied Energy 1997, 57(1), 25-35.
1. Kh ogali, A.; Al-Bar, O.F. A Study of Solar Ultraviolet Radiation at
Makkah Solar Station ; Solar Energy 1992, 48(2), 79-87.
Nov
Dec
–113.68
–81.86
-2
-2
1
3 Wm an d 449 Wm , respectively. A drop of 50% be-
tween th e m axim um an d m in im um values of UV is ob-
servable. A lin ear correlation between K an d K was also
v
t
foun d. Th e values of th e m on th ly h ourly average of UV
radiation for October, Novem ber, an d Decem ber were
foun d to be sim ilar to th ose of March , February, an d Jan u-
ary, respectively. On th e oth er h an d, th e values for th e
m on th s of July, August, an d Septem ber were sim ilar to
th ose of Jun e, May, an d April, respectively. A com parison
of UV radiation for Riyadh with oth er region s (i.e.,
Dh ah ran , Kuwait, Bah rain , an d Makkah ) revealed th at
th ey all h ave m axim um an d m in im um values in th e sam e
m on th s, with an exception of a sligh t sh ift for Kuwait
an d Bah rain .
About the Authors
Dr. A.M. Al-Dhafiri is an associate professor with the Phys-
ics Department, College of Science at King Saud Univer-
sity, P.O. Box 2455, Riyadh 11451, Saudi Arabia (e-mail:
adhafiri@ksu.edu.sa). Dr. M.S. Al-Ayed is an associate pro-
fessor with the Physics Department, College of Science at
King Saud University, P.O. Box 2455, Riyadh 11451, Saudi
Arabia (e-mail: malayed@ksu.edu.sa). M. Bin Mahfoodh is
a scientific researcher with the King Abdul Aziz City for Sci-
ence & Technology, P.O. Box 6086, Riyadh 11442, Saudi
Arabia (e-mail: mmahfodh@kacst.edu.sa).
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.
Ultraviolet Radiation; En viron m en tal Health Criteria No. 160; World
Health Organ ization : Gen eva, 1994.
2
.
International Lighting Vocabulary; In tern ation al Electrotech n ical Com -
m ission an d In tern ation al Com m ission on Illum in ation : Gen eva,
1
987.
Volume 50 J une 2000
Journal of the Air & Waste Management Association 1 0 4 9