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506


Chapter 1 I
        Exercise Performance

Source: 1973 Report. Chapter 7. pages 237 - 249.

607


Contents

Introduction___---______________________----------------
Studies of Smokers- _ _ ____ _____ -___ ___ __ _ ___ ______ _ __ _ __-
Studies Comparing Smokers to Nonsmokers:
  A&tie& Petyformance---- _____ -__---__-_- ____ -_-------
  Bicycle Ergometer Performance_- __ _ _ _ _ __ __ _ _ _ _ __ _ : ____ _
  Treadmill Performance_----- ______ -__-_-- ______ ---__--
  Perjormance in Other Tests of Fitness-_--_--------------
Discussion-_-___-___-_____---_-__-__------_______-------
Biomechanisms _--__-_____-_--_____ --_- ______- -_---_-___
summary--_-______---____________________-------------
References____--_____-__-___-___________-______________

rage
611
611

613
614
615
6U
616
616
617
618

609


Introduction

Although it has long been held by athletes nnd coaches that cigarette
smoking is associated with "shortness of wind" and impaired perform-
ance, until recently there has been little scientific evidence to support
this view. In the past few years, a variety of studies have appeared
dealing with the effect of cigarette smoking on the response of man
to exercise. The follolving is a revielr of these studies.
Age, sex, training, health, weight, and other factors are known to
influence exercise performance. Because most of the investigations
n-we carried out in healthy, youn g male volunteers, the groups rrere
quite comparable with regard to age, sex, and health ; ho\rever, weight,
training, and other factors were often inadequately controlled.
Furthermore, problems in study design and statistical analysis limit
the value of several of these studies.                  \
Many forms of exercise mere performed in these experiments, in-
cluding: pedaling a bicycle ergometer, running on a treadmill, running
on a track, swimming, stelj climbing, gripping a hand dynamometer,
and doing sex-era1 different exercise activities as part of a battery of
tests. Small to maximum amounts of work were carried out in the
various studies revelred.

Studies of Smokera

Most of the studies of habitual cigarette smokers followed a similar
format vzith respect to smoking: (a) The subjects refrained from
smoking for a few hours prior to testing, and (6) two test runs mere
performed, one without smoking and one in which smoking imme-
diately preceded the exercise or was incorporated with the exercise
protocol.
Several investigators (I, 1.5, 28) studied the effect of smoking on
maximum grip strength. Willgoose (28) reported a greater mean per-
cent. recovery of grip strength after the nonsmoking trial than after
the smoking trial. Kay and Karporich (15) and -tinderson and Brown
(I) all followed a protocol similar to that of Willgoose except that
they randomized the smoking and nonsmoking trials, and substituted

611


a "placebo" cigarette for the nonsmolring trial. In neither of these
studies =-ere statisticaIIy significant ditference3 obsen-cd between the
grip SCOM for the smoking and nonsmoking trials.

Reexs and Morehouse (24) administered a battery of tests to 15
colleges students. The tests mere: A tapping test, a strength test. a
jumping test, and the short form of the Harvard step test. h-o statis-
tically significant differences in performance Tere noted under con-
ditions of smoking or nonsmoking.

A total of 32 college students from intermediate swimming classes
abstained from smoking for 15 minutes, 2 hours, and 12 hours in astudy
conducted by Pleasants, et al. (23). Following the abstinence, they
sxam distances of 100 and 200 yards Although actual swimming times
were not published, the authors reported no statistically significant
differences between the mean srrimming times after the different
periods of abstinence for either distance.

In 1%6, Juurup and Muido (23) carried out several experiments
in rrhich three young cigarette smokers exercised on a Krogh's bi-
cycle ergometer. Smoking was found to increase the pulse rate at
rest as Tell as during exercise. Although the effect was less con-
sistent than on the heart rate, smoking was also associated rrit.h
elevated blood pressure. Smoking had no effect on oxygen consump
tion. Henry and Fitzhenry (13): in 1949, using the bicycle ergometer,
also found t.hat smoking exerted no et?& on oxygen consumption.
In the same year, Karpovich and Hale (I$) studied bicycle ergometer
performance in eight young men. In all subjects, the average riding
time was better in nonsmoking tests than in smoking tests; how-
ever, the results Eere statistically significant for only three of the
eight. subjects.

Kerr&an, et al. (16) more recently measured direct arterial blood
pressure, heart rate, and cardiac output in 25 habitual smokers at
rest and after exercise. Smoking two cigarettes produced statistically
significant (P<O.Ol) increases in cardiac index, heart rate, and arter-
ial mean pressure compared to the immediately preceding control
period. Exercise after smoking-resulted in an increase in cardiac in-
dex ore? either the resting period or the exercise period mhich fol-
lowed abstinence; the resultant cardiac index appeared to be approsi-
mately the sum of the exercise and smoking effects. Exercise tests
preceded by smoking were also associated mtih @nificantly higher
(P<O.Ol) and more prolonged elevations of blood pressure than those
not preceded by smoking.

In the study by Goldbarg, et al. (II) of nine habitual smokers
performing submaximal exercise on a bi&ycIe ergometer, car&was-
cular responses \vere measured via pulmonary and subclavian artery
catheters. -it rest, after smoking, the mean cardiac index and mean
heart, rate increased. During successively increasing levels of exercise,
the heart, mte \~as greater and stroke index Iolrer than values for

612


comparable work before smoking. The net etfect of smokinr KS to
decrease the efiiccncy of the lwnrt clurin~ rzcr~isc in thec\rprifht
position by causing a smaller stroke volume arrd a higher heart.
rate.

Rode and Shephard (26) in\-estigated near mnrimal treadmill eser-
cise performance in sis habitual smokers. -1 l-day abstinence from
cigarette smoking \ras associated with a 1% to %-percent decrease in
the oxygen cost of breathing. Yibstinence \ras also follo\red by a slave-
ing of the heart rate and a decrease in espirntory minute volume after
exercise.

The study of Krumholz, et al. (18) is different from those cited pre-
viously in that bicycle ergometer exercise performance was measured
in habitual smokers both before and after 3 to 6 seeks of abstinence.
Among the 10 subjects n-ho abstained from smoking for 3 weeks, there
was a statistically significant (P<O.O5) decrease in heart rate, oxygen
debt, and ratio of oxygen debt to total increase in oxygen uptake pro-
duced by the 5 minutes of esercise.

Using a "double 9-inch progressive st.ep test" Rode and Shephard
(25) studied several hundred participants of a smoking withdrawal
clinic at the time of entry and at a l-year followrp. Xmong those
who returned for the follo\wp and who gave up smoking, absolute
aerobic po"rer increased insignificantly ; hoxverer, the relative aerobic
po\ver diminished in both sexes among those who quit smoking because
of theIreight gain experienced.

Studies Comparing Smokers to Nonsmokers

Athletic Perfomance

In 1968 Cooper, et al. (6) evaluated 419 airmen during their initial
6 weeks on active duty in the USAF. A 12-minute maximum running
test was performed at, least 1 hour after cigarette smoking. The mean
distance covered in 12 minutes by the nonsmokers ~GEG significantly
greater (P<O.O5) than that covered by the smokers at the beginning,
the middIe, and the end of training. A11 categories of smokers and non
smokers improved their performance at the end of training; ho!\-ever,
the maximum change in performance of those smoking 10 to 30 cig-
arettes per day was significantly (P<O.OOl) less than that of non-
smokers.

David (7) administered a battery of tests to 88 military personnel,
aged 19 to 39 years. ;\. l-mile run was included in the testing, and cig-
arette smoking was associated with a significant decrease in perform-
ance in this event.

613


Some 45 special forces soldiers were investigated at sea level and
13,000 feet above sea level by Fine (8). The subjects were randomly
assigned to a placebo group or an acetazolnmide treated group. Cig-
arette smoking vzrs positively correlated to decrements in 600-y-ard
running performance from sea level to altitude in both groups.

Pleasants (E?) studied 106 students from intermediate university
swimming classes. Swimming times were measured for lOO- and 200-
yard distances before and after training and for BOO-yard distances
after training. The mean swimming times of nonsmokers were less
than those of smokers in six of seven listed categories, but these dif-
ferences were not statistically si,@icant.

Bicycle Ergometer Perfmnank

Chevalier, et al. (5) investigated cardiovascular parameters in 32
young physicians after a standard 5-minute ergometer test. Oxygen
debt accumulation among srnokers was significantly (P<O.Ol) greater
than among nonsmokers. The heart rate at rest and 3 minutes after
exercise was significantly (P<O.O2) faster in smokers than in non-
smokers.

using a 5-minute ergometer test: IS housestaff physicians, half of
whom smoked, vrere investigated by Krumholz, et al. (17') _ They noted
the following: Oxygen debt accumulation after exercise was signifi-
cantly (P< 0.@2) greater in smokers than non-smokers, the ratio of the
oxygen debt to total increased oxygen uptake during exercise was sig-
nificantly (P<O.OOl) greater in smokers than in nonsmokers, and
the diifusing capacity at rest and with exercise was significantly
(P<O.O5) decreased in smokers compared to nonsmokers.

Kerrigan, et al. (16) studied cardiovascular parameters in smokers
and nonsmokers at rest, during, and after a B-minute bicycle ergometer
ride. Cardiac index and bIood pressure values obtained during exercise
performed immediately after smoking rrere greater than those found
in nonsmokers performing the same exercise. Similarly, heart rate and
blood pressure remained elevated for longer periods in those who
exercised immediately after smoking than in nonsmokers performing
the same task.

Aerobic capacity scores were examined in 60 university student vol-
unteers by Peterson and Kelley (29) _ Subjects worked at submaximal
levels on a bicycle ergometer before, during, and after a training
Program. At all of these intervals, nonsmokers had significantly
(P<O.O5) high er mean aerobic capacity scores than smokers. Both
groups increased their aerobic capacity during training but non-
smokers consistently performed better throughout training.

614


Treadmill Performance

In 1360 Blackbum, et al. (4) carrictl out .sevrml measurements of
cardiovascular function after different nrno\ints of tirntlmill exercix
were performed bv 233 professional mtn. I>!) Ilnivcrjity students. and
414 railroad workers. The ditferenccs betn-ccn the smokc~s and non-
smokers were of small magnitude. Basal oxygen consumpt.ion was
slightly higher in smokers than in nomxnokcts. L~lso. resting pulse
rates were higher in smokers of most groups.

Cooper. et al. (6) studied 17 out of 419 airmen with treadmill tcst-
ing. Cardiopulmonary indices measured on the tmndmiil. including
maximum indices, were comparable in smokers and nonsmokers ex-
cept for a significant (P<O.Ol) reduction in the maximum minute
volumo among the smokers.

A total of l?ii prospective Canadian fircmcn performed the Balke-
l\var-e test of work capacity in treadmill studies carried out by Glass-
ford :lncl 1Ioxwll (10). The mcnn ~wrformancr scores of nonsmokers
were significantly (P<O.Ol) greater than thoxof smolicrs.

The effect of Gtnmin C su~)~)lcll~entntio~~ on treadmill exercise per-
formance was investigated in 40 male volunteers by Bailey, et al. (3).
Sigiificant ~lift'rrtwxs in ox)-gcn utilization and ventilatory function
bct.weeil smokcts and nonsmokers were noted in only two of the 24
separate anal>-ses of variance performed.

JZasimnl oxygen intake durin, n treadmill escrcise was examined by
JIcDonough, ct. al. (13) in 86 hralthy, middle-aged male volunteers.
Cigarette smoking was one of six variables which together provided
3 mllltiplo correlation coellicient of 0.X3.

Performnnce in Other Tests of Fitness

When physical fitness tests were administered to 88 military per-
~onnel bv David (7). cigarette smoking was found to be associated
wit11 a significant. (1'<0.001) decrease in performance in the dad@
and jump test. and a significant (P<O.O2) decrease in performance in
the crawling test.

I-sing -a step test, :I breath holding test. anti an ergometer test,
Franks (9) esnnlined x middIe-aged 111~11. So~w~~okcis were able to
11ohl tlrcbir breath longer and hat1 prcatrr \-ital capacity residual after
t!w stqb trst thn the slIlokels.

III I!)iI. \\`ysokinski (9) stlutlied 200 ~~oung Polish soldiers using
I,etulrov's test \vllicli iiicludccl 20 lime-hldillg cscrcises, a fast run for
"0 ~rcolltls. a1rtl ;I 1'1111 for :: milrutes. Ciqrrct te sntokillg was associated
witlr a significant (I'<O.Ol) reduction irr the \-ital capacity and a

615


marked rise in the pulse rate at rest and after exercise. Intense exer-
cise also caused a greater rise in the systolic blood pressure in smokers
than in nonsmokers.

Discussion

Most of the studies in habitual cigarette smokers compared exercise
performance in "smoking" and "nonsmoking" runs after only a few
hours of abstinence. In some studies, smoking adversely affected per-
formanm (II, 13,.24,16,18,96,28), while in others it did not (1,12,
16,93,24). Some of these apparently discrepant results are due to dif-
ferences in methodology and in amounts and types of work performed.
In all of the more recent studies of habitual smokers in which moderate
to near maximal amounts of work were performed and sophisticated
measurements of oxygen transport and cardiopulmonary function
were made, impairment of f&&ion during smoking trials was found
(II, 16,149s).
The data of Krumholz, et al. (18) a 1 so raise the question of whether
residual effects of cigarette smoking influence "nonsmoking" trials per-
formed after a few hours of abstinence; they found statistically sig-
nificant decreases in heart rate and oxygen debt produced by exercise
after 3 weeks of cessation.

The work of Rode and Shephard (25) suggests that physical fitness
improves with cessation, but this improvement may be negated if the
subject gains a substantial amount of weight after giving up smoking.

Several investigators compared exercise performance or postexer-
cise cardiopulmonary function of smokers to nonsmokers. Although
only minor differences betvzeen smokers and nonsmokers mere found
in a few of these studies (3,4,22), in most of them (5,6,7,8, 20,16,
27,20,29) the performance or function of the nonsmokers was better
than that of the smokers. Both nonsmokers and smokers improved
their performance with training, but nonsmokers maintained their ad-
vantage throughout training (6,ZU).

Biomechanisms

The cited studies indicate that cigarette smoking exerts its adverse
effect on exercise performance through several mechanisms. Cigarette
smoking appears to impair cardiac performance during exercise by
increasing the heart rate and exerting a variable effect on cardiac

616


output (5, 12, ZJ,I~, IS. X, 29). Cigarette smoking is associated mith
an increased oxygen debt after esercise (5. 18). Alsoo: one study indi-
cated that the osxgsn cost of hyperventilation was greater among
smokers than among nonsmoker; (3).

Some of these adverse edects of smoking on osidative metabolism
are mediated by the elevated cnrbosyhemoglobin levels found in
smokers. CO exerts these effects through one or more of the follo-cFing
mechanisms: (a) Reduction of the amount of hemoglobin available for
ox)-gen transport, (6) shift of the oxygen-hemoglobin dissociation
curve to the left with consequent interference in osygen release at
the tissue level, (c) induction of arterial hypoxemia, and (d) possible
interference with the homeostatic mechanism by which 2,3,CPG
controls the affinity of hemoglobin for oxygen (97). Because carbosy-
hemoglobin has a half life in the body of at least 3 to 4 hours, its influ-
ence may still be measurable sex-era1 hours after abstinence from
smoking (97).

-1 recent investigation of maximal muscular exercise during CO in-
toxication in five male volunteers demonstrated reduced maximal 0,
consumption in spite of a much higher heart rate and a relative hyper-
ventilation (22).

Xstrand and Rodahl (2) commented recently on the adverse effect
of cigarette smoking on oxygen transport: "All other factors being
equal, a reduction in the oxygen-transporting capacity is associated
with a corresponding reduction in physical performance capacity dur-
ing heavy or maximal stork * * *. Because a regular physical train-
ing program only increases the maximal oxygen uptake by some 10 to
20 percent, a 5 to lo-percent reduction in maximal aerobic power due
to smoking may play a significant role in many types of athletic events
and in very heavy work."

Other studies cited in this review document the adverse effect of
smoking on pulmonary diffusing capacity (18) <and on pulmonary
function with exercise (6: ~9).

Summary

Clinical studies in healthy, youn g men have shorrn that cigarette
smoking impairs exercise performance, especially for many types of
athletic events and activities in\-ol\.ing masimal work capacity. Some
of these etfects are medi;lted by reduced oxygen transport and reduced
cardiac and pulmonarv function.

617


Exercise Performance Keferences

(1) ASDEEYO~, J. V.. BBDW~. C. WV. A. study o! the erects of amoklnq upon @P
   strength and recupwaffon from local muscular fatfgue Research Quar-
    terly 22 (1) : 102-108, March 1951.

(2) ASTEASD, P.-O., RODARL, K. Factors affecting performance. In: Textbook
   of Work Physiology. New York, McGraw-Hill Book Co.. 1970, 689 pp.
(S) Bantr, D. A., CARRON. A. V., -, R. Q.. WEHTEB H. J. Vitamin C
  snpplementntton related to physiologfeal response to exercise in smoking
   and nonsmoking subjects. American Journal Of CbdCd KUtIifiOn 23(7) :
   9cG9l2, July 1970.

(4) Br&xmm, H., Bsoz~x, J., TAYLOE, H. L. Common circulatory measore-
   menta in smokers and nonsmokers. Circulation 22: 1112-1124. December
    1960.

(5) CBEVAZIEB, R. B., BOWEEE. J. A., BO~D~EANT, 9.. Ross. J. C. CircUlatOry
   and ventilatory effects of exercise In smokers and nonsmokers. Journal
   of Applied Physiology 18(Z) : 357-360, bfarch 1963.
(6) COOPEB, K. H.. GEY, G. O., BOTTENBER~, R. A. Effects of clgarette smoking
   on endurance performance. Journal of the American Xedlcal Association
   203 (3) : 189-192. Jan. 15.1968.

(7) DAVID, K. H. Age. cfgarette smoking. and tests of physIca fitness. Journal
   of Applied Psychology 52 (4) : 296-298. August 1968
(8) FINE, B. J. Personality traits as related to symptomatology and running
   performance at altitude under normal and drug (acetazoleamide) condi-
    tions. Perceptual and Motor Skills 27: 975-990. 1968.
(9) FEAXSS, B. D. Smoking and selected cardiowscular-respiratory measures.
   Research Quarterly 41(2) : l-10-144, May 1970.
(10) GLAS~FORD. R. G., HOWELL. JI. L. Smoking and physical Btness: A prelim-
    innry report. Canadian Family Physician 15(10) : 6@Xi2. October 1969.
(21) GOLDB.~G. A. S.. KRONE. R. J.. RESNEKOY. L. Effects of cigarette smoking
    on bemodJnamics at rest and during exexise. I. Kormal subjects. Chest
   60(6) : 531-536, December 1971.

(IZ) HENRY. F. hl., FITZHEXEY, J. R. Oxygen metabolism of moderate exercise,
    with some observations on the effects of tobacco smoking. Journal of
   Applied Physiology 2: 41X-468. February 19.50.
(1s) JUURUP, A, Jfuroo. L. On acute effects of cigarette smoking on oxygen
   consumption, pulse rate. breathing rate and blood pressure fn working
   organisms. Acta Physiologica Scandinavica 11 : 48-60, 1946.
(1)) ~XWICE. P. V., HAU, C. J. Tobacco smoking and physical performance.
   Journal of Applied Physiology 3: 616621, April 1951.
(15) KAY. Ff. `N.. KARPOVICH, P. V. Effect of smoking upon recuperation fromlo:
   ~a1 muscular fatigue. Research Quarterly 20: 250-256. 1949.
(is) K~IGAS, R.. JAIX, A. C.. DOYLE. J. T. The circulatory response to ciga-
   rette smoking at rest and after exercise. American Journal of the Jfedi-
   cal Sciences 25.5: 113-119, February 1968.
(17) -UMHoLz, R. A.. CHEVAL.~ R. B.. Roes, J. C. Cardiopulmonary function
   In young smokers. A comparison of pulmonary iunctIon measurements
   and some cardiopulmonary resgonis to exercise betn-een a group of young
   smokers and a comparable group of nonsmokers. Annals of Internal Uedi-
   tine W(4) : 603-610, April 1964.

(18) KRL'~\IHOLZ, R. A., c:HEVALIEtS R. n., ROSE. J. C. Changes in cardiopuf-
   monary fWctions related to abstinence from smoking. Studies in young
   cigarette smokers at rest and exercise at 3 and 6 weeks of abstinence.
   Annals of Internal Medicine 62(2) : 197-207, February 19&

618


(19) ~cDo.uocc~, J. R., Knauur. F.. Recce. R. A. Variations in mar&oat
    OXYgen intake with phy-sical actirIty In middle-aged men. Circulntlon
    41(5) : 743-751. May 1970.

(20) Pmssos. F. J.. hTELzEy. I). L Tbe erect of cigarette smoking upon the
   acquisition Of physical fitness during training 8s measured by aerobic
   capacity. Journal of the American College Uealth Association 17(3) :
    2.50-W. February 1969.

(PI) -AT. F.. DUJAEIJIN, J., DEZ~AXN~. R.. Parrr. J. M. Muscular exerdse
   during intoxication by carbon monoxlde. Journal of Applied Physiology
    M(4) : 5X%575. October 1971.

(22) PwEas~a. F.. Jr. Pretrainlng and post-tralnlng swimming endurance of
    smokers and nonsmokers. Research Quarterly 40(4) : 779-782. 1999.
(-OS) P~~aaaa18. F., Jr.. Genoarr. J.. RATL~F-F, J. XV., Jr. Effects of short perlods
    of abstinence from cignrette smoking on swimming endurance of chronic
    smokers. Research Quarterly 33(3) : 474479. 1966.
(24) RCE~FS, K. E.. ,\IOREHOUEE. L. E. The acute effect of smoking upon the physi-
    cal performance of habitual smokers. Research Quarterly 21: 24%2-18.
    1950.

(25) Root. A. S~~pndno. R. J. Smoking withdrawal and changes of cardiores-
   plratory tltness. American Review of Respiratory Disease 10-l(6) : 9X3-
    933. Decwnber 1971.

(26) Row, A, SEEPHW. R. J. The influence of cigarette smoking upon the oxy-
   gen cost of breathing in near-maximal exercise. Medicine and Science in
    Sports 3(Z) : 51G5. summer 1971.

(27) U.S. Prmmc Hrxrxn Smwrcn. The Health Consequences of Smoking. A Re-
   port of the Surgeon Geneml : 1972. U.S. Department of Xealth. Education,
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    158 pp.

(28) W~~looox, C. E. Tobacco smoking, strength, and muscular endoraoce. Re-
    search Quarterly 18: 219225.1947.

(29) WYBOH~~~GKI. 2. Effects of tobacco smoking on certain parameters reflecting
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619


Chapter 12

Harmful Constituents of Cigarette Smoke

Sourca: 1972 Report. Chapter 9, pager 137 - 150.

621


              Contents

                                      Page
The Dose Relationship . . . . . . _ _ . .   625
References .._.............._._...-.................   630

LIST OF TABLES

Table 1 .-Compounds in cigarette smoke judged most likely
to contribute to the health hazards of smoking . . . _ . . . . _ .   627
Table 2.-Compounds in cigarette smoke judged as probable
contributors to the health hazards of smoking . . . . . . . . . .   628
Table 3.-Compounds in cigarette smoke judged as suspected
contributors to the heaith hazards of smoking  . . . . . . . . . _   629

623


HARMFUL CONSTITUENTS OF CIGARETTE SMOKE*

Cigarette smoke contains a large number and a wide variety of
compounds which may result in complex and multiple pathophysio-
logical effects on various tissues and organ systems. Although the
constituents of cigarette smoke are usually divided for convenience
into the two categories of particulate and gas phases,** many of
them exist in a distribution equiIibrium, that is, they are present
partially in the gas phase and partially in the particulate phase.
This review concerns itself with judgments concerning the harmful
constituents of cigarette smoke whether these are found primarily
in the gas phase or in the particulate phase.
Constituents of cigarette smoke may enter the body by a variety
of routes. Theoretically, the route of entry and subsequent absorp-
tion could affect the degree to which various organs are subjected
to specific cigarette smoke constituents. Some constituents, par-
ticularly the water soluble components of the gas phase, may be
absorbed by the nasal and oropharyngeal mucous membranes, or
may be dissolved in the saliva and swallowed, thus allowing for pos-
sible gastric or intestinal absorption. Other constituents are ab-
sorbed along the tracheobronchial tree, and the distance which they
reach before being absorbed or deposited depends on such factors as
the depth of inhalation and the particle size. The absorption of gases
in the tracheobronchial tree appears to be in part dependent on the
adsorption of gases to particulate matter. Another factor affecting
the route and degree of absorption is the adequacy of pulmonary
clearance by which constituents deposited or dissolved in the mucous
sheath are delivered to the pharynx and then usually swallowed.
Of the hundreds of compounds identified in cigarette smoke, some
occur in the smoke in concentrations which may be considered sfi
ficient to present hazards to health. Other compounds appear in