Exhaust levels are high near to traffic, inside cars in queus and inside garages. Parents can warn their children to avoid places where exhaust can be smelt.  Physical activity such as cycling increases uptake of the pollutants. Keeping a distance to vehicles is then particularly important

Petersson, G\uf6ran

Chalmers Research

Exposure to Traffic Exhaust

Exhaust levels are high near to traffic, inside cars in queus and inside garages. Parents can warn their children to avoid places where exhaust can be smelt. <p> Physical activity such as cycling increases uptake of the pollutants. Keeping a distance to vehicles is then particularly important

Petersson, Göran

Chalmers Publication Library

MOTORISTS 
WALKING 
INDOOR 
CHILDREN 
PASSENGERS 
CYCLING 
OUTDOOR 
PARENTS 
Exposure to Traffic Exhaust 
Goran Petersson 
Chemical Environmental Science 
Chalmers University of Technology 
Contribution to the section "Pollution" in 
TRAFFIC AND CHILDREN'S HEALTH 
Lennart Kohler and Hugh J ackson eds 
The Nordic School of Public Health 
The European Society for Social Pediatrics 
NHV-Report 1987:2 
117 
Exposure to traffic exhaust 
G Petersson, Goteborg, Sweden 
In our urban society, everybody is always exposed to, and sur-
rounded by, varying concentrations of chemical compounds from 
traffic exhaust. This major air pollution problem is becoming in-
creasingly recognized as a threat to public health. The degree of 
hazard is related to the dose of the harmful substances absorbed, 
and thus in turn to the extent of the exposure and to physiological 
parameters. 
There is no such thing as a harmless dose 
With regard to chemical and toxicological complexity, traffic exhaust 
compares well with tobacco smoke. Consequently, no exact answer 
can be given to the commonly-posed question as to how dangerous 
traffic exhaust is. On the other hand, the following two statements 
are useful guidelines when dealing with air pollution from traffic 
exhaust. 
The degree of health hazard becomes rapidly smaller with de-
creasing doses, but not even the smallest doses can be regarded as 
harmless. 
An initial decrease in dose produces a comparatively large reduction 
of the health hazard, i. e. the first decrease is always the most 
valuable. 
ToxicologicaIly, the first statement refers to the presence of a large 
number of mutagenic and carcinogenic compounds in auto exhaust. 
For such compounds no harmless levels are though to exist 
(CederlOf et al 1978). The second statement is based on the con-
ventional toxicological concept of threshold levels (Casarett and 
Doull's Toxicology 1980) for the very numerous, genetically inactive 
exhaust components. From an ecological point of view, the same two 
conclusions can be drawn. Human beings as well as other organisms 
are biologically adapted to "clean air", and the larger the deviations 
from normal, the larger the health hazards according to basic ecolo-
gical principles related to the concept of limiting factors (Odum 
1971) . 
118 
Several countries as well as WHO define exposure limits for air pol-
lutants such as carbon monoxide and nitrogen dioxide in order to 
protect public health. Although such limits presuppose the occur-
rence of the particular compound alone, they are sometimes referred 
to in discussions on traffic exhaust pollution. It is important to 
realize that such comparisons grossly underestimate the health haz-
ards from traffic exhaust because the additive and synergistic ef-
fects of the multitude of other chemical components are not taken 
into account. 
Assessing exhaust exposure-
A knowledge of exposure levels in various environments is needed 
in order to plan effective measures aiming at reducing exposure. 
Extensive measurements of the amount of air pollution from traffic 
exhaust has been made all over the industrialized world. Tradition-
ally, the samples have been taken to a large extent at more or less 
standardized situations, especially in streets. Recently, expo-
sure-related methods have been more widely introduced, although 
such methods have been applied in work environments for a long 
time. Small mobile stations, and above all, personal sampling equip-
ment permit very versatile assessments of exhaust exposure. 
Traffic exhaust is composed of several hundred chemical compounds 
which can be determined -by -modern analytical methods. The spread 
of both gaseous and particulate components is fairly uniform, how-
ever. Therefore, it is usually sufficient to measure one component, 
e.g. carbon monoxide, or a few characteristic components, in expo-
sure studies. It should be observed that this approach applies to 
traffic exhaust but not to ozone and similar secondary -pollutants, 
which often constitute another severe problem. 
Exposure assessments reported in this chapter are based mainly on 
studies of unburnt hydrocarbons from traffic exhaust. Samples were 
taken with personal sampling equipment and analyzed by gas 
chromatography (Mattsson & Peters son 1982). The characteristic 
composition of hydrocarbons from petrol exhaust permits a 
differentiation from diesel exhaust and industrial and other sources. 
A few basic data on fuel and on emission control systems will 
roughly define the composition of petrol as well as diesel exhausts 
in any region. It is well known that the composition varies some-
what with f\le mode of driving, temperature, condition of the engine 
and other factors. The ratio between certain components may also 
be somewhat different inside a vehicle, at the roadside, inside a 
house, and indeed at any point and time. Furthermore, many haz-
ardous chemical species disappear by reaction, and others are 
formed by reaction at various distances from the exhaust pipe. 
119 
Basically. however. traffic exhaust should be viewed as spreading 
uniformly when strategies for assessing and reducing exposure are 
worked out. It is remarkable that "passive" smoking is commonly 
thought of in this way. whereas the similar problem of exposure to 
traffic exhaust is very seldom discussed in the same simple and 
straightforward terms. 
Distance reduces exposure 
Traffic exhaust is rapidly diluted by horizontal as well as vertical 
mixing. Consequently. concentrations decrease rapidly with the dis-
tance from the exhaust pipes. This elementary principle should be 
central in all local efforts to reduce exposure to traffic exhaust. 
Representative figures for horizontal spreading are given in Table 
1. At a distance corresponding to one block. concentrations are 
only about one tenth of those close to traffic. The difference is 
smaller when there is plain ground between the two points. and 
larger when there are trees. houses. or hills between them. When 
vertical mixing is restricted. e. g. by nocturnal ground-level 
inversions, the ratio is smaller but the absolute concentrations 
higher. The opposite is true under weather conditions with efficient 
vertical mixing. Concentration lowering with height tends to be 
even more efficient on average, due to the often limited vertical 
mixing. 
Obviously, the most efficient way of reducing one's exposure to 
traffic exhaust is to keep at a distance from exhaust pipes. The 
larger the distance the better, but the first few metres are the 
most important. This easily understood principle enables individuals 
to reduce their exposure to exhaust fumes in the immediate environ-
ment. Again. comparisons with the tobacco smoke problem may be 
helpful in understanding the problem. 
Motorists and passengers 
As indicated in Table 1, exposure inside motor-cars is usually much 
higher than outside exposure even on the near-by pavement. The 
reason is that each vehicle is enveloped by exhaust from the mo-
tor-car ahead. The shorter the distance to the motor-car ahead, the 
higher are the exhaust levels in the air passing into the vehicle 
behind. In addition, the motorist and his passengers are often 
exposed to very high concentrations of exhaust and fuel vapours in 
garages. inside parked cars. and at petrol stations. 
120 
A study in Goteborg, Sweden, demonstrated that the average levels 
of petrol exhaust in motor-cars were about three times higher than 
in buses and trams in which the air intakes are higher from the 
ground and which will partly use separate carriage-ways (Petersson 
1981). Where the tram lines were separated from exhaust-producing 
traffic, levels were still lower. Buses, on the other hand, were 
found to contain not only petrol exhaust but also diesel exhaust 
from their own engines. Diesel exhaust probably leaks into the bus 
mainly through open doors at bus stops. 
Table 1. Relative values of auto exhaust concentration, by site of 
sampling. 
Inside motor-car in queue 30 
On pavement by traffic stream 10 
10-20 m from traffic stream 5 
50-100 m from traffic stream 1 
Exposure inside vehicles and particularly inside motor-cars merits 
attention not only because of the comparatively high exhaust levels 
but also because of the frequent every-day use of motor-cars. A 
particular point of concern is the frequent use of motor-cars by 
pregnant women, and for transporting small children. A comforting 
point is that the individual can do much to reduce exposure, e. g. 
by keeping motor-car trips to a minimum, by avoiding heavy traf-
fic, and by always keeping an adequate distance from the vehicle 
ahead. Proper regulatory measures should make it necessary or at 
least easier for the motorist to keep a reasonable distance. They 
should also prevent queues at street and road sections which have 
bad ventilation and are located near to housing. 
Walking and cycling 
People who are walking or cycling are normally exposed to lower 
concentrations than those inside motor-cars, because of their posi-
tion outside the mainstream of exhaust fumes. On the other hand, it 
must be remembered that health hazards are related to the dose 
inhaled rather than to the exposure expressed as the concentration 
in air. The lung ventilation, Le. the air intake, is larger for 
pedestrians and particularly for cyclists because of their physical 
activity (Astrand 1977). A comparison between a cyclist and a mo-
121 
torist when covering identical distances is given in Table 2 
(Petersson 1981, Lidstrom, 1980). The dose inhaled by the cyclist 
when cycling uphill is very high because of his physical efforts. On 
the other hand his dose is very much lower on cycle tracks well 
separated from exhaust-producing traffic. It should also be 
emphasized that the total exposure of the motorist is more 
unfavourable than is apparent from Table 2 because of exposure 
related to parking and petrol. 
Table 2. Comparative air intake and traffic exhaust dose of cyclists 
and motorists at different distances between road (street) 
and cycle track.1 
Time Air Dose at Dose at Dose at 
intake o m 3 m 50 m 
Normal 2 2.5 4 2 0.5 
ground 
Level 1.5 2 2.4 1.2 0.3 
ground 
Uphill 3 4 10 5 1 
1 Concentration ratios cyclists/motorist were assumed to be 0; 8 at 
Om, 0.4 at 3 m and 0.1 at' 50'm. 
Many similarities exist between pedestrians and cyclists with respect 
to exposure and dose. The lung ventilation on walking is normally 
lower than when cycling, but on the other hand lung ventilation is 
very high on jogging and running (Astrand 1977). The more stren-
uous and long-lasting a physical activity is, the more important it 
is to keep as long distance as possible from exhaust pipes. The 
uptake of children during play activities may be high and play-
grounds should always be properly located with respect to traffic 
and vehicles. 
Cycle tracks and foot-paths efficiently separated from traffic and 
parking are a very important means' of reducing the uptake of ex-
haust fumes by cyclists and pedestrians. Indeed, the traditional 
street with pavements close to and on both sides of the traffic is 
clearly unsatisfactory and can almost be said to maximize exposure 
to exhaust. Current designs of street crossings are hazardous for 
similar reasons. In Figur'e 1 the fluctuations in exposure when 
walking along a street are illustrated. The maxima correspond to 
waiting at, and crossing, streets close to passing or stationary 
122 
vehicles. The two lowest levels correspond to street sections free 
from private motor vehicle traffic. Similar diagrams based on a 
knowledge of concentrations in various types of urban micro-
environments are useful in planning and effecting Changes aiming at 
reducing exposure to exhaust fumes. 
EXHAUST 
EXPOSURE 
o 5 10 15 
TIME (MIN.) 
Figure 1. Variations of exposure during a walk along a street (The 
Avenue, Goteborg, Sweden). 
Indoor exposure 
Intuitively, people may think that they are protected against traffic 
exhaust indoors. This is not the case because exhaust enters with 
ventilation air from outside the building. In principle, indoor 
concentrations are the same as those of the air entering from out-
side. This means that it is essential to supply air from the least 
exhaust-exposed side of a house and preferably from a high level 
above ground (cf Table 1). In extreme cases, such as flats and 
shops with natural ventilation and facing narrow streets with dense 
traffic, indoor exposure may be very high. 
Obviously, good opportunities for reducing indoor exposure are 
provided by keeping one side of a house "exhaust-free" rather than 
by levelling out the exhaust pollution in an area of a town. Cur-
rently prevailing efforts to reduce the top exhaust levels often give 
rise to a levelling-out effect and are then questionable. One street 
with, and the next parallel street" without, exhaust-producing traf-
123 
fic might be a fruitful planning model. This would also give cyclists 
and pedestrians I as well as parents and children, an important op-
portunity of avoiding traffic exhaust. The exposure-reducing ef-
fects would be surprisingly large (cf Table 1). 
A potential danger concerning indoor exposure to exhaust and fuel 
vapours is indoor parking. The dilution of pollutants in air by 
mixing is restricted indoors. Therefore, even small emissions such 
as those from a single motor-car may produce high concentrations in 
a garage. The spread from a garage inside a house to other parts 
of the house is difficult to prevent. Therefore, parking inside 
houses should preferably be avoided or carefully controlled with 
respect to air pollution. In multi-story car parks exhaust levels are 
commonly about five times higher than in streets with much traffic 
in spite of efficient ventilation. 
For the average citizen. exhaust exposure levels indoors at home 
and at work are considerably lower than in the traffic environment. 
On the other hand, exposure times are normally much longer in-
doors. 
In Figure 2. these facts are illustrated. The exhaust dose, 
assuming constant lung ventilation, corresponds to the area under 
the curve. In real life. respiration is increased during the day-time 
and particularly with physical activity (Astrand 1977), resulting in 
a corresponding increase in the absorbed dose. On an average, 
home, work-place, and traffic environment are likely to contribute 
about equally to the diurnal dose. Dose-reducing efforts are needed 
everywhere. Exposure (or dose) versus time diagrams may be help-
ful in discovering unacceptably large doses as well as contributions 
to the total dose which could be easily eliminated. 
EXHAUST 
EXPOSURE 
00 
• 
04 
• 
08 
I 
12 
---.,..., 
I 
16 
u 
I 
20 
Figure 2. Typical diurnal exposure pattern of an individual in an 
urban environment. 
24 
124 
Children - no time to lose 
From several points of view, children's exposure to traffic exhaust 
merits special attention, as they are thought to be more vulnerable 
than adults with respect to most exhaust· hazards. The potential 
effects of lead on children's health have been intensely -debated. It 
is, however, often forgotten that inorganic lead is only one of a 
large number of exhaust components with potentially deleterious 
effects on their mental abilities and physiology. Even health autho-
rities tend to over-emphasize comparisons with exposure limits set 
for individual compounds. Considering the extremely complex compo-
sition, additive and synergistic effects may actually be - responsible 
for the worst health hazards. 
An important point is the short time of maximum vulnerability of a 
small child. At the foetus stage, this time. may be on the order of 
weeks. This contrasts with current planning periods of several 
years for the introduction of exhaust regulations and for improving 
urban traffic environments. Therefore, it is essential not only to 
speed up these important planning activities' but above all to find 
means of reducing people's exposure, and particularly 'children's 
exposure as quickly as possible. As emphasized below, a sur-
prisingly large amount can be done to this end, both at the mu-
nicipal level and at the personal level. 
Local reduction ~f exposure 
A list of possible changes 8lmmg at effective exposure reductions in 
local environments is given below. Most· of them can give large re-
ductions because of the rapidly decreasing exposure relative to in-
creasing distance from the source of emission. Inexpensive -changes 
which can be performed within a short time have been emphasized. 
It is hoped that these suggestions by a planning amateur will 
inspire professionals to find more and better solutions and above all 
to realize them as quickly as possible. 
Very short time needed: 
Moving stop lines for vehicles, except bicycles, back from 
pedestrian crossings. 
Recommending long gaps between vehicles in queues, particu-
larly those with children as passengers (information cam-
paign) . 
125 
Introducing signs warning children from entering parking 
places, multi-story car parks and -garages. 
Preventing unnecessary parking within and near houses. 
Discouraging parking near dwelling-houses by selective park-
ing fees. 
Short time needed: 
Zones free from exhaust-producing vehicles in housing areas. 
Every' _ second street,. if possible, reserved for exhaust-free 
traffic in urban areas. 
Regulations against high vehicle density in critical street 
sections. 
Foot-paths and cycle tracks far separated from exhaust pro-
ducing traffic. 
Crossings pesigned and regul~ted to minimize exhaust expo-
sure of pedestri!lns and cyclists. 
Stops for public transport vehicles to be kept free from high 
exhaust levels. 
Indoor parking and parking close to houses, eliminated 
and replaced by various measures. 
Unnecessary traffic and parking removed from nurseries, 
schools and hospitals. 
Ventilation improved in houses with an exposed location. 
Parents can prevent exposure 
In practice, there will always be some delay in performing environ-
mental changes aiming at reducing exposure. Therefore, the partic-
ular importance of an immediate reduction in exposure make personal 
efforts to avoid exposure essential. The same is true of the analo-
gous problem of passive smoking. At the individual level important 
changes in habits and behaviour can often be made from one day to 
the next. An unpredjudiced scrutiny of exhaust exposure of indi-
viduals is also likely to reveal possible improvements in the local 
environment. Pregnant women and parents have a particular reason 
to be concerned about the problem. The following list of questions 
is intended to give some ideas to parents in particular: 
126 
Are your children using playgrounds well separated from ex-
haust-producing vehicles? 
Are your children choosing the best alternative with respect 
to exhaust exposure on their way to school? 
Are you choosing streets and shops with low exhaust levels 
when shopping with your children? 
Are you keeping a long distance to the vehicle ahead when 
driving with your children as passengers? 
Are you keeping your children out of your garage and park-
ing places? 
Are you choosing separate cycle tracks and foot-paths when 
you are out with your children? 
Are you telling your children to avoid places where exhaust 
can be smelt? 
Your children are most vulnerable to exhaust now. What can 
you do from tomorrow on to reduce their exposure? 


Exposure to Traffic Exhaust

Abstract

Similar works

Full text

Available Versions

Chalmers Research

Chalmers Publication Library