Impact of Traffic Emission on Air Quality in

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Impact of Traffic Emission on Air Quality in
A Developing City of Nigeria
P.N. Ndoke and O. D. Jimoh
Department of Civil Engineering, Federal University of Technology
Minna, Nigeria
Abstract
Minna is a developing city that lies between the Sahel and Guinea Savanna
regions of Nigeria, and occupies a land area of 490 ha. Its population has increased
from 70,000 in 1979 to over 300,000 in 2000. This increase has been attributed to a
number of reasons such as nearness to the federal capital city of Nigeria and economic
growth. During the period, the number of motor vehicles in the city increased by
400%. Although an increase in the motor vehicles eases the movement of people and
goods, it could lead to an increase in traffic emission, which would constitute
environmental and health hazards. A micro-scale analysis of the pollutants on a busy
road in the city was studied during the dry season. A piston hand gas pump with
detector tubes was used to sample CO, NO2, SO2, and CO2. Only traces of NO2 and SO2
were detected. The concentration of CO detected was as high as 15 ppm, which is a
little lower than the Federal Environmental Protection Agency limit of 20 ppm, and
was attributed to vehicle emission. In addition, the CO2 concentration was as high as
5000 ppm, which is still below the maximum level stipulated by the United States
Environmental Protection Agency, but was not due to traffic emission alone. Thus the
city is not under the threat of traffic pollution. This finding could serve as base-line
information for urban development vis-à-vis traffic management policy in Nigeria.
Keywords: Motor vehicle, air pollution, traffic management, urban development.
Introduction
Air pollution is defined as the
contamination of air by discharge of harmful
substances, which can cause health problems
including burning eyes and nose, itchy irritated
throat and breathing problems (USEPA 1994).
It was also reported that some chemicals found
in polluted air could cause cancer, birth defects
brain and nerve damage, and long-term injury
to the lungs and breathing passages in certain
circumstances. The concentrations of such
chemicals beyond a limit, and an exposure over
a certain period are extremely dangerous and
can cause sever injury or even death.
Air pollution can be classified into
natural air pollution which includes wind
blown dust, volcanic ash, and gases, smoke and
trace gases from forest fires, and anthropogenic
air pollution which includes products of
combustion such as nitrogen oxides (NOx),
carbon oxides (COx), sulphur dioxide (SO2).
Indeed, motor vehicles produce more air
pollution than any other single human activity
(WRI 1992). Nearly 50% of global CO,
hydrocarbon, and NOx emissions from fossil
fuel combustion come from gasoline- and
diesel-powered engines. In the city centers,
especially on highly congested streets, traffic
can be responsible for as much as 90–95% of
the ambient CO levels, 80–90% of the NOx and
hydrocarbons, and a large portion of the
particulates, posing a significant threat to
human health and natural resources (Savile
1993).
Air pollution problem has been well
documented in Europe and the US with motor
vehicles being the main contributors. In Europe
and the US, Small and Kazimi (1995) reported
that motor vehicles emission account for 32–
98% of national emissions of CO, volatile
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organic compounds (primarily hydrocarbons)
and NOx. Furthermore, Cline (1991) stated that
transportation accounts for an important
fraction of green house gases (especially CO2)
emission.
USEPA (1993) reported that transportation
sources were responsible for 77% of CO
emissions, 45% of NOx, 36% of volatile
organic compounds, and 22% of particulates in
the US during the year 1993. In the European
Union, pollution control measures have been
initiated over the past 20 years to reduce NO2
levels, but these measures have been offset by
increases in the numbers of vehicles on the
road (CEC 1992). In the UK, for example,
average concentrations of NO2 increased from
1986 to 1991 by 35%, mainly as the result of
increased emissions by motor vehicle traffic
(UK/DOE 1992). In the developing world,
automotive air pollution is mostly a problem in
large cities with high levels of traffic, such as
Mexico City, Bangkok, and Lagos, Nigeria. In
other cities, power plants, factories, and other
stationary sources still constitute the greatest
threat to air quality. However, even in some
smaller urban centers such as Peshawar,
Pakistan, and Katmandu, Nepal, air pollution
from motor vehicles is becoming an increasing
problem (UK/DOE 1992).
The impacts of motor vehicle emissions
extend far beyond the local area. The
transportation sector is the most rapidly
growing source of greenhouse gas emissions--
that is, emissions of chemicals that have the
potential to contribute to global warming
(IPCC 1995). These include CO2, chlorofluorocarbons,
NO, and CO. In 1990, about 22% of
CO2 emissions from fossil fuel use came from
the transportation sector. OECD countries are
responsible for about 70% of greenhouse gas
emissions attributed to transportation. However,
the share of emissions from developing
countries is expected to rise in the future
because of the growing sizes of their motor
vehicle fleets and their use of less efficient
fuel-burning technologies (IPCC 1995).
Cities embody the diversity and energy of
human pursuits. Urbanization brings about
increases in population, which lead to
corresponding increases in motor vehicles,
either for private or for public transportation.
The environmental costs of motor vehicle are
hard to measure and vary according to local
conditions. Health cost estimates from local air
pollution in the Los Angeles region of the US
in 1992 was reported by Small and Kazimi
(1995) to be $0.03 per vehicle-mile. McCubbin
and Delucchi (1997) corroborated this fact, and
stated further that health cost as a result of
truck emission could be as high as ten times
that of cars and small buses. In both studies
most of the health hazards are as a result of the
increased mortality due to the presence of
volatile organic compounds, NOx and SOx in
the inhaled air. The rest of the hazards are due
to minor illness from ozone (O3), formed in the
atmosphere from volatile organic compounds
and NOx.
Policy makers all over the world have
been partially successful in improving air
quality. In the US, the ambient levels of most
pollutants have been reduced steadily since the
1960s (Calvert et al., 1993, Harrington et al,
1995). Small and Kazimi (1995) reported that
Europe has lagged behind the US in emission
controls on motor vehicles. Africa is even
worse off. In Nigeria, the government has
banned the importation of vehicles over eight
years old. Good as this policy may look like,
what remains to be done is how to control
emission from the existing old vehicles plying
the streets and highways of Nigeria. Some of
the policies are aimed at reducing overall
vehicle use, so as to minimize congestion/or
pollution. However, these policies really do
little to reduce the twin effect of congestion
and pollution. According to Hall (1995) the
problem of congestion is specific to location
and time, whereas emissions are specific to
vehicle characteristics and driving behaviour.
The diesel or petrol-fired electricity generator
is also a source of air pollution, and it is
contributing to the choking air in cities like
Abuja and Lagos, which are plagued by daily
smog shrouding the skyline of the central city.
As Sub-Saharan African cities experience
increased urbanization and motorization, air
pollution, particularly from vehicles still using
leaded gasoline, is worsening. By providing
access to business and public facilities, urban
transport plays a critical role in the
development of urban areas and overall
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economic growth but it also generates a
number of externalities in terms of accidents,
noise, traffic congestion, and air pollution. The
latter is becoming a major environmental and
health concern in sub-Saharan Africa. High rate
of urbanization (4–8% in a number of cities)
expected to be sustained for the next decade,
combined with low-income solutions to daily
commuting, has resulted in the rapid increase
in pollutants emitted by motorized vehicles.
The Study Area
Minna is the capital of Niger State, and it
is 100 km from Abuja the Federal Capital City
of Nigeria. Its climate lies between the Sahel
and Guinea Savanna regions, and has two
distinctive seasons (dry and wet). The dry
season occurs between November and March
while the rainy season is between April and
October, with the peak rainfall in September.
The population of Minna was 60,000 in
1963, when the state was created. The
population had increased to 122,031 in 1991
with a growth rate of 2.8% (Minna Master Plan
1979). There has not been a corresponding
increase in industrial activities in the town.
Major industries in the town include small
agricultural processing industries, plastic
manufacturing industries, confectioneries,
pharmaceutical and surgical companies. On
the other hand, there has been an increase in
the number of vehicles for personal and
commercial use in the town. Thus, traffic
emission is expected to be a major source of air
pollution in the town.
An area of Minna town with the most
traffic congestion (Amogu 2001) was selected
for this investigation. The selected site is
located in the central business district of the
town and it is congested during the morning
hours of 7:30–9:30 a.m., when offices and
commercial centres opened for business and
4:30–7:00 p.m. in the evening when the offices
and business centres are closed. Traffic volume
and activity is high on the two-lane dual
carriageway road.
.
Method of Investigation
The census of registered vehicles was
obtained from the state licensing office. A
questionnaire, which is aimed at determining
the age of vehicles was prepared and
administered on a sampled population (50 for
private cars, 100 for motorcycles, 200 and 50
for commercial cars and buses). The sample
size was based on earlier traffic studies in the
area (Amogu 2001).
Vehicles were randomly chosen and with
the permission of the drivers, the gas sampling
pump and detector tubes were used to detect
the prevalent gases from the exhaust fumes. A
piston hand gas pump (RAE LP-1200 model)
was used to determine the proportion of the
gases as the car engines was started. The
second process of sampling involved open-air
sampling at the median of the highway, as well
as 10 and 20 m away from the highway, which
lies in the built-up area. Sampling was done at
2-min intervals with corresponding traffic
volumes being recorded. In order to identify
the maximum effect of traffic emission in the
city, measurements were taken during the dry
season (November and December), as
Baumbach et al. (1995) had shown that traffic
emission in Lagos is higher during harmattan
season than during the rainy session. Traffic
was counted and at intervals air was pulled into
the pump and the concentration of the pollutant
measured. The samplings were carried out on
working days during traffic congestion periods.
Results and Discussion
Fig. 1 shows the variation in the age of
motorcycles, private and commercial cars as
well as buses, based on the questionnaire and
information from the Federal Road Safety
Corps. The figure shows that the age of over
90% of motorcycles is less than ten years.
However, only 10% of commercial cars and
6% of buses fall within the same age group.
Eighty per cent of buses and commercial cars
are within the age group of 10–20 years. Most
of the exhaust pipes of the vehicles are
horizontal and discharge backward. It was
difficult to obtain the age of some vehicles as
225
the drivers were sceptical about the study. The
older the vehicles, the higher the proportion of
the pollutants emitted, indicating that
commercial cars and buses are main
contributor of traffic emission in Minna. The
proportion of older vehicles in Minna, a
developing city, agrees with other studies like
Faiz et al. (1994) who reported that low income
levels have been an incentive to import older
used vehicles in recent years, to use cheap twowheelers
and cheap fuel, and to postpone
vehicle maintenance. Such conditions result in
an increase in the emissions per km travelled,
slow speeds due to low investment in road
maintenance and traffic management.
Fig. 1. Variation of age of vehicles in Minna
Table 1 shows the statistics of registered
vehicles in the state licensing office. The table
shows that a total of 7,967 private vehicles,
4,557 commercial vehicles and 9,145
motorcycles were registered between 1993 and
2001. The number of vehicles registered before
1995 was 3,002, and motorcycles accounted for
1,677. It could be deduced that 13.4% of the
total motor vehicle population was registered
before 1995. This result does not mean that the
vehicles are less than ten years old because
most of the vehicles are imported into the
country as used vehicles. However, not all the
vehicles registered in the city remain and are
used in the city, many vehicles also migrate
from other cities to Minna.
Table 1. Registered vehicle census
Year Private Public Motor
cycles
Trucks/
buses
1993 387 261 445 14
1994 620 375 880 20
1995 968 644 1113 43
1996 975 472 890 23
1997 1015 556 1025 14
1998 983 418 986 12
1999 1019 542 1313 26
2000 1045 621 1250 28
2001 955 455 1252 33
The pump and detector tubes were able to
measure concentrations of CO and CO2 and
detect traces of SO2 and NOx. Fig. 2 shows the
level of CO measured during the dry season.
The CO emissions are higher at the median
than within the built-up area (that is at 10 or
20m away from highway). The concentration
of CO decreases with increase in the distance
from highway. It also corroborates De Rosa
(2003) assertion that traffic pollutants are
higher in concentration at the roadside or
median. De Rosa (2003) also reported that
young and middle aged men serving as
motorway tollgates attendants in Italy,
subjected to exposure to traffic pollution have
their fertility impaired. The maximum
concentration of CO detected was 15 ppm,
however, this is lower than the 48 ppm
stipulated by the WHO and 20 ppm stipulated
by the Federal Environmental Protection
Agency (FEPA) of Nigeria. The level of CO
measured is still within the safe limit, but
roadside vendors are however, being threatened
by some health hazards. For example, Greiner
(1991) stated that CO is a slow poison that kills
by reducing the oxygen supply in the body.
Fig. 3 shows the variation of CO2 at the
median as well as at 10m and 20 m away from
the highway. There is no distinct pattern in the
variation of CO2 with distance from the
highway. This is due to the fact that CO2 is a
product of combustion and respiration that can
be produced domestically, as well as from
industrial sources and motor vehicle emission.
The maximum concentration of CO2 was 5,000
ppm. This is less than the WHO stipulated
maximum of 20,000 ppm. However, Greiner
0
25
50
75
100
Age of vehicles (X)
Proportion %
Private Car Motorcycle Commercial Car Buses
226
(1991) reported that the presence of CO2
concentration from 2500 to 5000 ppm, could
cause headache, indicating that concentration
of CO2 within the study area is high enough to
cause health hazard. However, the level of
CO2 measured could not be attributed to
vehicle emission alone.
Fig. 2. Concentration of CO in the atmosphere
Fig. 3. Concentration of CO2 in the atmosphere
Although the trends and sources of
transport air pollution may somewhat vary
between cities, the impact on the society are the
same. Such impact includes health problems
mostly for children and the poorest, reduction
in productivity, poorer quality of life, and
degradation of the environment. Thus, the
results of this investigation could be
summarized as follows:
1. Traffic emissions in Minna City include
pollutants like carbon monoxide and
carbon dioxide as well as traces of
sulphur dioxide and nitrogen oxides.
2. The concentrations of the gases
measured are still within the limits
stipulated by the WHO and FEPA. This
implies that traffic emission in Minna,
which has a population of about
300,000 people with 3,000 vehicles, is
within the safe limit.
3. The low pollution level may be
attributed to the low industrialization
level of the city, a higher proportion of
non-polluting vehicles and the short
congestion peak periods in the city.
Conclusion
Urban air pollution patterns may vary
from one city to another depending on various
factors, and pollutants need to be identified and
quantified according to their potential sources.
References
Amogu, O. 2001. The relationship between
geometric design features and roundabout
performance in Minna. Unpublished B.Eng.
project, Dept. Civil Eng., Federal University
of Technology, Minna, Nigeria.
Baumbach, G.; Vogt, U.; Hein, K.R.G.;
Oluwole, A.F.; Ogunsola, O.J.; Olaniyi, H. B.;
and Akeredolu, F.A. 1995. Air pollution in a
large tropical city with high traffic density –
results of measurements in Lagos, Nigeria.
Sci. Total Envt. 169: 25-31.
Calvert, J.G.; Heywood, J.B.; Sawyer, R.F.;
and Seinfeld, J.H. 1993. Achieving
acceptable air quality: some reflections on
controlling vehicle emission. Science 261:
37-45.
Cline, W.R. 1991. Scientific basis for the
greenhouse effect. Econ. J. 101: 904-919.
CEC. 1992. The State of the Environment in
the European Community: Overview, Vol. 3.
Commission of the European Communities,
Brussels, Belgium.
De Rosa, M. 2003. Traffic pollution damages
men’s sperm. J. Human Reprod. 18: 1055.
Faiz, A.; Sinha, K.; and Gautam, S. 1994. Air
Pollution Characteristics and Trends.
Discussion Paper, World Bank, Washington,
DC, USA.
0
5
10
15
20
1 2 3 4 5 6 7 8 9 10
sample number
concentration
(ppm)
median 10m away 20m away
0
1000
2000
3000
4000
5000
6000
1 2 3 4 5 6 7 8 9 1011121314
Sample number
Concentration (ppm)
median 10m away 20m away
227
Greiner, T. 1991. Indoor air quality of CO and
CO2. Iowa State Univ. Extension Publ. No.
AEN-125.
Hall, J.V. 1995. The role of transport control
measures in jointly reducing congestion and
air pollution. J. Transport Econ. Policy 29:
93-103.
Harrington, W.; Walls, M.A.; and McConnel,
V.C. 1995. Shifting Gears: New Directions
for Cars and Clean Air. Discussed Paper 94-
26-REV Resources for the Future, World
Bank, Washington, DC, USA.
IPCC. 1995. IPCC Synthesis Report of World
Meteorological Organization, Intergovernmental
Panel on Climate Change. UNEP,
Geneva, Switzerland.
McCubbin, D.R.; and Delucchi, M.A. 1996.
The social cost of the health effects of motor
vehicle air pollution report II in the series:
the annualized social cost of motor vehicle
use in the U.S. based on 1990-1991 data,
report UCD-ITS-RR-96-3. Institute of
Transportation Studies, Univ. of California,
Davis, CA, USA.
Minna Master Plan. 1979. The Capital City of
Niger State, Final Report prepared by Max
Lock Group, Nig. Ltd. Town Planning
Division, Ministry of Housing and
Environment, Niger State, Nigeria.
Saville, S. B. 1993. Automotive options and air
quality management in developing
countries. Indust. Envt. 16 (1-2): 20, 32.
Small, K..;A and Kazimi, C. 1995. On the costs
of air pollution from motor vehicles. J.
Transp. Econ. Policy 29: 7-32.
USEPA. 1993. Guide to Environmental Issues,
Doc. No. 520/B-94-01 United States
Environmental Protection Agency,
Washington, DC, USA.
USEPA. 1994. National Air Quality and
Emissions Trends Report, pp. 2, 6, 46, 52.
United States Environmental Protection
Agency, Washington, DC, USA.
UK/DOE. 1992. The UK Environment, pp. 17 -
21. UK Dept of the Environment, London,
UK.
WRI. 1992. World Resources. World
Resources Institute, in collaboration with
the United Nations Environment
Programme and the United Nations
Development Programme. Oxford
University Press, New York, NY, USA.