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 10m and 20 m away from the highway,
which lies in the built-up area. Sampling was
done at 2 minutes 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.