ABSTRACT
The study investigates the concentrations of CO, NO2,
SO2, CO2 and HC arising mainly from the activities of
motor vehicles on the ambient air quality of selected sites in Kaduna
metropolis. The sites are situated in the Central market area, the Stadium
Roundabout, and Kawo area. Others include Bakin Ruwa Junction, Abuja Junction,
Sabon Tasha and a control site at the Angwa Rimi G.R.A. Furthermore, sites
situated about a distance of 100m from each of the traffic sites were
investigated. The sampling was carried out over both the dry and wet season.
Results from dry season survey indicate that the average CO concentrations at
the Stadium Roundabout peaked at 29.04ppm. The site also recorded highest
concentrations for NO2, SO2, CO2 and HC at
0.042ppm, 0.040ppm, 370.92ppm and 0.030ppm respectively. In the wet season, the
Stadium Roundabout recorded highest CO concentrations at 18.72ppm. NO2
was highest at 0.03ppm in Sabon Tasha. Both Stadium Roundabout and Sabon Tasha
area recorded highest SO2 concentration at 0.032ppm. Sabon Tasha
recorded highest concentrations for both CO2 and HC at 370.92ppm and
0.028ppm respectively. Results from comparison of the average CO concentration
with the National Ambient Air Quality Standard (NAAQS), showed that CO
concentrations in virtually all sites exceeded the 10ppm for an averaging time of
1 hour in both seasons. The same was true for SO2, which exceeded
the 0.01ppm limit for an averaging time of 1 hour. NO2 limit of
0.04ppm for a 1 hour averaging time was exceeded at Stadium Roundabout in the
morning hour, Central Market area in the afternoon, and in the evening hours at
Central Market, Stadium Roundabout and Bakin Ruwa all in the dry season. All
sites were within limit in the wet season. An assessment of the air quality
status during the dry season as adjudged using the AQI of the United States
indicates that CO concentration at all sites (except Abuja Junction) was “very
unhealthy”. During the wet season however, CO concentrations was “very
unhealthy” in Kawo, Central Market area and Stadium Roundabout, Sabon Tasha and
Bakin Ruwa were “unhealthy” while Abuja Junction was “moderate”. NO2
concentrations were “good” in both seasons for all sites. SO2 in the
dry season was “moderate” in all sites but was “good” in Abuja junction. In the
wet season, all sites were adjudged “good. Result from the model showed a
decrease in all pollutants concentrations with increased distance away from the
traffic sites. The model developed is therefore useful for planning of
residential and other facilities in Kaduna metropolis and beyond.
CHAPTER ONE
INTRODUCTION
1.1 PREAMBLE
The air we breathe is a mixture of gases and particulate
solid and liquid matter. Some of these substances come from natural sources
while others are caused by human activities such as our use of motor vehicles,
domestic activities, industries and businesses. Air pollution occurs when the
air contains substances in quantities that could harm the comfort or health of
humans and animals, damage plants and materials. These substances are called
air pollutants and can be either particles, liquids or gaseous in nature (Alias
et al., 2007). Keeping the air quality acceptable has become an important task
for decision makers as well as for non-governmental organizations.
As many cities around the world become more congested,
concerns increase over the level of urban air pollution being generated and in
particular its impact on localized human health. The more this relationship is
understood, the better chance there is of controlling and ultimately minimizing
such effects. Urban air quality is an issue that is currently on top of air
pollution agendas around the world (Colvile et al., 2001). Estimate worldwide
show that nearly one billion people in urban environments are continuously
being exposed to health hazards from air pollutants (Ahrens, 2003).
Air pollutants are airborne substances that occur in
concentrations high enough to cause adverse effects on health, the environment
and/or outdoor structures. Air pollutants can
affect health in different ways and
in varying degrees of severity ranging from minor irritation through serious
illness, to premature death (Dickey, 2000).
Air pollutant emissions come from both natural (biogenic
emissions) and anthropogenic sources. Although emissions from natural sources
can be substantial, and are indeed the dominant source in non-urban areas, this
study specifically investigates (anthropogenic) road traffic emissions in an
urban area. The emission of air pollutants has led to several air quality
issues such as photochemical smog, acid rain, visibility degradation and
nuisance. Although major efforts have been made over the past decades to reduce
air pollution and improve air quality, these issues have proven to be quite
persistent and continue to exist, despite the implementation of several air quality
strategies. A major factor in this is the strong and continued growth in road
traffic.
Road transport emits air pollutants from the combustion of
liquid or gaseous fossil fuels. Although thousands of air pollutants from road
traffic can be identified, most of them can be classified in the following
major groups according to their origins and formation processes:
a). Products of incomplete combustion, including carbon
monoxide (CO), particulate matter (PM) and hydrocarbons (HCs):
b). Products of high-temperature combustion processes,
including nitrogen oxides (NOx);
c). By-products of combustion due to impurities in the fuel,
including heavy metals and sulphur oxides (SOx);
e). Secondary air pollutants such as photochemical oxidants,
including tropospheric ozone (O3) and peroxyacetyl nitrate (PAN); and
f). Greenhouse gases, including carbon dioxide (CO2) and
methane.
Around the world, and particularly for CO, NOx and HC, road
traffic is the dominant, if not the most important, anthropogenic source of air
pollution in urban areas (Fenger, 1999). This is not only because of the
magnitude of its emissions, but also because pollutants are emitted in close
proximity to human receptors, which enhances exposure levels.
With the emission concentration in traffic being some 104 –
105 times above typical ambient background and released only a few tens of
centimeters above ground level, excellent dispersion is essential for dilution
of the pollutants in the ambient air (Colls, 2002; Abhishek and Colls, 2010).
Thus the meteorological conditions, in addition to concentration of activities,
which generates emission, account for the spatial and temporal variations. The
emission of vehicle pollutants into the atmosphere is an increasingly important
health issue that affects nearly everyone (Rouphail et al, 2001).
The health challenges faced by road users, passers-by,
residents and business operators in traffic flash points, having high
concentration of vehicular traffic during some periods of the day are worrisome
issues (Utang and Peterside, 2011). A comparison of the monitored and inventory
emissions with acceptable standards (threshold) is useful in determining the
extent of safety of road side business operators and hawkers in traffic
intersection and congested traffic points.
Generally, exhaust gas emission
concentrations vary, depending on the engine operating mode (idling,
accelerating, cruising and decelerating) (Colls, 2002). Deceleration and idle
are characteristics of peak traffic at road intersections, while high
acceleration and cruise are common at off peaks. Thus a spatio-temporal
variation in rate and type of air pollutant exists between and within peak and
off peak periods of urban traffic (Utang and Peterside, 2011). Once these
emissions are released into the atmosphere, dispersion processes transport and
dilute these emissions. In addition to dispersion, pollutants can also undergo
(chemical) transformation and deposition. Depending on the ground level
location, these processes results in certain ambient concentration levels,
which are referred to as immissions (Harssema, 1987), the extent of which is a
function of meteorological conditions, topographical characteristics and
distance between source and receptor.
The level of exposure to air pollutants depends on ambient
concentration levels and where sensitive receptors (e.g. population) are
situated in time and place. Health effects then depend on dose-effect
relationships, which may be obtained from epidemiological of clinical studies.
The magnitude of the effects subsequently determines the economic effects
(cost) of air pollution.
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Item Type: Project Material | Size: 97 pages | Chapters: 1-5
Format: MS Word | Delivery: Within 30Mins.
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