CHAPTER ONE
INTRODUCTION
1.1 Background of Study
Aerosol is a suspension of fine solid particles or liquid droplets in the
atmosphere. Examples are smoke, sea dust, volcanic dust, air pollution, etc. Aerosol
can also be a liquid substance, as a disinfectant or deodorant, sealed in a metal container
under pressure with an inert gas or other activating agent and released as a spray or
foam through a push-button valve or nozzle. Ocean water and sea salt are transferred to
the atmosphere through air bubbles at the sea surface. As this water evaporates, the salt
is left suspended in the atmosphere which forms aerosols. Air-sea exchange of
particulate matter contributes to the global cycles of carbon, nitrogen, and sulfur
aerosols.
Aerosols originate from a wide variety of natural and anthropogenic sources.
Anthropogenic aerosols are aerosols as a result of human activities which include
burning fossil fuels, biomass burning, direct emissions, etc. Natural aerosols include
volcanoes, condensation, forest fires, botanical debris, etc. The open ocean is one of the
major sources of natural aerosols, producing annually 1015-1016 g of sea-salt aerosols.
Sea-salt aerosols, together with wind-blown mineral dust, and naturally occurring
sulfates and organic compounds, are part of natural tropospheric aerosols. Sea salt
aerosols influence radiative transfer directly by scattering solar radiation and indirectly
by altering cloud droplet size distribution and concentration and contributes to
atmospheric corrosion (Gong et al., 1997; Syed, 2006).
It is believed that much of the removal of atmospheric aerosols occurs in the vicinity of
large weather systems and high altitude jet streams, where the stratosphere and the
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lower atmosphere become intertwined and exchange air with each other. In such
regions, many pollutant gases in the troposphere can be injected in the stratosphere,
affecting the chemistry of the stratosphere. Likewise, in such regions, the ozone in the
stratosphere is brought down to the Aerosol measurements can also be used as tracers
to study how the Earth’s atmosphere moves. Because aerosols change their
characteristics very slowly, they make much better tracers for atmospheric motions than
a chemical species that may vary its concentration through chemical reactions. Aerosols
have been used to study the dynamics of the Polar Regions, stratospheric transport from
low to high latitudes, and the exchange of air between the troposphere and stratosphere.
Aerosols can act as sites for chemical reactions to take place (heterogeneous chemistry).
The most significant of these reactions are those that lead to the destruction of
stratospheric ozone. Aerosols can be found in many typical household products such as
hairsprays, some typewriter correction fluids, deodorants, dry cleaning agents, petrol
lighter fuel, etc. There are serious risks associated with inhaling aerosols. Some
immediate side effects include sneezing, coughing, vomiting, diarrhea, slurred speech,
double vision, drowsiness, and muscle pain. Long-term use of aerosols can damage the
liver, kidneys, lungs, heart, and brain. Sometimes the damage will heal once the huffing
has stopped; sometimes however, it is permanent.
Other risks associated with the inhaling of aerosols include:
I. Suffocation – users have often passed out while inhaling with a bag over their
faces and died of suffocation.
II. Heart failure – results from strenuous activity immediately after inhaling.
III. Depression – some users get depressed, often resulting in suicide attempts.
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1.2 Statement of problem
The atmosphere contains more than just molecules of gases, there are also small
(micro and submicron) sized solid or liquid particles, which are called aerosols.
Aerosols come from natural sources such as condensation, freezing of water vapour,
volcanoes, dust storms, forest and grassland fires, vegetation and sea spray. These
particles affect the composition of the natural atmosphere. Aerosols are also, formed
from human activities such as burning fossil fuels and biomass, ploughing or digging
up soil (Hess and Schult, 1998). This anthropogenic contribution to the atmospheric
aerosol loading is not well established, neither is the level of the total aerosol loading
currently well defined (Andreae, 1996). Atmospheric aerosol particles consist of a
mixture of different substances (Andreae, 1996) such as organic matter, dust and sea
salt. Organic matter constitutes an important fraction of aerosol mass, both in remote
and urban locations; the presence of organic compounds in aerosol particles is due to
primary emission and secondary organic aerosol formation (Gilardoni et al., 2000).
Atmospheric dust constitutes of Na, Mg, Al, Si, P, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni,
Cu, Zn, Ba, As and Pb (Bates et al., 2008).
Sea-salts aerosols are chemical caries of species containing Cl, Br, I and S. The
Br and Cl, once mobilized by sea salt inorganic produces gaseous Br2 and Cl2 which
contributes in atmospheric Ozone depletion (Von Salzen and Dchlunzen, 1999;
Hallquist et al., 2003). Sea salts aerosols are of high concentrated salt origin and can be
propagated downwind to highly industrialized region and cause corrosion to industries
especially those located offshore (Syed, 2006). These aerosol types also exert a strong
influence on solar radiation, cloud formation, meteorological variables and chemistry
of the marine atmosphere. The coastal region of Lagos has high concentration of sea
salt aerosol which is a major pollutant from Atlantic Ocean in that region. Sea-salts are
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considered to be one of the major contributors to the total solid particles and also
referred to as particulate matter present in the atmosphere (Witek et al., 2000).
In the atmosphere, aerosols are regarded as pollutants because, they influence
the Earth’s climate system; both solar and terrestrial radiation budget impair visibility
by scattering and absorption and indirectly by providing the condensation nuclei for
cloud droplets. As well as influencing tropospheric photochemistry (Ina et al., 2002;
Highwood et al., 2000; Roberts et al., 2000; Bates et al., 2008; De Gouw et al., 2008).
Aerosols 1 and m
in diameter (coarse particles) are derived from soil dust and sea
salt (Raes et al., 1 995). Upon deposition, aerosols can harm humans, sensitive aquatic
as well as terrestrial ecosystems (Smimov et al., 2002; Bates et al., 2008). A measure
of the extent to which aerosols affect the transmission of sunlight is known as
atmospheric aerosol thickness (James, 1995; David, 1998). The intensities of aerosols
within an area are an indication of the levels of loading across that region. Therefore
this study investigates the transport profile and source-sink system for sea salt aerosols
over the coastal region of Lagos by utilizing the GPS information of the study region
to simulate meteorological variables and aerosol data over the area from the Air
Resource Laboratory (ARL) website.
1.3 Aim and Objectives
The research aim and objectives are;
1.3.1 Aim
The aim of this research work is to investigate the transport profile and the
concentration dispersion of atmospheric sea salt aerosol over the coastal region of
Lagos.
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1.3.2 Objectives of the study
The specific objectives are to:
i. determine the wind-field information over the coastal region Lagos area
of of Nigeria.
ii. determine the backward air mass trajectory for sea salt aerosol transport
pattern using Hybrid Single Particle Lagrangian Integrated Trajectory
(HYSPLIT) model.
iii. determine the concentration dispersion using Hybrid Single Particle
Lagrangian Integrated Trajectory (HYSPLIT) model.
1.4 Scope of the Study
This work uses the GPS information of Lagos to simulate meteorological
variables and aerosol data across the study region from the National Oceanography and
Atmospheric Administration (NOAA) and Air Resource Laboratory (ARL) via Real
Time Environmental Application and Display (READY) System. This data were
archived data obtained from existing data that have been stored by satellite imagery.
Windrose plot for the coastal region of Lagos were obtained between 8th and 14th of
June 2017 while HYSPLIT/GFS model (Global Forecast Model) was used to obtain
backward air mass trajectory at heights 0, 1000m and 2000m AGL (Above Ground
Level) between 11th and 19th of July. Also sea salt aerosol concentration plots where
developed using HYSPLIT/GDAS model at an altitude of between 5m and 1000m AGL
between 11th and 13th of June 2017.
