INVESTIGATION OF THE TRANSPORT PROFILE AND DISPERSION OF ATMOSPHERIC AEROSOL OVER THE COASTAL REGION OF LAGOS

INVESTIGATION OF THE TRANSPORT PROFILE AND DISPERSION OF ATMOSPHERIC AEROSOL OVER THE COASTAL REGION OF LAGOS

ABSTRACT

This study investigates the transport profile and source-sink system for sea salt aerosol

over the coastal region of Lagos. The study utilized the GPS information of the study

locations to simulate meteorological variables over the area from the Air Resource

Laboratory (ARL) website, The ARL/GFS model was used to determine the wind rose

information between 8th and 14th of June, 2017. In addition, backward air mass

trajectories were determined at various heights of 0m, 1000m and 2000m above ground

level (AGL) for aerosol transport patterns as well as concentration dispersion using the

Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model.

The result showed that aerosols are of sea salt origin which evolved from the sea of the

Atlantic Ocean. The maximum wind speed for the period considered from 8th to 14th

June 2017 was 4 to < 7 m/s range in SW direction and as such complete calmness was

not observed during the period under consideration. The highest frequency of wind

blown was 56% which implies that 56% of atmospheric sea salt aerosol were

transported during the study period. The backward concentration trajectory indicated

that the maximum aerosol pollution reaching Lagos was 2.1 x 10-10 mg/m3 which were

from the Atlantic Ocean and the minimum was about 5.0 x 10-16 mg/m3. Since these

pollutants are most likely sea salts which are highly corrosive, adequate corrosion

protection is recommended.

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

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.

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 seasalt.

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

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.

TOPIC: INVESTIGATION OF THE TRANSPORT PROFILE AND DISPERSION OF ATMOSPHERIC AEROSOL OVER THE COASTAL REGION OF LAGOS

Chapters: 1 - 5
Delivery: Email

Number of Pages: 65

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