THE PHYSIOCHEMICAL PROPERTIES OF RAIN WATER IN ONITSHA

TABLE OF CONTENTS

CHAPTER ONE

1.0    INTRODUCTION

1.1    OBJECTIVES OF THE RESEARCH

1.2    LITERATURE REVIEW

1.2.1 ORIGIN

1.2.2  RAIN FORMATION

1.2.3 CAUSES OF ACID RAIN

1.2.3.1       NATURAL PHENOMENA

1.2.3.2       ANTHROPOGENIC ACTIVITIES

1.2.4 CHEMISTRY OF RAIN

1.2.4.1       GAS PHASE CHEMISTRY

1.2.4.2       CHEMISTRY IN CLOUD DROPLETS

1.2.5 ADVERSE EFFECT/POLLUTION

1.2.6 PREVENTION AND CONTROL OF ACID RAIN

CHAPTER TWO

2.0    MATERIAL AND METHODS

2.1    SAMPLE COLLECTION

2.2    PHYSIOCHEMICAL PARAMETERS

2.3    REAGENTS

2.4    INSTRUMENTS

2.5    METHODOLOGY

2.5.1 pH DETERMINATION

2.5.2 SULPHATE DETERMINATION

2.5.3 NITRATE DETERMINATION

2.5.4 HCO₃^- DETERMINATION

2.5.5 DETERMINATION OF PHOSPHATE (ASCORBIC ACID)

2.5.6 DETERMINATION OF ELECTRICAL CONDUCTIVITY

2.5.7 DETERMINATION OF TOTAL SUSPENDED SOLID (TSS)

2.5.8 DETERMINATION OF TOTAL DISSOLVED SOLIDS (TDS)

CHAPTER THREE

3.0    RESULTS

CHAPTER FOUR

DISCUSSION, CONCLUSION AND RECOMMENDATION

DISCUSSION

CHAPTER ONE

1.0    INTRODUCTION

          Acid rain has become a phenomenon that draws a lot of attention. Even recently, there was a panic in the country and in the world at large as forcast was made of deadly dangers associated with acid rain. The prediction was that the initial or first would be acidic.

          The U.S department of energy estimates that since 1960, there have been more than four thousand (>4000) oil spills, discharging several millions barrels of crude oil into the ponds, ditches, creeks, beaches, streams and rivers in Nigeria especially in the Niger Delta[1]. These have impacted negatively on the environment, economic life and health of the people[2].

          Onitsha as a case study is a commercial urban city with a very dense population, a lot of industries (including small scale, medium and large scale industries) and also a high use of gasoline generators in homes, offices, churches, schools and industries. Because of the unstable supply and the demanding nature of power (energy) in all establishments, the use of gasoline generators becomes inevitable which has led to extensive gas flare. The smoke that comes out of the gas flare does not just contain sooty grey particles but also many invisible gases that can be very harmful to our environment. These gases (especially nitrogen oxide and sulfur dioxide) react with the tiny droplets of water in clouds to form sulfuric and nitric acids. The rain from these clouds then falls as acid rain[3].

          Natural process such as bacterial action on soils, forest fires and lightening can contribute significantly to the high value of this acid forming gas in the atmosphere e.g HCO₃^-. Actually, all rain tends to be acidic because of the equilibration of water with atmospheric carbon dioxide, yielding a pH of 5.6 – 6.5, then precipitated with a pH below 5.0 as a result of significant anthropogenic contribution of pollutants mainly sulfur dioxide and nitrogen oxide[4].

1.1    OBJECTIVES OF THE RESEARCH

          In carrying out this research, we have in mind;

·                    To study the rainfall pattern in Onitsha from the first rain of the year and as the rain progresses. Three centers have been carefully selected (Awada, Omagba and Fegge) to represent a totality of the entire town.

·                    To analyze the concentration of the following physiochemical properties (parameters) of the rain samples collected. pH, electrical conductivity, SO₄^2-, NO₃^-, PO₄^3-, HCO₃^-, TSS (Total Suspended Solids) TDS (Total dissolved solids).

·                    To evaluate the obvious economic, environmental and agricultural effects of the rainfall pattern from the data or information gotten from the second objective.

1.2    LITERATURE REVIEW

1.2.1 ORIGIN

Since the industrial revolution, emissions of sulfur dioxide and nitrogen oxides to the atmosphere have increased[5][6].

          In 1852, Robert Angus Smith was the first to show the relationship between acid rain and atmospheric pollution in Manchester, England [7]. Though acid rain was discovered in 1852, it was not until the late 1960s that scientists began widely observing and studying the phenomenon. The term “acid rain” was generated in 1972[8]. Canadian Harold Harvey was among the first to research a dead lake public awareness of the acid rain in the U.S which increased in the 1970s after the New York times promulgated reports from the Hubbard Brook Experimental forest in New Hampshire due to myriad deleterious environmental efforts demonstrated to result from it[9].

          Occasionally, pH reading in rain and fog water of well below 2.4 have been reported in industrialized areas [5]. Industrial acid rain and fog water of well below 2.4 have been reported in industrialized areas [5]. Industrial acid rain is a substantial problem in Europe, China [10], Russia and areas down-wind from them.

          These areas all burn sulfur containing coal to generate heat and electricity. The problem of acid rain not only has increased with population and industrial growth, but has become more widespread. The local pollution has contributed to the spread of acid rain by releasing gases into regional atmospheric circulations[12][13].

          Often depositions occurs in a considerable distance downwind of the emissions with mountainous regions tending to receive the greater deposition (simply because of their higher rainfall). An example of this is the low pH of rain compared to the local emission which falls in scandinavia[14].

1.2.2  RAIN FORMATION

          Because the energy necessary for evaporation is supplied by sunlight, the largest sources of water vapour are tropical and semi

tropical oceans. When warm, moist air rises in updrafts, it expands, cools and its relative humidity  increases. When the humidity is slightly in excess of 100%, the moisture condenses on slightly small aerosol particles called condensation nuclei. This forms fog and cloud not all clouds form rain but when it does, it is by one of these processes. The first one by Bergeron, Norwegian meteorologist, takes place by only in the part of the cloud that is below the freezing point of water. In such cloud, when a minute ice crystal forms, the crystal grows very rapidly. Because ice is the stable form of water below 0⁰C (32⁰F), it has a lower vapour pressure than the super-cooled droplets, moisture therefore evaporates from the super-cooled droplets and condenses on the fewer ice crystals. These crystal gradually increases in size, eventually becoming large enough to fall from clouds as snow. Much rain is produced when snow melts as it cascades from clouds into warmer air[15].

          In the second process, collision and coalescence of many fine clouds droplets form raindrop. Collision of cloud droplets occurs as a result of their relative motion, which may rise because of Brownian movement or because some droplets are larger and fall faster than others. As they overtake and collide with small droplets, they coalescence with them, becoming even small droplets, they coalesce with them, becoming even larger and fall even yet faster by this process, they eventually grow to rain drop size. Chemists believe that some of the drops by this process get so large that they break up under aerodynamic forces into two or more somewhat smaller drops. These smaller drops in turn grow until they become unstable and break up, thus producing raindrops growth by chain reaction. There is evidence that in thunderstorm electrical forces may aid the rain forming process by accelerating collision and coalescence and droplets.

          Raindrops ranges in size from less than 0.008 inch to about 0.23 inch in diameter. Raindrops do not exceed 0.23inch in diameter because of surface tension which keeps them intact is insufficient to withstand the aerodynamic forces tending to pull them apart. The rate of fall of a raindrop is determined by the balance between its weight and its aerodynamic drag[15].

1.2.3 CAUSES OF ACID RAIN

          The most important gas which leads to acidification is sulfur dioxide. Emission of nitrogen oxides which are oxidized to form nitric acids is of increasing importance due to controls on emissions of sulfur containing compounds. About 70tg(s) per year in the form of SO₂ comes from fossil fuel combustion and intensity, 2.8Tg(s) from wild fires and 7-8Tg(s) per year from volcanoes [16].

1.2.3.1       NATURAL PHENOMENA

          The principal natural phenomena that contribute acid producing gases to the atmosphere are emissions from volcanoes and those from biological processes that occurs on the land, in wetlands and in the oceans, The major biological source of sulfur containing compounds is dimethyl sulfide. Nitric acid in rainwater is an important source of fixed nitrogen from plant life and is produced by electrical activity in the atmosphere such as lightening. Acidity deposits have been detected in glacial ice thousands of years ago in remote part of the globe[12].

1.2.3.2       ANTHROPOGENIC ACTIVITIES

          The principal cause of acid rain is sulfur and nitrogen compounds from human sources, electricity generation, factories and motor vehicles, coal power plants are other sources of the polluting components that constitute acid rain. The gases can be carried hundreds of kilometers in the atmosphere before they are converted to acids and deposited. In the past, factories had short funnels to let out smoke but this caused many problems locally. Thus factories now have taller smoke funnels. However, dispersal from these taller stacks causes pollutants to be carried farther causing widespread ecological damage. However, livestock production also plays a major role. It is responsible for ammonia produced through human activities which significantly contributes to acid rain[17].

TABLE 1:  SOURCE OF ACID IN CLEAR AND POLLUTED AIR

1.2.4 CHEMISTRY OF RAIN

Combustion of fuels creates sulfur dioxide and nitric oxide. They are thus converted to sulfuric and nitric acid [18].

1.2.4.1       GAS PHASE CHEMISTRY

In the gas phase, sulfur dioxide is oxidized by reaction with the hydroxyl radical through an intermolecular reaction.

SO₂ + OH           HOSO₂

Which is followed by;

HOSO₂ + O₂              HO₂ + SO₃

In the presence of water, sulfur trioxide SO₃ is converted rapidly  to sulfuric acid.

SO_3(g)+ H₂O_(l)           H₂SO₄

For nitric acid, nitrogen dioxide reacts with OH to form nitric acid.

NO₂ + OH             HNO₃

1.2.4.2       CHEMISTRY IN CLOUD DROPLETS

When clouds are present, the loss rate of SO₂  is faster than can be explained by gas phase chemistry alone. This is due to reaction in the liquid water droplets.

HYDROLYSIS:

Sulfur dioxide dissolves in water and then like carbon dioxide, hydrolysis in a series of equilibrium reactions.

SO_2(g) + H₂O            SO₂ . H₂O

SO₂ .H₂O             H­­⁺  + SO₃^-

HSO₃^-                  H⁺SO₃ ^2-

OXIDATION:

There are a large number of aqueous reactions that oxidize sulfur from S_(IV)  to  S_(VI), leading to the formation of sulfuric acid. The most important oxidation reactions are with ozone, hydrogen peroxide and oxygen (7).

1.2.5 ADVERSE EFFECT/POLLUTION

          Acid rain has been shown to have adverse impact on forest, freshwater and soils, killing insects and aquatic life-forms as well as causing damage to building and having impact on human health.

SURFACE WATER AND AQUATIC ANIMALS

          Both the lower pH and higher aluminum concentration in surface water that occur as a result of acid can cause damage to fish and other aquatic animals. At pH lower than 5, most of the fish eggs will not hatch and lower pH can kill adult fish. As lakes and rivers become more acidic biodiversity is reduced.

          Acid rain has eliminated insect life and some fish species, including the brook trout in some lakes, streams and cracks in geographically sensitive areas, such as the Adirondack mountains of the United States. However, the extent to which acid rain contributes directly or indirectly through runoffs from the catchment to lake and rivers acidity (ie depending on characteristics of the surrounding watershed) is variable. The united states Environmental Protection Agencies (EPA) website states “of the lakes and streams surveyed, acid rain caused acidity in 75 percent of acidic lakes and about 50 percent of the acidic streams[19].

 SOILS

          Soils biology and chemistry can be seriously damaged by acid rain. Some microbes that are unable to tolerate changes of low pH’s are killed [20]. The enzymes of these microbes are denatured (change in shape so they no longer function) by the acid. The hydronium ions of the acid rain also mobilize toxins such as aluminum and leach away essential nutrients and minerals such as magnesium.

2H⁺_(aq) + Mg²⁺_(clay)                   2H⁺ _clay)++ Mg²⁺_{( aq)}

Soil chemistry can be dramatically changed when base cation such as calcium and magnesium are leached by acid rain thereby affecting sensitive species, such as sugar maple (acer Saccharum) [21][22].

FOREST AND OTHER VEGETATION

Adverse effects may be directly related to acid rain, like the acids effect on soil or high concentration of gaseous precursors to acid rain. High altitudes forests are especially vulnerable as they are often surrounded by clouds and fog which are  more acidic than rain. Other plants can also be damaged by acid rain, but the effects on food crops is minimized by the application of lime and fertilizers to replace lost nutrients. In cultivated areas, limestone may also be added to increase the ability of the soil to keep the pH stable, but this tactic is largely unstable in the case of wilderness lands. When calcium is leached from the needles of red space, these trees become less cold tolerant and exhibit winter injury and even death[23].

HUMAN HEALTH

          Scientists have suggested direct links to human health. Fine particles, a large fraction of which are formed from the same gases as acid rain (sulfur dioxide and nitrogen oxide) have been shown to cause illness and premature deaths such as cancer and other diseases[24].

OTHER ADVERSE EFFECT

          Acid rain can also damage building and historic monuments, especially those made of rocks such as limestone and marble containing large amounts of calcium carbonate. Acids in the rain react with the calcium compounds in the stones to create gypsum, which hen flaskes off.

CaCO_3(g) + H₂SO_4(aq)­                      CaSO_4(aq) + CO₂ + H₂O_(l)

          The effects of this are commonly seen on old gravestones, where acid rain can cause the inscription to become completely illegible. Acid rain also increases the oxidation rate of metals in particular copper and bronze[25].

1.2.6 PREVENTION AND CONTROL OF ACID RAIN

          The international community has responded to the problems of acid rain. By the 1970s, a number of attempts have been made to obtain an international convention to control emission, an example is the convention on long range transboundary commission for Europe which was ratified in 1983. Other convention to reduce SO and NO emission followed after. In these conventions the “tall chimney” policy of some countries came into serious criticism. The tall chimneys used by emitting industries ensured that the effluents gases are transferred for afield thereby reducing the effect of the emission in the country of origin while transferring it to other countries[15].

          The method by which acid rain problem was minimum were in too fold, ensuring that emission are curtailed and reclaiming of an already acidified body. The first technique entails tackling the issue from source and may involve process changes but particular efficient effluent gas management has been better and acceptable option.

          In the United States many coal-burning power plants use flue gas desulfurization (FGD) to remove sulfur containing gases from their stack gases. And example of FGD is the wet scrubber which is commonly used in the U.S and many other countries. A wet scrubber is basically a reaction lower equipped with a fan that extracts hot smoke stack gases from a power plant into the tower. Lime or limestone in slurry form is also injected into the tower to mix with the stack gases and combine with the sulfur dioxide present. The calcium carbonate the limestone produces pH – neutral calcium sulphate that is physically removed from the scrubber. That is the scrubber turns sulfur pollution into industrial sulfates.

EMISSIONS TRADING

          In this regulatory scheme, every current polluting facility is given or may purchase on an open market an emission allowance for each unit of a designated pollutant it emits. Operators can then install pollutants control equipment and sell portions of their emission allowances they no longer need of for their own operations, thereby recovering some of the capital cost of their investment in such equipment. The intention is to give operators economic incentives to install pollution controls[26].

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