Nick Drake

24-Apr-02

 

 

I have chosen to research Acid Pollution because the environmental effects of this process are both very evident and their origins can be easily traced. Acid pollution affects many different areas: in gases, ‘acid precipitation’ or as it is more commonly known, acid rain erodes buildings, affects human respiration and destroy agricultural land. In water, acid pollution can destroy ecosystems as acidic components break down the nutrient rich environment leaving it lifeless and non-recyclable.

Pollution occurs by either and or both: ‘Dry-Deposition’ if polluting source is local and falls directly onto the nearby area and does not include interaction with water molecules, or ‘Wet-Deposition’ which delivers acidic pollutants that have travelled in the atmosphere for many hundreds of miles, pumped from high industrial chimneys. Unlike domestic rubbish or car pollution which can be easily collected, controlled and identified, the acidic particles which lie in the air erode metal structures, certain kinds of stone, leather, paper and textiles. (Elsworth p34)

 

All chemical states of acid pollution contain Sulphur Dioxide SO₂ and Nitrogen Oxides NO_x. Sulphur dioxide constitutes 70% of total acid rain, Nitrogen oxides, 30%. (Ellsworth, p6)

In gaseous form , the Sulphuric component mixes with monatomic oxygen particles high in the troposphere producing Sulphur Trioxide SO₃ (reaction 1.1) which later reacts with water to form Sulphuric Acid H₂ SO_4, (reaction 1.2) , ‘acid precipitation’. (Wellburn, p26)

 

SO₂  + 0  ® SO₃   (reac. 1.1)

SO₃  + H₂0  ® H₂ SO₄   (reac. 1.2)

 

Also in gases, Nitrogen Oxides appear in two polluting forms, Nitrogen Dioxide NO₂ and to a lesser extent, Nitric Oxide NO, this gives rise to the popular general naming of Nitrogen based pollution to take the form of NO_x (Wellburn, p60) . A combination of reactions to nitric acid, firstly with ozone to produce nitrogen dioxide (reaction 1.3) then reaction with hydroxyl radicals, form Nitric Acid (reaction 1.4) which attaches itself to water molecules in clouds and falls as acid precipitation. (Wellburn, p71)

 

NO + 0₃ ® NO₂                        (reaction 1.3)

NO₂ + H₂0 ® HNO₃                 (reaction 1.4)

 

These two atmospheric pollutants, sulphuric acid and nitric acid arrive in marine ecosystems through either dry or wet deposition. Dry deposition removes all oxides of nitrogen by absorption into the sea, at ground level including being taken up by vegetation (Wellburn, p73) Wet-deposition into rivers, lakes and the hydrosphere occurs when a chemical attachment is made with water. Water reacts with sulphur trioxide to produce sulphuric acid (reaction 1.2) and reacts with nitrogen dioxide to form nitric acid (reaction 1.4). Both these acidic pollutants reach the surface through precipitation.

 

We now know that sulphur dioxide and nitrogen oxides undergo chemical change when in the atmosphere transforming them into powerful acids. Where these chemicals originate from is also of great interest. What is definitely sure is that these chemicals are not purely a man-made problem that has only existed for the last hundred years. Sulphur dioxide is emitted into the atmosphere from the following sources and their percentages

Oceans            40%

Coal                 30%

Oil                    15%

Biogenic processes    7%

Industry                       5%

Volcanoes                   3%

From these figures we see that the total of man-made emissions is 50%.

As with any academic research, bias is found in nearly every source of data relating to a topic and different sources claim differing percentages on the amount that man as a total is responsible for. It is safe to say however that man does account for up to 50% of the total emissions which means that in only 250 years of mechanisation and technologies, Western Europe and the US have matched and are exceeding natures carrying capacity to recycle such quantities of sulphur dioxide . 90% of man-made emissions of sulphur dioxide arise from the urban and industrialised areas of Europe, N.America, India and the Far East (Wellburn p23)

As we can see above, coal burning produces the greatest amount of sulphur emissions into the atmosphere. Oil refining, and oil and natural gas burning are the subsequent highest man-made polluters. These three are fossil fuels, burned in power stations and factories and released high into the atmosphere by tall stack chimneys delivering the sulphur dioxide and nitrogen oxides internationally; from the UK across the North Sea to Sweden, Netherlands and Norway.

Natural emission of sulphur dioxide occurs from biogenic decomposition and excretion, volcanoes, hot springs, waves breaking and other fluvial processes which in total amount to 50% of the total released sulphur dioxide into the atmosphere. This process has been occurring for many millions of years, in a environmental equilibrium controlled by nature, which saw only moderate fluctuations over many hundreds and thousands of years.

It was the industrial revolution, running as it did on vast quantities of coal and later oil, that started the dis-equilibrium in the air (Elsworth ,p6). Affected areas were once only industrial towns and cities such as Manchester and Leeds, where heavy industry dominated the skyline and produced chemical clouds, ‘smogs’. That was 250 years ago, before the industrial expansion which has spread throughout economically viable world. North America, Europe, Japan and Central Asia are now showing the signs of acidic imbalance in local atmospheres, more acidic freshwater supplies, respiratory problems in humans, building and material damage and crop yield reduction.

The causes of Nitrogen Oxide emission come from mainly industrial pumping of Ammonia NH_3. Ammonia is also produced naturally in both a reaction with N₂ in a process called the Haber reaction, which occurs in the atmosphere. NH₃ also produced from the natural decomposition of decaying animals, plants etc or as escaping gases during the artificial manufacture of fertilisers. (Wellburn, p61)

Another big cause of Nitrogen Oxide emissions, come from a natural process of microbial respiration patterns that use Nitrogen Oxide to respire as opposed to the natural chemical oxygen. The waste products from this process are both Nitrogen and Nitrogen Oxide, along with the decomposition of agricultural land on which this process, called denitrification takes place. This process is not good for agriculture, it destroys crops and takes the rich nutrients out of the soil. Nitrification which is the opposite of denitrification, where ammonium or oxides are converted by oxygen-dependant microbes, encourage aeration and return both oxygen and nutrients to the affected area. With the use of artificial fertilisers, a farmer is deliberately disturbing the natural balance between these two processes, and discourages nitrogen fixation. Any excess fertiliser remaining after application and not draining away is removed by denitrification. This imbalance that then develops from farmer’s ignorance or miss-application has led to an increase in the atmospheric levels of nitrous oxide as denitrification has increased.

 

The effects of acid rain are felt by more and more people every day. Wet-deposition means that the acidic chemicals fall, in mist, hail sleet and snow; however their frequency and location are neither stable or uniformly distributed. Different areas are affected at different times, for instance, during the 1950’s much of what the UK as an industrial nation produced was pumped high in the atmosphere to Scandinavia, although it did take the problem out of the UK’s hands, Sweden, Norway and Finland were left with rotting trees, buildings and stone faces that were reducing at rates up to 10cm per year. As an example of the affects to our freshwater from ‘wet-deposited’ acid rain, pristine conditions (man does not exist), our rain would fall at around 5.6pH, which is slightly alkali. However since the interaction of man and his industry, we see concentration of rainfall ten times more acidic @ <4.5pH in the eastern seaboard of the USA or Northern Europe. (Wellburn, p109). Both wet and dry processes transport sulphates and nitrates to soil systems, which increases soil acidity and eventually leads to the reduction of soil fertility.

Within hydrosphere's, some animals and plants die not as a direct result of the acid itself but because the acid may destroy a plant or animal on which it is dependant. There is a total loss to all levels of the food chain within a hydrosphere. The result is a dead ecosystem, a few resistant microbes and plankton remain but in no way matching the species diversity and numbers seen before. (Elsworth, p24). Fish do build up a resistance to acid levels but only over a long time period with species evolution. A sudden change that results from wet or dry deposition kills many fish.

Buildings as mentioned before as also affected by the falling of acid-rain, buildings across Europe are showing very visible effects of chemical corrosion. It is estimated the annually the effects of acid rain on buildings cost £2bn in Europe, Asia and N.USA. Large quantities of sulphur dioxide and hydrogen fluoride eat away at architectural detail in ancient buildings, corrode stone and stucco work, and seriously weaken walls, roofs and many metal elements. (Elsworth, p33)

 

 In researching this topic, I have had access to different sources of information. One of the books I have was produced by the WATT commission which is a government funded and controlled body representing the power companies. In this report was the acknowledgement of acid rain production coming from both natural and man-made causes. What is more evident however is that the WATT commission see the natural causes for sulphur dioxide and nitrogen oxide emissions as significantly more in volume than man interactions and additions. There is definitely bias in this report, although that is hardly surprising considering they represent the reason why we are experiencing such ‘un-natural’ levels of acid pollution across the industrialised world.

What we as a species must acknowledge is that we are an insignificantly small part of what is a massive, complex system of nature that has existed for millions of years, slowly adapting to gradual changes in temperatures, atmospheric chemical composition etc. Our 50% is only going to increase both in percentage volume and acidity. Man, money and greed is still enveloping the world, more areas now are producing industrial exhausts of sulphur dioxide and nitrogen oxides along with many other polluting chemicals such as aluminium, lead, tin, waste products. In only 250 years we have matched the natural emissions which have taken 6,000,000,000  years to develop. Maths suggests that one is developing quicker than the other, out of control.

 

Word count: 1,766

 

Bibliography

 

·          Acid Pollution and Acid Rain – The Biological Impact

Alan Wellburn –1988

 

·          Acid Pollution, Acid Rain and the Environment

WATT Commission Report - 1988 

 

·          Acid Rain

Steve Elsworth – 1984

 

·          Acid Rain in Europe – Counting the cost

Helen ApSimon, David Pearce, Ece Ozdemiroglu