Presentation

16. 3. 2006

Libor Zouhar

Acid rainAcid rain

What is acid rain?

It is rain that is more acidic than normal rain.

pH (normal rain) = 5,6

Normal rain is slightly acidic due to the presence of carbonic acid formed by the mixture of CO2 and rainwater. CO2 + H2O H2CO3

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slightly = mírně due to = v důsledku mixture = směs, smíchání

pH (acid rain) < 5,6

pH of acid rain

Usually: 5,0 – 5,5

The most acidic rain is in the US in some industrial areas (pH = 4,3).

The pH scale is logarithmic.

(e. g. pH6 is ten times more acid than pH7 and pH5 is one hundred times more acid than pH7 )

Sources of acid rain

SO2

Sulphur dioxide is formed by the burning of fossil fuels, such as coal, that contain high quantities of sulphur.

NOx

Nitrogen oxides are produced by various industrial activities and are present in car exhaust fumes.

Formation of acid rain

Acid rain usually forms high in the clouds where sulfur dioxide and nitrogen oxides react with water, oxygen and oxidants. This forms a weak solution of sulfuric acid and nitric acid. Sunlight increases the rate of most of these reactions.

The chemical reactions that change air pollution to acid rain can take from several hours to several days.

__________________________________________________rate = poměr, podíl

2SO2 + O2 + 2H2O 2H2SO4

 4NO2 + O2 + 2H2O 4HNO3

Forms of acid rain

A more precise term for acid rain is acid deposition, which has 2 parts:

Wet deposition:

Dry deposition:

__________________________________________________refer to = odkázat naprecise = přesný

Wet deposition refers to acidic rain, fog and snow.

Dry deposition refers to acidic gases and particles. About half of the acidity in the atmosphere falls back to earth through dry deposition.

deposition = uložení

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precipitation = srážky

Expansion of acid rain on the world

occurrence = výskyt affected = zasažený, ovlivněný moderately = mírně

Effects of acid rain on environment

Acid deposition has a variety of effects, including damage to forests and soils, fish and other living organisms, materials, and human health.

Some fish and animals, such as frogs, have a hard time adapting to and reproducing in an acidic environment. Many plants, such as evergreen trees, are damaged by acid rain and acid fog.

Ecosystem = biological organisms + environment.

The plants and animals living in an ecosystem are highly interdependent._______________________________________________________

interdependent = vzájemně závislý

_______________________________________________________harm = poškodit, poškození

Some concrete examples:

How does acid rain affect fish and other aquatic organisms?

Acid rain causes a cascade of effects that harm or kill individual fish, reduce fish population numbers, completely eliminate fish species and decrease biodiversity.

As acid rain flows through soils, aluminium is released into the water. So, as pH in a lake or stream decreases, aluminium levels increase. Low pH and increased aluminium levels are directly toxic to fish.

Low pH and increased aluminium levels cause chronic stress that may not kill individual fish, but leads to lower body weight and smaller size and makes fish less able to compete for food and habitat. Some types of plants and animals are able to tolerate acidic waters. Generally, the young of most species are more sensitive to environmental conditions than adults. At pH 5, most fish eggs cannot hatch. At lower pH levels, some adult fish die. The result is, that some acid lakes have no fish.

stream = tok, potokcompete = soutěžit

habitat = přirozené prostředí

hatch = líhnout se

How acid rain harms trees and other plants?

Acid rain does not usually kill trees directly. Scientists know that acidic water dissolves the nutrients and helpful minerals in the soil and then washes them away before trees and other plants can use them to grow.

At the same time, acid rain causes the release of substances that are toxic to trees and plants, such as aluminium, into the soil. Scientists believe that this combination of loss of soil nutrients and increase of toxic aluminium may be one way that acid rain harms trees.

Affected trees are weak, they can be more easily attacked by cold weather, diseases or insects that kill them.

Acid rain can harm other plants in the same way it harms trees.

helpful = užitečný

Thank you for your attention.Thank you for your attention.Thank you for your attention.