Effects of Air Pollution

    ACID RAIN when acidic gases dissolve in the moisture in the air, acids are formed. The acids fall on the earth as 'acid rain' and pollute fresh water sources.

Acid rain is the outcome of the emission from industries releasing sulphur and oxides of nitrogen.When these oxides come into contact with water vapour, acids result, with dramatic effects. There is an increased acidity of the soil, damage to crops and forests and frequently, the death of fish in lakes and rivers is observed. Acid rain indirectly mobilises heavy metals such as cadmium and mercury, which are absorbed by plants and enter the food chain.

Due to CO2, rainwater is slightly acidic with pH of 5.6. SO2 and NO2 of air can increase this acidity and make the pH < 5.0. This is "acid rain". Due to this lakes acidify. Fish and other aquatic animals are killed. Forests are destroyed. Buildings and monuments of marbles and limestone suffer as CaCO4 is converted to CaSO4, which is more soluble and dissolves. Leather, fabrics are affected and animals also suffer.

Effects of acid rain

Acid rain causes acidification of lakes and streams and contributes to damage of trees at high elevations (for example, red spruce trees above 2,000 feet) and many sensitive forest soils. In addition, acid rain accelerates the decay of building materials and paints, including irreplaceable buildings, statues and sculptures that are part of our nation's cultural heritage. Prior to falling to the earth, SO2 and NOx gases and their particulate matter derivatives, sulfates and nitrates, contribute to visibility degradation and harm public health.

    GREEN HOUSE EFFECT Increasing carbon dioxide in the atmosphere due to industrial activity & burning of fossil fuels traps more heat, changes the climate, melts the polar ice caps & submerges coastal areas.

Carbon dioxide may be an insignificant gas, a mere 0.03%of the earth's atmosphere, but plays a useful role in absorbing the radiant energy of the sun. Due to industrial activity the carbon dioxide level in the atmosphere has increased substantially.

The effect of carbon dioxide on the temperature of the earth is what is termed the "Greenhouse Effect". It behaves like the glass in a greenhouse, allowing the heat from the sun through to the earth but preventing some of itfrom being radiated back through the atmosphere. Carbon dioxide traps more heat and thereby increases the earth's temperature. Scientists fear that if the temperature rises by even a few degrees, it will melt the polar ice caps which, in turn will submerge vast areas of land.

    OZONE DEPLETION EFFECT Halons (CFCs) destroy the protective ozone layer and let in harmful ultraviolet rays, causing skin cancer and affecting plant life.
 

The earth is protected from the sun's ultraviolet radiation by a layer of ozone high up in the stratosphere. Without this layer of ozone, life would have been impossible. But, again, due to human intervention there is a disruption of the ozone layer leading to certain types of skin cancer.

Ozone is continuously produced and decomposed. The quantity of ozone is relatively less (3,300 million tonnes) compared to 3865 million tonnes of nitrogen. Some of the factors which lead to the disruption of the ozone layer are the increased release of nitrogen oxides into the atmosphere, the increase of supersonic aircraft (SSTs) and the presence in the atmosphere of chloroflurocarbon (CFCs) which are used as refrigerants, in fire extinguishers and as propellants in aerosol spray cans.

Other effects of air pollution

Ozone causes reduced pollination and yellow spot formation on leaves, thus affecting the rate of photosynthesis.

Sulphur dioxide is converted to sulphuric acid in the presence of moisture and iron, which are present in dust, nails, etc. This results in yellowing, weakening and corrosion of materials.

- Courtesy by : C.P.R.Environmental Education Centre, Chennai               

Climate Change

Energy from the sun drives the earth's weather and climate, and heats the earth's surface; in turn, the earth radiates energy back into space. Atmospheric greenhouse gases (water vapor, carbon dioxide, and other gases) trap some of the outgoing energy, retaining heat somewhat like the glass panels of a greenhouse.
Without this natural "greenhouse effect," temperatures would be much lower than they are now, and life as known today would not be possible. Instead, thanks to greenhouse gases, the earth's average temperature is a more hospitable 60°F. However, problems may arise when the atmospheric concentration of greenhouse gases increases.

Since the beginning of the industrial revolution, atmospheric concentrations of carbon dioxide have increased nearly 30%, methane concentrations have more than doubled, and nitrous oxide concentrations have risen by about 15%. These increases have enhanced the heat-trapping capability of the earth's atmosphere. Sulfate aerosols, a common air pollutant, cool the atmosphere by reflecting light back into space; however, sulfates are short-lived in the atmosphere and vary regionally.

Why are greenhouse gas concentrations increasing? Scientists generally believe that the combustion of fossil fuels and other human activities are the primary reason for the increased concentration of carbon dioxide. Plant respiration and the decomposition of organic matter release more than 10 times the CO2 released by human activities; but these releases have generally been in balance during the centuries leading up to the industrial revolution with carbon dioxide absorbed by terrestrial vegetation and the oceans.

What has changed in the last few hundred years is the additional release of carbon dioxide by human activities. Fossil fuels burned to run cars and trucks, heat homes and businesses, and power factories are responsible for about 98% of U.S. carbon dioxide emissions, 24% of methane emissions, and 18% of nitrous oxide emissions. Increased agriculture, deforestation, landfills, industrial production, and mining also contribute a significant share of emissions. In 1997, the United States emitted about one-fifth of total global greenhouse gases.

Estimating future emissions is difficult, because it depends on demographic, economic, technological, policy, and institutional developments. Several emissions scenarios have been developed based on differing projections of these underlying factors. For example, by 2100, in the absence of emissions control policies, carbon dioxide concentrations are projected to be 30-150% higher than today's levels.
 

Changing Climate

Global mean surface temperatures have increased 0.5-1.0°F since the late 19th century. The 20th century's 10 warmest years all occurred in the last 15 years of the century. Of these, 1998 was the warmest year on record. The snow cover in the Northern Hemisphere and floating ice in the Arctic Ocean have decreased. Globally, sea level has risen 4-8 inches over the past century. Worldwide precipitation over land has increased by about one percent. The frequency of extreme rainfall events has increased throughout much of the United States.
 

Increasing concentrations of greenhouse gases are likely to accelerate the rate of climate change. Scientists expect that the average global surface temperature could rise 1-4.5°F (0.6-2.5°C) in the next fifty years, and 2.2-10°F (1.4-5.8°C) in the next century, with significant regional variation. Evaporation will increase as the climate warms, which will increase average global precipitation. Soil moisture is likely to decline in many regions, and intense rainstorms are likely to become more frequent.

Calculations of climate change for specific areas are much less reliable than global ones, and it is unclear whether regional climate will become more variable.

Economic Effects

The air pollution greatly causes economic problems to human- beings, plants and animals. The society gets poorer when forests are harmed by pollution. The manifestation of pollution injured  forests are difficult to detect .The reports of pollution injured forests gave rise to concern about pollution-caused declines in forest wealth .

Scientists view that decline in ozone layer is the primary reason for forest damage and acid rain deposits is the most contributing factor.

Effects on Plants

Physiological and developmental processes of plants are affected by UVB radiation, even by the amount of UVB in present-day sunlight. Despite mechanisms to reduce or repair these effects and a limited ability to adapt to increased levels of UVB, plant growth can be directly affected by UVB radiation.

Indirect changes caused by UVB (such as changes in plant form, how nutrients are distributed within the plant, timing of developmental phases and secondary metabolism) may be equally, or sometimes more, important than damaging effects of UVB. These changes can have important implications for plant competitive balance, herb ivory, plant diseases, and biogeochemical cycles.

The air pollution affects the plants in the following ways