ACID RAIN - DEFINITION
         Scientists have discovered that air pollution from the burning of fossil fuels is the major cause of acid rain. The main
     chemicals in air pollution that create acid rain are sulfur dioxide (SO2) and nitrogen oxides (NOx). Acid rain usually forms
     high in the clouds where sulfur dioxide and nitrogen oxides react with water, oxygen, and oxidants. This mixture forms a mild
     solution of sulfuric acid and nitric acid. Sunlight increases the rate of most of these reactions. Rainwater, snow, fog, and
     other forms of precipitation containing those mild solutions of sulfuric and nitric acids fall to earth as acid rain.
        Acidity is measured using a pH scale, with the number 7 being neutral. Consequently, a substance with a pH value of less
     than 7 is acidic, while one of a value greater than 7 is basic.  Generally, the pH of 5.6 has been used as the baseline in
     identifying acid rain, although there has been much debate over the acceptance of this value. Interestingly enough, a pH of
     5.6 is the pH value of carbon dioxide in equilibrium with distilled water. That means, acid ran is defined as any rainfall that
     has an acidity level beyond what is expected in non-polluted rainfall.  Any precipitation that has a pH value of less than 5.6
     is considered to be acid precipitation.
 

The three main sources of acid deposition are:

    1. Coal in electricity
    2. Base metal smelting
    3. Fuel combustion in vehicles
 

                                        This is a small diagram that shows where some of the pollution comes from
                                                           and where it goes to when it turns into acid rain.

EFFECT ON LAKES AND AQUATIC ECOSYSTEMS

        One of the direct effects of acid rain is on lakes and its aquatic ecosystems. There are several routes through which acidic  chemicals can enter the lakes. Some chemical substances exist as dry particles in the air while others enter the lakes as wet particles such as rain, snow, sleet, hail, dew or fog. In addition, lakes can almost be thought of as the "sinks" of the earth, here rain that falls on land is drained through the sewage systems eventually make their way into the lakes. Acid rain that falls onto the earth washes off the nutrients out of the soil and carries toxic metals that have been released from the soil into the lakes. another harmful way in which acids can enter the lakes is spring acid shock. When snow melts in spring rapidly due to a sudden temperature change, the acids and chemicals in the snow are released into the soils. The melted snow then runs off to streams and rivers, and gradually make their way into the lakes. The introduction of these acids and chemicals into the lakes causes a sudden drastic change in the pH of the lakes - hence the term "spring acid shock". The aquatic ecosystem has no time to adjust to the sudden change. In addition, springtime is an especially vulnerable time for many aquatic species since this is the time for reproduction for amphibians, fish and insects. The sudden pH change is dangerous because the acids can cause serious deformities in their young or even annihilate the whole species since the young of many of such species spend a significant part of their life cycle in the water.

        Sulphuric acid in water can affect the fish in the lakes. Sulphuric acid (H2SO4) directly interferes with the fish's ability to take in oxygen, salt and nutrients needed to stay alive. For freshwater fish, maintaining osmoregulation is key in their survival. Osmoregulation is the process of maintaining the delicate balance of salts and minerals in their tissues. Acid molecules in the water cause mucus to form in their gills and this prevents the fish to absorb oxygen as well. If the buildup of mucus increases, the fish would suffocate. In addition, a low pH will throw off the balance of salts in the fish tissue. Salts levels such as the calcium (Ca+2) levels of some fish cannot be maintained due to pH change. This results in poor reproduction - their eggs produced would be damaged; they are either too brittle or too weak. Decreased Ca+2 levels also result in weak spines and deformities.
 
 

        Lakes that have been acidified cannot support the same variety of life as healthy lakes. As a lake becomes more acidic, crayfish and clam populations are the first to disappear, then various types of fish. Many types of plankton minute organisms that form the basis of the lake's food chain are also affected. As fish stocks dwindle, so do populations of loons and other water birds that feed on them. The lakes, however, do not become totally dead. Some life forms actually benefit from the increased acidity. Bottom plants and mosses, for instance, thrive in acid lakes. So do blackfly larvae. Not all lakes that are exposed to acid rain become acidified. In areas where there is plenty of limestone rock, lakes are better able to neutralize acid. In areas where rock is mostly granite, the lakes cannot neutralize acid. Unfortunately, much of eastern Canada where most of the acid rain falls has a lot of granite rock and therefore a very low capacity for neutralizing acids.
 
 

Here is a small graph that shows how much for the SOx emissions that are let into the air.
 
 
 

Here are the effects of an acidified ecosystem on the natural environment:
 

As water pH approaches	Effects
6.0	~~crustaceans, insects, and some      plankton species begin to disappear.
5.0	~~major changes in the makeup of the       plankton community occur.  ~~less desirable species of mosses and     plankton may begin to invade.  ~~the progressive loss of some fish      populations is likely, with the more      highly valued species being generally      the least tolerant of acidity.
Less than 5.0	~~ the water is largely devoid of fish. ~~the bottom is covered with       undecayed material.  ~~the nearshore areas may be      dominated by mosses. ~~terrestrial animals, dependent on      aquatic ecosystems, are affected.      Waterfowl, for example, depend on      aquatic organisms for nourishment      and nutrients. As these food sources      are reduced or eliminated, the quality      of habitat declines and the      reproductive success of birds is      affected.

What you can do to help reduce acid rain emissions

In the home
  Install a low-flow showerhead.
  Run the dishwasher only with a full load.
  Run the washing machine with a full load.
  If using an automatic dishwasher, let the dishes air dry.
  Hang dry some—or all—of the laundry.
  Buy energy-efficient appliances.
  Avoid the use of air conditioners altogether.
  Turn out the lights in empty rooms and when away from home.
  Consider installing compact fluorescent bulbs instead of high-wattage incandescent bulbs.
  Turn off the hot water tank when going away for extended periods of time.
  Install additional insulation on the hot water tank and pipes.
  Insulate and draft-proof your basement.
  Weather-strip doors and windows.
  Turn down the heat at night and when away from home.
  If you have a forced-air furnace, change or clean its filters at least once a year.
  Don’t use sink garbage disposal units.

In the yard
  Consider changing to a low-maintenance landscape.
  If you have a pool, keep a cover over it when you are not using it.

While shopping
  Look for products bearing the EcoLogo. They minimize the use of environmentally hazardous
  substances and maximize energy efficiency and the use of recycled materials.
  Buy locally produced or grown items from local stores and businesses. They don’t require the
  transportation energy of imported products.

Transportation
  Walk, ride your bike or take a bus to work.
  Share a ride with a friend or co-worker.
  Have your engine tuned at least once every six months.
  Check your car tire pressure regularly.
  Use alternative fuels, such as ethanol, propane or natural gas.
  Avoid unnecessary idling.
  In the winter, warm your car’s engine with a block heater for two to three hours prior to driving, rather
  than plugging in the battery overnight.
  Reduce the number of trips you make in your car.
  Drive at moderate speeds.
  Take the train or bus on long trips.
  Go CFC-Free.
 

Here is my work cited and some other sites on the topic of Acid Rain:

 ~~  http://expert.cc.purdue.edu/~neni/
 ~~  Effects of Acid Rain on People
 ~~  Water Science : Acid Rain
 ~~   Pro and Con
 ~~   Acid Rain: A student's First Sourcebook
 ~~  http://www.geocities.com../RainForest/Canopy/1035/
 ~~  The Effects of Acid Rain