Acid Rain

A  number of oxides can be used to produce acid rain.

Sulphur in coal will combine with oxygen to form sulphur dioxide. 

Sulphur + oxygen   sulphur dioxide

S + O2          SO2

Sulphur dioxide can react with water directly to form sulphurous acid

sulphur dioxide + water    sulphurous acid

SO2  +  H2O H2SO3

Sulphurous acid can react with oxygen and water to form sulphuric acid.

sulphur dioxide + oxygen + water    sulphuric acid

2SO2 + O2 + H2O    2H2SO4

As stated in previous posts, vehicle exhausts produce nitrogen dioxide as follows

nitrogen + oxygen   nitrogen dioxide

N2 + 2O2    2NO2

This in turn reacts with water to form nitric acid and nitrous acid

nitrogen dioxide + water    nitric acid + nitrous acid

2NO2 + H2O    HNO3  + HNO2

Acid rain forms in the atmosphere as these gases react with the water that is already in the atmosphere has a number of consequences.  When it reaches the ground, it can have a number of consequences:

1. Damaging the foliage of plants
2. Rapid leaching of essential nutrients from the soils
3. Releasing heavier metals from the soil (e.g. copper, zinc) so that they have toxic effects on plants.
4. Acidifying waterways causing fish kills.
5. Damaging statues or parts of buildings made of limestone and marble (some types of sandstone are also candidates for damage)

As the cartoon implies, the acid emissions of one country can affect neighbouring areas.  This was the case in Canada where northern USA emission damaged the environment.  In Scandinavia acid forming pollution from western Europe again caused damage.

In 1983 an international treaty, The  Convention on the Long-Range Transport Air Pollutants (LRTAP) came into force with 50 signatories to try and reduce the emissions that produce acid rain.  More on this later.

Global warming and Greenhouse Gases

This is a topic that has been in the news lately. A number of scientists and authorities are stating that without rapid action, the earth could warm by up to 6 degrees before the end of the 21st century.  Changing weather patterns and climates may have dire consequences in the long term.

The greenhouse effect occurs because greenhouse gases let sunlight (shortwave radiation) pass through the atmosphere. The earth absorbs sunlight, warms then reradiates heat (infrared or long wave radiation). The outgoing long wave radiation is absorbed by greenhouse gases in the atmosphere. This heats the atmosphere which in turn re-radiates long wave radiation in all directions. Some of it makes its way back to the surface of the earth. So with more carbon dioxide in the atmosphere, we expect to see less long wave radiation escaping to space at the wavelengths that carbon dioxide absorb. We also expect to see more infrared radiation returning back to Earth.


Greenhouse gases include:

1. Carbon dioxide.

The biggest contributor to global warming by volume produced and net effect.  CO2 is produced by the combustion of fossil fuel in a combustion reaction, which should be familiar to you from junior classes.  It is also caused by the breakdown of carbon in soils as a result of deforestation.

Fuel + oxygen         Carbon dioxide + water.

2. Methane.

This is significant because 1 part of methane is up to 20 times better at reflecting infrared radiation compared to CO2.  It is produced by ruminant animals (burping, not farting), rice paddies and landfills.

3. Nitrogen dioxide

This gas is becoming more problematic due to its increasing levels.  This gas is produced by the by combination of nitrogen and oxygen in car engines.  Because air is a mixture of these 2 gases, when it is drawn into the cylinder, some of the energy produced by the burning of the fuel combines to form nitrogen dioxide

N2  +   202        2NO2

Graphs showing the levels of these gases follow below

I should point out that this temp data does require some processing, but the link between historical temps and CO2 levels is striking. Of concern is the spike in the blue line at the end, that is a result of our activity.  This is unprecedented in the 450,000 year history of the atmosphere preserved in ice cores.





There is now pretty much consensus that global warming is happening now and that it will get worse in the next 100 years.  For example the average global temps for 11 of the last 12 years have been the warmest recorded.  There is no evidence to suggest a change in solar activity or other geological phenomenon. Only a small group of people feel that there is no such thing as climate change.  The part up for debate now is the extent that global warming will happen.