~Air Pollution~

-Introduction

-Pollutants
 ~Sulphur dioxide
 ~Nitrogen dioxide
 ~Carbon monoxide
 ~Ozone
 ~Particulates
 ~Lead

-API
 ~What's API?
 ~In Hong Kong
 ~Equipment
 ~API figures

-Photochemical Smog
 ~What is it?
 ~Problems
 ~Effects

-Acid Rain
 ~How it is formed?
 ~Effects

-Global warming
 ~Greenhouse effect
 ~Effects
 ~What can you do?

-Measures
 ~Part 1
 ~Part 2
 ~Part 3
 ~What can you do../1
 ~What can you do../2

The natural greenhouse effect is a phenomenon created by the heat energy radiated by the sun and greenhouse gases normally present in the atmosphere. In simple terms, energy from the sun falls on the earth. The solar energy is either absorbed by the Earth or reflected back into space. About half of the solar energy is absorbed, warming the atmosphere and the Earth's surface. The Earths surface re-radiates most of the absorbed energy. Carbon dioxide, water vapor and a few other gases absorb some of this infrared energy and hold it back.

The trapped energy keeps the average Earth temperature at about 15 . Without carbon dioxide and water molecules in the atmosphere to trap heat energy, the Earth would be at an average temperature of -25 .

In fact, the greenhouse effect is essential for life on Earth.

The greenhouse effect would be constant if the greenhouse gases remain in their normal concentrations. However, over the past fifty years, production of carbon dioxide, nitrogen oxides and methane has risen sharply. Moreover, a new type of chemical - the chlorofluorocarbon, or CFC - has been introduced as a refrigerant, solvent and aerosol propellant. CFC is a very powerful greenhouse gas because it can trap a lot of radiation. This results in enhanced greenhouse effect, causing a rise in the Earth's surface temperature. The increase in temperature due to enhanced greenhouse effect is known as global warming.