As the world is getting more and more denselypopulated,air pollution has become a severeproblem.
Air pollution mainly derives from four majorhuman activity sectors:industry,energy,transportation andagriculture.
Energies are needed to run factories,to power trains,planes and buses.
Nearly all ofthese energies are produced by burning fuels,which would cause air pollution.
Scientists arestudying new ways of generating electricity that can be less damaging to the environment.
Theincreased public environmental awareness has led to the advent of activities such as recycling.