Matter

Modern science has proven the instincts of early philosophers to be correct.The atom is the fundamental building block of the elements. When a large numbers of atoms and molecules interact with each other in different ways they make either solids, liquids, or gaseous matter. The phase in which matter occurs depends upon external conditions such as temperature and pressure as well as the strength of the attractive forces between the atoms or molecules. When the attractive force is very strong, the movement of individual atoms or molecules is restricted and the matter becomes rigid and solid. At the opposite end of the spectrum, when the intermolecular forces are very weak, atoms and molecules move about without affecting each other except where a direct collision occurs. This latter case is a gas.

In the atmosphere, all three phases exist under the same external conditions creating complex pollution mixtures that can have unexpected results on climate.

(Image by Daniel Rosenfeld, Hebrew University of Israel from The NASA Website.)

Consider the matter shown in this satellite image. The dense concentration of powerplants, factories, trucks, and automobiles on the U.S. east coast continuously emit solid soot and other solid particulate pollutants into the gases of the atmosphere. These small particles suspended in the air often end up interacting with clouds(made of water droplets), forming more, smaller droplets than those found in an unpolluted cloud. In this satellite image the yellow clouds scattered over the northeast are polluted clouds with small water droplets. The pink clouds over Canada have larger droplets, and are relatively clean. Because the aerosols prevent cloud water droplets from growing large enough to precipitate, this type of pollution can reduce rainfall.