The Earth's atmosphere [local] is composed primarily of nitrogen (78%), oxygen (21%), water, argon and carbon dioxide. Each of these gases have unique and interesting chemical properties [local] (original page by James Plambeck no longer available). While nitrogen and oxygen make up the bulk of the atmosphere, many other compounds and elements are found in trace quantities [local].

Today From Space: The Earth's Atmosphere: Near Real-Time Research Imagery [local].

Atmospheric chemists [local] are interested in understanding the chemical composition of the natural atmosphere, the way gases, liquids, and solids in the atmosphere interact with each other and with the earth's surface and associated biota, and how human activities may be changing the chemical and physical characteristics of the atmosphere.