Chapter 1 the earth and its atmosphere. Inward motion around low leads to rising motion, due to conservation of mass (results in cooling, condensation and precipitation, thus lows are associated with stormy weather) Atmosphere thin envelope of gases and tiny particles that surround earth (essential for life, contains oxygen and carbon dioxide for life-sustaining processes, supplies water and shields life from harmful uv radiation from. 99% of gases extend only 30 km above earth"s surface. Most weather occurs within the first 10-15 km. Nitrogen, oxygen, argon, water vapour, carbon dioxide (n and o experience little change, but co2 and others are increasing in concentration) Clouds are not gas condensed vapour in the form of liquid droplets. Smog contains reactants of nitrogen and ozone. Ozone = primary component in photochemical smog. Majority of water on the planet is from outgassing. Air density is greatest at the surface and decreases as you go up. Atmospheric pressure always decreases with decreasing height.