Acronym for the Global Atmospheric Watch program, the purpose of which is to provide data, scientific assessments, and other information on the atmospheric composition and related physical characteristics of the background atmosphere from all parts of the globe. The measurement program includes greenhouse gases, ozone, radiation and optical depth, precipitation chemistry, chemical and physical properties of aerosols, reactive gases, radionuclides, and related meterological parameters. See the GAW Web site.
Group additivity method as implemented in the NIST Chemistry Webbook. See http://webbook.nist.gov/chemistry/grp-add/ for a group additivity method that predicts enthalpies of formation and entropies. Group additivity methods assume that a molecule can be broken down into separate parts (groups), each of which contributes additively to the total enthalpy or entropy. For example acetone is composed of two methyl groups (each adds -42.7 kJ/mol) and a carbonyl group (which adds -131 kJ/mol) for an estimated enthalpy of formation of -216.4 kJ/mol.