For gases present at low concentra2ons the parts per

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Unformatted text preview: N2, O2, Ar, H2O are present in atmosphere at very low concentra2ons and are referred to as TRACE GASES. •  It is trace gases that we are generally concerned about in dealing with issues related to atmospheric contamina2on. •  For gases present at low concentra2ons, the ‘parts per..’ family of units is frequently used to express concentra2ons. [Review Text Book Box 3.1: Par2al Pressure] •  For measuring quan22es of gases that take up a large propor2on of the atmosphere, frac2onal or percentage concentra2ons are used, –  •  but in contrast to solids and liquids these are usually expressed on a molar, pressure, or volume basis, not on a mass basis. One part per million of a gaseous molecule in air means there is one molecule for every 1 mill...
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