A foreign substance mixed with or attached to a given substance to enable the distribution or location of the latter to be determined subsequently. There are several types of tracers which are used: (i) A physical tracer is one that is attached by physical means to the object being traced; (ii) A chemical tracer is a chemical with properties similar to those of the substance being traced with which it is mixed homogeneously; (iii) An @I03350@ is a unique isotope, either @R05077@ or an enriched, uncommon @S05900@ isotope, of the element to be traced; (iv) A @R05089@ is a physical or chemical tracer having @R05092@ as its distinctive property which allows detection at small concentrations and hence after large transport distances. The composition of aerosols in the @T06522@ has been used as a qualitative tracer of air masses. The elemental analyses (determined by @N04116@ @A00093@, @X06710@, etc.) of the aerosols transported from various sources or source regions sometimes have characteristic patterns which are used to define qualitatively the origin of tropospheric aerosols collected in other geographical regions.
PAC, 1990, 62, 2167. (Glossary of atmospheric chemistry terms (Recommendations 1990)) on page 2217 [Terms] [Paper]
PAC, 1994, 66, 2513. (Nomenclature for radioanalytical chemistry (IUPAC Recommendations 1994)) on page 2525 [Terms] [Paper]