This approach is generally applied to particulate matter under 2.5μm in diameter because of the formation mechanisms and the health risks associated with this size regime.
The compound must react slowly enough in the atmosphere that it is chemically conserved from the emission source to the receptor site where an ambient sample may be taken.
[2] Tracer compounds must then be of primary origins (not formed in the atmosphere), which are created through condensation and coagulation of mainly combustion and biological sources.
Examples of some results of preferential emissions from sources include hopanes, polycyclic aromatic hydrocarbons and steranes [4] from different types of mobile sources, retene and methoxyphenols from wood smoke, odd n-alkanes and even n-alkanoic acids from vegetative detritus, cholesterol and the C16 and C18 n-alkanoic acids from cooking, and lighter n-alkanes from brake wear.
This approach assumes that an ambient air sample has particulate matter contributions from a linear combination of emission sources.