The GCE equations

Mass ej. from AGB+PNC Mass ej. from O starsd Processes tending to restore the gas 0.8 Mq pc-2 Gyr-1 0.05 Mq pc-2 Gyr-1 

Sources a Binney Tremaine (1987) b Kulkami Heiles (1987) c Jura (1989) d Pottasch (1984) e Lacey Fall (1985). 

In the standard case there are four variables to be calculated the total system mass M (not counting non-baryonic dark matter), the mass of gas g, the mass existing in the form of stars (including compact remnants) s and the abundance Z of the element(s) of interest, assuming certain initial conditions and laws governing the SFR and flows of material into and out of the system. 

Galactic chemical evolution basic concepts and issues 

The abundance of a stable (i.e. non-radioactive) element in the gas (and in newly formed stars if the ISM is homogeneous) is governed by 

---