Our notation is somewhat different from many reports of the EPA and other organizations because we follow the custom of physics and engineering textbooks where a single letter is used for the “family name” of a variable, with subscripts to distinguish different variants. We choose subscripts that are fairly explicit and in most cases self-explanatory.
It is helpful to distinguish different substances by adding subscripts to some units: for instance mwat3 for a m3 of water. Likewise we sometimes add a subscript to the mass for clarity, e.g. kgsoil for a kg of soil.
To minimize the risk of confusion about units for items that can be stated as quantities or as rates (i.e. quantity per time), we indicate rates by dots over the respective symbol, the usual notation for time derivatives; for example if m = mass of emitted pollutant (kg), ṁ = emission rate (e.g. kg/yr).
For certain variables we sometimes add the location x as argument to indicate a possible dependence on the location where they are evaluated; when x is not shown, the average over the entire region is understood, for example kdep = average of kdep(x) over all locations x and SERF= population-weighted average of SERF(x).