The model is used for estimating short-term concentrations of primary and secondary reactive pollutants resulting from single or, in some special cases, multiple sources if they are aligned with the mean wind direction. The model is capable of simulating the complex interaction of plume dispersion and non-linear photochemistry. If Carbon Mechanism IV (CBM-IV) is used, emissions must be disaggregated into carbon bond classes prior to model application. A major feature of RPM-IV is its ability to interface with input and output files from EPA's Regional Oxidant Model (ROM) and Urban Airshed Model (UAM) to provide an internally consistent set of modeled ambient concentrations for various pollutant species.