A new model is described for computing in-chamber actinic flux using site specific conditions that include time of day, air pressure, total column ozone, total column water vapor, relative humidity, aerosol type, aerosol optical density at 500 nm, and the spectral albedo of the aerosol. Included in this model are a highly accurate solar coordinate model, two broad band models for predicting the Total Solar Radiation (TSR) and Eppley Ultraviolet Radiometer irradiances, a TFE film transmission model, a total chamber transmission model, a reflective floor model, and a treatment for clouds. This model runs on MS/PC-DOS type machines. A description of how these models were used to compute the in-chamber actinic flux every 16-minutes for every day in the UNC database is given. A description is also given of how these new actinic fluxes were used with kinetic data on species absorption cross sections and quantum yields to computer the photolysis rates of 20 reactions. A separate column contains the appendices for this document.