Processes which govern important surface photochemical reactivity include the interaction of clouds with solar radiation. To date, many photochemical models have used algorithms that date from the 1980s, particularly those that are RADM-based (EPA-CMAQ, MAQSIP, etc). The authors have thoroughly investigated some of the major deficiencies with these algorithms and have tested and implemented a revised sub-model in the MAQSIP-RT real-time forecast model. This paper will describe the previously existing deficiencies, discuss the new sub-model, and present test results that show the improvements in surface layer ozone predictions.