EPA's Regional Oxidant Model (ROM), a three-dimensional model capable of describing photochemical smog on scales of 1000 km, is being used to analyze large scale pollution patterns and the effectiveness of particular emissions control strategies on reducing ozone concentrations. The ROM demands considerable computation time to perform its calculations, particularly the chemical calculations. The model currently simulates at much less than one-half of 'real-time' on a VAX 11/780 (one day of model time requires over two days of simulation time). A feasibility study was performed to support the design of a computing solution to accelerate the simulation. The study suggested the construction of a prototype parallel multiprocessor system using off-the-shelf computers, interconnected by Ethernet, as a low-risk method of increasing software performance up to 10-20x over uniprocessor speed. The prototype consists of 22 rtVAX 1000 computers as processing elements (PEs), and a VAXstation II/GPX host computer. Current work is focused on developing a variation of the tiled ROMMP (Regional Oxidant Model Multi-Processor), in order to distribute the entire computational problem to the PEs. This approach is expected to avoid the host-computational bottleneck, and achieve high levels of utilization on all the PEs in the prototype.