A modular ductwork assembly decontaminates an air stream circulating within a heating, ventilation and air conditioning system. The liquid sprayer includes a spray liquid storage unit and a main body for supporting the spray liquid storage unit and a power supply unit. The frame is attached to a structure of a road vehicle. The side wall has an opening for inserting ballast between the first and second surfaces into the sleeve, and the sleeve is of suitable size and shape to hold the ballast.